Preparation And Performance Analysis Of Early-strength Delayed-expansion Cement Grouting Material

As improve cement and concrete performance,hardening accelerator and expansion agent are widely used in bridges,tunnels,energy,water conservancy and hydropower projects and other constructions.On the one hand,because of high-alkali,high quantity and other factors,traditional hardening accelerator can reduce concrete durability and safety.Therefore,it is greatly restricted in some projects.On the other hand,affected by chemical and drying shrinkage,concrete is prone to crescent-shaped pores in closed conditions which leads to a decrease in the strength of it structure.Expansion agent provides solutions to this defect and significantly reduces the negative impact.However,due to the premature participation of the traditional expansion agent in the hydration reaction,not only will the early strength of the concrete be significantly reduced,but also easily lead to premature expansion and loss of expansion energy.In addition,the water consumption is difficult to be replenished from the outside.Therefore,in the later period of hydration reaction,the expansion agent remaining in the voids of the concrete could hardly sustains the expansion due to the lack of water required for the reaction.This paper takes OPC system as the research project,aiming at its low early strength,prone to "crescent" porosity and other defects,the composite hardening accelerator and modified microcapsule expansion agent compound performance has been systematically studied.The optimal formulations of the composite hardening accelerator component and the microcapsule expansion agent component were investigated and determined by the progressive compounding method and the single factor analysis method.The performance mechanism were discussed by experiments and microscopic characterizations.The main contents and results are listed as follows:Under the water-cement ratio 0.4,curing temperature 20? and humidity 97%conditions,The effects of C11 · A7 · Ca7,Ca(SCN)2 and TEA early hardening accelerator on the early strength of the cement were studied,and the optimal formulation of the early strength agent was obtained by progressive compounding.The proportion of each component is:C11·A7·CaF2 4%+Ca(SCN)2 0.1%+TEA 0.02%+PC 0.1%.The hardening accelerator obtained by the experiment has obvious effect on the improvement of the cement early compressive performance,the fluidity and the setting time fully comply with the relevant national regulations.The 1d compressive strength of the test block reached 14.5 MPa,which was 98.6%and 35.5%higher than the reference and control groups respectively.It can be found that the composite early strength agent can provide a large amount of Ca2+ during the cement hydration reaction and complex reaction with metal ions in the liquid phase by using microscopic characterization methods.Accelerating the hydration reaction rate of cement clinker,produce aluminum glue,water crystal garnet with stable crystal structure and increase the number of products of AFt and C-S-H.Reducing the duration of induction period of hydration reaction and cumulative pore volume in cement stone,improving the strength and density of the blocks.By using St as a hard monomer,BA as a soft monomer,AIBN as an initiator,and IPA as a disperse solvent,a solution polymerization method is used to polymerize St-BA copolymer on the surface of the HCSA expansion agent to form a polymer microcapsule.Taking the expansibility of ordinary Portland cement as the evaluation index,the microcapsule expansion agent and its expansion efficiency were studied by means of single factor inspection method and XRD,DTG,SEM and other analytical methods.Experimental results shows that,the increase of the reaction temperature and the increase of the reaction time are favorable for the improvement of the polymer coating efficiency.However,if the reaction temperature is too high,the activity of the initiator will be affected,resulting in a decrease in the coating rate.Changing the monomer ratio and the amount of the initiator will cause changes in the molecular size of the polymer,thereby affecting the coating efficiency of the polymer.Polymer coating performance is best under the conditions of reaction temperature 80 ?,reaction time 5h,ratio of BA to St monomer 2:1,volume ratio of monomer and IPA 1:2,and AIBN dosage 2%of monomer mass.Under the condition that the mass ratio of HCSA(mass ratio of cement)is 10%,the expansion delayed about 2h,the maximum free expansion rate is 3.39%,and the expansion rate tends to be stable after 30 h,which is about 0.67%.Increased 12.6%and 63.4%compared to uncoated expansion agents.Improving the effective expansion of HCSA.The optimal composite hardening accelerator and the optimal microcapsule expansion agent were compounded and cured for 1d under standard curing conditions.The multi-energy efficiency compound performance was tested and studied.When the distribution ratio of each group is C11·A7·CaF2 4%+Ca(SCN)2 0.1%+TEA 0.02%+PC 0.1%+microcapsule expansion agent 10%.The early strength performance and early expansion performance are the best.The 1d compressive strength reached 16.4 MPa,which was 2.25 times that of the baseline group;the fluidity was 201 mm;the initial setting time was 331 min,and the final setting time was 376 min.In addition,the early expansion rate of the cement test block has greatly increased,and there is a significant delay in the expansion process.After the hydration reaction proceeded for about 5h,the expansion rate of the cement paste peaked at about 3.61%.Subsequently,it decreases as the hydration reaction time increases.When the hydration reaction proceeded for 30h,the expansion rate gradually became stable,and the expansion rate reached 0.84%,which was a 195%increase compared to the reference group.