Analysis of damage models and mechanisms of mechanical sand concrete under composite salt freeze-thaw cycles

Mechanical sand concrete (MSC) deterioration in bridge engineering within cold -salt environments in the West was investigated. This study evaluated the salt -freezing resistance and damage models of granite mechanical sand concrete (GMSC) and tuff mechanical sand concrete (TMSC) under composite salt freezing -thaw cycles, using multiple indicators such as mass loss, relative dynamic elastic modulus, flexural strength, and compressive strength. A mechanistic study on the evolution of microscopic pores was conducted using nuclear magnetic resonance technology. The results showed that with an increase in composite salt freeze - thaw cycles, both TMSC and GMSC exhibited a decreasing trend in all indicators except for mass loss, which initially decreased and then increased. The relative dynamic modulus of elasticity decreased by 13.8 % and 17.4 % after 125 freeze - thaw cycles for TMSC and GMSC; compressive strength decreased to 36.16 MPa and 35.01 MPa; and flexural strength decreased to 4.977 MPa and 4.973 MPa, respectively. Combined with the T 2 spectrum analysis of NMR, it can be seen that with the increase of the number of freeze -thaw cycles of the composite salt, the internal porosity of the TMSC structure increases from 1.91 % to 2.55 %, and the GMSC from 2.1 % to 2.86 %, and the harmful pore percentage increases by 1.73 times and 1.75 times, in turn, compared with that before the freeze-thaw.Thus, TMSC demonstrated superior salt -freezing resistance compared to GMSC. This study offers a reference and guidance for adopting MSC in cold and salty western regions.