Electronic Thesis and Dissertation Repository

Degree

Master of Engineering Science

Program

Civil and Environmental Engineering

Supervisor

Dr. Moncef Nehdi

Abstract

The grouted dowel connection is a simple and cost-effective connection used in many precast concrete structural systems. The required dowel length is currently designed as a regular bar in reinforced concrete, which underestimates the bond strength, thus resulting in excessive connection lengths. Furthermore, precast wall construction continues throughout cold weather, where in-situ heating of the grout used in the grouted dowel connections is usually conducted for short periods of time. Hence, early-age exposure to subfreezing conditions may affect the quality of the grout and subsequently the bond strength of the connection, which can compromise structural integrity.

In this thesis, full-scale pullout tests were performed and their results were compared with relevant data in the open literature in order to develop a reliable design equation for predicting the required dowel development length. The equation was found to produce results three times smaller than that determined by the ACI 318-14 code, while being desirably 10% more conservative than equations proposed in previous research.

The effect of subfreezing exposure on the bond strength of the connection, along with the mechanical properties, hydration process and pore size distribution of the grout were also examined. Grout specimens were initially cured at ambient temperature (23 ± 1°C) for one day and then placed inside an environmental chamber at -10°C. The compressive strength of the grout was monitored at additional temperatures of 1°C and -20°C. It was found that early-age subfreezing curing temperatures reduced the compressive strength of the grout, leading to increased dowel embedment length to achieve bar fracture. The bond strength of the connection remained proportional to the square root of compressive strength, even when subsequent to early-age subfreezing exposure.


Share

COinS