Just wondering when a concrete floor will crack, will it when it freezes or thaws, or does it make any difference. I know there are a lot of variables like settling in the mix, but just wondering. We've had temperature swings from 23 below zero to 45 degrees!
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When will concrete crack?
- Thread starter rinker1
- Start date
Junkman
Well-known member
The density of concrete makes it difficult for the concrete to react quickly to temperature changes, so heat and cold has very little effect on aged concrete. Usually cracking is a result of settling under the concrete, or water getting under the concrete and freezing. This causes direct stress points that result in the cracking. The only time that I can think of concrete being effected by heat and cracking is in sidewalks when they don't provide an expansion joint to allow for the thermal expansion of the concrete.
if water sits on the concrete and freezes it wan cause the surface to shale.. unless you get air entrained it has little bubbles for the water to expand into as it freezes
"One of the greatest advances in concrete technology was the development of air-entrained concrete in the late 1930s. Today, air entrainment is recommended for nearly all concretes, principally to improve resistance to freezing when exposed to water and deicing chemicals. However, there are other important benefits of entrained air in both freshly mixed and hardened concrete. Air-entrained concrete contains billions of microscopic air cells. These relieve internal pressure on the concrete by providing tiny chambers for the expansion of water when it freezes. "
"One of the greatest advances in concrete technology was the development of air-entrained concrete in the late 1930s. Today, air entrainment is recommended for nearly all concretes, principally to improve resistance to freezing when exposed to water and deicing chemicals. However, there are other important benefits of entrained air in both freshly mixed and hardened concrete. Air-entrained concrete contains billions of microscopic air cells. These relieve internal pressure on the concrete by providing tiny chambers for the expansion of water when it freezes. "
Benchloader
Well-known member
The method concrete is poured can have an effect on how or when it may crack.
The place in the MI thumb area I lived in has 50+ year old concrete garage floor and drive. It was poured on a good base with rebar. No cracks at all yet.
Where I live now in LA the concrete began cracking a week after it was poured. I'm constantly killing grass growing up through the cracks.
The habit here is to lay "fiber re-enforced" concrete directly on the clay (ground).
The place in the MI thumb area I lived in has 50+ year old concrete garage floor and drive. It was poured on a good base with rebar. No cracks at all yet.
Where I live now in LA the concrete began cracking a week after it was poured. I'm constantly killing grass growing up through the cracks.
The habit here is to lay "fiber re-enforced" concrete directly on the clay (ground).
boiler7904
Well-known member
Temperature doesn't really matter. It's the forces acting on the concrete that will determine if and when it will crack. Concrete is great in compression but has virtually zero tensile strength unless it is steel reinforced. A reinforced slab will span a void in the base material until the slab is subjected to adequate load to overcome the strength / density of the concrete - typically 4,000 psi for a slab. Should water get into a void in or below the concrete and freeze, it can exceed the strength of the concrete causing it to crack.
seatec
Member
Is there any thing I can put in the crack to fill it up like epoxy to keep water out, mine just started to crack in 2 places, lots or rebar in it and insulation, so it cant get in it from bottem and I dont put water on floor, but could spill something in it. Wayne
Torque1st
MEMBER EMERITUS
Use a penetrating sealer on the entire surface. A self leveling urethane can help with a crack. Follow directions...Is there any thing I can put in the crack to fill it up like epoxy to keep water out, mine just started to crack in 2 places, lots or rebar in it and insulation, so it cant get in it from bottem and I dont put water on floor, but could spill something in it. Wayne
Boiler7904 is correct on the forces and mechanisms involved.
Fibermesh helps with initial shrink cracking but as far as I have been able to determine it does little or nothing for strength.
Placing concrete over bare ground will almost guarantee cracking.
Last edited:
Richard Givan
Well-known member
The concrete guy who did all the work on my house told me that he guaranteed two things: "It'll get hard--and it'll crack."
He made good on both promises.
He made good on both promises.
Hardware
Well-known member
The concrete guy who did all the work on my house told me that he guaranteed two things: "It'll get hard--and it'll crack."
He made good on both promises.
Ditto on that
Hardware
Well-known member
I made lots of precautionary measures but i develpoed some cracks near my my mandoor and my sidewalk. oh well
Newbie here but let me throw in my 2 cents. As a contractor I usually tell customers there are 2 types of concrete. The two kinds? Concrete that has cracked and concrete that is getting ready to crack. We always compact the substrate, use expansion joint and steel but still sometimes it will still crack.
tcianci
Well-known member
Everyone here is right on the money about concrete, but it doesn't always crack. A couple of things you need to do in addition to a compacted substrate (compaction must be done in shallow layers to be effective, you can't dump 10" or so of gravel in a hole and run over it with a vibratory compactor and call it a day). One sure fire way to make sure your substrate is solid, is to puddle the daylights out of it with water. It's time consuming and messy but it works great. Also make sure that the stuff you are pouring on is well drained. We always put about 4 to 6 inches of crushed stone under a slab. If you live in an area subject to frost be sure that the edge of your slab at any door opening goes all the way down to your footing. I have seen many jobs where the foundation of the garage is backfilled and the fill/gravel runs right over the footing where it is depressed to allow for the door opening and then the slab is poured. If you think about it you now have a concrete sandwich with gravel in the middle. Moisture will wick through the gravel that is over the footing and under the slab and it will heave and crack garanteed. Another cause of cracking that often does not get planned for is shrinkage. If you have a slab with a dog leg in it for instance, it will most likely develop a crack from the crotch of the dog leg, radiating to the next closest edge across the slab due to shrinkage as the slab cures. This is a good place for an expansion (contraction?) joint. If you have any doubt about concrete shrinking as it cures, just look closely at the joint between your slab and your foundation walls in your cellar or garage. That concrete was wet and right up against those walls when it was poured but now you will probably see a gap there.