Page 107 - ICJ Jan 2023

TECHNICAL PAPER COLLECTOR’S EDITION

Due to issues relating to sustainability and limited CONCRETE AND THE ROLE OF
natural resources, it is clear that the use of recycled AGGREGATES
and secondary aggregates (RSA), for example Concrete is the most widely-used, second only
crushed concrete and asphalt and industrial by- to water in volume consumption terms, and
products such as fly ash and blast-furnace slag, most important of all construction materials. It
will grow. However, currently, it is only in the USA, is in fact, a whole family of materials that can be
Japan, parts of Western Europe and Hong Kong tailored to almost any use, and can be made using
where developments and regulations have been a wide variety of raw materials, available locally
sufficiently put in place that the use of RSA exceeds throughout the world. In its simplest form, it is a
10% of the total aggregate usage. Consequently, composite material in which fragments of relatively
worldwide the use of RSA stands at approximately inert minerals (aggregates) are held together by
750 million tonnes (<3% of total aggregate use). a cementing medium (cement paste). There are
many potential types of cement, but the most
The largest single-source of RSA that could be used important are currently based on Portland cement.
in construction is that arising from construction,
demolition and excavation waste (CDEW). In most The cementing medium has two main functions.
countries, CDEW makes up a significant proportion
(approximately 55%) of the national total, and its • To fill voids between aggregate particles
use is recognised as key from material resource providing lubrication of the fresh (plastic)
2
and sustainability perspectives. As a result, a concrete and water tightness and durable
significant amount of research and development structure in the hardened concrete.
activities in recent years have focused on the
development of technologies for recycling these • To give strength to hardened concrete.
wastes as RSA. However, these activities alone The aggregate in concrete has three main
will not achieve wide-scale use for RSA without functions.
improvements in their supply that will in turn
stimulate potential increases in user demand and • To provide a relatively cheap filler for the
a more receptive market further down the chain. cementing material.
Furthermore, it is necessary to overcome perceived
perceptions with regard to the quality of RSA, and • To provide a mass of particles which are
for producers and users to recognise that there suitable for resisting the action of applied
are appropriate uses for these aggregates, that loads, abrasion, the percolation of moisture
will reduce the demand on natural resources. This and the action of weather.
concept of appropriate use of aggregates, and a • To reduce the volume changes resulting from
proposed performance-related approach that will the setting and hardening process and from
enable its implementation is also addressed in this moisture changes in the cement paste.
paper.

108 The Indian Concrete Journal | November 2018