other ready mix manufactures. This is a hybrid approach between centralized batch plants and traditional on-site mixing. Each type of system has advantages and disadvantages, depending on the location, size of the job, and mix design set forth by the engineer. Transit mixed ready mix versus volumetric mixed ready mix A centralized concrete batching plant can serve a wide area. Site-mix trucks can serve an even larger area including very remote locations that standard trucks cannot. The batch plants are located in areas zoned for industrial use, while the delivery trucks can service residential districts or inner cities. Site-mix trucks have the same capabilities. Volumetric trucks often have a lower water demand during the batching process. This will produce a concrete that can be significantly stronger in compressive strength compared to the centralized batch plant for the same mix design using the ASTM C109 test method. Centralized batch systems are limited by the size of the fleet. It may take upwards of 10 minutes to batch and load out one 9 - 12 yard (6 - 9 m3) truck depending on the plant size and type. They are unable to change mix designs in the middle of an individual batching process, but can quickly offer a greater range of mixes overall as a central yard has more stock capacity for different types of cement, aggregates, and admixtures than a single truck has room for on site. Volumetric mixers can seamlessly change all aspects of the mix design while still producing concrete, as long as the raw materials are on site. They can continuously mix quality concrete for an indefinite time while being continuously loaded with fresh materials. They can produce 1 yard of concrete in as little as 40 seconds depending on the mix design and batch plant size outfitted. Centralised batching, using the same supply of materials over a long period (a fixed plant will likely have a fixed set of suppliers in its locality), the same scales which can be calibrated by weighbridges, the same measuring equipment for admixtures, moisture etc, and often the same batching operator, can have tighter tolerances for mixes, use a centralised lab to design and verify dozens of mixes to different specifications across multiple jobs for that plant, and can therefore produce a very predictable, consistent result for major projects. Each plant will have a batching recipe book (or equivalent automated batching program)