Experimental study of the effect of alkali-silica reaction of aggregate on the bond behavior between concrete and rebar

نوع: Type: thesis

مقطع: Segment: PHD

عنوان: Title: Experimental study of the effect of alkali-silica reaction of aggregate on the bond behavior between concrete and rebar

ارائه دهنده: Provider: Maryam Abbasiyan Taeb

اساتید راهنما: Supervisors: Freydoon Rezaie

اساتید مشاور: Advisory Professors: Ebrahim Ghiasvand

اساتید ممتحن یا داور: Examining professors or referees: Morteza Madhkhan- Mostafa Moghadasi- Gholamreza Ghahremani

زمان و تاریخ ارائه: Time and date of presentation: 2024

مکان ارائه: Place of presentation: Faculty of Engineering

چکیده: Abstract: Alkali-silica reaction (ASR) is a reason for the destruction of concrete structures over time and a threat to their durability. This reaction causes the concrete to expand, crack, and then lose its strength. This research quantitatively examines the effect of fine or coarse granularity of reactive aggregate and changes in water-cement ratio on the bond strength of concrete by two methods of pull-out and beam under ASR. In addition, the effect of reactive fine and coarse aggregate on the mechanical properties of concrete, including compressive strength, tensile strength, and modulus of rupture, as well as the amount of expansion occurring in concrete due to the ASR over time, were investigated. For this purpose, six concrete mixtures were made from different combinations of reactive and non-reactive coarse and fine aggregates with water to cement ratios (W/C) of 0.45, 0.5 and 0.55. Then, a number of cubic, prismatic, and cylindrical specimens were cast with 12 and 16 mm diameter rebars and concrete beams with 16 mm diameter rebars and immersed in sodium hydroxide solution for 90 and 180 days. The results showed that the ASR over time decreased the compressive strength, tensile strength, modulus of rupture, and bond strength of concrete in both methods, and with the reduction of the size of the reactive aggregate, the loss of strength and the growth of expansion intensified. By increasing the diameter of the rebar from 12 to 16 mm in the pull-out test, the bond strength was further reduced due to the reaction. Also, changing the size of reactive aggregates, W/C, or immersion time had no effect on the failure mode of the same pull-out specimens reinforced with 12 mm diameter rebar. But by changing the diameter of the rebar from 12 to 16 mm, the ASR caused a change in the failure mode of the specimens from rebar sliding to concrete splitting. Finally, a bon-slip model was proposed for the tested pull-out specimens. As the ASR progressed, the energy absorption capacity of all specimens decreased. Reducing the size of the reactive aggregate caused a further decrease in the energy absorption capacity of all the beam specimens and most of the pull-out specimens. The occurrence of the reaction led to a decrease in the stiffness of all the beam specimens and pull-out specimens with a diameter of 12 mm, and the decrease in the size of the reactive aggregates worsened. But it did not have a significant effect on the stiffness of the 16 mm diameter pull-out specimens. The testing methodology had an effect on the bond behavior of the specimens, the failure mode and the bond-slip curve. Therefore, it is recommended to use the beam method for studies that need to measure the actual bond stress between rebar and damaged concrete caused by ASR. Also, reduction of the W/C as much as possible to control the loss in mechanical strength of concrete caused by the ASR is not always effective, but there is an optimal value for the W/C. With the increase of W/C, the loss of bond strength of pull-out specimens reinforced with 12 mm rebar intensified, but in the case of specimens reinforced with 16 mm rebar, the loss of bond strength and changes in W/C ratio did not have a constant trend. Both options of reducing the W/C ratio or replacing the reactive aggregate were suitable solutions to improve the bond behavior of the damaged concrete caused by the ASR. But as the ASR progressed in the long term, the effect of the first option became less. In addition, it seems that the second option is a more appropriate solution to control the negative effects of the ASR on the bond behavior of thicker rebars in the long term.

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