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FEATURE CEMENT AND CONCRETE
Choosing the right cement for the right application
To build structures that will last, cement consumers need the right type of cement. We take a look at the different types of cement and its applications.
• Precision grouts, repairs and formulated
The three main strength classes of cement
General purpose cement that gains strength at
All cement is mainly classified into three
an early stage
strength classes:
The 32,5N is a general-purpose blended cement
It is also ideal for use with cement extenders
• 32,5Mpa
that reaches strength at a normal age and that is
that enhance the concrete properties such as
• 42,5Mpa
suitable for general use in:
silica fume and fly ash or Slagment.
• 52,5Mpa
• Concrete for home or building structures • Mortar, plaster and screed applications.
This figure is typically accompanied by either an
cement products.
CONCRETE MIXING PROPORTIONS Concrete is made up of four elements: cement,
‘N’ or ‘R’, which denotes the time it takes for the
General purpose cement that has normal
sand, stone (aggregate) and water. The cement:
cement to reach the suitable strength.
strength gain
sand: stone: water proportions are critical as
The 42,5N general purpose blended cement is
it determines the compressive strength of the
• The N implies that it will have normal strength gain
a highly versatile cement that is suitable for a
concrete, which in turn establishes the capacity of
• The R implies early/rapid strength gain.
comprehensive repertoire of concrete, mortar
the structure you build to withstand loads.
and screed application. It can be blended to achieve This is important to know, as a structure that
all the required strengths of concrete for the same
Choose the right cement for the right application
requires early stripping of formwork could benefit
applications as the 32,5N mentioned above. This
Point of departure would be to select the right
in being poured with a concrete containing an ‘R’
cement type is more forgiving where only poor
cement for the right application and to check that it
type of cement over an ‘N’ of the same class. The
quality local sand is available.
complies with the relevant specifications to ensure
‘R’ cement will achieve a higher early age strength.
a lasting end product. High performance cement that requires early
CEMENT STANDARDS
strength
Input equals output
Questionable materials will produce questionable
42,5R and 52,5N cement are high-performance
Apart from choosing the right type of cement
results. For the South African built environment, it is
cements that are suitable for civil engineering and
for the right application, it is also critical to take
recommended to use cement that complies with the
structural concrete applications that require early
an uncompromising approach to the quality of
requirements of South African National Standards
strength and cold-weather concreting. This includes:
the cement you choose, to ensure structures
(SANS) 50197-1. All cement products sold in South Africa should fully conform to the requirements of the strength classes as specified by SANS 50197-1, as well as the National Regulatory Of Compulsory Specifications (NRCS) requirements. MAY 2020 DIY & INDUSTRIAL TRADE NEWS
that will last. • High-strength concrete, pre-cast elements and ready-mix • Water-tight, structural and pre-stressed concretes
Consult manufacturers’ guidelines for ideal mixing proportions As soon as you’ve selected the cement that is