Study on gas transport characteristics of manufactured sand concrete and modeling of random hierarchical bundle based on pore structure

Overexploitation of natural sand has caused severe damage to the environment, and manufactured sand to replace natural sand has become an inevitable trend in construction projects. Anti- gas permeability performance is an important index characterizing the durability of concrete, and its performance directly affects the service life and quality of concrete structures. This study evaluates the feasibility of applying manufactured sand to concrete based on its mechanical properties. In addition, we systematically investigated the influence of the properties of manufactured sand on the pore structure and gas permeability resistance of concrete with different strength grades. Furthermore, we established a random hierarchical bundle model based on the nuclear magnetic resonance(NMR) and predicted the gas permeability coefficient by simulating the pore structure distribution of concrete. The following test results were derived: First, at the same strength grade, the late compressive strength of limestone (LMS) and granite manufactured sand (GMS) concrete is higher than that of natural river sand (NRS) concrete. Therefore, choosing manufactured sand as a fine aggregate to formulate concrete in practical engineering applications is feasible. Secondly, by comparing the gas permeability resistance of concrete with different fine aggregate mechanism sands, it was found that small aggregate particles can significantly improve the gas permeability resistance of concrete. Finally, the pore structure significantly affects the anti-gas permeability property of manufactured sand concrete, in which the pore content in the range of 10-100 nm is the main factor affecting the gas permeability coefficient. Moreover, the NMR-based stochastic layered beam model predicts the gas permeability resistance of concrete with a maximum deviation of up to 30.89 %.