Thermal Properties of Epoxy-Based Adhesive Reinforced With Nano And MicroParticles For In-Situ Timber Bonding
—CB10TSS thixotropic and room temperature cured epoxy based adhesive specially formulated for in-situ bonding of pultruded rod into timber for repair and strengthening of timber structures. The glass transition temperature for CB10TSS is 31.7ºC which considered low for outdoor exposure. Therefore CB10TSS was modified by reinforcing it with nano-and micro-particles and denoted as Nanopox (CB10TSS/nanosilica), Albipox (CB10TSS/liquid rubber) and Timberset (CB10TSS/ceramics). Thermal properties of epoxy adhesives were studied by using dynamic mechanical thermal analysis (DMTA) and differential scanning calorimetry (DSC). Albipox showed significant improvement in the glass transition temperature but Timberset has the highest Tg, due to high modulus of ceramic particles. A second scan for all the adhesives increased Tg which shows that the room temperature cured adhesives are not fully cross-linked. In DSC scan, typical graphs of heat flow versus temperature able to describe more characteristic of the curing behavior such as a sharp and deep endothermic dip at Tg which corresponds to a rearrangement of the molecules and the wide and shallow endothermic dip at around 100°C is associated with moisture in the adhesive.
Influence of temperature on the curing of an epoxy adhesive and its influence on bond behaviour of NSM-CFRP systems
Abstract In NSM-CFRP installations, the mechanical behaviour of the strengthening system is strongly influenced by the epoxy adhesive, particularly at early ages. In the present work, the influence of temperature on the curing process of the epoxy was investigated. Three distinct temperatures were studied: 20, 30 and 40 °C. The elastic modulus of the adhesive was monitored through EMM-ARM (Elasticity Modulus Monitoring through Ambient Response Method). Direct pull-out tests with concrete specimens strengthened with NSM CFRP strips were carried out at the same three distinct temperatures to compare the evolution of bond performance with the E-modulus of epoxy since early ages. The results showed that increasing the curing temperature significantly accelerated both the curing process of the epoxy adhesive and the evolution of bond performance. The EMM-ARM technique has revealed its ability in clearly identifying the hardening kinetics of epoxy adhesives, allowing also thermal activation analysis. Finally, existing models for predicting temperature-dependent mechanical properties were extended to also describe the bond behaviour of NSM-CFRP applications.
Experimental study on bond behavior between high-strength grout and deformed steel bars
Abstract Engineers use high-strength grout to connect precast concrete members for its low shrinkage and good fluidity. This paper designed 87 central pull-out specimens using the control variable method to investigate the influence of factors on the rebar-grout bond property such as compressive strength, steel grade, bar diameter, transverse stirrups, and bond length. The test result showed that improving grout compressive strength (85.8 MPa–122.7 MPa) cannot improve the bond strength, which was different from the previous conclusions of concrete pull-out tests. Simplified formulas were presented for calculating the characteristic values of bond strength, residual strength, peak slip, and relative slip of load-holding platform based on parameter analysis. Then, a constitutive model was proposed to predict the full-range bond stress-slip curve of high-strength grout and steel bar specimens from bearing to failure. Finally, FEA models were established to evaluate the applicability and accuracy of the constitutive model.