Advanced Materials Research Vols. 250-253

Abstract: With rapid development of the national open mining coal resources, which generated lots of open-pit slope, and typically coal(rock) layered slope，under the external and internal structure function, it caused massive landslide with time increasing. Large coal(rock) slope deformation is not instantaneous, but rather the result of a long slow rheology, which is the main forms of creep; which is a serious threat to mining enterprise and the safety of workers. Appling the maximum tensile stress theory and establishing the creep rupture judgment criteria, And finite description of the creep cracks initiation, expansion and gathering. Based on FEPG software, programmed creep rupture module, it generated crack at the vertical direction of first principal stress vector, The crack propagation continue to find the maximum of the first principal stress, which achieved tensile strength and creep craze of elements, this process is continuously cycled. In Haizhou open-pit national mine-park, simulated the coal(rock) separation layer creep rupture, and the results of measurement and simulation was coincided; its study provided basis for prevention and disaster of coal (rock) slope.

Abstract: The purpose of this paper was to investigate the mechanical behavior and failure mode of recycled concrete brick masonry wall under cycling in-plane load. These models of masonry walls were constructed in the laboratory and experimented under in-plane cycling load. The masonry wall was made of recycled concrete bricks joined by mortar, with gypsum lining on both faces. A simulation based on the experiment was carried out using the finite element software ANSYS. In the proposed FE model, the recycling concrete bricks and joints were modeled separately, allowing for nonlinear deformation characteristics of the two materials. The results of the experiment and the finite element analysis were analyzed and compared. When the stress distributions were taken into consideration in the experiments and solutions of ANSYS, it was observed that the stress concentration occurred on two diagonals of the masonry wall. The destruction process and characteristics of the masonry wall were obtained by the experiments. The results of finite element method matched experimental results very well. The FE software ANSYS can be used in the analysis of recycling concrete brick masonry walls under in-plane cycling load and strength capacity.

Abstract: For the purpose of enhancing concrete performance and conserving freshwater, we proposed a new technique of making desalinated sea sand concrete. Salinity qualified desalinated sea water with alkaline potential is obtained through a set of self-made dual membrane electrodialyzers and membrane electrolyzers. Sea sand is sluiced by the obtained desalinated sea water before it is made into concrete. The desalinating device is portable and easy operating, and outputs qualified sea water to the requirements of desalinating sea sand. The method of sluicing sea sand is proved to be practical and effective. It is found that, comparing to standard concrete, concrete made of desalinated sea sand and alkaline potential water has better mechanics performance and better protection for steel bars. Both desalinated sea water and sea sand contain a certain amount of OH^- ions, which helps reducing the ratio of Cl^-/OH^- in concrete and thus inhibit the Cl^- ions from rotting or carbonating concrete; concrete durability is therefore enhanced.

Abstract: In this paper, firstly, discontinuous Galerkin method for improved Stokes equation is proposed. We derive a discontinuous Galerkin (DG) finite element formulation for the improved Stokes equations. Special case of the generalized solution equation for linear and stationary improved Stokes equations retrogresses into generalized solution equation for classical Stokes equation. It is proved that the classical solution and the generalized solution is consistent for the improved Stokes equations, existence and uniqueness of generalized solution for the improved Stokes equations are also proved.

Abstract: In order to forecast the mining process of oil and gas field rightly, simulate the flow process of reservoir fluid accurately and reveal the fluid distribution law, it must be considered that multiphase fluid seepage caused by water injection and exploitation, the change of stress state and the coupling between the reservoir deformations. According to the basic theory of rock mechanics, fluid mechanics in porous medium, geologic mechanics, calculated mechanics and fluid-solid coupling seepage, a mathematical and numerical model of seepage field and stress field coupling is developed in porous medium and a computer program is designed with the method of finite element technique. The Coupling Law of depressurizing exploitation Seepage field /Stress field in porous medium is studied. By the method of numerical simulation the variation law of stress-strain with time and space around borehole of impermeable rock medium, variety law of rock physical properties parameters is studied. Results show that the quantity of change nearby oil well and the change gradient is bigger, so it reduces very quickly to the oil deposit boundary,the stress and the strain are also biger in the oil well control area's influence area.

Abstract: Even though the use of fly ash in concrete is nowadays a common practice, its relatively slow pozzolanic reactivity hinders its greater utilization; hence efficient methods of activation are on demand. This study was carried out to evaluate the influence of lime as a chemical activator on the mechanical and durability properties of high strength fly ash concrete. Mixtures were made with 0, 30, 40, and 50% of cement replaced by low calcium fly ash. Corresponding mixtures were also made with the same amount of fly ash and addition of 10% of lime to each mixture. For each concrete mixture, slump, compressive strength, water absorption, sorptivity, apparent volume of permeable voids, and resistance to chloride-ion penetration were measured. The results obtained showed that addition of lime improved the compressive strength significantly at all ages. The strength of all the fly ash mixtures containing lime surpassed that of the corresponding Portland cement mix at 60 days. Addition of lime also improved the sorptivity and resistance to chloride-ion penetration of the fly ash concrete. It however increases the water absorption and the volume of permeable voids of the fly ash concrete.

Abstract: In this paper, by using scanning electric micrograph and mercury intrusion porosimetry, the effects of three types of retarders such as citric acid, sodium polyphosphate, as well as bone glue on crystal morphology and pore structure of hardened gypsum paste have been systemically studied and then the internal cause of strength loss are put forward. The results show that the addition of retarders reduces supersaturation degree in liquid phase during early hydration of hemihydrates, and causes the change of the growth habits and transformation of crystal morphology of dihydrate gypsum from need-like to short prismatic, which correspondingly leads to large size crystals and weakening of the interlacing together of individual crystals. As a result, pore structure of hardened gypsum paste is worsened, which is mainly embodied in the increase of pore size and macro-pore (＞1μm ) fraction to a large extent, ultimately leading to the strength loss of hardened gypsum paste.

Abstract: Effects of citric acid on crystalline habit and crystal morphology of gypsum dihydrate were analyzed in great detail. The retarding mechanism of citric acid was also discussed from the standpoint of crystal growth by use of Scanning Electric Microscope and X-ray Photo Technology. The results shows that due to the complexion between citric acid and Ca²⁺, the initial supersaturation degree in liquid phase is greatly decreased, correspondingly the number of nuclei newly formed reduces and the growth rate of dihydrate slows down, so the crystal has enough time and space to grow, as a result, the crystal size becomes much larger in presence of citric acid. Citric acid is preferably adsorbed on c-axis which has the fastest growth rate and hinders its growth. Therefore the relative growth rate and crystal habit of various crystal faces are changed, consequently leading to the transformation of dihydrate crystal from need-like to short prismatic. Furthermore, the transformation is gradual as a function of citric acid addition, the higher the dosage, the larger the dihydrate crystal formed. After the addition of citric acid, the retarding effect produced and the reduction in strength of hardened gypsum paste are closely related with the variation of crystallization habit and crystal structure of hydration products.

Abstract: In this paper, a concrete sulfate corrosion-resistance admixture is developed with anhydrite (CaSO₄), super fine slag powder (P800) and anhydrous calcium sulfo-aluminate (C-S-A). It is optimized by means of systematical research on specific surface area, setting time, expansion ratio, compressive strength ratio, corrosion resistance coefficient and expansion coefficient of 20 mixes, which are designed based on the hydration mechanism and performance requirements according to JC/T1011-2006. This new type sulfate corrosion resistance admixture has good performance and completely satisfies the requirements of industry standard JC/T 1011-2006 regarding “Sulfate Corrosion-Resistance Admixture for Concrete”, and has declared Chinese national invention patent (201010256189.2).

Abstract: In order to study prism compressive strength of recycled coarse aggregates-filled concrete, recycled coarse aggregates of particle size for 40-80mm were made from abandoned brick and concrete blocks. 4 groups of recycled coarse aggregates-filled concrete prism objects were made, and the compressive strength of the specimens were done. Using the finite element analytical software(ANSYS) , the stress nephogram and fractured condition of recycled coarse aggregate-filled concrete were obtained after the establishment of the geometric model, calculational model and mechanical model. The results showed that numerical simulation results were good agree with the actual experimental results.