Concrete and its Properties 2

Concrete is the pourable mixture of cement, water, sand, and gravel that hardens into a super-strong building material. Concrete is commonly used to cast building foundations, sidewalks, slabs and columns and even highways are all made of concrete.

Proportioning and mixing concrete

The proportion of each material in the concrete mixture affects the strength and durability of the final hardened concrete. Though measurement by volume is suitable for minor projects in large scale projects the proportions are best determined by means of weight as the use of volume may not be as accurate. When proportioning the concrete mixture the environment in which the concrete is to be used should be carefully considered; ie exposure to sea water, trucks, cars, forklifts, foot traffic or extremes of hot and cold.

A good concrete mix should produce concrete that is easily workable, cohesive when plastic and can be easily placed at a favorable cost. The mix should give a strong and durable concrete when it sets and hardens.

Properties of Concrete

Properties of concrete are divided into two major groups;

1. Fresh Concrete Properties

2. Hardened Concrete Properties

In this article and the subsequent series that will follow we shall focus our attention on Fresh Concrete, its properties, challenges and how to avoid them.

Fresh Concrete

Fresh concrete is the type of concrete that is still in its plastic form. This is also referred to as "Green Concrete".

Properties of Fresh Concrete

Properties that determine fresh concrete are;

•    Setting

•    Workability

•    Bleeding

•    Segregation

•    Hydration

•    Air Entrainment

1. Setting

Setting of concrete is the hardening of concrete before its hydration or before it gains strength.

Concrete setting is related to the setting of cement paste. Thus cement properties may greatly affect the setting time.
Some of the factors that influence or affect the setting of concrete include;

• Water-Cement ratio - It is water cement ratio that basically governs the setting of the concrete. The correct proportion of water cement ratio will guarantee a perfect and fast concrete setting.

• Type of cement - Cement affects the hydration process and therefore setting of concrete. Cement is the    paste that holds or binds all the ingredients. The quality of cementing material used greatly determines how well fast the setting will come out.

• Cement content - Cement content in the concrete mix should be in the right and advised quantity.

• Type of Aggregate - Rough and angular aggregates are preferable as they provide greater bonding.

Other factors include humidity and temperature.