Study and comparison of the effect of natural zeolite and silica fume on mechanical properties of recycled aggregates concretes

The present study was conducted to compare the effect of natural zeolite (Z) and silica fume (SF) pozzolans on the mechanical properties of recycled aggregates concrete (RAC’s). The RCA’s made with using different levels of recycled coarse aggregates instead of natural coarse aggregates. To improve quality of RCA’s, the introduced pozzolans were replaced with different levels of ordinary Portland cement (OPC). To determine and compare the mechanical properties of concretes, 24 mix designs were made and different tests done as compressive strength at the ages 7, 28 and 91 days, and the tests as splite cylinder tests (SPT), modulus of elasticity and ultra-pulse velocity (UPV) at the age of 28- day. The obtained results generally showed that in duration of 28 days, the usage of silica fume could results in about 40 MPa compressive strength for RCA’s with 100% of recycled coarse aggregates; meanwhile using natural zeolite was not able to give target strength of design. Using 10% of silica fume instead of OPC in RCA’s specially RCA’s having 25% of recycled aggregates caused in the mechanical properties of RCA’s be rarely like those natural aggregate concretes. Although, using 10% of zeolite in concrete could improve some mechanical properties, but the concretes containing silica fume gave superior mechanical properties than those of zeolite.