According to an admixture manufacturer's recent industry survey, about 85% of all ready-mixed concrete produced today contains a liquid admixture. Producers look to the chemical and integral ingredients of air entrainment, water-reducers, and plasticizers as necessary to produce superior concrete that's workable and durable.But batching concrete requires precise measurement. Measuring and then dispensing admixtures in the concrete batching process requires special equipment that must be precise enough to maintain accurate, consistent dosages from batch to batch. Whether you use a manufacturer's equipment or own your own, it's important to develop procedures that ensure dosage accuracy. ASTM C 94, "Standard Specification for Ready-Mixed Concrete," defines the basic system requirement. The Concrete Plant Manufacturers Bureau's concrete plant standards include the same accuracy requirements as ASTM C 94. The American Concrete Institute, in two of its documents, also makes recommendations regarding admixture dispenser systems. ACI 212.3R, "Chemical Admixtures for Concrete," and ACI 304R, "Guide for Measuring, Mixing, Transporting, and Placing," both have sections dealing with dispensers. The technology for these systems is well established and does not seem to be changing significantly. These electro-mechanical systems are subject to wear and to failure. Here are a few pointers for ensuring accurate dosing:
- For new dispenser installations involving several admixture products, do two things. Verify that the correct product is coming out of the correct dispenser.
- Calibrate the units on a regular basis according to the dosages that you will be using on a routine basis.
- Use the sight tubes on the bottles.
- Consider installing an industrial videotaping system on the sight tubes to provide documentation.
- Learn enough to maintain and troubleshoot.
Article includes a table of typical admixture dosages. Keywords: admixture, dispensing, dosage, Badger Meter, volume, weight, calibrate