Grey entropy analysis on effect of pore structure on compressive strength of aeolian sand concrete

Abstract: Aeolian sand is an ultra-fine sand formed by wind and sedimentation in the desert and Gobi region，its SiO2 content is higher than that of ordinary sand, and its particle size is smaller than that of ordinary sand. Abundant aeolian sand resource can be used to prepare a new type of green concrete. In order to investigate the influence of the pore structure of aeolian sand concrete on the compressive strength, the aeolian sand concrete and the ordinary concrete are selected as the research group and the control group, respectively, and the compressive strength of which is tested. With the help of nuclear magnetic resonance testing technology, the lateral relaxation time distribution of the two groups of concrete is determined for 3, 7, 14, 21 and 28 days curing ages. According to the relationship between the lateral relaxation time and the pore radius, the pores of the two groups of concrete are divided into four intervals: 0-0.1, >0.1-1.0, >1.0-10 and >10 μm. Meanwhile, the influence of pore structure parameters and pore radius distribution on the compressive strength of the two concretes under different curing ages is studied by using grey correlation entropy analysis. Based on this, the relationship between concrete pore structure and compressive strength is established. The results show that the lateral relaxation time curve of aeolian sand concrete mainly present the structure of "primary and secondary peaks", and the ordinary concrete mainly present "three peaks" structure. The lateral relaxation time of aeolian sand concrete is between 1.703-5 353.567 ms, and the lateral relaxation time of ordinary concrete is between 2.097-4 347.013 ms. The spectral area of the two concretes first increase and then decrease with the curing age. The maximum spectral areas of the aeolian sand concrete and the ordinary concrete are 11 789.33 and 10 672.11, respectively. The porosity of the two concretes first increase and then decrease. However, after 28 days hydration reaction, the porosity of aeolian sand concrete increase by 14.3%, from 3.5% to 4.0%, with the decrease of saturation of bound fluid by 5.6% and the increase of the free fluid saturation by 2.2%. The hydrated product preferentially fill the small pores during the hydration process of the aeolian sand concrete. The porosity of ordinary concrete decrease by 16.1%, from 3.1% to 2.6%, with the increase of saturation of bound fluid by 66.7% and the decrease of the free fluid saturation by 11.2%. The hydrated product preferentially fill the large pores during the hydration process of the ordinary concrete. After 28 days of hydration reaction, the proportion of pore radius in the range of 0-0.1, > 0.1-1.0 and > 10 μm of aeolian sand concrete decreases, the proportion of pore radius in the range of > 1.0-10 μm increases, the pore radius in the range of 0-0.1-1.0 μm of ordinary concrete increases, and the pore radius in the range of > 1.0-10 and > 10 μm decreases. The most influential factors for the compressive strength of the two concretes are the saturation of bound fluid and the proportion of pore radius of 0-0.1 μm. The grey entropy correlation degrees of the saturation of bound fluid of the two concretes are 0.980 4 and 0.979 1, respectively. The grey entropy correlation degrees of 0-0.1 μm pore proportion of the two concretes are 0.988 2 and 0.988 8, respectively. A grey model GM (1, 3) is established for the influence of saturation of bound fluid and proportion of pore radius of 0-0.1 μm on the compressive strength of concrete. The average relative errors between predicted values and experimental values of two concrete GM (1,3) models are 4.11% and 2.43%, respectively. This study provide a reference for practical engineering applications of aeolian sand concrete.