Moisture and Temperature Effects on Interface Mechanical Properties for External Bonding

Abstract

In order to develop rational guidelines for strengthening by external bonding, it is necessary to clarify longterm performance of interfacial bonding property. In this paper, moisture effects on bonding properties at FRP-concrete interface and temperature/moisture effects on bonding properties at PCM-concrete interface are presented. Shear bond strength of FRP-concrete interface is affected by moisture because resin-concrete adhesion strength is affected by moisture. Among tested CFRP external bonding systems, wet-layup CFRP systems all show the strength reduction, while prefabricated CFRP systems all show the strength increase after immersion. The bond stress-slip relationship and interfacial fracture energy also change, which can explain the change in shear bond strength. The reduction in shear bond strength does not show clear dependency on resin strength/stiffness reduction. The observed big variation in shear bond strengths reported in past studies can be explained by difference in interface roughness, since chemical bond is affected by moisture but mechanical bond is not. Tension/shear bond strength of PCM-concrete interface is affected significantly by temperature but less by moisture. The tensile/shear bond strength is less than tensile/shear strength of constituent materials (PCM and concrete). The reduction in tension/shear bond strength depends on the reduction in tensile/shear strengths of PCM and concrete and then estimated by proposed equation which is a function of PCM and concrete strength. The ultimate loads of beams strengthened by PCM overlay can be predicted by the proposed model in which the proposed tensile/shear bond strength is applied. Under high temperature, the failure mode can be changed from flexure/shear failure to debonding failure due to the reduction in shear bond strength.

Durability Enhancement Effect of Silica Fume on the Bond Behavior of Concrete–PCM Composites under Environmental Conditions

“…In the past experimental study [41][42][43], the performance of the concrete-PCM interface at a different temperature levels up to 60 • C was explored experimentally for a short-duration temperature exposure. At a temperature exposure of 60 • C and 40 • C, a significant reduction in interfacial shear strength was reported compared to 20 • C. Reduction in interfacial strength was also observed under different moisture content conditions (continuous immersion in water and wetting/drying cycles) [44,45]. A detrimental influence of elevated-temperature exposure for a short duration on flexural behavior of the PCM-strengthened RC beams, such as a reduction in flexural strength, the occurrence of debonding failure, and an increase in crack width and crack spacing, was also observed experimentally [56][57][58][59].…”

“…Composite specimens were exposed in two series to study the influence of elevated temperature and moisture content in the laboratory, which resemble real environmental conditions. The specific duration of exposure under different conditions was chosen following the previous study [41][42][43][44][45] to keep the exposure duration as long as possible considering the time restraint in the laboratory and to infer longer-term applicability of the mentioned factors.…”

“…The durability issue under environmental conditions considering monolithic samples has been observed via experimental investigation in many previous studies [32][33][34][35][36][37]. In the technical literature, few studies have also been found that observed the durability issue on composite (repaired) samples under a freeze-thaw cycle [38][39][40], elevated temperature [41][42][43][44][45], etc. Severe degradation of the interfacial properties of the composite samples was found during long-term exposure.…”

Influence of continuous and cyclic temperature durations on the performance of polymer cement mortar and its composite with concrete

“…PCM and its composite specimens at temperature levels of 20, 40 and 60 ℃ were examined, and a significant tensile strength reduction was observed with an increase in temperature [13][14][15]. With different wetting/drying cycles and continuous immersion in water for several days, a marginal influence on the tensile strength was also observed [13,16,17]. The shear and flexural bond behaviour was investigated at elevated temperatures, and the bond strength reduction for [3] both bulk and composite specimens were noticed [18,19].…”

“…Three point bending test on the PCM and its composites under TMD. 13 143.1.3 Influence of temperature cycles 15Cyclic temperature conditions were applied by simulating the day-night variation of16 summer and a seasonal variation of the tropical region. For the day-night variation case, 60 and 17…”