The use of recycled concrete aggregates has the potential to provide extensive economic and environmental benefits the industrial world. Use of recycled concrete aggregate, not only reduces the need for dumping of demolition waste in landfill but also reduces the consumption of new natural aggregates. While the use of recycled concrete aggregates is not currently economically viable in Australia, in some other countries, particularly in Europe, legislation, economics and environmental concerns have forced the construction industry to use at least small amounts of recycled concrete aggregates in new construction. The effects of including recycled concrete aggregates in new concrete mixes, is an area that is currently not particularly well studied or understood.
This thesis contains two major parts. Firstly it presents a review of the available literature on the topic. It then contains an experimental study designed to determine the effects of the inclusion of various proportions of recycled concrete aggregates on the mechanical properties of concrete.
A modest number of studies have been conducted on the use of recycled concrete aggregates in new concrete mixes. After reviewing contemporary literature, it becomes apparent that there are many contradictions and inconsistencies in the results from different studies. It becomes clear however, that the use of recycled concrete aggregates does have some negative impact on many mechanical properties of concrete.
The literature shows that the inclusion of recycled concrete aggregates (RCA) in new concrete mixes yields a variety of effects on the properties of the concrete including density, compressive strength, flexural/tensile strength, modulus of elasticity, drying shrinkage, creep, durability and workability. These changes mainly stem from the residual mortar of the original concrete adhering to the crushed aggregates.
The experimental part investigates the properties of four concrete mixes including, 0%, 20%, 50% and 100% RCA content respectively. The results indicated that in general as the proportion of RCA content increased in the new concrete mix, the compressive and flexural strength together with the modulus of elasticity decreased. These were in agreement with contemporary literature. However, the 20% RCA mix yield quiet amazing results. It possessed a higher compressive strength and modulus of elasticity relative to the control mix and a similar cohesiveness and workability.