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When they poured the slab for a new house the forecast was for chance of light scattered showers, but while they were pouring they got hit by a light sprinkle and then near the end it rained hard for maybe 1/2 hr.
The next day the slab looked hard, but it also appeared to be clear to translucent for the first inch or so.
Given that the slab is 3 or so inches thick, I am concerned about strength and durability.
It has been sitting now for about 4 months. Are there any tests that one can do before buying to be reasonably satisfied of the structural integrity of the slab?
Since it is in an active soil area, it will be stressed in the future. It is a post-tension slab. Only the garage area is left uncovered, the rest has carpet and tile. (There is a flat landing area that is "slab level" at the front of the garage and then the rest slopes down about 1".
Thanks.
structural engineer is one who could give you best answer--one who designs slabs...who is the contractor that poured the slab...what kind of warranty does he provide
As another poster pointed out, either a structural engineer or call another concrete subcontractor who might be able to advise you. Overly wet cement can indeed do bad things to the strength and durability of the concrete.
Quote:
Originally Posted by kwakTexas
When they poured the slab for a new house the forecast was for chance of light scattered showers, but while they were pouring they got hit by a light sprinkle and then near the end it rained hard for maybe 1/2 hr.
The next day the slab looked hard, but it also appeared to be clear to translucent for the first inch or so.
Given that the slab is 3 or so inches thick, I am concerned about strength and durability.
It has been sitting now for about 4 months. Are there any tests that one can do before buying to be reasonably satisfied of the structural integrity of the slab?
Since it is in an active soil area, it will be stressed in the future. It is a post-tension slab. Only the garage area is left uncovered, the rest has carpet and tile. (There is a flat landing area that is "slab level" at the front of the garage and then the rest slopes down about 1".
Thanks.
FYI: this practice is not done any longer as it costs too much money and takes the concrete too long to set up (for the BUILDERS pocketbook) but they USED to put sprinklers on freshly poured concrete. The longer it takes for the concrete to cure the better in MOST cases. They have to put special chemical admixtures IN the cement mixture to make it cure faster. TONS of foundations have been poured in the rain. Our first house...... it rained for a week after they poured it. Never had a single problem w/ the foundation. I'm about 2 miles from that house now and it still has done just fine after 15 years (omygosh, we signed the contract to build that house 15 years ago about last week - WOW).
Below are some tidbits of info about curing concrete. As you can see one way to do it is by SUBMERGING the poured concrete IN water. The rain did not hurt it at all.
FYI: the terms "concrete" and "cement" are not the same. Cement is in powder form and is an ingredient used to make concrete.
Curing
In all but the least critical applications, care needs to be taken to properly cure concrete, and achieve best strength and hardness. This happens after the concrete has been placed.
Cement requires a moist, controlled environment to cure – hydrate – fully.
The cement paste hardens over time, initially setting and becoming rigid though very weak, and gaining in strength in the days and weeks following.
It does not set by drying out, but by the cementitious material chemically reacting with the water – hydrating. The pictures above show two of many ways to achieve this, ponding – submerging setting concrete in water, and wrapping in plastic to contain the water in the mix.
Properly curing concrete leads to increased strength and lower permeability, and avoids cracking where the surface dries out prematurely.
Care must also be taken to avoid freezing, or overheating due to the exothermic setting of cement.
Improper curing can cause scaling, reduced strength and abrasion resistance and cracking.
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Concrete Strength
The amount of water in concrete while it is being placed is normally more than needed for curing. However, concrete that dries out too quickly may not retain enough water for the hardening process -- a chemical reaction called hydration.
Temperature greatly affects hydration. While hot weather can make concrete harden and gain strength faster, it ultimately leads to a weaker concrete than one which has been kept cool (50 to 70 degrees Farenheit) during its first few days.
The goal is to keep concrete cool and moist so it gains strength slowly, but efficiently. Laboratory tests show that moist-cured concrete can be twice as strong as concrete cured in a dry environment.
Freeze-Thaw Resistance
Curing can help concrete be more resistant to damage from freezing and thawing. As long as hydration continues, the cement paste hardens and becomes more dense. If concrete is cured properly, it will be less porous than uncured concrete -- making it more difficult for water and salts to penetrate. Properly cured concrete also is more wear-resistant and less susceptible to dusting and scaling.
Moist Curing
Probably the best method for curing concrete, although sometimes the least practical, is to flood the surface continuously with water for the first week after placement. Do not let the concrete dry out. Contractors sometimes will recommend to a homeowner to wet a new driveway during its first week. But, if concrete dries between soakings, this alternate wetting and drying may actually damage the concrete. If you are going to water cure, keep the sprinkler going continuously for at least one week.
source:Guidelines for Curing and Sealing Concrete (broken link)
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What does it mean to "cure" concrete?
Curing is one of the most important steps in concrete construction, because proper curing greatly increases concrete strength and durability. Concrete hardens as a result of hydration: the chemical reaction between cement and water. However, hydration occurs only if water is available and if the concrete's temperature stays within a suitable range. During the curing period-from five to seven days after placement for conventional concrete-the concrete surface needs to be kept moist to permit the hydration process. new concrete can be wet with soaking hoses, sprinklers or covered with wet burlap, or can be coated with commercially available curing compounds, which seal in moisture.
Curing is one of the most important steps in concrete construction, because proper curing greatly increases concrete strength and durability. Concrete hardens as a result of hydration: the chemical reaction between cement and water. However, hydration occurs only if water is available and if the concrete's temperature stays within a suitable range. During the curing period-from five to seven days after placement for conventional concrete-the concrete surface needs to be kept moist to permit the hydration process. new concrete can be wet with soaking hoses, sprinklers or covered with wet burlap, or can be coated with commercially available curing compounds, which seal in moisture.
Properly Curing Concrete Slabs
Why cure concrete. Curing serves two main purposes.
It retains moisture in the slab so that the concrete continues to gain strength
It delays drying shrinkage until the concrete is strong enough to resist shrinkage cracking.
Properly curing concrete improves strength, durability, water tightness, and wear resistance.
How to cure concrete.
Water cure-the concrete is flooded, ponded, or mist sprayed. This is the most effective curing method for preventing mix water evaporation.
Water retaining methods-use coverings such as sand, canvas, burlap, or straw that are kept continuously wet. The material used must be kept damp during the curing period.
Waterproof paper or plastic film seal-Are applied as soon as the concrete is hard enough to resist surface damage. Plastic films may cause discoloration of the concrete-do not apply to concrete where appearance is important.
Does anyone else remember seeing builders put out sprinklers on freshly poured slabs? Man, they sure don't go thru the trouble of doing that anymore. I also remember after reading one of those "tidbits" above people standing out w/ the hose watering down their new driveway after having one poured.
I constantly hear about how bad the clay is on houses and virtually every house is expected to have foundation problems.
I am originally from MN and we do have some heavy clay areas up there as well. The difference is (until the big NAFTA era/construction boom/cheap labor) up there, they actually did all of those things to the concrete. Rarely do they have foundation problems in the older houses...even in clay areas.
Down here, you see all kinds of zigzagging bricks, etc. Everyone says if you just keep your soil moist it won't happen...how about if contractors and builders do it right in the first place?
At a minimum, you have to let the concrete sit 3 weeks (from what I've read) with daily sprinkling. You see houses being built on top of setting concrete after 2 days.
I am originally from MN and we do have some heavy clay areas up there as well. The difference is (until the big NAFTA era/construction boom/cheap labor) up there, they actually did all of those things to the concrete. Rarely do they have foundation problems in the older houses...even in clay areas.
But in MN, the frost line is much deeper than in TX and as a result you either have a basement or a slab that goes much deeper than in TX.
MN basement footings are some 8ft down, where the soil is usually much more stable than just 2ft down, and chances are that the footings are massive.
My current house in Dallas has a really crappy pier-and-beam foundation where I guess the piers go down maybe 4 feet into soft clay and it is moving all the time (built in 1963).
My previous house in Garland had a modern post-tension slab and sat on soil with limestone 2 feet under the topsoil (planting trees myself was not fun in that soil...). It is rock-solid. They didn't sprinkle the foundation when it was built in 2000, though.
When they poured the slab for a new house the forecast was for chance of light scattered showers, but while they were pouring they got hit by a light sprinkle and then near the end it rained hard for maybe 1/2 hr.
The next day the slab looked hard, but it also appeared to be clear to translucent for the first inch or so.
Given that the slab is 3 or so inches thick, I am concerned about strength and durability.
As others have mentioned, moisture isn't bad but helps curing concrete. Excessive rain usually doesn't impact the integrity but can mar the surface. Washing the soft surface is done to expose aggregate (without grinding), if you want that look. If you want a nice, smooth surface, rain can ruin it.
Also, your slab is just 3 inches thick (or should I say thin)? That would be too thin for even a patio slab (min. 4").
haing it rain on concrete can indeed ruin it because of what the water does to the chemical balance in the concrete--if the balance is not right--the concrete will be too crumbly -- so it is not so much the wet effect as the leaching effect...
as poster pointed out---the 3 in is a BIG factor--don't think even a city inspector could/would have passed a slab that was THAT thin---
our foundation is visible for at least 8-12 inches around the house (havenl't measureed it) and has concrete below ground level not visible...
haing it rain on concrete can indeed ruin it because of what the water does to the chemical balance in the concrete--if the balance is not right--the concrete will be too crumbly -- so it is not so much the wet effect as the leaching effect...
as poster pointed out---the 3 in is a BIG factor--don't think even a city inspector could/would have passed a slab that was THAT thin---
our foundation is visible for at least 8-12 inches around the house (havenl't measureed it) and has concrete below ground level not visible...
No, the rain is VERY GOOD for it. It only strenghtens it. Years ago they used to actually put sprinklers on the foundations as soon as they poured them and let them go like that for several days. Concrete is even poured IN water. Look at the supports for bridges and boat ramps (poured one of those myself). Water is VERY GOOD for the foundation to cure. Check out the links I've posted. Some even SUBMERGE freshly poured concrete in water. The longer it takes to cure the better and the ONLY way it can take longer to cure is if it never dries out.
It is when the poured concrete is LACKING in water/moisture that it becomes crumbly. It MUST have the water to properly cure.
What is NOT GOOD is if indeed the foundation is only 3 inches No, that should NOT pass a city inspection.
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