Mechanical behavior of adhesive anchors under high temperature exposure: Experimental investigation

Abstract

The improvement in mechanical and adhesion properties of polymer resins have allowed to progressively substitute cast-in place rebars by polymer-based anchors in some applications, by providing equivalent or even higher mechanical properties at ambient temperature. However, a temperature increase has the effect of weakening the bond and leads to a significant decay in the bearing capacity of the adhesive anchors. This paper presents a study of the phenomena that occur at high temperature in an adhesive anchor when exposed to high temperatures by means of two pull-out test procedures and by thermomechanical characterization of the polymer resin. Results showed that the resin glass transition is the responsible for the decay in the fire resistance of adhesive anchors. The paper highlights the non-conservative aspect of the current design method used to calculate the fire resistance of chemical anchors and proposes to consider the pull-out curves as input data.

Fire design of post-installed bonded rebars: Full-scale validation test on a 2.94 × 2 × 0.15 m3 concrete slab subjected to ISO 834-1 fire

“…Indeed, temperature seems to be the factor that affects the most the mechanical behavior of chemical PIRs. In a previous paper [23], we showed that the temperature increase up to values blow the resin glass transition temperature leads to increase the mechanical properties of chemical PIRs due to the resin post-cure phenomenon. However, when temperature exceeds the resin glass transition temperature, a change in viscosity and physical state occur [24], leading therefore to a new bond stress distribution along the bond joint [25] [26].…”

“…The relationship between the bond strength and temperature is obtained experimentally through pullout tests performed by applying a constant bond stress in the adhesive joint. The description of the test procedure and the main results are presented in a previous paper [23]. The tests are performed on steel rebars bonded into concrete cylinders (160 mm diameter and 250 mm height) using the same epoxy resin than that will be used in the full-scale fire test.…”

“…The bond resistance decay at elevated temperatures is mainly caused by a set of physical, chemical and mechanical phenomena such as resin glass transition. These phenomena are detailed and examined from experimental and theoretical point of view in a previous paper [23].…”

“…The influence of the heating increase rate was studies in [5], and it is shown that high heating rates can generate a thermal gradient along the steel rebar and consequently can lead to a new bond stress distribution. To conclude, the mechanical behavior of chemical PIRs at high temperature seems to be very complex due to several mechanical and physicochemical changes happening at the adhesive joint, affecting its mechanical properties [23] [27]. Therefore, fire is a potential hazard which should be taken into account when designing structures containing chemical PIRs [28].…”

“…[22] has carried out several pull-out tests at different temperatures and proposed an empirical method allowing deducing the bond stress value at different temperature ranges. Pinoteau et al [26], Eligehausen et al [34] and Lahouar et al [23] have proposed a "bond resistance integration method" allowing predicting the time of collapse of postinstalled rebars using thermal calculations and bond resistance variation at different temperatures. This method was validated in [26] by performing a full-scale ISO fire test on a cantilever-wall connection using chemical PIRs and figures today on the European Assessment Document (EAD) 330087-00-06.01 [35].…”