Because of the increasing difficulty in obtaining natural aggregate, alternative aggregates have been considered in the construction industry. One of the feasible alternatives is to reuse construction and demolition waste as aggregates, called recycled aggregate, to make new concrete called recycled aggregate concrete (RAC). However, the compressive strength of RAC is usually poor due primarily to the high water absorption capacity, high porosity, and weaker bond of interfacial transition zone between recycled aggregate and new cement mortar. This paper presents the results of a comprehensive experimental study on RACs made of 100% recycled coarse aggregate. Three different mixing approaches, several surface pretreatment methods with two different pretreatment materials were used to improve the compressive strength of RAC. The experimental results showed that proper surface pretreatments and mixing approaches can improve the quality of RAC significantly. The water-cement ratio of pretreatment mate...

The purpose of this paper is to investigate the diffusivity of the interfacial transition zone (ITZ) experimentally using cementitious composite materials made of rod-shaped aggregates and cement mortar. Two types of tests were conducted: the porosity distribution of the ITZ at different distances from aggregate surface was measured by backscattered electron images, and the water vapor diffusivity of the composites was measured by the penetration rate of water vapor through thin slides of specimens. The surface roughness of rod-shaped aggregates was considered as a testing parameter. The diffusivity of ITZ was calculated based on the measured diffusivities of the composite and it was also modeled according to the measured porosity distribution within the ITZ. The results showed that the porosity of ITZ decreases with increasing distance from the aggregate surface, a rougher aggregate surface decreases the porosity of ITZ in the first 10 μm from the aggregate surface, and the ratio of averaged wate...

Most concrete structures and buildings are under temperature and moisture variations simultaneously. Thus, the moisture transport in concrete is driven by the moisture gradient as well as the temperature gradient. This paper presents an experimental approach for determining the effect of different temperature gradients on moisture distribution profiles in concrete. The effect of elevated temperatures under isothermal conditions on the moisture transport was also evaluated, and found not to be significant. The non-isothermal tests show that the temperature gradient accelerates the moisture transport in concrete. The part of increased moisture transfer due to the temperature gradient can be quantified by a coupling parameter D_HT, which can be determined by the present test data. The test results indicated that D_HT is not a constant but increases linearly with the temperature variation. A material model was developed for D_HT based on the experimental results obtained in this study.