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	Raw Materials Sand, gravel, and cement are transported to the concrete plant by truck. Certain materials, such as inert aggregates, are typically stored outdoors in stockpiles. Moisture-sensitive materials, such as cement and flyash, may be stored in high-capacity silos. Batching + Mixing As the materials are needed, they are transported by conveyor to large storage bins at the top of the block plant. At the start of production, the raw materials are discharged into a weigh batcher, which measures the correct proportion of dry materials for the mix. The dry materials are mixed for several minutes before water and admixtures are added. The proportioning of the mix is carefully controlled by computer. Most concrete block is produced using zero-slump concrete, which requires a minimal amount of water. Molding + Curing After mixing is complete, the batch is discharged into a hopper and compacted into molds. Each mold consists of a re-usable, one-piece mold box with replaceable liners. The molds are compacted using pressure and vibration to assure an even distribution of concrete. The compacted block is pressed out of the mold onto a moving conveyor belt. As the block travels down the belt, a rotating brush removes loose particles of aggregate from the top surface of the block. At this stage of the process, the uncured blocks as referred to as "green." The "green" blocks are mechanically loaded onto a curing rack. Fully-loaded curing racks are then transported by forklift into an available steam-curing kiln. Racks of concrete block are placed in the steam-curing kiln at normal temperature for a holding period of 1-3 hours. This "presetting" allows the blocks to harden slightly. Steam is then gradually introduced, increasing the kiln temperature incrementally, until peak temperature (usually 165-170 degrees) is reached. The blocks are then allowed to "soak" in the steam for 12-18 hours. Finally, the moist air is exhausted to allow the blocks to dry. Storage + Transport Pallets of cured block are then removed from the kiln and transported by forklift to outdoor storage yards. Steam-cured block typically reaches 90% of its final strength within 2 to 4 days. Large quantities of standard-sized blocks are stored until ready for transport to the jobsite. Blocks are transported by flat-bed truck to the jobsite. slide show main