Comparative Study of Different Bonding Agents for Substrate–Overlay Concrete

Abstract

Recent studies to examine feasibility of alkali activated material (AAM) as bonding agent between substrate and overlay concrete were either metakaolin based AAM or fly ash–based AAM. Till date, limited studies were carried out to investigate suitability of ground granulated blast furnace slag (GGBS) based alkali activated materials as bonding agent between substrate and overlay concrete. Therefore, in the present study an attempt has been made to use GGBS based AAM as bonding agent between substrate and overlay. In addition, cement paste and epoxy were also used as bonding agents for comparison. Three types of surface preparation to substrate concrete viz. smooth surface (without any surface preparation), wire-brushed surface and rough surface were used along with bonding agents to examine the effect of substrate surface preparation on the behavior between substrate and overlay concrete. Mechanical performance of substrate-overlay specimen was measured using slant shear test, split cylinder test, and modulus of rupture test. Test results indicated that choice of bonding agent and surface preparation method significantly affected the performance. Order of measured slant shear strength was: Epoxy composites > Cement paste composites > AAM composites > No bonding agent. For both split cylinder and modulus of rupture test, order of measured strength was: Epoxy composites > AAM composites > cement paste composites > composites with no bonding agent. If substrate-overlay concrete specimen without any bonding agent and without any surface preparation is taken as reference, AAM showed (160%–530%) relative slant shear strength, (368%–645%) relative split tensile strength and 158% relative modulus of rupture respectively. However, bonding agents could not enhance performance of composite specimens up to the level of monolithic specimens, whatever was the surface preparation. Rough surfaced composites with different bonding agents were able to alter the failure mode of composite specimens from pure adhesive failure to other modes.