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In this study, aeolian sand was used as fine aggregate to partially replace natural river sand in the range of 25 to 100% to prepare aeolian sand concrete (ASC). The ASC under freeze–thaw conditions in chloride environment was studied. Based on the compressive strength loss rate and the relative dynamic modulus of elasticity (the relative DME) obtained from the study as damage variables and combined with the Weibull distribution model, the freeze–thaw damage model of ASC was established to predict the service life of ASC in China's northwestern cold regions. The microstructure of ASC under freeze–thaw conditions was also observed and studied. The results showed that 100% ASC had the best frost resistance, and the compressive strength loss rate and relative dynamic elastic modulus after 200 freeze–thaw cycles were 18.2 and 90.8%, respectively. These evaluation indexes show that the concrete has not reached the freeze–thaw damage state. The linear damage evolution model can accurately predict the durability of ASC in a cold environment, and predict that the service life of 100% ASC in 3.5% chloride solution is more than 25 years, which meets the requirements of concrete in water conservancy projects in Northwest China. [ABSTRACT FROM AUTHOR]

As one of the key materials used in the civil engineering industry, concrete has a global annual consumption of approximately 10 billion tons. Cement and fine aggregate are the main raw materials of concrete, and their production causes certain harm to the environment. As one of the countries with the largest production of industrial solid waste, China needs to handle solid waste properly. Researchers have proposed to use them as raw materials for concrete. In this paper, the effects of different lithium slag (LS) contents (0%, 10%, 20%, 40%) and different substitution rates of recycled fine aggregates (RFA) (0%, 10%, 20%, 30%) on the axial compressive strength and stress-strain curve of concrete are discussed. The results show that the axial compressive strength, elastic modulus, and peak strain of concrete can increase first and then decrease when LS is added, and the optimal is reached when the LS content is 20%. With the increase of the substitution rate of RFA, the axial compressive strength and elastic modulus of concrete decrease, but the peak strain increases. The appropriate amount of LS can make up for the mechanical defects caused by the addition of RFA to concrete. Based on the test data, the stress-strain curve relationship of lithium slag recycled fine aggregate concrete is proposed, which has a high degree of agreement compared with the test results, which can provide a reference for practical engineering applications. In this study, LS and RFA are innovatively applied to concrete, which provides a new way for the harmless utilization of solid waste and is of great significance for the control of environmental pollution and resource reuse. [ABSTRACT FROM AUTHOR]

The coal gangue coarse-aggregate content in ordinary concrete should not be too large. In order to further improve the utilization rate of coal gangue coarse aggregate, this study used the principle of "strong wrapped weak" to prepare high-performance concrete. This study considered four factors, namely, water–binder (W/B) ratios, non-spontaneous combustion coal gangue (NCCG) coarse-aggregate contents, fly ash–slag mass ratios, and silica fume coating to prepare high-performance concrete. The workability, mechanical, and durability properties were studied, and the changes in the interfacial transition zone (ITZ) of concrete before and after sulfate attack and freeze–thaw cycles were analyzed based on the SEM test. The life prediction of NCCG coarse-aggregate high-performance concrete was carried out based on the grey system GM(1,1) prediction model. The results show that the NCCG coarse-aggregate contents have the greatest effect on compressive strength, sulfate resistance, and frost resistance. The W/B ratio has the greatest effect on the anti-carbonization properties. Fly ash–slag mixing can obtain better durability. Considering the effect on the design service life of high-performance concrete, NCCG coarse aggregate is used to prepare high-performance concrete in North China, and the recommended content is 60%; in the Northwest and Northeast regions, the recommended content is 45%. This study provides a basis for the preparation of high-performance concrete with NCCG coarse aggregate. [ABSTRACT FROM AUTHOR]

Concrete is a commonly utilized material in the construction of infrastructure in Northwest China. However, its durability in saline environments is hindered by its susceptibility to salt and freeze-thaw erosion. By incorporating basalt fibers (BF), reticulated polypropylene fibers (RP), and calcium carbonate whiskers (CW) into concrete, the crack resistance of the material can be enhanced from the micro to macro level. Previous research has yet to thoroughly examine the enduring erosion resistance of CW-BF-RP concrete (CBPC) over extended periods amidst diverse salt-freezing conditions. Additionally, the precise mechanism through which CW impacts the deterioration of the interfacial transition zone (ITZ) between fibers and the cement matrix remains incompletely elucidated. This study examines the variability in compressive strength, mass loss, and damage degree of CBPC when exposed to various types of salts (sulfate/chloride) and erosion conditions of different concentrations. And the corrosion mechanism of CBPC in different freeze-thaw conditions was revealed by Fourier Transform Infrared Spectroscopy, Thermogravimetry, Nuclear Magnetic Resonance, Scanning Electron Microscopy and Atomic Force Microscopy. The findings suggest that the strength reduction rate, mass loss rate, and damage degree of CBPC increase with the rise in salt concentration and freeze-thaw cycles. The three indicators in chloride salt conditions are significantly higher than FW, with values of 78.64%, 223.6%, and 309.0%, respectively, compared to 47.63%, 155.4%, and 162.4% in S-3, indicating that CBPC exhibits greater resistance to sulfate salts than chloride salts. The consumption of CH is a key factor in the occurrence of AFt and Friedel's salt and pore degradation. Concrete pore degradation between 3.25μm and 6.81μm leads to rapid disintegration, with detachment of the mortar occurring when the pore size reaches 31.95μm. CW maintains its integrity in sulfate salt and FW conditions, but experiences severe corrosion in chloride salt. At this point, the maximum ITZ of 7.5 μm for BF is less than that of 22.8 μm for RP, indicating that the bonding of BF to the matrix is stronger than that of RP. The longitudinal height difference of fiber-cement aggregate ITZ in chloride conditions ranges from 42.8 nm to 59.8 nm, creating water channels of 5.70μm to 6.91μm, thereby weakening the adhesion of the matrix. Finally, a Wiener stochastic model is established for life prediction under different salt-freezing conditions, with the maximum life expectancy in sulfate conditions being 1.26–1.86 times that in chloride conditions. These research findings can provide theoretical references for the durability design of concrete in the salt-freezing areas of northwest China. • Add CW-BF-RP into concrete to study the freeze-thaw endurance degradation law. • The decrease rate of each index of concrete increases with the increase of salt concentration. • CW suffers from severe corrosion due to the decrease of concrete alkalinity in chloride salt condition. • ITZ deterioration in chloride salt condition is significantly greater than that in sulfate and FW conditions. • Wiener stochastic model can effectively characterise the endurance life of concrete in salt-aggressive environments. [ABSTRACT FROM AUTHOR]

In the construction industry, it is imperative to replace natural sand with manufactured sand. The environment in northwest China is very complex and harsh. The application of manufactured sand concrete in such a harsh environment needs scientific and comprehensive research to meet the requirements. However, there is a gap in the study of sulfate freeze-thaw resistance of manufactured sand concrete in the complex environment of Northwest China. Therefore, this study investigated the northwest environment, designed an indoor sulfate freeze-thaw cycle experiment system close to the real environment, and designed a conductive titration method to test the sulfate ion content in hardened concrete. The influence of the freeze-thaw cycle on the diffusion depth of sulfate ions in manufactured sand concrete was studied. Finally, the following conclusions are obtained: In the process of conductometric titration, hydrochloric acid is used as the dissolution solution, Ag 2 O and CO 2 are used as neutralizers, and Ba(NO 3) 2 is used as the titration solution, which can perfectly eliminate the significant influence ions in the test solution, and can accurately test the content of sulfate ions in hardened concrete. The sulfate ion content of concrete at different depths was tested, and it was found that the two sides of sulfate erosion caused by freeze-thaw cycles were mainly reflected in about 100 freeze-thaw cycles. The limit number of freeze-thaw cycles N 0 and the limit diffusion depth X 0 are proposed, and the diffusion equation of manufactured sand concrete under the action of sulfate freeze-thaw cycles is derived. The proposed diffusion parameter v is unique to the concrete, which can well judge the sulfate freeze-thaw resistance of the concrete. When v is closer to 0, it shows that the resistance of concrete to sulfate freeze-thaw erosion is better. For the northwest environment of China, the manufactured sand concrete should ensure v < 6; the environment in Northwest China has a very complex multi-factor erosion environment. It is worth noting that this study is only applicable to laboratory conditions. To improve the accuracy and reference value of experimental research, future research needs to add more comprehensive environmental impact factors and collect actual data in the northwest environment of China for verification. • A detailed conductivity test method for sulfate ion content in hardened concrete was designed. • The diffusion equation of manufactured sand concrete under sulfate freeze-thaw cycles is derived by proposing the limit number of freeze-thaw cycles N 0 and the limit diffusion depth X 0. • The diffusion parameter v proposed by is a new concept, which can be used to judge the key index of sulfate freeze-thaw damage, and is of great significance for evaluating the frost resistance of manufactured sand concrete in the northwest environment of China. [ABSTRACT FROM AUTHOR]

As the drilling shafts in the western mines of China are going to cross the deep water-rich and weakly cemented rock layer, investigating the mechanical properties and energy evolution of shaft lining concrete within the context of hydro-mechanical coupling is crucial. In this study, concrete compression tests were conducted using the TAW-2000 rock testing machine. The concrete damage and rupture mechanisms were analyzed using a combination of mercury intrusion porosimetry and scanning electron microscopy. Moreover, a thorough investigation of the energy evolution throughout the concrete stress-strain process was conducted. The key results include the following: (1) The formulation of the normalized decay equation for the characteristic strength of concrete under hydraulic coupling was derived by computing the ratio of pore water pressure to confining pressure as the characteristic parameter. (2) The effective shear strength reduction factor characterizing the impact of water pressure on the effective shear stress with a correlation coefficient greater than 0.999. (3) The pore water pressure adversely affected the pore size distribution within the concrete, enhancing the connectivity between pores. (4) The total input energy, elastic energy, and dissipated energy were positively related to the confining pressure and negatively related to the pore water pressure. The energy consumption ratio served as a tentative criterion for assessing the strength failure of the shaft lining concrete, which is considered to be in a critically stable state when the energy consumption ratio is 1. These results provided valuable insights into the damage laws and energy-driven mechanisms of shaft-lining concrete under hydraulic coupling conditions. • The formulation of the decay equation for the characteristic strength of concrete under hydraulic coupling was derived. • The impact of water pressure on the effective shear stress was analyzed according to the effective stress principle. • The concrete damage and rupture mechanisms were analyzed by mercury intrusion porosimetry and scanning electron microscopy. • The energy evolution law of shaft lining concrete under hydro-mechanical coupling was obtained. [ABSTRACT FROM AUTHOR]