دانلود رایگان مقاله انگلیسی بررسی قدرت پیوند بین بتن و تقویت به عنوان یک عملکرد سطوح جایگزین بتن بازیافتی - الزویر 2018

Abstract

The objective of this study was to determine the effect of replacing coarse natural aggregates for recycled concrete aggregates (RCA) on the bond strength between deformed mild reinforcing steel and surrounding concrete. Two different RCA replacement levels were considered, 50% and 100%, and were compared to a conventional concrete mixture. To evaluate bond strength, 18 direct pull-out specimens were tested with both No. 13 and No. 19 reinforcing bars and nine full-scale beam specimens were tested with non-confined contact lap splices located at mid-span. Analysis of the test data indicates that replacing more than 50% of coarse natural aggregates results in diminished bond strength over concrete containing only virgin natural aggregates. This result suggests that the existing equation for development and splice length as reported in ACI 318 may require additional modification factors to account for the diminished bond strength when associated with replacement of coarse aggregates with RCA.

Conclusions

To study the bond strength of reinforcing steel in RAC, 18 pull-out specimens as well as nine full-scale beam splice specimens were tested. Based on the results of this study, the following findings and conclusions are presented: Pull-out Specimens: The bond strength for the RAC-50 mix exceeded the CC mix by approximately 20%. The bond strength for the RAC-100 mix exceeded the CC mix by approximately 10%. All of the specimens had similar load-slip response. All of the specimens failed by an adhesion failure or local crushing between the reinforcing steel ribs and the base concrete. Beam Splice Specimens: The bond stress-slip behavior for both the CC and RAC beam specimens was very similar, essentially linear until failure. The cracking pattern for both the CC and RAC beam specimens was very similar, consisting of vertical flexural cracks at each end of the splice and horizontal splitting cracks along the splice region. The bond strength for the CC mix exceeded the RAC-50 mix by approximately 10%. The bond strength for the CC mix exceeded the RAC-100 mix by approximately 30%. General: The RAC mixes had enhanced bond strength with the reinforcing steel compared to the CC mixes when the failure did not result due to splitting, as evidenced by the pull-out specimens. However, when the failure was initiated by splitting of the concrete, the RAC mixes had lower bond strength compared to the CC mixes, as evidenced by the full-scale splice specimens. There is very good agreement between the concrete mechanical properties (splitting tensile strength and fracture energy) and the full-scale splice specimen test results, primarily due to the splitting type of failure mode.