| A large number of buildings are under construction in China these years,while strengthening became urgently necessary for lots of existing structures.However,some disadvantages exist in the traditional templates for newly constructed structures,including serious waste,complexity of construction,environmental pollution and durability problem.Common strengthening methods adopted on the existing structure are also restricted by some deficiencies,such as durability problems,and the lack of practicability and economy.As a kind of novel green material with light weight,high strength and advantageous durability.BFRP(Basalt Fiber Reinforced Polymer)is the key to solve the above problems.In this paper,a new type of BFRP cement mortar slab is developed,which consists of high strength cement mortar and BFRP mesh bar and can fully develop the advantages of material properties.The slab in the concrete structure can not only be used as a permanent template of newly constructed structures,but also serve as a strengthening material for the existing structures.Therefore,it can improve the strength and durability of structures effectively.In this paper,the mechanical properties of BFRP cement mortar are studied and the methods of structural strengthening are discussed,including flexural strengthening,shear strengthening and a technology of permanent template.The research are summarized as follows:1)Flexural tests are conducted on 18 pieces of cement mortar slab which are divided into 6 groups.The parameters include:strength of cement mortar,types of reinforcing material in cement mortar(thin BFRP grid,dense BFRP grid,BFRP mesh,dense stainless steel grid),and the existence chopped fibers.The results reveal that the cracking load of the specimen increases significantly by 51.1%when the strength of cement mortar increases by 35.2%,but the increase of flexure strength is only 12.0%.The slabs made of BFRP mesh reinforced cement mortar have the best ductility and the highest ultimate load,but their cracking load is 10.9%less than the slabs made of dense BFRP grid and 23.7%than those made of stainless steel grid.The addition of the chopped fiber increases the cracking load effectively by 98.1%,but has little effect on the ultimate load,which only increased by 14.3%.Furthermore,experiments are also conducted to examine the tensile and shear properties of BFRP cement mortar slabs.2)Shear strengthening are implemented on 6 RC beams by BFRP cement mortar slabs in this study.The parameters include:the binder type of the slab;the existence of anchor bolt;the thickness of the adhesive;the thickness of the mesh in the slab.The results of static loading tests indicate that the shear capacity of the structure strengthened by the slabs made of polymer mortar increases by 61.3%,and the shear capacity of the beams strengthened by 15mm-thick slab increases by 54.4%.The shear capacity of the beams strengthened by slabs made of 2mm-thick mesh reinforced slab increases by 68.1%,which is only 6.8%higher than the corresponding increase of the specimens with lmm-thick grid.The calculation method of shear strengthening is proposed,and the calculated results are in good consistence with the experimental results.3)Flexural strengthening are conducted on 4 RC beams by BFRP cement mortar slab.The test parameters include:the anchorage methods of reinforcing slab s;the diameter of the grid in the BFRP cement mortar slab.The results show that the anchorage strength of the single-row anchor is insufficient,in which case a debonding occurs on the slab and the structure is destroyed prematurely.The strengthening effect of the double-row chemical bolts is relatively better,and the ultimate load increases by 20.3%.The 5mm grids(with higher strength than 3mm grid)debond from the cement mortar slab at failure.So reinforcement effect decreases when the grid strength increases.However,the ultimate load of specimens with 5mm grids increased by 19.6%.When BFRP cement mortar slab was applied for flexural strengthening of RC beam,a reasonable selection of BFRP grid strength and a reliable anchorage method are necessary.The calculation method of flexural strengthening is proposed.The calculated results are in good agreement with the experimental results.4)12 RC beams are cast using permanent template,which are divided them into 4 groups.Test parameters include:the existence of permanent template using BFRP cement mortar slab;the thickness of the grid in permanent template;existence of chopped fiber in permanent template.The results show that the interface between the permanent template and the cast-in-place concrete is reliable.The permanent template increases the flexural capacity by 54%?176%and makes the structure have better ductility,with the deflection ranging from 2 to 4mm.Failure of 3mm grid is observed in permanent template,while no failure of 5mm grid occurs in the permanent templates.However,the 5mm grid debonds from the permanent template at failure.The beams with 5mm grid have higher strength and better ductility than those with 3mm grid;the cracking load of permanent template increases by 29.7%with addition of chopped fiber,but the flexural capacity of the beams decreases by 9.6%.Finally,based on the basic performance test of BFRP cement mortar slab,the stability of stiffness of permanent template under construction load is calculated and results show that the optimal template fixture spacing is 0.8m and the bottom mold support spacing is 0.45m. |
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