The Qinghai–Tibet Plateau is the main permafrost area in China. Concrete structures constructed on permafrost are affected by the early negative-temperature environment. In particular, the negative-temperature environment seriously affects the strength growth process and the frost resistance of concrete (FRC). Therefore, this study considered the influence of the gas content, water–binder ratio (w/b), age, and other factors on the strength variation law and FRC under −3 °C curing conditions. Nuclear magnetic resonance (NMR) was used to analyze the pore structure of concrete before and after freeze–thaw cycles (FTCs). The results showed that the compressive strength of the concrete (CSC) under −3 °C curing was only 57.8–86.4% of that cured under standard conditions. The CSC under −3 °C curing showed an obvious age-lag phenomenon. The FRC under −3 °C curing was much lower than that under standard curing. The porosity of the concrete under −3 °C curing was greater, with a higher percentage of harmful and multi-harmful pores than that under standard curing. The concrete properties deteriorated primarily because curing at −3 °C hindered the hydration reaction compared with standard methods. This hindrance resulted in diminished hydration development, weakening the concrete’s structural integrity. Under both curing conditions, when the gas content was between 3.2% and 3.8%, the frost resistance was the best. This is because a gas content within this range effectively enhances the internal pore structure, therefore relieving the swelling pressure caused by FTCs. Based on the freeze–thaw damage (FTD) model proposed by previous authors, a new model for the CSC under −3 °C curing reaching that of the concrete under standard curing for 28 d was established in this study. This advanced model was capable of accurately assessing the FTD of concrete structures in permafrost regions. Finally, the life expectancy of concrete in Northwest China was predicted. The life of the concrete reached 46.9 years under standard curing, while the longest life of the concrete under −3 °C curing was only 12.9 years. Therefore, attention should be paid to constructing and curing concrete structures in cold environments.

To research the performance of low-temperature sulfate corrosion resistance of concrete mixed with stone-powder in saline soil area of Qinghai-Tibet Plateau. In this work, the influence of the water-to-binder ratio and stone powder types on the low-temperature sulfate erosion behavior of cement-based materials was studied, and in order to predict its erosion life, a Wiener stochastic process model was established. The results show the following: 1) The samples of limestone powder cement-based materials (LCBM) with different water-to-binder ratios showed the same law in sulfate erosion; the greater the water-to-binder ratio is, the more serious the sample is eroded, and the difference is the rate of erosion reaction. The greater the water-to-binder ratio is, the earlier the characteristic peak of thaumasite appears. The electric pulse accelerated erosion lifetimes of the cement-based limestone powder with water binder ratios of 0.3, 0.4 and 0.5 were 185 days, 136 days and 110 days, respectively. 2) Quartz stone powder cement-based materials (QCBM) showed different erosion laws compared with LCBM. When soaked in sulfate, the macroscopic and microscopic changes of QCBM were basically in a mineral additives state, However, when the electric pulse accelerated the erosion, the QCBM was more severely attacked than the LCBM. The final erosion products of the cement-based limestone powder with water binder ratios of 0.4 are not only gypsum and ettringite but also thaumasite, while the quartz powder cement-based materials with water-binder ratios of 0.4 are only gypsum and ettringite.

A persistent-luminescent epoxy composite was developed by incorporating SrAl₂O₄:Eu²⁺,Dy³⁺ (SAO), Al₂O₃ nanoparticles, and carboxylated cellulose nanofibers (CNFs) into an epoxy matrix. Its tribological behavior, tribofilm formation and evolution, and post-wear persistent luminescence were systematically investigated under reciprocating sliding against steel. The results show that Al₂O₃ markedly reduced material loss and promoted a milder wear regime, while CNFs maintained the improved wear resistance and partially restored late-stage persistent luminescence retention before sliding. Interfacial analyses revealed the formation of organic-inorganic tribofilms on both the worn composite surface and the steel counterface. The worn-surface tribofilm contained epoxy-derived debris and retained SAO-related components, whereas the counterface tribofilm contained transferred composite-derived species together with tribo-oxidation products of the steel surface. The interfacial tribofilm system is considered to contribute to surface protection by reducing sustained direct contact, while the more developed worn-surface tribofilm favors the retention of SAO-related components. However, its dark and compacted state may attenuate light emitted from the worn region. This work provides a mechanistic basis for understanding and regulating the coupled mechanical and optical functions of tribofilm in persistent-luminescent polymer composites.

To address the high carbon emissions generated during the production of cement, lime, and other traditional soil stabilizers and to promote the resource utilization of industrial solid waste, this study proposed a low-carbon loess stabilization scheme using tuff powder (TP), fly ash (FA), and ground granulated blast-furnace slag (GGBS) activated by alkaline solutions to fully substitute conventional cement and lime. A series of macroscopic tests, including unconfined compressive strength, water immersion, and triaxial shear tests, were carried out on stabilized loess. Combined with microcharacterization including X-ray diffraction (XRD), scanning electron microscopy (SEM), and nuclear magnetic resonance (NMR) spectroscopic testing, this study systematically evaluated the mechanical performance, water stability, and microstructural evolution of stabilized loess and quantified its global warming potential (GWP). Macroscopic test results reveal that the composite binder consisting of 15% multi-source solid waste (TP:FA:GGBS) = (1:1:3), 3% NaOH, and 3.2% Na₂SiO₃ (relative to solid waste mass) delivers the optimal comprehensive performance of stabilized loess. Alkali activation significantly accelerates early strength development, and both compressive and shear strengths are markedly improved compared with samples treated solely with solid waste. Furthermore, decreasing the activator modulus further enhances mechanical properties and water resistance. Microscopic characterizations demonstrate that alkali activation stimulates the pozzolanic reaction of active components in solid waste, generating cementitious gels that bind soil particles and unreacted solid waste to form dense network matrices. As a fine filler, TP also acts as a nucleation sites for hydration product crystallization, which facilitates the formation of cementitious phases.

In this paper, a highly ductile polyvinyl alcohol fiber engineered cementitious composite (PVA-ECC) was developed by replacing quartz sand (QS) with tuff stone powder (TP) at different replacement ratios of 20%, 40%, 60%, 80%, and 100%. The resulting mechanical properties and drying shrinkage were determined for the developed ECC. Qualitative and quantitative analyses of hydration products, pore structure, and micro-morphology of ECC were conducted by X-ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy, pore size and porosity, and scanning electron microscopic imaging. The influencing mechanism of tuff stone powder content on ECC performance was also studied at a micro level. It was found that with the increase in the replacement ratio of tuff stone powder, the ultimate tensile strain and tensile peak stress of ECC all exhibited an increasing trend, which declined afterward. The variation in compressive and flexural strengths also showed a similar pattern. When the replacement ratio of tuff stone powder was 40%, the ultimate tensile strain, peak tensile stress, flexural strength, and compressive strength were higher than the control group by 15.1%, 4.7%, 16.3%, and 10.7%, respectively. When the content of tuff stone powder did not exceed 80%, it could fill the internal pores of the ECC matrix, which reduced harmful pores. With the increase in tuff stone powder content, calcite content increases gradually while the Ca(OH)₂ amount decreases. It can be seen that tuff stone powder can improve ECC hydration products. However, incorporating tuff stone powder does not produce new hydration products. Incorporating tuff stone powder increased the drying shrinkage of ECC, and the value of drying shrinkage increased with the increase in the replacement ratio of tuff stone powder.