Study On Rheology And Mechanical Properties Of Concrete With Marble Dust

In recent years,scholars at home and abroad have paid more attention to the research of concrete mixed with stone powder.Studies have shown that adding marble dust(MD)into mortar can improve the compressive strength and the pore structure,reduce the shrinkage and permeability.However,different scholars have different opinions on the effect of MD on concrete performance,and the effects of MD on rheological properties of concrete was rarely studied.The recent research mainly focused on using stone powder to relpace cement(known as cement replacement method),but the improvement on the performance of concrete attributed to this method is marginal,and the amount of cement replacement is usually small.Some other studies also have proven that the use of stone powder to replace fine aggregate(known as fine aggregate replacement method)can also improve the compressive strength of concrete and has higher economic benefits.In recent years,some scholars have proposed a new method,in which paste(water plus cement)was replaced by equal volume of stone powder but with the W/C ratio unchanged.This method is called paste replacement method.This method can significantly enhance the compressive strength and reduce a large amount of cement used.However,it is unclear whether the fine aggregate replacement method and the paste replacement method are effective for the concrete with MD.Based on the above background,this study applied the fine aggregate replacement method and the paste replacement method,designed a series of concrete mixes with MD as fine aggregate replacement and a series of concrete mixes with MD as cement paste replacement.The experimental tests include flow spread test,V-funnel test,L-box test,sieve segregation test,rheometer measurement test and concrete axial compression test.The research contents mainly divided into the following three parts:(1)Based on the fine aggregate replacement method,16 concrete mixes with varied MD contents and water/cement(W/C)ratios were designed,carried out flow spread test,V-funnel test,sieve segregation test,L-box test and rheometer measurement test,to investigate the effect of MD on the rheological properties of concrete mixtures.The results show that with the increase of W/C ratio,the flow spread,flow rate,and rebar passability of the concrete mixture can improved,the yield stress and apparent viscosity would reduce,but the overall change was marginal.With the increase of the MD content,the flow spread,flow rate,and rebar passability of the concrete mixture increased,the yield stress and apparent viscosity decreased,but the sieve segregation index(SSI)would improve.In general,the influencedegree on the fresh properties of concrete is in the order of MD content > W/C ratio.In the fine aggregate replacement method,when the W/C ratio was 0.40 and the MD content was12%,the river sand could be reduced by 34.3%,and the workability,fluidity and passability of concrete were superior,showing good comprehensive benefits.(2)The above 16 groups of concrete mixtures were casted,cured,and carried out axial compression test to investigate the influence of the MD content on the mechanical properties of concrete.The results show that: in general,the compressive strength and elastic modulus of concrete were reduced by vibration,means that the vibrating process can be eliminated if MD was added as fine aggregate replacement to produce self-consolidating concrete.With the increase of W/C ratio,the slope of the rising section of the axial stress-strain curve was smaller,and the descending section was gentler,and the compressive strength and elastic modulus of concrete decreased.When the W/C ratio was relatively low(0.40 and 0.45),with the increase of the MD content,the slope of the rising section of the axial stress-strain curve was larger,and the descending section was steeper,and the compressive strength and elastic modulus of concrete increased.When the W/C ratio is relatively high(0.50 and 0.55),with the increase of the MD content,compressive strength and elastic modulus of concrete first increased and then decreased,and achieved the maximum values when the MD content was8%.Vibration,W/C ratio and MD content have no obvious effect on the Poisson's ratio of concrete.In the fine aggregate replacement method,when the MD content was 12% and the W/C ratio was 0.40,the river sand can be reduced by 34.3%,and the compressive strength and elastic modulus can be improved by 30.4% and by 11.2%,respectively,showing high environmental and economic effects.(3)Based on paste replacement method,19 concrete mixes with different MD content and W/C ratio were designed to investigate the effect of MD content on the SP dosage and mechanical properties of concrete.The findings show that: as the W/C ratio increased,the SP dosage required to achieve the target slump reduced,but compressive strength and elastic modulus of the concrete reduced.As the MD content increased,the SP dosage increased,the slope of the rising section of the axial stress-strain curve is larger,the descending section is steeper,the compressive strength and elastic modulus of concrete significantly improved,but the Poisson's ratio changed marginally.In the paste replacement method,when the marble content was 9% and the W/C ratio was 0.45,the cement content can be reduced by 26.5%,the compressive strength and elastic moduluscan be increased by 25.2% and by 20.6%,respectively,and the SP demand was only 2%,showing very high environmental and economic comprehensive benefits.