Optimum design for sustainable green bonded concrete overlays: failure due to sheer and delamination

摘要

Adequate interfacial bond performance of Bonded Concrete Overlay (BCO) systems requires novel integration of material mixture design, compatibility model development, and interfacial bond design. This entails the use of the right materials, on the right substrate, in the right way, in order to secure the best possible composite behaviour. The overall composite performance of BCOs depends largely on achieving the right proportion of blend for the overlay material. The use of mixture experiments provides a flexible, easy, and quick way of optimizing multi-component materials of this nature. This study describes the use of optimization techniques within the concept of material mixture experiments for proportioning and designing the material constituents of a Bonded Roller Compacted Fibre Reinforced Polymer Modified Concrete (BRCFRPMC). By constraining the range of variability of the constituents, a feasible design space was created with 13 experimental points treated based on the required structural and elastic properties of the overlay. The optimum consistency-time for full consolidation and composite behaviour with the substrate ordinary Portland cement concrete (OPCC) was established between 34.05 and 34.87 seconds, while the resulting apparent maximum density achieves between 97.11% - 98.03% of the theoretical air-free density. In addition, compressive strength response at early and matured ages of 3 and 28 days were satisfied at 100% desirability. The elastic modulus response at age 3 showed 0% desirability, but attains about 99.96% of the target response by 28 days. The verification experiments conducted on each response property shows that positive correlations exist between the measured responses and the predicted values from the optimization analysis. Also, the bond capability of the optimum designed overlay material was evaluated using both tensile and shear bond strengths parameters. The overall assessment results showed that the overlay material exhibits good bonding with the substrate OPCC and would be able to withstand substantial stresses where sufficient surface texture is provided for aggregates interlocking. Other material properties included in the evaluation process of the overlay material included its tensile strength, coefficient of thermal expansion, and drying shrinkage. Stresses in the overlay, substrate, and at the interface were assessed analytically under various differential movement related conditions. Though the interface and the overlay material exhibited sufficient strength against thermal and shrinkage cracking, the theoretical shrinkage cracking in the overlay was predicted at 6.92MPa when fully restrained axially. Further, for effective fracture process description of the interface, experimentally determined parameters in shear and tension were coupled in Mixed-Mode Finite Element Analysis using differential edge deformation model between the overlay and the underlay. The results indicated that delamination in partial fracture process varied from that of complete fracture process, influenced distinctly and largely by the magnitude of the applied load. Other influencing factors in the analyses included the elastic mismatched properties, initial edge defect size, and the plane of loading. Lastly, analytical solution to the FEA problem was implemented using the proposed Modified Eigenvalue Buckling Analysis (MEBA). The result indicated that the proposed analytical method simulates and compares well with the FEA result. The proposed method also provided a good technique for predicting the Mixed-Mode Buckling failure Mode-Shape of the overlay.