Relationship between fractal feature and compressive strength of fly ash-cement composite cementitious materials

Abstract

Microscopic pore structure and compressive strength of fly ash-cement composite cementitious materials at 20 °C and 60 °C measured by mercury intrusion porosimetry and compressive strength test. Microscopic pore structure was analyzed from porosity, pore volume, total pore surface area, average pore diameter, median pore diameter, most probable diameter, threshold diameter and fractal feature. The fractal dimensions of each specimen were calculated by Menger Sponge. The regression analysis between fractal dimension and pore structure parameters were fitted by linear function, quadratic polynomial function, power function and exponential function, respectively. Eventually, the relationship between pores structure and compressive strength was characterize by the mathematical model between the optimal comprehensive parameter of pores structure and compressive strength. And the T-test and F-test were used to reveal the significance of the regression parameter and function. Research results showed that the fractal curves of all specimens consist of four segments. The pores have obvious fractal features in Region I and Region IV, while presented no-fractal feature in Region II and Region III. In Region I and Region IV, fractal dimension followed the exponential function with average pore diameter, median pore diameter, most probable diameter and threshold diameter, consistent with quadratic polynomial function with porosity, pore area and pore volume, and accords with the positive power exponential function with compressive strength. Thus, the morphology of hierarchical aggregates expressed by fractal dimension can reflect the relationship compressive strength and pore structure in fly ash-cement composite cementitious materials more directly.