THE EFFECTS OF CLIMATIC CONDITIONS AND BRICK CONTENT ON RECYCLED ASPHALT PAVEMENT AND RECYCLED CONCRETE AGGREGATE AS UNBOUND ROAD BASE

This study evaluates the use of recycled concrete aggregate (RCA) and recycled asphalt pavement (RAP) as an unbound road base. This investigation looked at the climatic behavior (i.e., temperature effects, wet/dry cycling) of RAP and RCA and the effects of brick content on the resilient modulus and plastic strain (as an index) of RCA. The two chapters of this thesis individually discuss each one of these studies. The recycled materials used in this study came from a large geographical area covering eight U.S. states including California, Colorado, Michigan, Minnesota, New Jersey, Ohio, Texas and Wisconsin. Basalt and a quartz/granite/limestone blend meeting Minnesota Department of Transportation?s Class 5 gradation standard were used as control materials. Resilient modulus tests were conducted on the materials according to protocol 1-28a of the National Cooperative Highway Research Program (NCHRP). Modifications were made to the triaxial cell for resilient modulus to accommodate varying temperatures (7 �C to 50 �C) to test the materials at. The Power function proposed by Moosazedh and Witczak (1981) and NCHRP models were fitted to the resilient modulus test data to estimate resilient modulus as a function of stress state. The NCHRP model provided higher coefficients of determination than the Power function model. A summary resilient modulus (SRM) was calculated from the Power function and NCHRP models at a bulk stress of 208 kPa, which is typical for a base course and the recommended bulk stress value for NCHRP 1-28a. External LVDT data provided more reliable SRM values than internal LVDT data. The effects of temperature on resilient modulus of the RAP and RCA were evaluated using NCHRP 1-28a protocols at 7, 23, 35, and 50 �C. No decrease in SRM was observed in the RCA and natural aggregates tested. A decrease in SRM of approximately 37% and 30% was observed for both TX and CO RAP, respectively, tested between the 23 �C and 35 �C temperatures; however, this decreasing trend did not continue between 35 �C and 50 �C where it stabilized. This decrease in SRM is suggestive of a critical temperature between 23 �C and 35 �C where the physical characteristics of the asphalt binder coating the aggregates is altered. The increased temperature caused the strain rate to increase in all RAPs, but no effects occurred in the natural aggregates or RCAs tested. NJ RAP had the highest strain rate, followed by TX RAP and then CO RAP. Most of the increase in strain rate occurred within the first 1,000 cycles (conditioning phase) of the resilient modulus test. Total cumulative plastic strains achieved in RAPs were generally high (> 7%), which is similar to results reported in the literature, but increased temperature increased the rate at which the plastic strain was achieved. Due to this trend, RAP that is placed and compacted during the warmest time of the year could act to reduce the total plastic strain accumulation after pavement is laid. A procedure to evaluate the effects of wetting and drying of RAP and RCA on particle degradation was developed. Two RCAs, two RAPs, and two natural aggregates were tested at 5, 10, and 30 wet/dry cycles. Micro-Deval and particle size distribution tests were conducted on the materials after their specificed wet/dry cycle. No trend was observed in Micro-Deval loss percentage or particle size distribution due to wet/dry cycles, which suggests that wetting and drying of recycled material has no effect on particle degradation. One of the most costly and time consuming impurities to remove before and during crushing of recycled materials is brick because of its extensive use as a fa�ade material covering concrete buildings. To study if brick is a major impurity in RCA, compaction tests and resilient modulus tests were completed on RCA mixed with brick at 0, 10, 20, and 30% brick by mass. Four RCAs were used: NJ, OH, MN, and TX. Compaction tests were completed at 0% and 30% brick on all RCA materials except NJ RCA due to lack of materials. When compared to 0% brick specimens, optimum moisture content increased and dry unit weight decreased in all RCAs mixed with 30% brick. This was attributed to brick having higher absorption and lower specific gravity and dry unit weight than RCA. Water drained out of the compaction molds if more water than OMC was added, not allowing maximum dry unit weight to decrease. No apparent trends were observed between SRM and brick content three of the four RCAs tested, but a decrease in plastic strain was observed with increased brick content