CONST MTRLS & TESTING: CONCRETE

Concrete is the combination of cement with aggregates, both fine and coarse, with enough proportion of water. Although more commonly called cement, it is technically called concrete.

There are two ways to check proportioning of materials in concrete.

1. Nominal mix which would be following an arbitrary set of proportions already had been checked. This kind of mix is possible for the lower strength requirement of concrete from 5N/mm2 to to 20N/mm2. 

courtesy of the Balance

2. Design mix is the one to be designed as per required in the structure. This is the mix used for high rise structures as they needed higher strength of concrete.

 Click here for downloadable notes on Concrete


Different kinds of concrete are also stipulated in ASTM 150 whereby Type I is the concrete used for all general works and the others - Type II until V - are for special situations. Apart from these 5 main types of concrete, there are also special types of concrete.
 
Workability is one aspect which needs to be given attention with concrete. Workability is the east of working with concrete - transporting, batching, placing, etc. Since workability is in direct proportion with water content, proper proportioning should be done not to sacrifice strength of concrete.

courtesy of Taracon Precast

Pre-cast concrete is a type of concrete which is fabricated from the plant as per specification and then later transported on site. These concrete members usually carry enormous amount of strength which is impossible to attain on site.

Pumped concrete, on the other hand, is concrete which is used for the higher floors of a structure.This type of concrete has high workability, which means it has more amount of water than usual, the strength is just compensated with the use of additives.