Effect of concrete composition and self-healing method on bond behaviour of cracked normal concrete and self-consolidating concrete

Abstract

The interaction between the steel reinforcing bar and surrounding concrete is one of the most important issues that control the efficiency of the composite behaviour of reinforced concrete structures. Moreover, a good interfacial behaviour between concrete and reinforcement is necessary to achieve durable performance for a reinforced concrete structure. However, most previous studies have focused on the interfacial behaviour of reinforcing bars with the undamaged and intact surrounding concrete. There are only few researches on pre-cracked concrete with different pre-cracking conditions. Moreover, there is a need for developing practical solutions to mitigate interfacial damages due to the pre-cracking phenomenon. Hence, this thesis intends to experimentally and analytically study the reinforcing steel-concrete bond behaviour in presence of the pre-cracking phenomenon. Additionally, a practical approach is studied to determine the self-healing possibility of cracks at the rebar-concrete interaction. Two types of superabsorbent polymers (SAP) are used in concrete mixtures, in dosages of 0.25%, 0.50%, and 1.0%, to accelerate the self-healing process. The used methodology consists of a pre-cracking process along with re-curing periods (healing periods) for healing splitting cracks. Splitting test (Brazilian test) is used to simulate pre-loading and to obtain initial precracking. Crack widths of 0.10-0.50 mm are studied in the present thesis. A total number of 230 pull-out tests are carried out to obtain the rebar-concrete interfacial response in terms of bond-slip envelope curves, allowing examination of the initial bond stress, bond strength, residual bond stress, average bond stress, and energy observed by the bond mechanism. Seven concrete types are tested in the present thesis including normal concrete (NC) with a normal slump, NC with flowing slump, NC with air-entraining admixture (AE), self-consolidating concrete (SCC), SAP modified NC, SAP modified air-entraining NC, and SAP modified SCC. Finally, statistical analyses are performed to better investigate and point out the main findings. Experimental results show that the pre-cracking phenomenon leads to a significant reduction in the bond strength, average bond stress, and residual bond stress. Bond strength degradation is presented as a function of crack width. Results show that crack widths larger than 0.15 mm have a considerable impact on bond properties. Moreover, Results regarding bond strength reduction due to pre-cracking show that compared to NC, SCC is less sensitive to this phenomenon. The higher value of slump flow can be the main reason for this observation. Regarding the self-healing method, results indicate that SAP particles significantly promote strength regaining in the pre-cracked concrete, exposed to wet-dry cycles, especially for a 14 higher dosage of SAP and crack width smaller than 0.30 mm. Air-entraining admixture has a considerable impact on the performance of the self-healing process so that concrete containing AE has a higher healing improvement factor as compared to the non air-entraining mixture. Scanning electron microscopy (SEM) analysis shows a large amount of calcium, oxygen, and carbon in healing products at both internal and external surfaces of cracks. This study would be an initial investigation of the crack-healing in the critical region of the rebar-concrete interaction, which should be continued by further research, notably the effect of AE on the crack-healing of SAP concrete and influence of supplementary cementitious materials (SCMs) on the results of the present thesis. Moreover, results of the present study demonstrate that SAP particles are more efficient in SCC mixtures, as compared to NC mixtures, to heal the initial cracks at the rebar-concrete interface. Moreover, micro-CT scanning results show that the improvement healing factor for self-sealing of cracks is higher than self-healing (strength recovery) one, as more efforts are needed to regain strength recovery than the crack closure.

Date	19 Dec 2020
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Lotfi Guizani (Supervisor) & Claudiane Ouellet-Plamondon (Co-supervisor)