چكيده به لاتين
Nowadays, scraping damaged concrete and adding a new layer of concrete to old concrete is one of the ways to repair damaged concrete and to increase the load bearing capacity of existing concrete members. Proper adhesion of concrete overlay to old concrete is one of the most important parameters in this repair method. Therefore, in this study, the influence of factors on adhesion including old concrete roughness, mechanical properties of new concrete overlay as well as the use of epoxy resin and hydroxyethyl methyl cellulose as bonding agents were investigated. The effect of epoxy adhesive thickness on the interlayer adhesion strength is also considered in the simulation. Different roughness modes of the old concrete surface were evaluated, including surface left as cast, wire brushed surface and chipping surface (chipping hammer). Two types of concrete with 40 and 70 MPa compression strength were also used to evaluate the effect of mechanical properties of new concrete on adhesion. First, the roughness parameters of the old concrete and the mechanical properties of the new concrete were evaluated and then the highest adhesion strength was used as the optimal design for subsequent experiments. After selecting the optimum design, epoxy adhesive and mortar containing cellulose based powder were applied on the optimum specimens and the effect of interlayer bonding agents was investigated by studying the shear and tensile strength of the fabricated specimens. For each of the mentioned methods, four bi-surface shear and Brazilian tensile tests were performed to obtain adhesion strength. Based on the experimental and simulation data, the results show that with increasing compression strength of new concrete and concrete roughness, adhesion strength increases. The addition of epoxy resin adhesive to the optimum sample also significantly increases the adhesion strength. The shear and tensile adhesion strength of these specimens increased by 230 and 300%, respectively. Adding mortar containing cellulose based powder slightly reduced the adhesion strength of the optimum design. The reduction of shear and tensile strength of these specimens was 9.5 and 3.1%, respectively. The simulation results of bi-surface shear and Brazilian tensile tests, show that as the thickness of the epoxy resin adhesive increases, shear and tensile stresses decrease. For example, increasing the thickness from 0.5 to 1 mm resulted in a decrease of 15.5 and 7.1% for interlayer shear and tensile stresses, respectively.
