Advanced Materials Research Vols. 287-290

Abstract: Close packing of the fine particles is one of the core technologies of preparation of reactive powder concrete. This paper introduces the concept of soil liquid limit in close packing evaluation. Theoretically, the closer of particles pack, the lower is the water demand. The mixture with a lower water demand is expected to have a lower liquid limit. Mixtures were obtained by measuring the cone penetration at different moisture content. By means of numerical fitting and linear interpolation, the liquid limits of the mixtures were obtained，where the software of Matlab was used. The close packing condition of the powders particles could be predicted according to the liquid limits. Strength test confirmed that application of liquid limit in mixing proportion design of reactive powder concrete is feasible. So, this may be a new way for the preparation of reactive powder concrete.

Abstract: This work investigates Al 6061 alloy with graphite particle impregnated metal matrix composites under dry sliding conditions. The conventional casting techniques were used for preparing the composite material. Experiments were conducted under dry sliding conditions for determining the wear behavior of Al 6061 alloy- Graphite composite material with varying wt % graphite content under different sliding speeds and at different loads. Sliding distance of 250m was commonly used for the wear test. A pin on disc machine was used for conducting the wear test. The test was conducted under atmospheric conditions. Wear rate decreases with increased sliding speed and increases with increasing load. Worn surfaces of the composites were examined through scanning electron microscope. The wear loss of the composite material with 5Wt % graphite was found to be minimum with respect to sliding speeds and loads.

Abstract: The effect of active alumina on the sintering behavior of andalusite powder was studied. The results revealed that the addition of active alumina delayed the decomposition of andalusite and primary mullitization, beginning temperature of secondary mullitization was about 1350°C. The temperature at which the effect of expansion of the secondary mullitization emerged was about 1400°C, and the expansion effect of secondary mullitization did not yet complete at 1600°C.

Abstract: Usually, marine carbonate gas reservoirs contain formation water with high content of CO₂&H₂S, It is difficult to satisfy the requirement of cementing quality in the gas reseroirs exploration due to the corrosion effect of formation water on cement. In this thesis, corroding tests of cement in formation water, which derived from a development well in northeast Sichuan province, were based on the simulation environment condition of 90°C under 0.1 MPa, 5 MPa and 10Mpa. Performances of cement including mineral composition, microstructure and permeability before and after corrosion were measured by TG-DTA, SEM, XRD and gas permeability and porosity of dense rock core tester. The results show that main corrosion products of cement being corroded in formation water with high content of CO₂&H₂S are ettringite, CaCO₃ and CaSO₄, both strength reduction and gradual rising of permeability can occur as testing pressure increasing. Accordingly, the corrosion mechanism and the damage process of cement under formation water with high content of CO₂&H₂S are expounded in the end.

Abstract: This paper presents the results of experimental study on the effects of adhered mortar content on strengths and durability of concrete. Compressive, tensile and shear strengths, modulus of elasticity, drying shrinkage and carbonation were tested on concrete mixtures with the water cement ratio of 0.43, 0.50 and 0.60 using 3 kinds recycled coarse aggregate and a riversand. The test results of concrete indicated higher compressive, tensile amd shear strengths and higher modulus of elasticity for concrete using recycled corase aggregate with lower adhered mortar content, lower absorption and higher specific gravity. Recycled aggregate with higher adhered mortar content also showed significunt adverse effects on drying shrinkage and carbonation. In conclusion, the upper limit of adhered mortar content of coarse recycled aggregate to keep up the quality of aggregate and concrete equal to natural coarse aggregate and those concrete is considered to be 15%.

Abstract: This paper presents results of impermeability and frost resistance tests of a series of high strength concrete which will be used in Yuncheng coal mine shaft lining. And the shaft is one of the most difficult to construct using freezing method because of the extreme thick overburden soil. The results show the impermeability and frost resistance of the selected concrete mix proportion options can meet the special requirements of the shaft construction. It’s due to the low water-cement ratio, admixture and water-reducing agent decreases void caused by excess water. And the composite mineral admixture forms bubbles to cut off the tiny water permeable channels in cement stone. Also the filling effect and pozzolanic effect caused by fly ash contribute a lot. The research on high strength concrete used in shaft of coal mine with thick overburden soil is still rare worldwide.

Abstract: With the development of oil industry, the high strength-toughness drill pipe suited to the task of sour environment and ultra deep wells would be considered more and more important. A new drill pipe steel, which was designed with the proper decrease of C content and increase of Cr, Ni, Mo, Nb and V alloy element, was developed and studied in this study. Large deformation hot rolling technology was used to obtain ultrafine grains microstructure. The results showed that the yield strength of this new drill pipe steel had reached 150ksi with the impact toughness more than 150J, which can perfectly meet the “leak-before-break” crack principle. The new low-alloy carbon steel drill pipe in the controlled yield strength grade 150ksi showing excellent sulfide stress cracking resistance and strength-toughness have been developed. Based on the observation of scanning electron microscopy and transmission electron microscopy, several kinds of carbide particles including (Nb, Mo, V)C with nanometer scale, were distributed in tempered sorbite matrix. The objective of this work was to study the relationship between carbide precipitation and strength-toughness by optimizing element design, thermo mechanical control process and heat treatment of drill pipe steel.

Abstract: Lime fly-ash stabilized aggregate is the commonly material used as semi-rigid base course of pavement and the performance of pavement directly affects its service life. This paper focuses on pavement performance of dense skeleton lime fly-ash stabilized aggregate in gravelly conditions. Test results show that coarse aggregate of lime fly-ash stabilized aggregate can form skeleton structure and has the advantage of high strength and other better material properties which can meet the requirements pavement.

Abstract: For further study of mechanical properties of concrete-filled steel box columns (CFSBCs) with longitudinal stiffeners, axially loading tests of CFSBCs with longitudinal stiffeners was conducted to obtain their ultimate bearing capacity and failure modes. The test results were compared with those of hollow steel box columns with longitudinal stiffeners. Cross section of the test specimen was scaled from a chord member of Dongjiang Bridge. The experimental results show that failure mode of CFSBCs with longitudinal stiffeners is local buckling of steel plates, which is different from that of concrete-filled thin wall steel tube columns with longitudinal stiffeners. Although longitudinal stiffeners can prevent global buckling of steel plates, the effect is less obvious than that of concrete-filled thin wall steel tube columns. Meanwhile, three-dimensional finite element models (FEM) of the specimens were modeled using computer program ANSYS to obtain bearing capacities and load-strain curves. The FEM results coincide quite well with the test results. Further, influence of width to thickness ratio on mechanical behavior of CFSBCs was analyzed using FEM.

Abstract: According to the postulation on dense packing of aggregates, the paper discusses the dense packing method of various aggregates and its coefficients, and offers the mix proportion design method of concrete. The research results indicate that using method of the mix proportion design based on the theory on dense packing of aggregates, aggregates can play a maximum role, especially the micro-aggregate effect of the fly ash, then the compactness of concrete is raised effectively, the quantity of cement is reduced and the endurance of concrete is improved.