Mechanical Properties of Concretes with Recycled Aggregates and Waste Brick Powder as Cement Replacement

The cement industry is responsible for around a 5% of the CO2 emissions worldwide and considering that concrete is one of the most used materials in construction its total effect is significant. An alternative to reduce the environmental impact of concrete production is to incorporate certain amount of residuals in the dosing, limiting the replacement percentages to avoid significant losses in the mechanical properties of the final material. This study analyses the variation in the mechanical properties of structural concretes with recycled aggregates and waste brick powder as cement replacement to test the effect of the simultaneous use of different residuals in the same material. All concretes are dosed for a compressive strength of 30 MPa. The recycled aggregates are obtained from prefabricated pipe debris with a compressive strength of 20 MPa. The waste bricks are obtained from construction demolitions. Four levels of replaced cement by waste brick powder are considered: 0%, 5%, 10% and 15%. Also, two kinds of samples are studied regarding the amount of recycled aggregates: 0% and 30%. All these levels are combined to analyze the effect of both residuals in the mechanical properties of the concrete through compressive strength tests, flexural strength tests and elasticity modulus tests, all of them after 28 curing days. Results show that when no recycled aggregates are used, the cement can be replaced up to a 15% by waste brick powder. But when both residuals are combined the amount of waste brick powder recommended without significant losses in the final material properties is limited to a 5%. Replacing a 30% of the aggregates together with a 5% of the cement can considerably reduce the environmental impact of the final material.