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Concrete shrinkage
- Thread starter AELLC
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Not likely. Most shrinkage is out in the first year after placement. While it continues indefinitely, the rate of shrinkage declines with age.
There are some conditions that could cause this....if the concrete were sealed from outside drying influence, then the conditions changed after 10-15 years such that initial drying shrinkage that was delayed by sealing could then take place...you get cracks to widen.
There are some conditions that could cause this....if the concrete were sealed from outside drying influence, then the conditions changed after 10-15 years such that initial drying shrinkage that was delayed by sealing could then take place...you get cracks to widen.
EngineeringEric
Structural
Per J. Francis Young: The three major factors of shrinkage (autgenous, drying, thermal) occur and nearly stop within the first 400 hours from mixing. The RH can effect this as well as temperature (thermal) and admixtures; But regarless, concrete shrinkage is minimal to non-existent after 7 days of placement.
Engineering Eric....the conditions that Mindess, Young and Darwin describe are the initial shrinkage characteristics. By no means will shrinkage stop at 7 days, 28 days or even 180 days. Do a little more reading of Mindess, Young and Darwin...then check Neville for a definitive treatise on concrete shrinkage.
For your own observation, most commercial concrete is going to be placed with a w/c ratio that exceeds 0.50. As the w/c ratio increases, so does shrinkage...both short term and long term. Take a look at control joints that are cut into concrete slabs. When cut, there will be either no crack below the cut or a very tight crack below the cut. Check it at 7 days, 28 days and 6 months...you'll see that shrinkage doesn't stop at 7 days.
For your own observation, most commercial concrete is going to be placed with a w/c ratio that exceeds 0.50. As the w/c ratio increases, so does shrinkage...both short term and long term. Take a look at control joints that are cut into concrete slabs. When cut, there will be either no crack below the cut or a very tight crack below the cut. Check it at 7 days, 28 days and 6 months...you'll see that shrinkage doesn't stop at 7 days.
How do you know when the shrinkage occurred?
Assuming the visible evidence of the shrinkage is cracking, are you sure it is due to shrinkage? Could it be due to thermal effects, ground movement, or a combination of all three?
Doug Jenkins
Interactive Design Services
Assuming the visible evidence of the shrinkage is cracking, are you sure it is due to shrinkage? Could it be due to thermal effects, ground movement, or a combination of all three?
Doug Jenkins
Interactive Design Services
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Ron,
OK I think faulting is where the crack propagates zig-zag fashion - no it does not.
Cracking is only at grout lines, in a straight line, far apart (13' or more). Only one cracked tile where the tile was saw cut for the patio door jamb.
There is a 3/16" gap between the tile and the baseboard at the exterior wall, but this narrows down to no gap at all where the floor edge is at the patio door. (Could the stem wall be actually displaced outward except at the patio door where the stem wall may have been terminated?)
Crack width about hairline to 3/32" elsewhere, only slightly tented in one location.
Not sure what type soil at my house, but I do know this was all formerly agricultural fields. There is some potential for soil swelling/collapsing due to moisture level, but this varies per exact location. I looked at a report for some other location:
Stiff sandy clay inter-bedded with loose to dense silty to clayey sand and sandy silt. Soil plasticity varies, low/non-plastic to low-medium. Potential for soil compressibility varies from low to moderate (1.0 to 5.5%). Potential for Soil Expansion moderately low.
OK I think faulting is where the crack propagates zig-zag fashion - no it does not.
Cracking is only at grout lines, in a straight line, far apart (13' or more). Only one cracked tile where the tile was saw cut for the patio door jamb.
There is a 3/16" gap between the tile and the baseboard at the exterior wall, but this narrows down to no gap at all where the floor edge is at the patio door. (Could the stem wall be actually displaced outward except at the patio door where the stem wall may have been terminated?)
Crack width about hairline to 3/32" elsewhere, only slightly tented in one location.
Not sure what type soil at my house, but I do know this was all formerly agricultural fields. There is some potential for soil swelling/collapsing due to moisture level, but this varies per exact location. I looked at a report for some other location:
Stiff sandy clay inter-bedded with loose to dense silty to clayey sand and sandy silt. Soil plasticity varies, low/non-plastic to low-medium. Potential for soil compressibility varies from low to moderate (1.0 to 5.5%). Potential for Soil Expansion moderately low.
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- #12
I apologize for this because it is not really engineering - to change the subject - a frequent matter when being consulted by a realtor when a professional home inspector calls for a structural engineer's opinion -
Cracks in gypsum wallboard. Everyone (realtors, public in general) seems to think they are due to structure settling - yes, that is true at my house in one location, but I think most are due to some sort of wallboard shrinkage (and most cracks are straight, at the tape lines) - any thoughts?
Cracks in gypsum wallboard. Everyone (realtors, public in general) seems to think they are due to structure settling - yes, that is true at my house in one location, but I think most are due to some sort of wallboard shrinkage (and most cracks are straight, at the tape lines) - any thoughts?
Both types of cracks, if that is what you call them, are commonly in the finish materials, no fault of the structural elements. Floor tile joint separation can be avoided to a large extent by using a good quality flexible adhesive when installing the tiles. Wallboard separation at joints is just due to poor attention to the joint taping, or in some cases, thermal movement which causes separation at the weakest points, e.g. corners and openings.
AELLC..faulting is when one side of the crack is higher/lower than the other side.
Drywall cracks are commonly caused by material shrinkage after the house is dried in and the AC starts to take the construction moisture out of the materials. Common at corners and re-entrant corners like door openings.
Drywall cracks are commonly caused by material shrinkage after the house is dried in and the AC starts to take the construction moisture out of the materials. Common at corners and re-entrant corners like door openings.
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