This means that ready-mixed concrete should be placed within 30 to 45 minutes of the batching process to hold slump and mix design specifications in the USA, though in the UK, environmental and material factors, plus in-transit mixing, allow for up two hours to elapse. Modern admixtures and water reducers can modify that time span to some degree. Ready-mixed concrete can be transported and placed at site using a number of methods. The most common and simplest is the chute fitted to the back of transit mixer trucks (as in picture), which is suitable for placing concrete near locations where a truck can back in. Dumper trucks, crane hoppers, truck-mounted conveyors, and, in extremis, wheelbarrows, can be used to place concrete from trucks where access is not direct. Some concrete mixes are suitable for pumping with a concrete pump. In 2011, there were 2,223 companies employing 72,925 workers that produced ready-mix concrete in the United States. Advantages of ready-mix concrete Materials are combined in a batch plant, and the hydration process begins at the moment water meets the cement, so the travel time from the plant to the site, and the time before the concrete is placed on-site, is critical over longer distances. Some sites are just too distant. The use of admixtures, retarders, and cement-like pulverized fly ash or ground granulated blast-furnace slag (GGBFS) can be used to slow the hydration process, allowing for longer transit and waiting time. Concrete is formable and pourable, but a steady supply is needed for large forms. If there is a supply interruption, and the concrete cannot be poured all at once, a cold joint may appear in the finished form. The biggest advantage is that concrete is produced under controlled conditions. Therefore, Quality concrete is obtained, as a ready-mix concrete mix plant makes use of sophisticated equipment and consistent methods. There is strict control over the testing of materials, process parameters, and continuous monitoring of key practices during the manufacturing process. Poor control on the input materials, batching and mixing methods in the case of site mix concrete is solved in a ready-mix concrete production method. Speed in the construction practices followed in ready mix concrete plant is followed continuously by having mechanized operations. The output obtained from a site mix concrete plant using a 8/12 mixer is 4 to 5 metric cubes per hour which is 30-60 metric cubes per hour