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Concrete Mike
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Discussion Starter · #1 ·
Why does 80% of all concrete defect problems occur in the residential field? Is it because the non use or lack of water reducers? It is because of the use of a fresno to soon traping the bleed water at the surface? Is it the use of a sealer to soon(not cure)?
 

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Too much water added or too high slump for easy placement and finishing problems.

Here, you will have a hard time getting concrete delivered for any exposed job (driveway, sidewalk) if it is not 4000 psi minimum, 3-5" slump and 5-7% air and adding any water (unless a liability waiver is signed before unloading) voids all guarantees. A couple of producers require 4500 psi, since the cost of cement is just a material pass through cost (not a profit item) and controls are cheaper than the liability since there is little control once the mix is on the job. The exceptions are the small, lower priced ready-mix producers without controls and technical support, but they still are entitled to compete on price.

Concrete strength is not that expensive compared to the labor cost or supplier liability and the strength requirement eliminates one of the questions for a good suppliers, which is usually also certified for major and DOT projects.

Cracking due to shrinkage is totally on the contractor's back because of the location and timing of the control joints/sawing. Finishing and scaling is also the contractor's responsibility since they are part of the contractors ability and skill.
 

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Concrete Mike
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Discussion Starter · #3 · (Edited)
Too much water added or too high slump for easy placement and finishing problems.

Here, you will have a hard time getting concrete delivered for any exposed job (driveway, sidewalk) if it is not 4000 psi minimum, 3-5" slump and 5-7% air and adding any water (unless a liability waiver is signed before unloading) voids all guarantees. A couple of producers require 4500 psi, since the cost of cement is just a material pass through cost (not a profit item) and controls are cheaper than the liability since there is little control once the mix is on the job. The exceptions are the small, lower priced ready-mix producers without controls and technical support, but they still are entitled to compete on price.

Concrete strength is not that expensive compared to the labor cost or supplier liability and the strength requirement eliminates one of the questions for a good suppliers, which is usually also certified for major and DOT projects.

Cracking due to shrinkage is totally on the contractor's back because of the location and timing of the control joints/sawing. Finishing and scaling is also the contractor's responsibility since they are part of the contractors ability and skill.
So there is no profit by the material house on adding more cement to the mix? I can order a MS800lb mix at the same cost as a 6sac 4000lb mix? So adding more concrete to the mix will lesseen the liability of the concrete supplier, really? Does concrete with lower cement content have a lower E and thus curl less?
How would you determin if the cracks are shrinkage? Could random cracks be caused by severe overloads, before or after the break of the job? Is that the contractor's responsibility? Or maybee chemical attack? What about deicer salts? Can that cause scaling as well? Is that also the contractor's responsilitty?
 

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Twisted Cameron
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I think it has a lot to do with the fact that a lot of guys who are slinging mud don't know a lot about concrete. I have worked for several different ppl pouring mud, and discuss some of their practices with my father who is a concrete construction engineer.

He has guided me in a great direction, and has shown me some of the mistakes I have been taught to be normal finishing and placement practices.
 

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Concrete Mike
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285 Posts
Discussion Starter · #5 ·
Too much water added or too high slump for easy placement and finishing problems.

Here, you will have a hard time getting concrete delivered for any exposed job (driveway, sidewalk) if it is not 4000 psi minimum, 3-5" slump and 5-7% air and adding any water (unless a liability waiver is signed before unloading) voids all guarantees. A couple of producers require 4500 psi, since the cost of cement is just a material pass through cost (not a profit item) and controls are cheaper than the liability since there is little control once the mix is on the job. The exceptions are the small, lower priced ready-mix producers without controls and technical support, but they still are entitled to compete on price.

Concrete strength is not that expensive compared to the labor cost or supplier liability and the strength requirement eliminates one of the questions for a good suppliers, which is usually also certified for major and DOT projects.

Cracking due to shrinkage is totally on the contractor's back because of the location and timing of the control joints/sawing. Finishing and scaling is also the contractor's responsibility since they are part of the contractors ability and skill.
 

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Some people are professional contractors with extensive expeience and some have not seen to much or have the experience or reputation to build on. Certification are easy to get and don't always mean that much in a law suit or insurance claim.
 

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Concrete Mike
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Discussion Starter · #7 · (Edited)
Some people are professional contractors with extensive expeience and some have not seen to much or have the experience or reputation to build on. Certification are easy to get and don't always mean that much in a law suit or insurance claim.
That is true in some states, but not all. They are all easy to obtain (degree, certification) as long as you show the inishative to get them. On hand experience with the combination of a degree or certification will outweigh the other. That is why there are experts, and thats why there are general experts. Just like MD compared to a specialist.

Another point i would like to make as well, just because a cement supplier is DOT approved does not make there material superior over the non DOT approved. I do agree they conform with a regulated product, but some DOT material suppliers have alot of brokers (owner operator) that carry the concrete to site, they have a tendency of not washing there drums out prior to a new load. That will contaminate the load and make it "HOT" , you will not learn that in a book. One thing my father taught me as a child "tunnel vision can make you go blind".
 

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Concrete Mike
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Discussion Starter · #8 ·
I think it has a lot to do with the fact that a lot of guys who are slinging mud don't know a lot about concrete. I have worked for several different ppl pouring mud, and discuss some of their practices with my father who is a concrete construction engineer.

He has guided me in a great direction, and has shown me some of the mistakes I have been taught to be normal finishing and placement practices.
I do agree with you, on the other hand alot of the problem is the owner, general contactor, project superintedent and formans. They think quanity and exclude quality. Then they cry wolf when the job turns out wrong. Any consultant,certified inspector,aci cert or engineer can give you a educated guess on a concrete defect, but they can not certainly determine the cause. Only a petrographic test can show the problem with certainty. It sound like you have a great father.
 

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Hoven
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Because 80% of homeowners go for the cheap price over doing it right because they are allowed to. Commercial sites have the mandates and funding included to do the job to a set of engineered specs. Also when times got tight guys started jumping trades, there is nothing stopping homeowners from calling for a load of concrete which is wrong in my opinion. The stuff can give nasty burns. I wish I had 20 bucks for every story I have heard over the years about some homeowner in his old nikes ,his buddy, a 30 rack and an iron rake getting all burned up and having to pay for truck time to boot. There is no savings. There's always seems time and $ to do it right the second time.
 

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Concrete problems

Most of the response's you have gotten give a very vague answer, the real question that needs to be asked is "what problems are you experiancing?" The answer to your question can be answered if you narrow it down. I have been in the ready mix industry for over 20 years and hold certifications in mix design, batching, dispatch, placement, finishing and trouble shooting. I can help you if you can give a more direct question to the area of the problem.
 

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Porper Curing

I have to agree with you there, A lot of problems can be solved with proper curing. But, it seems that most of the people do not have either the knowledge or do not want to take the time to apply proper curing methods. I have noticed through the years that this also applies to contractor's.
 

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Much of my comments were related to my experience as a concrete inspector and 40 years experience in various cement related industries.

In the accounting done by most ready-mix concrete is marked up according to the raw material cost, Adding cement (not concrete) to mix does raise the cost somewhat, but very little goes to profit because delivery, labor and overhead are added on a per yard basis no matter what the raw material cost is.

Where I now live, our major producer does take an arbitrary position at times, but they have so many different mix designs. The special mixes are available at any time. I had a small (14x22) exposed aggregate patio poured and the guys came to wash it at 7:00 AM, they discovered the exposed retarder was mislabeled and did not work. They started to tear it out immediately an when they were almost done, they called for a "McDonalds mix", which is a pigmented mix with special aggregate. The truck was there in 30 minutes and they had it poured and sprayed before noon, so they could go fishing. That is the reason they have requirements on mixes supplied for certain mixes for certain uses since they have all the test reports and can deliver any one on order from most plants. Obviously, they are certified and they chose to leave the crumbs to the cheap producers that cannot compete on tough specs or delivery. - They do have almost 300 trucks in the local area and a concrete and mortar lab and they work on the classes for contractors, inspectors and lab technicians. They also have direct access to a petrographic facility that has analyzed most guaranteed mixes. If there is a problem with a guaranteed mix, they will do a petrographic exam if there is a reason to suspect placemen or excess water applied for finishing. That is the reason they are able to refuse orders they do not feel are worth the liability. Being certified does not guarantee good concrete, but it separates the men from the boys.
 

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Concrete defects

My experiance in the ready mix concrete industry has taught me that the majority of cement plants are state certified and comply with proper testing methods. Also the cost of concrete is due to the large over head cost, maintance alome in the ready mix industry is amoung the highest cost in the trucking industry. However, one has to take into consideration that the mix designs are based on a 4 inch slump, which is what state jobs will pour at or even a lowerr slump. But, residentuial jobs are poured at a much higher slump, from a 5 inch to an 8 inch slump, this alone will cause many problems, if you want to pour at this kind of slump you need to let the cement company know they can make ajeutments to the mix to allow for this type of slump and still maintain strength. Or, you could have a super plasticizer added to the mix, but remember these change's will cost more per yard.
 
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