Evaluation of back-calculated elastic moduli of unreinforced and geocell-reinforced unbound granular material from full-scale field tests

This paper presents a field-scale experimental track over a poor subgrade with an unreinforced section and a geocell-reinforced section subjected to in-situ performance tests. Plate load tests and Benkelman beam tests were carried out distributed in several unreinforced and reinforced layers. The objective was to: (1) examine the variability of the elastic modulus of unbound granular material (UGM) due the influence of its thickness and the presence of poor subgrade in its base, (2) evaluate the modulus improvement factor (MIF) generated by the geocell reinforcement in the UGM and (3) verify the most appropriate condition to apply the MIF to transport infrastructure design. The results showed that there is a significant influence of the thickness of the UGM layer on its elastic modulus when the layer is supported directly over a soft subgrade. The MIF values obtained in field suggest that its determination is mostly related to the UGM maximum elastic modulus rather than its decreased values (by virtue of poor subgrade or reduced thicknesses), and that the analytical formulation presented for MIF calculation has good predictive capability to be applied to pavement design.     

Role of cement content on the properties of self-flowing Al2O3 refractory castables

In this work, Al₂O₃ self-flowing castables (SFCs) were produced based on various cement contents. The SFCs were sintered at 1273 K, 1573 K and 1773 K and the exhibited properties were experimentally determined. Among the properties determined in this work are bulk density (BD), apparent porosity (AP), water absorption (WA), cold crushing strength (CCS), modulus of rupture (MOR) and fracture toughness (K_IC). It is found that additions of 5% cement lead to SFCs with maximum MOR and K_IC values after firing at 1773 K. Firing at 1573 K leads to a reduction in both, MOR and K_IC. In SFC containing 3% cement, maximum K_IC values of 3.53 MPa m^1/2 were achieved after firing at 1573 K. In the low cement SFCs (1 wt%) after firing at 1773 K the exhibited K_IC values were below those obtained in either the SFC-3 or SFC-5, but they were significantly high (3.43 MPa m^1/2).     

复合地基基本工作机理及存在问题综述

本文介绍了复合地基的发展现状、基本工作机理 ,并对复合地基的承载力计算方法和沉降计算方法进行了分析 ,最后对复合地基计算中存在的问题进行了探讨     

蜂窝板夹芯面内弹性模量的理论分析

蜂窝芯材的弹性模量的确定是夹层结构设计的基础，文章通过3D有限元方法与以往以Eule，梁理论为基础的金属蜂窝夹芯板的等效弹性模量的计算理论进行比较分析，结果表明在t／l相对较小的情况下，用W—K公式较为合适。并结合算例证实了夹芯等效弹模对整板面外刚度的贡献是较小的。     

MAS小波的钢板表面缺陷边缘检测的研究

针对钢板表面缺陷与背景的对比度差、边缘复杂、采光不均、噪声较大等特点,应用一种基于MAS小波变换进行钢板表面缺陷边缘检测。该方法由Lipschitz指数阐明了图像的边缘几何结构,通过分析图像中不同类型的奇异点,并结合尺度独立算法区分了目标图像中不同类型的边缘,有效的提取了钢板表面缺陷图像的边缘。实验结果表明,基于MAS小波算法可以有效提取图像中阶梯型边界,检测到的缺陷边缘轮廓较为清晰,且去噪能力较强,检测效果优于传统的同类方法。     

Compressive stress-strain model for low-calcium fly ash-based geopolymer and heat-cured Portland cement concrete

This research focuses on elucidating the present knowledge gaps in geopolymer concrete's engineering properties, specifically its stress-strain behaviour. Geopolymer concrete (GPC) is an emerging alternative to ordinary Portland cement concrete (OPCC), and is produced via a polycondensation reaction between aluminosilicate source materials and an alkaline solution. As a relatively new material, many engineering properties of geopolymer concrete are still undetermined. In this paper, the compressive strength, modulus of elasticity and stress-strain behaviour of ambient and heat-cured GPC and OPCC have been studied experimentally. A total of 195 geopolymer concrete cylinders and 210 Portland cement concrete cylinders were tested for the above mentioned characteristics. Based on the experimental results, constitutive models describing the complete stress–strain behaviour in uniaxial compression have been developed for the low-calcium fly ash-based geopolymer concrete and the heat-cured Portland cement concrete.     

Mechanical properties of roller compacted concrete containing rice husk ash with original and recycled asphalt pavement material

This study focused on the effects of rice husk ash (RHA) on the mechanical properties of roller compacted concrete (RCC) designed with original and reclaimed asphalt pavement (RAP) materials. The RCC mixes were produced by partial substitution of cement with RHA at varying amounts of 3% and 5%. Four aggregate combinations including the mix with original aggregate, coarse RAP + fine original aggregate, coarse original aggregate + fine RAP and total RAP were considered. The main experimental design consisted of the compressive strength and three points bending tests. Bending test was used to measure the modulus of rupture, material’s energy absorbency and analyse the fatigue response of RCC mixes. All tests were performed after 7, 28 and 120 days curing except the fatigue test that performed on 120 days specimens. Adding RHA resulted in higher optimum moisture content (OMC) and lower maximum dry density. Furthermore, adding RAP with different dimensions reduced the OMC and maximum dry density. The material’s flexibility improved upon replacing 3% cement by RHA. However, the energy absorbency reduced by increasing the RHA content to 5%. The fatigue life of RCC mixes containing RAP material was lower than the conventional one. Furthermore, replacing the coarse aggregate by RAP led to higher fatigue life than the fine aggregate. There was a strong relationship (R² > 0.90) between the energy absorbency and fatigue response of RCC mixes. At higher stress ratios of 0.72, the mix with higher energy absorbency behaved better under repeated loadings. Besides, a reverse relationship was found between the fatigue life and material porosity. Adding 3% RHA reduced the porosity especially after 120 days curing and improved the fatigue resistance. However, the addition of RHA to 5% resulted in higher porosities and lower fatigue lives.     

Nano-scale modulus mapping of biological composite materials: Theory and practice

The mechanical behavior of materials depends to a large extent on their properties at the nanoscale and, therefore, novel characterization techniques with sub-micron spatial resolution were developed in the last decades. Among them are the variety of tools for probing local elastic and viscoelastic properties of materials, the methods such as nanoindentation and AFM- and nanoindenter-based measurements using force modulation. In this review, we describe the nanoindenter-based nanoscale modulus mapping technique, which emerged as an extremely powerful tool for providing quantitative information on the storage and loss moduli distributions in complex nanocomposites. Since the tip penetrates only a few nanometers into the materials, this technique provides a superior lateral resolution in the order of 20 nm. All aspects of the method are covered, including a historical perspective, theoretical analysis, instrumentation, and examples of its application for studying multiphase structures and interfaces. The main focus of this review is the challenging field of natural bio-composites, which consist of stiff and compliant components, often with nanometric dimensions. Gradients of mechanical properties across the nm-sized features in biological materials are of upmost importance for their mechanical performance. Quantitative information on the nano-scale moduli distributions in these structures can hardly be achieved by other means.     

Density and Young׳s Modulus of ternary glasses close to the eutectic composition in the CaO–Al2O3–SiO2-system

The elastic properties and the density of ternary glass forming systems within the CaO–SiO₂–Al₂O₃-system (CAS) were evaluated. Different glass compositions near the lowest eutectic (1170 °C) composition within the CaO–Al₂O₃–SiO₂-system have been melted from pure raw materials. Their target compositions differed not more than 4 wt% for each component. Exact chemical compositions were measured by x-ray fluorescence. The density, and acoustic properties were determined and the Young׳s Moduli were derived herefrom. It was of special interest to obtain information on these properties and their dependencies upon small variations in the composition. The density values were between 2.600 and 2.667 g cm⁻³ and the packing density factors V_p of the oxides glasses using the ionic radii of Pauling were in the range from 0.559 to 0.571. The determined data were compared to different model calculations. Density model calculations show relative deviations between 2 and 6%. The values calculated from the model for Young׳s Modulus by Makishima and Mackenzie (1973) [1] were somewhat smaller than the measured ones. The correction by Rocherulle et al. (1989) [3] of the Makishima model showed better agreement with the measured values.     

Evaluation of percentage oil yield,energy requirement and mechanical properties of selected bulk oilseeds under compression loading

The present study examined the percentage oil output, energy and mechanical properties of selected bulk oilseeds namely pumpkin, hemp, sesame, milk thistle, cumin and flax by a uniaxial compression process of a maximum load capacity of 500 kN and a preset speed of 5 mm/min. Each sample was measured at 60 mm pressing height with a plunger using the pressing vessel of diameter 60 mm. The results show that milk thistle seeds required the highest force corresponding to the highest stress and energy demand for recovering the oil in both the bulk oilseeds and seedcakes. However, pumpkin seeds produced the maximum residual oil yield of 24.99 ± 0.04%, followed by sesame seeds at 21.29 ± 1.82% and then flax seeds at 22.61 ± 0.31%. The study revealed that higher energy is required to produce the maximum oil yield with minimum residual oil in the seedcake by continuous pressing.