Roller-compacted concrete is a zero-slump concrete that is transported, spread and compacted using large, earth-moving plant. Because of the need for high-capacity plant and equipment for RCC, it is most suited to use in large-scale construction and for mass concrete works.
Since the early 1980s, RCC has gained general acceptance as an appropriate material and method for the construction of dams, and hundreds of large RCC dams have been completed worldwide. It has also been successfully used for pavement construction in many overseas country, such as Canada, the USA and Spain.
During its early development, RCC was perceived as a low quality, low-strength mass material. But it has since become possible to produce a wide range of concrete qualities by roller compaction, with the most common product being a dense, high-quality and relatively high-strength concrete.
RCC for dams:
RCC for dams is generally a relatively low-strength concrete similar in strength to the concrete used in mass concrete dams. Experience and testing have demonstrated the properties of hardened RCC to be similar to those of conventional mass concrete. Differences are more apparent in the fresh state: in RCC, these relate primarily to lower water and cement contents and a higher aggregate content.
Differences in the hardened concrete include:
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The volume change of RCC after set is reduced, as a result of less drying shrinkage (due to less water in the mix), less heat of hydration (because of lower cement content) and a lower effective long-term temperature reduction;
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Creep is reduced as a result of lower total paste content, lower thermal stresses and an early capacity to carry low levels of compressive stress; and
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Higher densities are achieved due to the use of continuously-graded aggregates and tighter control on aggregate shape. Consequently, the total aggregate content is increased.
RCC for pavements:
Roller-compacted concrete pavements (RCCP) have not been widely used in South Africa. There have been some test sections predominantly in the 1980s and 1990ss which were assessed using a Heavy Vehicle Simulator and RCCP did prove effective enough to have been used in a number of low volume road and industrial projects around the country.
So, what is roller-compacted concrete pavement?
RCCP has similar strength properties and consists of the same basic ingredients as conventional concrete pavements, but has different mix proportions. These strengths are generally significantly higher than that for RCC used in dam construction. Fresh RCCP is stiffer than typical zero-slump conventional concrete. RCCP is typically placed with an asphalt-type paver equipped with a high-density screed followed by a combination of passes with rollers for compaction. RCCP is constructed without forms, dowels or reinforcing steel. Joint sawing is not required, but when specified, cuts are spaced further apart than with conventional concrete pavements. RCC pavements can and have been constructed by labour-intensive methods for low-volume roads.
With well graded aggregates, adequate cement content and dense compaction, RCCP can achieve strength properties equal to those of conventional concrete. Achieving a dense product is key to good performance of RCCP.
The primary benefit of roller compacted concrete pavements is that they can be constructed more quickly and cost-effectively than conventional concrete pavements and some multiple lift asphalt pavements. The actual cost saving depends on volumes and complexity of paving.
Other benefits include:
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The lower paste content results in lower shrinkage and reduced cracking;
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RCCP can be designed to have high flexural, compressive and shear strengths, allowing heavy repetitive loads without failure, and to withstand highly concentrated loads;
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Its low permeability gives good durability and resistance to chemical attack;
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Costs related to joint maintenance can be eliminated or reduced;
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It shows good abrasion resistance under heavy traffic; and
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Layer placements as thick as 250 mm are possible in a single lift, depending on the mix and equipment used.
However, there are some limitations and challenges to using RCCP. These include:
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A lack of smoothness and profile which may not be suitable for high-speed traffic. This can be addressed by diamond grinding or a thin asphalt which, however, adds to the cost;
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Multiple lifts must be carefully planned to ensure a delay of less than an hour between lifts;
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Pavement edges are difficult to compact adequately; and
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Placing RCCP in hot weather requires extra protection and vigilance to minimise water loss due to evaporation.
RCC pavements are generally used for:
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Ports, intermodal facilities, and heavy industrial facilities;
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Light industrial areas;
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Airport maintenance areas, and parking lots. Unsurfaced RCCP is not recommended for aircraft traffic due to possible dislodging of loose aggregate particles;
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Major arterials, often with a diamond ground surface or thin asphalt surfacing in higher speed areas;
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Low-volume rural roads;
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Local community streets; and
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Widening of existing roads or provision of surfaced shoulders.
