The prevalence of antibiotic residues was 41.26% . A logistic regression model found no significant associations between gross pathological lesions and the presence of antibiotic residues. We recommend that the regulating authorities strongly consider routine testing of carcasses for antibiotic residues to protect meat consumers. Future studies should research on farming practices contributing to the high prevalence of residues. The human population is growing and urbanising. These factors are driving the demand for animal-sourced proteins. The rising demand is favouring livestock intensification, a process that frequently relies on antibiotics for growth promotion, treatment and prevention of diseases. Antibiotic use in livestock production requires strict adherence to the recommended withdrawal periods. In Kenya, the risk of residues in meat is particularly high due to lack of legislation requiring testing for antibiotic residues in meat destined for the local market. We examined pig carcasses for gross pathological lesions and collected pork samples for antibiotic residue testing. Our aim was to determine if a risk-based approach to residue surveillance may be adopted by looking for an association between lesions and presence of residues. In total, 387 pork samples were tested for antibiotic residues using the Premi The global human population has been steadily rising, and estimates project an increase from the current 7 billion to 9.6 billion people by 2050. Most of the population growth is expected in Africa, which has an annual growth rate of 1.2% . Globally, it was reported in 2017 that about 73% of all antimicrobials produced are used within food animal production  with pigAlthough antibiotics have the potential to improve production levels with regard to producer income and food security, when used inappropriately residues can be present in meat. These residues present public health risks such as allergenicity, toxicity, carcinogenicity and disruption of normal gastrointestinal flora therefore becoming a One Health issue. Residues may also promote the development of antibiotic-resistant microbes . There hFailure to observe withdrawal periods has been cited as a major contributor to antibiotic residues in foods of animal origin . Prior rIdeally, food meant for human consumption should be free of antibiotic residues. Since a zero-residue level in meat may be impractical, the joint Food and Agriculture Organization of the United Nations and World Health Organization (FAO/WHO) Codex Alimentarius Commission has set maximum residue limits (MRL), above which meat is considered unsafe for human consumption . This reIn Switzerland, studies have established that risk-based sampling is 100% efficient in detecting tetracycline residues in calves . AnotherTo date, and to our knowledge, no study has investigated the prevalence of antibiotic residues in pork in Kenya. Therefore, this study aimed to establish the prevalence of antibiotic residues in pigs slaughtered and consumed in Nairobi and its environs. As a preliminary step to considering a risk-based surveillance system for Kenya, we also investigated the association between gross lesions detectable at slaughter and antibiotic residues in order to determine if gross lesions detectable at slaughter may be a suitable indicator to use in such a program. We hypothesized that animals with gross pathological lesions may have either been treated with antibiotics resulting in residues or may have originated from farms with generally poor husbandry practices, increasing the likelihood of both poor adherence to withdrawal times and presence of gross lesions in pigs presented for slaughter. A total of three hundred and eighty seven pork samples, each from an individual pig, were collected and tested for antibiotic residues. 126 of these 387 meat samples tested positive for the presence of antibiotics residues above the MRL. The apparent prevalence of antimicrobial residues above the MRL in the sampled population was 32.55% (95% CI 28.08–37.37%). Considering the reported sensitivity and specificity of the diagnostic assay, a true prevalence of 41.26% (95% CI 34.53–48.45%) was calculated. The prevalence of gross lesions in the full study population has been previously described  and onlyOn univariate analysis, no statistically significant associations were found between gross pathological lesions and antibiotic residues in pork samples as seen in the last column in p values of <0.2 and thus were included in the logistic regression model. Variable combination with the lowest Akaike Information Criterion (AIC) figure was picked as the best model. This model included sex, tail bites and hindlimb bursitis variables. The variance inflation factors output for sex, tail bites and hindlimb bursitis were 1.005, 1.008 and 1.01, respectively, indicating that these predictor variables were unrelated. No statistically significant associations were identified from the logistic regression model as shown in Sex, liveweight, tail bite lesions and hindlimb bursitis variables had We identified a high prevalence of antibiotic residues above the MRL in pork consumed in Nairobi and its environs. These findings indicate poor adherence to withdrawal periods by farmers and potential public health hazards to pork consumers through toxicity, allergic reactions and potential contribution to antimicrobial resistance development. Contrary to our hypothesis, we found no statistically significant associations between gross lesions and antibiotic residues in this population. ®Test  a broad-spectrum antibiotic screening method to detect the presence of residues above the MRL. Although the Premi®Test has been certified for use as a screening test based upon its comparability to current reference tests [®Test as a sole analytical technique, as was used in this study. Due to resource limitations, we utilised Premice tests , the sence tests . This in®Test can vary among antibiotic classes. This means that there is a possibility that certain classes of antibiotic were not detected in this study. Sub-optimal detection of tetracyclines [®Test have previously been reported, indicating that a parallel screening test sensitive for these classes of antibiotic in particular may be required to ensure all positive samples are accurately detected. Although we adjusted the reported prevalence to account for the reported diagnostic performance, the sensitivity and specificity of the Premicyclines ,24 and qcyclines  in chickFreezing has been demonstrated to reduce the concentration of some antibiotics in meat  which maDespite the possibility that some positive samples may have been incorrectly classified as negative through use of an imperfect screening test and freezing effects, there is a worryingly high prevalence of residues over MRL as indicated in this study. One possible explanation for the high prevalence of antibiotic residues in pork is that Kenyan authorities lack laws requiring testing of antibiotic residues for locally consumed meat . The lack of current legislation in this area results in no financial or legal consequences for farmers and traders to present animals for slaughter where residues may still be present. Lack of legislation and current paucity of data on residues in food products may also lead to low level of awareness among farmers and consumers on the potential public health threats of these residues perpetuating a relaxed attitude to withdrawal periods. It has been established that 100% of veterinary shops in Nairobi sell antibiotics without prescriptions with the buyer’s/or farmer’s preferences guiding purchasing decisions . In ruraThe current legislative deficit can be rectified by regulatory bodies, such as the Kenya Veterinary Board (KVB) and the Veterinary Medicine Directorate (VMD). The two bodies should impose stricter regulations on sale of antibiotics by ensuring that antimicrobials are only accessible to licenced animal health practitioners. This should be combined with raising awareness among stakeholders regarding the negative health impacts of antibiotic residues in animal-sourced proteins. Kenya’s National Action Plan on containment of antimicrobial resistance proposes residue testing as a strategic intervention . The estIn regulating antibiotic usage, regulatory authorities should encourage farmers to engage with cost-effective disease prevention alternatives. These include timely vaccinations, emphasis on biosecurity measures at the farm and appropriate stocking density. These alternatives will support animal health by reducing both the transmission and susceptibility to pathogens, thus reducing overreliance of antibiotics. These lessons should be taught using agricultural economic models that illustrate the benefits of disease prevention over treatment. Thereafter, legislation may be amended to require testing for residues in locally consumed meat. Such recommendations will supplement Kenya’s National Action Plan of containing antimicrobial resistance and maintaining the efficacy of antimicrobials. Very few willingness-to-pay studies have been performed for animal source products in Kenya, though one recent study indicates that antibiotic use had a negative impact on consumers’ willingness-to-pay for chicken . SimilarAt this stage, we have not identified any gross pathological lesions that may be used as predictors for the presence of antibiotic residues that could be utilised as an indicator in a risk-based surveillance program. Future studies should examine antimicrobial use at the farm level and may find other relevant factors which may be useful indicators for risk-based surveillance.This study was approved by the International Livestock Research Institute, Institutional Animal Care and Use Committee (ILRI IACUC Ref no. 2019-36) and the Institutional Research Ethics Committee (ILRI-IREC 2020-14). An additional permit was obtained from the National Commission for Science, Technology, and Innovation permit (NACOSTI/P/20/4847). Both the national and county Directorate of Veterinary Services granted permission to conduct the study at the local abattoir.This cross-sectional study was conducted between 5 January and 5 March 2021 in a medium-sized, non-integrated abattoir, which slaughters an average of 215 pigs per week for sale. Consumption occurs in Nairobi and its environs . A minimThis antibiotic residue study was embedded in a larger study, researching food safety and animal welfare themes that required 529 pigs to be sampled. The study site and sampling strategy have previously been described in detail . All pigWe had a team of 7 members and for ease of data collection the abattoir was divided into 3 stations, i.e., recruitment, evisceration area and dispatch point with each member assigned different roles. At the recruitment station, the person presenting the pig for slaughter was approached and study objectives explained to him or her. If they agreed to participate, an informed consent form would be filled in, and data collection begun. Data on the pig’s origin, farm size, husbandry type, sex and live weights were collected and recorded. We did not consider breed since the majority of the pigs presented to the slaughterhouse were of ‘European origin or European mix’ with previous studies on pig breeds in Kenya showing a heterogeneous control . TherefoBiceps femoris muscle [At the evisceration area, carcasses were visually examined for any gross pathological lesions. Two members of the research team, both qualified veterinarians, were responsible for inspecting the carcasses and collecting biological samples. One member examined the carcass for external lesions including ear marks (lacerations made on the ears of pigs with a sharp object to identify their pigs), tail bites, loin bruising, tether wounds, hindlimb bursitis and lacerations. The presence and absence and severity of each lesion was recorded as 1 and 0, respectively. The second team member examined thoracic and abdominal cavities and associated visceral organs namely lungs, heart and liver for cysts, abscesses, pleurisy, pneumonia, and milk spots in the liver. The lungs, liver and heart were collected, labelled and put in Ziploc bags for further examination at ILRI post-mortem room for gross pathological lesions. Finally, at the dispatch point, a 9 cm by 7 cm by 2 cm sample was collected from the left-side of s muscle . These sIn the post-mortem room, lungs, heart and liver samples were inspected for lesions that may have been missed due to the rapid slaughter process at the abattoir. The 7 lung lobes were scored according to the BPEX Pig Health Scheme . The crahttps://opendatakit.org/) and later uploaded to the ILRI server. Data was cleaned and checked for consistency on a weekly basis. Each sampling day took an average of 4 h.All collected data were entered into an Open Data Kit (ODK) form on a mobile phone . This kit is a micro-inhibition screening test containing Bacillus stearothermophilus spores in an agar medium and a bromocresol purple indicator. In the absence of inhibitory substances, antibiotics in this case, the spores germinate and multiply to form an acid. This causes the bromocresol indicator to change colour from purple to yellow. If antibiotics are present above the MRL, the colour of the indicator remains purple and was recorded as a positive result [®Test is one of the most commonly used screening test for β-lactams, macrolides, tetracyclines and sulphonamides in meat in the EU with confirmatory tests generally utilised to confirm positive samples [Pork samples were tested for antibiotic residues using the Premie result . Premi®T samples . ® , which contains Penicillin as its active ingredient, was spiked into the positive control ampoule. Nothing was added to the negative control ampoule. The Premi®Test incubator was pre-heated to 64 ºC. The 2 control ampoules were placed in the incubator, covered with foil, and incubated for approximately three hours. After this period, the negative control turned yellow while the positive control retained it purple colour as shown in Before testing the 387 pork samples, we ran positive and negative controls. The negative meat sample was obtained from Farmers Choice. This a model firm and food processing plant that adheres to best farming practices, withdrawal periods and food safety standards. Its design and operations have been certified under ISO 22000:2005 on Food Safety Management Systems. The facility is licensed by the Director of Veterinary Services to exports their meat products and we are confident that residues would not be present. We bought 500 g of pork from Farmers Choice and obtained 100 µL of meat juice using a meat juice extractor. Further, 20 µL of meat juice was added to 2 ampoules. In addition, 2 mL of BetamoxThe frozen pork samples were defrosted on the bench, and a meat juice extractor was used to extract 100 µL of meat juice from each of the defrosted pork sample. The juice was vortexed to obtain a homogenous sample. Further, 20 µL of the vortexed juice was added to a pre-labelled ampoule corresponding to the pig ID and incubated at room temperature for 20 min. The ampoules were turned upside down to pour out meat juices and flushed with deionised water. They were then placed on a rack in an upside down position for 5 min to allow them to dry completely.The ampoules were then placed in the incubator that had been preheated to 64 ºC, as seen in https://www.R-project.org/). Prevalence of antibiotic residues at 95% confidence interval was calculated using the epi.prev function under the epiR package [All the uploaded data were downloaded as .csv files  from the ILRI server, cleaned and loaded into R version 4.2.2 for analysis . Since they were all below 2, they were all retained in the model. A logistic regression model was then built utilising the generalised linear model function in the MASS package, utilising the binomial family since the outcome was binary . An initClose to half of the pork destined for consumption in Nairobi and its environs contained antibiotic residues above the recommended maximum residue limit. This poses potential public health risks to pork consumers. Action is urgently needed to address the underlying antibiotic misuse that has resulted in such a high prevalence of residues in pork. We recommend that regulating authorities strongly consider routine testing of carcasses for antibiotic residues for the protection of public health. We acknowledge that the establishment of a residue surveillance program would require huge investment in diagnostic technologies, e.g., high-performance liquid chromatography mass spectrometry for confirmatory testing, training of staff in sample collection and testing and the creation and management of an appropriate data management system. In addition to the fixed investments, there would be additional per-sample costs . To reduce the cost of residue surveillance, a sampling plan would be required, which could be based upon random or risk-based sampling. The lack of a significant association between gross pathological lesions and the presence of antibiotic residues suggests that, for the time being, we cannot recommend a risk-based surveillance system based on gross lesions as predictors of residues in this population until antibiotic access enforcement is addressed. Future studies should research farming practices and antimicrobial use contributing to the high prevalence of residues.To ensure better practices in the sale and use of antibiotics, appropriate legislation must be developed and enforced. There needs to be random testing of meat samples for residues and condemning of carcasses that test positive for residues. Meanwhile, producers should be sensitized on the judicious use of antibiotics and importance of adhering to recommended withdrawal times. Antibiotic stewardship, food safety and improved health outcomes will be ensured through this multifaceted approach.


Recycled insulation concrete is a novel form of eco-friendly, energy-saving concrete that aims to achieve low-carbon energy savings and sustainable development by combining resource recycling with building energy savings to realize the recycling of solid waste resources, which has significant environmental, social, and economic benefits and broad market application potential.Construction and agricultural waste recycling have gained more and more attention recently as renewable resources. Straw and construction waste, both of which are widespread in northern Fujian, were investigated in this research. The orthogonal test was used to investigate the effects of recycled aggregate, straw, and glazed hollow beads on the mechanical and thermal properties of recycled insulation concrete. The influence of different factors on the macroscopic characteristics of recycled insulation concrete was examined using scanning electron microscopy (SEM). The optimal mix proportion for recycled insulation concrete that satisfies mechanical performance standards and provides superior insulation performance was then determined using the total efficacy coefficient method. According to the research findings, the heat conductivity of recycled insulation concrete decreases as its dried density decreases. A 100% recycled coarse aggregate replacement rate, 1% straw content, and 10% glazed hollow beads replacement rate are the optimal mix ratios for recycled insulation concrete. With a compressive strength of 20.98 MPa, a splitting tensile strength of 2.01 MPa, a thermal conductivity of 0.3776 W/(m China’s environmental pollution and energy shortages have become increasingly conspicuous due to the country’s burgeoning economy and construction industry. On the one hand, the frequent remodeling, tearing down, and new construction of buildings have produced a large volume of construction solid waste ,2,3. WitNumerous studies on the mechanical properties of recycled concrete have been conducted in recent years, but not many on its thermal properties ,14,15,16Plant fiber has numerous advantages over conventional fiber, including low cost, green environmental protection, and convenient materials. Plant-fiber concrete is a novel form of eco-friendly concrete . The maiGlazed hollow bead insulation concrete is ordinary concrete to which glazed hollow beads  and admixtures have been added. With the typical physical and mechanical capabilities of concrete, as well as thermal insulation properties, this new type of concrete is an eco-friendly building material ,30,31. Ze, Zhang  developeg et al.  mixed glThis study aimed to develop a new type of building material for the building envelope that not only meets the mechanical requirements of the building envelope but also provides superior thermal insulation. By using an orthogonal test, the impacts of recycled aggregate, straw, and hollow glazed beads on the mechanical and thermal characteristics of recycled insulation concrete were investigated. Based on the test findings, the mechanical and thermal characteristics of recycled insulation concrete were assessed, and the ideal mix ratio was established using the total efficiency coefficient technique. Compared to conventional concrete, recycled insulation concrete can recycle construction waste and agricultural waste, thereby reducing resource waste and achieving resource recycling in accordance with the principles of sustainable green development ,36,37. T3. This research employed PAs illustrated in 3, and a water absorption rate of 1.51%, as determined by sieving. The sand for this experiment was natural river sand supplied by Wuyi Mountain sand and gravel manufacturers, with a particle size of 0~5 mm, an apparent density of 2610 kg/mGlazed hollow beads from Henan Xinyang Chenxin New Material Co., Ltd., Xinyang, China were chosen for this test. On the exterior of the glazed hollow bead material are irregular spherical particles, while the interior has a porous cavity structure. The surface is glazed, smooth, level, and closed. It is an inorganic and lightweight insulation material with excellent functionality and sustainability. The straw was composed of rice straw, which is commonly in northern Fujian, and the rice straw was manually sheared to eliminate the fiber portion. The length of the straw was 1~3 cm, and its width was 2~3 mm. The straw fibers needed to be washed with tap water 2–3 times, drained, dried, and stored in a dry location to prevent moisture. Jiangsu Subote New Materials Co., Ltd., Nanjing, China manufactures polycarboxylate superplasticizer with a water reduction rate of 25~30%.As there are no relevant regulations for the mix ratio design, the recycled insulation concrete studied in this experiment is a new type of thermal insulation material that is primarily deemed to be used in the building envelope, based on its intended application. Recycled insulation concrete contains light aggregate which are glazed hollow beads in place of a portion of sand that is found in sand lightweight concrete. The preliminary foundation mix design was carried out in accordance with the “Ordinary Concrete Mix Design Regulations ” and “LiThe water absorption rate of the glazed hollow beads in 24 h is 230%, according to ow beads ,41.The breakage rate of the glazed hollow beads was measured based on the basic mix ratio of the concrete. Four experimental groups were conducted, in which glazed hollow beads replaced 0%, 5%, 10%, and 15% of the sand mass in the basic mix ratio of the concrete. The quantity of water released from the breakage of glazed hollow beads and the breakage rate of glass beads were calculated as shown in Equations (1) and (2):According to When compared to natural coarse aggregate, recycled coarse aggregate absorbs water almost three times as well. The additional water consumption of recycled coarse aggregate was calculated in order to lessen the effect of the high water absorption of recycled coarse aggregate on the effective water–cement ratio. . Equatio3) was utilized. The content of glazed hollow beads is the mass percentage of replaced sand, the content of recycled coarse aggregate is the mass percentage of recycled coarse aggregate replacing natural aggregate, and the content of straw is the mass percentage of cement.This test utilizes the orthogonal test method, with compressive strength, splitting tensile strength, thermal conductivity, and dry density serving as test indicators; the orthogonal table design is depicted in According to Standard GB/T 50081-2002 for Mechanical Properties of Ordinary Concrete , the mecThe thermal performance of the recycled insulation concrete was determined using the GB/T 10294-2008 standard ; 300 mm Scanning electron microscopy (SEM) is mainly employed for observing the surface morphology of specimens via secondary electron signal imaging or backscattered electron imaging . After tim is the sum of test indicators corresponding to the im indicates the average value of im. The optimal level and optimal mix ratio of factorim. i represents the degree to which a change in the level of factor i = max min. The greater the i, the greater the factor’s influence on the test indicator and, consequently, the greater its importance [Range analysis includes two steps: calculation and judgment. The diagram of range analysis is shown in portance .As shown in 1B1C1 according to the im values. The sequence of factors affecting splitting tensile strength is as follows: glazed hollow beads > straw > recycled aggregate. The optimal scheme of splitting tensile strength is A1B1C1. In conclusion, glazed hollow beads are the primary factors influencing the mechanical properties of recycled concrete.According to i is as follows: 0.5699 (glazed hollow beads) > 0.3013 (recycled aggregate) > 0.1277 (straw). The following is the ranking of the factors that influence thermal conductivity: glazed hollow beads 4B4C4 has the greatest thermal insulation performance, according to the im.According to Despite the fact that range analysis is straightforward, it has limitations and cannot estimate the size of the experimental error. Therefore, analysis of variance was carried out on the results of the orthogonal experiment to determine whether the change in the test results was due to the change in factor levels or to the error .The variance analysis of mechanical properties is illustrated in According to The variance analysis of insulation performance is depicted in According to 2j groups and In order to find a balance between the four test indicators selected for this experiment and determine the mix ratio of recycled insulation concrete that provides excellent thermal insulation performance while meeting the requirements for mechanical properties, the total efficiency coefficient method was utilized to analyze the four test indicators . As a reIn the test, benefit indicators such as compressive strength and splitting tensile strength were used, with a higher result indicating a greater benefit. Formula (6) was used to normalize the mechanical characteristics of the concrete, such as splitting tensile strength and compressive strength. Thermal conductivity and dry density are forms of cost indicators for which lesser values are preferable. The thermal conductivity and dry density of concrete, which were normalized according to Equation (7), represent the insulation properties of the concrete .Benefit indicator normalization calculation :Cost indicator normalization calculation :The total efficacy coefficient of the group 3, respectively. The strength of recycled insulation concrete fulfills the GBT1490-94 “Technical Specifications for Light Aggregate Concrete” specification, which states that “the reasonable range of concrete strength for both load-bearing and thermal insulation envelope structures is LC5~LC15”. Under the condition of meeting the standard’s mechanical property requirements, the thermal conductivity of recycled insulation concrete is 0.3776 W/(mThe highest total efficiency coefficient was found in group 14, as indicated in According to 2 crystals, which causes the cement slurry to solidify and harden more slowly and to exhibit the “slow coagulation” phenomenon, so that the mechanical properties are diminished [As shown in minished . Under tminished ,48.As shown in As the proportion of straw in recycled insulation concrete increased from 0% to 3%, its thermal conductivity decreased by 19.57%. As seen in the microtopography of the straw in The thermal conductivity of the recycled insulation concrete decreased by 61.80% as the replacement rate of glazed hollow beads increased from 0% to 15%. As depicted in formance .The following describes the degree of influence for mechanical properties: glazed hollow beads trump recycled aggregate and straw. In terms of thermal conductivity, glazed hollow beads have a greater impact than recycled aggregate and straw.3.The optimal mix ratio of recycled insulation concrete was found in the 14th orthogonal test group. The recycled aggregate replacement rate in this group was 100%, the straw content was 1%, and the glazed hollow beads replacement rate was 10%. The compressive strength of recycled insulation concrete with this optimal mix ratio is 20.98 MPa, the splitting tensile strength is 2.01 MPa, the thermal conductivity is 0.3776 W/(mThe equation for the relationship between thermal conductivity and dry density is The macro performance and internal microstructure were simply combined in this investigation. In the future, macroscale, mesoscale, and microscale can be combined to study the internal heat transfer mechanism of insulation concrete more thoroughly.This study only takes into account the mechanical properties of recycled insulation concrete; future studies may take into account the durability of recycled insulation concrete in order to apply it to various building structures and increase the rate at which solid waste resources are utilized.The preliminary investigation of this novel type of recycled insulation concrete yielded the following findings and prospects:


Based on an unconfined compressive strength test, non-contact full-field strain measurement system, and scanning electron microscopy test, the effects of aggregate particle composition, shaking time, fly ash content, fiber length, and fiber content on the strength and permeability of permeable concrete were studied. The results show that the strength and water permeability of permeable concrete are negatively correlated with an increase in shaking time. When the aggregate particle size is 5–10 mm, the permeable concrete has both good strength and permeability. Proper incorporation of fly ash improves the compactness inside the structure. The influence of different lengths of glass fiber on the strength of permeable concrete first increases and then decreases, and the permeable property decreases. With the same fiber length, the strength increases first and then decreases with an increase in the content, while the porosity and water permeability coefficient decrease. Under the test conditions, when the length of glass fiber is 6 mm, and the dosage is 2 kg/m Today’s global trends are changing rapidly, and research related to cementitious composites tends to be green, environmentally friendly, and sustainable ,2. In thhttps://www.statease.com) to optimize the mix ratio parameters of permeable concrete, such as cement dosage, water-cement ratio, aggregate gradation, and particle size and concluded that the water–cement ratio had no obvious effect on the performance indexes of permeable concrete. Cheng et al. [The construction and promotion of “sponge cities” is an important development in the field of urban construction. Permeable concrete is mainly used in urban construction because of its characteristics of high strength, green environment, and good drainage effect ,4. Domesg et al.  proved tg et al.  illustrag et al.  confirmePermeable concrete has good characteristics of water permeability, but it has certain deficiencies in strength and durability. Therefore, domestic and foreign scholars have mixed polypropylene fiber, basalt fiber, and carbon fiber into permeable concrete ,20,21 toAt present, there are relatively few studies on short-cut glass fiber-reinforced permeable concrete. Based on this, this paper adds glass fiber with different lengths and contents to permeable concrete to study the forming method, aggregate particle composition, and fly ash content of permeable concrete and studies the influence of the length and content of glass fiber on various performance indexes of permeable concrete. The optimum fiber length and incorporation ratio were obtained, the fiber reinforcement mechanism was revealed, and a theoretical reference was provided for its application in road engineering.The cement used in this test is ordinary Portland cement with a strength grade of P.O 42.5. The physical properties are shown in m is the mass of various materials; ρ is the apparent density of the material; P is the target porosity; c is the cement; f is the admixture; g is the coarse aggregate; w is water; and a is a water-reducing agent.In this test, the volume method was used to prepare the specimens. According to the Technical Specification for Pervious Cement Concrete Pavement (CJJ/T135-2009) , the desThe specimens used in the test were prepared according to Technical Specification for Pervious Cement Concrete Pavement (CJJ/T135-2009) , and theAll of the aggregates used in the test were cleaned, with the aim of removing surface sand and impurities, dried, and sieved through a drying oven to obtain a single size.An HJW-30 single horizontal shaft mixer was used to mix the cement and auxiliary cementitious materials for 30 s first, and then, the aggregate was added with continual mixing for 90 s to ensure that the materials were fully mixed.After the dry material was mixed evenly, the water-reducing agent and water were added, and mixing continued for 90 s.The glass fibers were soaked in 1.5% polycarboxylic acid water-reducing agent solution for 5 min, and then, the fibers were taken out and dried. The dried fibers were divided into 3–5 equal parts to achieve the best possible dispersion of the glass short-cut fibers. In the mixing process of step 3, one part of the glass fiber was evenly sprinkled in the mixture, and the fiber was added while mixing and then the step was repeated until all the glass fibers were mixed in to ensure that the fibers were well dispersed in the mixture.Shaking and molding test was performed using a Tianjin Qingda Testing Instrument Manufacturing Co., Ltd.  product of a 70-type shaker with a vibration frequency of 2860 times/min. The mold was placed on the shaking table and a 50 mm-high baffle was placed around the outer edge of the mold. The finished slurry was then injected into the mold up to 2/3 of the baffle, and the switch was turned on to shake the mixture for the desired amount of time. After shaking, the baffle was removed. A scraper was used to gently scrape off the excess slurry and flatten the top surface.After, the specimen was poured and covered with plastic film to prevent water loss. Then, it was left for three days at room temperature before the specimen was removed from the mold. After the specimens were removed from the molds, they were placed in a curing box at a constant temperature of 20 °C until the required age for the test.The mechanical property test was carried out in accordance with the test method in the Standard for Test Methods of Concrete Physical and Mechanical Properties (GB/T 50081-2019) , and a mIn this paper, the porosity of permeable concrete was tested by the weight method, which is based on the principle of using the mass difference between dried and saturated specimens to characterize the magnitude of the buoyancy value of the specimen after the pores are filled with water. The pore space is divided into connected, semi-connected, and closed pores. The connected pores play a major role in permeable concrete, and the semi-connected pores are in a relatively stagnant state during the drainage stage, which is ineffective for the drainage effect. Therefore, it is the effective porosity, i.e., the ratio of effective pore volume to total volume, that determines the water permeability coefficient of permeable concrete. The test method is shown in P is the porosity of the specimen, %; M1 is the mass in water of the specimen, g; M2 is the dry mass of the specimen, g; ρ1 is the density of water, g/cm3; and Vt is the volume of the test block, cm3.The permeable concrete was soaked in water for 24 h to saturate the mass M1 of the specimen. The specimen was taken out, wiped dry, and placed in the air to dry, and after the mass was constant , the mass of the specimen in the air was weighed M2, and Vt is the volume of the permeable concrete specimen. The open porosity P of permeable concrete can be calculated according to Equation (2):The water permeability coefficient is an important test index of permeable concrete. This paper followed the Chinese standard specification “Technical specification for pervious cement concrete pavement” CJJ/T 135-2009  to test TK is the water permeability coefficient of the specimen, mm/s; Q is the amount of water seepage within the specified time, mm3; L is the thickness of the specimen, mm; A is the surface area of the top surface of the specimen, mm2; H is the water level difference, mm; and Δt is the water flow time.In the process of water injection, the flow rate of water injection is constantly adjusted to ensure that the water level difference “H” is constant during the test time so as to ensure that the pressure on the upper surface of the test block is constant. The permeability factor is calculated in accordance with Equation (3):A QUANTA 200 scanning electron microscope (SEM) was used to observe the solidification and hardening morphology of the cementing material between aggregates and the binding state of the fiber and cementing layer, as displayed in Fly ash is one of the most common mineral fillers, the effectiveness of which has been confirmed by practical experience ,30. Fly When the aggregate particle size is 5–10 mm, the internal structure of the test block is relatively dense, with good strength and water permeability. When the aggregate particle gradation is 10–15 mm, due to its large size, low packing density, easy dislocation between aggregates under pressure, and a large part of the cement slurry existing in the void, this results in the low utilization rate of the cement slurry. During shaking and molding, the cement slurry that exists in the void rapidly sinks due to the action of gravity, resulting in a prominent bottom sealing phenomenon and low water permeability coefficient. However, when the side is used as the top surface of the pressure, the strength increases. Therefore, from the comprehensive consideration of strength and water permeability, the optimal aggregate particle size is 5–10 mm.3). As can be seen in 3, which is 25.41% higher than that of the test block without fiber. When the fiber content is 5 kg/m3, the peak stress is 10.342 MPa, which is 30.32% lower than that of the test block without fiber. The reason is that the increase in fiber content affects the bonding force of the internal cemented layer, and the uneven dispersion causes fiber aggregation; however, this increases the deformation effect and improves the compressive toughness. Therefore, the strength of the test block is low, but the strain value is large at high content.3, the strength reaches the maximum value, and the water permeability coefficient remains at a high level. The reason is that in a certain fiber volume content range, the increase in fiber content will cause the phenomenon of “clumping” and plugging the pores; when the effective porosity is reduced, the water permeability coefficient will be reduced.In order to study the failure law of permeable concrete, Vic-3D technology was used to study the vertical strain of permeable concrete during compression. In order to explore the reinforcement mechanism of fiber in a cement matrix, the wrapping condition of fiber in a cement matrix was analyzed by a scanning electron microscope. α influenced by the fiber is introduced. Reinforcement factor α is the efficiency of fiber content to improve the peak strength of the test block. The reinforcement factor α is calculated according to Equation (4):In order to further explore the influence of glass fiber on permeable concrete, the strength reinforcement factor 2 generated by cement hydration reacts chemically with SiO2 in the glass fiber, weakening the structural relationship between the fibers and causing deterioration of their mechanical properties.According to the concept of “crowding factor” , when th(1)The shaking time has a significant influence on the strength and water permeability of permeable concrete. With the extension of shaking time, the strength of the test block gradually increases, and the water permeability coefficient gradually decreases. When the shaking time is 3 s, the performance of the test block is the most balanced; that is, it has high strength while satisfying good water permeability.(2)Fly ash can enhance structural compactness and improve slurry fluidity. When the fly ash content is 7.5%, the permeable concrete has high strength while ensuring good workability.(3)With the increase in aggregate particle composition, the porosity of permeable concrete showed an increasing trend, and the water permeability coefficient first increased and then decreased, and the strength relationship was 3–5 mm > 5–10 mm > 10–15 mm. The strength and water permeability of the test block can be maintained at a good level when the aggregate particle size is 5–10 mm.(4)3.The porosity and water permeability coefficient of permeable concrete is degraded when glass fiber of different lengths and dosages is added. With an increase in glass fiber length, the compressive strength of permeable concrete first increases and then decreases. With an increase in glass fiber content, the changing trend of the compressive strength of permeable concrete is closely related to the fiber length. Under the test conditions, the optimal fiber incorporation length is 6 mm, and the content is 2 kg/m(5)Glass fiber was mixed into the permeable concrete, and the fiber network was formed through the bonding effect of cement slurry so as to strengthen the reinforcement effect. The reasonable incorporation of fiber can not only have a better permeable effect but also improve strength and slow down the development of cracks, which has a certain value for the application of road engineering.


Exposure of concrete to acidic environments can cause the degradation of concrete elements and seriously affect the durability of concrete. As solid wastes are produced during industrial activity, ITP (iron tailing powder), FA (fly ash), and LS (lithium slag) can be used as admixtures to produce concrete and improve its workability. This paper focuses on the preparation of concrete using a ternary mineral admixture system consisting of ITP, FA, and LS to investigate the acid erosion resistance of concrete in acetic acid solution at different cement replacement rates and different water–binder ratios. The tests were performed by compressive strength analysis, mass analysis, apparent deterioration analysis, and microstructure analysis by mercury intrusion porosimetry and scanning electron microscopy. The results show that when the water–binder ratio is certain and the cement replacement rate is greater than 16%; especially at 20%, the concrete shows strong resistance to acid erosion; when the cement replacement rate is certain and the water–binder ratio is less than 0.47; especially at 0.42, the concrete shows strong resistance to acid erosion. Microstructural analysis shows that the ternary mineral admixture system composed of ITP, FA, and LS promotes the formation of hydration products such as C-S-H and AFt, improves the compactness and compressive strength of concrete, and reduces the connected porosity of concrete, which can obtain good overall performance. In general, concrete prepared with a ternary mineral admixture system consisting of ITP, FA, and LS has better acid erosion resistance than ordinary concrete. The use of different kinds of solid waste powder to replace cement can effectively reduce carbon emissions and protect the environment. Concrete is one of the most extensively used building materials in the world, and its durability is exceptionally significant in structural design, especially in infrastructure design, where the performance of concrete exposed to acidic environments is one of the critical issues of concrete durability ,2. ExposRegarding the improvement of the operational performance of concrete structures in acidic environments, some studies have shown that using different kinds of admixtures and new materials can improve the performance of concrete. In addition, the use of biocide to inhibit the growth of acid bacteria is also one of the effective ways to achieve this ,4. The eAlthough the use of SCMs to enhance the durability of concrete has been extensively studied ,27, mostThe P.O 42.5 Portland cement (OPC) was selected as the binder, meeting the Chinese standard GB 175-2007. At different CRRs, ITP, FA, and LS were used to replace OPC. The chemical compositions and specific surface areas of ITP, FA, and LS are listed in The mixed proportions of concrete are listed in For specimen preparation, ITS and ITR were dried in the oven at 105 °C for 24 h. Before the dried ITS and ITR were placed into the blender for 1 min, the weighed OPC, ITP, FA, and LS were put into the blender for 1 min. Finally, the water and water reducer were mixed well, and all of them were dumped into the blender for 2 min. After mixing, the mixtures were put into a 100 mm × 100 mm × 100 mm mold and consolidated using a vibrating table for 30 s. The specimens were cured at a standard curing condition of 20 ± 2 °C and 95 ± 5% relative humidity for 24 h before being tested.(1)Acid erosion: The acid erosion test consisted of 99.5% concentrated acetic acid being configured into an acidic solution with pH = 3. During the erosion process, the concentration of the saturated solution was adjusted every seven days to keep the concentration of the solution stable. The saturated solution was replaced once every 30 days, and the soaking cycle was 60 days.(2)CSL) was computed as follows:tf is the average compressive strength (MPa) of three specimens for the standard curing 28 days and sf is the average compressive strength (MPa) of three specimens for the acid erosion 60 days.Compressive strength loss: The Shenzhen Universal testing equipment was used to test the concrete cube’s compressive strength in line with Chinese standard GB/T 50081-2019, and the compressive strength loss ((3)ML) of concrete was then determined as followsMass loss: The mass test measures the mass of the specimen after 28 days of the standard curing and the mass of the specimen after 60 days of acid erosion. The mass of the concrete was measured using an electronic scale with a precision of ±1 g. At the measurement time, the specimens were rinsed with tap water, and then dried at 50 ± 2 °C for 48 h. The mass loss ((4)Apparent deterioration: The apparent deterioration test examined soaking concrete specimens in an acetic acid solution that causes apparent changes by recording the apparent changes of acid erosion on concrete specimens in the early, middle, and late stages.(5)MIP: Taking the concrete specimen, a 15 mm thick slice of concrete was cut out with a cutter before a core was drilled and sampled using an electric drill and a hollow drill bit with an inner diameter of 8–14 mm. The sample contained no aggregate. After sampling, the specimen was immersed in anhydrous ethanol for seven days to terminate hydration. Finally, the specimen was baked for three days at a temperature of 50 ± 2 °C to obtain the sample to be tested. The pore distribution was determined using the AutoPore Iv 9510 high performance automatic mercury injection instrument.(6)SEM: Taking the concrete specimen, a 3–5 mm thick slice of concrete was cut out with a cutter before using an electric drill to drill a core sample in the slice. After sampling, the specimen was immersed in anhydrous ethanol for seven days to terminate hydration. Then, the sample was placed in an ultrasonic cleaner to clean, and finally put into an oven at a temperature of 50 ± 2 °C for three days to obtain the sample to be tested. The micromorphology was determined by ZEISS Gemini 300 scanning electron microscope.2) to form C-S-H gels [The 28 d compressive strength of concrete after standard curing with different CRRs is shown in S-H gels ,34, whicThe acid erosion 60 d compressive strength of concrete with different CRRs is displayed in The 28 d compressive strength of concrete after standard curing with different w/b is presented in The acid erosion 60 d compressive strength of concrete with different w/b is shown in The mass and ML of concrete at different CRRs is exhibited in The mass and ML of concrete at different w/b are exhibited in The process of concrete test block being soaked by acid solution is displayed in The particle pore distribution of concrete is displayed in The SEM of the multi-solid waste mineral admixture concrete is presented in The study focuses on the durability of ITP-FA-LS ternary mineral admixture concrete under acetic acid erosion. The compressive strength, compressive strength loss, and mass loss of concrete were analyzed by different CRRs and different w/b, and the microstructure of concrete was conducted using MIP and SEM. The following conclusions can be derived:(1)When the CRR is 20%, the standard curing 28 d compressive strength of concrete is the highest, which is higher than OPC concrete. When the w/b is 0.42, the standard curing 28 d compressive strength of concrete is the highest. The activity of ITP is significantly increased after grinding. Appropriate mixing with FA and LS can help with the particle gradation and produce a micro-aggregate effect. A volcanic ash reaction occurs, which has a strong hydration reaction ability and makes the compressive strength of concrete increase.(2)Concrete eroded with acetic acid solution after 60 days. When the CRR is greater than 16%, especially at 20%, the concrete strength increase rate after acid erosion 60 d was the largest and showed strong acid erosion resistance. When the w/b is less than 0.47, especially at 0.42, the concrete strength increase rate after acid erosion 60 d is the largest and shows strong acid erosion resistance. The good volcanic ash activity of FA and LS improved the pore structure of concrete, and improved the amount of cementation and cementation process. The filling effect increased the compactness of concrete to a certain extent, strengthened the acid penetration resistance of concrete, and hindered the transport of ions in acetic acid solution in the pores of the concrete.(3)Acidic solution erosion deteriorates the concrete surface. At the same time, there is a loss of mass of concrete, which is minimal when the CRRs is 20% and minimal when the w/b is 0.42; all of them are smaller than the ML of the OPC concrete specimen. The ternary mineral admixture system consisting of ITP, FA, and LS resulted in more delicate pores and a denser structure of concrete, which effectively hindered the erosion of concrete by acetic acid solution.(4)The mineral doping system reduces the permeability of the erosion medium. To a certain extent, it can alleviate the erosion of acid solution concrete through MIP and SEM, which confirms that the concrete has lower internal porosity and better density. The ITP-FA-LS ternary mineral admixture concrete has better acid erosion resistance than OPC concrete.


Enamel demineralization can occur as a side effect during orthodontic treatment with fixed appliances and should be detected as early as possible. A new approach to assess demineralization is a system consisting of a photosensitive protein that binds to free calcium ions at the enamel surface. A camera is then used to visualize the bioluminescence spots. This in vitro study aimed to evaluate the ability of the bioluminescence technology to assess artificially demineralized enamel adjacent to various orthodontic brackets.In all, 108 human enamel samples were allocated randomly to groups with different orthodontic bracket material: stainless steel, titanium, ceramic. Initial lesions were created adjacent to the brackets. The samples were assessed by bioluminescence before and after demineralization. Images were assessed for presence of bioluminescence spots (yes/no). To quantify the bioluminescence measurements, the images’ pixel values (P) were calculated within a defined area (F) adjacent to each bracket before and after demineralization. Quantitative light-induced fluorescence measurements  were performed as the reference standard for demineralization.p < 0.0001). The bracket material had no influence on the bioluminescence measurements. All samples showed fluorescence loss with a median ΔF of −9.52% (±3.15) and a median ΔQ of −1.01% × mm2 (±3.34), respectively.After demineralization, bioluminescence spots were visible (yes/no decision) in 87% of the samples. The pixel analysis of the bioluminescence spots showed significantly higher pixel values after demineralization compared to baseline (The bioluminescence technology is a promising tool to demonstrate demineralization adjacent to different orthodontic brackets in vitro. Orthodontic treatment with fixed multibracket appliances is a common method to treat malpositioned teeth. A standard procedure is to attach brackets on the labial or lingual surfaces of the teeth. Treatment with multibracket appliances makes oral hygiene more difficult and leads to undesired adverse effects to the teeth and the surrounding structures . IncreasEarly detection of demineralization adjacent to brackets is challenging. Although visual assessment is an important method for detecting initial lesions, it is often subjective; thus, subsidiary methods may provide additional benefit in objectifying and documenting demineralization, including digital documentation. Furthermore, remineralizing measures can only be used effectively if demineralization is detected early and the evident success of remineralizing procedures, also in terms of follow-up, can significantly improve patient cooperation.The recently introduced Calcivis® Imaging System  is a method based on the bioluminescence technique for detecting demineralization in enamel. It is known that during demineralization of the enamel, free calcium ions are released , 33. TheTo date, only a few studies have been performed to detect active caries lesions and distinguish them from sound or inactive lesions , 16, 17.The use of extracted human teeth was approved by the ethics committee of the medical faculty of the Philipps University of Marburg (reference no. 132/19). A sample size calculation was performed using the software G*Power, V 3.1.9.2 . Based oThe teeth were stored after extraction in a 0.001% sodium azide solution for disinfection. In case of presence of adherent soft tissues they were carefully removed. According to the protocol of the manufacturer of the bioluminescence device the teeth were cleaned with a cleaning paste with an RDA (relative dentin abrasivity) value of 120  applied with a rotating white cup brush with nylon filaments . The remaining paste was removed with a multifunctional syringe using water and air, and the teeth were stored in deionized water afterwards. The buccal surfaces of the teeth were examined under a stereomicroscope  at ×16 magnification. Care was taken to ensure that every surface was without signs of demineralization or enamel defects. Then, the samples were fixed on plexiglas slides .On each sample  orthodontic brackets were bonded following the instructions for use: the enamel surface was etched  and rinsed with water after 30 s. The teeth were dried and orthodontic brackets were bonded in the center of each sample  and were light cured . Three different bracket types  were used to evaluate whether the material  has an influence on the bioluminescence measurements: group A = equilibrium® mini ; group B = equilibrium ti® ; and group C = discovery® pearl .To create an internal control group, one side of each sample was covered by an acid resistance clear nail polish . Hence, this site was protected from demineralization. To produce initial enamel lesions, the samples were covered with a layer of an 8% methylcellulose (approximately 2 cm) on top of which 0.1 M lactate buffer was placed in excess at a pH of 4.6  at 37 °CA bioluminescence system for in vitro application was used for quantification of free available calcium on the tooth surfaces according to manufacturer’s operating manual. The methodology was already published for use in occlusal surfaces . In brieThe bioluminescence measurements were performed at baseline and after demineralization. The images were examined for luminescence areas on the surface which correspond to freely available calcium. First, yes/no decisions were made for the presence of luminescence spots on the images. Then, the luminescence area was marked and the number of the colored pixels in the area was assessed. Mean pixel values and the area of the luminescence spots in the areas of interest were calculated and compared prior to and after demineralization.2, related to lesion volume) were analyzed [As a nondestructive method, QLF measurements were performed to quantify the demineralization . The measurements were performed at baseline and after demineralization. Average percentage of fluorescence loss with respect to the fluorescence of sound tissue  and fluorescence loss times the area  and nonparametric tests were used for further analysis . McNemar test was used to evaluate the differences in the Calcivis readings (luminescence spots yes/no). The significance level was set at α = 0.05.The statistical evaluation was performed using the software MedCalc® (v19.2.1). Data were tested for normal distribution using the Shapiro–Wilk’s test (p < 0.001) representing demineralization areas adjacent to the brackets . The luminescence spots between the different bracket groups did not differ significantly after demineralization . The pixel values of the bioluminescence areas in each bracket group are summarized in Table Software analysis of the luminescence spots showed significantly higher pixel values and areas after demineralization , respectively. There were no significant differences between the bracket groups after demineralization . The values for the percentage of fluorescence loss (ΔF and ΔQ) in each bracket group are summarized in Table After demineralization, all samples showed a distinct fluorescence loss with a median ΔF of −9.52% ±3.15) and a median ΔQ of −1.01% × mm.15 and aIn Figs. Enamel demineralization is one of the most undesired side effects of fixed orthodontic treatment. High treatment demand and occurrence of biofilm-related complications requiring professional care were named to make orthodontic treatment a potential public health threat . In ordeThe detection of demineralization at sites that actively lose mineral content at an early stage is challenging. Visual–tactile examination has been established for the detection of active caries lesions , 22, altThe present study was the first to evaluate the ability of the system to assess demineralization on smooth surfaces adjacent to orthodontic brackets. The results indicate the suitability of the bioluminescence technique to visualize artificially demineralized areas. A shortcoming of the bioluminescence system is the lack of any scale for quantification of demineralized areas. Currently, only a yes/no decision can be made with regard to the presence of luminescence spots, and the assessment of the colored bioluminescence spots was much easier on the computer screen than on printed images. Thus, in order to quantify the findings, an attempt was made to represent the measurements in numbers by calculating the pixel values in the luminescence spots using image software. The results show that luminescence spots were detectable after demineralization (yes/no decision) and that significantly higher pixel values were measured after demineralization of the enamel compared to the values from baseline measurements Table . HoweverLooking at Figs. Streptococcus mutans and that other factors such as the quality of the bracket type, the level of individual oral hygiene, bonding and age may have greater influence [In the present study, the quantity of luminescence spots between the different brackets groups did not differ significantly, indicating that the presence of brackets would not affect the bioluminescence measurements. Some studies demonstrated no differences in the adherence of cariogenic streptococci to stainless steel, ceramic, or plastic brackets , 21. On nfluence .The use of QLF is a common method to assess demineralization adjacent to orthodontic brackets , 30, 32.In the present study, the ability of the bioluminescence technique to detect artificially produced demineralization adjacent to orthodontic brackets was demonstrated. At the time when our study was performed, only a device for in vitro use was available. Recently, the bioluminescence technology was introduced for in vivo detection of active demineralization and the findings of our study can be transferred to the clinical situation in the near future. Based on the results and within the limitations of an in vitro study, the conclusion can be drawn that demineralization adjacent to orthodontic bracket of any material can be demonstrated digitally by means of bioluminescence. This allows a more objective assessment of active demineralization compared to visual detection and monitoring of tooth hard tissue, for example, in adolescents undergoing orthodontic treatment.In further studies, the performance of the bioluminescence method to assess demineralization should be evaluated clinically. In addition, studies are needed to evaluate the ability of the bioluminescence method to also assess remineralization of enamel using different remineralizing agents.


Ultra-high-performance concrete (UHPC) has greater mechanical and durability performance than normal concrete (NC). Using a limited dosage of UHPC on the external surface of NC to form a gradient structure could significantly improve the strength and corrosion resistance of the concrete structure and avoid the problems caused by bulk UHPC. In this work, white ultra-high-performance concrete (WUHPC) was selected as an external protection layer for normal concrete to construct the gradient structure. WUHPC of different strengths were prepared, and 27 gradient WUHPC-NC specimens with different WUHPC strengths and interval times of 0, 10, and 20 h were tested using splitting tensile strength to reveal the bonding properties. Fifteen prism gradient specimens with the size of 100 × 100 × 400 mm and a WUHPC ratio of 1:1, 1:3, and 1:4 were tested using the four-pointed bending method to study the bending performance of the gradient concrete with different WUHPC thicknesses. Finite element models with different WUHPC thicknesses were also built to simulate the cracking behaviors. The results showed that the bonding properties of WUHPC-NC were stronger with less interval time and reached the maximum of 1.5 MPa when the interval was 0 h. Moreover, the bond strength first increased and then decreased with the decline in the strength gap between WUHPC and NC. When the thickness ratios of WUHPC to NC were 1:4, 1:3, and 1:1, the flexural strength of the gradient concrete improved by 89.82%, 78.80%, and 83.31%, respectively. The major cracks rapidly propagated from the 2 cm position to the bottom of the mid-span, and the thickness of 1:4 was the most efficient design. The results simulated by finite element analysis also proved that the elastic strain at the crack propagating point was the minimum and was easier to crack. The simulated results were in good accordance with the experimental phenomenon. Howeve solved ,4. Concre solved ,6,7. Ulte solved ,10,11,12e solved ,14, and e solved ,16. Howee solved ,18. Meane solved ,20,21,22The functional gradient approach is a common method used to design materials with the desired performance and is often used in nanomaterial synthesis ,25,26,27The bonding property is one of the key points for the gradient concrete, which is affected by many factors, such as stiffness, roughness, moisture, and shrinkage . Since tIn this work, a white UHPC (WUHPC)-NC gradient concrete was constructed to significantly improve the mechanical strength, corrosion resistance, and aesthetic appearance with a small dosage of WUHPC so that this gradient concrete could be widely used in urban buildings, city overpass bridges, and landscape architectures. WUHPC was designed as a thin overlayer to control the dosage and protect the inner NC from an exposed environment. The interval time of two concretes, and the strength degree of WUHPC were varied to study the bonding performance of the gradient concrete to determine the optimal mixed ratio and formation technology. The bending properties of the WUHPC-NC gradient concrete were also evaluated by flexural strength and four-pointed bending. Finite element analysis was used to reveal the strain distribution in the concrete and to predict the crack position. The research steps are illustrated in P·W 52.5 White Portland Cement (WPC), P·O 42.5 Portland Cement (PC), white silica fume (WSF), metakaolin (MK), limestone powder (LP), and Fly ash (FA) were selected as binder materials. The physical properties and the chemical compositions of the binders are shown in To reveal the effect of the strength gap on the bonding performance of the gradient WUHPC-NC, the WUHPC with different strengths was prepared in this experiment. The WUHPC was prepared by WPC, LP, WSF, MK, and sand without coarse aggregate. The strength of WUHPC was adjusted by W/B ratio, mineral admixture substituted ratio, and fiber content, while the hybrid fiber ratio was kept with SSF:HSF = 2:1. The detail of mix proportions and the designed strength of WUHPC and NC are listed in For WUHPC preparation, powder materials, including WPC, WSF, MK, LP, and sand, were first dry mixed in a container, then water and WR were added with continuous stirring until the uniform matrix was formed. Last, steel fibers were slowly added in 2–3 min. The preparation method of NC was traditional; the powders and stones were mixed with water in a blender.To form the gradient concrete, the prepared WUHPC and NC were cast successively into the mold of 100 × 100 × 100 mm for the splitting tensile strength test and 100 × 100 × 400 mm for the bending strength test. Twenty-seven samples were used in the splitting tensile strength test, and 15 samples were used in the bending test in total. Three different interval times between WUHPC and NC casting were chosen, which were 0 h, 10 h, and 20 h as a comparison. Additionally, the thickness ratios of WUHPC to NC of 1:1, 1:3, and 1:4 were prepared to reveal the optimal dosage of WUHPC, which is shown in The bonding property between WUHPC and NC in the gradient concrete was characterized by the splitting tensile strength. During the test, the specimen was pleased in the mold, with the interface verticalness. Two steel sticks were put at the junction of two materials; then, a vertical load was applied to the steel sticks at the rate of 0.05 MPa/s. The experimental setup is shown in According to standard ASTM C1069 , a univeThe specimens of NC and WUHPC with the size of 100 × 100 × 100 mm and 40 × 40 × 160 mm were used for compressive strength testing, and the load rates applied for two concretes were 0.5 MPa/s and 2.5 MPa/s, respectively. For each group, three specimens were tested, and the average results were calculated as the compressive strength. The morphology and the element distribution of the gradient concrete at the joint region were analyzed by scanning electron microscopy (SEM). The specimens around the joint area were cut into slices with a thickness of 5 mm by a high-speed precision cutting machine. Then, the test slices were immersed in anhydrous ethanol to stop hydration.The cementitious materials in concrete reacted to harden with time; it was easily understood that shorter interval time resulted in a longer reaction time of two concretes and led to stronger bonding strength. Once WUHPC and NC were cast together with an interval time of 0 h, the contact region was fresh and blended to react continuously and form a complete block. When the interval time increased, the activity of cementitious materials declined, and the surface began to lose plastic characteristics after the initial setting time so that an obvious boundary was generated at the interface between two concretes, which would weaken the bonding property. Additionally, with the strength increased, the matrix of WUHPC became denser, and the fresh NC was hard to mix at the interfacial position, resulting in a lower splitting tensile strength. Furthermore, compared with U2 and U3, more steel fiber was used in U2, the bonding property of the interface was better than in U3, and the splitting tensile strength was also increased.The morphologies of the split surface of the gradient concrete samples after the test are shown in In The flexural strength of U2, NC, and the gradient concretes with different WUHPC thicknesses are summarized in The flexural strength was mostly determined by the ultimate load capacity under four-point bending. The results showed that when the thickness of WUHPC: NC = 1:3, the gradient concrete could bear the highest bending load. This proved that even with a small dosage of WUHPC, the gradient structure also performed an equivalent mechanical behavior to WUHPC under bending conditions.Due to the high strength and the reinforcement of fiber, the deformation of WUHPC was much better than NC, and it did not rupture after the ultimate load. With the WUHPC dosage of 1/3, the gradient concrete showed similar deformation properties with pure WUHPC.The photos of cracks in the gradient concrete after four-point bending tests are present in In sum, the mechanical strength of the gradient concrete composited with a small dosage of WUHPC was more closed to that of the pure WUHPC and was much better than NC. When the gradient concrete with a thickness ratio of 1:4 between WUHPC and NC was used in the construction, the mechanical strength was significantly improved with limited materials cost increase, and this might be accepted in field applications.The morphology of the gradient concrete around the contacted area is shown in To analyze the difference between the two concretes, the element mapping crossing the boundary was tested and shown in The morphology and the linear element mapping of the matrix proved that there was indeed a transition zone in the gradient concrete, but the width of this zone was decreased with the increase of interval time. With the interval time of 0 h, two pieces of concrete were fresh and well-flowed. When they come into contact together, the matrix at the interface may blend into the other part due to gravity. That is why the elements Si and Ca vibrate at distances 120–160 μm in The size of the finite element modeling was 100 × 100 × 400 mm, which was composed of different thicknesses of WUHPC. The thickness ratios of WUHPC and NC were 1:4, 1:3, and 1:1, respectively. The contact mode between WUHPC and NC was binding, which was perfect bonding. The support sticks were rigid without displacement change. The mesh size was set to 20 mm, shown in The total deformation refers to the amount of displacement generated when a structure is subjected to load, which reflects the stiffness of the structure. The equivalent plastic strain was used to determine the position of the yield surface once the material was strengthened. The total deformations and equivalent elastic strains of the gradient concrete were simulated and analyzed by finite element analysis. It was found that when the gradient concrete was subjected to four-point bending, the displacement and the strain at the center part were the largest, so the cracks usually started from the bottom of the middle part. When the pressure was constant, the total deformation of the gradient concrete decreased with the increase of WUHPC thickness, but the total deformation reduction rate also decreased. By comparing the equivalent strain contours of the gradient concrete, it could be found that there was a region on the upper side of the split point of the gradient concrete where the strain was the minimum, which was why the split occurred.(1)The splitting tensile strength of the gradient concrete increased with the shorter interval time and reached the maximum once the strength gap between WUHPC and NC was moderate. With the increase of interval time, the boundary of the gradient concrete at the joint surface became more and more clear, which was not conducive to the bonding surface.(2)WUHPC could effectively improve the flexural performance of the gradient concrete, but this effect was not linearly increased with the thickness of WUHPC. When the thickness ratios of WUHPC to NC were 1:4, 1:3, and 1:1, compared with NC, the flexural strength of the gradient concrete increased by 89.82%, 78.80%, and 83.31%, respectively. From the results, the small dosage of WUHPC could significantly improve the bending properties of NC.(3)In the bending process, WUHPC was stressed first, and the cracks developed upward from the middle bottom of WUHPC, but the total development was relatively slow. Therefore, the deformation of the gradient concrete increased in the early stage, but when NC was stressed, the crack development speed increased. Moreover, there was a crack-splitting point that was independent of the thickness of WUHPC. In the experiment, the optimum thickness ratio (WUHPC:NC) of the gradient concrete was 1:4.(4)The total deformation and equivalent elastic strain of WUHPC with different thicknesses under the same pressure were simulated by finite element analysis. The results showed that the damaged area of the gradient concrete was easy to occur in the middle position, which was consistent with the cracking position of the gradient concrete. The equivalent elastic strain at the crack splitting point was smaller than that around it, which resulted in easy cracking, and the simulated results were close to the experiment.(5)By comparing the deformations of the middle bottom, the joint surface, and the center position, the displacement difference between the bottom and the middle section gradually decreased with the increase of WUHPC thickness. Therefore, the thickness of WUHPC was not suggested to be too large.(6)The steam curing method was adopted for the gradient concrete in this study. Although the curing time was greatly shortened, the steam curing condition could not make the gradient concrete be formed on a large scale, which was not conducive to its application in practical engineering. At the same time, due to the difference between WUHPC and NC, steam curing would promote hydration, leading to a large shrinkage stress, which might not be conducive to the bond performance of the gradient concrete.The combination of WUHPC and NC in the gradient concrete possessed better bending strength than plant NC. By studying the influence of pouring technology on the bonding property of the gradient concrete and the influence of WUHPC thickness on the flexural property of gradient concrete, the following conclusions are drawn through the numerical simulations by finite element analysis.


The appearance of cracks is one of the reasons that affect the performance of asphalt pavement, and traditional repair methods have the potential problem of causing adverse effects on the environment. In this paper, an environmentally friendly method for asphalt concrete crack repair was investigated using microbially induced calcite precipitation (MICP) for asphalt concrete cracks of different widths , and the effectiveness of repair was evaluated using nondestructive and destructive experiments. A varied ultrasonic pulse velocity was used to evaluate the healing process, and it was found that the samples with an initial crack width of 0.5 mm showed the most significant increase in wave velocity of 18.06% after repair. The results also showed that the uniaxial compressive strength and indirect tensile strength of the MICP-repaired samples recovered up to 47.02% and 34.68%. Static creep test results showed that MICP-repaired samples with smaller width cracks had greater resistance to permanent deformation. The results of uniaxial compressive strength tests on larger width (3 mm) cracks repaired by MICP combined with fibers showed that the strength of the samples was significantly increased by the addition of fibers. In addition, the SEM/EDS results showed that the MICP products were spherical calcite particles with a particle size distribution from 0 to 10 μm. This study shows that MICP has some potential for repairing cracks in asphalt concrete of different widths within the range investigated. Asphalt pavements are widely used in traffic engineering all over the world because of the advantages of a short construction period, a smooth surface, and comfortable driving . There aThere are generally two types of solutions for this pathology. One acts before the development of cracks and the other after the appearance of cracks, the former being a proactive way to reduce the possibility of cracks and the latter being a reactive repair after the cracks appear. The first method is to enhance the crack resistance of the asphalt mix, with the effect of preventing the extension of cracks or reducing the likelihood of cracks appearing. This approach includes enhancing the bonding effect of the binder  andRecently, promising results have been achieved in eco-friendly fracture repair using biocolloid technology. Inorganic materials precipitated by microbially induced calcite precipitation (MICP) for the effective repair of cracks in cement concrete, brick, mortar, and rock have been extensively investigated due to their environmental friendliness and low-carbon nature ,18,19. TIt has been shown that pure inorganic materials can be used to rapidly repair asphalt concrete cracks in municipal pavement manhole structures . In addiIn this paper, the effect of MICP on the repair effect of cracked asphalt concrete of different widths was investigated experimentally, and the repair performance of cracked asphalt concrete, including uniaxial compressive strength, indirect tensile strength, and permanent deformation, was evaluated. In addition, the physical morphology and chemical components were analyzed using scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS) analysis.iP  is as shown in Equation (1):dmax is the maximum size of the particle and n is the Talbot index (n < 1).The binder used for the asphalt concrete samples was cationic emulsified asphalt  produced by Dongguan Dongjiao Asphalt Co. The aggregates for the asphalt concrete samples were crushed gravel, mineral powder, and coarse and medium-fine sand, with 10% asphalt content for each sample. Based on the Talbot classification method , the masThe total mass of each sample was 800 g. The grading of the aggregates at a Talbot index of 0.5 is shown in To investigate the effect of pre-crack width on MICP repair, intact samples and samples with crack widths of 0.5 mm, 1.0 mm, and 1.5 mm were designed for direct MICP repair, as well as samples with crack widths of 3 mm for MICP repair with fibers. It has been shown that the maximum crack depth of asphalt concrete in the field is less than 50 mm . In thisNCHRP Report No. 425 [The bacteria used in this experiment were Bacillus pasteurii because of its significant advantages, such as easy extraction and nonbiological pathogenicity. The composition of the liquid nutrient medium used in the experiment was urea (20 g/L), soy protein (5 g/L), casein (15 g/L), and sodium chloride (5 g/L), and the pH of the medium was adjusted to 7.3 with NaOH. After the nutrient medium was prepared, the bacteria were inoculated into the culture medium at a rate of 1%. Finally, the inoculated bacterial culture was put into a constant temperature shaker and incubated at 30 °C and 130 rpm for 24 h. The OD600 and conductivity were measured every eight hours until their OD600 and conductivity reached about 2 and 20, respectively. An equimolar urea–calcium chloride solution with a concentration of 1 M was used as the MICP cementing solution.The repair method varies depending on the width of the crack.For small-width cracks (≤1.5 mm), precast cracked asphalt concrete samples were repaired by peristaltic pump drip injection. A BT100M peristaltic pump was used to simultaneously pump 10 mL of bacterial solution and cementing solution into the cracks at a rate of 3.0 rpm for eight days. The crack repair is shown schematically in For samples with large-width cracks (3 mm), the MICP repair process used a peristaltic pump to simultaneously pump 20 mL of bacterial solution and 20 mL of the cementing solution into the cracks at 20.0 rpm, and the fibers , as shown in The effect of MICP repair on the strength of small-width asphalt concrete cracked samples was determined using indirect and direct methods. For the indirect method, a conventional nondestructive test method called ultrasonic pulse velocity (UPV) was used to assess the degree of internal damage . Prior tP is the load when the sample is damaged and A is the cross-sectional area of the sample parallel to P.An indirect tensile strength test was used to characterize the asphalt mixture in the tensile state , which ccσ) of 0.12 MPa , as shown in Creep stiffness modulus is an important parameter for evaluating the deformation performance of asphalt concrete. According to NCHRP Project 9-6(1) , the tescqEt) applied to the sample; and εc(t)).υ(t) is the uniaxial deformation of the sample in time t and The split samples were analyzed using a scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) to obtain the microscopic morphological characteristics and chemical composition of microbial mineralization products.The electron microscope and energy dispersive spectrometer used in this experiment were both from Hunan Kewei Testing Technology Co., Ltd., and the parameters were as follows: the model of the electron microscope was JSM-7610FPlus with a magnification of 500~10,000 times; the model of energy dispersive spectrometer was ULTIM MAX 40, and the detection elements were mainly C, O, and Ca.As The greater the ultrasonic velocity, the better the repairing effect of asphalt concrete cracks. Therefore, the ultrasonic detection method can indirectly reflect the healing efficiency of asphalt concrete cracks. The results of the ultrasonic method for asphalt concrete before and after crack repair are shown in It can be seen that the ultrasonic velocity coefficient of variation for the three crack widths does not change much before and after the 8-day healing time b, and thThe asphalt concrete samples consisted of a solid and a gas phase because the asphalt concrete samples were sufficiently dry prior to the ultrasonic pulse velocity test. Due to the speed of propagation of the sound in solids being greater than that in air, when the cracks are filled, the solid phase of the asphalt concrete increases, the gas phase decreases, and the wave velocities show an increasing trend. The structural integrity of the 0.5 mm crack-width samples is greater than that of the 1.0 mm and 1.5 mm crack-width samples, and it is less difficult to form an effective ‘bridging’ effect on both sides of the crack than in the 1.0 mm and 1.5 mm crack-width samples, so the increase in wave velocity is most significant. The speed of the ultrasonic pulse increases as the crack width decreases, which is consistent with experimental expectations, and is in line with the results of Jongvivatsakul et al.  who showThe above analysis shows that microorganisms can produce mineralization products for repairing asphalt concrete cracks of different widths, and the repairing effect is better for samples with smaller crack widths than those with larger crack widths.3, thus allowing load transfer. The results showed that the stress concentration at the crack tip was reduced. As a result, the compressive strength of the cracked asphalt concrete increased to 1.05, 0.90, and 0.64 MPa. In addition, the compressive strength ratios were up to 78.94%, 67.67%, and 48.12% compared to the control samples. The increase in strength with crack healing is consistent with the increase in pulse velocity. Zheng et al. [The compressive strength of the mortar samples is shown in g et al.  and Qiang et al.  confirmeThe asphalt has a strong bond between the aggregate and the calcium carbonate, which helps to form a bridge between the two sides of the crack . The UCSThe indirect tensile strength (ITS) of MICP-repaired cracks of different widths is shown in 3 distribution. The researchers found similar effects for potential applications in terms of indirect tensile testing following the bacterial repair of cracks in cement mortars [It is speculated that the lower value of ITS may be due to insufficient crack healing and the formation of an imperfect bond between cracked samples. The samples with larger crack widths repaired by MICP showed smaller ITS. One reason for this may be the lack of bonding between the cracks and the smaller size and microstructure of the CaCO mortars . Therefo mortars . The minThe results of the static creep test are shown in 3 bridge formed is less likely to break in the middle, so it has a greater ability in preventing permanent deformation.The researcher, Manfro , found tSEM scans  show thaThe particle size distribution of the particles in A total of three EDS scans were performed in this experiment, and the analytical results are shown in (1)In the MICP repair process, the different fibers added in the cracks, even though they have the same quality, show different repair effects due to their different softness and volume, resulting in different distribution patterns in the cracks and different interaction relationships with the asphalt binder, aggregates, and MICP products.(2)In the case of basalt fiber, its texture is hard, and it plays the role of strengthening the interconnection between calcium carbonate particles, and also provides the landing point for bacteria; in the case of polyester fiber, its texture is soft and it is more aggregated and distributed under the infiltration of slurry, which plays the local geotextile effect; for glass fiber, its softness and hardness are between basalt fiber and polyester fiber, and due to its longer length, it becomes entangled in the cracks. This winding effect can also strengthen the cementation between calcium carbonate particles, aggregates, and fibers to a certain extent; in the case of steel fibers, it has the hardest texture and the largest mass in the same volume, and the interlocking between fibers can also lead to the local siltation of calcium carbonate when repairing cracks via MICP due to the sinking through gravity, resulting in the effect with steel fibers where the MICP repair only occurs in a certain depth range of the cracks.The reasons for the above results can be inferred as follows:m is the mass of fiber added and cV is the crack volume.3, the best doping mass of steel fiber is about 0.83 g/cm3, and the best doping mass of polyester fiber and glass fiber is more than 0.31 g/cm3. The specific values are subject to further experimental study.It can be seen in the figure that the best doping mass of glass fiber is about 0.18 g/cmThe spherical calcium carbonate particles of MICP mineralization products have better fluidity and dispersion , which aSince the propagation speed of acoustic waves in solids is greater than that in air, the denser the mineralization quantities in products, the greater the measured wave speed, and the better the filling effect of cracks . After tThe adhesion between the microbial mineralization products and the cracks of the asphalt concrete samples depended upon the compatibility between the roughness of the crack surface and the mineralization products, while the strength of the mineralization products depended on their own properties . Since tIn order to facilitate quantitative research, all of the repair work in this paper was carried out on regular cracks. However, in practice, regular cracks are almost nonexistent, and, therefore, the effect of irregular cracks on the repair effect needs to be considered. Irregular crack extensions make it difficult to control the percolation path of the biological slurry within the crack and make the repair more difficult and complex. In future research, the percolation channels of MICP slurry under complex fracture extension and the mechanism of MICP product attachment under such complex percolation can be further explored.(1)The wave speed increased from 1545.36, 1536.96, and 1528.65 m/s to 1824.52, 1734.97, and 1683.33 m/s for crack widths of 0.5 mm, 1.0 mm, and 1.5 mm, respectively, and the uniaxial compressive strength for the MICP-repaired samples also increased compared to the unrepaired samples by 78.94%, 67.67%, and 48.12%, respectively. In addition, the recovery rates of indirect tensile strength were 34.68%, 32.19%, and 13.64%, respectively.(2)The static creep test results showed that the creep modulus of the MICP samples was finally stabilized at 123.85 MPa, 54.83 MPa, and 49.83 MPa after 3600 s of constant pressure loading, indicating that the repaired MICP with a crack width of 0.5 mm had greater resistance to deformation.(3)3, which was mainly in the form of spherical calcite. the particle size of CaCO3 was mostly concentrated within 10 μm, with an average value of 4.54 μm.SEM and EDS images showed that the MICP product of this study was CaCO(4)3 for glass fibers, about 0.83 g/cm3 for steel fibers, and over 0.31 g/cm3 for polyester and basalt fibers.The results of MICP combined with different fibers to repair large-width cracks showed that the addition of fibers contributed to the filling effect of the MICP product in the cracks of the as-built concrete. the UCS results showed that the optimum dose was about 0.18 g/cmIn this study, the effectiveness and mechanism of the (MICP) technique for repairing asphalt concrete with different crack widths were investigated through a series of experiments. Several conclusions were drawn as follows:The above findings indicate that the asphalt concrete samples with single cracks repaired with MICP showed some degree of recovery in performance. In general, the repair effect increased significantly as the crack width decreased. When the crack width was more extensive, the combined repair effect of MICP and fiber was better than the direct MICP repair.