civil engineering

Concrete Mix, Concrete Mix Design

Concrete is made of cement and water to form a binding agent, and then sand and aggregate that provide its substance. Admixtures are used to provide special qualities, and these can include either water reducers of varying capabilities or set modifiers.
by Cindy Grawl

Determining the best mix design for decorative concrete is like creating a recipe for a gourmet treat — it should take advantage of the best qualities of the various ingredients in it to produce the specific product for your needs. When it comes right down to it, according to Kelly Idiart, vice president customer service, Central Concrete, San Jose, California, good quality concrete is the same for both decor and nondecor applications. Much is dependent on job site conditions, with their specific moisture levels, subgrades, finishes and cure practices.

More specifically, mix design for decor will vary depending on the region of the country, the site, and the type of finish the project will receive, says Ward Malisch, Senior Managing Director, Technical Operations, the American Concrete Institute (ACI), Farmington Hills, Michigan. On general principles, he says, there is no one-size-fits-all mix design. He suggests that a good mix take into account three elements:

1. the properties of the concrete in its plastic state as it comes out of the truck,
2. the finished concrete's strength to withstand loads and durability to withstand freeze and thaw cycles, and
3. economics — how expensive it is. If it is possible, he says, reduce the amount of raw materials used as much as possible while retaining strength and durability.

It all begins with proportion, says Malisch, getting the right ratios of each ingredient. Concrete is made of cement and water to form a binding agent, and then sand and aggregate that provide its substance. Admixtures are used to provide special qualities, and these can include either water reducers of varying capabilities or set modifiers. Finally, air entrainment products and fibers add strength and durability, while color gives a special aesthetic. Each one plays a role in making the concrete both beautiful and long-lasting. Here's how: