Modern Quarrying January-February 2016

TECHNICAL REPORT RECYCLING

Drying shrinkage of concrete made from recycled materials

Does concrete composed of recycled concrete aggregate suffer from higher shrinkages and lower densities and strengths compared with concrete composed of virgin aggregates? In this article Bradley Whiting, Timothy McCarthy and Eric Lume describe the methodology and outcomes of trials undertaken on a commercially available recycled concrete aggregate.

Due to the adhered mortar found on the aggregate particles, the RCA had rougher particle textures, increased water absorptions and lower densities than conventional aggregates. As a result, the RAC mixes suffered lower compressive strengths and higher drying shrinkages than the control mix. Reducing C&D materials One area that has been the subject of much research and investigation in recent times is how to reduce the quantity of demoli- tion and construction waste sent to land- fill. According to the Australian Bureau of Statistics (2007), the construction and demolition industry contributed 42% of the solid waste produced in 2002-2003. Of this, only 44% was recycled in some form, with the remaining waste sent to landfill. While landfill can result in some pos- itive outcomes, such as reclaiming land from disused quarries, a report prepared for the Department of the Environment, Water, Heritage and Arts by Hyder Consulting (Pickin, 2009), has found many regions throughout Australia are reaching their landfill capacities. The paper argues that the reliable supply of landfill is a scarce resource that should be used conservatively (Pickin, 2009). Continued studies investigating ways to encourage the recycling of con- struction and demolition waste materials

Bradley Whiting, Timothy McCarthy and Eric Lume are based at the School of Civil, Mining and Engineering, Faculty of Engineering, University of Wollongong, NSW.

T his paper describes the proce- dure and results of a range of experiments conducted on a commercially available recy- cled concrete aggregate (RCA). The work quantifies the effect RCA has on the drying shrinkage of new concrete mixes, termed recycled aggregate concrete (RAC). The RCA product was characterised by analysing thin sections, particle shape

and texture, particle size distribution, percentage of solid contaminants, water absorption and particle densities. Three concrete mixes were prepared and tested for seven and 28-0day com- pressive strengths and 112 days of drying shrinkage. The mixes include a 40 MPa conventional aggregate mix and two equivalent RAC mixes, one utilising 30% fly ash as a partial cement replacement.

Studies are showing that improvements are still required in the performance of structural concretes that incorporate recycled aggregates.

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MODERN QUARRYING January - February 2016