Experimental Research On Behavior At Elevated Temperature Of RC Shear Beams Strengthened With High-performance Ferrocement Laminate

High performance ferrocement Laminate (HPFL) technology is a new method to reinforce the reinforced concrete (RC) structure, by which a kind of high performance composite mortar and reinforcing steel bar mesh are used to repairing and strengthening the RC structure. It has a lot of superior advantages and the people in structural strengthening domain pay great attention to it and are interested in it more and more. So, it has a high theoretical research value and it promises a broad prospect of popularization and application.Compared with the strengthening method with steel sheets or FRP which uses organic agglutinant, the HPFL strengthening method using inorganic bond material has superior fire resistance, but the thickness of layer is small, so it is necessary to research the fire resistance and elevated temperature resistance in depth.In this paper, the High-temperature performance of 9 RC shear beams strengthened with U-type HPFL layer and 1 comparative beam is researched. The main contents are summarized as follows.(1) The HPFL strengthening method regularly adopts U-type layer to strengthen RC beams, and the layer tends to debond easily under high temperature, there is a close relationship between roughness of concrete and debonding. Through the study on roughness of concrete surface, a new method of measurement is put forward, evaluation of roughness and division grade of it is also presented .The results show that the method can quantitatively describe the concrete surface roughness very well and the grade of roughness can explain the interfacial strength under elevated temperature satisfactorily. The results can be reference for the engineering application of HPFL strengthening method.(2) The failure mode under high temperature is analyzed; the failure temperature is investigated, and the fire resistance of strengthened beams is analyzed. Then, the mechanisms of debonding and bursting under high temperature are investigated. At last the effects of roughness, the initial load and different temperature rising on high-temperature performance of strengthened beams are analyzed . The test results indicate: the presence of HPFL significantly delays the original beam damaging under high temperature, and this improves the fire resistance of strengthened beams obviously ; The effect of surface roughness is significant, according to grade of flame resisting, roughness of concrete surface should be controlled strictly in strengthening design; the initial load has great influence on high-temperature performance of strengthened beams, with the increase of initial load, the fire resistance decreases rapidly.(3) Equivalent time of strengthened beams under different temperature rising is analyzed. The result shows that, test results coincide well with the theoretical calculation by using Ingberg model when K=400℃, which can be used to evaluate the equivalent time of RC beams strengthened with HPFL in fire.(4) The calculating formula of ultimate bearing capacity under high temperature is derived and established. Considering influence of surface roughness, coefficientΨis introduced to the formula. The results indicate that: the calculated value and test results are agreeable. It has a great reference value in strengthening design .