This article presents physical and mechanical properties of concrete composites that include waste thermoplastic elastomer (TPE) from the production process of car floor mats. Waste elastomer (2–8 mm fraction) was used as a substitute for fine aggregate in quantities of 2.5, 5.0, 7.5, and 10% of the cement weight. For all series of concrete, the following tests were carried out: compression strength, bending tensile strength, splitting tensile strength, absorbability, density, resistance to water penetration under pressure, frost resistance, and abrasion resistance, according to applicable standards. Moreover, SEM/EDS analysis was carried out on the surface microstructure of synthesized concrete composites. It was proven that the use of production waste from the production process of car floor mats in the quantity of 2.5% does not influence the change of the concrete microstructure and it does not result in the decrease of the mechanical parameters of concrete modified with waste. All concrete modified with the addition of waste meet standards requirements after carrying out 15 cycles of freezing and thawing, and the average decrease in compression strength did not exceed 20%. Adding waste in the quantity of 2.5% allows for limiting the use of aggregate by about 5%, which is beneficial for the natural environment. Concrete, which is a composite material with a cement matrix, is commonly used in the construction industry. A systematic increase in the quantity of manufactured concrete causes the use of large quantities or natural aggregates, and the excessive use of natural resources results in environment degradation. Therefore, in recent years, many research centers have carried out tests concerning the possibility of using various waste materials, such as domestic and industrial waste , bottom Moreover, tests concerning the use of waste recyclate from polyethylene and polypropylene ,21,22,23An increase in the quantity of synthetic fibers above such level results in the worsening of the mechanical properties of modified concrete. There is also much information on the use of waste polystyrene ,30,31,32Currently, a large quantity of polymer waste materials is available on the market, which are of no practical use. However, it is worth testing them to possibly use them in the production process of composite materials. This group covers waste thermoplastic elastomer from the production process of car floor mats. According to the waste catalogue , waste f3, the average quantity of chlorides in the. water was 31.5 mg/dm3, and the average quantity of sulphates in the water was 53.8 mg/dm3.The following concrete was used for the tests: Portland cement CEM I 42.5R , which meets the requirements of standard PN-EN 197-1, sand, gravel aggregate with 2–8 mm and 8–16 mm fractions, water, additives of CHRYSTO Plast 331, and CHRYSTO Air LB , as well as waste thermoplastic elastomers from the production process of car floor mats at the production company Gumotest . The waste used in this research was a thermoplastic elastomer  based on an ethylene propylene diene blend (EPDM). Following initial crushing, production waste  was crus3/min. The results of thermogravimetric analysis (TG), differential thermogravimetric analysis (DTG), and differential scanning calorimetry (DSC) are presented in TGA-DTA analysis was carried out for the waste used in the tests. The test was carried out in the thermal analysis device Jupiter STA 449 F5  in the temperature range from 30 to 600 °C, with the temperature increase rate 10 °C/min in an air atmosphere, and with the gas flow rate 100 cmFive series of concrete were prepared. To design the composition of the concrete mixture of the reference concrete (RC), an experimental method developed by Professor Kuczyński was used. It is the most popular Polish computational–experimental method of designing a concrete mix called the method of successive approximations or starting with iteration. It involves the calculation of three unknowns, i.e., the amount of cement, water, and aggregate, by using three basic equations: strength, tightness, and water demand (consistency). The obtained results are verified experimentally. The water–cement ratio was assumed to be 2:22 and the consistency class was assumed to be S2. To prepare the reference concrete, Portland cement CEM I 42.5R, the mixture of gravel–sand aggregates with a particle size distribution of 0–16 mm and a sand content of 33.1%, tap water and plasticizing admixture CHRYSTO Plast 331 in the quantity of 0.35% of the cement weight, and air entraining admixture CHRYSTO Air LB in the quantity of 0.2% of the cement weight were used. The reference concrete (RC) was modified with waste thermoplastic elastomer from the production process of car floor mats. The waste was added to concrete in the quantities of 2.5%, 5.0%, 7.5%, and 10% of the cement weight, adjusting the volume of gravel aggregate with a particle size distribution of 2–8 mm. The series of concrete were identified as S1-1, S1-2, S1-3, and S1-4, accordingly, and the composition of the designed mixtures is presented in For all concrete mixtures, the consistency was defined according to standard PN-EN 12350-2:2011 , and theSEM/EDS analysis of the microstructure of the synthesized concrete composites that included the waste thermoplastic elastomer was also carried out. Scanning electron microscopy (SEM), LEO Electron Microscopy Ltd., Cambridge, UK) was used for the tests, which was equipped with a system for chemical composition analysis based on X-ray energy dispersion—EDS .For the concrete mixture of the reference concrete, an S2 consistency was assumed (concrete slump at 50–90 mm). After preparation of the concrete mixture, samples were collected to define the consistency class and air content in the concrete mixture. For the reference mixture (RC), the slump was 70 mm, which corresponds to the S2 class. Air content in this mixture was 3.5%. For concrete mixtures modified with the waste thermoplastic elastomer (S1-1–S1-4), the slump was between 50 and 75 mm, which also corresponds to the S2 consistency class . The airFor each series of concrete, 18 cubic samples with a 150 mm side were prepared, which were subject to compression strength tests after 7, 28, and 56 days of the curing period under laboratory conditions. For the results obtained in the individual series, the standard deviation and confidence level at 95% were identified. The reference concrete (RC) after seven days of curing was characterized with an average compression strength of 46.6 ± 0.95 MPa, whilst after 28 days it was 57.0 ± 1.59 MPa, and 61.9 ± 1.19 MPa after 56 days . The aveThe addition of the waste thermoplastic elastomer to concrete also influenced the bending strength and splitting tensile strength of the concrete . Adding 3, the reference concrete was classified into a standard concrete category according to standard PN-EN 12390-4:2001 [3. The reference concrete obtained an average depth of water penetration equal to 65 mm. For the series of concrete modified with the waste thermoplastic elastomer, the average depth of water penetration was from 60 to 67 mm. The lowest value of the tested parameter (60 mm) was obtained for series S1-1, in which 2.5% of production waste was used, whilst the highest value (67 mm) was obtained for concrete series S1-4, in which 10% of the said waste was used. In the event of the reference concrete (RC), the abrasion strength was 7.4 cm3/50 cm2. For the concrete modified with the waste of thermoplastic elastomer, a lower abrasion strength was obtained than for the reference series concrete—it was 2.7–6.8%.The next stage of tests was to determine the absorbability, density, water penetration under pressure, frost resistance, and abrasion resistance of the concrete . The abs0-4:2001 . SimilarA frost resistance test was carried out for all series of concrete. For each series of concrete, 12 cubic samples with a 100 mm side were prepared, of which six samples were subject to frost resistance tests, and six samples were left in water as the reference samples. In the event of the reference concrete, the average decrease in compression strength after 150 cycles of freezing and thawing was 4.4%, and the average weight loss was 0.34% .In the event of the concrete modified with the waste thermoplastic elastomer used as the substitute for gravel aggregate with particle size distribution 2–8 mm in the quantities of 2.5% and 5.0% of the cement weight, a lower average decrease in the compression strength than for the reference series concrete was noted. The average compression strength of the concrete after the frost resistance tests decreased, along with an increase of the amount of production waste added to the concrete. The lowest decrease in the average compression strength after the frost resistance test was noted for concrete series with the addition of 2.5% production waste, where it was 2.4%, whilst the highest (11.6%) was noted for concrete containing 10% of production waste. After the frost resistance test, the average weight loss was at the level of 0.05–0.34%. None of the samples cracked and there were no scratches.During the next stage of tests, analysis of the surface layer of the synthesized composites was carried out, mainly defining their morphology and elemental composition. Tests of the properties and structures of concrete composites containing a waste thermo-plastic elastomer from the production process of car floor mats, as well as analysis of obtained the results, showed the suitability of this waste type for the production of concrete. The early compression strength of concrete (tested after seven days of curing) modified with production waste in the quantity of 2.5% of the cement weight that was used as the substitute for fine gravel aggregate was similar to the compression strength of the reference concrete. On the other hand, in the event of concrete containing waste in the quantities of 5.0%, 7.5%, and 10% of the cement weight, a decrease of a seven-day compression strength was noted at the level between 5.5% to 11.3%. Similarly, the compression strength tested after 28 and 56 days of curing of samples of concrete modified with 2.5% additive of waste was comparable to the strength of the reference samples (increased by 0.3–1.4%). The addition of a higher quantity of waste resulted in a decrease in the values of this parameter by 9.6–22.6% in the event of samples tested after 28 days, and by 11.3–24.4% in the event of samples tested after 56 days of curing. The tests showed that adding a waste thermoplastic elastomer to concrete in the quantities of 2.5% and 5.0% of the cement weight as a substitute for fine gravel aggregate with a particle size distribution 2–8 mm had a positive impact on the increase of the bending strength of concrete. For concrete of these series, an increase in the bending strength by 3.1% and 2.2%, accordingly, as compared to the reference concrete, was noted. Concrete modified with waste in the quantities of 7.5% and 10% showed a decrease in bending strength by 0.8% and 4.2%, accordingly, as compared to the reference concrete. The addition of production waste in the quantities of 2.5% and 5.0% also had a positive impact on the splitting tensile strength of concrete. For these series of concrete, this parameter was higher as compared to the reference concrete by 9.0% and 13.5%, accordingly. In the event of concrete modified with waste in the quantities of 7.5% and 10%, a decrease in the splitting tensile strength of the concrete by 5.3% and 12.3%, accordingly, as compared to the reference concrete, was noted.3. This allowed for classifying them into the standard concrete category. Both the reference concrete and the concrete modified with waste thermoplastic elastomer obtained absorbability at the ca. 5.0% level. All concretes modified with the waste thermoplastic elastomer met the standard requirements. After 150 cycles of freezing and thawing, the average decrease in compression strength did not exceed 20%, and the average weight loss did not exceed 5%. Therefore, it may be concluded that it is beneficial to add a waste thermoplastic elastomer from the production process of car floor mats in the quantity of 2.5% of the cement weight to concrete, which allows for the saving of natural resources and decreases the costs of concrete manufacture by 20 kg/m3, which is about 5.0%.All concretes modified with waste obtained lower densities than the reference concrete, which was between 2000 and 2600 kg/m


Quality of life (QOL) has been considered as an important outcome indicator in holistic care for HIV-infected people, especially as HIV/AIDS transforms from a fatal illness to a chronic condition. This study aimed to identify trends and emerging topics among research concerning the QOL of people living with HIV/AIDS (PLWHA). The analyzed data were English papers published from 1996 to 2017, searched and extracted from the Web of Science Core Collection. Collaborations between countries and the correlation between the keywords were visualized by VOSviewer while the abstracts’ content was analyzed using exploratory factor analysis and Jaccard’s’ similarity index. There has been an increase in both the number of publications and citations. The United Nations of America leads in terms of paper volume. The cross-nation collaborations are mainly regional. Despite a rather comprehensive coverage of topics relating to QOL in PLWHA, there has evidently been a lack of studies focusing on socio-cultural factors and their impacts on the QOL of those who are HIV-infected. Further studies should consider investigating the role of socio-cultural factors, especially where long-term treatment is involved. Policy-level decisions are recommended to be made based on the consideration of cultural factors, while collaborations between developed and developing nations, in particular in HIV/AIDS-ridden countries, are strongly recommended. Human immunodeficiency viruses (HIV) is one of the leading causes of disability and mortality worldwide, with more than 76.1 infected people and 35.0 million deaths ,3. In 20Quality of life (QOL), as noted by the existing literature, has been described as an umbrella term for a variety of human needs, including the position in life, goals, standards, expectations, and concerns in the context of the culture and value systems. It manifests within patients as symptomatic, social functioning, and spirituality . In termThus, in order to improve the quality and effectiveness of HIV/AIDS treatment and prevention programs, qualitative as well as quantitative analyses on the QOL of PLWHA are needed. In 2017, Cooper, et al. conducted a systematic review on the finding of existing reviews on QOL of the HIV/AIDS-infected population in various aspects, including the development, validation, and effectiveness of the most commonly used instruments . Though Our study adopts the scientometrics approach that gathers and analyze publications on a global level, coupled with more a technical analysis approach applied to the content of papers’ title and abstract to identify emerging research topics as well as the current level of international collaboration in research on the QOL of PLWHA. This study aims to supplement the current literature while uncovering research gaps, suggest directions for future studies, and act as a reference point for priority settings and strategies initiating in HIV/AIDS management. Serving as the best approach to evaluate evidence, the increase in the number of systematic reviews of QOL regarding HIV/AIDS could provide an insightful view of various aspects, including evaluating the effectiveness of instruments, clinical intervention, and HIV/AIDS programs in vulnerable populations. In addition to having a limited scope of research; such reviews also remain lack of the comparison of findings over time and overlap with information. Several researchers use bibliometrics with the expectation that it could fill the gap in the literature and provide the research trend using quantitative analysis. It can be seen that the bibliometric approach sometimes could not draw a full picture because the majority only present the number without a comprehensive reading of the literature . In ordeThe current study is a part of a larger project, Global Analysis for Policy in Research (GAPRESEARCH), that aims to set priorities in global health evolution and provide empirical evidence for designing effective interventions and policies ,30,31,32A search for HIV/AIDS publications was performed on the Web of Science (WoS) Core Collection. This database was prioritized because it has covered all scientific publications with full cited reference indexing since 1900 and allowed downloading information with a diversity of research disciplines that far outweigh other databases such as Scopus or MEDLINE . We applied a search query containing the search terms of “HIV” OR “human-immunodeficiency-virus” OR “AIDS” OR “Acquired-Immune-Deficiency-Syndrome”. Data were extracted in a unit of 500 publications from the first publication in the dataset end up in 2017. As the process was conducted in July 2018, we excluded all papers published in 2018 as the partial coverage of publications published in 2018 would not fully reflect the publication trend of the year. The selection criteria for study subjects were English peer-review articles, including original articles and reviews see . Any papThe retrieved data consisting mainly of publication indexes were contained the following information: Title; years of publication; the total number of papers; citations up to 2017; usages/number of downloads; keywords (authors’ keywords); authors’ affiliations; most prolific countries and collaborations. In order to describe the change of publication over time, we calculated several fundamental domains including the speed of publication , the level of reader attention (mean cited rate per year), the level of short-term and long-term interest (mean usage rate last 6 months/5 years). We also illustrated the major topic clusters and landscapes of QOL in the field of HIV/AIDS by calculating the frequency of co-occurrence of keywords and synthesized from abstract’s content. The extracted data were sorted by Macro in Microsoft Excel to calculate the indexes. The connection among countries by sharing co-authorships’ data (we applied full counting for papers sharing by more than one country), networks of co-occurrence authors’ keywords, and clusters of topic groups were visualized by VOSviewer . The cluster topics of QO were then identified from the frequency of keywords and named by expert opinions. The exploratory factor analysis (EFA) and Jaccard’s similarity index were performed using STATA software version 15.0. This index was defined as the magnitude of the intersection divided by the magnitude of the union of two sets of co-occurring terms; thus, multi-dimensional scaling could be used to adjust a point for a topic category, the distance between items and color presented the partnership of certain key terms. To measure the likelihood of research trends , we utilized exploratory factor analysis (EFA), which allows us to test the variance in the domains and landscape appearing from the abstract’s contents. The summary of the technique used for analyzing is described in Cluster 1 (red) refers to the network of countries in the two regions: South-East Asia and the Western Pacific. Cluster 2 (purple) indicates the link of the USA with European countries and Saudi Arabia. Cluster 3 (blue) illustrates international collaborations between the Americas, South Africa, and some countries in Asia. Cluster 4 (brown and green) demonstrates the co-authorship between countries within Southeast Africa. In addition, they have an additional link with England. The European countries tend to associate with each other by geographical areas, such as orange, pink, light blue, and yellow (French West Africa). Cluster 1 (red) covers mental health, social, and associated factors. It includes psychological disorders ; social behavior ; specific HIV groups , and regions . Cluster 2 (blue) presents physical health-related aspects: treatment, outcome, mortality, and disability. Cluster 3 (green) indicates ART adherence studies: study design and laboratory results.The top 50 emerging research domains have been discovered from the content analysis of abstracts using exploratory factor analysis . Mental By analyzing the volume and abstract contents of global publications on the QOL of PLWHA during 1996–2017, our research captured and visualized the level of attention, current research trends, and the global networking of researches. The results show rather extensive coverage of topics in the existing literature, ranging from physical-related aspects to mental health, from issues concerning clinical trials to social support. Nonetheless, the current bibliography shows the lack of socio-cultural factors involved in the development and measurement of QOL. Our study reports an increase in the number of papers using QOL as an important instrument for evaluating HIV/AIDS interventions since 1996, when highly active antiretroviral therapy (HAART) was first introduced . On the Knowing the association between the QOL of PLWHA and the effectiveness of HIV programs, QOL has been used as a criteria in assessing HIV/AIDS prevention programs, clinical treatment, and harm reduction strategies ,40,41. TEven with the advancement of health services as well as the high ART coverage, the HIV/AIDS programs remain complex, contextual, and are often referred to as complicated because appropriate recommendations vary according to subpopulation and epidemiological context . PreviouThe analysis of a principal component of terms in titles and abstracts reveals that QOL tends to co-occur with terms relating to mental disorders and high-risk populations, including adolescents, children, women, and gay. Disclosure, discrimination, and stigma have also been found to appear together with the aforementioned terms, along with keywords like barriers and primary care . This fiDespite the positive findings of the study, several limitations should be mentioned. As our search strategy was conducted via Web of Science Core Collection solely and only English reviews and articles were included, despite the extensive coverage of WoS and the dominance of English publications, there is a chance that relevant publications not recorded in such a database and/or in other languages would be missed. Our decision to use only the term “quality of life” when conducting a publication search would also filter out possibly related papers where variations of the construct such as “satisfaction with life”, “well-being”; “satisfaction” or “value of life” were used instead. Thus, further researches are strongly encouraged to consider investigating deviations of “quality of life” both as a term and a concept, especially research with a sociological focus. In addition, future studies may also be conducted in the form of systematic reviews and meta-analyses, for instance, on how QOL can or has been used as a measurement for assessing the effectiveness of HIV/AIDS treatments or interventions.Using bibliometrics analysis, we illustrate the development and current global trends of research on the QOL of PLWHA. Meanwhile, the results of the text mining techniques adopted provide a picture of current emerging research trends and topics and highlight research gaps. Despite a rather comprehensive coverage of topics relating to QOL in PLWHA, there has evidently been a lack of studies focusing on socio-cultural factors and their impacts on the QOL of those that are HIV-infected. Further studies should consider investigating the role of socio-cultural factors, especially where long-term treatment is involved. Policy-level decisions are recommended to be made based on the consideration of cultural factors, while collaborations between developed and developing nations, in particular with HIV/AIDS-ridden countries, are strongly recommended.


Storing waste in concrete instead of landfills is environmentally friendly and also might make concrete more sustainable if some part is replaced with cement. This article presents a new way of valorising hazardous waste, namely ilmenite MUD from the production of titanium dioxide, which is used as a reactive additive to concrete. In fact, there are currently no articles presenting the way of valorisation that is presented in this paper. The global annual production of MUD is estimated to be about 0.7 million tons. Valorisation is possible due to the additional rinsing and filtering in the factory, which also confirms the novelty of this article. In this operation, the most hazardous compounds are returned back to the factory process. Rinsed mud (RMUD) is a pozzolanic reactive material with the potential use as a substitute of a part of Portland cement in concrete and other cementitious binders, like siliceous fly ash (FA). The level of RMUD pozzolanic activity is as high as the activity of siliceous fly ash. Comparative tests of concretes containing RMUD and fly ash, such as compressive strength, bending strength and shrinkage, were conducted. The concrete containing RMUD reached almost 90% of compressive and 108% of bending strength after 28 days of curing, compared to FA concrete. The results presented in this article are very promising and might point to a new way of valorising ilmenite mud waste. Concrete is increasingly used as a material in which to store waste instead of sending it to a landfill ,2,3,4. P2) is a white pigment, with a high refraction index and a high level of opacity, that is widely used all over the world mainly for the production of paints, plastics and paper. TiO2 is typically produced with one of two methods – chloride and sulphate. Each of these methods has its advantages and disadvantages. The chloride method generates far less waste products than the sulphate method, but for the production of TiO2 in the sulphate method, raw materials with lower concentration of TiO2 can be used. The global annual production of TiO2 in both methods is about 5.7 mln tons, of which about 35% is produced in the sulphate method. In Europe, the sulphate method is used for about 65% of production [Titanium dioxide , which is produced during the leaching of raw ilmenite with concentrated sulphuric acid. The leaching process, according to Reaction (1), can be described as:The main part of ilmenite is dissolved in acid but some remains, including all of the insoluble impurities from the ilmenite mineral. After separation of the solution, the liquid is carried to the next steps of the production, while mud remains. In most factories, MUD is categorised as a hazardous material according to European classifications  and is tIn the literature, one can find suggestions for the possible valorisation of MUD waste. Potgieter et al.  attempteGazquez et al.  used mudThe most promising idea found in publications is the addition of waste to red ceramic, as described by Contreras et al. ,19. TheyThis article presents a new way of valorising ilmenite mud waste as the authors did not find any similar publications. The idea was to use the waste as an additive to concrete. The global annual production of cement in the years 2014–2016 was calculated at about 4 bln tons [The high concentration of the remaining sulphuric acid (about 15%) makes this material useless for cement composites. Even after neutralisation with calcium hydroxide, the content of calcium sulphide is so high that it might increase setting time and lower the propagation of the compressive and bending strengths of cement. In order to counter these problems, a special batch of ilmenite mud waste was produced in the factory that has been additionally rinsed with water and filtered – rinsed mud (RMUD). As it was found, the leach contained some amounts of titanium sulphoxide, which is a very useful material for the production of titanium dioxide and, thus, it has returned to the production process. The process of rinsing mud decreased the content of sulphuric acid from about 15% to 1%. It also increased the percentage amount of silicon dioxide and aluminium oxide, and it lowered the content of most heavy metals. Heavy metals were immobilized in mortars that were not causing an environmental risk, and neither was the level of radioactivity of the raw RMUD . All the–consistency of fresh mix–density of fresh mix–compressive strength–flexural strength–water absorbability–water permeability through concrete–shrinkage–scanning microscopy (SEM/BSE+EDS)This article presents the results of tests of concrete with the addition of RMUD compared to the same concrete containing siliceous fly ash in the place of RMUD. The following tests were made:After neutralisation of the remaining sulphuric acid with calcium oxide to a slightly acidic solution , RMUD was dried at a temperature of 105 °C. Then, it was sieved through a 0.5 mm sieve to discard larger conglomerates. Neutralisation to a slightly acidic pH aimed at stalling the start of a pozzolanic reaction of the material before it came into contact with the cement binder. As the reference concrete, siliceous fly ash was used according to the EN 450-1 standard . Common –minimum strength class C20/25–3minimum cement content 260 kg/m–maximum water binder ratio 0.65Two types of concrete  were prepared according to the EN 206  standardAs aggregates, typical pebble gravel 2/8 and 8/16 coarse aggregate from central Poland, rinsed with mining sand, were used. 3 because, as the results of pre-tests showed, 260 kg of cement was not enough to reach the projected strength class on the 28th day.The amount of RMUD was 10.8% of the mass of the binder. This value was calculated from the statistical optimisation of mortars with the addition of RMUD . Table 2The properties of the fresh mix, such as consistency, using slump loss according to the EN 12350-2 standard  and the Concrete cubes of 150 mm were formed according to EN 12350-1 . After 2Samples of concrete with dimensions of 100 × 100 × 500 mm were formed. After demoulding, they were cured in water at a temperature of 20 ± 2 °C for 28 and 90 days. Flexural strength was tested according to EN 12390-5 . SamplesThe absorbability of concrete was tested according to PN-B-06250 . Cubes oWater permeability through concrete was tested according to PN-B-06250  on six 1Shrinkage tests were performed on 100 × 100 × 500 mm samples of concrete according to PN-B-06714-23  using AmFor scanning microscopy observations, 100 mm concrete cubes were prepared. They were cured in water at a temperature of 20 ± 2 °C for 90 days. After that time, they were cut to sizes appropriate for microscopic analysis. After drying them at 40 °C, they were saturated with resin under a vacuum. After hardening, the resin samples were polished and vapour-deposited with gold.Scanning electron microscopy (SEM) observations were carried out using the Leo SEM microscope  with a microscan EDS detector . Secondary electrons (SE) and back-scattered electrons (BSE) images were collected. 3) and fly ash (2.65 g/cm3) had no influence on the density of the fresh concrete mix. This was probably caused by the relatively small amount of additives to the mass of concrete. Another reason might be that the addition of RMUD caused a slight rise of air content, which is observed in mortars , do not show such an increase, according to Gołaszewski et al. . The compressive strength of FA concrete after 28 days was slightly higher than that of RMUD concrete. After 90 days, that difference had grown, although authors have proven similar levels of pozzolanic activity for RMUD and fly ash . There aThe differences of flexural strength for both concretes are smaller than the calculated uncertainty of the test method (± 0.5 MPa).The differences of water absorbability for both concretes were smaller than the calculated uncertainty of the test method (± 0.3 MPa). The addition of about 10% of cement mass RMUD in the place of fly ash did not show any significant differences in water absorbability. Observed differences might be due to air entrained by the addition of RMUD. The results of water permeability through concrete are presented in The shrinkage of the RMUD concrete was almost the same as the FA concrete. The differences were well within the calculated range of uncertainty (± 0.03 mm/m). No effect of expansion was observed, which might indicate that small amounts of sulphuric acid from the waste do not affect sulphate corrosion of the concrete in these circumstances.FA samples were visibly less porous than RMUD ones. RMUD samples contained unreacted particles of waste such as: ruthyl, pyroxenes, plagioclases and slightly reacted silicon dioxide. Also, partly leached ilmenite grains with a CSH phase with a partly modified composition were observed between ilmenite layers. RMUD concretes contained an almost unreacted silicone dioxide glass phase with additions of other constituents, such as magnesium, aluminium, sodium calcium and traces of titanium iron and manganium . 4AF phases as relicts of the clinker phase. The CSH phase in RMUD and FA concrete was very similar and, in addition to calcium and silicon, also contained some amounts of aluminium, sulphur and, in some areas, traces of iron and titanium. A higher concentration of magnesium was observed in some parts of the CSH phase in RMUD concrete. The aggregate-grout zone was rich in portlandite.Both concretes contained CA and CIlmenite mud waste from the production of titanium dioxide is a hazardous waste. As shown by the presented results, however, after some modifications, it might become a very useful material. Rinsing MUD with water helps to get rid of any remaining sulphuric acid and some of the heavy metals. The filtrate that is created during the process is also useful in further production of titanium dioxide. Thus, the process of rinsing does not generate any further waste. As shown by the test results, RMUD is a pozzolanic active material and might be used just like siliceous fly ash in cement composites. The addition of RMUD to concrete, as compared with that of fly ash, has no significant influence on the main properties of the fresh concrete mix (such as consistency or density). Its influence on compressive strength is quite similar to that of fly ash. The differences between compressive strength after 28 and 90 days of curing shows the potential activity of the material. Other publications  show cle–Slightly increase of consistency of fresh mix.–No influence on density of fresh mix.–Compressive strength reached 89% and 82% after 28 and 90 days of curing, respectively.–Bending strength reached 108% and 96% after 28 and 90 days of curing, respectively.–Water absorbability and water permeability were almost the same.–Shrinkage during period of 360 days was almost the same.–No structural defects were observed or any failures especially in zones surrounding grains of waste.The results of the tests performed did not show any disadvantages of using RMUD as a part of the binder in cement composites compared to fly ash. The following features has been observed in RMUD concrete compared to FA concrete:This study has shown that concrete might be successfully used as a store for this type of waste without it decreasing the concrete’s functional features. The most observed differences might be explained by the slight amount of air that entered the mix, which was caused by the addition RMUD to concrete.


The main objectives were to study the influence of the formulation parameters on the properties: shrinkage and creep, accelerated carbonation and water absorption, by capillarity, and by immersion. The lifetime of structures produced with the studied LCC was estimated, considering the durability performance, regarding the carbonation effect on the possible corrosion of the steel reinforcement. LCC mixtures with reduced cement dosage and high compactness, despite the high W/C ratios, have low shrinkage and those with higher strength have reduced creep, however depending on W/Ceq ratio. Those mixtures can be formulated and produced presenting good performance regarding carbonation resistance and, consequently, a long lifetime, which is mandatory for a sustainable construction. LCC with 175 kg/m3 of cement dosage is an example with higher lifetime than current concrete with 250 kg/m3 of cement; depending on the XC exposure classes (corrosion induced by carbonation), the amount of cement can be reduced between 37.5% and 42%, since the LCC with 175 kg/m3 of cement allows reducing the concrete cover below the minimum recommended, ensuring simultaneously the required lifetime for current and special structures.The sustainability concerns of concrete construction are focused both on the materials’ eco-efficiency and on the structures’ durability. The present work focuses on the characterization of low cement concrete (LCC), regarding time-dependent and durability properties. LCC studies which explore the influence of the formulation parameters, such as the W/C (water/cement ratio), W/Ceq, , W/B (water/binder) ratio, and the reference curves, on the aforementioned properties are limited. Thus, several LCC mixtures were formulated considering two dosages of binder powder, 350 and 250 kg/m Current forecasts indicate an increase in cement consumption worldwide from the current annual value of around 4.2 billion tons to about 5.2 billion tons by 2050 . With th2 by 2030 and up to 8% by 2050 are expected. Associated with this measure, it is equally important to congregate the mechanical, time-dependent and durability properties, and the lifetime requirements of concrete structures. Currently, concerns about the durability and long-term performance of concrete are obstacles that limit the use of some additions in many applications. Water absorption, carbonation depth, shrinkage and creep performances are some of the parameters that can be used as indicators of durability and long-term performance of concrete.One of the solutions to mitigate the environmental impact associated with the production of the clinker, proposed by the European Cement Association (CEMBUREAU) in 2013 [During the design phase of a concrete structure, the service life is established, corresponding to the period during which it meets the requirements for safety, functionality, and aesthetics without unforeseen maintenance costs . These rBoth durability and serviceability behaviors of reinforced concrete structures are influenced by time-dependent properties, mainly shrinkage and creep. Creep results from the viscoelastic behavior of concrete and corresponds to its deformation with age when subjected to constant stress level, which starts after the elastic deformation originated by loading. Nevertheless, it can be analyzed as basic creep (constitutive) and drying creep . Those values are fundamental to predict the total creep deformation. The increase of creep deformation is more accentuated soon after the load is applied and it reduces with increasing age, although it tends to stabilize generally before one year of age ,6,7. The0)-Equation (1), over age t is predicted by Eurocode 2 (EC2) [0); type of cement; cross-sectional dimensions; compressive strength of concrete (fcm); and thermo-hygrometric conditions (relative humidity and temperature). The notional creep coefficient, φ0, is obtained from Equation (2) and considers those parameters, being the evolution curve obtained from Equation (3).The type and dosage of cement and the water/binder ratio significantly affect the concrete creep , but tha 2 (EC2)  and by M 2 (EC2) , accordics, or total shrinkage, is the dimensional variation mainly caused by the combined effects of the drying shrinkage, εcd, and the autogenous shrinkage, εca. However, the sum of drying and autogenous shrinkage values is a simplification, since both parameters are caused by the reduction of the relative humidity (RH) of the concrete. Drying shrinkage occurs due to evaporation at the concrete’s surface, while autogenous deformation is caused by partial emptying of the gel pores as a consequence of cement hydration [cd with age depends on the concrete strength, type of cement, geometry, curing conditions and initial age of drying. In EC2, the evolution of εca with age depends only on the concrete strength, while in MC10 it depends on both concrete strength and cement type. The drying shrinkage component, εcd (t), can be estimated, according to EC2, using Equations (4)–(6). In these, the estimated drying shrinkage, εcd,0, considers the most influent parameters mentioned above and βds  defines the shape of the shrinkage evolution curve.The shrinkage deformation, εydration ,16,17. Nydration  and MC10ydration , the evoShrinkage of concrete must be characterized or reliably predicted because, if excessive, it causes undesired effects for reinforced and prestressed concrete elements, namely: (i) transversal cracking, due to the restriction of reinforcement, compromising strength and durability of structural elements; and (ii) excessive pre-stress losses, changing the structural behavior. Thus, the concrete formulation parameters must take into account the shrinkage minimization, in addition to complying with the other specifications, thereby contributing to guarantee the quality and durability of the concrete structures. The increase of concrete shrinkage is mainly influenced by factors such as: the increase of binders dosage and the hydration heat; the increase of water/binder ratio; the increase of the air volume in the paste and the permeability of the concrete; the worsening of thermo-hygrometric curing conditions (high temperatures and low relative humidity); the reduced age at the start of drying; the lower stiffness of the aggregates; and the reduction of cross-section dimensions ,18,19.226Ra), thorium (232Th) and potassium (40K), and their specific activity may exceed the average specific activity [In general, several supplementary cementitious materials can be used as additions to the binder paste of concrete, in a strategy of cement partial replacement, being the pozzolanic additions and ground granulated slags the most effective and promising additions to that purpose. Between the commonly used pozzolanic additions are silica fume, fly ash or metakaolin, among others, which generally improve concrete workability, strength and durability ,23,24,25activity . The addAccordingly, the present work has as main objectives: (i) to produce low-cement concrete (LCC) mixtures varying the main composition parameters, namely, the compactness and the water/binder ratio, the cement dosage with partial replacement by combined additions and the granulometric reference curve; (ii) to relate the cement dosage and the mechanical strength of concrete, as well as other formulation parameters, with the evolution and amplitude of the shrinkage and creep; (iii) to evaluate the influence of the compactness of the mixtures, and also W/C and W/B ratios, on the development of shrinkage and creep, as well as on other properties of concrete related to durability; (iv) to analyze the influence of the reference curves, Faury and Alfred, on concrete creep; (v) to relate the formulation parameters of the mixtures with the water absorption of concrete, by immersion and by capillarity, as well as with the carbonation depth; (vi) to estimate the lifetime of structures produced with the characterized LCC, taking into account the resistance to carbonation, which is associated with the corrosion risk of the steel reinforcement; (vii) to compare the results obtained with the standards and study possible improvements.Recently, several researchers have investigated the individual effect of the high volume of fly ash as a partial replacement of Portland cement, and have objectively proved that these additions have a significant influence on the concrete properties ,30,31,32The granulometric optimization and the use of superplasticizer also contribute to the improvement of the efficiency of the binder paste and the durability and strength of the concrete ,34,41, aProblems with durability of concrete are generally associated with the mentioned parameters, generally in matrices with high porosity and excess of water , providiThe use of different granulometric curves in the optimization affects the relative proportions of the aggregates used, which in turn influence the compactness, the workability, and the Young’s modulus . Regardi3), with a target consistency of class S3 (very plastic consistency); (ii) low-cement (LC) series, with a reduced dosage (250 kg/m3), varying the effective cement dosage in substitution regime with the addition of limestone filler and fly ash, with a dry consistency and low cohesion.In order to evaluate the formulation parameters of the binder paste and the efficiency of granulometric optimization in the mechanical performance of concrete with low-cement content, Costa et al.  and Frei3), the water/cement (W/C) ratio consequently varies. The substitution of cement by additions was defined giving priority to the filler until a maximum equal to the cement mass was reached, followed by the complement of fly ash, when necessary, until the dosage for the binder powder was reached. A subseries of C concrete was also formulated, named C_B, varying the compactness values from 0.81 in C series to 0.835 and to 0.855 in mixtures C200B and C175B  and the amount of binder powder (having 250 kg/m3 in LC concrete and 350 kg/m3 in C concrete). In the LC series, formulation by the Alfred’s curve  was considered. The other series or subseries  were formulated using the Faury’s reference curve. In LC250 mixture, a compactness variation, between 0.86 and 0.80, and consequently the W/B ratio were also considered for LC mixture with 250 kg of cement dosage (resulting in LC250 and LC250A mixtures). The dosages of all constituents mentioned are shown in The formulated mixtures were referenced considering the amount of cement . At 28 days of age, the following properties were also characterized: splitting tensile strength, fctm,sp, according to EN 12390-6 [3; flexural strength, fctm,f, following the standard EN 12390-5 [3; the Young’s Modulus, Ecm, according to the specification of National Laboratory of Civil Engineering (LNEC) E-397 [3. The average values of that properties are shown in The determination of the compressive strength, was carried out according to EN 12390-3 , in cubi 12390-5  in two pC) E-397  in two p3 prismatic specimens  water absorption by immersion, which was carried out on cubic specimens with 100 mm edge and according to LNEC E394 specification [The durability performance was characterized by the following tests : (i) watfication ; and , Equation (6), the value of the second part of the denominator was adjusted, from 0.04 to a βshape coefficient, Equation (7), which can assume values of 0.06 for concretes of C series and 0.08 for concretes of LC series, allowing a better adaptation of the evolution with age , relation b suggestc(t)  have similar evolutions and amplitudes, with creep coefficients close to 1.6 at 210 days of age. LC175 concrete has a smaller creep amplitude compared to those mentioned (creep coefficient close to 1.3 at 210 days of age), as expected, because it has a higher cement dosage and greater strength. Despite the reduced influence of the granulometric curve is proven in creep coefficient, the creep deformation is lower in concrete with Alfred’s curve, since the Young’s modulus of those concretes  are 11% to 30% higher than those formulated by the Faury’s curve . That difference is higher in concretes with a lower cement dosage and decreases with the increase of its dosage. With the exception of LC250A concrete  and C200 (concrete with compactness of 0.84), which showed a creep coefficient at 210 days, from 1.92 to 2.12, respectively. The remaining concretes show a similar evolution and amplitude, whose coefficient is around 1.6 at 210 days. Part of the influence of these values is evidenced by the different mechanical strengths, as mentioned.The results obtained for the creep characterization are presented through the evolution, over time, of the creep coefficient, φc(t) , with thc , Equation (3), the exponent of that ratio, αt, was adjusted from 0.30 to 0.15, Equation (8), obtaining a better adaptation of the evolution with age , which represents the mass ratio between water and equivalent cement, presents the best fit , best fit .cm) coefficient, Equation (9), the result of the correlation obtained was incorporated in determining this coefficient. Due to the verified dispersion, the amplitude of the correlation was reduced in order to ensure conservative predictions, resulting in a new proposal to predict coefficient β(fcm), expressed by Equations (10) and (11).Knowing that the amplitude of the creep curves strongly depends on the β, eq ratio, the creep curves of the characterized concrete have much better adjustment compared to experimental results  gel resulting from hydrated cement occupies the voids inside the matrix, also reducing absorption, because the matrix is more dense and less porous. The ratio that incorporates compactness and W/Ceq was studied, which provides the best correlation, and this relation is shown in Furthermore, in each series, C and LC, it is clear that the water/equivalent-cement ratio, W/Ci, Sa(ti), in mg/mm2.The capillarity test allows the determination of the amount of water that concrete absorbs by suction, through small pores. In both series, the water absorption by capillarity occurs with greater intensity in the first 24 h and tends to stabilize over time, which occurs earlier for concretes with increased compactness and higher cement dosage. As the water starts to penetrate the concrete by capillarity, it is noticed that after the saturation of the pores at the lowest level of the specimen, the water level tends to rise. The maximum height that the water can reach is limited by the pressure difference between the free surface of the water outside the concrete and its surface in the capillary pores of the concrete, and also by the gravitational action. Hence the tendency for water absorption by capillarity to stabilize over time [3, concrete LC250A have reduced compactness of 0.8, being the main reason for high capillary absorption.In C75 concrete there is also a pronounced initial evolution, but with an increasing trend until 72 h and with much higher values, at least 45% at 24 h and 80% at 72 h, comparatively with the other concretes. This must be associated with the reduced compactness combined with very low cement dosage, despite the high content of fly ash (FA/C = 2.7). When comparing this concrete with the others, it is noted that LC250A succeeds it with high capillary absorption, presenting a behavior with similar tendency, however less pronounced. Despite the cement dosage of 250 kg/mWhen comparing results of C75 and LC75, it is noted that the latter presents lower values of capillary absorption than the C75, from 35% at 3 h to 65% at 72 h, increasing the difference with the duration of the test. Those differences are essentially due to greater compactness of the LC75, given that both concretes contain the same amount of cement and a high content of fly ash (1.3 times the proportion of cement in LC75 and 2.7 in C75). In these mixtures, it appears that the high fly ash content did not have much impact on the difference between the results of both concretes, otherwise, the differences could be smaller. This must be associated with low cement dosage, since the fly ash forms the gel of calcium silicate hydrates crystals (CSH), which improve the performance of the concrete, from the reaction with released hydrated lime (CH) during the clinker hydration . As ther3 of fly ash in the paste, while the compactness of LC125 concrete is 0.86 but does not contain fly ash. Due to the significant difference between the compactness of the two concretes, it would be expected that the difference between the capillarity absorption values would be significant. This situation did not occur, thanks to the presence of fly ash that allows the reduction of absorption by capillarity.The previous comparison did not allow assessment of the influence of fly ash on capillarity absorption results, since both concretes had high FA/cement ratio, but very different compactness. However, when comparing LC75 with LC125, both with the same compactness, it is noted that the former shows lower capillary absorption than the LC125, from 18% in lower test duration to 43% for higher duration, also increasing the differences with the duration of the test. This difference proves the effectiveness of fly ash in LC75 concrete, also emphasizing that the LC125 has a cement dosage about 67% higher than that of the LC75 , but sim3, and approximately equal compactness, however differing on powder content (250 kg/m3 on LC175 and 350 kg/m3 on C175B) and on fly ash content (C175B contains 75 kg/m3 of fly ash). The combination of fly ash with cement may be associated with that improvement in C175B binder paste, because this addition allows the development of new compounds that fill the pores of concrete matrix.The C175B and LC175 concretes show similar and better capillarity water absorption results than the other concretes, however LC175 concrete shows slightly lower results in the first 24 h, and from that period the trend was reversed, with the concrete C175B having inferior absorption. Considering that both concretes have the same amount of cement, 175 kg/mThe differences found in the different formulated concrete can be seen from the analysis of a (in milligrams per square millimeter) as a function of the square root of time, obtained for each mixture, as well as the slope that expresses the capillary absorption coefficient of the concrete. According to Browne’s classification cited in Coutinho [a, are less than 0.1 mg/(mm2·min0.5); medium quality for concretes whose coefficients are between 0.1 e 0.2 mg/(mm2·min0.5). It can be seen that C75 concrete can be classified as medium quality, C250 starts with medium quality and obtains a better classification over time, while the rests are classified as high quality.Coutinho : high quThe results of capillarity absorption allow us to conclude that just increasing the cement dosage does not imply an improvement in the durability characteristics of the concrete, clearly demonstrating the importance of packing optimization and of binder paste, as its impact is significant on the compactness of the concrete .The concrete carbonation is associated with the penetration, by diffusion, of carbon dioxide into the concrete. When it is dissolved in concrete, it induces chemical reactions to dissolve the crystalline phases of concrete, such as calcium hydroxide (CH) giving rise to the production of carbonates, such as calcium carbonate, which leads to a reduction of concrete pH ,67. Therd, in millimeters. Looking at the carbonation development curves along the square root of time  and to predict the service lifetime of the reinforced concrete structures using the developed concretes and the standard covers. Those calculations were based on the degradation model by corrosion of reinforcements, developed by Tuutti, and on the recommendations described on LNEC specification E465 [g) equal to 50 years, with a reliability class RC2 , which corresponds to a safety factor γ equal to 2.3; (ii) special structures with a tg equal to 100-year-old, with a reliability class RC3 , which corresponds to a safety factor γ equal to 2.8.Based on the results obtained in carbonation test, it is possible to calculate the minimum concrete cover, cion E465 . Two typdi, at several days of exposure to carbon dioxide, with a concentration, Cacel, approximately equal to 90 × 10−3 kg/m3, the carbonation resistance, RC65 (kg·year/m5), was determined using Equation (12). The results are shown in To compute the minimum necessary cover, it is essential to calculate the carbonation resistance, RC65, of the studied concretes, to define the design period of initiation, tic, and, finally, to calculate the carbonation depth for various environmental exposure classes XC. Therefore, based on the experimental carbonation depth values, Cic, is the difference between the intended service lifetime for the reinforced concrete structure, tg, and the propagation time, tp, affected by the safety factor mentioned above, see Equation (13). The propagation time depends of the environmental exposure class and was considered the minimum accordingly to the specification of LNEC E465 ticmin,dur, is determined using Equation (14) and considering a time equal to tic  is possible to slightly reduce the required compactness to achieve a similar carbonation resistance, comparatively with the produced concretes with 250 kg/m3 of total powder (LC series), because higher quantities of powder improve the workability, which may reduce the porosity of the matrix [The results show that it is necessary to use a minimum quantity of cement to assure that concrete develops the proper resistance against carbonation . To bettpactness b,d. In te matrix .eq ratio reflects both effects analyzed above, compactness and equivalent dosage of cement, in one parameter. This ratio was related with cmin,dur and it is clear that a ratio above 0.72 increases significantly the concrete cover required to protect the reinforcement steel .The prediction of the possible service lifetime for reinforced concrete structures produced using the developed concretes and the covers recommended in the codes was carried out for several environmental conditions XC and for both types of structures S4 and S5. Equation (14) was used to determine the tC65, more than enough for the exposure class XC, having a margin to decrease the minimum cover used in reinforced concrete structures. On XC2 conditions, the service lifetime values are quite high because the carbonation depth, Cd, is very low in terms of environmental conditions. For special structures and under XC4 in wet regime conditions, only the LC175 and C250 presents a proper performance, since they are the only ones with a predicted service lifetime higher than 100 years.Analyzing the values in 3. Nevertheless, it is generally possible to produce concretes with low-carbon cements that provide a proper performance against carbonation and, consequently, a long service life, which is a major step to achieve a more sustainable construction sector.These results also show that concretes with very low dosages of cement, like LC75, C75, LC125 and C125, are not appropriate to provide proper protection against corrosion under XC exposure conditions. It can also be stated, comparing the LC250A with C250, but that is not only the equivalent dosage of cement that matters concerning this resistance, it is also very important to use in this type of concrete a limestone filler to ensure a certain quantity of powder in the mixtures, which must be around 350 kg/mThe possible addition of fibers into LCC may be an important future research topic to improve the carbon reduction and its sustainability even more. The bond strength between steel rebars and low cement concrete is significantly improved by the higher compactness of LCC ; thus, i3) promotes reduced shrinkage, tending to increase with the increase of cement dosage; however, in concrete with powder dosage of 350 kg/m3, the increase of compactness tends to gradually decrease shrinkage; (ii) due to the inadequacy of the EC2 prediction of shrinkage, compared to experimental values, a correction is proposed to improve the curves development, where a βshape coefficient assumes different values (0.06 for concrete with powder of 350 kg/m3 and 0.08 for concrete with powder of 250 kg/m3); (iii) beyond the parameters considered by the concrete codes, the concrete compactness has a noticeable influence on the amplitude of concrete shrinkage, mainly when combined with reduced binder powder (250 kg/m3) and very reduced cement dosage, where the experimental/prediction ratio of shrinkage can go down to 0.4.Shrinkage: (i) LCC concrete with high compactness of 0.86 and reduced powder dosage (250 kg/m3), does not have a relevant influence on the evolution and amplitude of creep coefficient; (ii) similarly to the known behavior of current concrete, the creep coefficient is highly influenced by the concrete strength; thus, LCC presents reduction of creep coefficient for concrete with high compactness (0.86) and higher cement dosage (175 kg/m3), which has also higher strength; (iii) a divergence between the shape of the creep curve experimentally obtained and that according to EC2 is noticeable; however, the shape of the creep curve can be improved significantly by adjusting the αt coefficient on βc  parameter, from 0.30 to 0.15, for LCC; (iv) there is a huge difference between experimental and EC2 predicted values for the creep of LCC, mainly in concretes with lower cement dosage and with lower compactness (0.80 to 0.81), thus with higher W/B ratio, the creep being ratio experimental/code around 0.3; (v) W/Ceq ratio has a significant influence on that difference, therefore, a corrective parameter is proposed to be included on the β (fcm) coefficient of EC2 to significantly improve the code prediction, namely Creep: (i) the granulometric reference curve (Faury vs. Alfred), in concrete with reduced binder powder 0.2/Compactness6, proved by correlation analysis, has high influence on water absorption.Water absorption by immersion: (i) the increase of compactness has a great influence on the reduction of water absorption, since the values for concretes with lower compactness (0.80 to 0.81) are close to 15% and those values reduce to below 10% for concretes with compactness of 0.86; (ii) the W/C3).Water absorption by capillarity: (i) high compactness of LCC combined with higher cement dosage significantly reduces the capillary absorption; (ii) fly ash addition as partial replacement of cement also promotes a significant decrease in capillary absorption; however, its excessive dosage may jeopardize the concrete performance regarding capillarity; (iii) the capillary coefficients of the LCC characterized allow all concretes to be classified as high quality, except the one with reduced compactness (0.81) and very reduced cement dosage (75 kg/m3 of binder powder) exhibits much lower carbonation depth than the corresponding C series (concrete with lower compactness and 350 kg/m3 of binder powder); (ii) maintaining the binder dosage, the carbonation depth decreases with the increase of cement or equivalent cement dosages, since it reduces the W/Ceq ratio; (iii) the higher the amount of fly ash incorporated in the concrete, replacing cement dosage, the lower the carbonation resistance, because it increases the carbonation velocity; (iv) it is possible to produce concrete with good structural performance, with low binder powder of 250 kg/m3 and only 175 kg/m3 of cement dosage, developing higher carbonation resistance, in circa 10%, than current formulation concrete with 250 kg/m3 of cement dosage and binder powder of 350 kg/m3.Carbonation resistance: (i) maintaining the cement dosage, compactness increase has a significant influence on reducing carbonation depth, since the LC series (concrete with high compactness of 0.86 and with 250 kg/m3 (even though with very different formulation parameters) have adequate resistance to carbonation for general exposure; for those concretes the minimum required covers are lower than those presented in EC2, reaching differences of up to 17 mm; (ii) the compactness increase has also high influence on reducing the minimum cover, since it increases the concrete strength and carbonation resistance; reducing the concrete compactness implies increasing the cover, even if higher cement dosage is used; the LCC with 175 kg/m3 of cement and compactness of 0.86 presents much higher resistance to carbonation compared to that of all formulated concrete, including those with equivalent cement dosage between 200 and 250 kg/m3.Minimum cover required to avoid corrosion induced by carbonation: (i) it is necessary to use a minimum cement dosage, since only concretes with cement dosage equal or higher than 175 kg/m3 of cement dosage have, submitted to XC2 and XC3 conditions, service lifetime values above the minimum, for current (50 years) and special (100 years) structures and, for XC2, the values are quite high; (ii) for special structures and under XC4 in wet conditions, only the LC175 and C250 have adequate performance, the first due to the high compactness and the latter due to higher cement dosage, being the only mixtures with an expected lifetime of more than 100 years.Lifetime of structures due to carbonation exposure: (i) higher cement dosages promotes longer lifetime; concretes with at least 175 kg/m3 of cement dosage reveals adequate combined mechanical, time-dependent and durability performances; (ii) concrete LC175 (with high compactness of 0.86 and powder dosage of only 250 kg/m3) is revealed to be the most eco-efficient of the concretes studied herein, since for current and special structures, and for any type of XC exposure, it is possible to reduce the cover below the standard minimum, presenting a long lifetime; (iii) the amount of cement can be reduced between 37.5% and 42%, depending on the environmental exposure classes XC, comparing the LCC concrete which contains only 175 kg/m3 of cement with the minimum recommendation of 280 kg/m3, for XC2 and XC3, and 300 kg/m3 for XC4.LCC mixtures with a good performance and a long lifetime: (i) concrete with at least 175 kg/mBased on results analysis of the experimental study of concretes with low cement content (LCC), developed by varying the dosage of binder, the compactness, the rate of cement replacement by additions and the granulometric reference curve, it was possible to draw the following conclusions.


The chord lengths, specific surface areas, contents and spacing coefficients of the pores in the designed concretes are measured and analyzed. The results show that concrete mixture incorporated with 5% silanized rubber and 3% nanosilica shows good synergetic effect by considering both mass loss and relative dynamic modulus of elasticity (RDME). The freeze–thaw damage degree of the concrete could be reduced by adding high elastic rubber particles, due to filling and constraining pores, and resulting in better uniform pore distribution and smaller pore spacing coefficient. Furthermore, the correlations between frost resistance and pore are analyzed and proposed.This paper aims to develop frost-resistant concretes, and investigate their pore structures and freeze–thaw damage mechanism. The frost-resistant concrete mixtures are designed by using rubber particles and nano-SiO With thsistance .However, due to the significant difference of physicochemical properties between organic rubber and inorganic cement concrete, the process of combining them is often complex, resulting in poor compressive performance . The add2 [The freeze–thaw damage of concrete has been a critical scientific topic since the 1940s, and some hypotheses and frost damage theories have been proposed and researched . Some re2 .In order to improve the frost resistance of concrete, some probable measurements have been investigated, such as using hydrophobic coatings, adding air entraining agents and optimizing the matrix by modified raw materials ,13,14. R2.The frost resistance and mechanical properties are dependent on the pore structure, such as pore morphology and pore size distribution . Then, f2 are listed in 3. The rubber particles are produced from recycled waste tires, the average particle size is 140 µm and specific density is 1.11 g/cm3. In order to improve the bond between rubber and matrix, both normal and silanized rubber particles, respectively, are utilized and researched in this paper. The mixtures are designed including following materials: cement P.C. 32.5R, fly ash, nanosilica, river sand, coarse aggregate, rubber particle, plasticizer and water. The physical and chemical properties of cement are shown in 2, rubber and silanized rubber on the performance of frost-resistant concrete, another six mixtures are designed based on the control concrete, as shown in 2 is added by partially replacing powder (cement and fly ash) by mass. The contents of rubber and silanized rubber particles are calculated by the mass of cement, and partially replace the sand by volume.The recipe of the control concrete is shown in The freeze–thaw cycle test is conducted according to the Chinese standard GB/T50082-2009 [To analyze the pore structure of concrete after a freeze–thaw cycle test, a commercial pore structure analyzer  is utilized. Each concrete sample is cut and polished into 6 square slices (100 mm × 100 mm × 10 mm). Then, the intersections of concrete slices are scanned by the Airvoid with a testing resolution of 2 µm.lm), specific surface area of the pore (a), the air content (A) and the average pore spacing coefficient (L).l is pore diameter. N is total number of pores. ln is number of pores per unit volume. S1 and S are the pore area and whole concrete area, respectively. P is the volume rate of hardened cement paste without air pores, %.The parameters and characteristics of the pores should have great impact on the mechanical and frost resistance properties of concrete . To compIn order to characterize the propagation mechanism of pore structures under freeze–thaw cycles, the concrete pores can be categorized into four types based on the pore size distribution and testing result , as showIn this paper, the microstructure characteristics of freeze–thaw damaged concrete samples were observed by FEI QUANTA 250  scanning electron microscope.2, the compactness of the cement concrete is significantly improved, and the pore content is also significantly reduced, which indicates that nano-SiO2 improves the internal structure of cement concrete. The reason is that the size of the nano-SiO2 particles is small. According to the surface and small size effect, the number of atoms on the surface increases. Under the conditions of more unsaturated bonds, higher surface energy and chemical activity of particles, it is easy to combine with other atoms to form a uniform and stable state. The addition of silylated rubber can change the microstructure of concrete particles and pores, and improve the adhesion between the rubber particles and the concrete [2 has an effect on the microstructure of concrete. There is basically no crack on the boundary between hydration products and concrete aggregates, and they are closely linked to each other. The distribution of hydration products is particularly uniform. The C–S–H and AFt of the structure are more than ettringite AFt. No large pores and voids were found in the microstructure.concrete . The addThe frost resistance of concrete is usually described and characterized by mass loss and the relative dynamic modulus of elasticity (RDME) . Figure 2. In the presence of nano-SiO2, the frost resistance of concrete is enhanced based on the results of the mass loss and RDME loss. However, the improvement on mass stability is not as much as the RDME. Frost-resistant concrete incorporated with both silanized rubber and nano-SiO2 can retain relatively higher mass and RDME values even suffering from 300 freeze–thaw cycles. For example, the MR5N0.5 and MR5N3 still have approximately 70% RDME. It indicates that there exits a positively synergistic effect between silanized rubber and nano-SiO2 on frost resistance.In this study, the mass of the concrete firstly increases because of absorbing the water. After more than 125 freeze–thaw cycles, the mass of the specimen declines. This phenomenon also fully shows that when evaluating the frost resistance of concrete, its mass loss is a variable parameter. When the parameter changes to a negative, it indicates that the concrete has a macro failure  studied 2 for developing frost-resistant concretes, considering both mechanical strength and freeze–thaw resistance. This study recommends using 5% silanized rubber and 3% nano-SiO2, namely, a mixture of MR5N3.To sum up, it is necessary to add appropriate contents of the rubber aggregate and nano-SiO2 tend to decrease the total pores. The addition of nano-SiO2 could density the microstructure by the pozzolanic effect. It helps to improve the hydration degree and produce more C–S–H gel by reacting with Ca(OH)2, and then fills the small pores [ll pores . The conll pores  investig2 are greatly enhanced. The addition of rubber aggregates is the most important factor in the pore structure, after which are the silanized rubber aggregates, and rubber and nano-SiO2. In this study, the mixture of MR5N3 has the appropriate contents of silanized rubber and nano-SiO2, occupying more than 90% of pores smaller than 200 μm, which results in its improved properties such as compressive strength and frost resistance.2 have a relatively higher specific surface area of pores, which is in line with the research by Zhu et al. [u et al. . To unde2 shares a similar total pore area to that in the control concrete. It indicates that rubber can strengthen the elasticity of pores, and then improve the frost resistance. 2 contributes to slightly reduced air contents. The air content distributions vary greatly for the different concrete mixtures, as shown in 2 is suggested at less 4% air content. The air content or porosity greatly affects the frost resistance of the hardened concrete. 2 shows the fastest development of air content, which means its freeze–thaw damage propagates rapidly. The mixture of MR5N3 has the slowest air content development, which indicates 5% silanized rubber aggregates and 3% nano-SiO2 have positive synergistic effect on frost resistance. The fine rubber aggregates can fill in some pores and especially improve the elasticity of pores, then enhance the frost resistance [To analyze the change of air content during freeze–thaw damage, the air content development is tested after each of 50 times freeze–thaw cycles, as shown in sistance . HoweverMeanwhile, this paper also conducts statistical analysis on the pore number per unit area in concrete after freeze–thaw cycles. A higher increased pore number per unit area indicates a worse frost resistance, as shown in With the increase in freeze–thaw cycles, the absolute number of pores increases but the growth rates decrease. Based on analysis of the pore number growth rate after different freeze–thaw cycles, it shows that the pore number increases sharply in the first 50 freeze–thaw cycles, especially in the middle pore. The pore size changes from large to small in the order of Control > NSC0.5 > RC-7.5 > MRC-5 > MR5N3, and the growth rate of extra large pores is the smallest. At the beginning of the freeze–thaw cycle, the micro and nanopores expand under the action of frost, and microdamage occurs, which is manifested by the sharp increase in the number of small and medium pores in the concrete. With the gradual increase in freeze–thaw times, the microdamage leads to the interconnection and expansion of small pores, forming macropores, and the number of pores at all levels increases with the increase in freeze–thaw times. The increase in the number of extra large pores is the main factor affecting the freeze–thaw damage.The pore spacing coefficient represents the average distance between each pore, which is the most important factor affecting the frost resistance of concrete. A larger pore spacing coefficient results in a worse frost resistance, due to the greater hydrostatic pressure and osmotic pressure produced by water in concrete pores during freezing and thawing. On the contrary, if the pore spacing coefficient is smaller, the frost resistance of concrete is better. The pore spacing coefficients of the different concretes are shown in L and frost resistance including mass loss and RDME, as illustrated in 2 is more than 65%, while the mass loss rate is less than 4%. The best frost-resistant concrete corresponds to the pore spacing coefficient of about 330 μm. Therefore, the frost resistance of the concrete incorporated with silanized rubber and nano-SiO2 is better than that of ordinary concrete.This paper also researches the relationship between average pore spacing coefficient 2, and investigates their pore structures and freeze–thaw damage mechanism. The mass loss, relative dynamic modulus of the elastic, chord lengths, specific surface areas, contents and spacing coefficients of pores are tested. The main conclusions of in this paper can be summarized: 2 to partially compensate for the strength loss. The silanization of the rubber could further enhance the interfacial bond between the rubber and the matrix, thus improving strength and frost resistance.The addition of an appropriate content of rubber aggregates could greatly improve the frost resistance of concrete, but usually decreases the mechanical strength. It is necessary to add nano-SiO2 is the best modified mixture, which is recommended for developing frost-resistant concrete.Considering both compressive strength and frost resistance, concrete incorporated with 5% silanized rubber and 3% nano-SiOThe damage degree develops with the increase in freeze–thaw cycles, resulting in the continuous reduction of mass loss and the dynamic modulus of elasticity. The highly elastic rubber improves the stiffness, pore size and distribution, which thus significantly increase frost resistance.A more homogenous pore distribution can withstand a higher expansion pressure generated by freezing, which contributes to a better frost resistance. With the increase in freeze–thaw cycles, both pore area and diameter increase, and the increased degree of the pore diameter is more remarkable than that of the area.The pore structure and frost resistance can be characterized by the chord length, specific surface area, air content and average pore spacing coefficient. This research proposes to comprehensively utilize those parameters as quantitative evaluation indexes of frost resistance.This paper develops frost-resistant concretes incorporated with rubber aggregates and nano-SiO2 can improve the frost resistance of concrete, which will become an effective tool for improving the performance of concrete. Further research is necessary to investigate the effects of the long-term performance of the frost-resistant concrete and its practical engineering applications.The main conclusions have verified that silanized rubber and nano-SiO


To evaluate research listed as “Submitted” on orthopaedic surgery residency applications for eventual publication rates and quality.As the orthopaedic surgery residency selection process becomes increasingly competitive, the number of research publications listed on applications continually increases. However, the utility of using publications listed as “Submitted” in the applicant evaluation process remains unknown.Demographic and publication data were retrospectively collected from 1303 applications to an orthopaedic surgery residency program. The PubMed database was used to verify “Submitted” publications for (1) publication fruition or (2) publication mismatch, defined as discordance between the listed journal of submission and the eventual journal of publication.P < 0.01). Demographic data were not predictive of having an unverified publication.A total of 594 applications (45.6%) listed ≥1 publication as “Submitted.” Out of 1636 “Submitted” publications, 565 were unverifiable (32.5%). Of the 1071 verified publications, 362 (33.8%) experienced publication mismatch. Within this subgroup, a significant difference existed between the mean impact factors of the listed journal of submission and the eventual journal of publication (1.5 ± 2.7 versus 3.0 ± 2.5, Publications listed as “Submitted” in orthopaedic surgery residency applications frequently remain unpublished or are published in less impactful journals than originally intended. Gaining admission to an orthopaedic surgery residency is a demanding task. The modern applicant typically pursues multiple elective away rotations in orthopaedic surgery before being selected for a series of interviews, during which they must present themselves as accomplished well-rounded individuals who have a genuine interest in the field of orthopaedic surgery. To achieve success in the residency selection process, applicants must seek to distinguish themselves from their peers through a variety of objective and subjective metrics, including United States Medical Licensing Exam (USMLE) step 1 and step 2 scores, letters of recommendation, and clerkship grades.2 This statistic consists of both “verified” publications that have been published in print or online by a scientific journal and “submitted” projects that are not yet published or currently under consideration by a scientific journal. Unfortunately, given the competitive nature of matching into orthopaedics, this “submitted” project category presents an opportunity for applicants to overrepresent or misrepresent their research accomplishments to appear as more competitive candidates.One such metric that is commonly used to evaluate applicants is scholarly research activity. The number and quality of research publications listed on an application can provide insight to an applicant's ability to understand the scientific process and carry out a research project from inception to completion. Additionally, the presence of orthopaedic research helps demonstrate an applicant's interest in the field of orthopaedic surgery. Given the increasingly competitive nature of applying to orthopaedic surgery residencies, the quantity of scholarly research disclosed by applicants has increased drastically. From 2007 to 2016, the mean number of research abstracts, presentations, and publications listed on applications to orthopaedic surgery residency programs increased nearly threefold, from 3.0 to 8.2.345678910111213141516 Rates of misrepresentation in orthopaedics have significantly decreased over the last 20 years, likely due to the advent of including PubMed identification numbers in the Electronic Residency Application Service (ERAS) standardized residency application.12 While previous studies have examined publication misrepresentation among verified publications, no study to date has examined the outcomes of publications listed as “submitted” at the time of application to orthopaedic surgery residency. These “Submitted” publications have no associated PubMed identification, which prevents their outcomes from being verified during the residency application process.Publication misrepresentation has already been well-studied in multiple fields, including orthopaedics.Interpreting the value of these “Submitted” publications therefore remains unclear. Thus, the purpose of this study was to examine a population of orthopaedic surgery residency applicants to characterize the likelihood of eventual publication of research projects listed as “Submitted” at time of application to orthopaedic surgery residency. We also sought to identify applicant demographic factors that may affect the likelihood of eventual publication and compare the impact factor of a publication's listed journal of submission with that of its eventual journal of publication. We hypothesized that the eventual journal of publication would have a significantly lower impact factor than the listed journal of submission.Demographic and research publication data from three application cycles (2013 to 2014 through 2015 to 2016) were retrospectively collected from applications to an orthopaedic surgery residency program at a large academic center. These applications cycles were chosen to provide for sufficient time (>1 year) for “Submitted” publications to be reviewed and published in scientific journals. All applicant data were deidentified after data collection and before data analysis. Demographic data consisted of applicant age, gender, US World and News Report medical school research funding ranking, USMLE step 1 score, USMLE step 2 score (when reported), Alpha Omega Alpha membership, status as American medical graduate (AMG) versus international medical graduate (IMG), the presence of an advanced degree (defined as a Master's degree or PhD), and the presence of additional research time beyond the standard four-year medical school timeline to perform scholarly work  publication fruition and (2) concordance between the journal of submission as listed on the ERAS application and the final accepting journal as identified by the PubMed database. If there was difficulty in accessing an article through a journal's website, an Internet search engine was used. Research conference podium presentations and posters listed as “Submitted,” as well as articles listed as submitted to nonpeer reviewed publications, were excluded from data collection. Verified publications were defined as publications confirmed via the PubMed database to be published in a scientific journal. Unverified publications were defined as those that could not be identified via the PubMed database or Internet search engine or those containing incorrect authorship listings. Publication mismatch was defined as discordance between the listed journal of submission on the ERAS application and the eventual journal of publication as reported in the PubMed database. Impact factors were derived from Journal Citation Reports; unlisted journals were assigned an impact factor of 0. Continuous variables were compared using a 2-tailed Student P = 0.072). A total of 1636 “Submitted” publications were listed among these 594 applicants, resulting in a mean of 2.75 “Submitted” publications per applicant  listed one or more publications as “Submitted.” The proportion of applicants with one or more “Submitted” publication ranged from 41.1% to 47.2% over the three years of the study, though no significant difference was observed between years . Applicants who had taken a year off from their medical training to perform research (n = 136) had a significantly higher number of “Submitted” publications than applicants whose medical training was uninterrupted (n = 458) . However, these applicants who had taken a year off from their medical training also had significantly more unverified publications . Similarly, applicants from National Institutes of Health (NIH) Top 40 institutions (n = 301) had significantly higher numbers of “Submitted” publications than applicants from non-NIH Top 40 research institutions (n = 293) , but no significant difference was seen in rates of unverified publications between the 2 groups (P = 0.86).When examining relationships between applicant demographic factors and unverified publications, IMGs (n = 6) had significantly more unverified publications than AMGs (n = 588)  publications eventually appeared in a different journal than the journal listed on the residency application  although our results likely differed from these prior studies because our publication outcomes were tracked for a minimum of 3 years after residency application submission. The successful publication rate reported in our findings mirrors that from Okike et al,18 who found similar rates of successful publication at 3 years after a rejection from the Journal of Bone and Joint Surgery. While these results do not serve as a direct comparison to our study, they provide a good approximation of the time required for a “Submitted” publication to reach publication in a scientific journal. Additionally, the publication of research from residency applicants may be even more of a challenge as applicants switch institutions. This rate of persistently unpublished work should also prompt program directors to continue to encourage their new trainees to complete prior scholarly work.In our study, 35% of “Submitted” publications were not successfully published, despite at least 3 years of time, since the final included application cycle. This observation would support program directors and faculty interviewers placing less weight on “Submitted” publications when reviewing residency applications. Rates of successful publication among “Submitted” research publications have been previously studied in residency applicants from nonorthopaedic fields. Approximately half of all publications listed as “Submitted” in urology and radiology residency applications were successfully published after 1 and 2 years, respectively.19 There may be several factors contributing to our results. IMG match rates into orthopaedic surgery have historically been well below AMG match rates,20 and this knowledge may influence IMGs to pursue additional scholarly research to bolster their application, which in turn increases their chance of having unverified publications. Additionally, IMGs have been shown to be held to a higher standard than AMGs during the residency screening process,21 which may further contribute to a perceived need for increased research output that leads to more unverified publications. However, given the few numbers of IMGs in this study, the possibility is that these results were driven by sample size alone and that further investigation with larger sample sizes is warranted.We did identify that the likelihood of having an unverified publication was significantly higher for applicants with a greater number of “Submitted” publications. Additionally, applicants from NIH Top 40 research institutions will likely have more “Submitted” publications as their home institutions are shown to have higher levels of scholarly research activity. However, it is unclear why IMGs had significantly more unverified publications than AMGs. The literature surrounding this topic is inconclusive, as some studies have shown IMGs to have higher rates of research misrepresentation, whereas others have found no differences from AMGs in fields outside of orthopaedic surgery.17 our findings regarding impact factor are in line with these prior studies, which found that the impact factor of the final journal of publication is significantly lower than the original journal of submission. Despite the prevalence of publication mismatch, it is difficult to know if it is driven by applicants' willful intent to gain a competitive advantage through deception or by factors beyond their control. It has been previously shown that applicants who list multiple unpublished manuscripts to inflate their resume have an increased chance of matching into a competitive specialty22; thus, it is possible that applicants list multiple unpublished publications as “Submitted” to appear more favorably to residency selection committees. However, given that successful publication rates in high-impact orthopaedic surgery journals can be as low as 20%23 and that applicants are typically not the primary decision-makers when choosing a journal of submission, it is also possible that publication mismatch occurs as an almost inevitable aspect of the research publication process and does not represent applicant deceit. Additional studies into publication mismatch and the authors' motivations behind selecting journals of submission may help further our understanding of this topic.Publication mismatch was moderately prevalent within our study because 33.8% of “Submitted” publications experienced publication mismatch with eventual publication in a less impactful journal than originally intended. Though rates of publication mismatch range from 41% to 49.2% in the nonorthopaedic literature,As increasing amounts of research publications are being listed on ERAS applications, the results of our study will be useful to program directors and others involved in the residency selection process as they select candidates for interview and final rank list. In the future, research publications may play a larger role in these selection processes given current plans to transition USMLE step 1 results from a scaled scoring system to a pass/fail system. Given the significant portion of self-reported “Submitted” publications that remained unverifiable in our study, the number of “Submitted” publications does not currently appear to be a reliable measure of an applicant's research productivity. However, modifications made at several points in the residency application process would improve the utility of using “Submitted” publications to evaluate applicants and provide residency selection committees with valuable data to aid in their decision-making. The online ERAS application could be adjusted to allow for real-time updates with accepted, rejected, or resubmitted publications to allow applicants to accurately represent of their research status at the time of residency interviews. Applicants could also be required to provide a proof of submission for all “Submitted” publications, or journals of submission could be required to assign a reportable identification number similar to a PubMed ID to each “Submitted” publication. Finally, in addition to these proposed changes, interviewers should also take time to clarify the current status of all works listed as “Submitted.” This step is especially important given the three- to 5-month lag time between when applicants submit their residency applications and when they participate in in-person interviews for orthopaedic surgery residency programs.Our study was able to follow up on a large sample of “Submitted” publications from orthopaedic surgery applicants and define the rates of successful publication and publication mismatch. However, our study also had several limitations. First, our study was a retrospective analysis of applications, which limits the conclusions we can draw from our results. Second, this study was performed at a single academic institution and may represent a biased study population, which limits the generalizability of our results. Third, it is possible that some unverified publications were actually published in journals not accessible through PubMed, Medline, or Google Scholar and thus were not verifiable using our methodology.“Submitted” publications listed on orthopaedic surgery residency applications frequently remain unpublished or published in less impactful journals than originally intended. This phenomenon is likely multifactorial in origin. Given the current uncertainty surrounding such publications, they are not good predictors of an applicant's research productivity. However, changes to the application process that allow for reliable reporting and verification of “Submitted” publications may help to clarify their impact and improve upon the decision-making framework of future residency selection committees.


This makes it possible for one to realize a low-cost optical sensing system with a detection limit as high as 10−6 refractive-index-unit, even when a cheap optical spectrum analyzer with low-resolution  is used for the wavelength-shift measurement.A design rule for a Mach-Zehnder interferometer (MZI) sensor is presented, allowing tunable sensitivity by appropriately choosing the MZI arm lengths according to the formula given in this paper. The present MZI sensor designed by this method can achieve an ultra-high sensitivity, which is much higher than any other traditional MZI sensors. An example is given with silicon-on-insulator (SOI) nanowires and the device sensitivity is as high as 10 The demand for label-free, low-cost, highly-sensitive and compact optical sensors keeps increasing rapidly in many areas, such as biological, environmental and chemical detections ,7,8,9,10S1, which is determined by the optical waveguide structure. Recently, silicon-on-insulator (SOI) nanowires have been widely used for optical sensing, because of the high sensitivity of the waveguide, which results from the enhancement of the evanescent field, due to submicron cross section and the ultra-high index contrast Sd is 157iN and il are the effective index and the length of the i-th MZI arm waveguide , respectively, m is the interference order, and λ0 is the central wavelength. When the analyte covered on an arm waveguide has a refractive index change of Δns, the corresponding variation ΔN1 of the effective index is given byS1 is the so-called waveguide sensitivity , where ∆φ is the phase difference between the two MZI arms. It can be seen that there is a notch at the designed center wavelength 1550 nm, as expected. A higher interference order m makes a narrower notch, which is helpful in order to distinguish a smaller wavelength shift, due to the refractive index change. Fortunately, a small wavelength shift can be distinguished easily, even when choosing a moderate interference order m. Furthermore, a small interference order m is preferred to have short MZI arms, so that the MZI sensor becomes compact.m = −10, and the corresponding lengths of the MZI arms are l1 = 227.08μm and l2 = 228.84 μm. N1 = 0 and 1 × 10−4, respectively. It can be seen that the notch wavelength shifts from 1550 nm to 1650nm. The wavelength shift Δλ is as large as 100 nm and the corresponding device sensitivity S2 = Δλ/ΔN = 106nm/RIU. In this way, the detection limit for the refractive index change is as high as 10−6 RIU, even when using an OSA with a low resolution of ~1 nm. It can be seen that the MZI sensor with such an ultra-high sensitivity is beneficial, because one does not need a high-resolution OSA for the measurement of the spectral responses. An on-chop spectrometer, which usually has a relatively low resolution, will be available. This becomes very attractive for realizing a low-cost optical sensing system. In theory, it is even possible to further achieve a sensitivity as high as e.g., S2 = 107 nm/RIU, by designing the MZI arm lengths appropriately when needed. In practical terms, one should realize that the sensitivity of the MZI sensor will be limited, due to some non-idealities. For example, when the powers split to the two MZI arms are not identical, the extinction ratio of the notch will degrade. In this case, there is no sharp notch, and thus a small wavelength shift might not be resolved. Fortunately, it is possible to achieve very uniform 1 × 2 3-dB power splitters on silicon by using mature symmetric Y-branches [ε| will increase to break the condition |ε| << 1. A possible solution is to introduce a thermally tuned phase-shifter to compensate the random variation of the lengths l1 and l2.Therefore, in the following calculation, we choose branches , or adiabranches . Another6 nm/RIU (or higher). With such an MZI sensor, it is possible to detect a very tiny refractive index change as small as 10−6 RIU, even by using an OSA with a low resolution of ~1 nm. This is really helpful because a moderate/low-resolution OSA can be available for the measurement of the spectral responses. In particular, it is even possible to integrate with an on-chop spectrometer, which usually has a relatively low resolution. In this way, it becomes very attractive for realizing a low-cost optical sensing system.In summary, we have presented a novel design rule for achieving an MZI sensor with ultra-high sensitivity. For any given optical waveguide system, we have shown that tunable sensitivity can be achieved for an MZI sensor by choosing the MZI arm lengths appropriately. An example has been given with SOI nanowires, and the device sensitivity can be as high as 10