Properties of concrete blocks made with recycled concrete aggregates

From block wastes to new blocks

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Large amounts of construction and demolition wastes (C&DW) especially concrete wastes are generated annually and will increase in the future. Until now, only a small fraction of concrete wastes is re-used as recycled concrete aggregates (RCA) in the manufacture of concrete. In this paper, the feasibility of using RCA obtained from old concrete block wastes in the production of new concrete blocks is studied. Concrete block wastes from Belgian Company PREFER 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.