Properties of concrete with recycled construction and demolition wastes: a research experience in belgium

Construction waste management is a quite important economic and environmental deal for our societies. More than 2 million tons demolition and construction wastes are annually produced only in Wallonia, Southern Region of Belgium; recycling has clearly to be promoted.
Concrete block wastes were crushed in the laboratory by a jaw crusher and the different fractions of laboratory produced RCA were characterized by measuring the hardened cement paste content, the density, the porosity and the water absorption. Results clearly show that, the recycled sands possessed significantly higher cement paste content and higher water absorption than coarse RCA. Then, concrete blocks with different substitutions (0%, 30%, 100%) of natural aggregate by the same volume fraction of RCA were manufactured. The fresh properties (slump, density, air content), and mechanical properties (compressive strength) were studied. The compressive strength of concrete decreased as the substitution of RCA increased. Results show that the compressive strength of concrete made with 100% RCA could reach 8 MPa after 28 days. Therefore, the use of RCA obtained from old block wastes in the production of new blocks can be envisaged depending on their class of exposure and the grade requirement.
Moreover, the influence of the fine recycled concrete aggregates (FRCA) on the mechanical and durability properties of concrete was studied. The industrial FRCA produced from recycling center was used into concrete. The concretes with different substitutions (0%, 30%, 100%) of natural sand by the FRCA were manufactured. Mechanical properties (compressive strength) and durability properties (capillary absorption, carbonation depth, and freeze/thaw resistance) were investigated. The results show that the compressive strength of concrete decreased as the substitution of FRCA increased. Durability of concrete could be strongly influenced by the high porosity and water absorption of fine recycled concrete aggregates.