What is concrete?

Concrete is a building material made from cement, aggregates (rock and sand), water and admixtures (chemicals that enhance or modify the properties of concrete). Concrete is one of the oldest, most widely used and versatile building products known to man.

What is the difference between cement and concrete?

Cement is an ingredient in concrete. It is the ingredient that forms a paste with the water, sand and admixtures and fills the space between the coarse aggregates (rock) and binds the rocks together. The term “cement” is commonly misused to refer to concrete.

What is curing and how do I cure my new concrete slab?

Concrete hardens as a result of hydration, that is the chemical reaction between cement and water. Hydration occurs only if water is available and if the concrete’s temperature stays within a suitable range. After placing concrete, the concrete surface needs to be kept moist for a period of time to permit the hydration process. This period is referred to as the curing period and is usually 5-7 days after placing conventional concrete. New concrete can be wet with soaking hessian, sprinklers or covered with wet hessian or plastic sheets or can be watered with commercially available curing compounds which seal in moisture.

Why does concrete crack?

Like all other materials, concrete will slightly change in volume when it dries out. This change in volume brings about tensile stresses with the concrete which causes it to crack. This is the reason that contractors put joints in concrete pavements and slabs to allow the concrete to crack in a neat, straight line at the joint, allowing it to move when the volume of the concrete change due to shrinkage. The prevailing weather conditions may also contribute to cracking with the risk most likely on warm days, dry days with low humidity and/or windy days.

Why use Prestressed Concrete vs Poured Concrete?

Prestressed concrete has very good crack control and strength to weight ratio. Precast concrete is able to create longer, thinner spans than poured concrete.

What is ready mix?

Ready mix, also known as ready mixed concrete, is concrete that is delivered in truck that agitate and/or mix the concrete on the way to the job or at the job site. The concrete is delivered in a plastic or unhardened state.

What is reinforcement and why should I use it in my slab?

Concrete is strong in compression (squashing) and weak in tension (stretching). The introduction of steel (reinforcement) in concrete improves the strength of concrete in tension. In a slab-onground, reinforcement increases the tensile strength and helps control the width of shrinkage cracks. If soil conditions are known to be poor, e.g. expansive clay soils, consult a structural engineer.

Can I add water to the ready mixed concrete at the site?

NO! Restrain masons at the site. Do not force Transit Mixer Operators to add water to ready mixed concrete. Consequences of such actions can be severe. Properly designed ready mixed concrete contains optimum water. Inform the ready mixed concrete supplier if workability (slump) of ready mixed concrete is not as expected. If required, dosing of admixtures along with a small quantity of water would be done by the ready mixed concrete supplier´s technical personnel.

What is precast concrete?

Precast concrete is a construction product produced by casting concrete in a reusable mould or “form” which is then cured in a controlled environment, transported to the construction site and lifted into place.