Fast-setting concrete is ideal for setting posts because there's no mixing—you simply pour the dry concrete from the bag right into the hole, then add water.
Although dry pouring of concrete might be fine for filling fence-post holes, it should be avoided as a placement method for concrete slabs if you want the concrete to look good and last for the long term.
Dry concrete is a fast-setting concrete mix that does not require mixing. It comes in a bag and can be poured directly into the post hole. Dry concrete is ideal for setting posts because it eliminates the need for mixing and sets quickly.
Because wet mix already contains water, it usually needs to be used no later than 24 hours before the mixture is impacted. Dry mix, on the other hand, offers a lot more flexibility regarding storage, as contractors can stock up on several bags of dry mix in bulk, and only use it when needed.
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.
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. Too little water leads to structurally weak concrete, and too much will disrupt effective curing and cause flaking, shrinking, divots or cracks.
ANSWER: Keeping concrete moist helps the curing process. Concrete hardens as a result of a chemical reaction, called hydration, between cement and water, not because it dries. The hardening, or curing, continues as long as moisture remains in the concrete.
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.
Dry concrete is mainly used in places where it will be in contact with the ground because it will collect water from it, needed to bind the mortar (hydration process). Dry cement mortar is therefore used in all substructures, sleepers or for soil stabilization.
The cement within a concrete mix doesn't contain any natural bonding agents – so when fresh concrete is added on top of an existing layer of concrete, the two won't join together. Once cured, the new concrete will simply sit on top as a separate layer. This will not produce a strong, serviceable floor.
If the weight of the concrete deforms the dirt base in any way, the entire concrete structure will be flawed. All of that is not to say that it is impossible to pour concrete over dirt. You can absolutely do it successfully, but you need to follow a specific process.
Many construction specialists recommend watering it down five to ten times per day, for the first week, starting 2-4 hours after it has been poured. The first two to four hours lets the concrete “finish”, which refers to the setting process.
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.
Standing water remaining on your concrete slab surfaces for an extended period of time means more than just cracks can occur. Damage to sealant is likely, which can further lead to mold and/or algae thriving.
Water allows the cement to solidify, providing the reaction necessary for the mixture to harden. The less water a person uses, the weaker the strength of the mix.
The shelf-life of concrete mix usually varies from a couple of months to several. If it has been stored in an airtight container in an environment where the temperature and humidity have been controlled (which is highly unlikely), it may last up to a year.
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.
Adding more water to the concrete increases workability but more water also increases the potential for segregation (settling of coarse aggregate particles), increased bleeding, drying shrinkage and cracking in addition to decreasing the strength and durability.
Water can be added when the truck arrives on site provided the exact slump and/or cement-water ratio isn't exceeded. Adding water should always follow ASTM C 94, Standard Specification for Ready Mixed Concrete.
Rain on freshly finished concrete can damage the surface, and in extreme cases, wash the surface off the concrete exposing the aggregate. To prevent this, covering the concrete with hessian will protect the surface from running water, reducing the risk of erosion.
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.
Because concrete is a very porous material, it will absorb any moisture that it contacts. This can cause pooling. Without crushed stone, pooling water will settle under it and erode your slab. Adding a layer of crushed stone will add proper drainage, as well as create a barrier between your slab and the ground.
Whether you pour concrete for a walkway or patio, a strong gravel base is required to prevent the concrete from cracking and shifting. Gravel is especially important in clay soil because it doesn't drain well, which results in water pooling under the concrete slab and slowly eroding the soil as it finally drains.
The simple answer is to prevent the concrete from cracking and breaking.