The terms concrete and cement are often used interchangeably, but cement is actually an ingredient in concrete. The basic ingredients of concrete are Portland cement, sand and water. Portland cement is the type used most often in the mixing of concrete. It's not a brand of cement but a generic term, much as "stainless" is a type of steel. Because concrete is soft when mixed, it can be formed into any shape—a bridge, outdoor benches, a sidewalk. As it dries and hardens, concrete becomes stronger.
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Mixing Concrete Without Sand
While sand is the most common aggregate used to create concrete, you can also mix cement with gravel, crushed stone or even pieces of old concrete. The key to success will be the ratio of the mixture. The basic equation for making concrete is: 60 to 75 percent aggregate material (sand or the other aggregates mentioned) mixed with 10 to 15 percent cement. The amount of water you mix in will depend on the aggregate material, but you'll want somewhere between 15 to 20 percent of water.
The Right Mix of Materials
The proper ratio of materials will determine the strength of your concrete. Cement and water act as the paste of the concrete. If you don't have enough paste, the concrete will dry with a honeycombed surface and may be too porous. If you have too much paste, the concrete will be easy to spread but more likely to crack when it dries.
The water to cement ratio is very important when mixing concrete. The best concrete has the lowest amount of water possible without sacrificing the flexibility of the concrete.
The Portland Cement Association of America's Cement Manufacturers recommends using the rule of sixes for a good result.
- Mix six bags per cubic yard of concrete.
- Add 6 gallons of water per bag of cement.
- Allow a curing period of six days.
- And, if concrete will be subject to freezing and thawing, you'll need an air content of 6 percent.
Uses for Concrete and Water, Minus an Aggregate
Cement mixed with water alone creates a grout which can be used for repairing any damage on concrete structures. This cement-based grout mix is also used in situations where normal concrete won't work, such as underwater concreting.
Concrete is used all over the world because it is durable, economical and versatile. It's also one of the safest building materials around if you use basic precautions, including wearing gloves, safety goggles and a mouth cover.