When it comes to construction projects, the quality of the building materials used plays a very pivotal role in determining the finished product, high-quality materials will result in great buildings that will withstand the test of time. Ballast is one of the key building materials used in construction. ballast is a mix of sand and gravel which is then mixed with cement to produce concrete. This guide will break down ballast as a building material in kenya.

Why use ballast?

Ballast is used to strengthen the concrete. Ballast is mixed with cement to form concrete, the aggregates in ballast helps in binding the concrete together, therefore, increasing the overall strength of the concrete, the amount and type of ballast used will directly affect the concrete strength with the heavier ballast making stronger concrete.

In screed concretes, however, which require the finish to be as smooth as possible, ballast is left out and only sand without gravel is used to form screeding mixtures which are ultimately weaker than the regular concrete and will need more reinforcement such as metal bar addition.

How to know good ballast material for the construction of a residential home in Kenya.

Below are the Requirements for good ballast material

  • Hand-picking

     Good ballast should be able to withstand handpicking without significantly disintegrating.

  • Strong

    Good ballast for concrete production should be able to withstand pressure from loading and be able to resist crushing under dynamic loads.

  • Drainage

    Another characteristic of good ballast should be able to have good drainage with minimum soakage.

  • Resistance 

    Good ballast should offer great resistance to abrasion and weathering and be large enough to prevent capillary action.

  • Size

    The size of ballast varies from1.9cm-5.1cm gauge. stones of larger sizes are not preferred and the best ballast is the one which contains stones of  1.9-5.1cm gauge in size with reasonable proportion.


Types of ballast in Kenya

This is the best ballast material and it satisfies all the specifications and requirements of good ballast material. natural stones like granite and quartzite make excellent ballast which is hard and nonporous.

  • Gravel ballast

Next in rank in suitability for ballast is gravel which is obtained from riverbeds and gravel pits. Because it occurs naturally gravel is quite affordable compared to broken stone and is easily available.

However, it should be sieved and cleaned to eliminate small size gravel and some amounts of clay which may affect its drainage.

Sand ballast is a term used to refer to a blend of sand, small stones, and gravel. The type of sand used is sharp gritty sand which is used for concrete mixes and loosening clay soils.

Sand ballast is reasonably a good material because it is cheap and provides good drainage.

Cost of ballast as a building material in Kenya

When used for residential construction purposes, the cost of a lorry of ballast with an average of 22 tonnes in Kenya ranges from Ksh 30000-40000. This price, however, varies depending on whether the ballast is a machine or manually cut with the machine cut ballast being more expensive. Aside from per lorry , ballast can also be charged per ton which varies from as low as Ksh 1500 to 1800 per tonne depending on the type of ballast you want. These rates are subject to change with different seasons.


In Conclusion

To conclude, broken stone ballast is the best material to use for mixing concrete for residential construction in Kenya because it is hard and tough therefore holds and binds the concrete components together to form a strong and durable concrete mixture. 

99 Construction Guide
99 Construction Guide

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