How to Solve Common Concrete Problems
Concrete is a relatively easy material to manage. However, you can run into huge problems if it is not worked on properly. Concrete problems vary but could include discolorations, shrinkage, scaling, and various other problems. Here are some common concrete problems to look out for and a guide on how to solve them.
Concrete should be of one color if you are using the correct batch and materials from the Ready Mix. However, concrete discoloration could occur if there are sudden changes to the cement material, if the finishing operations are rushed or if calcium chloride is added. All concrete ingredients must comply with the American Society for Testing and Materials (ASTM) standards.
How to solve concrete discoloration:
- Specify with the ready-mix supplier your tolerance levels
- Prepare a uniform subgrade
- Wait until all the water has evaporated before finishing the concrete
- Avoid hard troweling on the exterior surface
Another common concrete problem is scaling. Scaling occurs when the concrete surface breaks off and keeps peeling away. Scaling could also occur if non-air entrained concrete is exposed to freeze-thaw cycles, inadequate concrete strength, or inadequate curing procedure.
How can concrete scaling be avoided:
- Use a low slump-air (6 to 7 percent) in the entrained mix
- Wait till water has been evaporated from the surface
- Do not use salt or other chemicals during the winter season
One of the most repeated problems in concrete is crazing. Crazing occurs when the surface shows several interconnected fine cracks or when the cement paste comes up to the surface and shrinks. Although the concrete strength probably is not affected, cracks will show up when the slab is damp.
How to avoid crazed concrete:
- Cure the concrete in a timely manner
- Use a moderate slump concrete without bleeding and segregation
- Do not finish concrete until all water has evaporated
- Do not dust dry cement on the surface while water is present
- Do not sprinkle water over the concrete while finishing it
- If the weather could produce high evaporation rates, spray some water onto the subgrade, so it will not absorb the water from the concrete mix
Concrete can crack easily. It's unpreventable, however, it can be controlled. This is one of the main problems when constructing with concrete. Cracking can be the result of one or a combination of factors, such as drying shrinkage, thermal contraction, subgrade settlement, and applied loads. In the case of a wall, if a crack is not structural, or not too wide ( the acceptable crack width is subjective but it could range from 1/16” to 1/4”), or isn't leaking water, it should be considered acceptable.
How to reduce cracking of concrete:
- Remove topsoil, soft spots and organic material in the subgrade
- Compact all loose soil underneath the concrete slab
- Slope the subgrade for proper drainage
- Design a flexible concrete pavement that could accommodate load and movements
- Install concrete joints accordingly by sawing, forming or tooling a groove
- Place, finish and cure concrete accordingly depending on the weather conditions
- Do not finish concrete if it has not finished bleeding
- Do not overwork concrete surface
- Avoid rapid drying conditions or use a set retardant admixture
- Minimize the mix water content by maximizing the size and amount of coarse aggregate and use low-shrinkage aggregate
Concrete curling occurs when there is a difference in both temperature and moisture of the top and bottom surface. When curling occurs, the slab of the surface becomes unsupported from the base.
How to avoid concrete curling:
- Use proper curling techniques
- Place concrete joints accordingly
- Use low water content or use water reducing admixtures
- Use the largest possible aggregate size
- Ensure proper bonding when applying thin topping mixes
- Use enough, not excessive, amount of steel reinforcement in the slab
- Place concrete on a damp but absorptive sub-grade so that all the bleed water is not forced to the top of the slab