How to identify quality concrete products

Wednesday January 29 2020
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Compound pavers look great. However, if made of poor quality concrete mixture, they cannot handle the heavy foot traffic. Photo by Ismail Kezaala

More and more people are adopting concrete compound designs. Concrete products are used in construction works to accommodate the gradual weather conditions.

Some people have taken to making their own concrete products such as pavers, blocks and other small precast materials for cost effective measures. Attaining quality is measured by the performance standard in terms of strength and durability within the environment. Most concrete materials don’t fail in strength hence they don’t crack. However, they fail due to disintegration or weathering away in the harsh conditions. They deteriorate and are washed away over time.

When we look at how to deliver effective buildings, quality is cost-based. It is vital to evaluate the exposure conditions on a building. The part of the building that is more exposed to harsh conditions should have strong blocks. The internal walls have less exposure hence any block of low strength can work, including unburnt bricks.

Apollo Buregyeya, a cement and concrete expert, says the strength requirement for blocks to carry loads is less than one megapascal. But if they have different megapascals, they will crumble.

Pavers are much stronger than blocks because they are exposed to direct rain. If one finds the latter crushed by a car, then they had little cement content. Buregyeya shares some principles to consider while making quality concrete products.

Raw materials
First of all, the need for the right raw materials, proportioned in the right way. Right proportion depends on the product and material characteristics for example a block needs 5-10 percent of cement content while a paver needs 10-20 per cent. Others depend on the particle properties and fineness of materials. Different kinds of sand have different properties. One needs to adapt to the materials they have. The life span of the material rotates on the durability and strength of the product.

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Machinery
Machinery used in the quarry to blast or crush stones determines the quality of stone dust. Technology in terms of handling and compacting them consistently affects the quality of the products.

Labour
Ferdinand Ahabwa, a construction manager, emphasises workmanship is about the labourers doing the right thing. A skilled producer knows how to balance quality and profit.

Mixing materials
It is vital to find out about the mixing process; how one blends and mixes raw materials so that they are evenly distributed to ensure the consistency of the quality of the material.
Hand mixing is not advisable for large scale production. There is a mixer for concrete and block making materials. Buregyeya adds that the former is a drum mixer that rotates and mixes by gravity because of sufficient water to make the materials flow. It’s for wet concrete, electricity and fencing poles.
There is also a pan mixture. It uses a spoon effect for blocks, pavers and other small precast products.

Compaction force
The compaction energy immersed within the mould; the higher the compacting force, the better the product. Compacting force is a function of the energy, strength of the machine and time of compaction.
A machine that can give you a force of 400kilonewtons endowed with stronger arms and heavy weight compacts instantly, which is a factor to consider.
“The longer you spend compacting, the better. If one has a weak machine but compacts for a minute. Another stronger machine compacts for five seconds, both give the same strength. Machines with higher level of productivity exhibit this in strengthening and shortness of time taken to compact.” Buregyeya adds. He says it is not advisable to produce so many products beyond the capacity of the machine. Because the products will be light as a result of under compacting. After the materials have been moulded and compacted, they are handled with care, for the chemical processes responsible to gain some strength from their position and later stockpiled.
Curing process
The materials need wetting because water facilitates strength development; also known as a curing process. One needs to find out how long they cure their blocks, pavers and must be cured preferably a minimum of seven days.
“Don’t be quick to stockpile blocks. Cement gains strength over time and loading them before they are strong can introduce micro cracks and weaken the fresh blocks. Cure the blocks well so that the cement can react and give us the strength we want,” Buregyeya emphasises.

Quality control measure
When buying blocks or pavers, if one can afford to, they should use a bathroom weighing scale. It costs Shs 40,000. Pick three blocks randomly and weigh, if all blocks have a small variation like 25, 26, 27, it’s acceptable but if the variation is big, then it indicates the quality of the product isn’t good. Weight is related to strength hence the heavier, the stronger, Buregyeya points out.
In addition to that, Ahabwa recommends, lab tests with samples for quality control. Some signs of duplicated materials include crumbling very fast or breaking according to the ratios made.

Visual inspection
One should be able to see if the materials are broken or having chippings and if the chippings are beyond five per cent of the production out of about 100 blocks, then you need to watch out. There is a tendency to break, Buregyeya opines.

Consistency
There should be consistency in colour and shape.
“Colour change means change in material and change in mixes. Quality is also an issue of shape. Take a measuring tape and see the dimensions of the block. A good company will have standard uniform dimensions to avoid inconsistent dimensions of the products,” Ahabwa adds.

Basic impact tests
Most blocks on the market pass for their strength. Hit these blocks from a full height of six feet and if they crush or break on normal ground not in grass or concrete, then they are weak.

Maintenance
One of the first steps in paver maintenance is to regularly clear the area of dirt and debris. You can use a stiff push broom to remove any loose materials on the pavers. This will prevent the surface of the stones from being scratched or damaged. To remove minor stains from pavers, rinse the surface of the stones with a garden hose. For more severe stains, brush the soiled area with mild, soapy water. You can also use one part vinegar mixed with ten parts warm water.

Costs

Each paver goes for Shs700 along Salama Road, Kampala,
Fence poles cost Shs35,000.
Bio-digesters are Shs1.2m.
Road kerbs are Shs15,000

editorial@ug.nationmedia.com

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