The Civil Engineering Contractor April 2018 | Page 30

INSIGHT
Getting the mix
right
By George Evans
Concrete quality is made of as many elements as the material
itself. Getting them into perfect balance is critical.
C
oncrete is a composite material.
It is made up of various
constituents, among them
cement, sand, aggregates, and various
chemical compounds. When you know
this, you can begin to understand that,
when it comes to concrete, quality is
equally complex.
The first point of call should be to
define what we mean by quality. There
is simply no absolute measure: in the
final analysis, quality is related to how
closely the product meets the need of a
specific user. When producing concrete,
it is thus critical to understand fully
what it is being used for.
One must also understand that
measuring quality presents challenges,
because concrete is made up of so many
different types of material and can be
28 - CEC April 2018
influenced by other factors such as how
it is transported and stored. Clearly,
the more consistent the quality of the
cement and other elements that go
into concrete, the more consistent and
predictable its results will be — and
thus the higher the quality.
In practical terms, then, consistency
is a key driver of concrete quality.
While there are many factors that
influence concrete quality in South
Africa, looking at them in four
categories gives us the opportunity to
understand where South Africa fares
globally.
• Quality of the raw materials.
There are many facets to this category.
Obviously, the consistent quality
of the cement itself is paramount,
but variations in each of the raw
materials must be taken into account.
For example, the moisture content of
the sand would likely vary from load
to load. If this is not monitored,
the producer or the builder might
have to adjust the amount of water
used, but this would in turn affect
the plasticity and durability of the
finished product.
• The proportions of the mix.
It is necessary to control the proportion
of each raw material very tightly or the
characteristics of the concrete will be
affected, and thus its ability to meet
the use case.
Raw material quality and proportion
mix obviously interact with each
other. Together, they have the largest
influence on concrete quality.
• Type of sampling used. An