Influence of Recycled Concrete Aggregates on Strength Properties of Concrete

The demand to use recycled aggregates in concrete is getting more important. However, to obtain a sustainable road, it is necessary to construct durable pavements and therefore to use concrete of good and reliable quality. The use of recycled aggregates will give environmental advantages but could lead to excessive shrinkage and lower strength and durability. This paper investigates a new approach towards the use of recycled concrete aggregates, in which the mortar phase present in the recycled aggregates is taken into account. The study, carried out in the framework of a master thesis at Ghent University, comprises the comparison of concrete properties for different concrete mixes with recycled concrete aggregates (RCA) using the equivalent mortar volume method (EMV method) and the more conventional method. The concrete mix design that was used is typical for the Belgian road construction. Several mixes were tested in the laboratory for mechanical and physical characteristics. In order to compare the different methods, three types of concrete mixes were prepared: - with only natural aggregates, - with use of RCA in a traditional design, - with use of RCA using the EMV method. In this study the concrete properties were evaluated by performing pressure tests, bending tests and splitting tests on lab made specimens. Also the modulus of elasticity and the shrinkage properties were measured. First conclusions indicate a severe loss of strength but also a decreased shrinkage. This paper will not only focus on the comparison between the conventional method and the EMV method, but will also point out some interesting characteristics of the use of recycled aggregates by analysing some international research publications.