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

Abstract

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 T2 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.