Table 11-4 While most of this discussion has focused on RCA concrete mixes for use in the surface course, it applies to the use of RCA in lean concrete base courses as well. RCA was used in lean concrete bases before it was used in concrete surfaces. Table 11-4 summarizes the properties of hardened concrete using RCA. Design of RCA for Asphalt Mixtures RCA can also be used in the development of asphalt surface or base course mixes, as the typical RCA roughness and angularity contributes to overall stability and surface friction (ACPA 2009). Moreover, the presence of the mortar fraction on the RCA can reduce the occurrence of stripping in the asphalt. However, RCA tends to absorb more asphalt binder than conventional aggregates because of higher porosity and absorption capacity of RCA, which often makes its use Table 11-. Properties of hardened concrete using RCA (Snyder et al. 1994). Property RCA Mixes Generally lower due to the reduction of the percent of natural Compressive Strength aggregates. Generally slightly lower, but it varies depending on the quality of the Flexural Strength original aggregate and the amount of recycled fine aggregate used. Generally 20 to 40 percent lower than mixes with natural aggregates Modulus of Elasticity due to the lower elastic modulus of the RCA particles. Freeze-Thaw Superior to virgin aggregate mixes. Reduced potential due to the crushing of original aggregate to D-Cracking Durability smaller sizes. Increased potential due to increased surface areas of the aggregates ASR that have been crushed. Bond Strength with to virgin aggregate mixes, but reduced if recycled fines are Reinforcement used. Creep Higher due to the higher cement fraction. Drying Shrinkage Higher due to the higher cement paste fraction. Structural Design Considerations Conventional concrete pavement design procedures can be followed for concrete pavements utilizing RCA concrete. However, special consideration must be given to the low abrasion resistance of RCA and its typically smaller top size (used to reduce durability problems) to obtain good long-term pavement performance. These properties of RCA tend to cause poor load transfer conditions at undoweled joints or at transverse cracks, a condition that can lead to pumping, faulting, and corner breaks. Consequently, the following recommendations are provided to improve the structural performance of concrete pavements constructed with RCA (Snyder 1994; ACPA 2009): JPCP: Use shorter joint spacing (to reduce crack opening).
Table 11-4 While most of this discussion has focused on RCA concrete mixes for use in the surface course, it applies to the use of RCA in lean concrete base courses as well. RCA was used in lean concrete bases before it was used in concrete surfaces. Table 11-4 summarizes the properties of hardened concrete using RCA. Design of RCA for Asphalt Mixtures RCA can also be used in the development of asphalt surface or base course mixes, as the typical RCA roughness and angularity contributes to overall stability and surface friction (ACPA 2009). Moreover, the presence of the mortar fraction on the RCA can reduce the occurrence of stripping in the asphalt. However, RCA tends to absorb more asphalt binder than conventional aggregates because of higher porosity and absorption capacity of RCA, which often makes its use Table 11-. Properties of hardened concrete using RCA (Snyder et al. 1994). Property RCA Mixes Compressive Strength Generally lower due to the reduction of the percent of natural aggregates. Flexural Strength Generally slightly lower, but it varies depending on the quality of the original aggregate and the amount of recycled fine aggregate used. Modulus of Elasticity Generally 20 to 40 percent lower than mixes with natural aggregates due to the lower elastic modulus of the RCA particles. Durability Freeze-Thaw Superior to virgin aggregate mixes. D-Cracking Reduced potential due to the crushing of original aggregate to smaller sizes. ASR Increased potential due to increased surface areas of the aggregates that have been crushed. Bond Strength with Reinforcement to virgin aggregate mixes, but reduced if recycled fines are used. Creep Higher due to the higher cement fraction. Drying Shrinkage Higher due to the higher cement paste fraction. Structural Design Considerations Conventional concrete pavement design procedures can be followed for concrete pavements utilizing RCA concrete. However, special consideration must be given to the low abrasion resistance of RCA and its typically smaller top size (used to reduce durability problems) to obtain good long-term pavement performance. These properties of RCA tend to cause poor load transfer conditions at undoweled joints or at transverse cracks, a condition that can lead to pumping, faulting, and corner breaks. Consequently, the following recommendations are provided to improve the structural performance of concrete pavements constructed with RCA (Snyder 1994; ACPA 2009): JPCP: Use shorter joint spacing (to reduce crack opening).
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