Residual Cementing Properties in Recycled Concrete

Bangladesh is a densely populated country depending largely on her agricultural products. In this country, there is an upcoming need to demolish the old low rise buildings and replace those with high rise ones for housing its increasing population and gradual industrialization. Recycling stone and brick aggregate concretes by crushing and converting them into coarse aggregates and fines for use in new concreting is an established trend.

Hydration in concrete continues over time as along as enough water is available to react with different components of cement. However, the rate of hydration slows down significantly with time. The reaction rate is governed by the composition of cement, temperature and the effective surface area of cement particles. In all cases, we know from electron microscopy that the only outermost surfaces of a cement particle is responsible for hydration whereas interior sections remain eventually unhydrated. Under favorable condition, the unhydrated fraction of cement grains can give additional strength. It is known as the residual cementing property. When we are recycling the concrete, it is perhaps possible that some unhydrated fractions of cement grains can take part later in the process of hydration. When cements also contain pozzolans, the phenomena is much more expected. We are working to evaluate the latent cementing properties in recycled concretes in the context of cement chemistry and material science. The outcome is important from energy and resource recovery viewpoint.

The fundamental contribution of Prof. Amin on identifying the occurrence, origin and quantification of residual cementing properties of recycled aggregates and fines from demolished brick and stone aggregate concrete open the door for appropriate utilization of existing resources. This will not only promote saving of cultivable land by reducing the demands of clay bricks used for new concrete making but also extends the possibility of reducing the cement content while using recycled aggregates and fines. All these points do have significant counts in the context of environmental protection and conservation of nature.