Development And Study Of Reinforcement Technology With Inserts Of Cement-based Material Component

Cement-based materials are widely used in construction engineering and other fields due to their high compressive and flexural resistance.However,this material may suffer cracking even under low tensile loads and also shows brittleness when failure,which reduces the capacity and durability of buildings and even leads to structural damage.Therefore,it is very important to study the technique of reinforcing the structural components that mainly made by cement-based materials.In this paper,a simple new reinforcing technique combining steel sheet and cement-based material is proposed and studied.This technique consists two steps.First,grooves are gouged near the cracks on those cement-based structural components.Then,a special-shaped reinforcement piece is embedded by the same cement-based material.With this method,the components can be repaired and even reinforced to no less than their initial bending performance.According to the principle of structural bionics,the insert can be made of metal or composite materials in the shape of dumbbell or figure 8,the middle connection part of the insert penetrates through the crack,and the shield heads at both ends are embedded with the original cement-based material component to realize the reinforcement of the component.In order to study the feasibility of reinforcement technology with inserts,four kinds of artificial cracks were made and two types of reinforcement pieces,namely,dumbbell-shaped steel insert and C-shaped wire insert,were adopted in the experiment.Not only the capability of different types of reinforced specimens has been studied,but also the influence of different types of cracks and the performance of different designs of steel inserts are compared.Based on the experiment plan,numerical modelling was conducted by ABAQUS software to simulate the mechanical performance of several reinforced specimens with dumbbell-shaped inserts.A typical crack shape was selected for modeling.The feasibility of the experiment has been analyzed,while 8 cases with different kinds of insert shapes were discussed for optimization purpose.By comparing the distribution of the maximum principal stress and the ultimate bearing capacity of these numerical cases,considering the boundary effects,the influence of the shield head radius and the connection length were investigated.Afterwards,the flexural tests of an undamaged and a repaired cement-based component were carried out,along with the material compression tests.Based on the test results,the finite element model was calibrated.For the optimization of dumbbell-shaped inserts,the experiments on ultimate bearing capacity and middle crack extrusion were conducted,where 13 kinds of inserts with different shield head radius,connection length,connection width,thickness or shield head shapes were involved.With the same mix ratio and test set-up,different groove process,pre-groove and cut-groove,were adopted on the cement-based material specimens to explore the construction feasibility.The influence of cement grade and mix ratio on the reinforcing performance was also included in this research.The experimental results show that the insert reinforcement method studied in this papercan improve the flexural performance of the cement products with initial cracks to the level of undamaged ones.The strength of the repaired specimen increases by 22%-58% without bonding failure.The phenomena and results of experiments support that the finite element modeling and analysis are reasonable,and the assumptions made in the numerical study are reasonable.The finite element model can not only simulate the loading process and the change of stress distributions accurately,but also predict the ultimate strength with only 2.2%error from the experiment profiles.This can be taken as the verification of the numerical study.The same model can partly replace the experiment work in the following research and greatly reduce the experiment workload.The results of the optimization experiment show that the size and shape of the insert are closely related to the repairing performance.Increasing of the radius and the connection length of the dumbbell-shaped insert can significantly improve the flexural capacity of the reinforced cement-based component.The repairing test results of the cut-grooved specimen show that the technique is feasible in construction because the steel sheet was successfully embedded in the damaged specimen by the newly cast grout.Additionally,the repairing performance can be further improved by adding more grout near the end of the shield because the strength of components repaired by I-shaped groove is about35% higher than that of the cases with square-shaped grooves.This technique also has the advantages like easy operation,high reliability and low cost.