Roller-compacted concrete

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Roller-Compacted Concrete (RCC) is a special blend of concrete that has the same ingredients as conventional concrete but in different ratios. It has cement, water, and aggregates, but RCC is much drier and essentially has no slump. RCC is placed in a manner similar to paving, often by dump trucks or conveyors, spread by bulldozers or special modified asphalt pavers. After placement it is compacted by vibratory rollers.

RCC is typically used for concrete pavement, but it is increasingly used to build concrete dams because the low cement content causes less heat to be generated while curing than do conventional massive concrete pours. For dam applications, RCC sections are built lift-by-lift in successive horizontal layers resulting in a downstream slope that resembles a concrete staircase. Once a layer is placed, it can immediately support the earth-moving equipment to place the next layer. After RCC is deposited on the lift surface, small dozers typically spread it in one-foot-thick layers (300mm).

The first RCC dam built in the USA was the Willow Creek Dam on Willow Creek, a tributary in Oregon of the Columbia River. It was constructed by the Army Corps of Engineers between November 1981 and February 1983. Construction proceeded well, within a fast schedule and under budget (estimated $50 million, actual $35 million). On filling though, it was found that the leakage rate between the compacted layers was unusually high. Remedial grouting at a further cost of $2 million was required to reduce this. Concern over the dam's safety has continued, especially as Heppner had already suffered a dam collapse and fatal flooding with about 250 deaths in 1903. Within a few years of construction, problems were noted with stratification of the water and anoxic decomposition producing hydrogen sulfide. Concerns were expressed that this could in turn give rise to sulfuric acid, and thus damage to the concrete. Controversy continued for some years and the handling of the problem itself has been criticized. In 2004 an aeration plant was installed to address the root cause, as had been called for 18 years earlier.