Understanding the Basics of Concrete

• 19 April 2020
• Construction Focus
• 8469 Views

Concrete has been used widely internationally. It is durable and flexible in its usage. As a construction material, it is robust and able to give sound reduction and fire-resistant properties.

Raw materials

The raw or constituent materials are one of the most important factors prior to the successful design and construction of concrete structures. Hence it is paramount to ensure that raw materials are carefully selected in the first instance.

The basic raw materials are:

1. Cement

2. Aggregates (Fine / course)

3. Water

The behaviour of Portland cement is measured by its class (i.e. Class 42.5 according to specifications by the consultant). However, the cement source, country of origin and batch are some of the major factors that affect the exothermic hydration reactions. This has various impacts on the setting time and heat dissipation issues.

Aggregates are divided into fine and coarse aggregates – generally, sand and stones. They act as the inert materials in concrete and account for the 60-70% of the volume of concrete. Factors that affect the concrete caused by the influence of aggregates are:

• Grading

• Durability

• Particle shape and texture

• Abrasion and skid resistance

• Absorption, adsorption and surface moisture

Generally, rough-textured, angular, and elongated particles require more water to produce workable concrete than smooth, rounded compact aggregate, and cement content must also be increased to maintain the water-cement ratio. The normal rule of thumb is to avoid flat and elongated aggregates.

Void content between particles is a large topic as it affects the amount of cement paste required for the mix. The following are some of the norms:

1. Angular aggregates increase the void content.

2. Larger sizes of well-graded aggregate and improved grading decrease the void content.

3. Absorption and surface moisture of aggregates are measured when selecting aggregate because the internal structure of aggregate if made up of solid material, has voids that may or may not contain water.

4. The amount of water in the concrete mixture must be adjusted to reflect the moisture conditions of the aggregate.

5. Abrasion and skid resistance of aggregate are critical when the aggregate is to being used in concrete such as for heavy-duty pavements which are subjected to heavy abrasion.

Generally, the water used should be clean and free from harmful material. The PH value of the water has effects on the concrete structures and is especially critical in the specification of the water-cement ratio. This ratio influences various properties such as workability, strength and durability.

After the process of the material selection, the materials are carefully mixed using a recommended and approved mix design and then they are fed into a mixing plant which we commonly call a Ready Mixed Concrete Batching Plant. The most widely used are Wet Mixed Plants. The design mix is very important as it is a secret recipe that involves various steps, calculations and laboratory testing in order to find the right mix proportions. These mix proportions’ ultimate objective is to make the concrete construction economical in achieving the required or target strength of structural members.

The final result is to produce quantity concrete using excellent materials to allow a successful project construction. Increasing dosage of the raw materials of any type does not add benefits to the final product without proper design planning. Instead, this ill-conceived action increases the cost for the ready-mixed batching plant and results in further depression of profits.

The author is the Director of Hong He Supply Pte Ltd. He is an Engineer with more than 20 years’ experience in the concrete and asphalt industry. 

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