Experimental Study On The Performance Of Grouting Materials For Underwater Bored Pile Repai

With the rapid development of construction industry,the number of underwater engineering projects increases,and the amount of underwater undispersed concrete increases.Underwater cast-in-place pile is the foundation of all underwater engineering,but there will be a variety of problems during construction or service,in order to ensure the safety of the project,it needs to be repaired and strengthened.Cement-based grouting material has superior performance,combined with its characteristics of fast setting and fast hardening,using high quality admixture modified cement-based grouting material,so that it can be used for underwater grouting pile repair and reinforcement,can effectively shorten the construction period,so as to achieve the goal of emergency repair and construction.On the basis of cementbased grouting material,by adding flocculant,water reducing agent,redispersible emulsion powder and coagulant adjusting agent,systematic test research was carried out on the underwater sulfoaluminate cement grouting material and underwater Portland cement grouting material,and finally the grouting material for repairing underwater grouting pile with good fluidity,high strength,strong dispersion resistance and small expansion was prepared.Through orthogonal test,three kinds of quartz sand with different grades were analyzed to determine the optimal aggregate density combination.At the same time,the influence of water-binder ratio on the performance of underwater sulfoaluminate cement based grout was studied,and the reasonable water consumption was selected.Single-factor tests of admixtures such as flocculants,redispersible emulsion powder,boric acid and sodium citrate were designed to analyze the effects of four admixtures on the working and mechanical properties of the underwater sulfoaluminate cement based grout,and to determine their respective optimal dosage.Through the study of different cementing systems,the optimal cementing material mix ratio was obtained: 74% sulfoaluminate cement + 12% Portland cement + 6%anhydrite + 4% fine beads + 4% fly ash.The initial fluidity of sulfoaluminate cement-based grout under water is more than 255 mm,the compressive strength of 28 d under water is 53 MPa,the content of suspended turbidity is less than 125 mg,the PH value of water sample is less than 9.5,the water-land strength ratio of 7d and 28 d is more than 85%,and the free expansion rate of 28 d is less than 0.030%.The optimum mix ratio composite material has been successfully applied in Liaocheng engineering project in Shandong province.The application shows that the underwater sulfoaluminate cement based grouting material has the advantages of convenient construction,high strength and good water dispersion resistance.Further study of underwater Portland cement based grout,mixed with sulfoaluminate cement,systematically explore the effects of Portland cement and sulfoaluminate cement of different proportions on the performance of grout,to determine the proportion of composite cement.On this basis,flocculant,redispersible emulsion powder,fly ash and fine beads are used successively to control the properties of underwater Portland cement based grout.The fly ash in the cementing system can increase the fluidity and improve the underwater compressive strength of grout.Fine sinking can improve the fluidity of grouting material,but can not improve the compressive strength under water.Then scanning electron microscope(SEM)was used to analyze the microstructure of the grouting material formed under water for 28 days,and it was found that the hydration products such as calcium silicate hydrate gel and ettringite cross and bond together,improving the internal structure compactness.Through the type of cement,the amount of admixtures,mineral admixtures and other factors of the experimental study,determine the cement material mix ratio: Portland cement 81%+ sulfoaluminate cement8%+ anhydrite 5%+ fine precipitation 3%+ fly ash 3%;Admixture content: PNF0.32%,redispersible emulsion powder 0.9%,PCE-M1.4%.the material meets the following properties:initial fluidity ≥ 255 mm,28d underwater compressive strength up to 53 MPa,suspended turbidity content ≤120mg,water sample PH ≤8.8,7d,28 d water-land strength ratio of more than 85% and other characteristics.Based on the loss of slurry under the action of dynamic water and the splitting tensile strength of C40 old concrete after repair and reinforcement,the reinforcement performance of two grouting materials for repairing underwater cast-in-place piles is compared and analyzed.Compared with underwater sulphoaluminate cement-based grouting material,underwater silicate cement-based grouting material has good water dispersion resistance,and the slurry loss in impact test and erosion test is 3.08% and 4.49% respectively.After repairing and strengthening C40 old concrete with underwater sulphoaluminate cement-based grouting material and underwater silicate cement-based grouting material,the splitting tensile strength is 2.75 MPa and 2.82 MPa,respectively.The splitting tensile strength is higher than the original C40 concrete,and the failure position is located at the old concrete or at the interface,which shows that they have the ability to repair and strengthen C40 concrete.