Strains of high-performance and ordinary concretes depending on the cement paste volume and the w/c ratio

Abstract

The test results of 15 high performance concretes (HPCs) and ordinary concretes allowed to explain the influence of different volumes of cement paste on shaping the deformation properties of concrete under temporary compressive load. Increasing the volume of the paste by 100 dm3/m3 and reducing the volume of coarse aggregate at the same time reduces the modulus of elasticity and significantly increases the compressive strain at the peak stress. When increasing the volume of cement paste, smaller changes in properties were observed in ordinary concretes than in HPCs, modulus of ordinary concrete elasticity decreased by 4–9%, and compressive strains at the peak stress increased by 18–23%. However, in HPCs the changes are greater. Modulus changes are 7–28% and strains at the peak stress changes are from 19% to 41% at w/c = 0.25. It was found that the compressive strength of all concretes with the smallest volume of cement paste at each w/c ratio from 0.25 to 0.60 was the highest. Increasing the volume of cement paste in concretes for each w/c ratio causes a large increase in the compressive strains at peak stress.Hence, the likely causes of changes in the examined properties are the reduced adsorption of water on the smaller surface area of the aggregate, which dries less bulk cement paste, increasing the aggregate-cement paste interfacial transition zone (ITZ) width, which is visible on the scanning electron microscopy (SEM) images taken. When the volume of the aggregate is larger and the volume of the paste is smaller, as a result of water adsorption by the larger surface area of the aggregate grains, the actual (effective) w/c ratio in bulk paste decreases, resulting in improved strength and deformation properties.