The disposal of steel slag leads to the occupation of large land areas, along with many environmental consequences, due to the release of poisonous substances into the water and soil. The use of steel slag in concrete as a sand-replacement material can assist in reducing its impacts on the environment and can be an alternative source of fine aggregates. This is the very first paper that seeks to experimentally investigate the cumulative effect of steel slag and polypropylene fibers, particularly on the impact resistance of concrete. Various concrete mixes were devised by substituting natural sand with steel slag at volumetric replacement ratios of 0%, 10%, 20%, 30%, and 40%, with and without fibers. Polypropylene fibers of 12 mm length were introduced into the steel slag concrete at 0%, 0.5%, and 1.0% by weight of cement as a reinforcing material. Performance evaluation of each mix through extensive experimental testing indicated that the use of steel slag as partial substitution of natural sand, up to a certain optimum replacement level of 30%, considerably improved the compressive strength, flexural strength, and tensile strength of the concrete by 20.4%, 23.8%, and 17.0%, respectively. Furthermore, the addition of polypropylene fibers to the steel slag concrete played a beneficial role in the improvement of strength characteristics, particularly the flexural strength and final drop weight impact energy, which had a maximum rise of 48.1% and 164%, correspondingly. Moreover, integral structure and analytical analyses have also been performed in this study to validate the experimental findings. The results obtained encourage the use of fiber-reinforced steel slag concrete (FRSLC) as a potential impact-resistant material considering the environmental advantages, with the suggested substitution, of an addition ratio of 30% and 1.0% for steel slag and polypropylene fibers, respectively. The global inclination toward industrial development has made waste management one of the most perplexing dilemmas. The economic advantages of this rapid industrialization go hand in hand with the production of environmentally hazardous wastes . As an i2O3 untreated slag in concrete as a sand-replacement material and found marginal improvements in different strength characteristics of the concrete. Furthermore, Guo et al. [Furthermore, the construction industry is looking for sustainable, economical, and environmentally friendly construction systems for saving the world. Therefore, the use of steel slag in concrete is a promising concept , as conco et al.  investigo et al. . Recentlo et al.  conducteOn the other hand, the construction industry is also concerned about the brittle nature of concrete, which has low tensile strength and behaves poorly under impact-type loadings ,25,26, aPrevious studies revealed that few researchers have examined the use of steel slag as fine aggregate in concrete to enhance its static performance, whereas limited research data exist on the impact behaviors of the steel slag concrete. Additionally, researchers either focused on the improvement of the environment by using industrial wastes or on the brittle nature of concrete with the adaptation of fibers, not considering both aspects. In recent times, most of the construction carried out consists of concrete structures which behave poorly under impact loadings. Any improvement in the basic composition of concrete leading to amelioration in its energy absorbing capacity would have a profound effect on the construction industry. To overcome the inherent weakness of concrete structures under impact loadings, the use of polypropylene fibers in steel slag concrete can be a promising solution for enhancing the impact performance of concrete as they are abundantly available in most countries and are less costly than steel fibers. Therefore, this research aims to experimentally examine the impact resistance and mechanical properties of fibrous and non-fibrous concrete, with waste steel slag as sand-replacement material and the addition of polypropylene fibers, for the very first time. Consequently, the authors believe that the coupled effect of polypropylene fibers and waste steel slag in concrete will contribute to the efforts of the community for a sustainable environment and will also be a valuable addition to the civil engineering world by evolving energy absorbent construction materials for utility in various infrastructure projects.This section deliberates on the material properties, concrete mix proportions, and testing procedures that were implemented to obtain the desired parameters.2O3) of various shapes ranging from massive boulders to dust were generated. Based on the particle size, waste slags are mainly categorized into three types comprising large boulders, sand-sized scrape, and extremely fine dust particles.The Ordinary Portland cement  meeting the requirements of ASTM C150/C150M-21  was used2 are evident that there are negligible chances of pozzolanic activity due to steel slag. Coarse aggregates of particle size ranging from 19.0 to 4.75 mm were employed in this research. Particle size distribution of aggregates was performed by implementing ASTM C136/C136M-14 [In the current study, sand-sized (4.75 to 0.075 mm) “Scrape” steel slag was used in concrete mixes in the “as received” form without any added screening to economize the mix designs. Physical observation showed that the fine aggregates were clean, free from clay and any other organic deleterious substances. The chemical composition of steel slag was also analyzed and has been compared with the cement in C136M-14 , and resC136M-14 , as showTo examine the effects of natural sand substitution with steel slag and the addition of polypropylene fibers on mechanical performance and impact behavior of concrete, fifteen concrete mixes were cast in the research laboratory utilizing the materials introduced in 3) capacity. For the preparation of slag only concrete group mixes, the cement and aggregates were mixed in a dry condition for three minutes first, then water was added. Then, the horizontal drum was further rotated for three to five minutes for uniform mixing. The desired slump range of 75–125 mm was easily achieved in normal concrete with a w/c ratio of 0.48 without requiring the use of a super-plasticizer. However, with this fixed w/c ratio, hybrid mixes having steel slag and fibers were not workable. The lower workability of mixes was compensated by adding super-plasticizer in varying dosages of 0.9~1.01% to achieve the desired slump. As far as the mixing of the other two fibrous concrete groups was concerned, the concrete ingredients were added to the mixer by a three-layer method to ensure uniform fiber dispersion [Subsequently, after finding out the properties of materials and mix proportions of materials, different-shaped concrete specimens were cast to acquire the dimensions given in spersion ,41. The Three specimens for each set of test parameters were prepared. Before casting, the molds were thoroughly cleaned, bolted, and oiled from the inside. Slump tests were conducted on each concrete mix, according to ASTM C143/C143M-15a . ConcretExperiments were performed for the determination of different strength parameters as per the applicable procedures illustrated in the ASTM standards listed in  on samples of 150 mm diameter and 300 mm height. ASTM C39/C39M-15a  was implε within the elastic limit. Stress–strain curves and Equation (1), as per guidelines of ASTM, C469/469M-14 [Moreover, the same setup was used for the computation of modulus of elasticity, which is the ratio of change in compressive stress /469M-14  were appε2 = Longitudinal strain produced due to The ACI committee in its report entitled ACI 544.2R-89  explainsThe drop weight impact test was performed on the concrete disks with a diameter of 150 mm, and height of 63.5 mm. The disks were obtained by cutting the standard cylinder of 150 mm diameter into the required height of 63.5 mm. According to this method, a hammer of 4.5 kg was repeatedly dropped from a height of 457 mm on a concrete disk of 63.5 mm in height and 150 mm in diameter. The impact was transferred from the hammer to the concrete specimen through a hardened steel ball of diameter 63.5 mm. This method serves the dual purpose of uniformly transferring impact force in each hammer drop and developing an effective shock wave due to point impact loading. The steel ball was kept in its place on the concrete disk with the help of a steel pipe of a slightly larger diameter than the steel ball connected to steel plates on both sides. The steel plates were rigidly connected to the side columns of the testing apparatus. The hammer drops were continued until the first visible crack was observed on the concrete specimen surface. Once the initial crack was observed, the number of drops of the hammer to cause the initial crack was recorded. The hammer drops were again continued until the final failure of the specimen occurred. The final fracture was considered as a state in which the concrete specimen splits into several fragments and touches the boundary of the specimen. The impact resistance of fibrous and non-fibrous steel slag concrete was then determined in terms of initial and final impact energies using the counted number of drops as per Equations (2) and (3), respectively.m = Mass of hammer used = 4.5 kgs.g = Gravitational acceleration = 9.81 ms−2.h = Height of fall of the hammer = 457 mm.This section presents the explanation of findings from experimental work. The mechanical performance of each concrete group has been evaluated by compressive strength, modulus of elasticity, flexural strength, splitting-tensile strength, unit weight, and water absorption test, and the results are summarized in From the comparative studies of the experimental results, reflected in The stress–strain relationship of non-fibrous and fibrous concrete groups is shown in Furthermore, closely examining the modulus of elasticity results given in An increase in modulus of elasticity is at maximum at 30% substitution value. Amplified bonding between the cement paste and aggregate particles due to the high angularity and hardness of the steel slag may be the cause of this increase. With an additional increase in the steel slag substitution, a decrease in the modulus of elasticity was observed. This finding is somewhat compatible with Guo et al.  and DharC78M-15a . ResultsC78M-15a  and MohaC78M-15a , who disThe variations found in splitting-tensile strength (iN) and ultimate failure (fN), along with the calculated impact energies using Equations (2) and (3) are given in The number of hammer blows borne by the concrete disk specimens for the initial cracking  exhibited 732 kN mm of final impact energy which increased to 1261 and 1343 kN mm upon the addition of 0.5% and 1.0% PP fibers (mix No. 9 and 14), respectively. This increase in the impact resistance of fiber-reinforced slag concrete is due to the combined effect of steel slag and PP fibers. The increase in fiber dose raised the fiber density in the mixtures; therefore, more PP fibers were available per unit area to bear the impact forces. Moreover, fibers changed the direction of crack growth and restricted the opening of cracks as can be seen in the failure patterns shown in The inclusion of fibers also influences the post-first crack resistance, i.e., Water absorption is an important parameter to comment on the durability of concrete. It is simply the measure of concrete resistance in aggressive environments because it indirectly reflects the perviousness of concrete. The results of water absorption are produced in The dry unit weight of each mix was also checked, and the resulting values are produced in Microstructural analysis of slag concrete is performed with the help of scanning electron microscopy (SEM) using the Everhart–Thornley detector (ETD) and through-lens detector (TLD) to examine the integral structure and combined effects of steel slag and polypropylene fibers. The SEM images obtained are produced in Ec and R2, due to introduced elastic behavior because of the addition of fibers, as shown in The experimental results are assessed analytically in this section using polynomial and linear regressions  to elabotrengths b,c. The The experimental data have also been compared with ACI-318M-14  strengthp-values are given in This section discusses the probability distribution of the mechanical and impact behaviors of all studied concrete mixes. The use of waste steel slag leads to greater uncertainties in experimental results because of its high angularity and irregular-shaped particles along with varied sizes. However, the extent of these uncertainties can be well realized through statistical analyses. Therefore, the probability distribution of various concrete properties is carried out in this research with the help of the computer program OriginLab. Normality of experimental data has been carried out by the calculation of p-values through a goodness-of-fit test by the Shapiro–Wilk method, and the resulting p-values are calculated by assuming the normal distribution with a significance level of 0.05. Correspondingly, any p-value which is equal to or lower than 0.05 means that the assumption is not satisfied, and the data do not fit the normal distribution with 95% confidence [p-values given in The nfidence . CompariMechanical properties of slag concrete increases with the increase in volumetric substitution ratio of steel slag up to 30% and then reduces. Hence, the optimum content of natural sand replacement with the steel slag is 30%.Polypropylene fibers have a small effect on compressive strength as compared with the improvements in other mechanical parameters of fiber-reinforced steel slag concrete specimens. Fiber addition of 1.0% to the weight of the cement is discovered to be the optimum dosage for all strength parameters.Sand replacement with the steel slag enhances the stiffness and brittleness of concrete. The static modulus of the best-declared mix without fibers  is 20% higher than the control concrete. The addition of PP fibers improves the post-first crack performance and ductility of the concrete, slightly reducing the modulus of its elasticity to 6% in SL30F1.0.The cumulative use of steel slag and PP fibers increases the compressive, flexural, and split tensile strength for the optimized percentage replacement of sand without fibers by 26%, 48%, and 32% with regard to the referenced mix.The combination of steel slag and PP fibers meaningfully improved the drop weight impact resistance of steel slag concrete. The maximum improvement of 108% and 164% in initial and final impact energies are reported, respectively in SL30F1.0 when compared with those of control concrete.Water absorption reduces, and dry density increases with the growth in steel slag content. The increases of 2.1%, 3.5%, 4.1%, and 4.5% in dry density are observed upon 10%, 20%, 30%, and 40% steel slag incorporation with respect to control concrete, and these increases are within the limits of normal density concrete stated in ACI 304.3-12 “Heavyweight Concrete”.The microstructural studies validate the bridging action of PP fibers and the high angularity of steel slag as a major reason for the enhancement of mechanical parameters of FRSLC.The analytical studies reveal that mechanical and impact behaviors of FRSLC mixtures followed a normal distribution and are the best fit for this study. Moreover, the expressions developed for the FRSLC models are better than the ACI-318M-14 models.An experimental investigation was conducted to explore the influence of PP fibers on the static and impact performance of the concrete having steel slag as sand-replacement material. The experimental investigations showed that fiber-reinforced slag concrete (FRSLC) exhibited better mechanical and microstructural properties than control concrete. The conclusions drawn from the study are summarized as follows: Based on the findings obtained and analyzed behaviors, FRSLC is anticipated to be successful in reducing the unfavorable effects of the steel slag by utilizing its large quantities in the concrete. Moreover, it also plays a significant role in evolving the energy-absorption capabilities of concrete. Among the investigated types of the FRSLC, concrete mix with 30% steel slag as a sand-replacement material and the addition of 1.0% polypropylene fibers is the most effective because it depicts the highest improvement in most of the investigated parameters, compared with other studied mixes. However, this study has been conducted for low-velocity impact loads; therefore, a similar study under high-velocity impact is recommended to be conducted on a prototype model of structures in order to proceed toward its practical applications.


Three-dimensional concrete printing (3DCP) is an innovative technology that can lead to breakthrough modifications of production processes in the construction industry. The paper presents for the first time the possibility of 3D printing concrete–geopolymer hybrids reinforced with aramid roving. Reference concrete samples and concrete–geopolymer hybrids composed of 95% concrete and 5% geopolymer based on fly ash or metakaolin were produced. The properties of the samples without reinforcement and samples with 0.5% (wt.) aramid roving were compared. The frost resistance tests, UV radiation resistance, and thermal conductivity were evaluated for samples that were 3D-printed or produced by the conventional casting method. Compressive strength tests were carried out for each sample exposed to freeze–thaw cycles and UV radiation. It was observed that after the frost resistance test, the samples produced by the 3D printing technology had a minor decrease in strength properties compared to the samples made by casting. Moreover, the thermal conductivity coefficient was higher for concrete–geopolymer hybrids than concrete reinforced with aramid roving.  Global population growth is contributing to the development of the construction industry. The United Nations predicts that the world’s population will grow to 8.5 billion in 2030, 9.7 billion in 2050, and 10.9 billion in 2100. Consequently, such an increase in the world population will increase the demand for new residential and service buildings [2 emissions, and high energy consumption [One of the basic and most frequently used materials in building construction is concrete, due to its design parameters, properties, and low cost ,4. Unforsumption . The des2 emissions and lower energy consumption [One type of material that is an excellent alternative to ordinary Portland cement (OPC) is geopolymers . A geoposumption . Geopolysumption , repair sumption , and heasumption . In termsumption .In recent years, there has been a dynamic development of 3D concrete printing (3DCP) using the extrusion method. This technology consists of linear extrusion of cement mortar layer by layer without the use of formwork, which can reduce production costs, increase the speed of production processes, and allow the economical production of geometrically complex elements ,14. AddiPartial replacement of cement with other materials allows for the production of hybrid cement-geopolymer concrete. Earlier it was shown that Portland cement can be partially replaced by various materials , such asHybrids are most often produced by mixing cement and other cement material in appropriate proportions and then activating such a mixture with a previously prepared alkaline solution. In our work, we produced concrete–geopolymer hybrids by preparing concrete and the geopolymer separately, and then by mixing them in appropriate proportions. We produced the hybrids using two methods: casting into molds and 3D printing ,30. The In this study, class F fly ash  and Metakaolin KM 60  were used as a precursor for the production of geopolymers. The chemical composition of the raw materials is presented in Concrete specimens and concrete–geopolymer hybrids were prepared for the tests. To prepare the concrete mixture, the cement (CEM I 42.5R) and sand were mixed in a 1:1 ratio. The water to dry weight mixture ratio was 0.125.The geopolymer mass was made by mixing fly ash or metakaolin with sand in a 1:1 ratio. An alkaline activator solution which consisted of 10 M sodium hydroxide and an aqueous solution of sodium silicate (R-145) in a molar ratio of 1:2.5 was added to the raw materials. All components were mixed in a GEOLAB cement mortar mixer  for 15 min. In the geopolymer blends containing fly ash, the liquid-to-solid ratio was 0.28; 0.35 for blends based on metakaolin.To prepare concrete–geopolymer hybrids, the concrete, and geopolymer mass were mixed in the proportion of 19:1. The mixtures were produced by casting and 3D printing methods. Aramid roving was added to part of the samples in an amount of 0.5 wt.%. Roving was placed at 1/3 and 2/3 of the height of the specimen. The percentage of selection of roving as well as their distribution were based on the results obtained in the previous work . GeopolyBy producing samples by casting, the prepared mixtures were poured into molds with dimensions of 50 mm × 50 mm × 50 mm for tests in a climatic chamber and for tests of compressive strength; 100 mm × 100 mm × 100 mm for frost resistance and abrasion resistance tests; ⌀ 55 mm × 23 mm for thermal conductivity tests. The molds were shaken to remove trapped air. The samples were cured for 24 h at 75 °C, then removed from the mold and stored under ambient conditions.−1. The diameter of the printing nozzle was 15 mm and the thickness of the printed layer was 30 mm.For the production of samples by 3D printing, the models for printing were designed in the Blender software. The samples were printed on the ATMAT Galaxy 3D printer . Printing was performed at ambient temperature with a printing speed of 150 mm sThe compositions of the produced concrete samples and concrete–geopolymer hybrids are presented in The degree of frost resistance of concrete and concrete–geopolymer hybrids was tested using the standard method in accordance with the PN-B 06265. The samples were subjected to 150 cycles of freezing at −18 ± 2 °C and defrosting at 18 ± 2 °C. The obtained results were then compared with the test results for the reference samples stored in water at the temperature of 18 ± 2 °C.2. After the tests of resistance to UV radiation, the compressive strength tests and the grayscale color changes were carried out.The UV aging tests in the climatic chamber were carried out in accordance with the following standards: UV radiation resistance test—PN-EN ISO 4892-2:2013-06; color change test—PN-ISO 105-A02:1996. The resistance to UV radiation was tested using the following parameters: nominal power of the lamps: 3 × 1700 W; filter: daylight; method: A, cycle 1; total test time: 720 h, wavelength measurement range: (300–400) nm, irradiance (300–400 nm): 60 W/mmax was reached. Compressive strength was calculated on the basis of the obtained results.Strength tests were carried out at a temperature of 20.8 ± 0.2 ÷ 21.4 ± 0.2 °C and relative air humidity of 38.9 ± 2.0 ÷ 43.1 ± 2.0%. The samples were subjected to the compressive force F until destruction and the maximum force FThe evaluation of the color change in gray scale was carried out according to ISO 105-A02. The color change was assessed as a team in a room with the lighting in accordance with PN-EN ISO 13076:2012, at a temperature of 20.5 ± 0.2 ÷ 21.7 ± 0.2 °C and relative air humidity of 40.1 ± 2.0 ÷ 42.4 ± 2.0%. The color of the UV irradiated and UV non-irradiated samples were compared on a gray scale ranging from 5 being no color change at all to 1 being the lightest and biggest change in color. One sample from each lot was not exposed (as a reference sample). Each series of samples was tested by comparing the reference sample with at least the two exposed samples.r and measurement Δmw did not exceed 0.1%.The study of thermal conductivity consisted in determining the thermal conductivity coefficient λ under steady heat flow conditions, which was carried out using a single-sample plate apparatus of the FOX 50 type, with heat flux density sensors, with a horizontal orientation and the location of the hot side of the sample: the bottom. The tests were carried out in accordance with the PN-EN 12664:2002 standard. Measurements were made for at least 4 replicates of each analyzed variant. The temperature difference across the thickness of the sample did not exceed 10 °C. The test specimens were conditioned for 6 h at a temperature of 23 ± 2 °C and relative humidity of 50 ± 5%. Relative mass change during conditioning ΔmThe individual stages of the production and testing of samples are shown in The results of the compressive strength test of samples without the addition of aramid roving depending on the production method are presented in The results of the residual compressive strength tests carried out after the frost resistance test of the samples are shown in After the performed freeze–thaw cycles, as in the case of the reference samples, the samples made by the casting method were characterized by a higher compressive strength (29–47 MPa) than the samples produced by the 3D printing method (16–24 MPa). The addition of aramid roving caused a decrease in the compressive strength of the samples by about 30% compared to the samples without reinforcement. The exception is hybrids based on fly ash, for which the introduction of roving increased the compressive strength by 18%. The highest strength was achieved by hybrid samples based on fly ash.In general, after the frost resistance test, there was usually a decrease in the compressive strength of concrete and concrete–geopolymer hybrids. In the case of samples made by casting to molds, this decrease was up to 27% compared to the reference samples, while for 3D-printed samples the decrease in compressive strength compared to the reference samples did not exceed 12%.Öztürk  also notAfter the frost resistance tests, the mass losses for individual samples were determined. The results are shown in Regardless of the composition, the samples produced by additive methods showed greater mass losses after the frost resistance test than for samples made by casting into molds. The smallest mass loss occurred for concrete samples reinforced with aramid roving (0.64%) made with the conventional method. The greatest loss occurred for the same type of material but produced with 3D printing (1.06%).In the case of the printed concrete–geopolymer hybrids, the mass loss was about 8–12% higher than for the cast samples. However, a greater disproportion was noted for additively produced concrete samples, for which the mass loss was as much as 24–27% higher than in the case of samples made with conventional methods.On the basis of the tests, it was found that the tested samples obtained a frost resistance level of F150.Any building material undergoes a slow degradation process, which is influenced by factors such as temperature, humidity, UV radiation, and mechanical influence. The kinetics of this process depends, among others, on the exploitation environment, possible defects in the structure, or the intensity and types of factors causing the changes. Therefore, both raw materials and products, for safety reasons, should be analyzed by the aging tests. The tests allow for the elimination of design and construction errors and slow down the degradation processes of the final products. When assessing the resistance of the material to environmental conditions, its resistance to exposure to UV radiation and water is most often tested.UV radiation can significantly reduce the aesthetic value, as a result of the aging of protective gel coatings used for bridge cornices. UV radiation breaks down the polymer chains, thereby releasing fillers and dyes onto the surface of the elements.Moreover, testing the resistance to UV radiation is necessary to determine the durability of the material properties over time. Therefore, tests were conducted to determine the changes in the properties of the samples after exposure to UV radiation. The results of the compressive strength tests of the samples carried out after the UV aging tests in the climatic chamber are shown in On the basis of the results presented in After the tests of resistance to UV radiation for samples made by casting into molds, a decrease in compressive strength was observed in comparison with the reference samples . There wThe results of the examination of the color change in the gray scale are presented in On the basis of the results obtained from the conducted tests, it was found that the UV radiation did not cause any significant changes in the color of the samples, regardless of their composition or the method of production.Thermal conductivity tests were carried out only on samples made by casting into molds. The limitation to preparing samples using the 3D printing method was the 15 mm diameter of the printing nozzle. Therefore, it would be difficult to produce specimens with dimensions of ø 55 mm × 23 mm containing aramid roving in accordance with the methodology of sample preparation.For the study of thermal conductivity, samples with high strength recorded in previous tests were selected. The tests were carried out for samples with and without the addition of aramid roving. The obtained results are presented in The tested concrete samples reinforced with 0.5% aramid roving were characterized by the lowest thermal conductivity coefficient, and thus, such material better insulates against heat losses. Concrete–geopolymer hybrids with the addition of an ash-based geopolymer and hybrids with the addition of a metakaolin-based geopolymer reinforced with roving obtained similar values of the thermal conductivity coefficient, respectively, 0.5334 W/m·K and 0.5353 W/m·K. Among the tested samples, the best thermal conductivity was achieved by concrete–geopolymer hybrids with the addition of geopolymer based on fly ash, reinforced with aramid roving. The addition of roving to the hybrid increased the thermal conductivity coefficient from 0.5334 W/m·K to 0.7413 W/m·K.The thermal conductivity of concrete is mainly related to porosity and pore size ,39. The The properties of innovative concrete–geopolymer hybrids reinforced with aramid roving and produced by 3D printing technology were compared with samples prepared by the casting method. The effects on frost resistance, UV radiation, and thermal conductivity properties were determined.Generally, after the freeze–thaw cycles, the compressive strength of concrete and concrete–geopolymer hybrids decreased. The concrete–geopolymer hybrids made by 3D printing were characterized by a compressive strength that was about 40–57% lower than the samples made by casting. This may be the effect of the presence of weak interface connections between the layers. Moreover, the addition of aramid roving caused a decrease in the compressive strength of the samples by about 30% compared to the samples without reinforcement. All of the tested samples had a frost resistance level of F150.UV radiation test showed that the 3D printed hybrids with the addition of a metakaolin-based geopolymer exhibited the highest strength. The addition of roving reduced the strength properties of the samples after UV aging tests, and, in this case, exposure to UV radiation further decreased the mechanical properties of concretes and hybrids produced by conventional methods. For 3D printed samples, aramid roving caused an increase in compressive strength after UV exposure. The addition of uniform orientation roving may eliminate the effect of weak boundaries between the printed layers.Thermal conductivity tests showed that among the tested samples, concrete reinforced with aramid roving was characterized by the lowest thermal conductivity coefficient. As a result, concrete provides better insulation against heat loss. The addition of aramid roving increased the hybrid’s thermal conductivity by almost 40% compared to the material without reinforcement.


Background: Emerging evidence supports the use of billing data to identify stewardship targets in primary care. Standardizing an approach to antibiotic prescribing rate (APR) calculations could facilitate external benchmarking. Methods: Using methodology and an ICD-10 dictionary validated in urgent care clinics,1 we created an expanded ICD-10 dictionary to incorporate additional ICD-10 codes from primary care associated with antibiotic prescriptions  (Fig. Conclusions: The expanded ICD-10 dictionary allowed for classification of more encounters in primary care; however, it did not meaningfully change antibiotic prescribing rates. Antibiotic prescribing rates were likely diluted by classifying more encounters without identifying an associated increase in antibiotic prescribing. A more sophisticated classification system may help to accommodate the diversity and volume of ICD-10 codes used in primary care.Clin Infect Dis 2020;70:1781–1787.1. Stenehjem E, et al. Funding: NoneDisclosures: None


Aging and corrosion of reinforced concrete structures (RCS) is becoming a global problem, thus proper procedures for simulating the structural performance of corroded RCS should be assessed. Among the main corrosion effects, concrete cover cracking and reinforcement cross-section reduction may influence the materials’ constitutive laws, moreover the confinement contribution and the lateral instability of the longitudinal rebars can be modified. In the present paper, the predictive models available in the scientific literature to assess the materials’ mechanical properties of corroded RCS are recalled and employed into a novel model to derive the theoretical moment–curvature relationships for the cross-section of square and rectangular corroded reinforced concrete elements. The model accounts for cover spalling, buckling of longitudinal reinforcing bars, reduction in confinement pressures, reduction in concrete constitutive law due to the concrete cracking induced by rust formation and decay of mechanical properties for corroded reinforcements. The obtained results are compared with the classical simplified models for corroded RCS, highlighting that buckling and confinement variations cannot be disregarded into a reliable modelling strategy, especially when local ductility plays a key role in the performed investigations. Most existing reinforced concrete (RC) structures in industrialized countries have at least 40 years ,2 and arUnder corrosion, RC elements progressively decrease their structural capacity due to: (i) concrete cracking and the decay of its compressive strength ,10, (ii)Consequently, the whole structure under seismic actions may have a performance worse than the estimated one. Nowadays, the assessment of corroded RC structures is mainly modeled by considering the steel and  the concrete deterioration ,19,20,21The main object of the present research is to propose a novel simplified model to assess theoretical moment–curvature relationships for rectangular/square corroded reinforced concrete elements. The model accounts for the corrosion effects on: (i) concrete cover cracking, (ii) concrete confinement, (iii) steel constitutive law, and (iv) lateral instability of the longitudinal reinforcement. Moreover, a parametric analysis is carried out to evaluate the most effective modeling strategy for corroded reinforced concrete structures. The obtained results, compared to the ones derived for classical simplified models, allow the assessment of the optimal modelling strategy which assesses the sectional response of corroded structural elements in RCS. A sensible reduction in the structural capacity of corroded RC elements is observed for corrosion levels higher than 10% in mass loss ,25. At tSince the corrosion products have a density lower than the sound steel, a radial internal pressure stresses the concrete when the reinforcements corrode. Once the tangential stresses caused by the oxides’ expansion exceed the concrete tensile strength, cracks progressively grow in the concrete cover and enlarge, increasing the corrosion level . k is a coefficient related to bar roughness and diameter, cε0 the strain at the peak compressive stress cf; and aveε the smeared tensile strain in the cracked concrete defined as:n represents the number of corroded bars, rustρ is the ratio of volumetric expansion of the oxides with respect to the virgin material, D is the initial reinforcement diameter, b0 is the section width in the virgin state and CL is the corrosion level expressed in mass loss.According to , the tenThe experimental tests carried out on corroded specimens by  allow thInstead, according to the experimental campaign performed on concrete cores extracted by corroded piers , the regMoreover, in , the peaα is the yield strength reduction factor for corroded transverse reinforcement , β is a strain correction coefficient . The parameter ek is the confinement effectiveness coefficient defined according to [Finally, the classical Mander’s model  is adaptrding to .spA is the sectional area of transverse reinforcement, sd is the diameter of spiral reinforcement, s is the vertical spacing between spirals, slA is the cross-section of longitudinal reinforcement and cA is the concrete core sectional area.Similarly, in  the follcε0 is axial strain of unconfined concrete corresponding to maximum unconfined stress. cε0 = 0.002 can be assumed when test data are not available;sρ is the ratio of volume of transverse reinforcement respect to the volume of confined concrete core;cf0 is the compressive strength of unconfined concrete.In the previous relationships (Equations (6)–(8)):CL, while the ultimate deformation can follow a linear or an exponential trend. A complete review on the degradation laws of corroded reinforcements can be found in [The shape of naturally corroded steel reinforcement is well simulated by the artificial corrosion . Therefofound in .l/ϕ) higher than 10 [The state-of-the-art on the monotonic behavior under compression highlighted that the buckling effects become relevant for slenderness ratios .The neutral axis position φ, the bending moment M is given by:Knowing the neutral axis position and consequently the relative curvature Ax the neutral axis at the cover cracking; subsequently, the sectional behavior at the post-cracking stage (point A’) is evaluated imposing a curvature Bx the neutral axis and εsy the yielding strength of the corroded reinforcement. When the concrete starts to crush, a check on the concrete strains is necessary. If the maximum strain of both concrete and reinforcement is lower than the materials’ ultimate strain at the spalling stage, a collapse without spalling can occur, and the moment–curvature relationship can be limited to the point C, defined by evaluating the ultimate bending moment U = MCM and the ultimate local curvature Uϕ = Cϕ. This means that the corroded section breaks down when the concrete cover reaches an ultimate strain larger than the conventional 3.5‰ , the contribution of the concrete in tension is considered and the section is characterized by a curvature fined in ) or, altposed in . In bothCx the neutral axis at the cover spalling. In this condition, the local ductility can be estimated as UM = DM.If, instead, the spalling starts (point C’), the sectional collapse occurs at the concrete core crushing. The latter condition is evaluated according to the constitutive law defined in  for conc2 is considered. The materials and reinforcement arrangement are defined according to the provision of the Decree of Italian Ministry of 30 May 1972 that introduced the use of ribbed bars for RC structures [λ and the concrete confinement level) as well as a different mechanical percentage of longitudinal reinforcement ω  are considered. As usual, the mechanical percentage of longitudinal reinforcement ω is defined as cf0 and yf0 are the concrete compressive strength and the yielding strength of the uncorroded section, respectively. On the reference element, different corrosion levels are introduced according to the modelling strategy applied in On the theoretical basis previously described, a parametrical analysis has been carried out, with the main aim to assess the better modeling strategy for the corroded reinforced concrete elements. As a reference, a typical column designed about 50 years ago and characterized by a rectangular section 30 × 50 cmructures . In detaWith the main aim to evaluate the most performing modeling strategy, simplified approaches are finally implemented, and their results are compared to the reference one.ADm) was introduced and evaluated as U,corrM and U,0M the ultimate bending moment of the corroded and sound section, respectively. In ADm is plotted as a function of the corrosion level (CL) expressed as st,A0 and st,corrA are the reinforcement cross section in the sound and corroded condition, respectively. For the sake of simplicity, in the parametric analysis both stirrups and longitudinal reinforcements are assumed as affected by the same corrosion amount. According to previous results obtained by the author in more simplified approaches [rdN is the design axial load according to [The performance of the reference element is firstly analyzed in terms of load-capacity reduction. At this aim, the nondimensional ultimate bending moment after corrosion  is alwaADm  is compared with the one estimated by disregarding: (i) only the buckling occurrence (AD no bucklingm), (ii) only the concrete cover (AD no coverm), (iii) both the concrete cover and the buckling occurrence (AD no cover+bucklingm). Since the buckling occurrence mostly affects the plastic hinge zone of columns subjected to seismic excitation, only the cases characterized by a maximum (ν = 25.65%) or intermediate superimposed axial load (ν = 15.39%) are considered.To evaluate the effectiveness of simplified models in catching the sectional response of the corroded section, the nondimensional ultimate bending moment after corrosion If the buckling effects are disregarded in the modelling approach , the simFinally, the classical simplified models are considered, disregarding the concrete cover and eventually the influence of the lateral instability of the longitudinal reinforcement . In detaADμ) is introduced, defined as U,corrμ and U,μ0 the local ductility of the corroded and sound section, respectively. Once assessed the corrosion influence on the sectional load-carrying capacity, the response in terms of local ductility is investigated. At this aim, the nondimensional local ductility after corrosion  is compared with the one estimated by disregarding: (i) only the buckling occurrence (AD no bucklingμ), (ii) only the concrete cover (AD no coverμ), (iii) both the concrete cover and the buckling occurrence (AD no cover+bucklingμ). Finally, the effectiveness of the simplified models in simulating the response of the corroded section in terms of local ductility is investigated considers only the cases characterized by ν = 25.65% or ν = 15.39%, according to the choice made in the previous section. At this aim, the nondimensional local ductility after corrosion  in which all the modality of collapse  are accounted for.The obtained results show that load-carrying capacity depends on: (i) the assumed level for the axial load . Finally, as highlighted by the comparison with some experimental results, it is worth underlining that the local response well catches the structural response of corroded reinforcement concrete elements, provided that excessive slips between reinforcing bars and concrete, i.e., due to fixed-end rotation effects, are avoided. Where this last condition is not fulfilled, more accurate theoretical or numerical models accounting for the occurrence of reinforcement slip in the tensile stage should be considered.


With an increase of suction efficiency of fresh concrete pumping in confined spaces, the laminar flow state will be damaged by the return flow caused by distribution value direction changes and concrete gravity. This is a fact, but one which is rarely studied. In this work, the flow state, flow velocity, and suction efficiency of fresh concrete pumping are simulated using the coupled smooth particle hydrodynamics and Discrete Elements Method (SPH-DEM). The rheological parameters and Herschel-Bulkley-Papanastasiou (HBP) rheological model are adopted to simulate fresh concrete in the numerical simulation model. The study reveals that the error between the slump experimental result and that obtained by the HBP model is negligible. A model is therefore established for numerical simulations of the suction efficiency of fresh concrete pumping. An experimental concrete pumping platform is built, and the pressure and efficiency data during pumping are collected. A comparison of the numerical simulation with experimental results shows that the error is less than 10%. Despite advances in computer technology and numerical simulations, several problems regarding the pumping and delivery of fresh concrete have not been solved, such as its rheological behavior, precipitation, and water secretion. Knowing the rheological behavior of concrete during pumping and delivery may help to improve performance ,2,3. HowCurrently, there are many studies on the components of concrete and the application of various additives to improve its quality. Roussel  categoriThe conventional CFD method treats concrete as a single fluid phase, ignoring many solid aggregates, steel fibers, and other components. The Eulerian method is applied to calculate concrete grid fluxes to obtain the velocity variation of the flow process and its shear deformation region ,8,9. SomThe DEM method discretizes concrete into particles such as aggregates, and slurry, and performs simulations using the friction coefficient and collision restitution coefficient among different materials. For example, Krenzer et al.  mixed drThe multi-phase fluid-solid coupling method is usually used to study the flow of concrete in a static pipe or an L-box without an external load. Gram A  utilizedThe smooth particle hydrodynamics (SPH) method, in which the continuous fluid phase medium is discretized into individual particle locations, can create a realistic three-dimensional simulation. Many software packages for the SPH method are available for public use, such as the open-source Dualsphysics . The SPHThe flow of fresh concrete in pipes has received the attention of many scholars, while concrete pumping has not. Most recent studies have focused on the effects of material additions on concrete properties, while the suction efficiency and concrete flow in the pumping cylinder and pipe have attracted very little attention.In summary, previous studies on fresh concrete using DEM have paid little attention to the laminar flow state during pumping. Conventional CFD methods generally do not correspond to actual concrete composition ratios. On the other hand, most studies related to the CFD-DEM double-way coupling have focused on discontinuing the static pipes only. Therefore, the need for new research approaches to describe the continuous pumping and components of fresh concrete has been recognized.The suction efficiency of concrete pumping is numerically simulated in this work using coupled SPH-DEM  open-source software coupled with the Project Chrono open-source software). Firstly, SPH-DEM is utilized to create a fresh concrete simulation and analysis model. Secondly, the practicality of the SPH-DEM to produce new concrete is proved by experimentally evaluating the numerical simulation features of the concrete using concrete aggregate grading and slump flow tests, as well as a rheometer. Then, experiments are performed using the verified completed concrete and numerical models of the pumping process. Finally, the theoretical velocity of concrete movement in the cylinder is compared to that of the numerical simulation.SPH  is one oty. Ye T  determinFor slightly compressible fluids , the SPH is usually approximated by replacing it with an artificially incompressible fluid, which is the basis of most finite difference algorithms. Another approach to SPH calculations is to approximate a weakly compressible fluid, which requires that the speed of sound is large enough for density fluctuations to be negligible. When the air pressure is negligible, the form can be described by Equation (4), according to Morrison :(4)P=c2ρlagrossi , β = 100 in Wang .SPH adopts the smooth kernel function for calculations. If the particle boundary is within the particle computational domain of the SPH smooth kernel function, the second-order accuracy of the calculation and analysis can be guaranteed. However, when intersecting with the boundary, the smooth kernel function is truncated by the boundary, and its integral value is no longer 1. The computational error will cause a loss of the second-order accuracy of the SPH smooth kernel function . To solvInelastic fluid behavior is common in several non-Newtonian applications. Springless fluid behavior is expressed as the shear rate in follow equation:In rheology, the standard Bingham model  is usualIn Equation (7), if  results . TherefoIn Equation (8), if There are two unique coefficients, As indicated in The particle force is divided into normal and the tangential forces. Both are made up of the material’s completely elastic collision force and damping dissipation force. The normal force can be calculated using Coulomb’s law of friction, as in Equations (10) and (11).Experiments on concrete-related ratios and the slump-related gradation related to slump are required to determine the judgement criteria of the pumping procedure. The concrete is proportioned and matched in accordance with the characteristics listed in The aggregate is sieved for size and density, and graded in order to refine the concrete for the pumping. The results are displayed in The aggregate in After being certified, the aggregates are mixed into the concrete. Then the mixed material described in Slump tests were carried out for both proportions of the concrete described in After that, the rheological properties of fresh concrete and the related rheological coefficient are measured, as shown in The focus of this work is the response of the concrete suction process relative to an actual physical model during concrete pumping; hence, the pumping mechanism is shown in As concrete is not transparent, it is difficult to observe the changes of internal shape during delivery. Improving the concrete pump inhalation efficiency means observing and studying the experimental process by using a concrete pump which is constantly inhaling and pushing out concrete. As a result, the performance of the total quantity of concrete inhaled by the pump can be characterized by using the weight of the concrete pump output. This yields large amounts of data and records the mass during the delivery. Before pumping, the concrete density is determined, and the concrete output squared is calculated using the concrete weight.The hydraulic pump output flow rate can be determined, and the average efficiency in many pumping trials can be calculated using the ratio of the two flow rates. The experimental process should be performed ten times, with each group employing concrete pumps. The findings on efficiency and mass are displayed in According to the experimental results, the mass of every ten pumping instances was 1890–2380 kg. The average weight of each pumping in the 12 groups was 2156 kg. The pumping efficiency was 82.1–92.61% using the hydraulic pump output flow rate as determined from the hydraulic system. The pumping efficiency for the 12 groups was 86.9%, on average.In this work, the HBP model was adopted to investigate the rheological behavior, and the DEM method was employed to solve the forces between the fluid and the solid. The HBP model is an excellent non-Newtonian fluid model for simulating fresh concrete, and it can accurately simulate the Bingham or Power-law models used to describe slurry flow.To offer a thorough depiction of the pumping process, the concrete simulation analysis model, which is a comparison of the experimental data, first had to be calibrated. The parameters of the simulation model were defined based on the experimental results listed in The simulation of the Group 1 slumps is shown in In The simulation results of Group 2 are shown in The simulation analysis results of Group 2 were compared with the experimental data, as shown in The flow during concrete pumping is difficult to observe and represent, since it is in a restricted environment. Furthermore, there is no clear theory for how aggregate and slurry are separated in concrete, and this can only be determined by waiting for the former to accumulate, resulting in pipe obstruction. To describe the pumping process completely using the current computer technology, it is necessary to compare the pumping efficiency of a simulation analysis with the actual efficiency to determine whether they are compatible.Therefore, the mass of concrete pushed via the pumping cylinder is approximated by that sucked by the pumping cylinder, i.e., the conservation of mass. It is critical to investigate the efficiency and mass sucked by the pumping cylinder. The experimental process is complex. As such, simulation analyses were used to find a way to optimize the experimental prototype, which can be understood as approximating and matching the changing trend of the simulation analysis system and the actual experimental model. The actual experiment model contains too much information in the edges and corners, increasing the difficulty for the simulation analysis model to focus on real issues. Therefore, the edges and corners must be simplified. The redundant hole features in the pumping structure model shown in The Y–Y section is shown in The distribution valve is in the left position of the cylinder when the pumping model is at 0 s; after a reversal at 0.2 s, it moves to the right position. In accordance with the experimental procedure, the stirrer was operating at 20 rpm. Pumping in the experimental process was repeated 20 times per minute. The matching pumping speed was approximately 1 m/s, and the simulation analysis speed was assumed to be 1 m/s. The pumping cylinder of the simulation analysis model was 1.4 m long. When the suction finished after 1.4 s, the simulation analysis showed that the suction full tube position was 1.2 m, which corresponded to a single inhalation of 85.714%. The suction efficiency of the physical experiment was calculated to be 86.9%, as shown in The Bingham fluid in the pipe with the resolved motion velocity gives the flow velocity of concrete in the pipe via Equation (15):r/R, the parameters of the moving process were introduced into the preceding equation. The velocity of the concrete radial motion in the pipe is shown, and the two analyses are compared in To obtain the theoretical velocity in the respective region of The theoretical motion velocity of Bingham fluid in the pipe was well fitted to that in the numerical simulation.This work aimed to develop a new method to determine fresh concrete behavior during pumping.The results showed that the SPH-DEM method could be utilized to simulate fresh concrete through slump tests. The rheological parameters of fresh concrete were identified by a rheometer. The slump test error between simulation and experiment results was compared and shown to be less than 10%. Therefore, the SPH-DEM numerical simulation could potentially be used to react a real physical model.A numerical simulation model of the pumping process was established to analyze the effects of variations in the plastic viscosity of fresh concrete on the suction efficiency. In addition, the suction efficiency was studied experimentally. The numerical simulation results were compared with the experimental results, and the average error of suction efficiency was less than 5%.The gradient variation of the pressure loss along the pipe (Dp/L) was calculated and the theoretical flow rate of concrete in the pipe was analyzed. Compared with the numerical simulation, the theoretical velocity analysis showed that the results from the SPH-DEM numerical model approached those of the theoretical analysis. The issue of the pipe blocking mechanism is an intriguing one which should be further explored in future research.


The results show that the utilization of MTS reduces the slump of MTSC to a certain extent. When the MTS content is lower than 40%, the gypsum introduced by MTS and C3A in cement undergoes a hydration reaction to form ettringite, which decreases the number of pores with a diameter less than 0.1 mm and promotes strength development in MTSC. Additionally, when the MTS content exceeds 40%, the large amount of gypsum reacts to form more ettringite. The expansive stress generated by the ettringite severely damages the pore structure, which is not conducive to the mechanical properties of MTSC. In addition, the leaching of hazardous substances in MTSC is insignificant, and the incorporation of cement can effectively reduce the risk of leaching hazardous substances in MTSC. In summary, it is completely feasible to use MTS to replace RS for concrete preparation when the substitution rate of MTS is less than 40%, with no risk of environmental pollution. The results and adaptation in the concrete industry can reduce the carbon footprint, which is in line with the current trend in civil and materials engineering.In this work, manganese tailing sand concrete (MTSC) was prepared using manganese tailing sand (MTS) in replacement of river sand (RS) to alleviate the shortage of RS resources and achieve clean treatment and high-value resource utilization of manganese tailing stone. The effects of MTS content on the slump, mechanical strength, air void characteristics, hydration products and micromorphology of MTSC were studied experimentally. The leaching risk of harmful substances in MTSC was also explored by testing the concentration of Mn In 2020and (RS) . TherefoIn response to these problems, many studies have been conducted by relevant researchers ,6,7. BleMoreover, as the world’s largest producer, consumer and exporter of manganese metal, China accounts for more than 97% of the global production of manganese metal ,13. WithIn summary, RS, as one of the main raw materials for concrete, has led to frequent geological disasters due to large-scale RS mining as concrete usage has increased dramatically. In addition, with the rapid development of the manganese industry in China, the accumulation of a large amount of manganese tailing stone seriously occupies the land and has the risk of environmental pollution. Therefore, it is urgent to explore the alternatives of river sand and the resource utilization of manganese tailing stones. Based on these, this paper first made manganese tailing stone into manganese tailing sand (MTS) and then used MTS to partially or fully replace river (RS) sand to prepare manganese tailing sand concrete (MTSC). With the content of MTS as a variable, the effect on the slump, mechanical properties, pore characteristics and microstructure of MTSC was studied. The influence of MTS on the hydration of concrete and the risk of leaching harmful components were discussed. A suitable replacement rate of MTS without losing the basic properties of concrete was proposed. The results of the study not only provide a new way for the clean and high-value utilization of manganese tailing stone but also offer a new solution for the transitional consumption of RS.3, water absorption is 0.68%, and mud content is less than 1%. The concrete mixing water was domestic water.The cement used in this study was P·O 42.5 ordinary Portland cement. The main properties and chemical compositions of cement are shown in The preparation process of MTSC is shown in (1) Slump: The slump test of MTSC was carried out according to “the national standard of the People’s Republic of China: Standard test methods for the performance of ordinary concrete mixes (GB/T 50080-2016)” .(2) Strength: The flexural strength (loading rate of 0.2 kN/s), compressive strength (loading rate of 0.5 MPa/s) and splitting tensile strength (loading rate of 0.05 MPa/s) of MTSC were tested by using a microcomputer-controlled constant loading pressure testing machine K was introduced to quantify the strength contribution of MTS. Assuming that Equation (1) holds, the strength of MTSC after mixing with x content MTS is σ, and the strength contribution K of MTS can be calculated according to Equation (3) by combining Equations (1) and (2).K is strength contribution value; x is the dosage of MTS; σ0 is the strength of concrete without MTS, MPa; σe is the strength contribution of unit MTS, MPa; σ is the strength of concrete mixed with x content MTS, MPa;Additionally, in order to investigate the strength effect of MTS in MTSC, the strength contribution value (3) Pore structure: The MTSC sample with an age of 28 d was cut into slices, and then the uneven surfaces of these slices were polished using a grinding machine. Then, the surfaces of the specimen were coated with black ink, and the mixture of ZnO and petroleum jelly was applied again after the surfaces of the specimen were dried. The excess coating on the surfaces was wiped off when the holes on the surface of the specimen were completely filled. The hardened concrete, porous structure analyzer  was used to analyze the characteristics of the pore structure of MTSC;−1 for 10 h and left for 14 h. Finally, the supernatant was taken to test the content of Mn2+ by using the water quality tester .(4) Leaching of harmful substances: The leaching test of MTSC was carried out by the horizontal oscillation extraction process. After crushing and grinding the samples to a particle size of less than 0.075 mm, then 5 g of the sample was placed into a beaker and stirred for 2 min in a magnetic stirrer with a solid–liquid ratio of 1:10. The sample was then placed on a constant temperature shaker and shaken at a frequency of 160 min2 environment) for the composition of the physical phases and mineral phase alterations.MTSC specimens were crushed after curing to 28 d. Samples with a particle size less than 5 mm were taken, and hydration was prevented by using isopropyl alcohol. MTSC flake samples were taken out, and their hydration products were observed using scanning electron microscopy (SEM). The remaining samples were ground in a mortar and passed through a 0.075 mm sieve. The samples were analyzed by X-ray diffraction  and thermogravimetry . Compared to the concrete without MTS, the incorporation of MTS increases the peak strength of ettringite and decreases the peak strength of portlandite. The results are consistent with the results of TG/DTG curves. It is noteworthy that the gypsum appears in MTSC-10, which indicates that the partial gypsum does not participate in the cement hydration reaction when all RS is replaced by MTS.The XRD patterns of MTSC-0, MTSC-3, MTSC-4 and MTSC-10 are shown in In conclusion, the TG/DTG curves and XRD patterns of MTSC show that the increasing dosing of MTS results in the growth of gypsum content, which promotes the formation of ettringite in MTSC. However, the reduced production of portlandite in MTSC is not beneficial to the development of mechanical properties. Therefore, the optimum content of MTS in MTSC should not exceed 40%.The SEM images of MTSC-0, MTSC-3, MTSC-4 and MTSC-10 are shown in In addition, compared with MTSC-0, the flaked portlandite content in MTSC-3 and MTSC-4 is slightly reduced. The fewer portlandite is generated in MTSC-10. This indicates that the incorporation of excessive MTS reduces the amount of portlandite. This is in full agreement with the results of TG/DTG curves and XRD patterns. Moreover, it was further verified that the preparation of concrete by replacing RS with MTS in an appropriate amount could promote the development of concrete strength. Therefore, the purpose of RS resource saving was achieved.3A in the cement [The substitution of RS by MTS for concrete preparation is an economical and resource-saving method . Therefoe cement ,40. The e cement , which c3A in cement by hydration to form ettringite. However, when the content of MTS is low, the ettringite generated by the reaction between gypsum and C3A fills the voids of MTSC, which makes its structure dense and enhances the mechanical properties of MTSC, while when the content of manganese tailing sand is high, the reaction generates too much ettringite produces expansion stress, which leads to the strength of MTSC decreasing. Therefore, the preparation of MTSC by replacing RS with an appropriate amount of MTS not only does not reduce the strength of concrete but even improves it. Additionally, the excessive amount of MTS is not suitable to replace RS for preparing concrete.The abovementioned studies showed that compared to RS, MTS contains gypsum, which can react with C2+ in MTS and MTSC. It can be seen that the leaching concentration of Mn2+ in MTS is 4.27 mg L−1, which meets the requirement of Mn2+ concentration of less than 5 mg L−1 in the National Standard of the People’s Republic of China: Sewage Discharge Standard (GB/T 8978-1996) [2+ in MTSC prepared by using MTS also meets the requirements. This is consistent with the results in 2+ in MTSC is significantly lower. This is primarily because cement hydration creates an alkaline environment for Mn2+ solidification, allowing Mn2+ to be converted into stable MnO(OH)2 precipitation. Moreover, Mn2+ may replace part of Al3+ in the C-S-H gel during cement hydration to form a stable structure, thus reducing the leaching of Mn2+. In addition, the dense structure of MTSC also prevents the leaching of Mn2+, making the leaching concentration of Mn2+ in MTSC dramatically lower than that in MTS. Therefore, the use of MTS for concrete preparation can realize the clean treatment of MTS and reduce the risk of environmental pollution from MTS.The chemical compositions of MTS  indicate78-1996) . TherefoIt is not feasible to use MTS to replace all RS for concrete preparation. However, when the substitution rate is less than 40%, MTS has little effect on the slump and mechanical properties of concrete and even has a positive effect. There is also no risk of environmental pollution in MTSC.Moreover, the preparation of concrete with MTS realizes the high-value resource utilization of manganese tailing stone and alleviates the problem of shortage of RS resources. As the MTSC (lower than 40% substitution) exhibited good workability and mechanical properties, it may be recommended for all construction activities. The results are not only in line with the concept of carbon reduction in the concrete industry but also with the current trend in civil and materials engineering.Although this work provides guidance for the application of MTS in concrete, the effect of MTS on the long-term performance and durability of concrete needs to be further investigated.2+ in MTSC was also examined. Based on the results from this study, the following conclusions can be drawn:In this paper, the effect of MTS content on the properties and microstructure of MTSC was investigated. The basic properties of MTSC were analyzed by the slump, flexural strength, compressive strength and splitting tensile strength experiments. The pore structure characteristics and microstructure of MTSC were characterized by the hardened concrete pore structure analyzer, TG/DTG, XRD and SEM. The leaching concentration of Mn(1) When the content of MTS is lower than 40%, the decrease in the concrete slump is insignificant, but when the dosing of MTS exceeds 40%, the slump of concrete decreases obviously;(2) Compared with MTSC-0, the flexural and compressive strength of MTSC in the early stages (3 d and 7 d) can be improved effectively when the amount of MTS is less than 40%, but the flexural and compressive strength at 28 d not be improved obviously. The flexural and compressive strength of MTSC can be significantly reduced when the amount of MTS is more than 40%. Moreover, with the increase in MTSC content, the splitting tensile strength of MTSC at 28d first remains constant and then decreases;(3) The incorporation of MTS can reduce the number of pores with a diameter of less than 0.1 mm in concrete and make the pore distribution uniform. However, the excess MTS can cause the number of large pores with a diameter greater than 0.2 mm in concrete to rise sharply. Additionally, the air content in hardened MTSC shows a trend of decreasing and then increasing with the increase in MTS content;(4) MTS can be hydrated with cement mainly due to the presence of gypsum. With the increase in MTS content, the amount of ettringite in MTSC increases. In addition, excess ettringite interacts with each other to form expansion stress and squeeze the pores, which is not conducive to the development of concrete strength;2+ in all MTSC is lower than 5 mg/L. Moreover, cement-based materials can reduce the risk of leaching hazardous substances. Therefore, there is no risk of environmental pollution in the preparation of MTSC by using MTS.(5) The leaching concentration of Mn


Collectively, the replacement of cement with DE could not only improve the concrete strength but also reduce the consumption of cement, thereby lessening the cost of construction as well as indirectly reducing the carbon footprint.Portland cement porous concrete (PCPC) has received immense interest recently due to its environmental aids. Its porous structure helps to reduce the water runoff amount while improving the recharge of groundwater. Earlier studies have concentrated on illustrating and knowing the functional as well as structural properties of PCPC. However, very few studies are available on PCPC in combination with natural silica sources as supplementary cementitious materials (SCMs). Most SCMs are by-products of industrial manufacturing processes and cause some environmental concerns, but with their pozzolanic effect, they could be utilized as partial substitute materials for ordinary Portland cement (OPC) to enhance the strength as well as durability performance. The aim of this study is to evaluate the effects of diatomaceous earth (DE) as a supplementary cementitious material for partial substitution of OPC for Portland cement porous concrete application. Compression strength, split tensile strength, and flexural strength tests were performed to determine the effect of partial replacement. To investigate the impact of test variables, basic tests, including void content and water permeability, were also performed. Compared to the control concrete, the results show that a 15% replacement of cement with DE significantly increased the compressive strength (by 53%) while also providing adequate porosity and better water permeability. Statistical analysis (ANOVA) and regression analysis showed that there is a significant ( Most of the places covered with impervious surfaces, such as concrete, due to urbanization, resulted in groundwater table reduction. Pervious concrete pavements, which are open-graded concrete with interconnecting pores with excellent water permeability and porosity, minimize the issue by allowing the seep-through of rain and stormwater into the ground ,2. The t2 into the atmosphere, which has an adverse effect on the global environment [2  and water to form C-S-H  [Cement, one of the most extensively utilized construction materials, has caused the emission of a considerable amount of COironment ,10. Mostironment ,12,13,14ydrates) , which iydrates) ,17. The ydrates)  and alsoydrates) . Fly ashydrates) . It was ydrates) . The usaydrates) . When ceydrates) . The strydrates) .Diatomaceous earth (DE) is reported to exhibit pozzolanic activity when blended with cement ,26. DE iPrevious studies mainly focused on illustrating and knowing the functional as well as structural properties of PCPC; however, very limited studies evaluated the effects of natural silica sources as supplementary cementitious materials for PCPC application. On the other hand, although the application of DE in concrete and building materials is not a new topic, there are very few studies on the use of DE for Portland cement porous concrete application. The main objective of this study is to improve the understanding of the effect of DE in pervious concrete. In this study, the cement was partially replaced by DE as an SCM. A series of experimental tests, such as consistency and water demand, compressive strength, split tensile strength, flexural strength, void content, and water permeability tests, were conducted on the samples.The production of PCPC includes cement, coarse aggregate, water, and diatomaceous earth as its primary constituents. In this study, the addition of a small fine aggregate (10%) was applied to the mix in terms of improving the strength of the concrete. In addition, the cement was replaced by various amounts of DE.A single source crushed rock having an average particle size of 19 mm was used in this research. The typical grading of coarse aggregate used in PCPC conforms to the specifications of ASTM C33/C33M . Accordi3. Using a JEOL-JSM-IT 200, equipped with EDS, the scanning electron microscopy (SEM) test was carried out. SEM test specimens, in powder forms, were put on platinum-coated carbon adhesive tape and were subjected to characterization examination utilizing a voltage of 15 kV in a high vacuum camper. The phase composition of cement was characterized using the X-ray diffraction (XRD) analysis. The sample was prepared in powder form, put inside a sample holder, and mounted on a triple-axis (Ge-220) monochromatic detector. At room temperature, the sample analysis was carried out utilizing 45 kV, 40 mA, with 2 exploration range. The scanning electron microscope (SEM) and X-ray diffraction (XRD) images of cement are shown in The cement used in this study was commercial ordinary Portland cement (OPC) with the market branded as Coramantal and conformed to ASTM C150/C150M-22, 43 N, , with a Clean tap water was employed for material washing and other experimental purposes. The water quality used in this study was drinkable, as discussed in ACI 301 . The rat3. The specific gravity of DE in standard drying conditions was obtained at 2.06, while it was evaluated at 1.92 after oven drying with absorption of 6.71%. The SEM images of DE at 50 µm and 2 µm are represented in The DE samples were collected from Jaipur, Rajasthan, India. After one day of natural surface drying, the obtained DE sample was crushed and sieved by using a sieve size of 200 μ. Following that, the DE powder was dried in the oven for 24 h at 100 °C. The DE particles showed a bulk density of 775 kg/m3 was used.To find reliable mean values, triplicate specimens were prepared for each test group. The samples were prepared as per ASTM C1688/C1688M . The mix3. Cement was partially replaced by DE by weight at various contents of 5%, 10%, 15%, 20%, and 25%. The different mix ratios are given in The total volume of solids, including the aggregates, water, and cementitious materials, was estimated to be 0.85 mI = ratio of infiltration (mm/h), M = weight of infiltrated water (kg), D = infiltration ring inner diameter (mm), t = time taken for the measured volume of water to infiltrate the concrete (s), and K is 4,583,666,000 ((mm3 s)/(kg·h)).The compressive strength test was performed at the age of 7 days and 28 days by following the ASTM C39  testing 2S, C3S, and C3A 2, while reacting with water, which reacts with alumina and amorphous silica in DE to generate an excessive amount of C-S-H. The excess amount of C-S-H can replace the pore holes in the concrete mix and refine and densify the interfacial transition zone (ITZ) between aggregate particles and cement paste [The average split tensile strength of PCPC specimens on days 7 and 28 is shown in nt paste . The immnt paste . Moreovent paste . Similarnt paste .2 and Ca(OH)2 contributed to the bending resistance, thereby increasing the flexural strength [strength . Saidi estrength . However2 and caused C-S-H gel formation, which helped to fill the pores in the concrete and made the PCPC denser than the control concrete. The addition of DE in cement concrete could reduce the voids. This result is similar to the previous findings of [K = 1,273,240 ((mm3·kg)/(m3·g)), A= weight of dry specimen (g), B = weight of specimen underwater (g), ρw = experimental water density (kg/m3), D = average specimen diameter (mm), and L = average specimen length (mm).As mentioned previously, the volume displacement method was used to determine the amount of void content in each cylindrical sample at the age of 28 days. dings of . HoweverThe values of the permeability coefficient are presented in c = Young’s modulus of concrete, and cF= compressive strength of concrete.p < 0.05) in the physical properties of concrete upon the addition of DE, and the optimum concentration of cement to be replaced by DE was found to be 15% (One-way ANOVA (SPSS 17) was used to find the significance between the control mix and various replacement mixtures. Further, regression analysis was performed to define the relationship between various physical features of PCPC, and the goodness of fit was represented as scatter plots . The reso be 15% . Figure o be 15% B. This mo be 15% C. Finallo be 15% D with thThe diatomaceous earth was observed to be a lightweight SCM having soft minerals with a rich amount of amorphous silica. The SEM image showed that the diatomaceous earth particles have high porosity.It was observed that the water demand gradually increased up to the optimum inclusion of DE, but the higher replacement of cement with DE resulted in a drastic increment in water demand.The strength of pervious concrete containing diatomaceous earth increased in all replacements. The 25% replacement showed only a slightly higher strength than the control mix on the 28th day. However, the 15% replacement, the optimum content, exhibited 54.45%, 36.84%, and 37.84% higher compressive, split tensile, and flexural strengths, respectively, compared to the control mix.The correlation between porosity and permeability showed an inverse relation upon increasing diatomaceous earth concentration. The desired porosity of 15.42% was achieved in 15% replacement. The relationships between Young’s modulus and compressive strength with both experimental and predicted values by partial replacement of cement by diatomaceous earth were almost similar within the range of 10–15%.The addition of diatomaceous earth as an SCM in cement would decrease the amount of cement consumption, contributing to the reduction of carbon footprint in the atmosphere.Although several studies explored the potential use of DE in concrete, there are very limited works on the use of DE for Portland cement porous concrete application. Therefore, the aim of this research was to evaluate the performance of PCPC having cement partially replaced by DE. The study results can be summarized as follows:


The effects of concrete strength on flexural bearing capacity, deformation characteristics, and failure modes of UHSCFST specimens were discussed. Test results showed that the bending failure modes of UHSCFST specimens were the same as those of ordinary ones. The failure of UHSCFST specimens was attributed to excessive deflection, and local buckling occurred in the compression zone. Moreover, the bending capacity of the specimens did not decrease, even if they had yielded. Although ultrahigh strength concrete was poured, all of the specimens displayed outstanding bending ductility. The main function of core concrete was to provide radial restraint for the steel tube to avoid premature buckling. When the steel content of the specimen section was constant, the strength increases of core concrete had a slight impact on the bending failure mode, bearing capacity and ductility of UHSCFST specimen. The research results can deepen the understanding of the mechanical behaviors of the UHSCFST composite truss structure.Based on the project of the Guansheng Qujiang Bridge, the flexural mechanical properties of an ultrahigh strength concrete filled steel tube (UHSCFST) were discussed. A total of six UHSCFST beam specimens were tested, and the cube strength ( Concrete filled steel tube (CFST) is a composite structural material formed by pouring concrete into a steel tube. According to its mechanical characteristics, CFST is suitable for an axial compression member. As a flexural member, its advantages cannot be highlighted ,2. Thereckf = 27 MPa) and aerated mortar (ckf = 8 MPa) into the steel tube respectively. It was found that the flexural bearing capacity and ductility of the specimens filled with ordinary concrete were higher than those of the specimens that filled with aerated mortar, and the flexural bearing capacity of the former was about 30% higher than that of the latter. Arivalagan et al. [ckf = 0.88–32.3 MPa) on the mechanical properties of CFST specimens, and indicated that the flexural bearing capacity of the specimens increased with the enhancement of core concrete strength. However, Al-Obaidi [ckf = 25–45 MPa) had little effect on the flexural bearing capacity of CFST composite structural members. Faxing [cuf = 46–77 MPa)-filled steel tubes. What about if ultra-high strength concrete (>C80) is used to fill the steel tube? Is there any difference in flexural failure mode and ductility between UHSCFST members and ordinary CFST members? There are almost no relevant reports at present, and these issues need to be addressed.It is generally agreed that the support of core concrete within the tube has a positive effect on the mechanical properties of CFST under bending, and its bearing capacity and ductility are significantly improved compared with empty steel tubes ,7,8,9,10n et al.  studied l-Obaidi  believed. Faxing ,15 and C. Faxing  also obtIn China, several reinforced concrete arch bridges have been built, the main arch skeletons of which were composed of UHSCFST trusses ,4, and CThis paper is organized in five sections. Guansheng Qujiang Bridge is a 320 m reinforced concrete half-through arch bridge located in Guang’an, Sichuan Province, China. The main arch construction technology of reinforced concrete arch bridge mainly adopts a cantilever casting method, rigid skeleton arch forming method, etc. In the past, the strength grade of concrete poured in the rigid skeleton main pipe did not exceed C80, and its bearing capacity was limited. Therefore, when the reinforced concrete of the main arch is constructed on the rigid skeleton, it needs to be divided into eight rings, which is a complicated process and takes a long time. However, pouring C100 concrete in the rigid skeleton main tube can obviously improve its bearing capacity, and only two rings are needed for the main arch reinforced concrete . As show(1)Specimen designAs shown in (2)Specimen productionThe main and branch tubes were cut into the designed length, and welded together according to the intersection line. The rust and debris on the inner wall of the steel tube were removed, and the pipe wall was wetted with water. After that, the main tubes were placed vertically to fill concrete. When the pipe is full, the top concrete should be smoothed and sealed with plastic film. The specimens were leveled after 7 days. Then, the branch tubes were filled with mortar, and the end faces were smoothed and sealed for curing similarly.The main tubes and branch tubes were all made of Q345 steel. The mechanical properties of the steel tubes are shown in C60, C80, and C100 Concrete were used to fill the main tubes of different specimens respectively. The raw materials of concrete were the same as Guangshen Qujiang Bridge. The mix proportions and key properties are listed in cuf) reached 115.2 MPa at the age of 28 d, which met the requirements of engineering design.It should be noted that the mix proportion of C100 concrete is completely consistent with the actual project. Polycarboxylate superplasticizer was added when the mixing the concrete. Polycarboxylate superplasticizer was added when the mixing the concrete. The solid content of water-reducing agent was 50%, and the water-reducing rate was 63%. After the dry mixture was evenly mixed for 10–15 s, the water-reducing agent and water were added and stirred for another 120 s. The lump and slump flow of the mixture were 255 mm and 640 mm, respectively, showing satisfactory cohesiveness, wrapping, and fluidity. The expansive agent was a composite high-energy expansive agent consisting of calcium oxide, calcium sulphoaluminate, and magnesium oxide . All spe(1)Test equipment and measuring pointsIn order to analyze the strain distribution and development of different sections during the loading process, strain measuring points were arranged in the following positions: the midspan section of main tube (section 4-4), section 3-3, and section 5-5 near the branch tube weld, section 1-1 and section 7-7, which were 20 mm away from the edge of the support, and the 1/4 span section . Meanwhile, another two strain measuring points (No. 49 and 50 strain gauges) were arranged at the bottom of the branch tube to observe whether the branch tube yields before the main tube. There were 50 strain gauges in total, as shown in (2)Loading planFirstly, the load is applied in stages by force control. Each load level is taken as 1/10 of predicted ultimate load. When obvious nonlinear characteristics appear on the load-midspan deflection curve, the load level is reduced to 1/15 of predicted ultimate load. After loading, it should be held for 2 min to observe deformation of the specimen. If yield stage comes, it will be converted to displacement control and loaded slowly and continuously. While one of the following situations occurs, the loading can be stopped and then unloaded: the ratio of deflection to span is close to 1/25 ; main tube cracking; main tube collapsed seriously; branch tube buckling.At the initial stage of loading, the load increased in proportion to the midspan deflection . When thThe typical load–midspan deformation curve (P–ω curve) of each specimen is shown in The distribution and development of deflection along the specimen length under different loads are shown in The section strain distribution of the three types of CFST specimens along the length was symmetrical, which has nothing to do with the core concrete strength. Therefore, the half span specimen of C100 UHSCFST was taken as the representative to elaborate the section strain distribution and development of the specimens.As shown in The measured loads are shown in Muc1 and Muc2 respectively. ueM/ucM1 is about 1.03–1.15, while ueM/ucM2 is about 0.97–1.06. It can be seen that the results calculated by literature [In terature  are moreterature ,15. Ther(1)The main failure mode of UHSCFST specimen was the overall bending failure, with slight local buckling in the compression zone, and the integrity of the section was maintained well.(2)The bending failure mode of UHSCFST members resembled that of ordinary CFST, and core concrete strength had little influence on the bending failure mode of UHSCFST.(3)UHSCFST had high flexural ductility. After the specimen yielded, the bearing capacity was enhanced slowly with the increase of deflection. The load value presented no reduction until the specimen was destroyed.(4)The increase of core strength had little effect on the flexural bearing capacity of UHSCFST. The main function of core concrete is to support the steel tube wall, and avoid its local collapse and improve the bending stiffness of composite section. However, this effect tends to be stable with the enhancement of core concrete strength, which should be taken into account in establishing the calculation method of UHSCFST bending capacity.According to the experiment of this paper, it is not difficult to draw the follow conclusions: