FAQ

Q?Why is temperature important?
A.

Concrete gains strength through a complex chemical reaction that involves hydration of the cement paste. This reaction is temperature sensitive. If it is too cold, below 32 degrees F, the cement will not hydrate fast enough, the water in the mix may freeze, and the concrete will not set and develope the designed strength. If it is too hot, above 90 degrees F, the cement will hydrate rapidly, and the concrete may set before it is properly placed and finished. The recommended temperature range for proper concrete placement is between 50 F and 85 F.

Q?If the slump is TOO HIGH, what can be done to make the concrete usable?
A.

Not much – unless you have a pallet of bagged cement readily available, and adding extra cement is allowed by the Architect/Engineer. If not – send the truck back!
For every inch of slump over the designed maximum, you will have to add approximately 20 lbs. of dry cement per yard of concrete in the mixer to bring the water/cement ratio back close to the design value. So if the slump is 6″ and the maximum is 4″, and there is 10 cu. yds of concrete on the truck, you will need to add 400 lbs of dry cement to the mixer and mix the concrete for at least three minutes before discharging it. Its labor intensive and expensive.

Q?If the slump is too low, what can be done to make the concrete workable?
A.

It depends on what you mean by too low. Spec. concrete is usually designed with a maximum slump of 3 inches. Non-spec. concrete is designed with a maximum slump of 5 inches. If the concrete delivered to the project is so stiff that it cannot be discharged from the truck – contact the concrete plant. The concrete may not be batched properly, or may be starting to set up. To add additional water to concrete, above the maximum designed value, will cause problems in the hardened concrete.

Q?What is better a HIGH SLUMP or a low slump?
A.

This depends on the application and the design of the concrete mix. For normal concrete a moderate slump of 3″ to 5″ is desirable. High slump is desireable when the concrete must be placed around a high concentration of reinforcing steel. Low slump is desireable when concrete is placed in large open forms, or when the form is placed on a slope. The concrete mix must be designed for these special applications.

Q?What tests do you make on concrete?
A.

Tests on fresh concrete include slump, air entrainment, temperature, and unit weight. Tests on hardened concrete specimens include compressive strength, and in some cases flexural strength.

Q?What are the different kinds of concrete?
A.

Basic concrete mixtures are Regular, Air Entraining, and Pumpable (Regular and Air Entraining). Other “kinds” are designed for special applications. This includes modification of the sand/stone ratio, different size and kinds of stone (coarse aggregate, regular and lightweight), special additions which include Fly Ash, Silica Fume.

Q?Why can’t I pour the concrete rather than place it?
A.

Normal concrete is designed with a flowable workability, which means it can be conveyed to the pour site using smooth rounded chutes and still maintain its composition and not segregate. Adding more water to make it pourable usually causes segregation, not to mention the adverse effects of the additional water on the strength of the concrete. To make concrete more flowable or “pourable”, without adversely affecting the strength, one would add a Super Plasticizer admixutre. Here again there is a limit to the amount that can be added before the concrete begins to segregate

Q?How much water can I add to the concrete?
A.

Since the water/cement ratio controls the strength of the concrete, water cannot be added above the maximum established water/cement ratio for that particular concrete mixture. If more water is needed, then a proportional amout of cement MUST be added to maintain the water/cement ratio. Every gallon of water added to a cubic yard of concrete, above the design water/cement ratio, will decrease the compressive strength of that concrete by approximately 200 psi. So by adding and extra 5 gallons of water to one cubic yard of concrete, you will decrease the compressive strength by about 1000 psi!

Q?Why is my concrete dark in color or is blotchy ?
A.

Discoloration was caused primarily by calcium chloride retarding the reaction of tetracalcium aluminoferrites in the cement. When hydration of this compound is retarded, it retains its dark color; hydration lightens it markedly. Some discoloration that’s reported occurs when there’s no calcium chloride in the concrete and no hard troweling. This form of discoloration is believed by some to be related to water that’s trapped just beneath the surface during finishing. It seems to occur most often in coastal areas with high ambient relative humidities.

Q?How long can concrete remain in the delivery truck before its no good?
A.

The recommended time from when concrete is batched until it is considered “no good” is 2 hours, when the temperature is between 60 F and 80 F. If the temperature is lower, it may take a little longer for the concrete to begin accelerated hardening. When the temperature is higher, it is wise to monitor the concrete temperature, and if it rises above 90 F, discard the balance of the load.

Q?What controls the strength of concrete?
A.

The primary components that control the strength of concrete are the water and the cement contents. These two components are commonly referred to as the water/cement ratio. While properly graded sand and stone, and their relative amounts can affect the overall strength of the mix, the water/cement ratio has the greatest effect on the strength of the mix.

Q?What is concrete made of?
A.

Concrete is the mixture that results from blending hydraulic portland cement (or blended cement), sand, stone, water and admixtures.

Q?What performance should you expect from concrete placed around your home?
A.

Good quality concrete-properly proportioned, mixed, placed, finished and cured-will give maintenance-free service for many years. Concrete work, properly done, will usually last much longer than the need for which it was originally installed.
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Q?How do you find a good contractor?
A.

First of all, don’t pick a contractor entirely on the basis of cost. In concrete work, as in any business, you get what you pay for. Cost should be a consideration, but it should not be the only consideration. Knowledge, competence, integrity and experience are the qualities to seek in a contractor. To obtain the names of qualified contractors, talk to the dispatchers or friends and family. Then take a look at a few of the contractors’ completed jobs, particularly some which were done several years ago. If you like what you see, you can feel easier about seeking bids from them, knowing that they do good quality work

Q?Why should I cure concrete?
A.

It is important to cure concrete to retain as much moisture as possible in the concrete for the first three to seven days of its life. Curing also helps to maintain concrete temperatures between 50 and 90 degrees, which is helpful in the concrete gaining maximum strength. Curing is usually done by applying a coat of liquid curing compound to the concrete as soon as it is hard enough to walk on without making marks on the surface.

Q?Can concrete be made in colors other than normal gray?
A.

The possibilities are almost as limitless as your imagination! From an intermixing of multiple colors to matching the siding on your house, there’s sure to be a color you’ll like! Call or contact us for pricing and you can check colors out here at daviscolors.com.

Q?What does it mean to cure concrete?
A.

Curing is one of the most important steps in quality concrete construction and one of the most neglected. Effective curing is absolutely essential for surface durability. Fresh concrete must be kept warm and moist until the mixing water combines chemically with the cement (hydration). Without curing, the strength of the concrete is basically reduced in half. A 4000 PSI mix becomes a 2000 PSI mix at the surface with no curing.

Q?How do I know how much concrete to order?
A.

When you have measured the length and distance of the area you are interested in pouring, call our dispatch center and they will provide an exact measurement for your project.

Q?What strength concrete do I need?
A.

We recommend referencing job site permits, checking city ordinances or checking with your contractor for strength requirements.

Q?Why does concrete crack?
A.

The wet concrete will have a loss of volume as the concrete “sets” and continues to harden. This loss of volume occurs as shrinkage. That sets up tensile stresses causing cracks in concrete. Concrete cracking can be controlled but almost never eliminated.

Q?How do I control cracking?
A.

Concrete needs to be jointed to account for the shrinkage that will occur. Joint placement is determined by the thickness of the concrete.

Q?Will my concrete be stronger if I use wire mesh/Fibermesh reinforcing?
A.

No. Mesh reinforcing does nothing to make the concrete stronger. The mesh reinforcing will keep cracks from opening up once a crack has occurred.

Q?What kind of reinforcement should I use in my concrete?
A.

Much of that depends on what the concrete is being used for. In most cases, Fibermesh is an excellent no-hassle solution to providing additional strength. We also suggest using rebar or wire depending on the use

Q?What is the purpose of the Fibermesh?
A.

Intermixing millions of synthetic fibers into a cubic yard of concrete is meant to reduce or absorb micro-cracking that takes place when concrete begins to “set.” If micro-cracking is reduced or eliminated in the first few hours after placement, cracking may never take place.