Effect Of Fiber-reinforced Grout On The Pull-out Resistance Of Fully Grouted Rockbolt

During the service life of the rockbolt support system,the grout structural members are inevitably affected by different loads and environmental conditions.Due to which the damage and crack resistance of grout is reduced.It will accelerate the formation of cracks and results in failure.Where failure of rockbolt support system mostly occurs at the bolt-grout interface due to grout cracking,grout shearing,or interfacial debonding.As long as,grout is reinforced,which will greatly reduce the risk of unexpected accidents.Therefore,fiber-reinforced grout(FRG)was developed using steel fiber and silica fume(SF)for fully grouted rebar rockbolt to produce a high strength crack resistance FRG to overcome traditional grouts’ drawbacks.In this research work,15% SF replacement of cement by weight and steel fiber with three fiber volume fractions of 0.5%,1%,and 1.5% with two different fiber shapes of straight and wavy are used as an additive to improve the mechanical properties,resistance to crack and bond strength compared to plain grout.The main contents of this research work are as follows:Firstly,the effect of FRG on mechanical properties was investigated.It can be concluded that the FRG improves the mechanical properties of the grout.The result showed that 15% SF replacement significantly improved the compression,tension,and shear strength of the grout.The fiber volume fraction increment improved the grout mechanical properties and improved the UCS stress-strain curve’s post-peak behavior.Scanning electron microscopy(SEM)analysis demonstrates steel fiber proved to be excellent for crack bridging.Secondly,the specimen size effect on the plain grout was investigated under the direct shear test.The direct shear test was performed with three different sizes of cubic specimen(50×50×50,100×100×100,150×150×150 mm)and a cylindrical specimen of ?50×50 mm.The experimental results showed that the average peak shear strength,internal friction angle,and grout cohesion decreased with an increase in the specimen’s size.Where cylindrical shape specimen of ?50×50 mm attained lower shear strength compared to cubic 50×50×50 mm specimen.A simple mathematical equation was proposed for the prediction of the shear strength of grout with different cubic sizes.The proposed equation shows a good efficiency to predict shear strength.Thirdly,as a part of the research,a Laboratory scale Short Encapsulation Pull Test system was designed.The machine consists of four parts a Triaxial Cell,Cylindrical Hallow Ram Jack,Hydraulic power pack,and a pressure supplier unit.The design of the machine components is illustrated.The effect of confining pressure on the bolt-grout interface was investigated,and preliminary attained results were discussed.Finally,The Effect of 15% SF replacement of cement by weight(SFM)and FRG with three fiber volume fractions of 0.5%,1,1.5%,and two fiber shape straight(SSF)and wavy(SWF)on bond strength and load-bearing capacity(LBC)of fully grouted rebar rockbolt was investigated and compared with plain grout(MR).Totally,24 laboratory pullout tests were conducted with different grout mixes.The influence of several parameters such as confining pressure,fiber volume fraction,fiber shape,and UCS of grouts on bond strength of fullygrouted rebar bolt was investigated.It was discovered that increasing the fiber volume fraction increases the bond strength and changes the bolt failure from splitting to pullout because steel fiber contributes to blocking the brutal propagation and the coalescence of cracks due to its intrinsic rigidity.It was found that bond strength increases with an increase in confining pressure.The bond strength was almost linearly proportional to the UCS of grouts.The results confirmed that FRG improved the strength and overcame the drawbacks of plain grout,and can be used in mining and tunneling applications.