Advanced Materials Research Vols. 250-253

Abstract: A detailed observation on the penetration profile of chloride ions through a crack in concrete structures was carried out. Cracks were induced using a splitting tensile test, and average crack width was measured using an image analysis technique. Chemical analysis tests were conducted on cracked specimens, which were exposed to NaCl solution at a temperature of 20°C, after being cured for 28d. The results showed that the concrete specimens having cracks showed rapid penetration of chloride ion. The diffusion coefficient calculated according to Fick’s law also indicated that the chloride permeability increased with the increasing crack width.

Abstract: Prediction of cement compressive strength was studied with accelerated curing methods, e.g. warm water and boiling water curing. The results indicate that fineness and the type of cements is few influencing on the 28-day compressive strength, and the difference is not distinct between the two methods. The boiling water fast-curing method is recommended since it doesn’t need additional equipments and has the advantage of convenient and high-speed. The prediction equation adopts linear model, and robust estimation of parameters is also applied to eliminate influences of outliers.

Abstract: This paper reports the investigation on both high and normal strength concrete using a non-contact electrical resistivity facility. The bulk resistivity development (ρ(t)-t curves) of the fresh concretes was evaluated from casting to 72h. The relationship between the electrical resistivity and the pore structure obtained from mercury intrusion porosimetry (MIP) method was analyzed. And the compressive strength evolution of fresh high- and normal- strength concrete was studied based on the bulk resistivity at early ages. The experiment results indicated a linear relationship between the fractional porosity and electrical resistivity. A further correlation between the compressive strength and electrical resistivity was analyzed with Archie’s law. Based on these studies, it appears that the electrical resistivity test could provide information for the design, quality control, quality assurance, and utilization of both high- and normal- strength concrete.

Abstract: In this work, the solubility of phosphogypsum(PG) in water and saturated lime solution was determined in experiments carried out at different temperatures from 10 to 50°C. The solubility of natural gypsum(NG) was also studied at an attempt to find out differences in solubility between PG and NG due to the effect of impurities. The results show that in pure water media, PG dissolves more rapidly than NG at early time, and then equally with NG. With increasing the temperature of water, the dissolution rates PG decreased while that of NG increased. In saturated lime solution, compared with NG, the solubility of PG was distinctly influenced due to the existence of impurities. Possible reaction among soluble impurities and calcium ion retarded the dissolution of calcium sulfate dihydrate.

Abstract: Rockburst is a sudden disaster that endangers greatly the security of operators and facilities in the production.The problem of rockburst is the most important issues in the underground space. This paper describes the present situation of the disaster at home and abroad ,which includes the conception，classification, intensity classification, mechanism, forecasting, and prenvention. Based on these analysis, This paper summarizes the following questions：Conception and intensity classification of rockburst has not level , its major and minor influencing factors has not compartmentalized; without taking full consideration in the influence of rock mass structure and dynamic action in comprehensive prediction, and there are fewer considerations of it in practical project; Attribute weights of all the factors are always subjectivity, it can not give the mathematical explanation; Study on rockburst mechanism are not enough, It can not exactly prodict when and where occur,can not raise the perfect time to prenvent the disasters.At the end of this paper, it is pointed out that it is the emphasis topic which comprehensive prediction with computer.

Abstract: The paper carries out a study on the composition control of smelting low-carbon low-silicon and high-aluminum cold heading steel SWRCH6A using double-slag process for converter at No.3 General Plant of Steelmaking & Rolling of Masteel, analyzes carbon increasing and silicon increasing status in each smelting process, and studies the mechanical properties, microstructure and inclusion ratings of test steel samples. These results indicate that in smelting process the average carbon increasing △w[C]=0.014%, the average silicon increasing △w[Si]=0.030%, the average content w[Al]s is 0.030% and w[Al]s fluctuates from 0.015% to 0.041%,, but all targets of test steel samples meet the requirements of cold heading steel SWRCH6A.

Abstract: After heated to high temperature, the strength test of concrete cube specimens made by siliceous and calcareous coarse aggregates was carried out. We analyzed the influence of cooling methods and standing time on concrete compressive strength respectively. The test results show that the compressive strength is generally decreased with increase in temperature. The relative residual strength of calcareous aggregate concrete is higher than siliceous aggregate concrete at higher temperature, so siliceous aggregate concrete has more significant fire resistance than calcareous aggregate concrete. Between 200°C and 550°C, the cooling methods have a great influence on concrete strength. The minimum of concrete strength appears at the 28th day after elevated temperature for both calcareous aggregate concrete and siliceous aggregate concrete in air cooling condition, whereas the minimum appears at the first week in water cooling condition. In addition, concrete strength values become steady with the lapse of time after the fire.

Abstract: Aiming at the building in city, the dangerous sources in construction are analyzed. Some hazardous factors, which are fountains of the accidents, are certainly made. By accidental types analyzed, accident positions analyzed and accident-engineering sorts analyzed; the complexity and authenticity of accident sources in construction can be distinctly set forth. Some safety control measures are made, which can be used to reduce accidents and advance whole safety supervising level in construction.

Abstract: From the experimental research, the relations between the dynamic modulus of elasticity and natural vibration frequency of specified density concrete are studied, the static Young’s modulus and dynamic modulus are compared. Based on regression analysis, the influence of different Substitution ratio of lightweight aggregate, age of concrete and cement water ratio is studied. According to the test results, the formula of natural vibration frequency and the dynamic modulus of elasticity of Specified density concrete is given, which provide theory basis for the nondestructive detector of the specified density concrete.

Abstract: By finite element method, experimental results of the light-weight aggregate concrete composite slab are compared with the numerical simulation.. On the basis, nine composite slab specimen are designed. The loading process, includes the slab cracking, the yielding of steel plates, damaging of slabs are simulated, and the influencing factors, such as male pin, thickness of deck, and spacing of transverse shear reinforcing bars, etc. is studied. At last, the spacing of transverse shear reinforcing bars of light-weight aggregate concrete composite slab is given, and it is useful to the engineering design.