Improvement on strength and impermeability of recycled concrete made from crushed concrete coarse aggregate: Fid-Bau Portal

Improvement on strength and impermeability of recycled concrete made from crushed concrete coarse aggregate

Ryu, J.S.

It is generally accepted that the qualities of the mortar and the interface zones, as well as the mortar content of the original concrete, thus influence the properties of the recycled aggregate concrete. Following from this background, experiments were performed to examine the characteristics of recycled concrete made from crushed concrete coarse aggregate and to improve its strength and impermeability. More types of interfaces exist in concrete with recycled aggregate than in normal aggregate concrete. There is one interface between the original aggregate and the adhesion mortar (old interfacial transition zone (ITZ)) and another interface between the adhesion mortar and the new mortar in the recycled aggregate concrete (new ITZ). In order to improve the new ITZ at higher water-cement ratio and thus improve the strength and impermeability of the recycled concrete, two methods were examined: (1) the double mixing method (DM), and (2) the fly -ash addition method. It is shown that compressive strength and tensile strength increase by using DM and FA methods. For the case of the DM method, it is shown that compressive strength is increased by 17% and tensile strength is increased by 26%, compared with the control concrete. It is also proven that ITZ Vickers hardness of the concrete produced by DM method is larger than that of the control concrete.The chloride ion penetration test was carried out to examine the effectiveness of two improvement methods against permeability of the concrete. The Cl(-) penetration depht of DM and FA specimens was shallower than that of the control specimen.