Concrete Foundations – A Construction Guide

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Foundations are the base on which a structure, building, or component of a larger building is constructed. Foundations have their own unique designs and concreting these foundations requires a number of highly regulated steps, including site inspection and obtaining approvals from various authorities.

Inspection activities take place to ensure the safety of the ground environment. Foundations are generally made of concrete, a material that is long-lasting and relatively inexpensive with high strength and waterproof properties.

Good concrete foundations should have a perfectly proportionate concrete mix that should be approved by the appropriate authorities. The construction process for concrete foundations requires suitable formwork and the proper execution of activities such as shuttering, mixing the various ingredients to form the required concrete, and barrowing and pouring of the concrete.

Some common types of concrete foundations include:

• Concrete block foundation
• Concrete pier foundation
• Concrete slab foundation

Tools Required for Construction

The key tools required for building concrete foundations are listed below:

• Barrow
• Protective Personal Equipment (PPE)
• Batten
• Shovel

Materials Required for Construction

The typical materials required for building concrete foundations are listed below:

• Cement
• Sand
• Aggregate
• Brick

Undertaking the Work

The construction of concrete foundations does require a preparation process for the concrete mix. It is, however, equally important to test the soil, select the correct concrete, have this delivered, and to be knowledgeable on how to handle the concrete.

The key processes in the construction of concrete foundations are set out below :

1. Soil compaction
2. Preparation of the concrete mix
3. Formation of shallow strip foundations
4. Selection and delivery of the concrete

Soil Compaction

For any kind of concrete foundation, the most important initial process is soil compaction, which removes excess moisture and reduces air voids in the soil below and that which surrounds the area in which the foundations are to be built.

The following process will enable you to judge whether the soil on which you intend to construct a concrete foundation has a sufficient amount of water for compaction.

1. Take some soil and squeeze it to form the shape of a tennis ball.
2. Drop this soil ball down from a height of 1 ft.
3. Ordinarily, the soil ball will hold together when the moisture content is favorable and will then break into uniform pieces once dropped.
4. If the soil is very dry, you will find it difficult to make the ball. Too much  moisture in the soil will leave behind traces on your fingers.
5. To avoid these issues, make sure the soil is dried before compaction.

Preparation of the Concrete Mix

To prepare the concrete mix, you should keep the proportion of cement, sand, and aggregate in the ratio 1:3:6. You can also use ready-mixes with the same ratio of components.

Formation of Shallow Strip Foundations

1. For a shallow strip foundation, you will need a concrete strip that is 600 mm-wide.
2. Place the concrete strip at about a meter depth into the ground, and the depth of the strip should be a minimum of 150 mm.
3. Build two skins of brick from the ground level.
4. Fill the gaps between the two brick skins with a light concrete mix to prevent lateral pressure.
5. Use a wider trench while constructing the brickwork below the ground level.
6. The trench that you select should be sturdy, and the sides of the excavation should be straight and vertical.
7. Construction of formwork - a firm wooden structure that will keep the shape of the concrete work intact - will be required when soil falls out from the sides of the trench as it is excavated.

Selection and Delivery of the Concrete

As mixing the concrete by hand is not feasible, you will have to get the concrete delivered by a ready-mix lorry. For this, you need to specify the particular mix you need with the correct ratio and fix a delivery date with the supplier.

When you order the concrete, ensure that a suitable place is available for the concrete lorry to be parked and offloaded. This should be as near to the site as possible to ensure a clear access route between the lorry and the foundation trenches, to ensure a steady flow of barrow loads over the shortest distance. You should consult with neighbors on the concrete delivery.

The barrow must be held steadily as the concrete is loaded into the foundation trench. Whilst handling the concrete you should wear PPE, in particular to avoid eye and skin contact, as the concrete can cause alkali burns on the skin. The concrete should be leveled properly in the trench without any empty spaces. After the trench is filled to the specific level, use a batten to level the surface. Finally, use a shovel to remove the residual concrete during the process.

This article was updated on the 19^th August, 2019.