Influence of pre-saturation of recycled concrete used in the concrete mix

Concrete has been the most commonly used construction materials for many years, and as a result, the production of its main constituent material, Portland cement emits large amount of carbon to the atmosphere. With the increasing concern with the environment and intensifying desire to develop a sustainable environment, researchers are searching for new methods to reduce the carbon emissions associated with concrete production. The concrete industry is now under intensive pressure to change/modify current practices in order to reduce the waste generated. As a result, waste product recycling has been continually gaining increasing support over the past a few decades and research and investigations into the feasibility of utilising particular waste products for recycling have been continually increasing. A number of studies have been reported on the use of recycled concrete in concrete mix in recent years. In general, these studies showed that addition of recycled concrete reduced the strength of the concrete. A research project has been established at Central Queensland University to investigate different approaches for the use of recycled concrete in concrete mix and the promising preliminary results are achieved. This paper presents the preliminary experimental results from this project showing the effect of pre-saturation of the recycled concrete on the properties of concrete. Recycled concrete obtained from a local recycle yard was used in the concrete mixes. Varying amount of recycled concrete with and without pre-saturation was used to replace the coarse aggregate. Then the samples were tested for their strengths. The experimental results show significant increase in concrete strength in the samples containing the pre-saturated recycled concrete compared to the samples without pre-saturated recycled concrete. The results are analysed and discussed in terms of the efficiency of pre-saturation process when replacing the coarse aggregate with recycled concrete.