Experimental Study On Mechanical Properties And Shrikage Properties And Frost Resistance Of Recycled Concrete Designed With Equivalent Mortar Volume Method

This topic is a sub-project of the State Natural Science Fund project " Experimentstudy and design method to composite mechanical behavior of recycled concretemembers and mechanical properties of recycled concrete in the freeze-thawenvironment "(Project approval No.51278151).With the rapid development of construction industry in our country, more andmore concrete was consumed in21st century. Annual consumption of concrete hasreached as much as2billion cubic.This caused the problems of aggregate resourcescarcity and environmental pollution which were becoming more serious. Through acertain amount of preparation,we translated waste concrete to recycled aggregate forpreparation of recycled concrete, that can effectively solve the problems and ensurethe sustainable development in the industry.Nowadays,in the previous studies of the domestic and foreign researchers,recycled concrete has been proportioned based on direct weight replacement methodor direct volume replacement method.The two conventional methods treatedrecycled aggregate as a homogenous material. A new method of mixtureproportioning dubbed the “equivalent mortar volume(EMV)” method, was proposedby Fathifazl of Canada.The method was predicated on the fact that recycledaggregate was a two-phase material comprising mortar and natural aggregate. Whenproportioning recycled concrete, one must account for the quantity of each phaseand adjust recycled aggregate, natural aggregate and mortar content accordingly toachieve the same total coarse aggregate and total mortar volume as the naturalconcrete with the same specifed properties.According to Fathifazl’s research, recycled concrete proportioned by the EMVmethod has better mechanical properties and durability than that designed by theconventional method. But the research about the EMV was relatively fewer. Thispaper made in-depth study on mechanical properties, shrinkage properties and frostresistance of recycled concrete proportioned by EMV method. First,The basicprinciples of the “equivalent mortar volume” method were studied deeply and statedcomprehensively. Then the concepts of the true replacement rate and the falsereplacement rate were presented. Accuracy of the three quick laboratory testmethods for the determination of the residual mortar in the recycled aggregate wascompared. The pickling and freezing-thawing method was selected for engineeringpractice. At last the tests on mechanical properties, shrinkage properties and frostresistance of the recycled concrete proportioned by the EMV method and by theconventional method were conducted respectively when the false replacement rate was0%,30%,50%,70%. The studies shown that when the false replacement rate was30%, the difference between the EMV method and the conventional methodcould be ignored,when the false replacement rate was50%, the mechanicalproperties of the recycled concrete proportioned by the EMV method were betterthan the recycled concrete proportioned by the conventional method,when the falsereplacement rate was70%, the mechanical properties of the recycled concreteproportioned by the EMV method were a little worse than the recycled concreteproportioned by the conventional method. The shrinkage value of the recycledconcrete proportioned by the EMV method was less than the recycled concreteproportioned by the conventional method. The reduction extent was5%~25%. Therecycled concrete proportioned by the EMV method has comparable or evensuperior frost resistance than that designed by the conventional method.