Start curing the concrete as quickly as possible. A longer curing period than is generally required for compressive strength may be needed in cold weather to reduce cracking. Apply a curing compound or protect it with damp burlap or other covering for at least three days.
Concrete is less likely to crack if the moisture evaporates slowly, so your project will be much stronger if you spray it with water a few times each day for the first week after you've poured the project. The hotter and drier the weather, the more often you should spray the new concrete.
The majority of cracks occur within 2-3 days after concrete has been placed. These are preventive measures which will minimise cracking in that period: See that sub-grade is well-compacted.
Rest assured that even with the best floor design and proper construction, concrete cracks are very common and, in some situations, inevitable.
Applied-load cracking.
In residential concrete, 4 inches is the minimum thickness for walkways and patios. Garage slabs and driveways should be 5 to 6 inches thick if any heavy truck traffic is anticipated, otherwise 4 inches is adequate.
Premature drying or rapid drying results in surface tension build up, and this propagates as cracks at the surface. The occurrence, direction and size can vary greatly depending on weather conditions at the time of placement.
In hot weather, concrete might crack if joints are not cut within 6-12 hours after finishing concrete. In this condition, if you don't want to use a grooving tool to cut joints, there are early-entry dry-cut lightweight saws that can be used almost immediately after finishing.
Concrete that is not moist-cured at all dries too rapidly, and reaches less than half its potential design strength. It will also have a greater number of shrinkage cracks.
While plastic shrinkage cracks can happen anywhere in a slab or wall, they almost always happen at reentrant corners (corners that point into the slab) or with circular objects in the middle of a slab (pipes, plumbing fixtures, drains, and manholes).
QUIKRETE® Crack Resistant Concrete Mix (No. 1006-80) is a 4000psi (27.5 MPa) blend of properly proportioned stone or gravel, sand, Portland cement, special synthetic fibers and other ingredients approved for use in concrete. The synthetic fibers eliminate the need for wire mesh in slab-on-grade construction.
If the rain begins after 2-4 hours from concrete placement, the surface needs to be covered; otherwise, the concrete surface will suffer damages. If rains pound on concrete 12 hours after placement, the likeliness of any damage is negligible.
Effects of too much mixing water
Segregation of the concrete mix under certain conditions resulting in variable quality throughout the concrete mass. Cracking - with too much water, there will be lower tensile strength, and a tendency towards high shrinkage and subsequent cracking.
Rain falling on top of freshly laid concrete can damage the surface and compromise a level and floated finish.
For the most part, if the cracks are less than 1.5mm in width and the length is less than those specified in Australian Standards (generally ranging from 5mm to 15mm) then it can be assumed to be minor cracking that is acceptable.
Moist curing is a common method of concrete curing. It involves wetting the concrete slab often with water (5-7 times per day) for the first 7 days. This method ensures your concrete slab will be extremely strong and durable, because it allows the moisture to evaporate slowly, preventing cracks and shrinks.
If water evaporates too quickly, it will weaken the finished product with stresses and cracking. To put it simply, the goal is to keep the concrete saturated during the first 28 days. The first 7 days after installation you should spray the slab with water 5-10 times per day, or as often as possible.
The general rule of thumb is that concrete takes about 28 days to dry for every inch of slab thickness. Within 24 to 48 hours, the concrete will be ready for foot traffic.
In Australia, concrete slabs must be fixed in adherence with the Australian Standards AS 2870 and AS 3600. The most common slab thickness in Australia is between 85mm and 100 mm. The thickness of concrete slabs is usually stated in specification documents.
Contractors mainly use wet cutting for tile work, reinforced concrete, metal, bricks and masonry. It can produce long, clean cuts because it is less prone to overheating or wearing the blade. If electrocution is a potential hazard, consider dry cutting instead.
If you're wondering why your concrete cutter has suggested using wet cutting, it's because they value worksite safety above all. One of the biggest risk factors when dry cutting into concrete, mortar, bricks, pavers, tiles or anything that contains crystalline silica (quartz) is the emission of tiny harmful particles.
Yes, in about a month, hairline cracks should subside. While shrinkage cracks can show up on the surface within hours of having concrete poured, it takes a full monthfor new concrete to fully settle. Don't be surprised if cracks that seemed visible at first are nearly impossible to see after a month of settling.
Concrete cracking can show up at any time, even on a one year old slab like yours. It is possible the base under your driveway wasn't compacted correctly, and that may have caused the concrete to sink or settle slightly, and thus to crack.
Hairline cracks or cracks under 1/4-inch wide may not indicate serious underlying damage, but if water gets into them and repeatedly freezes and expands, and vehicles continue to drive over them, the cracks can get bigger and the problem can worsen. These cracks can usually be repaired.
How Long Should Concrete Dry Before it Rains. If rain is in the forecast for the days or hours after you expect to finish the job, you shouldn't have to worry. As long as the concrete is given 4 to 8 hours after mixing and finishing to set up, rainwater won't affect it nearly as badly as it could.
Yes, you can pour fresh concrete over existing concrete. As long as your concrete is in mint condition, this task is doable. If you decide to pour a new mixture over an old slab, be sure it is at least 2 inches thick.