Introduction to concrete building products
Practical Action
Sometimes special admixtures are added to concrete to make it more workable, set faster or slower,
or make it more frost resistant, for example. However, many such admixtures are usually very
expensive and more usually used for concrete cast-in-situ at the building site rather than at the
concrete products yard. They are therefore little considered further in this technical brief.
See the companion Technical Brief – Concrete Works: Information And Guidelines For Concrete
Products Makers And Builders Making And Using Concrete At The Building Site for further
information about the constituent materials for concrete and admixtures.
Since the invention and development of Ordinary Portland Cement (OPC) by Joseph Aspdin and
others in the first half of the nineteenth century, use of mortar and concrete made using OPC as
the binder has become very widespread throughout the world. OPC concrete can be mixed and
used at the building site where it can be considered as cast-in-situ concrete, fresh concrete
mixed at a plant away from the building site then transported to it by truck – known as ready-
mixed concrete, or cast into moulds to produce building components and elements at the
production yard that are transported for use at the building site after curing. The latter process is
called precasting and is the subject of this technical brief.
There are many thousands of small-to-medium-scale producers of concrete products throughout
the world. Wherever significant building activities are taking place and not that many building
materials producers and suppliers operating in the area there may be an opportunity to set up a
concrete products fabrication yard. The main requirements are a sizeable fairly level site, access
to a regular water supply and easy road access to the yard for transport of materials.
If the producer already owns the land or can rent a plot it can cost less than US$1,000 to set up
a very small manual operation, or less than US$10,000 for a slightly larger operation using
concrete vibration equipment. The producer can start by making concrete blocks, for which there
is a widespread and universal demand in many places. Micro concrete roofing (mcr) tiles have
also gained ground for roofing in many places in recent years and the prospective producer can
also consider making these instead of or in addition to concrete blocks.
Experienced producers of concrete blocks and tiles can consider diversifying into other more
specialised items and components, for which the purchase of additional moulds and equipment
would be needed. These can include concrete beams, columns and lintels – usually reinforced
with steel rods, pavers for roads and footways, floor and wall tiles, cylindrical water pipes,
ventilation elements, curved blocks for water tanks, window and door frames, pit latrine slabs,
paving slabs, fencing posts, balustrades, staircases, roadside kerbs and decorative or practical
garden ornaments.
Many experienced builders like to build with concrete blocks as they can put up buildings and
structures relatively quickly. Casual builders, including many households building their own homes
and business premises, can also prefer concrete blocks to other materials such as the smaller fired
clay bricks as they are easier to lay and there is less potential to make serious mistakes.
Both producers and builders using concrete products need to understand how concrete behaves
when it is freshly mixed, when it is placed into moulds, when it is curing in the moulds and outside
them, and when it is loaded and stressed as it is used in buildings. These subjects are covered in
greater length in the brief Concrete Works: Information And Guidelines For Concrete Products
Makers And Builders Making And Using Concrete At The Building Site. Here only a summary is
presented.
Characteristics of Fresh and Hardened Concrete
Concrete made with OPC is a very versatile material for making into a large variety of shapes
because just after it is mixed it can be highly workable and able to take the shape of the mould
into which it is poured.
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