Although the terms are often used interchangeably, cement is actually an ingredient of concrete. Concrete is a mixture of aggregates, ie: sand, stone and Portland cement.

Curing is the most important step in concrete construction, because proper curing greatly increases both concrete strength and durability. Concrete hardens as a result of hydration. (The reaction between cement and water). During the curing period, typically 5-7 days after placement, conventional surfaces need to be kept moist, covered or one can make use of commercially available curing compounds which seal in the moisture.

Extreme temperatures and high winds when exposed can make it more difficult to properly cure concrete. On hot days too much water can be lost via evaporation, and if the temperature drops below freezing, hydration can practically come to a standstill. In general the temperature of concrete should not fall below 10ºC.

Like all other materials, concrete will slightly change in volume when it dries out. The reason contractors put joints in concrete pavements and floors, is to allow concrete to crack in a neat, straight line at the joint where the volume of the concrete changes due to shrinkage. (On average every 4 metres.)

Concrete is tested to ensure that the material and compressive strength meets the required standards specified. Compressive strength is tested by taking concrete samples and making test cubes, curing these in a controlled environment and then measuring the force needed to break these cubes at prescribed intervals as they harden. (This is done at 7 and 28 days).

Too much water in the mix will produce a weaker, less durable concrete that may contribute to early flaking and spalling of the surface.

The most important factor here is the ratio of water to cement in the paste that binds the aggregates together. The higher this ratio, the weaker the concrete and vice versa.

Although we typically deliver in 6 cubic metre loads, our smallest delivery is 1 cubic metre. This may attract a transport surcharge.

Concrete hardens and gains strength as it hydrates. Although this hydration process continues for many years, it happens rapidly initially and diminishes over time. The ultimate strength will only be achieved over many years. But this would be impractical to measure, hence a time period of 28 days has been specified as the age at which all concrete should be tested .

Workability, consistency and segregation. Segregation is the degree at which the mixture binds, ie: stays together.

In order to place concrete as homogeneous as possible, with minimal cavities, such as air and water bubbles, thereby ensuring better strength and a quality finish, it is necessary to activate, ie: to excite mass so that each particle takes it’s correct position. This is typically achieved by using a poker vibrator ensuring tightly packed particles and air extrusion.