Strength Loss Rate Research Articles

Utilisation of silica-rich waste in eco phosphogypsum-based cementitious materials: Strength, microstructure, thermodynamics and CO2 sequestration

Phosphogypsum-based cementitious materials (PGCM) are commonly selected as substitutes to ordinary Portland cement (OPC), however, drawbacks, such as a restricted capacity for CO2 sequestration and reduced mechanical properties upon carbonation, limit the potential applications of PGCM. This study investigates the carbonation process mechanism of PGCM and explores to modify the hydration product classes of PGCM by using two silica-rich solid wastes, which are waste glass powder (WGP) and silica fume (SF). This innovative approach resulted in an improved carbon capture capacity and enhanced mechanical properties of PGCM. The addition of SF and WGP increased the compression strength of PGCM by 15.5% and 19.0%, respectively. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) were utilized to investigate the hydration mechanism of PGCM supplemented with SF and WGP, in order to gain a comprehensive understanding of their properties. The addition of SF and WGP to PGCM resulted in a 9.9% and 21.6% increase in thermal conductivity, respectively. Furthermore, the addition of SF and WGP facilitated higher CO2 sequestration rates for PGCM (49.76% and 44.05%, respectively), while after carbonation, the strength loss rates were reduced to 16.8% and 13.35%, respectively. Finally, a simple sustainability analysis showed that the utilisation of silica-rich waste in PGCM has environmental sustainability benefits.

Deterioration law and life prediction of aeolian sand concrete under sulfate freeze-thaw cycles

To study the deterioration law of aeolian sand concrete (ASC) under the coupling effect of sulfate freeze-thaw, this paper uses aeolian sand as a substitute for river sand to prepare ASC with different replacement rates (0%, 20%, and 100%). Freeze-thaw cycle (FTC) tests are conducted in different salt solution environments (5% Na2SO4, 10% Na2SO4, and 5% Na2SO4 + 3.5% NaCl) to analyze the changes in physical and mechanical properties, and the mechanism of performance degradation of ASC is analyzed by SEM, XRD and NMR. The results show that incorporating aeolian sand significantly improves the salt-freeze erosion resistance of concrete, and when the content is 100%, the impact on salt-freeze erosion on macroscopic properties such as mass loss and compressive strength is minimized, signifying the salt-freeze erosion resistance is the best. During the FTCs, the relative dynamic elastic modulus of concrete initially increases and then decreases, while the trend in mass loss rate reverses. SO42- and Cl- in the salt solutions react with the hydration products to form calcium vanadate, gypsum, and Friedel salts. During the initial stages of FTCs, erosion products fill the matrix pores, increasing the compactness of the concrete, which positively affects macroscopic properties. As the FTCs progresses, ice crystals and excessive erosion products accumulate, resulting in a further expansion of internal pores and cracks in concrete. Consequently, the ratio of harmful to beneficial pores continues to increase, resulting in freeze-thaw damage. After 200 FTCs, in the 5% Na2SO4 + 3.5% NaCl erosion medium, the internal cracks in aeolian sand concrete get bigger and the holes get larger, causing the most damage and deterioration. Different degradation indices are used to predict the residual lifetime of ASC based on a Wiener random probability distribution. The Wiener stochastic process effectively predict the lifetime of ASC under the coupling effect of sulfate FTCs, with the compressive strength loss rate as the most sensitive degradation index. Among them, for ASC-0, ASC-20, and ASC-100 in the 5% Na2SO4 + 3.5% NaCl environment, the maximum FTCs, based on the compressive strength loss rate, are 198, 206, and 213 times, respectively. This study could provide a theoretical foundation for the durability design of concrete structures in cold regions and other salt-frozen regions within Northwest China.

Influence of PVA fibers on the durability of cementitious composites under the wet–heat–salt coupling environment

Abstract To investigate the effects of wet–heat–salt coupling environment (WHSCE) and the content of polyvinyl alcohol (PVA) fibers on the durability of cementitious composites (CC), a series of durability tests were carried out. In this study, the salt concentration in the WHSCE was set to 5%, the temperature at 50°C, and the relative humidity at 100%. Six different contents of PVA fibers were set up in the test for exploring their effects on the durability (impermeability, chloride ion penetration resistance, freeze–thaw resistance, and chloride salt erosion resistance under dry and wet cycle conditions) of CC. The results showed that durability of CC under the WHSCE was enhanced regardless of the content of PVA fibers added. At the PVA fiber amount of 1.2%, the impermeability pressure, electric flux, mass loss rate, compressive strength loss rate, and compressive strength corrosion resistance coefficient under the WHSCE reached the optimal values. This indicated that the durability of CC was most favorable when the amount of PVA fibers was 1.2% since many engineering structures are subject to erosion by various factors in the ocean, which can inevitably affect the service life of the purchase. In this study, the effect of PVA fiber content on the durability of CC in complex environment is studied, which provides experimental data and analytical ideas for improving engineering located in the ocean, hoping to provide a theoretical basis for their subsequent application in practical engineering.

Axial compression performance of steel tube columns filled with slurry-wrapping recycled concrete after exposure to high temperatures

Due to frequent fire accidents and stone scarcity, fire protection design and recycled aggregates are issues that needed to be solved in the construction industry. Steel tubes and slurry-wrapping reinforcement treatment can effectively improve the load-bearing capacity of recycled concrete. This paper reports on the mechanical behavior of slurry-wrapping recycled aggregate concrete-filled steel tube (CFST) columns after exposure to high temperatures. Three series of 30 CFST columns were designed with the coarse aggregate type and exposure temperature as variation parameters: natural aggregate concrete-filled steel tube (NACFST) column, recycled aggregate concrete-filled steel tube (RACFST) column, and slurry-wrapping recycled aggregate concrete-filled steel tube (SRACFST) column. The results show that the failure pattern of the specimen is less affected by the exposure temperature and the coarse aggregate type. The compressive strength of the RACFST columns is significantly increased after the slurry-wrapping treatment. With the temperature increasing, the ultimate strength tends to increase initially and then drop. Since the recycled concrete has more pores, the compressive strength loss rate of the RACFST columns is lower than that of the NACFST and SRACFST columns at 800 °C. The lateral deformation factor is maintained until the exposure temperature reaches 400 °C and then begins to decrease as the temperature increase. It is not accurate to predict the strength of CFST columns after high temperatures by ultrasonic pulse velocity. The predicted strength of CFST column after high temperatures was compared with design codes, and an equation considering the material strength variation was proposed.

Mechanical properties and microstructure of nano-modified geopolymer concrete containing hybrid fibers after exposure to elevated temperature

Geopolymer concrete (GPC) has a promising future as an eco-friendly material for refractory engineering applications. It is significant to investigate the changes in mechanical properties of nano-modified geopolymer concrete containing hybrid fibers (NHF-GPC) after exposure to elevated temperature for construction fire-resistant design. In this study, the macro-mechanical property tests and micro tests were carried out on geopolymer concrete containing hybrid fibers with different nano-SiO2 (NS) contents (0–2 %) after exposure to different elevated temperatures (200–800 °C). The coupling relationships of compressive, tensile and flexural strengths of NHF-GPC with temperature and NS content were established separately. And the relative sound velocity and damage degree were selected as acoustic parameters to construct a relationship model with the compressive strength loss rate. The results indicated that the compressive, tensile and flexural strengths of NHF-GPC were enhanced at 200 °C, while higher temperatures significantly reduced the mechanical properties of NHF-GPC. At the same temperature, the compressive, tensile and flexural strengths of NHF-GPC all increased and then decreased with increasing NS content, and reached the peak at a NS content of 1.5 %. The matrix became denser at 200 °C, while at greater than 200 °C, the water evaporated, the number of microcracks increased abruptly, and the porosity enlarged. The mass loss of NHF-GPC after elevated temperature mainly occurred below 600 °C, when there was no new material phase generated inside the matrix. And the established model can be used for the identification on the strength damage degree after elevated temperature exposure of NHF-GPC, and it can offer a conceptual foundation for the assessment of elevated temperature damage and the life prediction of GPC in the practical applications.

Effect of PVA fibers on durability of nano-SiO2-reinforced cement-based composites subjected to wet-thermal and chloride salt-coupled environment

Abstract Marine engineering structures are often faced with complex environmental factors. It is the focus of current research to modify cement-based composites (CBCs) to achieve their high durability in complex environments such as seawater. In this study, the effect of polyvinyl alcohol (PVA) fibers on durability of nano-SiO2 (NS)-reinforced cement-based composites was investigated by simulating seawater environment and taking PVA fiber content as variable. In addition, based on the Weibull probability distribution model, the damage degree of NS and PVA fiber-reinforced cement-based composites (NFRCCs) subjected to wet-thermal and chloride salt-coupled environment (WTCSE) after 300 freeze–thawing cycles (FTCs) was predicted. The test results demonstrated that the NFRCC exhibited the most excellent durability subjected to WTCSE when the content of PVA fibers was 1.2%. Compared with the reference group only doped with NS subjected to WTCSE, its impermeability pressure increased by 150%, the chloride ion electric flux decreased by 31.71%, the compressive strength loss rate decreased by 19.00% after 125 FTC, and the compressive strength corrosion resistance coefficient of chloride salt erosion increased by 9.15% after 25 wetting–drying cycles. The predicted results of the Weibull probability distribution model indicated that the damage degree of NFRCC subjected to WTCSE after 300 FTC would not exceed 0.35. The microscopic test analysis showed that the incorporation of PVA fibers reduced the proportion of large pores and the overall porosity of NFRCC subjected to WTCSE. PVA fibers bridged microcracks while adsorbing NS and its hydration products, thus enhancing the adhesion of the substrate. This study provides a reference for the research of high-performance CBC in complex environment.

Experimental investigation of the interfacial bonding properties between polyurethane mortar and concrete under different influencing factors

As a repair material, polyurethane mortar has excellent mechanical properties. The aim of this study is to explore the mechanical properties and microstructure of the interface between polyurethane mortar and concrete. The effects of curing temperature (−20 °C, −10 °C, 0 °C, 10 °C, 20 °C), water saturation of concrete (0 %, 30 %, 70 %, 100 %) and roughness (0, 1.5, 3.0, 4.5, 6.0 mm) on the bonding interface strength (shear strength and splitting tensile strength) were investigated through shear and splitting tests. The microstructure of the bonded interface was analysed by scanning electron microscopy at different curing temperatures and water saturation of the concrete, and an interfacial bonding mechanism was proposed. The results of the study show that the strength of the bonded interface increases gradually as the curing temperature rises. At the same curing temperature, the strength of the bonded interface decreases with increasing water saturation of the concrete and is essentially linear. The rate of strength loss of high-water-saturation specimens increases gradually as the temperature rises. When the temperature is positive, the interfacial bond strength increases and then decreases with increasing roughness, and a critical value (4.5 mm) of roughness exists that makes the bond strength reach a maximum. At negative temperatures, the interfacial bond strength increases with increasing roughness. The grey correlation analysis shows that roughness has the greatest influence on the interfacial bonding performance, followed by curing temperature and then water saturation. The interfacial shear strength and splitting tensile strength have a good linear relationship under the influence of all factors. Microscopic tests show that the polyurethane mortar body structure loosens gradually as the curing temperature decreases. As the water saturation of the concrete increases, the interface width between the polyurethane mortar and concrete shows an overall tendency to increase.

Compression and bending of alkali-activated slag cementitious materials at high temperature

Alkali-activated slag cementitious material (AASCM) with manufactured sand can effectively utilise industrial waste slag and reduce river sand consumption. Steel fibres can effectively improve the mechanical properties of AASCM. Therefore, in this study, the influence of steel fibres and aggregate type on the compression and bending properties of AASCM after high-temperature treatment was investigated. The results show that the mass loss rate, compressive strength and flexural strength loss rate of AASCM with manufactured sand were higher than those with natural river sand at different temperatures. Steel fibres can increase the mass loss rate of AASCM; however, the influence of the steel fibre content on the mass loss of AASCM was not apparent. When the temperature was lower than 600°C, the compressive and flexural strength of AASCM was effectively increased by steel fibres, while, for temperatures higher than 800°C, the mechanical properties of AASCM did not improve, owing to the oxidation failure of steel fibres. Microstructure analysis showed that the number of microcracks in the AASCM increased, owing to the high silicon content of the manufactured sand, and the bond property between the steel fibres and cementitious materials decreased with an increase in temperature.

Brick-concrete recycled aggregate/powder synergistic preparation of pervious concrete

In order to improve the resource utilization rate of brick-concrete construction waste (BC-CW) and meet the demand of 'sponge city' construction for pervious concrete, a kind of brick-concrete recycled pervious concrete (BC-RPC) was prepared by brick-concrete recycled aggregate (BC-RA) / powder (BC-RP). The design was carried out from the two levels of cementitious material pastes and aggregate. Firstly, BC-RP was used as the main silicon-aluminum raw material to prepare a brick-concrete recycled powder based geopolymer (BC-RPG) for pervious concrete. It was determined that the content of BC-RP in BC-RPG was 50%, and the alkali content and modulus of the best alkali activator were 12% and 1.2, respectively. Then, the effect of BC-RA gradation and substitution rate on the mechanical properties of BC-RPC was studied by using BC-RPG as cementitious material and BC-RA as aggregate. The method of 'double grain composite substitution' was proposed to control the strength loss rate of BC-RPC. At the same time, the volume structure parameters (design porosity and pastes-aggregate ratio) of BC-RPC were optimized, and the optimum design porosity and pastes-aggregate ratio for BC-RPC preparation were determined to be 27% and 0.39, respectively. Finally, BC-RPC with coordinated mechanical and water permeability properties was prepared.

Potential improvement of clinker sand in the mechanical high temperature and transport properties with GGBS-based prepacked geopolymer composite

In this study, a new generation prepacked geopolymer composite (PGC) material that can meet different needs was obtained by combining geopolymer concrete (GPC) and prepacked aggregate concrete (PAC) technology. In the production of PGC, 5-8 mm quartz aggregates were placed in molds and, geopolymer mortar was injected between these aggregates. Aluminosilicate based blast furnace slag (GBFS) was used as binding in geopolymer mortars; sodium silicate (Na2SiO3) and sodium hydroxide (NaOH) was used as alkali activator. In addition, clinker aggregate in different proportions was used as fine aggregate (0–4 mm) in the production of mortar. Within the scope of the study, the physical, mechanical, permeability and high temperature resistance properties of PGC were investigated. The produced samples were cured at 30 and 60 °C for 6 and 8 hours. Hardened unit weights of PGC vary between 2342 and 2539 kg/m3, and sorptivity values vary between 0 and 0.04 kg/m2.min0.5. While the increase in curing temperature and curing time increases the hardened unit weight values, it decreased permeability values. While the increase of clinker aggregate in the mortar phase does not change the hardened unit weight, it significantly reduced permeability. When the PGC samples are cured at 30 °C, the compressive strengths are 20.38–39.03 MPa; when curing at 60 °C, the compressive strengths are 35.21–57.04 MPa. Flexural strengths, 2.35–6.96 MPa with 30 °C cure, achieved 4.27–9.93 MPa results with 60 °C curing. Increasing the curing time and curing temperature significantly increased the compressive and flexural strengths. The increase in the amount of clinker aggregate added to the mortar phase decreased the strength values. While the compressive strength values of PGC mixtures do not fall below 15 MPa after being exposed to 300 °C high temperature; after the application of 600 °C high temperature, it lost up to 70% of its strength. Increasing the curing time and curing temperature, increased the high temperature resistance. The increase in the amount of clinker aggregate in the mixtures, decreased the strength loss rate.

Stress–strain model of steel fibre-reinforced alkali-activated slag cementitious material after high-temperature exposure

Steel fibres can reduce the shrinkage of alkali-activated slag cementitious material (AASCM) and improve their strength. Therefore, it is of great significance to accurately predict the stress–strain relationship of steel fibre-reinforced AASCM after exposure to high temperatures to promote this green building material. The effects of temperature and steel fibres on the axial compressive strength, elastic modulus, peak compressive strain, and stress–strain curve of the AASCM were analysed. The test results showed that after exposure to high temperatures, there were two compression failure modes of AASCM: tensile failure and shear failure. After exposure to 200 °C, 400 °C, 600 °C and 800 °C, the average strength loss rate of AASCM was 38.8%, 58.2%, 75.8% and 90.1%, respectively. Below 600 °C, the steel fibre has a positive effect on the compressive strength, elastic modulus and peak compressive strain of AASCM, with the optimal volume fraction being 1.5%. Based on the test data, the existing models are compared and analysed. And a model for predicting the compressive strength, peak strain, elastic modulus and stress-strain relationship of steel fibre-reinforced AASCM was proposed.

Quantum dynamics simulations of the 2D spectroscopy for exciton polaritons.

We develop an accurate and numerically efficient non-adiabatic path-integral approach to simulate the non-linear spectroscopy of exciton-polariton systems. This approach is based on the partial linearized density matrix approach to model the exciton dynamics with explicit propagation of the phonon bath environment, combined with a stochastic Lindblad dynamics approach to model the cavity loss dynamics. Through simulating both linear and polariton two-dimensional electronic spectra, we systematically investigate how light-matter coupling strength and cavity loss rate influence the optical response signal. Our results confirm the polaron decoupling effect, which is the reduced exciton-phonon coupling among polariton states due to the strong light-matter interactions. We further demonstrate that the polariton coherence time can be significantly prolonged compared to the electronic coherence outside the cavity.

Examining Central Fatigue Pathways under Stress: Integrating Insights from Graph Theoretical Neural Modeling and Motor Cortex Excitability

Acute cognitive stress affects neuromuscular fatigue, but the underlying mechanisms are not well understood. The aim of this study was to identify the influence of stress on central fatigue and associated functional changes in the brain. Thirty participants, balanced by sex, performed intermittent elbow flexion contractions at 30% of their maximum strength till voluntary fatigue. Endurance time, strength loss, and voluntary activation loss rate were collected. Functional hemodynamic changes in the participants’ prefrontal and motor areas of the brain were also collected and used to calculate functional integration and segregation in the PFC and M1. Results show that stress had a facilitative effect on fatigability and the fatigue related decline in the functional integration and segregation of prefrontal cortex were not observed under stress. These findings demonstrate how the imposition of dual task demands in the workplace delays the perception of neuromuscular fatigue, thereby increasing the risk of injury.

Investigation of the performance of cement-stabilized magnesium slag as a road base material

The harmless, resource-saving, and large-scale utilization of magnesium slag (MS) from industrial waste has become an important topic for road research. The use of MS as a substitute for aggregate is a practical and efficient way to dispose of it. However, there is a lack of systematic research on how to standardize its use in road construction. The objective of this study was to investigate the applicability and feasibility of using MS for cement stabilized base course materials. The influence of different cement dosages, curing age, and gradation on the strength, stiffness and stability of cement-stabilized magnesium slag mixture (CMSM) was investigated, and the actual road performance of CMSM was analyzed by paving a test road. The results showed that the mechanical properties of the CMSM met the requirements for road base courses under medium-to-light traffic when the cement dosage was above 5%. The unconfined compressive strength loss rate of the CMSM was less than 13% for an immersion time of 1 to 7 days, and after 5 freeze–thaw cycles, the frost resistance coefficient of the CMSM was more than 85%. The performance of the CMSM was most affected by cement dosage and curing age, closely followed by mixture grading type. MS can enhance the development of the pozzolanic reaction, resulting in improved strength and compactness of CMSM. Overall, CMSM exhibited exceptional road performance and could reduce aggregate costs by 25% to 35%. The use of MS as an aggregate for road base courses offers a sustainable solution that not only maximizes the use of solid wastes, but also avoids the potential safety hazards and environmental pollution caused by improper disposal and stockpiling of MS.

Preparation and Properties of Masonry Mortar from Spontaneous Combustion Coal Gangue

To solve the problem of gangue stockpiling, this paper intends to study the feasibility of preparing masonry mortar based on spontaneous combustion gangue. After crushing the spontaneous combustion gangue, the gangue below 4.75 mm was selected, and substituted manufactured sand to prepare masonry mortar in equal quantity. The single factor test method was used to select the replacement rate of spontaneous combustion gangue, water-binder ratio (W/B) and water reducer dosage as variables to explore their effects on the basic properties of fresh mortar mixtures, such as fluidity, apparent density and water retention of fresh mortar, and the mechanical properties of hardened mortar. The anti-frost resistance of gangue mortar was evaluated by a freezing-thawing cycle test. SPSS.20 software was used for variance analysis, and the results showed that the replacement rate of spontaneous combustion gangue, W/B and water reducer dosage on mechanical properties of mortar differences are significant (P < 0.001). With the increase of the replacement rate of spontaneous combustion gangue, the mortar strength decreases, and with the rise of W/B, the mortar strength raises first and then reduces, while with the increase of the water reducer dosage, the mortar strength increases first and then decreases. Spontaneous combustion gangue mortar shows better anti-frost resistance under the freezing-thawing cycle. After 50 freezing-thawing cycles, the maximum mass and strength loss rate of mortar specimens are 2.4 % and 12.67 %, respectively. When the replacement rate of spontaneous combustion coal gangue is 100 %, the mechanical properties and anti-frost resistance of mortar both meet the requirements of the standard and realize the maximum utilization of gangue waste resources. This paper aims to provide theoretical support for the application of spontaneous combustion gangue in masonry mortar.

A new approach to improving the water resistance of MOC-solidified sludge using [formula omitted] ions

With the growing sustainability concerns and awareness of environmental conservation, utilizing magnesium-based cement in construction has garnered considerable attention in recent years. In this work, a novel and sustainable approach to treating sludge has been developed by incorporating NaHCO3 to enhance the properties of MOC (Magnesium Oxychloride Cement)-solidified sludge. Different properties were determined through various experimental techniques, such as unconfined compressive strength (UCS), durability, scanning electron microscopy (SEM), X-ray diffraction (XRD) tests, and mercury intrusion porosimetry (MIP) to assess the impact of NaHCO3 content, curing age, and other factors on the strength, water resistance, microstructure, and reaction products of MOC-solidified sludge. The results indicate that adding NaHCO3 significantly enhanced the compressive strength and water resistance of MOC-solidified sludge, with an optimum NaHCO3 content of 50%. However, excessive NaHCO3 content led to a reduced MOC content, as evidenced by a strength loss rate of approximately 50% when NaHCO3 content reached 200%. Adding NaHCO3 also produces hydrated magnesium carbonates in solidified sludge in addition to Phase 5 and Brucite (Mg(OH)2). The expansion and cementation properties of these reaction products effectively filled the pores of the samples, facilitating the bonding of soil particles, establishing a stable spatial network structure, and improving the resulting strength of MOC-solidified sludge.

Thermal shock behaviors of W/Cu joints with different structures

In this paper, three different W/W-Cu joints (W/W-16Cu (joint 1), W/FeCoNiCrCu interlayer/W-16Cu (joint 2), and continuous graded W-Cu (pure W∼W-16 Cu)/W-52Cu (joint 3)), were prepared by tape casting and infiltration using W and graded W skeleton as substrates. Thermal shock tests at temperature of 800 °C-RT were conducted for the W/W-Cu joints. The microstructure and properties evolution, and damage behavior of the joints under thermal shock were studied by experiment combing with finite element modelling. The results show that, after thermal shock, a crack through the interface is found in joint 1. In joint 2, a main crack originates from the edge of the interface (the position of the maximum thermal stress) and extends inward, and some microcracks occur in the W side near the interface in joint 2. But there is no obvious crack in joint 3. Joint 2 has the highest initial shear strength of 287 MPa, and the joint 3 has the highest residual shear strength. After 150 thermal shocks, the shear strength of joint 3 decreases from 268 MPa to 185 MPa, and the strength loss rate is 30.97 %, while the loss rates of joint 1 and joint 2 are more than 70 %.

Physical and Mechanical Properties of Expanded Polystyrene (EPS) Particle Lightweight Soil under Freeze-Thaw Cycles.

In seasonally frozen regions, the bearing capacity of soil decreases and gradually deteriorates after undergoing freeze-thaw cycles. To resolve this problem, based on the idea of frost-resistant filling materials, a filling scheme of expanded polystyrene (EPS) particles lightweight soil in cold regions was proposed. Unconfined compressive strength, direct shear, and micro-SEM tests were carried out to study the physical and mechanical properties of EPS particles lightweight soil under freeze-thaw cycles. The results indicate that the EPS particle lightweight soil has good frost resistance and can be used as frost-resistant filling material in cold regions. Under freeze-thaw cycles, EPS particle lightweight soil maintains good integrity; EPS particles can effectively reduce the frost heave rate, mass loss rate, and compressive strength loss rate of lightweight soil. The compressive strength depends on the EPS and cement contents: it decreases with an increase in the EPS content and increases with an increase in the cement content. The strength loss rate decreases with an increase in both. When the content of EPS is larger (more than 2%), the soil cement bound with EPS particles is limited, and the performance of lightweight soil decreases. The shear strength and cohesion decrease with an increase in freeze-thaw cycles and EPS content, and the internal friction angle follows no obvious rule with regard to the increase in freeze-thaw cycles but decreases with an increase in the EPS content. Based on the experimental results, an empirical formula for the compressive strength of EPS particle lightweight soil under freeze-thaw cycles was proposed. This study can provide a reference for the engineering design and application and provide new ideas for resolving freeze-thaw problems in construction engineering in cold regions.

Beyond time: Enhancing corrosion resistance of geopolymer concrete and BFRP bars in seawater

To improve the durability of Basalt fiber reinforced polymer (BFRP) bars reinforced geopolymer concrete (GPC), it is important to study the time-dependent variation of the corrosion resistance ability of GPC and BFRP in a seawater environment. This paper presents an experimental investigation to study the time-dependent mechanical properties and durability of BFRP bars and geopolymer materials synthesized by granulated blast furnace slag (GGBFS), fly ash, and silica fume. The resulting GPC and Portland cement (PC) concrete were exposed to artificial seawater. The mechanical properties of GPC were evaluated by analyzing and comparing the volume expansion and strength loss rates of GPC and PC concrete in an artificial seawater environment. The corrosion resistance of geopolymer (GP) mortar and PC mortar was evaluated by studying the migration ability and pore structure in corrosive ions attack (Cl−, SO42−, Mg2+) in artificial seawater. Moreover, the time-dependent tensile strength of BFRP was comparatively investigated by immersing in different solutions (tap water, artificial seawater, and alkaline simulated seawater). In addition, the dual interface transition zones (ITZs) characteristics of BFRP reinforced GPC under artificial seawater were also investigated by SEM and BSE tests. The results showed that the volume expansion rate and strength loss rate of GPC decreased by 77.6% and 8.7%, respectively, after 360 days of seawater corrosion compared with PC concrete. This enabled the development of a time-dependent strength model of GPC in marine environments. The coefficient of ions diffusion in GP mortar is much lower than that of PC mortar, and GP mortar shows excellent resistance to ion migration. In addition, the effect of seawater corrosion on the tensile strength of BFRP bars increases with the increase of bars' diameter, and the ultimate strengths of BFRP bars with diameters of 6 mm and 8 mm were 695 MPa and 663 MPa, respectively. The tensile strength degradation model of BFRP bars in geopolymer concrete under seawater corrosion was established. After 360 days of seawater immersion, the average porosity of the ITZ between geopolymer and aggregates, and the average porosity of the ITZ between geopolymer and BFRP bars increased insignificantly compared to that of PC concrete. This research can provide a theoretical basis for the service life prediction of BFRP reinforced geopolymer concrete within marine environments.

Performance of a New Grouting Material under the Coupling Effects of Freeze-Thaw and Sulfate Erosion.

In order to study the performance of a new cement-based grouting material under the coupling of freeze-thaw cycle and sulfate erosion, tests related to the performance of the new grouting material were designed and carried out to analyze the damage mechanism of the material under the coupling of freezing and thawing and Na2SO4 solution by testing the mass change, relative dynamic elastic modulus, compressive strength loss and mineralogical and microstructural properties of the new grouting material. The test results show that with the increase in the number of freeze-thaw cycles, the mass loss and compressive strength loss of the specimens in 15% Na2SO4 solution gradually increased, and the relative dynamic elastic modulus showed a decreasing trend. When the freeze-thaw cycle number was 30, the mass loss rate, compressive strength loss rate and relative dynamic elastic modulus of the specimens in Na2SO4 solution were 4.17%, 24.59% and 84.3%, respectively, which showed better erosion and frost durability. Mineralogical and microstructural analysis showed that SO42- in solution led to the decomposition of the C-S-H gel and the formation of CaSO4•2H2O inside the specimen, and the internal deterioration was exacerbated by the widening of the crack width being aggravated, suggesting that the rate of material deterioration under the coupling of the two factors increased.