Experimental study on microstructure evolution of aeolian sand concrete under the coupling freeze–thaw cycles and carbonation

Abstract

In order to study the influence of aeolian sand (AS), which is widely distributed in desert and sandy land areas, on the durability of concrete subjected environmental attack, some experiments of AS concrete at different conditions of freeze–thaw cycle and carbonation have been performed, while some microscopic tests, such as nuclear magnetic resonance (NMR), field emission scanning electron microscopy (SEM) and X-ray diffraction (XRD), were used to analyse the microstructure evolution of AS concrete. Results showed that, both freeze–thaw cycles and carbonisation have basically no influence on the number of pores with a radius of about 0.020 μm in AS concrete, which is the upper limit of gel pore size, but they can change the pore structure (porosity, pore size distribution) and relative dynamic elastic modulus. With increasing in the ratio of gel pore to harmful pore, there occur an increase in the relative dynamic elastic modulus and a decrease in the porosity of AS concrete, but the freeze–thaw cycle has more obvious influence on the relative dynamic elastic modulus and porosity than carbonation. AS can improve the freeze–thaw cycle and carbonisation resistance of concrete, and the AS concrete with 40% AS replacement has a more compact pore structure than ordinary concrete.