mix design and recycled aggregates effects on the concrete’s properties

An experimental program was carried out to study the properties of concretes with c25/30 and c35/45 resistance classes designed using natural aggregates and recycled ones provided from construction and demolition waste (c&dw). eight mixtures were prepared with different incorporation ratios of fine and coarse recycled aggregates. the physical and mechanical characteristics were measured and their evolution regarding to the paste volume, the equivalent replacement ratio and the quality of the interface between recycled aggregates and new paste has been investigated. scanning electron microscopic observations have revealed a good quality of the interface. it was found that water porosity is more dependent on the equivalent replacement ratio than on the volume of the new paste. the same conclusions are reported for the electrical resistivity which has been related to the water porosity. based on experimental results, it has been found that the archie’s law predicts the electrical resistivity as a function of water porosity for all type of concrete. the effect of mix design parameters and aggregates properties on the compressive strength has been investigated and a model is proposed on the basis of féret’s expression through experimental results and data points available in the literature. the modified expression is related to the aggregate fragmentation resistance expressed by the los angeles coefficient (la). the féret’s coefficient can be taken equal to 6.4 if la ≤ 20% and it is inversely proportional to la otherwise. with regard to the splitting tensile strength, it can be correlated to the electrical resistivity through a power law relationship. the elastic modulus, the peak and the ultimate strains are than rewritten as functions of the compressive strength and the replacement ratio to model the full stress–strain curve under uniaxial compression. furthermore, the validity of using ec2 to model the evolution of all mechanical properties with age is ensured.