Recycling of demolished masonry rubble.

Abstract

The recycling of demolished masonry rubble as the coarse aggregate in new concrete
represents an interesting possibility at a time when the cost of dumping such material
is on the increase. With growing concerns over the environmental impact of aggregate
extraction and the continued rise in aggregate demand in the UK, it is clear that the
market is now there for recycled and secondary aggregates.
The present investigation consists of experimental and theoretical studies into the
effects of using recycled aggregates to produce concrete instead of virgin aggregates.
The aggregates used have been recycled from construction and demolition waste. The
recycled aggregates were predominately made up of crushed bricks but the aggregates
did contain impurities such as timber and mortar. New bricks were crushed to form
an aggregate in order to investigate the properties of brick as a material without
impurities.
The physical properties of the various aggregates were firstly examined and compared
with granite aggregate, an aggregate proven in the production of good quality
concrete. Concrete was then produced with the aggregates and all the physical and
mechanical properties of the concretes were examined in some detail. The results
showed that recycled masonry aggregates can be used successfully to produce·
concrete of an acceptable standard.
New test methods were presented in this investigation to determine brick porosity and
water absorption. This involved the testing of broken brick fragments under vacuum,
rather than the testing of whole brick units by 5hrs boiling or 24hrs submersion in
cold water. The new test methods proved to be easy to perform and provided accurate
results.
A new test method for estimating the strength of bricks was presented. This involved
point-loading of masonry specimens to obtain strength index values. From the pointload
results, equations were presented relating the strength index values of brick
fragments to the compressive strength of whole brick units. This involved the development of shape factors for different masonry specimens. The point-load test is
easy to perform, presents a cheaper alternative to heavy compression machines and
can be used on site to determine the suitability of recycled bricks as the aggregate in
new concrete.