Experimental Study On Frost Resistance Of Medium And Low Strength Mold Bag Concrete

Hetao Irrigation District in Inner Mongolia is located in the northwest arid regions of China.Irrigation with water from the Yellow River is very important to the crops.The average water diversion quantity of irrigation is about five billion tons a year,that accounts for one-seventh of the Yellow River's transit water.However,it is cold in Hetao region,the canal lining is seriously damaged by frost heave,that cause a large amount of water loss and maintenance costs.To address the problem,the mold bag concrete was used for canal lining in this irrigation district and gets good results.But there are still some problems to be solved in order to meet the needs of both construction and antifreeze requirements for canal lining mold bag concrete.This paper was divided into three parts.At first,analyze the suitable construction parameters of mold bag concrete through the field tests.Then,choose the best fit admixture from several common use of mold bag concrete admixture,and find the proper dosage of mineral admixtures.At last,analyze the influence of air content loss on frost resistance of concrete through the test results between the concrete sample which has 1h time difference,and the influence of defoamer on frost resistance of concrete.The main research results of this paper are:(1)Extension degree have great influence in the filling process of mold bag concrete,the filling process might get the proper speed and quality when the extension degree is between 500 mm to 600 mm,otherwise the mold bag may get damage,the proper sand ratio is between 48~55%.(2)Choose PCA-Q005 polycarboxylate superplasticizer and K12 air entraining admixture because this combination have the lowest air content loss and extension degree loss,the best dosage of defoamer is 0.15% because the air content loss is the lowest.To the concrete mixed with different dosage fly ash and slag powder,analyze the change rule of air content loss and extension degree loss,the results shows that the best dosage is 30% fly ash and 20% slag powder because the air content loss and extension degree loss is lowest,the dosage of mineral admixtures will reduce the early strength of concrete,but the strength still meet the design requirement and will rise when the slag powder dosage get rise,meanwhile,the best dosage is 10% fly ash and 20% slag powder.And the best dosage is 30% fly ash and 20% slag powder in comprehensive consideration.(3)Through the results of freeze-thaw cycles tests between concrete sample which has 1h time difference,analyze the influence of air content loss on frost resistance of concrete,the results intend that the defoaming agent can effectively reduce the loss rate of air content in blending polycarboxylic acid concrete,and can reduce the quality loss rate by 13% ~ 19%,increased relative move modulus by 1% ~ 7%.After 1h mass loss rate of concrete will increased by 19%~47%,the relative move modulus will reduced by 2%~9%;With the same amount of air content,1h concrete and fresh concrete have the similar frost resistance,and the concrete antifreeze level achieve F300 when it have 4% air content and 3% air content after 1h.