| With the advantages of good integrity,strong adaptability to frost heaving and convenient for mechanized construction,the channel lined with mold bag concrete has been rapidly applied in Hetao irrigation area of Inner Mongolia.The research objective of this paper is to put forward the optimal proportioning parameter scheme of mold bag concrete to meet the requirements of various performance indexes,so as to guide the actual construction of mold bag concrete lining channel,and contribute to the further popularization and application of mold bag concrete technology.The suitable performance index of channel lining mold bag concrete should be:the strength grade is C25,the frost resistance grade is F250,and the slump flow degree should be in the range of 500 mm～600 mm.However,there is a contradiction between the requirements of water-binder ratio and unit water consumption for large fluidity and high frost resistance.How to make mold bag concrete achieve high frost resistance under large fluidity has become an urgent problem to be solved in production practice.The mix proportion design of bag concrete should adopt the following technical approaches:low water-binder ratio and low unit water consumption,mineral admixtures,superplasticizer,and increase the air content.However,the large use of superplasticizer and high air content will bring the problems of large time loss of air content,large time loss of fluidity,and many harmful bubbles to mold bag concrete.As a result,the pumping performance of mold bag concrete is reduced and the frost resistance is not easy to meet the design requirements.In order to achieve high frost resistance of mold bag concrete under high fluidity,this paper first carried out the variety optimization test of concrete admixtures such as water reducing agent,air entraining agent,antifoaming agent and viscosity modifying agent,and then studied the influence of antifoaming agent,viscosity modifying agent and air entraining agent on the workability,mechanical properties and frost resistance of mold bag concrete by using orthogonal test design,and analyzed the interaction effect on frost resistance of antifoaming agent and viscosity modifying agent.Then,based on the experimental results of admixtures,the influences of unit water content,water-binder ratio,fly ash content,slag content and activator content on the workability,mechanical properties and frost resistance of mold bag concrete are studied by using five element quadratic orthogonal combination design,and the interaction between fly ash and slag and the correlation between spacing factor and relative dynamic elastic modulus were analyzed.The frequency optimization method is used to obtain the reasonable range of the proportioning parameters of mold bag concrete,and the response surface optimization method is used to obtain the optimal proportioning parameters of mold bag concrete.Finally,in order to verify the rationality of the optimal proportioning parameters,based on the experimental results of proportioning parameters,the wet packing model is used to carry out the influence of coarse aggregate volume fraction on mold bag concrete.(1)PCA-Q005 polycarboxylate superplasticizer should be used in this test,K12 air entraining agent should be used.Polyether modified silicone antifoaming agent should be used,and hydroxypropyl methyl cellulose ether should be used as viscosity modifying agent.The effects of various factors on spacing factor,mass loss rate and relative dynamic elastic modulus are as follows:air content>antifoaming agent>viscosity modifying agent.Air content and antifoaming agent are significant factors,and viscosity modifying agent is an insignificant factor,and there is a significant interaction between antifoaming agent and viscosity modifying agent.When air content is 5.5%,antifoaming agent is 0.15%and viscosity modifying agen is0.03%,the relative dynamic elastic modulus is the largest.When the air content is 5.5%,the compounding of 0.15%antifoaming agent and 0.03%viscosity modifying agent synergistically slows down the trend of relative dynamic elastic modulus loss,reduces the air content loss rate by 64.28%,the slump flow loss rate by 55.04%,the number of harmful large bubbles by 81.38%,increases the number of small bubbles by 14.89%,and the spacing factor is reduced by 11.54%,and the relative dynamic elastic modulus is increased by 11.97%.(2)The effects of various factors on spacing factor,mass loss rate and relative dynamic elastic modulus are as follows:water-binder ratio>fly ash>unit water content>slag>activator.The unit water content,water-binder ratio,and fly ash content are all significant factors.With the increase of unit water content and water-binder ratio,the relative dynamic elastic modulus gradually decreases.With the increase of fly ash content,the relative dynamic elastic modulus first increases and then decreases,indicating that low water-binder ratio and low unit water content are helpful to achieve high frost resistance,and there is an optimal fly ash content.There is a significant interaction between fly ash and slag;when fly ash is 23%and slag is17%,the relative dynamic elastic modulus is the largest.It is better to compound fly ash and slag than to mix fly ash and slag alone.The critical value of the spacing factor of F250 is 338μm,and the critical value of the spacing factor of F300 is 252μm.(3)The reasonable range of the mix proportion of mold bag concrete with slump flow of500 mm～600 mm,strength grade of C25 and frost resistance grade of F250 is as follows:unit water content is 152 kg/m~3～160 kg/m~3,water-binder ratio is 0.38～0.41,fly ash content is 26%～35%,slag content is 14%～19%,the activator content is 1.93%～2.61%;the maximum relative dynamic elastic modulus is taken as the objective,and the slump flow and strength grade are taken as the constraint conditions,the optimal mix proportion of mold bag concrete is as follows:unit water content is 153 kg/m~3,water-binder ratio is 0.4,fly ash content is 28%,slag content is 15%,coarse aggregate volume fraction is 0.33,air content is 5.5%,activator content is 2.13%,dosage of superplasticizer is 0.75%,dosage of antifoaming agent is 0.15%.dosage of viscosity modifying agent is 0.03%,and the verified test results are good.(4)With the increase of the volume fraction of coarse aggregate,the wet packing density and relative dynamic modulus of modulus of mold bag concrete increase first and then decrease.When the volume fraction of coarse aggregate is 0.33,the maximum wet packing density and relative dynamic modulus of elasticity are obtained,which proves the rationality of the optimal mix ratio parameters.The correlation between the wet packing density and the slump flow and the relative dynamic elastic modulus is good.With the increase of the wet packing density,the slump flow and the relative dynamic elastic modulus gradually increase. |
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