The purpose of curing is to reduce the rate of heat loss of freshly placed concrete to the atmosphere and to minimize the temperature gradient across concrete cross section. Moreover, curing serves to reduce of the loss water from freshly placed concrete to the atmosphere.
The purpose of curing is to reduce the rate of heat loss of freshly placed concrete to the atmosphere and to minimize the temperature gradient across concrete cross section. Moreover, curing serves to reduce of the loss water from freshly placed concrete to the atmosphere.
Ponding: This method of thermal curing is readily affected by weather condition (cold wind). Moreover, a large amount of water used has to be disposed off the construction sites after curing. Polythene sheet: This method of curing is based on the principle that there is no flow of air over the concrete surface and thereby no evaporation can take place on top of the freshly concreted surface by provision of polythene sheets. However, it suffers from the demerit that polythene sheets can be easily blown off in windy condition and the performance of curing would be affected. Moreover, for water lost due to self-desiccation, this method cannot replenish these losses.
Dr David Ho, whilst he was at CSIRO Melbourne, did a series of experiments. These showed that sealing the concrete was not sufficient to get full curing. The increase in porosity was roughly equivalent to the increase obtained by reducing the strength of the concrete by one grade.
For the best curing:
1. as soon as the concrete can take the weight, apply a roll of we hessian over the concrete;
2. place a soaker hose and turn it on to trickle (for large areas, a distribution pipe and multiple hoses may be needed to ensure uniformity);
3 place a layer of polythene sheeting over all the hessian and hoses;
4.place a layer of insulation over the polythene;
5 place a layer of white polythene over the top
6 weight it down to prevent the wind removing it.
The thermal gradients from the first day to the second night are sufficient to cause significant cracking of slabs and columns even in warm weather.
This suspended slabs may not need the heavy insulation layer if the weather is benign. Large columns do.
I think the two mentioned way are completely differs, curing by ponding water may cause more troubles due to uncontrolled water quantity. On the other hand, using polyethylene sheets are more efficient but it will be a cost matter.
Ponding: This method of thermal curing is readily affected by weather condition (cold wind). Moreover, a large amount of water used has to be disposed off the construction sites after curing.
Polythene sheet: This method of curing is based on the principle that there is no flow of air over the concrete surface and thereby no evaporation can take place on top of the freshly concreted surface by provision of polythene sheets. However, it suffers from the demerit that polythene sheets can be easily blown off in windy condition and the performance of curing would be affected. Moreover, for water lost due to self-desiccation, this method cannot replenish these losses.
This answer is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.
Ayad,
Ponding suffers from 2 features:
1. Disposal of the water
2. leaching of the calcium.
Curing by ponding in lime water is what we do to cure cylinders. The work by Emeritus Professor David Ho, when he was at CSIRO, showed that water curing is best, fully sealed polythene next (probably along with forms in place), then curing compound.
Heat curing also reduces the effectiveness of the curing.
This was confirmed by RTA NSW - see Ho & Chirgwin, Curtis & Chirgwin, Ho, Chirgwin and Mak
http://www.sciencedirect.com/science/article/pii/0950061895000151
https://trid.trb.org/view.aspx?id=1202185
https://www.concrete.org/publications/internationalconcreteabstractsportal/m/details/id/6092
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