When a concrete mixture is too wet, it causes a greater amount of shrinkage during the drying process than is needed. As a result, the concrete has a great likelihood of cracking and for those cracks are likely to be a fairly good size.
The issue of adding too much water
This is where water pools on the surface of the drying concrete, which can lead to spalling and cracking on the surface. Not only will this hinder the strength of the concrete, but it will also result in a poor-looking final product.
DO spray new concrete with water. One of the most common methods for curing concrete is to hose it down frequently with water—five to 10 times per day, or as often as you can—for the first seven days. Known as “moist curing,” this allows the moisture in the concrete to evaporate slowly.
NOTE: the more water that is added to the mix the weaker it becomes; adding one extra quart of water per 80 lb bag can reduce the strength of the concrete by up to 40%.
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.
When a concrete mixture is too wet, it causes a greater amount of shrinkage during the drying process than is needed. As a result, the concrete has a great likelihood of cracking and for those cracks are likely to be a fairly good size.
How long does four to six inches of concrete take to cure? As stated previously, concrete takes approximately 26-30 days to reach its full strength. If the concrete is professionally poured and floated, the curing process should be sound and ensure proper hardening of the concrete base.
Strength Reduction
The excess water will not participate in the hydration process and retains in concrete even after hardening. This water will evaporate when exposed to atmosphere and form voids in the concrete. These voids formed are therefore responsible for the reduction of compressive strength of concrete.
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.
There are a few factors which lead toward soft concrete. Excess water is the biggest culprit but we also have to consider the following; poor or insufficient curing, too little cement, carbonation, incorrect proportion of trace ingredients such as pozzolans or shrinkage additives.
Your fresh concrete mustn't dry out during this period, especially if it is exposed to direct sunlight. One of the most typical methods for curing concrete is to hose it down with water—five to ten times per day, or as often as you can—for the first seven days.
Concrete typically takes 24 to 48 hours to dry enough for you to walk or drive on it. However, concrete drying is a continuous and fluid event, and usually reaches its full effective strength after about 28 days. Here are some of the basic facts regarding the question of concrete drying and curing time.
Water plays a critical role, particularly the amount used. The strength of concrete increases when less water is used to make concrete. The hydration reaction itself consumes a specific amount of water. Concrete is actually mixed with more water than is needed for the hydration reactions.
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.
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.
Water Pooling On Concrete
Water pooling can create lasting damage if not tended to right away. Soil washout under driveways can cause dips where the concrete is no longer supported. If water is pooling on your concrete driveway, it can lead to: Cracked, damaged concrete.
Despite being an incredibly durable material, concrete can be susceptible to damage, especially water damage. Concrete is porous and can absorb water, which can lead to cracking. This can allow water to travel further into a foundation which can lead to structural damage.
Water–cement ratios in the range of 0.40 to 0.60 are typically used. For higher-strength concrete, lower w/c ratios are necessary, along with a plasticizer to increase flowability.
Strength tends to increase, with mixing time, up to a point. However, over-mixing causes excess water evaporation and the formation of fine particles within the mix. This weakens the concrete and makes it harder to work with.
Among them, the ratio of water and cement is critical, because it directly determines the strength of concrete. If too much water is added, the strength of concrete will be lowered and cannot meet the construction requirement of the project. What's worse, it may cause peeling or disintegration.
After pouring and finishing the slab, you should wait 24-48 hours before removing concrete forms. You can remove the formwork once the concrete has enough strength to keep it from cracking. Concrete naturally contracts as it cures, so it should pull away from the forms and make them easier to remove.
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.
Curing should be started as soon as possible and should continue for a period of 5 days in warm weather at 70 ºF (21 ºC) or higher or 7 days in colder weather at 50 ºF to 70 ºF (10 ºC to 21 ºC).