Evaluation of Recycled Concrete for Use as Aggregate in New Concrete Pavements.
Evaluation of Recycled Concrete for Use as Aggregate in New Concrete Pavements | Engineering Books.
Contents of Evaluation of Recycled Concrete for Use as Aggregate in New Concrete Pavements pdf:
1. INTRODUCTION.
2. LITERATURE REVIEW.
3. EXPERIMENTAL PROGRAM.
4. TEST RESULTS AND DISCUSION
5. SUMMARY, CONCLUSIONS AND RECOMMENDATIONS
EXECUTIVE SUMMARY:
This study was performed for the Washington State Department of Transportation (WSDOT) and evaluated the use of recycled concrete as a replacement for natural aggregates in new portland cement concrete pavements. Recycled concrete aggregate (RCA) produced from demolished pavements in three geographically-dispersed locations in Washington state were used to perform tests on aggregate characteristics, fresh concrete properties, and hardened concrete properties. Variables included the source of the RCA, percent replacement of coarse natural aggregate with RCA (0%, 15%, 30% and 45%), and percent replacement of portland cement with type F fly ash (0% or 20%).
Four tests were used to characterize RCA properties including specific gravity, absorption capacity, Los Angeles abrasion loss, degradation value in various conditions, and alkali-silica reactivity. The conditions for which the degradation value was determined included the as-delivered unprocessed RCA, the processed RCA, and processed RCA mixed with natural aggregate at rates of 15%, 30%, and 45%. Overall, tests showed that RCA has a lower specific gravity, greater absorption capacity, and meets the WSDOT requirements on Los Angeles abrasion loss and degradation value once processed. Additional tests may need to be performed to evaluate potential deleterious expansion due to alkali-silica reactivity.
Three tests were used to determine if RCA had any effects on the properties of fresh concrete including slump, air content by the pressure method, and density. Slump and air content were controlled parameters in the batching process, with targets specified by WSDOT of 1-3 inches for slump and 4-7% for air content. It was a goal during the mix process to make concrete mixtures within the low end of each of those ranges. Slump was controlled by withholding mix water or adding water-reducing admixture (WRA), and air content was controlled by the amount of air entraining admixture used in the batch. RCA was found to decrease the slump and density of fresh concrete. RCA had no significant effect on air content.
Five tests were used to determine the effects of RCA on hardened concrete properties including compressive strength, modulus of rupture, coefficient of thermal expansion, drying shrinkage, and freeze-thaw durability. Test results showed that up to a 45% replacement of coarse natural aggregate with RCA had no significant effect on any of the hardened concrete properties tested. In addition, all samples tested met WSDOT minimum strength requirements for use in concrete pavements. It should be emphasized that these results were obtained using RCA obtained from demolished pavements incorporating high-quality original materials.
The results of this study indicate that RCAs of similar quality to those incorporated in this research would be viable for use in new concrete pavements. RCA had no significant effects on the compressive strength, modulus of rupture, coefficient of thermal expansion, drying shrinkage, or freeze-thaw durability of hardened concrete for up to a 45% replacement of coarse RCA for natural coarse aggregate. In addition, all results from tests on the RCA from the three sources and results concrete incorporating this RCA at up to 45% replacement met WSDOT requirements for use in new concrete pavements.
Further study should be performed to determine the minimum criteria RCA must meet for use as an aggregate in concrete pavements as well as to evaluate higher RCA replacement rates.
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