Tuesday, January 21, 2014

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Impacts of hot weather on concreting and protective actions

Concreting on hot weather can be difficult and also harmful for the quality of concrete. The dangerous thing about that is, the quality of concrete can never be fully undone. So, we need to take protective actions for concreting in hot weather.

But the question is, what is hot weather? In which climate condition we can say it’s hot for concreting.

Hot weather problems most commonly happen in summer but other climatic factors like high wind velocity and low relative humidity can occur at any time.

Hot weather can be defined when temperature is 32 ºc or above with windy conditions or relative humidity below 25%.

Impact of hot weather on concreting:
Hot weather increases the rate of evaporation of water from concrete. Thus the freshly mixed concrete need more water for achieving desired slump. More water increase the w/c ratio of concrete. And the increased w/c ratio decreases the strength of hardened concrete.

Another main concern of hot weather concreting is plastic shrinkage. Plastic shrinkage occur when newly placed concrete losses the moister rapidly from concrete surface.

Hot temperature also accelerates the hydration process of cement. This can be a cause for concrete cracking.

Hot weather also has a major impact on the setting time of concrete. That means concrete sets quickly in hot weather, therefore it requires quick finishing.

Protective actions for hot weather concreting:
It is better to avoid concreting on hot weather. But most of the time it is not possible to avoid because of tight project schedule. In this situation, the following actions can be taken to minimize the effects of hot weather on concrete-

·        Add water reducing admixture to concrete mix for maintaining w/c ratio.
·        If possible use largest amount & size of coarse aggregate to reduce the possibility of plastic shrinkage.
·        Mixing ice with concrete mix as pert of mixing water can decrease concrete temperature.
·        Avoid over mixing of concrete.
·        Arrange more workers for finishing the concrete quickly
·        Sprinkling water on forms and reinforcements before placing concrete (but no standing water should be allowed inside form).
·        Moisten the sub-grade prior to placement of concrete
·        Reduce the time between the mixing and placing of concrete.
·        Cover the newly placed concrete with plastic.
·        Protect newly placed concrete with sunshades or wind breaks whichever is possible.
·        After concrete fully set, start curing as soon as possible and continue cure the concrete for 7 days.

If these protective actions are properly followed, the hardened concrete will not lose its quality anymore.


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