Online Tutoring on the causes of Concrete Decay

Concrete is most widely used material for construction around the world due to its high durability. However, concrete deterioration may occur due to wide variety of reasons. Mostly there are combinations of factors that lead to concrete decay of which most significant causes will be discussed in this essay. The three main causes are use of vibrators during casting, lower percentage of water in concrete and density.

The first cause of cement decay is use of vibrators during casting. The use of vibrators with high amplitude as well as the lack of complete insertion of the vibrator head may result in bug holes (Johannessen, 2009). These holes are kind of surface defects due to entrapped air bubbles formation in the surface of formed concrete. Bug holes are than aggravated by the heavy application of form release agent and causes cement to decay.

 

Secondly lower percentage of water used in concrete preparation also causes cement to decay.  A low water to cement ratio leads to higher strength of concrete during the preparation of mix but it reduces the workability of cement. Water-cement ratio needs to be balanced within 0.4 to 0.6 to provide a solid workability without compromising the overall quality of the concrete mix (Portland Cement Association, 2002). Bu using the percentage of water in concrete, the concrete components separate out from each other and leads to lower chances of concrete decay.

Finally, cement decay is also caused by metal reinforcement. Whenever the steel or other metals corrode, the resulting rust occupies the whole metal and creates tensile stress in the concrete. This causes concrete to crack, spall or delaminate (Amleh & Mirza, 1999). The main cause of metal reinforcement is carbon dioxide in the air that dissolves the moisture under the surface of the concrete while reducing its alkalinity and its ability to withstand reinforcement against corrosion (Broomfield, 2002). As a result of the pressure, the cement decays by cracking.

 

Bibliography

Amleh, L. & Mirza, S., 1999. Corrosion influence on bond between steel and concrete. ACI Structural Journal, 96(3).

Broomfield, J. P., 2002. Corrosion of steel in concrete: understanding, investigation and repair. s.l.:CRC Press.

Johannessen, B., 2009. Concrete Works. In: Building Rural Roads. s.l.: International Labour Office; ILO’s Regional Office for Asia and the Pacific.

Portland Cement Association, 2002. Types and Causes of Concrete Deterioration, Illionis: PCA.