Research On Strengthening Mechanism And Microstructure Of Reactive Powder Concrete

Reactive powder concrete (RPC) is a new kind of cement-based material, which is of both ultra-high mechanical performance and high durability, composed of particles of similar modulus and size, made of a fine matrix with short steel fibers. In order to get high strength, high toughness and low porosity, the fineness and activation of the constituents of RPC should be improved so that the defects, such as voids and micro crack in the paste can be reduced. Based on this principle, the particles' sizes are selected from 0.1 μm to 1mm, and a very dense matrix is achieved by optimizing the granular packing of these powders.All the researches of the concrete are about density and durability in the end. The ultimate aim is to promote performance of the concrete. RPC is made from customary concrete components that are selected for specific chemistry and particle size. RPC stems from efforts to optimize the microstructure of the concrete matrix by precise gradation of all the mix particles to yield an optimum density. To optimize the mechanical behavior, the influence of the steel fibers and the particles packing are studied.By analyzing the strengthening mechanism of steel fiber concrete, it can be concluded that the fibers play a crucial role in RPC. The properties, number, space, orientation and the bonding of the fibers and the matrix have important relationship with ultimate failure. From the theory of the ordinary steel fiber concrete, it is easily obtained the strengthening mechanism of RPC. On the other hand, the interfacial transition zone (ITZ) is often considered to have important influence on mechanical and transport properties of concrete structures. And as for the superior properties of RPC, the characters of the ITZ are different from those of the ordinary concrete.The microstructure formation of the ITZ depends not only on the hydration, but also on the particle packing of cement particles. Because of the factors, such as the existence of "wall effect" and the method of compaction, the process of the particle packing will be affected. Considered the conditions all above and the reasonable structural forms, it is deduced the "arch structure" to simulate the formation of the particle packing. The arch formed by particles is used to approach the geometrical shapes of larger pores generated by the wall effect and water bulks during cement particle packing. Using this structure, the process of the particle packing is stated more clearly. It is can be proved that this presumption can illuminate the causation of the high porosity and the large pores of the ITZ compared with the bulk cement paste.Because the RPC is a special kind of concrete, through the relative theories about the ordinary concrete, it can be achieved the conclusion of the microstructure formation including the container wall and the aggregates.This thesis is supported by the National Science Fund project--Research on Static Strength of RPC Flexural Members (project number: 50478064). It is also supported by the international cooperation project "Modern Concrete Composites", cooperated with TU Delft and financially supported by KNAW of the Netherlands (project number: 04CDP038). As above reason, this thesis is written in English.