Concrete Mix

The concrete mix you use on your project should be workable and set-up with the appropriate timing. Here are some problems you may encounter in the concrete mix and information to help you correct them:

1st Aid for Concrete Problems:

Most problems can be fixed with a prepackaged Admixture (Fritz-Pak Corporation).

• Warm temperature and concrete is setting too quickly - Add a retarder to give you more time to finish the concrete before it hardens.
• Concrete is not very workable - To improve workability and durability without increasing the water content, add a super plasticizer (water reducer) and a finishing aid that enhances surface finishing characteristics.
• Avoid: Products that contain calcium chloride or chloride ions which can discolor colored concrete.
• Pozzolans - This admixture improves finishability, reduces permeability and efflorescence (concrete salts coming to the surface and causing white blotches) and minimizes the bleeding of color. Pozzolans may also cause retardation, so this is something you need to be aware of when using.
• Pouring in cooler temperatures - Use an accelerator to speed up the set time.
• Concrete that will be exposed to freezing and thawing - Use an air-entraining agent.

The directions on the back of the packages of the admixtures will show the concrete mixing ratios so you know how much to use.

It is important to try and keep the water content as low as possible without sacrificing workability. The lower the water content, the better the concrete will have these characteristics:

• Increased compressive strength and durability
• Lower permeability which will increase resistance to chemical attack - commonly happens through deicing salts
• Less volume change from wetting and drying
• Reduced shrinkage and cracking

For stamping concrete, you want a "thick mix" - one with sufficient amount of cement paste to provide a surface that will take an imprint well. Generally, 5 1/2 to 6 bags of cement per cubic yard of concrete.

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