Rock Products

MAR 2013

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SPECIAL REPORT quested about any limitations in the use of RCA for those states allowing it, and any environmental concerns they have related to it. A copy of the state���s specifications for RCA was also re��� quested. Thirty���nine states and the Dis��� trict of Columbia responded to the survey. Thirty���three of the responses indicated that RCA was allowed as an aggregate base, reinforcing the fact that RCA is a viable replacement for virgin aggre��� gates, and seven states did not cur��� rently allow it. Two of the states not currently allowing RCA were consider��� ing allowing its use, one of which sub��� mitted a draft specification they intend to use. One additional state that is pre��� dominantly rural stated that they would consider allowing RCA if re��� quested. One state not allowing it cited environ��� mental problems (pH and runoff) and durability issues with the larger parti��� cle sizes of their limestone and gravel. Another state noted that the use was stopped in the mid���1990s because of issues with clogged rodent screens at outlets of pavement drainage systems and the outwash damaged vegetation. That state has now developed a specifi��� cation to address these issues and is al��� lowing its use experimentally on one project. Figure 1 exhibits responses from the individual states reflecting whether or not the use of RCA as an ag��� gregate base is allowed. Most responders indicated that no environmental concerns existed. However, concerns about leachates, pH, freeze-thaw, corrosion of metal pipe, clogging of subsurface drainage caused by precipitates (tufa), asbestos, lead, and air quality existed with a few states. The details of these environmental issues are discussed below. States having concerns about leachates stem from several areas. One of these involves the alkalinity of water passing through the RCA layers that could lead to corrosion of metal culverts and rodent grates and could also damage vegetation. A South Dakota study noted that al��� though pH levels could initially be high, the low permeability of base courses will minimize the transport of water through them and ���is not considered a problem.��� (Cooley, 2007) FHWA re��� ported that research indicates only a small area near drainage outlets is af��� fected, and only for a short period of time after the initial construction. (FHWA, 2004) The AASHTO Standard Specification for Reclaimed Concrete Aggregate for Unbound Soil���Aggregate Base Course designated as M 319 also addresses this in Note 2 and states that appropriate limits should be set for the use of RCA in proximity to groundwa��� ter and surface water. States having this concern could address this by not using RCA base in low, wet areas, or where the base course is allowed to daylight into the edges of embank��� ments thereby exposing it to surface water. Another potential leachate issue in��� volves the possibility of precipitates (calcium carbonate) being formed that could clog filter fabrics and reduce the effectiveness of pavement subsurface drainage systems. (Van Dam, 2011) User Guidelines presented by the Recy��� cled Materials Resource Center sum��� marized research that offered a series of recommendations to limit the poten��� tial of the formation of such tufa���like precipitates, noting that this problem is not universal and that many are func��� tioning without any precipitate forma��� tion. (RMRC, 2008) Appendix X2 of AASHTO M 319 also addresses this issue. ASTM D 5101 can be used to compare the permeability of geotex��� tiles using virgin fine grained material and using the fine grained portion of RCA base materials to determine if a measurable impact exists. One state recommended limiting RCA fines in the base, designing drainage systems to ac��� commodate a limited quantity of As might be expected, individual states approach the use of RCA with some differences. Several states re��� quire that RCA conform to the same requirements in place for virgin aggre��� gate base. Two states (Arizona and Maine���s provisional draft specifica��� tions) allow up to 50 percent by weight blend of RCA with virgin aggre��� gate base. Some states require that RCA be generated from concrete within the project limits, or from an��� other state project, while other states have additional testing and storage re��� quirements if the concrete comes from an unknown source. Several states re��� quire the producer to be certified, while others require the producer to present a certification that the RCA does not contain hazardous materials. 24 ROCKproducts ��� MARCH 2013

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