Concrete Interface Composition Gradient In The Distribution Of Improvement And Its Impact On Concrete Performance

Functionally Gradient Material (FGM) is that the components and the structure of the material are gradient distribution from one side of the material to the other, which has been used in the fields of space industry, nuclear industry, energy industry, electron industry and the bioengineering. Fractal theory provides a useful tool to describe many irregular, complex, self-alike study objects in numerical quantities, up to now, which has been one of hotspots in the field of math, physics, chemistry, seismology, material science.In this paper, the concept of FGM was introduced into aggregate-cement paste interfacial zone in concrete .Through the pretreatment of aggregate, aggregates get roughness , cleaner and be of some active , which results in the aggregate and cement paste components display crossed and gradient distribution in interfacial zone and the interface weak zone is enhanced and interfacial inner stress is released. All these bring the improvement of the physical and mechanical properties of cement-based material. Meanwhile, the relations between the fractal dimension of aggregate surface character and bonding strength of interface, compressive strength of concrete are built. The experiment and analysis results indicate that:1 The surface character of pretreated aggregates are markedly changed : the surfaces of aggregates pretreatod by different acids gets roughness , cleaner and be of some active, then can react with cement paste and form hydrated product to rength inter facial linking. However, structure gets looser due to Na2SiO3 gel created on aggregates which easily results in the form of big crystals.2 The structure of ir.terfacial zones between the aggregates pretreated by acids and paste are improved and better gradient distribution of components is formed in it: the skeleton map of theinterface created by un-pretreated aggregates is smooth relatively and the one of the interface created by aggregates pretreated by acids gets more devious .which shows components and structure in the interface form a gradient distribution for a certainty due to aggregate roughness; from analysis of components in the interface , dot SEM and surface SEM both show a better gradient distribution of AK Si etc. elements. Compared with the one created by un-pretreated aggregates ,the linking of the interface created by aggregates pretreated by acids is better, meanwhile no cracks is formed , no big CH crystal and big Aft crystals are seen , the content of OS-H gel increases and holes decrease .3, As a result of the improvement of interface, the mechanical properties of concrete is markedly improved: the bonding strengths between cement paste and aggregate pretreated by H3PO4 and H2SO4 are increased 51% and 46% respectively; the compressive strengths of concrete prepared with aggregate pretreated by H3PO4, H2SO4 and HF are increased 32%, 30% and 26% respectively. Meanwhile, toughness and elastic deformation of concrete are slightly increased.1 > The numeric relations between fractal dimension of aggregate surface and the bonding strength , compressive strength are primarily built: the numeric function show the bonding strength and the compressive strength both raise with the raise of fractal dimension, and the relativity coefficient between fractal dimension of aggregate surface andbonding strength .compressive strength show the relativity is marked.The study shows that the chemical pretreatment of aggregate methodthrough which to improve aggregate-cement paste interfacial zone throwslight on the advance of cement-based materials' mechanical properties.