Experimental Study On The Microstructure And Basic Behaviors Of Recycled High Performance Concrete

In consistent with sustaining development, the recycled high performance concrete that is made from recycled concrete aggregates, fly ash, granulated blast-furnace slag and so on, could be a perfect solution to resource and environment preservation. Therefore, on the basis of experimental research, the basic behaviors and microstructure of recycled high performance concrete are studied in this thesis. The main contents of this thesis are introduced as follows:Firstly, the basic mechanical behaviors of high performance concrete are tested and the results indicate: the cubic compressive strength, axial compressive strength and tensile splitting strength of recycled high performance concrete are just a little lower than those of common high performance concrete. At the same time, the elastic modulus of recycled high performance concrete is evidently lower than that of common high performance concrete.When the concrete's strength enhanced, the elastic modulus of recycled high performance concrete increases, and moreover, the failure of the recycled high performance concrete is often broken by the interface between the recycled aggregates and the new mortar matrix. Secondly, the viewpoint of a two-layer interface of recycled concrete aggregates is put forward in this thesis, one interface is between the original aggregate and the old adhesive mortar, the other interface is between the old adhesive mortar and the new mortar matrix. And the morphology of concrete's hydrates, the defects and the microhardness values in the Interfacial Transition Zone(ITZ) of recycled high performance concrete are tested by using scanning electro microscopy, polarizing microscope and microhardness testing machine. The test results indicate: some voids, microcracks and loose hydrates of Ca(OH)2 crystal are existed in the recycled aggregate-matrix ITZ, and the microhardness values in the ITZ are lower than those of the mortar matrix body, but those disadvantageous features in ITZ gradually weaken and the ITZ become much stronger from the recycled aggregate to the mortar matrix body; as well the microhardness values in the ITZ increase with the concrete's strength enhanced and the growth of hydration ages of the recycled high performance concrete. However, the mineral fumes, such as fly ash, granulated blast-furnace slag and so on, can improve the performances of the ITZ of recycled high performance concrete and make the recycled aggregates concrete become much denser.Thirdly, the complete stress-strain curves of recycled high performance concrete are obtained from the test. It is found that the peak stress of recycled high performance concrete is just a little lower than that of common high performance concrete,while, on the contrary, its peak strain is obviously higher than that of common high performance concrete. Furthermore, both the peak stress and peak strain of recycled high performance concrete increase companying with the concrete's strength enhanced. Then a stress-strain relation model of recycled high performance concrete is constructed, and the theoretical curve is faithfully accord with the test curve; moreover, the"compressive strain energy"and the"brittle index"of recycled high performance concrete are defined and calculated, and the results indicate that both the compressive strain energy and brittle indexes of recycled high performance concrete increase with the concrete's strength enhanced.Finally, Chloride ion penetration of recycled high performance concrete has been tested in the study. The test results indicate that the resistance of chloride ion penetration of recycled high performance concrete has evidently intensified as the concrete's strength enhanced and the growth of hydration ages. As well the mineral fumes, such as granulated blast-furnace slag, fly ash and so on, can greatly improve the resistance of chloride ion penetration of recycled aggregates concrete, and the resistance of chloride ion penetration of recycled high performance concrete is lower than that of common high performance concrete. However, the resistance of chloride ion penetration of the recycled high performance concrete remains good, and it is satisfied with the durability of the engineering.The researches in the thesis would establish basis for studying the failure mechanism of recycled aggregates concrete and the non-linear analysis of recycled aggregates concrete structure, and the test results would also provide important references for constituting technical specification of the recycled aggregates concrete.