The Civil Engineering Contractor April 2018 | Page 24

TECHNOLOGY
In the mix
By Kim Kemp
Admixtures play a vital role to help concrete meet the construction sector’s stringent
requirements.
N
orman Seymore, head of
admixture producer Chryso
Southern Africa, explains
the now virtually indispensable role of
admixtures in concrete design.
CEC: How do admixtures improve
concrete performance?
NS: Admixtures can improve workability,
The Civil Engineering Contractor
(CEC): What exactly are
admixtures?
Norman Seymore (NS): Admixtures,
basically, are chemicals used to modify
— and enhance —concrete’s freshly
mixed, setting, or hardened properties.
They are added to the batch before or
during mixing.
CEC: What led to admixtures’
development?
NS: There has been a change in building
practices over the past few decades, with
more being expected of concrete than ever
before. The trend now is to use fluid concrete
that can be fitted and moulded into any
shape. However, concrete strength is non-
negotiable and that it why chemicals such
as admixtures were developed to enhance
concrete without sacrificing strength.
Donald Khoza evaluates the alkali content of cement and admixtures in the Chryso Centre of
Excellence laboratory, which provides a testing and advisory service to customers.
22 - CEC April 2018
develop high early strength, increase
ultimate strength, compensate for
temperature fluctuations, and improve
resistance to corrosion, shrinkage, or
freezing and thawing. They are also used to
overcome placement emergencies such as
equipment failure and other unexpected
delays. Admixtures also reduce the cost
of the concrete mix and compensate for
poor aggregate properties.
CEC: What are the main categories
of admixtures used in concrete
mixes today?
NS: Admixtures can be classified into