Concrete does not absorb any noticeable amount of water in a normal time frame.
A concrete mixture can be made from fine aggregates like sand, rocks, and cement but it doesn't dissolve in the rain or even when submerged underwater. The concrete also goes through a process called curing. It occurs when reactions eventually prevent water tightness on the concrete.
There is no way properly prepared concrete will absorb water. The purpose of using sand and gravel in the mixture is to keep the particles porous so that when water does land on or near a piece of concrete it will flow through all these voids between the sand and gravel particles until it reaches beneath an impermeable layer such as soil which acts as a sump for the flowing water.The final reason that concrete floor does not absorb water is that it already contains a high amount of water. The water is responsible for all the chemical reactions in your cement mix. Semi-solid concrete must be damp throughout the mixing and placing process so that all the ingredients mix together correctly and set to their optimal strength. Also, you can use portland cement which stays hard even on high relative humidity.
So why doesn't concrete floor crumble when it rains? The combination of sand, gravel and cement hold each other in place by forming an interlocking matrix through chemical reactions. The curing process holds everything together and because it has some give and flexibility to it, no matter how strong nor thick nor heavy a slab might be if set properly it will never need support because gravity won't cause it to fail.Concrete absorbs only an infinitesimally small amount of moisture until its ideal calcium-to-carbonate ratio has been reached. If the mixing process is started correctly, that ratio will never be reached because concrete sets properly within a couple of hours and then it will naturally resist absorbing any more water. Therefore, do not worry about your hardened concrete walls or concrete floors absorbing water.
No, there is no way concrete absorbs water. The cement mixture hardens and becomes waterproof to prevent any water absorption. Thus, it is not only indoor concrete surfaces that are safe from absorbing rainwater. Your outdoor surfaces can be safe too.
When making concrete you need to set and cure it properly to allow the chemical process and avoid coarse aggregates. Other concrete floors will not absorb an excessive amount of moisture in the soil due to its high-quality mixture. It already contains too much water and there's no need for additional moisture to make it work correctly. The sand and gravel particles in the cement harden and concrete mix interlocks with one another to keep everything sturdy.
Since each particle also forms thousands of tiny air pockets between itself and its neighbours, gravity can pull water down through them until any puddle evaporates or moves somewhere else. So, does concrete absorb water poured on top of it? No. Concrete will not absorb surface water even if you pour hundreds of gallons of water on top of a newly poured slab.Concrete is a porous structure, but not in a way that allows water to through the entire slab. But, it can absorb moisture and cause damage if too much builds up beneath your concrete for too long. There are chemicals that are released into concrete when it's being poured that seal the pores shut and prevent any more absorption.
There are several reasons why moisture might build up beneath the slab of your new concrete installation. If you don't seal the porous material until the concrete set and cures, then you should worry about the concrete absorbing water. There's a chance that water will flow through and pool underneath. If you don't choose an appropriate site for your project, rainwater might flow across the surface too quickly and wash away some of the sand and gravel particles holding together your steel mesh or other material that forms an internal frame for your concrete. Small tunnels, humid environments can cure slowly and bring down the concrete. There may be chemicals used to treat or prepare your soil that cause poor drainage. The water will pool underneath rather than sink into the ground. Those chemicals can take weeks or years to dissipate fully depending on what they're made from.
Concrete's compressive strength refers to how well it supports itself vertically and holds up against lateral loads such as wind and earthquakes. Moisture underneath the surface can cause this strength to decrease by several percentages.
Concrete's flexural strength refers to how well it supports itself when force is applied at its exterior, such as when it's supporting your new deck or patio slab. As with compressive strength, too much moisture beneath the concrete's surface will decrease this type of strength by several percentages.
Once you've determined that there is too much water underneath your concrete installation for proper curing, what steps can you take? First, remove any impermeable material from the space so that it doesn't continue acting as a barrier between pools of water and the concrete itself. Then you'll need to sweep away all standing puddles on your wet concrete floors. Doing this ensures they don't remain in place and gradually evaporate. You may also want to treat the area with a dehumidifier if it's safe and convenient to use. Doing this removes moisture from wet surfaces and leaves the concrete dry. If you can't immediately take any steps toward mitigating excess water, then you should at least cover the installation with a tarp or a vapour barrier until you can remedy the situation. Make sure that whatever material you use is taped down securely so that it doesn't flap loosely in windy conditions. Then weigh down the edges of your covering material with something heavy enough to hold everything taut. Yet, it should be small enough that rainwater won't pool on top of it instead of flowing across its surface into drainage areas below your concrete slab.
As long as a good concrete sealant is applied before the concrete dries, then it will help to seal concrete. The pores on the concrete's surface are blocked so that water flows across it rather than sinking into its pores. But even if you apply a quality concrete sealant like polyurethane sealants to your new installation, there are still several possibilities that moisture might infiltrate your concrete surface. Acrylic sealers are best for basement floors to ensure structural integrity and prevent water tightness.
First of all, if you don't use appropriate site preparation techniques prior to setting and curing your installation, then rainwater may flow across the surface too quickly for any sealant you use to be effective. Second, soil treatments used on your site, either chemicals or other additives, may compromise how well the sealant adheres over time. Keep an eye out for any peeling edges around areas where the sealant was applied.
Finally, if the concrete itself lacks climate control and has poor ventilation, then excess water may seep into it from below and compromise its strength and durability. For more information about concreting or concreters, take a look at the New South Wales Department of Fair Trading website.