Recycled construction and demolition concrete waste as aggregate for structural concrete

In major Egyptian cities there is a surge in construction and demolition waste (CDW) quantities causing an adverse effect on the environment. The use of such waste as recycled aggregate in concrete can be useful for both environmental and economical aspects in the construction industry. This study discusses the possibility to replace natural coarse aggregate (NA) with recycled concrete aggregate (RCA) in structural concrete. An investigation into the properties of RCA is made using crushing and grading of concrete rubble collected from different demolition sites and landfill locations around Cairo. Aggregates used in the study were: natural sand, dolomite and crushed concretes obtained from different sources. A total of 50 concrete mixes forming eight groups were cast. Groups were designed to study the effect of recycled coarse aggregates quality/content, cement dosage, use of superplasticizer and silica fume. Tests were carried out for: compressive strength, splitting strength and elastic modulus. The results showed that the concrete rubble could be transformed into useful recycled aggregate and used in concrete production with properties suitable for most structural concrete applications in Egypt. A significant reduction in the properties of recycled aggregate concrete (RAC) made of 100% RCA was seen when compared to natural aggregate concrete (NAC), while the properties of RAC made of a blend of 75% NA and 25% RCA showed no significant change in concrete properties.