Making quality Ready Mix Concrete requires constant monitoring of the materials provided by our suppliers, maintaining and keeping current with technological advances, keeping a watchful eye on the batching and delivery process and a continuing education of the personnel.
Low Water/Cement Ratio
The water/cement ratio is the total weight of water in the mix design (1 gallon = 8.33 lbs) relative to the total weight of cement per cubic yard. Basically, the lower the water/cement ratio, the better the concrete. To this end enough water should be added to consolidate the materials in the mix and have workable concrete.
The binding quality of the cement and water paste is caused by the chemical reaction know as hydration when the two ingredients are mixed. Only a small amount of water is needed for hydration to occur. Ready Mix Concrete would be very stiff and unworkable if the only water added to the mix was the water needed for hydration. Most of the water used in the mix is used to make the concrete workable (ease the placing of the concrete). As excess water is added to the concrete mix, the paste becomes thinner than necessary and lessens the strength of the concrete.
The Portland Cement Association and engineers recommend only using enough water to make the concrete plastic and workable. If very fluid mixes or mixes with high slumps are needed there are admixtures or superplacticizers that can be added to the concrete without impeding on the strength, and in fact can actually increase the strength.
Reason to Use less water:
• Increase strength
• Dense concrete which gives added resistance to weather
• Increased resistance to shrinkage cracks
• Less chance of a peeling or scaling surface
• Quality clean finish to the surface
• Maintain entrained air
Air entrained concrete is recommended for almost all concrete applications because of its ability to improve resistance to the freeze-thaw cycle. It also increases resistance to excess water and certain de-icing products. Air entrained concrete contains millions of microscopic bubbles or air pockets. These bubbles or voids relieve internal pressure on concrete as water expands when it freezes. Recommended air entrained content is 5% to 7% by volume. Air entrainment can be deteriorated when excess unnecessary water is added to the concrete or when the surface of the concrete is over finnished, which can cause spalling, scaling and surface cracks.
Certain materials such as cement contain natural air entrainment, as a result air content is tested and monitored on a regular basis to provide a consistent concrete mix.
A slump test is the test used to determine the consistency of Ready Mix Concrete. This test is performed by filling a slump cone (similar to an upside down ice cream cone with a hole at the bottom and top) with concrete than removing the cone. The slump in measured in inches for the distance between the top of the cone and the height the concrete slumped to after in cone was removed. In other words a stiff or tight mix will only slump 2 or 3 inches, where a wet mix will slump in excess of 7 inches.