Abstract: This work investigates the differences in hydration and pore structure between cement-based materials prepared (i.e., mixed and set) under low and standard air pressures. The study is divided into two parts, namely, a simulation test and a field investigation. In the simulation study, hydration products, hydration degree and pore structures of cement pastes and air-void characteristics of mortars prepared under different simulated air pressures were analyzed. In the field study, the densities of cement pastes and densities, strengths and air-void characteristics of mortars prepared in regions under different air pressures were tested. The results show that hydration products, hydration process and pore structure of cement pastes prepared under various air pressures are essentially unchanged. Compared to the average radius and spacing factor of air-voids in the mortar prepared under standard air pressure, those of air-voids in the mortar prepared under low air pressure are respectively 3.1% and 8.1% lower; however, the difference in compressive strength is less than 0.5%. In general, low air pressure during mixing and setting stages do not negatively affect the properties of cement-based materials. Therefore, the properties of concrete to be used in construction projects in high-elevation locations can reliably be established by testing specimens prepared at low elevations.
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