Ready-Mix Concrete

 Ready-mixed concrete is a major part of any concrete construction project. It is a convenient and efficient tool for building. The concrete is delivered to the site mixed and ready to be cast which saves time and money.

There are two types of ready-mix plants. A central mixing plant uses a stationary mixer to mix the concrete. The concrete is then transferred into the transportation vehicle. A truck mixing plant places all unmixed dry materials into a truck mixer. Water is added and mixing is then done in the truck. Many central mix plants have the ability to bypass the stationary mixer, thus making them a hybrid of the two types. Truck mixing plants are simplier and less expensive than central mix plants because they do not have a stationary mixer. This is important because less machinery means less potential problems. For long trips the dry materials can be held in the truck until it reaches the site where water is then added and mixing can be completed. The advantage of central mixing lies within the fact that a mixing truck can hold more completely mixed concrete than unmixed concrete. This means that there can be more concrete delivered with fewer trucks.

Besides a few small exceptions, all mixing plants have the same basic layout. The plants consist of aggregate storage, cement/pozzolan storage, batchers (aggregate batching, cement batching, water and admixture batching), dust collection system, feed system, and some sort of mixer (truck mixer or stationary mixer). Due to modern technology, the ready-mix plant can be operated from a remote location. A batch operator uses video equipment and computer systems to control the crucial areas of the plant.

The process of producing concrete in measured batches is called batching (Dobrowolski 17.1). Every ready-mix concrete plant uses this process to produce their concrete. Weigh Batching uses a hopper and a scale to batch all of the dry materials. The scale gives a readout of the weight of material in the hopper. Due to its consistent nature, water can be batched by weigh batching or volumetric batching.

All systems in a ready-mix plant must be constantly regulated to ensure that all specifications will be met. Each plant should meet or surpass all regulations specified in ASTM C-94. If a specification is not met, the desired concrete may not be achieved. Faulty concrete can cause significant delays on any project. This could cost the owner money and future business. The owner of the plant is responsible for meeting all environmental and safety regulations. As for all heavy machinery, operators must be educated about the hazards associated with the machines in order to run them safely and effectively. Highly visible warning signs must be present to protect the employees of the dangers. The owner must also meet all Environmental Protection Agency regulations.

The ready-mix concrete industry has been active for nearly ninety years and will continue to flourish long into the future. There have been some technological advancements but the basic idea remains the same.

Information Compiled By William Dougherty

References/Works Cited

American Concrete Institute Manual of Concrete Practice 1998, vol.2; American Concrete Institute, Farmington Hills, MI. 1998.

Annual Book of ASTM Standards 1998, vol 4.02; ASTM, West Consohocken, PA, 1998.

Dhir, R.K. Advances in Ready Mixed Concrete Technology. Pergamin Press, New York, 1976.

Dombrowolski, Joseph. Concrete Construction Handbook, 4th edition. McGraw-Hill Inc., New York, 1996.

Illingworth, J.R. Movement and Distribution of Concrete. McGraw-Hill Inc., London, 1972.

Kosmota, Stephen and William C. Panarese. Design and Control of Concrete Mixtures, Thirteenth Edition. Portland Cement Association, Skokie, Illois, 1988.

White, George R. Principles of Quality Concrete. John Wiley and Sons, Inc., New York, 1975.