The magic of concrete is that each constituent part must be in perfect harmony. Mixing an incorrect ratio of sand, stone, cement and water will yield an inferior product. One of the most common errors of the concrete mixing process is the addition of too much water.
Keep working the mix to find the perfect ratio – it's important that the right concrete mix ratio is reached before attempting to pour it. If this isn't done, you could end up with concrete which is too runny. The problem with soupy concrete is that it's far more likely to crack once it has dried.
- Overmixing concrete damages the quality of the concrete, tends to grind the aggregate into smaller pieces, increases the temperature of the mix, lowers the slump, decreases air entrainment, and decreases the strength of the concrete. Also, overmixing puts needless wear on the drum and blades of the transit mixer.
If your concrete mix is too wet it will also be more porous once cured, making it difficult to achieve the desired finish and potentially making it not fit for purpose. In short, a concrete mix that is too wet could seriously impact the durability, longevity and strength of your project.
Perhaps the most tell-tale sign of shoddy concrete pouring is the presence of cracks. The primary cause of cracks in dried concrete is tensile stress on the structure.
Work the mix with a hoe, gradually adding water, until the mix reaches a uniform, workable consistency. Properly mixed concrete should look like thick oatmeal and should hold its shape when it is squeezed in a gloved hand.
Spray: To maintain the proper moisture levels, concrete should be sprayed with water frequently. This is known as moist-curing. Most specialists recommend watering the slab 5 to 10 times per day for the first seven days. Moist-cured concrete can be up to 50% stronger than dry-cured concrete.
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.
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.
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.
Following compaction, the surface can be choked off with a fine-grade material to separate the vapor barrier from the concrete. 5. Avoid overworking the concrete, especially with vibrating screeds, jitterbugs, or bullfloats. Overworking causes aggregate to settle and bleed water and excess fines to rise.
Anytime that there is a higher water to cement ratio, it will decrease the strength and durability of the concrete. Water can breakdown the materials that concrete is made of. Create mold and bacteria in the concrete, and cause concrete foundations to move and shift. All of these result in cracks in the concrete.
A 2-hour shelf life has been a historic general rule of thumb that should not be exceeded based on setting time test data from cement manufacturers. In practice the time required will depend on the ambient and concrete temperature, cement type, mix proportions, the use of admixtures and consistence.
Scaling is one of the most common problems of concrete. In scaling, the surface layer of concrete gets deteriorated by getting peeled or by breaking off.
Pouring concrete over existing concrete is possible as long as you do so properly. When the old concrete serves as the foundation for your new pour, it needs to be a solid one.
When the surface of the concrete is not kept moist within the first 24 hours after the casting, the evaporation from the exposed horizontal surface results in plastic shrinkage cracks and a weak and dusty surface.
HOW DOES RAIN AFFECT CONCRETE? Rain falling on top of freshly laid concrete can damage the surface and compromise a level and floated finish.
Water facilitates the curing and hardening processes. Without it, the chemical reactions needed to form the hard crystals that give the concrete its strength can't take place.
Properly curing your concrete improves strength, durability, water tightness, and resistance for many years. The first 7 days after installation you should spray the slab with water 5-10 times per day, or as often as possible. Once the concrete is poured the curing process begins immediately.
For concrete to dry and reach its full strength, it typically takes about 28 days per inch of slab thickness. Once conditions are conducive for the concrete to cure at 85-90% relative humidity.
Any excess water not absorbed by the sand and cement rise to the surface. This leaves a pool of water on the surface of the concrete, which we call bleed water.
But if the sealer isn't applied uniformly to begin with, or if not enough coats are used, the slab will appear blotchy upon drying. This is caused by the sealer filling in some of the valleys, but not all, and failing to remain on top of the hills.
For large scale projects like buildings, concrete should last up to 100 years if it's properly cared for. Concrete projects that experience more wear-and-tear like sidewalks and driveways have an expected lifespan of about half that—50 years.
This means the moisture in drying concrete is going to leave essentially only from the top, causing the slab to shrink faster (concrete shrinks as it dries) on the top than the bottom, and curl upward in the process.