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The strength prediction of pervious concrete is hard to implement for the mix design due to the porous structure. This work studied the influence of the water-to-cement ratio on the fluidity, viscosity, and mechanical properties of cement paste. Then, the porosity, permeability, and compressive strength of the pervious concrete with various porosities were investigated, and the test results were fitted and analyzed. The result indicates that as the water-to-cement ratio increases, the viscosity of the cement paste reduces and the fluidity increases. The water-to-cement ratio has a negative linear relationship with net slurry strength. The porosity and permeability of pervious concrete fluctuate in accordance with the same rule as the water-to-cement ratio changes. The compressive strength of pervious concrete with varying design porosities increases initially, then declines as the water-to-cement ratio rises. According to the linear fitting analysis, when the water-to-cement ratio is constant, the permeability and compressive strength of pervious concrete have a positive and negative linear relationship with the design porosity, respectively. By analyzing the fitting results and combining the volume method of pervious concrete, a calculation method for mix proportion design is proposed to predict the strength of pervious concrete.

Mixing cement with seawater will cause the hydration process of cement to be different from that of ordinary cement, which will significantly affect cement's mechanical properties and durability. This article investigates the effects of chloride ion concentration, curing temperature, and nano-metakaolin content on the evolution process of Friedel's salts and ettringite (AFt) crystals in cement pastes. The study was conducted using X-ray diffraction (XRD), thermal analysis (TG), scanning electron microscopy (SEM), and mercury-intrusion porosimetry (MIP). The results show that chlorine salt can increase the production of Friedel's salt and ettringite, and the delayed AFt production increases by up to 27.95% after the addition of chlorine salt, which has an adverse effect on cement-based materials. Increasing the curing temperature and increasing the nano-metakaolin dosage increased the generation of Friedel's salt and decreased the delayed AFt generation, which resulted in a decrease in the length and diameter of the AFt crystals. After 28 days of high-temperature curing and the addition of nano-metakaolin, Friedel's salt production increased by 13.40% and 14.34%, respectively, and ettringite production decreased by 9.68% and 7.93%, respectively. Increasing the curing temperature and adding nano-metakaolin can reduce the adverse effect of delayed ettringite increases due to chloride ion binding. [ABSTRACT FROM AUTHOR]

The significant effect of desert sand on cement-based composites was observed in the previous investigation. However, how the composition of fine aggregate affects the formation of air void structure remains to be investigated. In this paper, mortars composed of five different sand mixtures were prepared, and the specific surface area (SSA) of the sand mixture with different content of fine aggregate was calculated. It was observed that the air void content decreased as the SSA value of the sand mixture increased. A negative-slope linear relation was observed between the SSA values and air void content in the composite construction sand fiber reinforced mortar system. With the increase of SSA, the air void number of every high-strength fiber reinforced mortar decreased from 12,446 to 6652. With the gradual increase of desert sand content, the count of air void number decreased. When the fine aggregate was completely desert sand, the air void content of the fiber-reinforced mortar dropped from 1.21% to 0.98%. Through the analysis of the 3D air void system, it can be concluded that the mixture of fine aggregate with different particle size distributions plays a positive role in optimizing the air void characteristics. Reasonable utilization of desert sand can significantly improve the pore structure characteristics and compressive strength of cement-based composites, which provides an effective theoretical basis for the development and utilization of desert sand resources. The function of different kinds of construction sand in the formation of air-void structure was investigated by X-CT technology. A negative-slope linear relationship was discovered between specific surface area (SSA) values and the entire air void content in the composite construction sand fiber reinforced mortar system. The mixture of river sand and desert sand plays a positive role in optimizing the air void characteristics and compressive strength. [ABSTRACT FROM AUTHOR]