Superthin Concrete Overlays
Better Roads Staff
“In the United States, we’re seeing RCC being used for roadway shoulders, industrial facilities, distribution centers, haul roads – and increasingly, for streets and roads,” says Jerry Voigt, PE, president and CEO of ACPA. “We’ve also seen it used as a base course for highway and other roadway applications.”
RCC is a special type of concrete that has the same ingredients as conventional concrete but in different proportions. RCC mixtures are drier than conventional paving concrete, so it has a lower water/cement ratio; RCC mixtures typically have zero slump. As is true with conventional concrete paving, RCC mixtures sometimes include more fly ash in place of some portland cement content, and mixtures very often contain fibers for added strength.
The technology has advanced somewhat along regional lines in North America. The Southeastern United States and Western Canada have had a relatively longer history of using RCC; however, the technology is rapidly gaining acceptance in other areas. In Canada, Rico Fung, P.Eng., LEED AP, director, Markets & Technical Affairs-Ontario for the Cement Association of Canada, Toronto, reports most applications in Canada are in Alberta, B.C. and Ontario.
“RCC is very cost effective, which is a key advantage for various applications,” says Voigt. “We’re seeing owners trying RCC instead of asphalt based on its cost. RCC can be placed with various types of equipment, with best results typically coming with high-density paving equipment. RCC is placed without forms and typically does not require finishing.”
Compaction is also a key factor in RCC paving. High-density pavers equipped with tamping bars can impart much of the required density (up to about 95 percent) directly behind the paver. Heavy-duty and/or medium-duty vibratory rollers follow immediately behind the paver to help increase compaction.
RCC does not use steel (rebar, dowels, or tie bars). Aggregate interlock provides shear resistance at joints and prevents displacement or faulting. In many instances, sawed joints are not required, but for some applications, longitudinal and transverse joints are cut with concrete saws.
Set up is generally fast and relatively simple for trained crews. The material also can be placed directly on a good quality subgrade, and generally requires no finishing work. RCC is cured, but it does not typically need to be covered with curing blankets, plastic, or the like.
As one might expect, roller-compacted concrete is a very strong material. The Portland Cement Association (PCA) says it has high flexural strength – from 500 to 1,000 psi. That means it can support heavy, repetitive loads without failure, and can span localized soft subgrade areas, which reduces maintenance costs and pavement downtime.
Moreover, RCC has high compressive strength – 4,000 to 10,000 psi, so it can withstand high concentrated loads and impacts from heavy industrial, military, and mining applications. RCC is a high-density, low-water-absorption material. That gives it excellent durability, even under freeze-thaw conditions. Water does not seep through RCC.
The low water content and low water/cement ratio of RCC provide its strength, low permeability, and durability. These properties also help RCC to be resistant to chemical attack. RCC also resists abrasion, making it a great surface for large vehicles.