Advanced Materials Research Vols. 194-196

Abstract: Environment climate conditions are important influencing factors on concrete carbonation rates. Influences of concrete internal microclimate conditions including internal temperature (T) and relative humidity (RH) and external climate conditions including wind speed and wind direction on concrete carbonation rates were studied through laboratory accelerated carbonation experiments. Models based on concrete internal microclimate conditions were established. Results indicate that internal T always present accelerating effects on concrete carbonation rates, while internal RH and pore water saturation degree (PS) show hindering effects on it. Wind direction and wind speed have certain effects on concrete carbonation rate, and the higher wind speed, the higher concrete carbonation rate is. For the same wind speed, carbonation rate is the highest for perpendicular direction.

Abstract: A liner system such as liner sheet underlying impermeable soil layer having hydraulic conductivity less than 1*10^-7 cm/s and a thickness larger than 100 cm is often used in china. As there is very little natural clay having such low permeability, bentonite is usually mixed into sand to decrease the permeability. In this paper, the compaction tests and permeability testing using flexible-wall permeameter are conducted. The test results show that the value of critical benonite ratio depends on bentonite ratio, and the hydraulic conductivity of the sand mixed with critical bentonite ratio for distilled water shows of the order of 1*10^-8 cm/s that satisfies the china standard requested as compacted soil liner of waste landfill. Finally, the permeability testing used leachate including calcium component was conducted.

Abstract: Based on surface chemistry, the force status of capillary pores of concrete is analyzed and the mechanical model of a single capillary pore in concrete is built with use of ANSYS, a sort of software for analysis and calculation. Then drying shrinkage strain of concrete is simulated. With the continuous evaporation of water, when the radius of concave water surface drop to a certain value, the corresponding shrinkage strain of concrete can be approximately calculated out. Finally the curve of gradually increasing concrete volume-shrinkage strain versus the decreasing radius of concave water surface is described. The existed errors of this simulation are analyzed,and some suggestion for improvements is given.

Abstract: To propose the damage model of concrete in the freezing-thawing cycles, the reasonable dissipation function and micro plastic deformation expression have been determined based on the continuum damage mechanics. The damage variable is expressed as a function of the number of freezing-thawing cycle. The damage is defined in terms of the loss of the dynamic elastic modules and the damage model of the concrete in the freezing-thawing cycles has been presented.

Abstract: The permeability resistance of concrete with ground phosphate slag(GPS) against chloride ion penetration was tested according to ASTM1202 and by nitrogen adsorption method. Test results show that by adding ground phosphate slag to concrete, the chloride diffusion coefficient of concrete decreases, and the permeability resistance of concrete against chloride ion penetration increases with improvement of its pore structure. The pores in concrete are refined and the percentage of the pores with diameter less than 20nm in concrete increases. The improvement of pore structure of the concrete by ground phosphate slag is much better than that by the ground granulated blast furnace slag or fly ash, while the addition is 30 percent. The ability of additive to improve the permeability resistance of concrete against chloride ion penetration is in following order: fly ash > ground phosphate slag > ground granulated blast furnace slag.

Abstract: A novel numerical model for simulating fracturing process of the heterogeneous materials such as rock or rocklike material has been developed and implemented in the FLAC, which is the numerical code for the engineering mechanics analysis. A constitutive model that captures an essential component of brittle material failure, that is, cohesion weakening and frictional strengthening (CWFS) is improved by taking accounting the elastic modulus of element may degrade when the element failure. Furthermore, a new energy index, Local Energy Release Rate (LERR), is put forward to simulate energy release during failure process by tracking the peak and trough values of elastic strain energy intensity before and after brittle failure. The numerical model has applied to simulate the initiation, propagation and coalescence of cracks in the failure processes of brittle material. Using this numerical model, we studied the failure processes of simulated rock specimens with different heterogeneity. The results suggest that the model is a powerful approach to the study of macroscopic fracturing behaviour of heterogeneous material.

Abstract: If concrete is observed at the microscopic level, it can be seen to contain many interfacial transition zones (ITZ), resulting in the weakening of its mechanical properties; as the physical properties of lightweight aggregates (LWA), such as their high absorption, are clearly different from those of normal weight aggregates (NWA), they may lead to variations in the ITZ of lightweight aggregates concrete (LWAC), making its mechanical behavior different from that of normal concrete.This study takes three types of LWA with different rates of absorption as its subjects in order to examine the effects of LWA absorbency on ITZ. The main variables tested include water/binder (W/B) ratio, amount of fly ash substituted for cement, and the saturation states of the four types of LWA, with three different types of microscopic tests used to observe the microstructure of ITZ in concrete, and analyze and compare their differences with ITZ in concrete made with NWA. The results of the study indicate that in LWAC, ITZ with weaker tensile strength did not appear around highly absorbent LWA; only the sample group with a W/B ratio of 0.29 did not show apparent absorption due to the higher viscosity of the mortar, resulting in a slight downward trend in tensile strength, but it was still superior to the tensile strength of ITZ in typical NWA.Observation using scanning electron microscopy (SEM) found that inner pores and cracks of ITZ in LWAC were all smaller than in NWC; X-ray diffraction (XRD) tests indicated that the amount of CH crystals in ITZ was greater than LWAC; and microhardness testing found that microhardness values were higher closer to the surface of the LWA, with some even exceeding that of concrete. The increase in the tensile strength of ITZ in LWAC subsequent to the addition of pozzolanic materials was limited; their improvement of the weakness planes formed by ITZ in NWA concrete, however, was more apparent. An LWA has higher water absorbency capacity when in an absolutely-dry condition, which can markedly increase the strength of ITZ; conversely, if an LWA is in saturated surface dry (SSD) condition, its ITZ behave like those of concrete.

Abstract: Effects of fly ash on the slump, slump loss with time, dispersibility and strength of nondispersible underwater concrete (NDC) were analyzed. The results show that fly ash can increase the fluidity of fresh DNC and reduce the loss of fluidity, but may be disadvantage for improving turbidity, especially fly ash more than certain range. The reinforcement of fly ash takes place at later ages and the amount of fly ash added which has little effect on later strength continues to be increased with ages. The results of field tests also indicate that NDC with 30% fly ash has very small sump loss and good antidispersibility and meets the requirements of compressive strength.

Abstract: Pore structure of sandstone has much influence on its hydrophilic characteristics. The results of pressured-mercury testing for sandstone are discussed in the paper with the help of fractal geometry theory. The effect of pore structure for sandstone is mainly discussed, combined the results of hydrophilic experiment. Results show that the pore structure of sandstone has single and multiple characteristics within some pore size. Four typical fractal characteristic are defined in the paper and it is found that characteristic of pore structure has much relation with its hydrophilic characteristics: hydrophilic rate of Sandstone with A or C-type fractal microstructure changes little and the double logarithmic hydrophilic relationship curve is always linear; however, the hydrophilic rate of ones with B and C-type fractal microstructure changes greatly and always taken as concave-convex.

Abstract: Poly (methyl methacrylate-co-divinylbenzene) [P(MMA-co-DVB)] microspheres were first synthesized by a simple photoinitiated emulsion polymerization methods. In this polymerization system, MMA, DVB, AIBN, isopropanol and hexahydrobenzene constituted the oil phase, SDS acted as the stabilizer and an 8 W Ultraviolet lamp was employed as the light source. Under the irradiation of the UV light, AIBN could be decomposed to produce radicals and initiate the polymerization of MMA to produce P(MMA-co-DVB) microspheres.The morphologies and structures of the products were characterized by Fourier transform infrared spectroscope (FTIR),size distribution, scanning electron microscope (SEM). The average diameters of the spheres increased with the content of DVB. The research may provide a quick, green and facile room-temperature approach to prepare polymer microspheres.