| The strengthening technology using textile reinforced mortar(TRM) is a new method to strengthen concrete structure, but the cement used in TRM is considered to be a significant factor that contributes to global warming. Geopolymer mortar is a new kind of green environmental-friendly material, which exhibits excellent mechanical properties and high temperature resistance. In this paper, the strengthening method of textile reinforced geopolymer mortar(TRGM) was proposed by replacing the cement mortar in TRM with geopolymer mortar. To investigate the feasibility and strengthening effect of TRGM shear strengthened RC beams, the following work was carried out in this paper, and some important conclusions was drawn:1. Through flexural, compressive and tensile strength tests of geopolymer mortar with eight kinds of formulations at ambient temperature, the optimum formula of geopolymer mortar was obtained. Based on this optimum formula, the flexural, compressive and tensile strength of geopolymer mortar after exposure to elevated temperatures and its physical and thermal parameters were tested, and also temperature-induced strength degradation of geopolymer mortar was explored by thermogravimetry and differential scanning calorimetry(TG-DSC) analysis. The test results show that:(1) geopolymer mortar with sand-binder ratio of 3, water-binder ratio of 0.45 possesses flexural, compressive and tensile strength of 9.3 MPa, 49.4 MPa and 3.84 MPa respectively, and exhibits good fluidity;(2) the flexural, compressive and tensile strength of geopolymer mortar increases at 100 ℃ and then rapidly decreases after 300 ℃, due to the removal of free water, bond water and crystal water present in geopolymer mortar;(3) natural drying shrinkage and thermal conductivity of geopolymer mortar are slightly smaller than that of ordinary cement mortar used in the benchmark test, and average thermal expansion coefficient of geopolymer mortar at the temperature between 25~100 ℃ is close to that of ordinary concrete.2. Bond properties between geopolymer mortar and old cement mortar, concrete substrate and textile was tested both at ambient temperature and after exposure to elevated temperatures. It shows that:(1) the bond strength of geopolymer mortar on old cement mortar and concrete substrate at ambient temperature reaches 2.15 MPa and 1.7 MPa respectively, and its residual bond strength is still 1.5 MPa after exposure to 300 ℃, which meets the specification requirement that the bond strength of mortar for strengthening or repair should be greater than 1.0 MPa;(2) the bond strength of geopolymer mortar bonding textile is 2.02 MPa, which is slightly lower than that of carbon fibre sheet bonded to concrete using epoxy resin as adhensive, but the bond strength almost keeps constant at temperatures below 300 ℃.3. Eight TRGM shear strengthened RC beams were tested under static load, and also one unstrengthened beam and one beam shear strengthened with textile using epoxy resin as adhensive were tested for comparison. The influence of textile layer number, grid size and anchoring method on bearing capacity of strengthened beams were investigated. The test results show that:(1) TRGM effectively restrains the development of oblique cracks of the original beam, and improves the cracking load of the bending shear zone;(2) the shear bearing capacity of beams strengthened by single layer and double layer of TRGM is increased by 47.1% and 105.9% respectively, compared with the unstrengthened beams, and it can get further improvment of 15~20% when taking steel plate anchorage;(3) the improvement on shear bearing capacity of horizontal fiber tow is limited, thus unidirectional fiber tow or hybrid textile can be used as beam shear strengthening material in practical engineering, to save material;(4) compared with the beam strengthened with textile using epoxy resin as adhensive, the shear capacity of TRGM strengthened beams is relatively lower, but geopolymer mortar exhibits better weather resistance, corrosion resistance and high temperature resistance than epoxy resin, therefore TRGM reinforcement method still has a good application prospect.4. Through the analysis of the shear mechanism of strengthened beams, the shear bearing capacity calculation formula of TRGM strengthened beam was proposed. It is found that:(1) the calculation values of the shear capacity from calculation formula for TRGM strengthened beam, derived from truss-arch model, are in good agreement with the experimental results of this paper;(2) the calculation values of the shear capacity from proposed formula are in good agreement with previous experimental results of TRM strengthened beams, thus this proposed formula can also be applied to shear bearing capacity calculation for TRM strengthened beams. |
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