Study On Structure Formation Mechanism And Features Of Cement Emulsified Asphalt Mixture

Asphalt pavement received most countries’ graces for its well-known excellent performance.In our country,almost 90%high-grade and national trunk highway adopted traditional hot asphalt mixture,which is in building,in reconstructing or in repairing.This type of mixture need to heat asphalt and aggregate to 150℃ or more,which will consume much energy,discharge abundant waste and dust,as that reason,the surrounding environment and worker’s health must be damaged.Cement emulsified asphalt mixture didn’t need to heat during the whole mixing,paving and rolling phrase,it saved energy,improved construction environment,reduced air pollution,and prolonged construction season。Cement emulsified asphalt mixture’s binding materials are complexes of organic compound cement and inorganic matter asphalt emulsion,which made this new type pavement material be more complicated,it not only posses the same places with asphalt mixture and cement concrete,but also has its own features。Before emulsion breaking,to make the emulsion uniformly dispersed on the aggregates’surface through mixing is the key solution of strength forming.Then the broken emulsion developed continuous and compact asphalt film on the aggregates’ surface.To achieve above demands,the mixture must posses enough mixing time,and the emulsion can’t break too fast.While fast opening to traffic as well as time limit hopes the emulsion break as soon as possible,so the mixture can develop strength in very short time.Compound technology aims to solve above-mentioned contradictions.Experienced three hierarchical comparisons on emulsion technical indexes,mixture’s construction performance and pavement performance,1.0%SBT with 0.8%MQK-1M was considered as the optimal compound proportion at last.Adopted TAM Air eight-channel trace thermal instrument to research cement hydration reaction in water,in acidic solution,in emulsifier solution and in asphalt emulsion,the results showed that acidic environment hindered cement hydration reaction,emulsifier had retarding effect on cement,and the asphalt emulsion’s package action greatly delayed cement hydration accelerative stage.Used Zetasizer Nano Zeta potential analyzer to measure zeta potential about emulsion and emulsion suspension liquid with different dosage cement or mineral powder,the results suggested cement promote emulsion’s demulsification,and the negative charged cement improve adhesion between binders and aggregates.Based on the AR2000ex rheometer,did rheological experiments about asphalt emulsion and asphalt emulsion mucilage with filler,the results displayed that cement accelerated mixture’s setting,curing and molding speed,which make the mixture forming hardening whole in a shorter time.Regarded Marshall stability,low temperature cleavage strength,shear strength and Cantabro flying loss as evaluation indexes,studied the effects from fine aggregates gradation,coarse aggregates gradation and key sieve pore passing rate on mixture’s performance.The experimental results revealed cement emulsified asphalt mixtures’ performances are quite sensitive to fine aggregates gradation’s variation,when fine aggregates proportion increased,mixtures’ whole performance will be improved,while mixtures’ performances are not sensitive to coarse aggregates gradation’s variation.4.75mm,1.18mm and 0.075mm passing rates’ variations have the most important effect on mixtures’ performances,also recommended passing rate’s change ranges of some sieve pores.By means of X-ray computed tomography scanning technology,and combined with macroscopic test results,this paper systematically researched cement emulsified asphalt mixtures’ microscopic void structure,and also put forward its distribution characteristics.With the increase of emulsion content,mixtures inside void dimensions decreased.When emulsion content to be 8%,and cement adding content reached 4%,large-dimension voids’proportion increased,and CT visual voids rate also increased.SEM and fluorescence microscope’s observation results showed cement emulsified asphalt mixture’s internal structure is looser than traditional hot asphalt mixture’s.In the cement emulsified asphalt mixture,vacancy left by bubble break,voids left by emulsion demulsification,various size pores existed in cement hydration products,pores inside aggregates together with the gaps between aggregates and aggregates after compacting constituted cement emulsified asphalt mixture’s complicated void structure.Have done experiments of mechanical properties,pavement performance and durability on cement emulsified asphalt mixtures with different binder composition,in which the dynamic modulus test results showed cement emulsified asphalt mixtures’ are good enough to satisfy the modulus design requirements from pavement structure.The shift factor of dynamic modulus principal curve reflected cement emulsified asphalt mixtures’ temperature sensitivity is lower than hot asphalt mixtures’.On the basis of above research results,the author proposed cement emulsified asphalt mixtures’ applicable situations under different traffic volume and different climate conditions.