Concrete mixing - Lab Report Example

e is influenced by the chemical composition of the cement, hydration as well as development of microstructure, admixtures, and characteristics of the aggregate. In addition, the quality is strongly influenced by placement, consolidation, as well as curing. The performance of the concrete throughout its service life is also largely influenced by the method employed in mixing, placing, curing and transporting the concrete. It is also necessary for the civil engineers to perform various quality control tests which should include slump tests, air content tests, as well as strength-gain-with-time tests.

It is a well known fact that concretes which are considered as good and those considered as bad may have the same ingredients. The difference between good and bad concretes may come about due to the expertise of the engineer as well as the technicians who handle the concrete during construction. Concrete has been employed in many more applications in the past few decades due to the advances that have been made in concrete technology. It is necessary for civil and construction engineers to be aware of the available alternatives to the conventional concrete, roller-compacted concrete and fiber-reinforced concrete.

The weight of air entraining agent should 0.05% of cement. Air is entrained in the concrete by the air-entraining admixtures which contain surface-active agents which are concentrated at the air-water interface. Bubbles are formed readily when the surface tension is lowered, and the bubbles stability remains after being formed. The mixing water foams with the air-entraining admixtures and the formed consequently locked into the paste during the hardening of concrete. The entrapped air voids are not the same as entrained air voids.

This is because the air voids are formed by chance when air enters the fresh concrete during mixing whereas the entrained air voids are formed on purpose as described above. The size of the entrapped air voids can be as large as 3 mm