After casting slab,there are lot of possibilities that hair cracks develop in the slab.There are lot of questions that why cracks are developed?some may thing that is there any defect in the cement we use or mixing time of concrete.But following 10 points will clear your confusion by which we can stop cracks in concrete that are:-
Water Cement Ratio – If the water-cement ratio is not maintained properly, it will form cracks in the slab. So we should always maintain the water-cement ratio mentioned in the mix design properly. Due to the high water-cement ratio, the concrete gets bleed, in which all the water of the concrete comes on the filter, which is a very vital reason for the cracks.
Presence of silt – The presence of silt in fine aggregate or sand also results in hair cracks in concrete. If the silt is present in the sand, it will not be able to bond with cement due to which the concrete will not be set and there will be hair cracks in concrete. So we have to check properly the silt content in sand.Silt content should not be more than 6%.
Vibrators used for compaction – During the casting of concrete we use a vibrator for compaction and for removing the voids. But excessive use of a vibrator is also not good for concrete. With this, the coarse aggregates settle down and fine aggregates start coming up due to which cracks are developed in the slabs.
Reinforcement Temperature – Crack has also been seen occasionally due to the overheating of the steel bar used in construction works. Therefore, we should take some measures in very hot weather.The steel shuttering of the base of slab will be very hot and to lower its temperature use cold water to sprinkle on the slab base plates.
The difference in Slump Test Values – When we do casting on-site, we do slump tests in many intervals by taking concrete from different lots. So the value of these different slump tests should not have much difference in the character, because of this also the cracks have been seen in the slab.
Types of Cement – You all know cement is of many types. Choosing the right cement in construction work can save you from getting cracks. You should choose cement keeping in mind the weather and work type. In the slab, if you use cement whose heat of hydration is very high, then the chances of cracks in the slab will become higher.
Environment Effects – The weather in which you are casting your concrete is very vital for your concreting process. If you do not pay attention, then cracks are inevitable in your slab.Never allow concreting in very hot weather. Try to do concreting in evening time so that the weather will cool down to a minimum range. Due to the provision of concreting in more hot weather, the plastic shrinkage in the slab is developed, due to which the cracks are there, which we have to avoid.
Slump test values – When we do casting on-site, we take a slump test by taking concrete from different lots. So the value of these different lot’s slump tests should not have much difference in the character, because of this also the cracks have been seen in the slab.
Cement Types – You all know cement is of many types. Choosing the right cement in construction work can save you from getting cracks. You should choose cement keeping in mind the weather and work type. In the slab, if you use cement whose heat of hydration is very high, then the chances of cracks in the slab will become higher.
Overheating of shuttering material – Cracks can also be seen occasionally due to the heating of the shuttering material especially for Steel shuttering material. But the effect is very minor.
Temperature of Concrete – According to ASTM C 1064, the temperature of concrete should be in between 27.7 ℃ to 35 ℃. If the temperature of concrete is more than 35 ℃, then we should use ice in concrete.
Lubrication– The application of grease or shuttering oil or any kind of Lubricant on the rebar can prove fatal for concrete. There will never be the bonding of concrete and bars due to which we can get cracks.
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