Research On Mix Proportion Design And Mechanical Properties Of ECC Materials On Cement Pavement

Engineered cementitious composite(ECC)refers to a novel type of cement-based material that exhibits high ductility,strain-hardening and steady cracking,whereas its wide applications are limited by its high raw material prices and the difficulty in fiber dispersion.With the concept of multi-scale hybrid fiber-polymer synergistic extension,ECC materials was prepared by employing ternary cementitious material system of "fly ash-silica fume-cement" and the domestic fibers(modified PP fibers+domestic PVA fibers+calcium carbonate whiskers)+polymerization(EVA).Thus,the ECC material that exhibits low price,high ductility,environmental protection and other characteristics for cement pavement was prepared.The admixture and best preparation process were determined by the pre-test.The optimal ratio was determined through orthogonal experiments.Subsequently,the scanning electron microscopy(SEM),energy dispersive spectrometer(EDS)and X-ray diffraction(XRD)were exploited to delve into the extension mechanism of the hybrid domestic fiber-polymer system.The results of this study are presented as follows:(1)In this study,HEC and polycarboxylic acid superplasticizer with the optimal admixture content of 0.05%and 0.8%,respectively,were determined by a flow expansion test.Given the colloidal sand fluidity and 3d and 7d bending strength,the optimal preparation method was developed:1.all powder+dry mixing of 2/3 domestic PVA fiber and calcium carbonate whisker for 5min;2.adding admixture solution and water and wet stirring for 5min;3.adding 1/3 domestic PVA fiber and modified PP fiber and then stirring for 6min.(2)By a orthogonal test,the effects of water-binder ratio,domestic PVA fiber content,modified PP fiber content and calcium carbonate whisker content on the mechanical properties of ECC material were determined.Given the compressive,bending and splitting tensile strength and bending ratio,this study determined the optimal water-binder ratio as 0.31,domestic PVA content as 1.0%,calcium carbonate whisker as 0.9%,and the content of modified PP fiber as 0.6%,respectively(3)Compared with the benchmark ECC,the hybrid domestic fiber-polymer ECC exhibited enhanced 7d,28d flexural strength and 28d split tensile strength,increased by 17%,12%and 17%,respectively.Besides,its 7d and 28d folding ratio increased by 32%and 23%,respectively.Its secondary compressive residual rate and the fifth flexural residual rate were at least 5%higher than those of the benchmark ECC,and its price was reduced by 4.61 lower than that of the benchmark ECC.(4)As suggested from the results of the microscopic test,the hydration products of the benchmark ECC were basically consistent with those of the hybrid domestic fiber-polymer ECC.The film-forming dispersion of EVA led to a decrease in strength,whereas it promoted the bonding between the fiber and the interface and optimized the interface transition zone The advantages of multi-scale interfacial hybrid fibers were complemented,and the ductility of cement pavement was enhanced as impacted by multiple nucleation sites and EVA film-forming network adsorption.