| Roller Compacted Concrete, Las Vegas Wash Bridge |
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 The Mojave Desert would be considered North America’s driest desert, with an average of about 4 inches of rain each year. The Las Vegas Wash is an oasis situated in this desert and is the only natural drainage channel covering the entire 1,600-mi.2 Las Vegas valley. Following floods in July 1999, the wash was hit badly as they sent around 4.5 billion gallonsof water in one day through the wash and at some points the banks had widened by 300ft. A committee has been set up to protect the Wash and address problems such as erosion, water quality, bed stabilisation, revegetation etc. The Rapid Mix 400 was used in several of these projects and Roller Compacted Concrete was selected as the construction material mainly for reasons of durability, speed of construction and geometric flexibility. One of the benefits of using the Rapid Mix 400 is that it has the mixing efficiency needed to evenly disperse the small amount of water used.  There was a 12-mile section of the wash which had experienced much channel degradation and the durability of this type of concrete was vital when considering potential flood damage. Hopes of using on-site alluvial materials were dashed when it was found that very little coarse aggregate was available in the alluvium. The concrete company contracted for theproject decided on importing an all-in-one aggregate blend with a maximum size aggregate of 1 in. 25 mm. In order to achieve the required 28-day compressive strength of 3,000 psi (21 MPa), 380 lb/cu yd (225 kg/cu m) of cement was added. During construction, water control was vital as the stream needed to be diverted and rerouted at times. |
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