MODIFICATION THE CEMENTIOUS MATERIAL OF ULTRA-HIGH-STRENGTH SLEEPER CONCRETE

This paper presents investigation results on the natural ultra-fine mineral flour of crystalline silica fume (CSF) and porous quartz sand stone (PQSS) which can modify cement mortar strength under hydrothermal synthesis reaction (HSR) in the autoclave-cured condition. The replacement of cement by CSF and PQSS can signifi cantly increase the Jflerural and compressive strength which reach 22MPa and 150MPa respectively and de-crease the porosity oj the cement mortar. The ratio oj fine aggregation, standard sand to cementions material has sig nificant influence on the mortar strength. The mechanisms involved in cement and natural mineral flour and the HSR are presented. CaO/SiO2 ratio ranges from 3. 20 to 1. 11. the main hydrate phase is C2SH and there is not Tober-morite through X-Ray diffraction qualitative analysis. The new and ultra-high strength cementious material as basic material of sleeper concrete can he used in prestressed reinforcement sleeper concrete.

Fabrication of Aluminium Matrix Composite Using Thixoforming Process for High Strength Material Components

Aluminium-based MMCs(metal matrix composites)have many potential applications in the automotive manufacturing industry,aerospace and military because the aluminum has a low density.Aluminum as a matrix with Al2O3 reinforcement has attracted interest to be developed in order to improve the mechanical property.The study carried out the formation of Al-5%Cu-4%Mg matrix with the reinforcement of Al2O3 by thixoforming process.In this paper,we studied the effect of semisolid thixoforming process on strength of Al-5%Cu-4%Mg matrix.The matrix used here was doped by Al2O3 with the volume fraction from 5%to 20%.It is found that strength of MMCs significantly increases with increasing volume fraction of Al2O3 reinforcement from 5%to 20%.This is due to a good wettability in interface region such as formation of spinel MgAl2O4 phase.Moreover,toughness of MMCs increases by process of semisolid thixoforming due to evolution of microstructure such as globular and fine grain structures.These results indicate that the thixocasting process conducted in this study could increase the value of the matrix hardness and tensile strength,so that such process opens up opportunity for application in the manufacturing industry.

Preparation and Microstructure Analysis of High Strength Cementitious Materials Containing Metakaolin

The preparation and microstructure analysis of high strength cementitious materials containing metakaolin (MK) was studied in this paper. The MK was prepared firstly,and then was mixed with fly ash,ground blast furnace slag,quartz powder and cement with different percentage to produce high strength cementitious materials. After cured under different environment,the compressive strength of such materials was tested. Techniques of X-ray diffraction (XRD) and scanning electron microscopy (SEM) were further employed to identify the composition and microstructure. The results obtained reveal that the compressive strength of such materials mainly effected by component of raw materials,the water binder ratio (W/B) and the curing regime. When the three factors above are optimized,the compressive strength of such materials can get to 156 MPa in maximum. The X-ray diffraction analysis and the scanning electron microscopic images indicated that under optimal curing condition,more raw materials can take chemical reaction and the microstructure is dense to yield good mechanical properties.

Impacts of High Field Magnetic Fields on Processing of Selected Materials

Various composite conductors and reinforcement materials are used for high field magnets in the USA National High Magnetic Field Laboratory.Typical composite conductors are Cu based metal-metal composites,whereas most of reinforcement materials have faced-center-cubic matrix and relatively low ductile-to-brittle transformation temperatures so they can perform at cryogenic temperatures.During the operation of the magnets,the mechanical stresses,magnetic fields and other extreme environments are imposed to the materials and materials are 'processed' during the service of the magnets.For instance,the conductors in the magnets are likely to experience higher temperatures than ambient during the operations if the electrical current density for producing high field is sufficiently high.Some of the conductors are fabricated by cold rolling or drawing that introduces lattice distortions and high densities of interfaces in unit volume.High temperature and high field exposure of the conductor may affect the characteristics of the lattice distortions and the interfaces.The lattice distortion and density of the interface affects the mechanical properties of the conductors,such as the tensile and yield strength,as well as the electric conductivity of the composites.Therefore,the materials after service are expected to have different properties compared to as-received conditions.The first portion of our paper will focus on relationship between the service and processing of the magnet materials in high field magnets.The high magnetic field can be used directly to process materials.In some cases,the material properties can be improved by more than 50%if the processing is undertaken in the high magnetic field.The improvement is due to the microstructure changes induced by high magnetic fields.Understanding the behaviors of the materials after they are exposed to high magnetic fields helps us to make good use of the high field processing approach efficiently to fabricate better materials,particularly when the magnetic fields are so high that the cost of building and operation of high field magnets cannot be ignored.In high field processing, phase transformation usually occurs in the magnetic fields.In such cases,one has to consider the impacts of high magnetic fields on critical points,which include transformation temperatures and chemistry,crystallographic structure and habit planes for nucleation and growth,and kinetics.The goal of this portion of research is to understand the microstructure evolution of the selected materials processed in high magnetic fields,and to relate such microstructural features to properties of the materials.