Concrete is a mixture of aggregate (sand and gravel), Portland cement and water. In some concrete an admixture is also a component. Each component has unique characteristics.
Aggregate: Sand and gravel sized from dust to 2-1/2". Rounded fragments are generally better. Do not use fragments larger than one-quarter the thickness of the slab to be poured. The larger the gravel the more cost effective the concrete and less chance for shrinkage.
Portland Cement: Cement is sold in 1 cubic foot bags; weighing 94 lbs. Bulk trailer loads can be purchased. There are five basic types of Portland cement.
Water: Must be clean and free of impurities.
Admixtures: Admixtures can be used in relatively small quantities to improve some properties of the fresh or hardened concrete.
Air-Entraining Admixtures are the most commonly used. This agent develops millions of tiny air bubbles in tine concrete, which makes the concrete more durable when exposed to freezing and thawing.
Water- Reducing Admixtures enable concrete to be placed at the required consistency while minimizing the amount of water used in the mixture. This results in stronger concrete.
Fibers are incorporated into the concrete to control cracking or improve abrasion and impact resistance.
To increase concrete strength..
Increase the amount of cement in the mix.
Decrease the amount of water relative to the amount of cement
Increase the density of the concrete.
Use coarser aggregate.
Compact the concrete with by vibrating or tamping in place
Concrete Mixtures by Volume
Application
Cement
Sand
Gravel
Normal static loads, no rebar; not exposed
1
3
6
Normal foundations & walls; exposed
1
2.5
5
Basement walls
1
2.5
4
Waterproof basement wails
1
2.5
3.5
Floors (light duty), driveways
1
2.5
3
Steps, driveways, sidewalks
1
2.25
3
Lintels
1
2
4
Reinforced roads, buildings, walls; exposed
1
2
4
Retaining walls, drive ways
1
2
3.5
Swimming pools, fence posts
1
2
3
Floors (light duty)
1
1.75
4
Watertight, reinforced tanks & columns
1
1.5
3
High strength columns, girders, floors
1
1
2
Fence posts
1
1
1.5
Thorough mixing of concrete is necessary to produce the strongest pour. When mixing concrete, mix the Sand and cement first until a uniform color is achieved, then mix in the aggregate. Add only enough water to make the concrete workable. Generally you need about 6 gallons of water per sack of cement. Less water relative to the cement makes the concrete stronger.
Bon Tool Co. has made a serious effort to provide exact and current information, but does not guarantee the accuracy of the data. Bon Tool Co. cannot assume responsibility for the application of information nor guarantee results.
