Experimental study of some mechanical properties of recycled concrete containing micro-silica, fly ash and natural zeolite

The present study studies the effect of the replacement of different levels of recycled concrete aggregates on the mechanical behavior of recycled concrete. In made concretes, natural aggregates have been replaced at three levels of 25%, 50% and 100% with recycled concrete coarse aggregates. In order to enhance the mechanical performance of these concrete, each of the pozzolans including micro-silica, fly ash and natural zeolite has been replaced with cement at three different levels. A total of 360 cube and cylindrical concrete specimens were made in the form of 40 mixing designs, and tests of compressive strength, tensile strength, static modulus of elasticity and ultrasonic pulse velocity at 28 days of age were performed. The results showed that, without the use of pozzolanic materials, up to 25% replacement of recycled coarse aggregate, there was no significant change in the mechanical performance of this concrete, while the higher replacement rates resulted in a significant drop in the mechanical performance of this concrete. The use of micro-silica, especially at the replacement level of 10%, has led to a very good performance of recycled concrete even in the case of full replacement of recycled coarse aggregates. Other pozzolanic materials used were also relatively less and in lesser intervals of recyclable materials to improve their mechanical properties.