Effects of washing of recycled aggregates on concrete properties

Abstract

As we progress further into the new decade, there has been an increasing demand and emphasis placed on sustainable construction. One such aspect of sustainable construction which the BCA is trying to implement is the use of recyclable materials in concrete production and civil engineering works. This will reduce the demand on natural materials such as sand and granite. There are numerous replacements for the sand and granite found in cement, which make up the fine and coarse aggregate component. These replacements include washed copper slag, steel slag, construction and demolition waste, recycled concrete aggregates, wood waste and milled waste. Because this field of sustainable construction is relatively new to the BCA and Singapore, therefore numerous test and consultations are carried out before the recycled concrete or eco-concrete is put into application. Currently, the BCA allows contractors to use eco-concrete for non-structural elements in buildings. For use in structural works, the BCA has to grant approval before work can be carried out using recycled concrete. As of such, this report was undertaken to investigate the effect which washing had on the use of recycled concrete aggregates and construction and demolition waste in concrete. In particular, the compressive strength and water absorption capabilities of the concrete were closely monitored. For this report, we tested 3 different grades of concrete: Grade 40 for low-medium strength, Grade 60 for medium-high strength, and Grade 80 for high strength concrete. On top of using 3 different grades of concrete, we also varied the amount of recycled fine and coarse aggregate which we used for our mixes. This was done so as to observe the effects which different percentage, by weight, of recycled aggregate had on the recycled concrete. Finally, we used 1 set of “virgin” aggregate, 1 set of unwashed industrial aggregate, 1 set of washed industrial aggregate and 1 set of aggregate which we washed ourselves.