Improvement Of Recycled Concrete Aggregate Properties By CO₂Curing

As a sustainable construction materials, recycled aggregate(RCA) produced byconstruction and demolition waste aim to replace natural aggregate. However,conventional recycled aggregate are attached on large amounts of cement paste.Because hardened cement paste is porous and contains abundant calcium silicatehydrates, RCA have higher water absorption and lower strength. These characteristicshave negative effects on properties of fresh and hardened concrete containing RCA,and limit its utilization.This paper adopts carbon dioxide treating RCA to improve the properties of RCA,and the properties of mortar prepared with RCA treated by carbon dioxide. The mainachievements are stated as follows:Carbon dioxide treating method can improve the physical and mechanicalproperties of RCA. It is found that the water absorption of RCA decreases, densityincreases by carbon dioxide treating. calcium silicate hydrates and calcium hydroxide,the main products of hydrated cement paste, can react with carbon dioxide andproduce calcium carbonate and silica gel. Carbonation products have higher molarvolumes than the parent hydrates calcium hydroxide and calcium silicate hyd rates, soan increase of density is expected.Carbon dioxide treating method has an obvious impact on RCA produced byoriginal concrete with lower strength. Those RCA gaines great enhancement on thephysical and mechanical properties, which are equivalent to, in some cases, evensuperior to those of RCA produced by original concrete with higher strength.The properties of mortar made with RCA treated by carbon dioxide are enhanced,such as the compressive strength, drying shrinkage and water absorption, are superiorto those of mortar made with RCA with no treatment.