Compressive Strength Loss Research Articles

Effect of waste steel fiber use on concrete behavior at high temperature

Recently, recycling of waste vehicle tyres which pose a significant risk to environmental health has become an important research issue due to environmental concerns worldwide. To handle the waste tyre pollution problem, recycling waste into new products and using waste to improve other materials’ properties can be considered. Waste vehicle tyres can be used in the production of energy and various materials, providing economic and environmental advantages. In this study, experimental studies were carried out on the use of waste tyre steel fiber (WS) obtained from the recycling of heavy vehicle tyres in concrete, including the goal of recycling and reducing the need for raw materials. In one experimental group, waste tyre steel was added to concrete at 0.4% by volume instead of fine aggregate, while in the other experimental group it was added at 0.8% by volume. In the study, in addition to mechanical analyses, many microanalysis experiments were carried out to understand whether there was a strong relationship between the results. The study was conducted at target temperatures of 400, 600 and 800 °C depending on the fire scenario for building and construction materials according to ISO 834 and ASTM E119 standards. Compressive strength losses and characterization changes in 15 cm cube plain concrete and composite concrete specimens exposed to targeted high temperatures for 60 minutes were compared in terms of strength. Ultrasonic pulse velocity (UPV), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential thermal analysis (DTA), X-ray diffraction analysis (XRD) and Fourier transform infrared spectroscopy (FTIR) analysis was also performed, as it was understood that there was not enough data in the literature regarding waste tyre steel fiber reinforced concrete. General results showed that fiber-added concrete made significant contributions to concrete performance at high temperatures.

Recycle of soda waste sludge as the limestone material for Portland cement: Chemical composition, physical properties and hydration mechanism

Soda waste sludge (SWS) was discharged from the ammonia-soda process for producing sodium carbonate. It is out of effective treatment method but primarily composed of CaCO3. Limestone material is the necessary raw material for the Portland cement production, accounting for more than 80 wt%. Thus, a Portland cement in this study was produced from the SWS with different Cl- content as the substitute for limestone, and its chemical composition, physical properties, and hydration mechanism was investigated. Results demonstrated that when the Cl- in SWS was reduced to 0.26 wt% through water scrubbing, the chlorine-bearing species such as Ca10Mg0.8[(SiO4)3.4(AlO4)0.6O2Cl], C11A7·CaCl2, and Ca3(SiO4)Cl2 in cement clinkers and the 3CaO·Al2O3·CaCl2·10 H2O and Ca10(SiO4)3(SO4)3Cl2 in its hydration products vanished. And the Portland cement produced from 25.64 wt% SWS meets standard requirements for 52.5-grade cement on the flexural and compressive strengths. Its permeability coefficient was increased from 186.27 ×10−13 m/s to 8.65×10−13 m/s, and the mass loss and compressive strength loss were decreased to 6.53% and 7.33%. Also, the mineral phase composition of cement clinker were the 3CaO·SiO2, 2CaO·SiO2, 3CaO·Al2O3, and 4CaO·Al2O3·Fe2O3, the hydration products were the CSH gels, Ca(OH)2, Al(OH)3, and 3CaO·Al2O3·3CaSO4·32 H2O. This work realizes the application of SWS as the substitute for limestone, which is beneficial to the resource treatment of SWS and the reduction of limestone mining.

Durability prediction of geopolymer mortar reinforced with nanoparticles and PVA fiber using particle swarm optimized BP neural network

Abstract In this study, polyvinyl alcohol (PVA) fibers and nanoparticles were incorporated to enhance the durability of geopolymer mortar (GM) with metakaolin (MK) and fly ash (FA). The dosage of nano-SiO2 (NS) was 0–2.5% and that of PVA fiber was 0–1.2%. The durability of GM includes resistance to chloride ion penetration, freeze–thaw cycles, and sulfate erosion. Compared with the single BP neural network (BPNN) model, a particle swarm optimized BPNN (PSO-BPNN) model was utilized to predict the resistance to chloride ion penetration, freeze–thaw cycles, and sulfate erosion of GMs with different dosages of nanoparticles and PVA fibers. In the model, the dosage of NS, PVA fiber, FA, and MK were used as input layers, and the durability parameters of electric flux, mass loss, and compressive strength loss of GMs were used as output layers. The result exhibits that the root mean square errors (RMSEs) of BPNN for resistance to chloride ion penetration, freeze–thaw cycles, and sulfate erosion of GM mixed with nanoparticles and PVA fibers are 145.39, 6.43, and 2.19, whereas RMSEs obtained from PSO-BPNN are 76.33, 2.87, and 1.03, respectively. The NN optimized by particle swarm algorithm has better prediction accuracy. The PSO-BPNN can be utilized for estimating durability of GM reinforced by NS and PVA fiber, which can provide a guide for the proportion design of GM with PVA fiber and NS as well as for the engineering practice in the future.

An experimental study on the sulfuric acid resistance of mineral additive mortars

Mineral additives are preferred to improve the physical, mechanical and durability properties of cement-based composites and to reduce the use of cement to prevent environmental pollution and high production costs. Within the scope of this study, a new pozzolanic material, ground profillite powder (GPP), was evaluated by comparing it with granular ground blast-furnace slag (GGBFS), and it was used as a substitute for cement at ratios of 5, 10 and 15% by weight. The effects of these two mineral additives on the mechanical and physical properties of mortars and their resistance to sulfuric acid (SA) were investigated. In the production of the mortar samples, CEM I 42.5/R-type Portland cement (ordinary Portland cement) was used as the binder, and 0–4 mm crushed sand was used as the aggregate. Mineral additive and non-additive mortars were produced in the laboratory environment in dimensions of 40 × 40 × 160 mm. Spreading values, bending and compressive strengths, water absorption and porosity values and weight and strength loss values under the effect of SA were examined comparatively. It was determined that the mortar samples produced using GPP showed higher resistance to SA attacks than the pure and GGBFS-added mortars, reducing weight losses up to 21% and compressive strength losses up to 30%.

The rainstorm waterlogging resistance of a novel fiber-reinforced self-compacting recycled pervious concrete after freeze-thaw cycles

The poor permeability of pervious concrete after freeze-thaw (F-T) cycles is a difficult issue in the face of frequent extreme rainstorms, causing urban rainstorm waterlogging problems (stagnant water depth exceeds 150 mm). A novel fiber-reinforced self-compacting recycled pervious concrete (NSPC) with low tortuosity artificial pore channel (APC) is a pervious material with high permeability and strength, and has potential application in pervious pavement at the coupling action of F-T cycles and rainstorm. In this study, the frost resistance, mechanical properties and permeability of C60 NSPC (pore diameter of 3 mm, porosity of 1.13%) with various steel fiber contents (0 vol%, 0.5 vol%, 1 vol%, 1.5 vol% and 2 vol%) were investigated, and then the rainstorm waterlogging resistance of NSPC after 300 F-T cycles was examined under 20-, 50- and 100-year rainstorm. Results showed that the macroscopic destruction of NSPC surface after F-T cycles always started near the APCs, and the existence of APCs aggravated the mass loss and the decrease of the relative dynamic modulus of elasticity. As the increase of steel fiber content, the compressive strength loss of NSPC decreased first and then increased after F-T cycles. The use of steel fiber enhanced the integrality inside the APCs of NSPC and reduced the APC clogging rate, which improved hydraulic-conductivity properties after F-T cycles. After 300 F-T cycles, NSPC with 2% steel fiber achieved an excellent rainstorm waterlogging resistance (stagnant water depth of 0 mm), regardless of the rainstorm return period. Through F-T damage analysis, in order to cope with waterlogging, the maximum FT failure thresholds of NSPC to prevent stagnant water of 50, 70 and 100 mm are 0.097, 0.125 and 0.161 respectively, equivalent to 196, 243 and 264 F-T cycles. This study designed a NSPC that can dissipate stagnant water after F-T cycles, which provided a promising route towards solving urban rainstorm waterlogging.

Evaluation of the acid degradation properties of colloidal nanosilica‐based cement pastes

AbstractThe present study examined the effects of colloidal nanosilica on the performance of cement paste samples exposed to nitric acid for a continuous period of 28 days. Compressive strength and weight losses in paste samples as a result of this attack were determined to be 66% and 27%. The inclusion of nanosilica up to 6% by weight reduced these sample losses by densifying the microstructure with its pore filling and pozzolanic effects. The addition of nanosilica decreased the flow of cement paste by 30%, but improved compressive and flexural strengths at the end of 28 days by up to 45% and 118%. The acid attack on the cement sample resulted in the formation of a degraded layer surrounding the unaltered core material. X‐ray tomography images showed this zone formation, and the scanning electron microscopy images revealed the degraded microstructure. The results of the x‐ray diffraction and nanoindentation tests confirmed the complete decalcification of the main cement hydrates, including calcium silicate hydrate and portlandite, as a result of acid attack. The results obtained suggest that the incorporation of nanosilica strengthens the microstructure of the cement matrix, thus improving the service life of structural concrete operating in chemical environments.

Study on the Degradation Effect of Carbonaceous Shale under the Coupling Effect of Chemical Erosion and High Temperature.

The southwest region of China has abundant groundwater and high-temperature geothermal energy. Carbonaceous shale, as one of the typical surrounding rocks in this region, often suffers from deterioration effects due to the coupled action of groundwater chemical erosion and high temperature, which affects the long-term stability of tunnel engineering. In order to investigate the deterioration effects of carbonaceous shale under the coupled action of chemical erosion and high temperature, carbonaceous shale from a tunnel of Lixiang Railway in Yunnan Province was taken as the research object. The microstructure and mineral composition of the samples before and after chemical erosion were obtained with a scanning electron microscope-energy dispersive spectrometer and an X-ray diffraction test. Then, triaxial compression tests were conducted on the samples under different time points and different temperature effects of chemical erosion, and the stress-strain curves and the deterioration laws under a single factor were obtained. An improved numerical simulation method based on the parallel bond model was developed, which can account for the coupled effects of chemical erosion and high temperature on the rock. By simulating the triaxial compression test of carbonaceous shale, the deterioration law of carbonaceous shale under the coupled action was discussed. The results show that chemical erosion has a significant deterioration effect on the triaxial compressive strength of carbonaceous shale, and the degree of deterioration is related to the erosion time. In the first 30 days of erosion, the triaxial compressive strength of carbonaceous shale decreased by 11.38%, which was the largest deterioration range. With the increase in erosion time, the deterioration rate gradually decreased; temperature had a significant threshold effect on the strength of carbonaceous shale, and a clear turning point appeared at about 200 °C. By simulating the deterioration effects of carbonaceous shale under the coupled action of chemical erosion and high temperature, it was found that the longer the duration of chemical erosion, the stronger the temperature sensitivity of carbonaceous shale, and the more serious the loss of compressive strength during the heating process. When the temperature was low, the strength of carbonaceous shale changed little, and some samples even showed an increase in strength; when the temperature was high, the strength of carbonaceous shale decreased significantly, showing deterioration characteristics. The numerical simulation method was compared and verified with the indoor test results, and it was found that the numerical calculation had a good agreement with the test results.

Mechanical properties of recycled brick powder engineering cementitious composites under freeze-thaw cycling environment

With the continuous advancement of urbanization construction, the number of discarded red bricks caused by construction demolition is impressive because of the characteristics of construction materials in the early stage of our country. This study used the recycled brick powder produced in crushing red waste bricks to partially or wholly replace quartz sand, combined with different doses of PVA fiber to prepare green recycled brick powder engineering cementitious composites (ECC). First, the strain hardening and multiple cracking behaviors of recycled brick powder ECC with different fitting ratios were verified using four-point bending tests. Then, a rapid freeze-thaw experiment was conducted to study the effects of different fitting ratios on the quality failure rate, phase dynamic elastic modulus, and compressive flexural resistance of recycled brick powder ECC. Based on the evaluation parameters of compressive strength loss rate and frost resistance, the ECC freeze-thaw prediction model of recycled brick powder was established by the Monte Carlo method to expand the number of samples. The research results show the best frost resistance of recycled brick powder ECC with a 25% recycled brick powder ratio and 1% PVA fiber. Scanning electron microscopy was used to observe raw materials and cement-based materials, and the reasons of macroscopic phenomena were explained from a microscopic perspective.

Assessment of mechanical and durability performance of silica fume and metakaolin as cementitious materials in high-performance concrete

AbstractThe present study aims to determine the effects of blending cementitious materials on the mechanical and durability properties of high-performance concrete (HPC). Densified silica fume and fine-grounded metakaolin are used as supplementary cementitious materials (SCMs). A total of 16 mixes containing both binary and ternary blending of SCMs were chosen for w/b ratios of 0.4 and 0.3 respectively. The hardened properties tested for the HPC mixes were compressive strength at 7, 28, and 90 days, flexural strength at 28 days, and modulus of elasticity at 28 days. Maximum strength gains up to 15%, 38%, and 23% for compression, flexure, and elastic modulus were observed in ternary mixes compared to binary mixes. Stress-strain behaviour of ternary mixes indicates increased tolerance of stress for the least amount of strain in the specimens. Based on the experimental results, empirical relations were developed and checked with the existing codes and by earlier researchers. The durability properties tested for HPC were water absorption at 28 days, acid attack, and sulphate attack at 28, 56, and 90 days. Ternary mixes improved the pore structure of HPC, resulting in a 56% reduction in water absorption and a 34% reduction in compressive strength loss due to immersion in 5% H2SO4 at 90 days. The findings of the study endorse that ternary blending of SF and MK can improve the engineering properties of HPC, and a mix containing SF 10% and MK 10% is recommended for the best results.

The impact of waste brick and geo-cement aggregates as sand replacement on the mechanical and durability properties of alkali–activated mortar composites

This study explores the potential of waste brick and geo-cement aggregates as substitutes for natural sand in alkali-activated materials (AAMs) for mortar production. With a focus on achieving net-zero construction and mitigating environmental impact, the study replaces Portland Cement (OPC) and virgin aggregates with waste materials and by-products. The investigation evaluates the substitution of sand (up to 100 % by weight) in AAMs with waste brick aggregates (WBA) and waste geo-cement aggregates (WGA) obtained from demolished construction and research lab waste, respectively. The research methodology involves assessing mechanical, durability, and microstructure properties to assess the performance of the developed AAMs with waste aggregates. Notably, AAM composites containing waste brick and geo-cement aggregates surpass natural aggregate composites in terms of mechanical strength, water absorption, freeze-thaw resistance, acid ingress, and chloride attack. The 7-day 50 % waste brick mixture achieved a maximum compressive strength of 61 MPa, while a 70 % waste geo-cement mortar mixture attained a maximum flexural strength of 12 MPa. Combinations, whether comprising waste brick or geo-cement mortar aggregates, demonstrate compressive strengths well over 40 MPa, rendering them suitable for heavy load-bearing structures. The 50 % waste geo-cement mortar mixture stands out with the lowest water absorption rate of 6 % and the least compressive strength loss of 13 % after the freeze-thaw test, with reductions of 6 % and 18 %, respectively, compared to the control. Additionally, 100 % waste brick AAMs exhibit the lowest compressive strength loss after chloride and acid attack tests, with reductions of 13 % and 2.5 %, respectively. When compared to all other mixtures, the 50 % waste brick aggregates mortar mixture obtained the best overall performance. The composites developed in this study affirm their suitability for use in heavy-load structural components, showcasing favourable mechanical and durable properties. These findings underscore the need for additional exploration in this direction to advance sustainable construction practices.

Strength Reduction Due to Acid Attack in Cement Mortar Containing Waste Eggshell and Glass: A Machine Learning-Based Modeling Study

The present study utilized machine learning (ML) techniques to investigate the effects of eggshell powder (ESP) and recycled glass powder (RGP) on cement composites subjected to an acidic setting. A dataset acquired from the published literature was employed to develop machine learning-based predictive models for the cement mortar’s compressive strength (CS) decrease. Artificial neural network (ANN), K-nearest neighbor (KNN), and linear regression (LR) were chosen for modeling. Also, RreliefF analysis was performed to study the relevance of variables. A total of 234 data points were utilized to train/test ML algorithms. Cement, sand, water, silica fume, superplasticizer, glass powder, eggshell powder, and 90 days of CS were considered as input variables. The outcomes of the research showed that the employed models could be applied to evaluate the reduction percentage of CS in cement composites, including ESP and RGP, after being exposed to acid. Based on the R2 values (0.87 for the ANN, 0.81 for the KNN, and 0.78 for LR), as well as the assessment of variation between test values and anticipated outcomes and errors (1.32% for ANN, 1.57% for KNN, and 1.69% for LR), it was determined that the accuracy of the ANN model was superior to the KNN and LR. The sieve diagram exhibited a correlation amongst the model predicted and target results. The outcomes of the RreliefF analysis suggested that ESP and RGP significantly influenced the CS loss of samples with RreliefF scores of 0.26 and 0.21, respectively. Based on the outcomes of the research, the ANN approach was determined suitable for predicting the CS loss of mortar subjected to acidic environments, thereby eliminating lab testing trails.

Research on printing parameters and salt frost resistance of 3D printing concrete with ferrochrome slag and aeolian sand

Aeolian sand (AS) and ferrochrome slag (FS), an industrial byproduct, are abundant in Inner Mongolia. Rational use of FS and AS resources can lead to better economic benefits. In this study, FS and AS were used as fine aggregates to prepare 3D printed concrete (3DPFAC). The effect of different printing parameters on the mechanical properties of 3DPFAC was investigated and the optimal printing parameters were determined. The durability of 3DPFAC in salt freeze-thaw cycle (FTC) environments was analyzed by FTC tests. The mass loss rate, relative dynamic elastic modulus, and compressive strength loss rate are used to characterize the performance degradation law of 3DPFAC and the mechanism of performance degradation is revealed by SEM, XRD, and bubble spacing analyzer. We conclude that the optimal printing parameters for 3DPFAC are 20 mm print nozzle diameter, 8 mm print layer height, 50 mm/s print travel speed, and consecutive print interval time. Under different production processes, the degree of damage and deterioration of concrete is 3D-Y (loading along the Y direction) > 3D-X (loading along the X direction) > JZ (pouring specimens). After 400 FTCs, the mass loss rates for JZ, 3D-X and 3D-Y were 3.02 %, 3.12 % and 3.56 %, respectively, the relative dynamic elastic modulus decreased to 71.78 %, 66.18 % and 58.64 %, respectively, with compressive strength loss rates of 21.0 %, 22.4 % and 24.0 %. Finally, the damage evolution equation for 3DPFAC is derived using the Weibull distribution model, and the lifetime prediction is performed based on the Weibull distribution damage model. The results can provide a theoretical basis for the application of FS and AS in the 3DPC domain.

Properties of fibre-reinforced self-compacting concrete subjected to prolonged mixing: an experimental and fuzzy logic investigation

This article investigates the effect of prolonged mixing on the rheological properties and compressive strength of fibre-reinforced self-compacting concretes (FRSCCs). Twenty FRSCC mixes with five cementitious material contents (300, 350, 400, 450 and 500 kg/m3) and three types of fibres and dosages (polypropylene at 0.1%, steel at 1.0%, or synthetic at 1.0%) were first produced. The mixes were then subjected to four mixing intervals of 20 min each (total mixing time = 80 min). The rheological properties of the fresh FRSCC mixes were examined, and the corresponding compressive strength of the hardened FRSCCs was subsequently obtained. Overall, the results from slump flow, T50, V-funnel and L-box tests on fresh mixes, as well as the 28-day compressive strength on the hardened FRSCCs, were in line with previous results reported in the literature. The results show that all mixes lost their self-compacting properties after 80 min of mixing. It was also found that mixes with high cementitious material contents (500 kg/m3) and highest polypropylene fibre dosage were most affected by prolonged mixing, with average losses of 30% and 35% in rheological properties and compressive strength, respectively. Based on the test results, this study proposes a novel fuzzy logic approach to predict the slump loss and at 28-day compressive strength loss of FRSCCs subjected to prolonged mixing. This article contributes towards a better understanding of FRSCCs after prolonged mixing, which can help make informed decisions about their use in new and repaired concrete structures.

Durability Properties of Macro-Polypropylene Fiber Reinforced Self-Compacting Concrete.

Concrete is one of the most commonly used construction materials; however, its durability plays a pivotal role in areas where the concrete is exposed to severe environmental conditions, which initiate cracks inside and disintegrate it. Randomly distributed short fibers arrest the initiation and propagation of micro-cracks in the concrete and maintain its integrity. Traditional polypropylene fibers are thin and encounter the problem of balling effects during concrete mixing, leading to uneven fiber distribution. Thus, a new polypropylene fiber is developed by gluing thin ones together, forming macro-polypropylene fibers. Thus, different amounts of fibers, 0-1.5% v/f with an increment of 0.5% v/f, are used in different grades of concrete to study their impact on durability properties, including resistance to freezing and thawing cycles, sulfate, and acid attacks. A total of 432 cube samples were tested at 28, 56, and 92 days. The results reveal that the maximum durability, in terms of compressive strength loss, is noted with a fiber content of 1% with improved resistance of 72%, 54%, and 24% against freeze-thaw cycles, sulfate attack, and hydrochloric acid attack, respectively, at 92 days. Thus, the resulting fiber-reinforced concrete may be effective in areas where these extreme exposure conditions are expected.

Macro-Meso Damage Analysis of Tunnel Lining Concrete under Thermal-Mechanical Coupling Based on CT Images.

The mechanical properties and failure modes of concrete are controlled by its mesoscopic material composition and structure; therefore, it is necessary to study the deterioration characteristics of tunnel lining concrete under fire from a mesoscopic perspective. However, previous studies mostly analyzed the damage and failure process from a macro-homogeneous perspective, which has certain limitations. In this paper, a thermal-mechanical coupling test device was modified to simulate the state of concrete under tunnel fire conditions. Combined with CT technology, the macroscopic properties and mesoscopic characteristics of concrete were observed. Features were obtained, such as the change in compressive strength under fire, as well as mesoscopic deterioration characteristics. The damage variable D was defined to quantify mesoscopic damage, and the link between mesoscopic deterioration characteristics and macroscopic performance was established, which can be used to predict compressive strength loss through mesoscopic characteristics.

Effects of elevated temperatures’ exposure on the properties of concrete incorporating recycled concrete aggregates

The concrete and its thermal gradient response must be considered when it is subjected to high temperatures. This study examines the impact of exposure to elevated temperatures (500 °C, 700 °C, and 1000 °C) on concrete's physical and mechanical properties incorporating recycled concrete aggregates (RCA). It emphasizes substituting RCAs for natural coarse aggregate (NCA) at 20%, 40%, 60%, 80%, and 100%. The intended behavior is post-heating; a cold sample serves as a control. The evolution of graduating temperature in the muffle furnace is similar to the ISO curve in a fire. The data analyzed indicate that a temperature rise affects the characteristics of recycled aggregate concrete (RAC). A heating level of 500 °C does not significantly affect the initial resistance, which is not the situation at temperatures of 700 °C and 1000 °C. Regarding residual strength, the concrete with 40% RCAs concrete performs quite well. At 700 °C, its strength loss in compressive strength is 24.4%, whereas the control concrete is 29.8%. Mass loss, capillary water absorption, water-accessible porosity and non-destructive tests reveal that elevated temperature damages RAC. Lastly, XRD, TGA, and SEM microstructural analyses are employed to interpret the fundamental mechanisms of heated RAC due to temperature changes.

Examination of the permeability of rubberized concrete with different water/cement ratios and their resistance against acid and sulfate attack

This study aims to examine the permeability and acid and sulfate attack of waste rubber-substituted concrete containing recycled rubber in three different grain size classes (chips, crumb and powder) with two different water/cement (w/c) ratios (0.4 and 0.5). Waste rubber at different ratios (0%, 4%, 8%, 12%, 16%, 20%, and 24%) was used in concrete by replacing fine and coarse aggregates. Sorptivity, electrical resistivity, and acid and sulfate attack tests were conducted on concrete cured for 90 days. Although the capillarity coefficient values increased with the waste rubber replacement ratio increase, a decrease occurred after the 20% waste rubber replacement ratio. In 12% waste rubber-substituted concrete (0.4WR12) with a water/cement ratio of 0.4, the electrical resistivity value (8.3 kΩ.cm) was the highest, and concretes with low permeability could be produced. As a result of the use of 16% waste rubber in the concrete, 75% less compressive strength loss was observed after the acid attack compared to the control concrete. In concrete with a water/cement ratio of 0.5, when the waste rubber ratio increased by up to 16%, the compressive strength losses caused by the sulfate attack decreased dramatically (95.76% less) compared to the control concrete. The rubberized concrete with a water/cement ratio of 0.5 showed high resistance to acid and sulfate attacks. The experiment results showed that 12% to 16% waste rubbers are ideal ratios. In this study, the water/cement ratio was a valuable parameter for the waste rubber ratio in rubberized concrete.

Comparative study on the effect of bauxite tailings on properties of magnesium-phosphate-cement-based materials before and after calcination

To study the recycling of bauxite tailings (BT) and the poor water resistance of magnesium phosphate cement (MPC), the effects of BT and calcined BT (CBT) on the setting time, fluidity, drying shrinkage properties, compressive strength, and water resistance of MPC were investigated. The results showed that BT and CBT regulated the setting time and fluidity of MPC, adjusted the pH of the MPC paste, and decreased the generation rate of hydration products. The incorporation of BT decreased the early strength and increased the late strength of MPC, while the incorporation of CBT increased the MPC strength during the 28 d duration. Further, the optimal incorporation amount of BT and CBT was found to be 15 wt%. Although the water resistance of MPC was improved by blending BT or CBT, the effect of CBT was more significant, with a 32% reduction in compressive strength loss in the CBT groups compared to the control group for 28 d of curing. The alumina in BT was calcined and activated such that AlPO4 produced by secondary hydration reaction with phosphate enhanced the bonding of the solids and filled the pores and cracks of the MPC specimens, thereby increasing the densities of the specimens and improving their water resistance.

Optimised performance of ultrahigh-performance silicomanganese slag concrete by water glass immersion

Silicomanganese slag (SS) is a byproduct of the ferroalloy industry. It causes environmental pollution and consume resources. In this study, water glass immersion was used to improve the performance of SS, which was utilised in the production of ultrahigh-performance concrete (UHPC). The results show that SS treated with a 2% water glass concentration for 24 h had 16 MPa higher compressive strength for composite than pure UHPC. Additionally, the treated composite had approximately half the mass and compressive strength losses of pure UHPC after freeze–thaw testing, indicating that the treatment had a significant positive effect on the freeze–thaw resistance of ultrahigh-performance silicomanganese slag concrete (UHPSSC). Microstructural analysis also showed that water glass immersion optimised the morphology of UHPSSC, contributing to improved mechanical performance and freeze–thaw resistance of the composite.

A study on the performance of alkali-activated materials prepared by thermochemical treatment of ladle furnace slag

In this paper, the effects of different calcination temperatures, flux types, and their corresponding additions on the thermal activation effect of the Ladle furnace slag (LFS) were investigated. A comparative analysis of the properties of the LFS-based geopolymer before and after thermal activation was carried out from a macroscopic perspective. The results showed that the 12CaO·7Al2O3(C12A7) in the LFS is more amorphous after thermal activation, leading to a prolongation in the setting time. When the calcination temperature reached 800 °C, the γ-C2S showed signs of transformation to β-C2S. This, in turn, undoubtedly enhanced the hydration properties of the LFS, as demonstrated by the compressive strength of the samples. In this regard, the compressive strengths of G-H-800, G-H-S5, and G-H-C10 after 28 days were 18.25 MPa, 18.47 MPa, and 24.38 MPa, respectively. They were found to be higher than those of the untreated sample G-Unheated at 8.0 MPa. In addition, the evaluation of the chemical resistance properties showed that the thermally-activated LFS-based geopolymer had good corrosion resistance in both NaCl and NaOH solutions, especially at high concentrations. The compressive strength loss rates of G-Unheated were 33.70% and 29.92% at NaCl and NaOH solution concentrations up to 2 mol/L, respectively. The lowest compressive strength loss rates of 9.21% and 17.83% could be achieved by LFS-based geopolymer after thermal activation under the same conditions. Nevertheless, the results of the high temperature resistance test showed that the compressive strength of the samples all increased at a temperature of 200 °C. However, when the temperature rose to 400 °C, the compressive strength of the samples decreased, except for G-Unheated, which showed a 2% increase in compressive strength. As the temperature was increased further, the compressive strengths of all samples were diminished.