Advanced Materials Research Vols. 261-263

Abstract: The present paper is a laboratory study on the effect of using silica nanoparticles with cellulose fibers in increasing compressive, flexural and tensile strength of concrete and the results has been compared with ordinary concrete made of cement alone. Evaluation is conducted based on a 28-day long period, and a 7-day short period; the results showed that the concrete containing a small percentage of nanoparticles, with a determined ratio of water and cement, in comparison with ordinary concrete with the same water and cement ratio, has improved considerably. For comparison, compressive, flexural and tensile strength of plain concrete and the concrete containing cellulose fibers is also measured. The results show that by each of these three criteria, strength of concrete containing nano-materials and the cellulosic fibers has been increased considerably. Finally, the relationship between compressive, flexural and tensile strength of concrete shows that the tensile and flexural strength of the concrete containing nanoparticles increases by increasing compressive strength.

Abstract: Nanotechnology is a science concerned with the design, construction and utilization of functional structures with at least one characteristic dimension measured in nanometres. Nanotechnology initially developed in the fields of physics and chemistry, and most fundamental developments still occur in these fields. Nanotechnology also needs to be applied in areas such as the engineering field. Obviously, the application of nanotechnology to science and engineering has increased in other fields over the years. One area which is one of the most active research areas in the field of nanotechnology is civil engineering. This paper presents a broad overview of the application of nanotechnology in the civil engineering.

Abstract: The present paper reviews the application of nanotechnology in geotechnical engineering, in which the concept of nanotechnology as well as the new concept of nanosol is explained. We have also given explanation for nanometer additives used in the introduced soil, different forms of nanoparticles, their specific properties, and effects of these nanoparticles on engineering properties of soil including index properties and strength, and analyzed the reasons through which these effects are caused. Furthermore, influence of recent advances in nanoinstruments and electron microscopes as well as their application in geotechnical studies.

Abstract: Based on the uniformity of magnetic field in shear circle, low magnetic field, and inconvenient of injecting magnetorheological fluid (MRF), the rotational parallel disk instrument for measuring the shear stress of MRF made by ourselves was improved. The magnetic circuit of the instrument was optimized using Ansys software, the parts and structure of leaking magnetic field were improved, and the uniformity of the magnetic field in shear circle plates was strengthen; when the current was 1.65A, the average magnetic field in shear circle plates was 0.9T. Then the influence on MRF by using different mass fractions of nano-Fe₃O₄ was researched, which indicate when the ration between the mass of nano-Fe₃O₄ and that of carbonyl iron particles is 5%, the characteristic of MRF is best.

Abstract: We synthesized the magnetic CoFe₂O₄ nanoparticles using a solution method in the presence of hexamethylenetetramine (HMTA) at 85 °C for 6 h. Their morphologies, structures, surface properties and magnetism were characterized by Field emission scanning electron microscopy (FE-SEM) images, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and Vibrating sample magnetometer (VSM), respectively. FE-SEM results show that the synthesized samples are irregular nanoparticles with average size range of about 40-120 nm. XRD confirms that the samples belong to the rhombohedral crystal system. The magnetic CoFe₂O₄ nanoparticles have the potential application in magnetic resonance imaging, high-density information storage and drug delivery.

Abstract: The Vetiver (Vetiveria zizanioides) micro/nano fibrils (VFs) were prepared by high intensity ultrasonication (HIUS). The relative crystallinity, the distribution of diameters and morphologies of VFs were investigated by wide angle X ray (WAXD), laser diameter instrument, optical microscopy and scanning electron microscopy (SEM), respectively. The micro/nano fibrils were used to modify melamine formaldehyde resin (MF) and the property of abrasion resistance of MF before and after modification were evaluated. It showed that when filling with 15% of VFs, the abrasion got the minimum value, i.e. the abrasion resistant was best.

Abstract: Micromechanics-based facture models have been proved to predict ductile fracture in steel structures with good accuracy. The stress modified critical strain (SMCS) model and the void growth model (VGM) are suitable to predict fracture initiation under monotonic loading. In order to calibrate the parameters in these models for the largely used Q345 steel in China, material tests, scanning electron microscope tests and finite element analyses were conducted. The test specimens were made from base metal, deposit metal and heat affected zone of Q345 steel to investigate crack initiation in welded connections. The results of this paper can be applied to predict ductile fracture in welded steel connections under monotonic loading.

Abstract: In order to utilize the waste steel slag effectively, three kinds of alkaline activator such as Na₂SO₄, Na₂SiO₃, Na₂CO­₃ were used to prepare steel slag cementitious material and measure its strength of 28 days and 60 days in the standard wet conditions. Microcosmic structure form of hydration products of cementitious material was analyzed by the test of SEM. The results indicate that: three activators on the strength of steel slag all have certain stimulation effect, and Na₂SO₄ has the apparent stimulation effect on the strength of steel slag, the analysis and test of SEM also shows that hydration products structure form of steel slag cementitious material added with Na₂SO₄ is much more than other two activators and is more helpful to improve steel slag strength.

Abstract: This paper contributes to numerically study the mechanical behavior of cement paste under compressive pressure. First, the main results from an experimental study on the mechanical behavior of cement paste are studied. Then an elastoplastique model with two flow mechanisms is proposed to describe the mechanical behavior of cement paste subjected to confining pressure. A particular emphasis is put on the pore collapse mechanism which is developed at higher confining pressure. Finally, numerical simulations and experimental data are compared in order to verify the capacity of the proposed model to reduce numerically the basic characteristics of cement paste under different levels of confining pressure.

Abstract: The existing disadvantage of traditional consolidation test apparatus in determining compressibility characteristics of high water content and high compressibility dredged fill is overcome by GDS consolidation test apparatus, which can accurately measure void ratio after consolidation tests under different consolidation pressures. Laboratory consolidation tests are performed on dredged fill of high water content from 110 percent to 150 percent in the Qianwan area Shenzhen by GDS consolidation test systems, the results are shown as follows: compression strain of dredged fill is 24.73 percent under small and first level consolidation pressure, which is approximately half of cumulative compression strain under whole consolidation pressure; Compression parameters including compression coefficient, bulk compression coefficient and compression modulus has a significant variation with void ratio decreasing under consolidation pressure from 6kPa to 400kPa, the variation of which is from several times to a hundred times, and the nonlinear power function relationship of consolidation pressure -void ratio is shown. GDS consolidation test systems will provide an advanced means for determining compressibility characteristic and compression parameters of dredged fill, and the research achievements in this test will provide a theoretical basis for determining nonlinear relationship of consolidation pressure -void ratio and the parameters for finite-strain consolidation behaviors numerical analysis of dredged fill.