EFFECT OF CALCIUMM LEACHING ON THE PROPERTIES OF CEMENT-BASED COMPOSITES

Cement-based composite is a porous material and may have severe damage such as rebar corrosion or leaching by long-term contact with water. Leaching process mainly induces calcium leaching and a progressive decalcification of hydrated calcium silicate. The cement hydrate would gradually dissolve toward the external surroundings. It is conjectured that the pore structure becomes coarser with dissolution of cement hydrate which results in the increase of permeability and decrease of strength of cement-based composites. Leaching is one of the major factors that alter the mechanical properties of cement-based composites. This study is aimed to investigate leaching effect on the properties of cement-based composites. Different specimens with two water/cementitious ratios and two mineral admixtures were cast and tested. An external electrical potential was applied to accelerate the leaching process. Compressive strength test, scanning electronic microscopy, thermo gravimetric analysis and X-ray diffraction analysis were conducted. Test results demonstrate that the calcium leaching reduces compressive strengths of concrete specimens, and the reduction effect is most prominent on the specimens without mineral admixtures. The leaching resistance increases with an increase in water/cementitious ratio and inclusion of mineral admixtures. The mineral admixtures would reduce the amount of calcium hydroxide and refine the pore structure through pozzolanic reaction. A fair relationship is found between calcium leaching and compressive strength.