Shrinkage cracks in concrete Shrinkage cracks in concrete generally occurs during fresh state of concrete usually within 1 to 2 hours of placement (when water from concrete evaporates from the surface). They varies in width from hair line to 3mm in width and from few centimeters to a meter in...
Precautions to minimize Plastic Shrinkage Cracks: The Plastic Shrinkage cracks occur on the surface of freshly placed concrete during finishing or soon after. In plastic concrete bleed water surfaces due to gravity. If the accompanying settlement is...
I see a cracks in concrete slab, does this happen due to concrete itself or due to workmanship problem.
To solve the Problem at your current locations - as the concrete is old and lot of materials were settled over the surface of the slab, the cracking is not clearly visible thus make it difficult to do a treatment.
First thing in a waterproofing procedure shall be; cleaning of slab top area, removing the loose materials and then filling the slab portion with water to do a leakage test atleast for 48 Hours.
Post 48 Hours you will come to know about currently leaking locations, remove the water from the top of the slab and with the help of angle grinder start grinding the slab top surface where you think a leakage is observed at bottom. in most of the cases leakage are from the same above location as seen from below. when you start grinding, you will find a crack in surface, once you found the crack just move across it and grind all surface wherever the crack pattern is taking you.
Below photo shows use of angle grinder to find crack at identified location from bottom.
Once you find the crack in its complete aspect, open it in "v" groove, below photo shows identified crack.
Post opening of the cracks, you can treat the crack with one of either way from below or any suitable way found by you to treat the crack.
1. Seal the crack with non-shrink grout by inserting nipples for pressure grouting at max 1 meter center to center distance and minimum 2 per crack for doing pressure grouting. on next day you can do pressure grouting by cement slurry.
2. You can fill the crack with cement and SBR mixture for minimum twice in period of 1 to 2 hour, as you pour this mixture, it also leaks down from below so after first pouring do second pouring, post to that do fill the crack with polymer modified cement mortar or any non-shrink grout.