Analysis of the influence of porosity of macroscopic pore on concrete strength by image method

Fifteen kinds of concrete with different air contents(by volume) were prepared by adjusting the air product(AP). The relationships between the 3, 7, 28d compressive strengths of concrete and air contents were investigated. An image analysis method was used to study the porosity(by volume) of macroscopic pore(diameter>200×103nm) of concrete with different air contents, and the effects of porosity of macroscopic pore and air content on 28d compressive strength of concrete were studied. The results show that 28d compressive strength of concrete has a stronger linear relationship with air content, and 3, 7d compressive strengths of concrete have a weaker linear relationship with air content. The sensibility of 28d compressive strength on the change of porosity of macroscopic pore is larger than that on the change of air content, which means that the porosity of macroscopic pore of concrete effects 28d compressive strength more significantly. By adjusting the air product the air content can be increased from 1.5% to 9.0% with porosity of macroscopic pore only increasing from 0.81% to 1.48%, and the ratio of porosity of macroscopic pore to air content can be decreased from more than 55% to 16% or so. It indicates that the air content of concrete can be controlled effectively, and the amount of macroscopic pore can be limited at the same time. ©, 2015, Tongji University. All right reserved.