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Laboratory Characterization of Recycled Concrete for Use as Pavement Base Material

The purpose of this research was to characterize both demolition and haul-back sources of recycled concrete material (RCM) available in Utah County, Utah, for use as pavement base material and to investigate the self-cementing behaviors of each. A telephone survey was conducted to assess the state of the practice with respect to the local use of RCM, and extensive laboratory testing was performed to evaluate the strength and durability properties of both sources of RCM. Laboratory testing included determinations of particle-size distributions, Atterberg limits, specific gravity values, absorption characteristics, moisture–density relationships, California bearing ratio (CBR), unconfined compressive strength (UCS), stiffness, resistance to freeze–thaw cycling, tube suction test (TST) moisture susceptibility classifications, and Los Angeles abrasion losses. The results of the testing indicate that marked stiffening and strength gain of the materials occur within a 7-day curing period, although the rate and extent of the increases are dependent on the material source. The higher fines content of the haul-back material corresponded to higher absorption, optimum moisture content, maximum dry density, CBR, UCS, and stiffness values compared with the demolition material, presumably because of the exposure of greater quantities of unhydrated cement in the production of the haul-back RCM. However, the haul-back RCM was characterized by a greater loss in stiffness after freeze–thaw cycling and received a marginal moisture-susceptibility rating in the TST, while the demolition RCM was rated as non-moisture-susceptible. Further research is needed to more definitively investigate the self-cementing mechanism of RCM.