Roller-compacted concrete

 

Roller-compacted concrete




Roller-compacted concrete (RCC) or rolled concrete (rollcrete) is a special mix of concrete that contains essentially the same components as conventional concrete but in different proportions, and with partial replacement of fly ash for Portland cement.Partial conversion of fly ash to Portland cement is an important aspect of RCC dam construction because the heat generated by fly hydrant is significantly less than the heat generated by Portland cement hydration.This reduces the thermal load on the dam and reduces the possibility of thermal cracking. RCC is a mixture of cement / fly, sh, water, sand, aggregate and common substances, but it has less water.The mixture produced is dry and basically no falling. The RCC is kept the same as the pavement; The material is delivered by dump truck or carrier, spread by small bulldozers or specially modified asphalt pavers and then by vibrating roller companies.

In dam construction, roller-compacted concrete began early development between 1961 and 1964, with the construction of the Alpe Gera Dam near Sondrio in northern Italy. Concrete was prepared in the same manner and manner but not rolled. In the 1970s, the RCC was considered a revolutionary material in engineering journals for the construction of dams.Initially and generally RCC was used for backfill, sub-base and concrete pavement construction but increasingly it is being used to build concrete gravity dams as less cement content and use of fly of heat generates heat while curing than conventional. Mass solid placements. Roller-compacted concrete has many more time and cost advantages than traditional mass concrete dams; These include higher rates of concrete placement, lower material costs, and lower costs associated with post-cooling and formwork.

Dam applications

For dams, RCC sections are built in successive horizontal layers per lift, resulting in a downhill slope similar to a concrete step. Once a layer is placed, you can immediately support earthmoving equipment to place the next layer. Once the RCC is deposited on the surface of the elevator, small dozers are typically spread in layers one foot thick (300 mm).

The first RCC dam to be built in the U.S. was the Willow Creek Dam on Willow Creek, a tributary of the Columbia River in Oregon. It was built between November 1981 and February 1983 by the Army Engineering Board. Construction went well, with a quick schedule and budget (estimated at $ 50 million, actual $ 35 million).At the initial filling, it was found that the leakage between the compacted layers within the barrier body was unusually high. This condition was treated with conventional repair grout at an additional cost of $ 2 million, which initially reduced leakage by nearly 75%; over the years, the leak has since fallen to less than 10% of the initial flow.However, concerns about the long-term safety of the dam remain, although only indirectly related to the construction of the RCC. Within a few years, problems were observed during construction related to the stratification of the reservoir water caused by upstream pollution and anoxic decomposition, which resulted in hydrogen sulfide gas.They expressed concern that this, in turn, could result in sulfuric acid, thereby accelerating damage to the concrete. The debate itself, as well as its handling, continued for several years. An aeration plant was installed in 2004 to address the root cause of the reservoir, as proposed 18 years earlier

 

 

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