Feasibility of using low grade recycled aggregates for concrete block production

The Hong Kong Government has set up sorting facilities to separate the inert portion of the construction waste (rock, rubble concrete, asphalts, sand, brick, tile, soil etc) from the non-inert portion (i.e. paper, timber, bamboo, plastic, metals) to facilitate better construction waste management. The intention is that the inert portion can be "reused" as a fill material for land reclamation. The non-inert portion would be disposed of landfills. It should be noticed that the characteristics of the inert construction waste are significantly different from that of crushed concrete rubbles that are mostly derived from demolition waste streams. This is due to the presence of higher percentages of non-concrete components (e.g. >10% soil, brick, tiles etc) in the sorted construction waste. This paper presents the results of a laboratory study to explore the feasibility of using the inert portion of the sorted construction waste (low grade recycled aggregates) for concrete block production. Three Series of concrete block mixtures were prepared by using the low grade recycled aggregates to replace natural coarse granite and 0, 25, 50, 75 and 100% replacement levels of crushed stone fine (crushed granite <5mm) in the concrete blocks. Test results on properties such as density, compressive strength, transverse strength and drying shrinkage are presented. The results gathered would form a part of useful information for recycling the low grade recycled aggregates.