Page 108 - ICJ Jan 2023

TECHNICAL PAPER COLLECTOR’S EDITION

Aggregates comprise 70-80% of the volume of The simplest and most common method for
concrete and exert a significant influence on characterisation of aggregates is on the basis of the
concrete properties. Generally, they are granular specific gravity, i.e. (i) normal weight, (ii) lightweight
materials derived from natural rock or natural and (iii) heavyweight. Further characterisation
sands and gravels. However, one of the facets may be achieved using the following: grading,
that has made concrete the world’s most widely shape, inclusions, bulk density, water absorption,
used construction material is its ability to absorb chemical composition and drying shrinkage.
a wide range of quality of materials, including Normal weight aggregates are the largest group of
recycled materials and industrial by-products, concrete aggregates. This group includes natural
as a component of the aggregate (and cement). sands and gravels, and crushed rocks, e.g. granite,
Increasingly common, and potentially more dolerite, basalt, limestone and sandstone. Recycled
sustainable, therefore is the use of recycled aggregates also fall within this group, in addition
aggregates (RA) processed from CDEW, and use of to manufactured aggregates such as air–cooled
other processed solid waste materials (secondary blastfurnace slag and recycled glass aggregates.
aggregates).
APPROPRIATE USE OF AGGREGATES IN
In selecting aggregates for use in concrete, certain CONCRETE CONSTRUCTION
constituents should be avoided. For example, Sustainability is generally recognized as a
reactive silica leads to deterioration of concrete foundation for resource and energy-saving
if moisture and alkali are present; weak friable technology developments in many fields, including
aggregate should not be used if hardness is a that of construction. Indeed, sustainability as a
desired concrete property; and a highly porous concept has grown beyond that of “sustainable
aggregate is potentially unsuitable with respect development” - development that does not
to aggressive permeation-based deterioration interfere with the needs of future generations,
processes (e.g. chloride ingress and carbonation). as originally defined in the Brundtland Report.
3
Subsequently, the term has been adopted to form
For most purposes an aggregate material should sustainable construction, sustainable concrete and
be hard and strong and free from deleterious sustainable construction materials.
impurities such as silt, clay and organic matter.
The latter may affect the cement setting and the
cement-aggregate bond. The physical, thermal
and chemical properties of the aggregate can
all affect the concrete performance. Some of
these properties are directly dependant upon the
parent rock whilst others are not. For example,
those dependent on parent rock are chemical
and mineralogical description, petrographic
description, specific gravity, strength, hardness,
and colour, whilst, surface texture, size and shape
are independent of parent rock.

The Indian Concrete Journal | November 2018 109