Applied Mechanics and Materials Vols. 357-360

Abstract: In order to prepare energy saving and environmental protection building materials, a new kind of concrete was made by the combination of corn stalks which is the main crop in northern China, natural pumice resources and cement. Corn stalks and pumice are all lightweight material with open pores and large water absorption; therefore they must be pretreated before preparing concrete by blocking holes to reduce the amount of grout. The raw materials used in the experiments are lightweight materials; it is advisable to adopt the pressure vibration molding process to reduce aggregate stratification.

Abstract: Porous concrete is one of the innovative and promising concrete products, which is featured with a relatively high water permeability rate. Compared with conventional concrete products, due to the lack of fine aggregates in the mix design of porous concrete, the void spaces between the coarse aggregates remains unfilled and causes a large amount of porosity in the hardened concrete mass. On the other hand, the strength of porous concrete is usually lower than that of the conventional concrete products due to the lack of fine aggregates. For the purpose of achieving a relatively high strength of porous concrete while maintaining a good permeability of pavements, the mix design of porous concrete is modeled as a Markov Chain Monte Carlo (MCMC) system and a Gibbs Sampling method based approach is developed to approximate the optimal mix design. The simulation results show that, by using the proposed approach, the system converges to the optimal solution quickly and the derived optimal mix design achieves the tradeoff between the compressive strength and the permeability rate.

Abstract: As one kind of Engineering Cementitious Composites (ECC), polyvinyl alcohol (PVA) fiber reinforced cement-based composites has specific strain hardening characteristics and multiple cracking properties. Thus it can exhibit excellent ductile properties and damage tolerance, which makes it being a potential material for critical components of seismic resistant structures. In order to investigate the flexural performance of PVA fiber reinforced cement-based composites, beam-type and sheet-type specimens made from PVA fiber reinforced cement-based composites were designed and four-point bending tests were conducted. The flexural toughness and flexural strength of PVA fiber reinforced cement-based composites were assessed via load-deflection curves. Experimental results indicate that PVA fiber reinforced cement-based composites can be used in critical structural components to mitigate the seismic response and to improve the seismic performance of structures.

Abstract: The effect of fly ash and nanoCaCO₃ on the viscosity of pastes was studied. The rheological value of cement paste was determined by the rotation rheometer NXS-11B. In the study, five different dosages (0%, 20%, 30%, 40%, and 50%) of fly ash and three levels of nanoCaCO₃, 0.5%, 1%, and 2.5%, were considered. Viscosity of the pastes, made with fly ash and nanoCaCO₃ at a constant water-to-binder ratio of 0.35, were measured and analyzed. The results indicate that the pastes with fly ash or/and nanoCaCO₃ still fit the Bingham model. The addition of fly ash reduced viscosity, however, the addition of nanoCaCO₃ increased viscosity. The effect of nanoCaCO₃ is more significantly than fly ash on viscosity.

Abstract: Since lamination parameters were found to represent the stiffness properties and the orientation of each ply, two major stages are defined to do the optimization. In the first stage which is called continuous optimization, the required lamination parameters will be obtained by VICONOPT but this has not been completed. This paper focuses on the second stage which is called discrete optimization. It consists of three programs and the major program is called OPBDP. Random values of required lamination parameters for 4, 8 and 16 plies lay-ups are chosen and assumed, then the results are computed and compared. What is more, a method called double up the plies is introduced and the results show that it could save a lot of solution time but is still only suitable for a small number of plies.

Abstract: As a new type of building materials, performance of SHCC admixed with silica fume and that exposed to different temperatures are of concern. Uniaxial tension test is conducted on specimens that with and without silica fume admixture, after being exposed to 6 different temperatures (20°C, 50°C, 100°C, 150°C, 200°C and 300°C) for 2 hours. The results show that the ultimate tensile strain of SHCC decreases along with the increase of temperature. However, the ultimate tensile strain remains above 1.2% when the temperature is less than 200°C. Incorporating silica fume into SHCC design indicates that the use of silica fume does not have much effect on the ultimate tensile strain of SHCC, but significantly improves the first cracking strength and ultimate strength of the material.

Abstract: Tailings use is an important environment program and also society subject. Iron tailing is an environmental pollution resources, but it can be used to produce autoclaved aerated concrete (AAC). The chemical composition of iron tailing and the mineral compositions were analyzed by XRD test. The content of radioactive substance in iron tailing was also tested. The testing results show that the iron tailing meet the requirment for AAC production. Iron tailing was sieved to analyze the gradation and was milled by the ball grinding mill machine to proper fineness. Based on the given material mixing ratio, sample test showed that the density of AAC varies from 438 to 629 kg m^-3 with different finenesses of iron tailing, and the height ratio of final height to casting height of AAC changes with the finenesses of iron tailing. The research findings have important lessons for the production of aerated concrete with tailing.

Abstract: This paper studied the ratio of dispersion of multiwall carbon nanotubes (MWNTs) in different surfactant solutions. Effects of surfactant type and concentration and MWNTs to surfactant ratio were investigated. Test results indicate that sodium dodecyl sulfate (SDS) and TNWDIS were better surfactants. Samples with SDS to MWNTs ratio of 6 or TNWDIS to MWNTs ratio of 0.6 had higher ratio of dispersion.

Abstract: This paper studied the electrical resistivity and piezoresistivity of specimen of cement paste made with multiwall carbon nanotubes (MWNTs). The twelve sodium dodecyl benzene sulfonate (SDBS) was used as surfactant. Specimen had a MWNTs to SDBS ratio of 1/4 and contained 0.2% NWNTs by weight. Different dispersal durations, 15min, 30min, 45min, were adopted. The test results show that under the same period of curing, when the dispersal time of MWNTs was 45min, the electrical resistivity of the composite was the biggest and the curve was the varied；with the age growth, the electrical resistivity increased obviously；with the increase of moisture content, the resistivity decreased significantly.

Abstract: Porous material with raised flexural strength 34.43 MPa and porosity 33.069% obtained at 1070 °C for 0.5 h, shows that its bulk density of the materials decreases down to 1.450 g/cm³ using FGD gypsum as aggregate. The closed porosity and dense structure of sample has been observed by SEM and the main crystalline phases of the sample using XRD techniques are quartz, mullite and anorthite. The calcium oxide from FGD gypsum decomposition helps to form the crystalline phase of anorthite and to improve the flexural strength of sample.