Why your beautiful ‘cabro’ is failing

Cabro paving
Anybody who has driven on paving block ‘cabro’ surfaced driveways and parking can attest to the aesthetic beauty.

This finishing is desired by developers and business owners as its additional value can attract more customers and at a higher price.

Paving blocks are concrete products that are easy to manufacture and at any location as long as there is adequate space and water.

This has made the use of paving blocks widespread. However, with easy entry and exit into this business, many untrained and unscrupulous business-people have infiltrated the trade, lowering the quality of the blocks and the final works done using them.

To avoid this disappointing eventuality, you need to know what to look for when buying the blocks and during construction of the driveway or parking.

The blocks are made of cement, sand, and ballast with water. To ensure the blocks are strong enough to carry vehicular loading, the mixing must be done in the right ratio and adequate curing for at least seven days.

Only river sand is allowed and any other materials must go through rigorous test before acceptance.

If quality control is not done properly, the blocks will wear away fast due to rainfall and break due to vehicle loading.

Major failures

The major failures caused by poor construction is ponding, deformation, and potholes.

The main causes of failure include leaving black cotton soil unexcavated to the allowed depth. This results in heaving that makes the surface uneven, leading to ponding and potholes. Then there is poor compaction of the ground and backfilling.

Where the stone layer is not well pitched the surface develops depression when used by vehicles. For stone layer, inadequate filling of voids may cause loosening and breaking of blocks. To avoid this, the blinding material, which is normally quarry dust or sand, must be vibrated using a light plate compactor until no more is lost into stone layer.

If this is not done well, the blinding material will later be lost into stone layer as vehicles vibrate the ground.

Poor drainage of the driveway or parking will cause ponding and allow water into the ground supporting the blocks. Once the ground is soaked, potholes will develop as the muddy material is pushed out.

To resolve these problems, engage an engineer who will study the type of soil, and ground topography and come up with an appropriate design.

During implementation, the engineer will need to visit the site regularly to approve each stage of construction.

- The writer, Eng Mungeria Kirimania, is the MD for Kiri Consult Ltd.  

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