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Title

BOND STRENGTH COMPARISONS OF DIFFERENT SUBSTRATE PREPARATIONS AND VARIOUS BONDING AGENTS USED IN CONCRETE OVERLAYS AND ENLARGEMENTS

Creator

Eberhardt, Keith

Date

2017, 2017-05

Description

The bond interface line of concrete overlays and enlargements has been the focus of engineers, contractors, and manufacturers for many years....
Show moreThe bond interface line of concrete overlays and enlargements has been the focus of engineers, contractors, and manufacturers for many years. Many products and procedures have been developed to help the contractor and engineering community achieve the highest bond strength of the repair material to the host material, or substrate, to provide a quality, long-lasting repair. It is well known that the difference between a successful overlay or enlargement and one that fails can be directly linked to the preparation of the bonding surface. The objective of this study is to compare what concrete removal techniques, or surface preparations, in conjunction with bonding conditions and agents have on achieving the best direct tensile and guillotine test results. A unique step of this research is to use an overlay material with the same mix design as the base slab. Most overlay materials are stronger and do not use the same coarse aggregate and cement. By having the substrate and the overlay concrete the same material, a true test of the bond can be accomplished as the core samples should fail in both the substrate and overlay. This study consisted of four concrete slabs that were poured and allowed to naturally cure for a full year. Afterwards, each slab used a different method to remove up to two and one-half inches of the substrate concrete to prepare for the overlay. Removal methods used were hydrodemolition, pneumatic impact hammers, abrasive blasting and a control slab that consisted of a light broom finish. Each panel was then divided into four sections and a different surface condition or bonding agent was applied to the substrate just prior to the placement of the overlay. The surface conditions and agents used were dry, surface-saturated dry (SSD), sand/cement slurry and an epoxy and cementitious material. After the overlay was placed, the overlaid test panels were allowed to remain in place and naturally cure for an additional year before test samples were taken. Results supported that any impact blow force to the surface yielded the worst results by almost 50% for both direct tensile and guillotine tests. Even a change in bonding agents could not overcome the damage to the surface of the base slab. These results support years of similar test reporting. There was no increase in test results using a bonding agent on any of the prepared slabs. The results were similar, and in some cases, less than a surface that was dry or SSD. The highest and most consistent results came from the slab that was either dry or SSD. Results indicate that a dry surface that is prepared with either abrasive blasting or hydrodemolition may yield the most consistent results as all other bonding conditions and agents are subject to difficulty in measuring the application accurately and can be highly susceptible to evaporation rates and variations in multiple mixing operations. A well prepared, clean, dry surface will yield the greatest and most consistent failure results and is the easiest to monitor and duplicate in field conditions.
M.S. in Civil Engineering, May 2017
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