Experimental Study on the High-Temperature Shear Performance of Asphalt Mixtures

The influence of temperature on the shear performance of asphalt mixtures and the feasibility of using the deformation strength as an index of the high-temperature shear performance of these mixtures were explored in this study. Taking AC-13C and AC-20C asphalt mixtures as the research objects, uniaxial compression, rutting, deformation strength, and uniaxial static load creep tests were carried out at temperatures 40°C, 45°C, 50°C, 55°C, and 60°C. The correlations between the deformation strength and modulus of resilience, compressive strength, dynamic stability, and stiffness of the asphalt mixtures were studied. The test results show that the influence of temperature on the compressive strength, resilience modulus, and deformation strength of the asphalt mixtures decreases significantly as the temperature increased, and the rutting deformation of the two kinds of asphalt mixtures increased as the temperature increased. Strong correlations exist between the deformation strength and the modulus of resilience, the compressive strength, and the dynamic stability of asphalt mixtures, so the deformation strength can be used as an evaluation index of the high-temperature shear performance of asphalt mixtures.

Materials Testing for Mechanical Properties—Problems and Solutions

This appendix provides readers with worked solutions to 25 problems involving calculations associated with tensile testing and the determination of mechanical properties and variables. The problems deal with engineering factors and considerations such as stress and strain, loading force, sample lengthening, and machine stiffness, and with mechanical properties and parameters such as elastic modulus, Young’s modulus, strength coefficient, strain-hardening exponent, and modulus of resilience. They also cover a wide range of materials including various grades of aluminum and steel as well as iron, titanium, brass, and copper alloys.

Materials Testing Fundamentals

Product design requires an understanding of the mechanical properties of materials, much of which is based on tensile testing. This chapter describes how tensile tests are conducted and how to extract useful information from measurement data. It begins with a review of the different types of test equipment used and how they compare in terms of loading force, displacement rate, accuracy, and allowable sample sizes. It then discusses the various ways tensile measurements are plotted and presents examples of each method. It examines a typical load-displacement curve as well as engineering and true stress-strain curves, calling attention to certain points and features and what they reveal about the test sample and, in some cases, the cause of the behavior observed. It explains, for example, why some materials exhibit discontinuous yielding while others do not, and in such cases, how to determine when yielding begins. It also explains how to determine other properties via tensile tests, including ductility, toughness, and modulus of resilience.

Experimental Study on the Effect of Compaction Work and Defect on the Strength of Soil-Rock Mixture Subgrade

Soil-rock mixture is a common filling material for earth dam and subgrade. In this study, research concerned on the evolution law of engineering characteristics of soil-rock mixture under different factors and the effect of defect on subgrade strength, and geotechnical tests were carried out to analyze the influence of different factors on engineering characteristics of soil-rock mixture in the study, and the physical model was carried out to analyze the effect of different compaction works on the resilient modulus, and the influence of defect on the strength was explored by manually preset loose body. The test results showed that (1) when the soil-rock mixture was graded, P = 78, the moisture content was 14%, and the engineering characteristics were optimal; (2) there was a positive correlation between compaction times and resilient modulus, and the stress transferred from the subgrade to soil was linearly distributed under the good condition of compactness; and (3) the existence of loose body not only reduces the modulus of resilience but also affects the stress transfer; the larger the loose body, the lower the resilient modulus and the greater the stress transfer.

Investigation on cement-improved phyllite based on the vertical vibration compaction method

The vertical vibration compaction method (VVCM), heavy compaction method and static pressure method were used to form phyllite specimens with different degrees of weathering. The influence of cement content, compactness, and compaction method on the mechanical properties of phyllite was studied. The mechanical properties of phyllite was evaluated in terms of unconfined compressive strength (Rc) and modulus of resilience (Ec). Further, test roads were paved along an expressway in China to demonstrate the feasibility of the highly weathered phyllite improvement technology. Results show that unweathered phyllite can be used as subgrade filler. In spite of increasing compactness, phyllite with a higher degree of weathering cannot meet the requirements for subgrade filler. With increasing cement content, Rc and Ec of the improved phyllite increases linearly. Rc and Ec increase by at least 15% and 17%, respectively, for every 1% increase in cement content and by at least 10% and 6%, respectively, for every 1% increase in compactness. The higher the degree of weathering of phyllite, the greater the degree of improvement of its mechanical properties.

3D printing PCL/nHA bone scaffolds: exploring the influence of material synthesis techniques

Background It is known that a number of parameters can influence the post-printing properties of bone tissue scaffolds. Previous research has primarily focused on the effect of parameters associated with scaffold design (e.g., scaffold porosity) and specific scaffold printing processes (e.g., printing pressure). To our knowledge, no studies have investigated variations in post-printing properties attributed to the techniques used to synthesize the materials for printing (e.g., melt-blending, powder blending, liquid solvent, and solid solvent). Methods Four material preparation techniques were investigated to determine their influence on scaffold properties. Polycaprolactone/nano-hydroxyapatite 30% (wt.) materials were synthesized through melt-blending, powder blending, liquid solvent, and solid solvent techniques. The material printability and the properties of printed scaffolds, in terms of swelling/degradation, mechanical strength, morphology, and thermal properties, were examined and compared to one another using Kruskal-Wallis nonparametric statistical analysis. Results Material prepared through the liquid solvent technique was found to have limited printability, while melt-blended material demonstrated the highest degree of uniformity and lowest extent of swelling and degradation. Scaffolds prepared with powder-blended material demonstrated the highest Young’s modulus, yield strength, and modulus of resilience; however, they also demonstrated the highest degree of variability. The higher degree of inhomogeneity in the material was further supported by thermal gravimetric analysis. While scaffolds printed from melt-blended, powder-blended, and solid solvent materials demonstrated a high degree of micro-porosity, the liquid solvent material preparation technique resulted in minimal micro-porosity. Conclusions Study results indicate that specific techniques used to prepare materials influence the printing process and post-printing scaffold properties. Among the four techniques examined, melt-blended materials were found to be the most favorable, specifically when considering the combination of printability, consistent mechanical properties, and efficient preparation. Techniques determined to be favourable based on the properties investigated should undergo further studies related to biological properties and time-dependent properties beyond 21-days.

Hardness and Elastic Modulus of Al-Based Composite Developed from Aluminium Piston Scraps Using Alumina and Snail shell as Reinforcements

This paper presents the relationship between the Young’s modulus and hardness of composites developed from recycled aluminium pistons reinforced with alumina and snailshells. The percentages of alumina and snailshells were kept within the range of 0-30 and 0-10 wt.%, respectively. Experiments were designed using response surface methodology (RSM) to evaluate the influence of the reinforcements on the tensile, hardness and Young’s modulus of the composites. The theoretical hardness was analyzed from the ratio of indentation hardness to indentation modulus while the Young’s modulus was evaluated from the composite equations. The results indicate that an increased fraction of the hybrid reinforcement does not necessarily translate to higher hardness value and Young’s modulus. The sample with the best characteristics has a tensile strength of 172.5 MPa, modulus of resilience of 28.28 GPa and hardness value of 44.9 RHN. The average experimental Young’s modulus of the samples is about 30% of the theoretical value of 86.5GPa while experimental hardness value of 44.90 is about twice that of the theoretical value. The discrepancy between the experimental and theoretical modulus is due to the assumption of a perfect crystal for the former as against polycrystalline crystals. The two samples with the highest modulus of resilience were chosen and further characterized. Scanning Electron Microscope images showed that the fillers in the two samples were well bonded with the aluminium matrix. Keywords - Mechanical Properties, Casting, Aluminum composite, Alumina and Snailshells

Fracture patterns and mechanical properties of GFRP bars as internal reinforcement in concrete structures

Glass Fiber Reinforced Plastic (GFRP) composites as rolled bars can be used as steel rebar to prevent oxidation or rust which is one of the main reasons concrete structures deteriorate when exposed to chlorides and other harmful chemicals. GFRP is successful alternative for reinforcement with high tensile strength- low strain, corrosion resistance and congenital electromagnetic neutrality in terms of longer service life. The main goal of the study is to investigate the mechanical and bonding properties of GFRP bars and equivalent steel reinforcing bars then compare them. GFRP and steel rebar are embedded in concrete block with three different levels. Mechanical properties of GFRP and steel bars in terms of strength and strains are determined. On the other hand; modulus of elasticity of GFRP and steel bars, modulus of toughness and modulus of resilience were calculated using stress-strain curves, as a result of the experiments. Pull-out tests are conducted on each GFRP and rebar samples which are embedded in concrete for each embedment level and ultimate adherence strengths are determined in terms of bar diameter–development length ratio. Yield strength, strain and modulus of elasticities of GFRP samples are compared to steel rebar. According to the test results reported in this study, GFRP bars are used safely instead of steel bars in terms of mechanical properties.

Bearing Behavior of the Fly Ash Deposits on Expressway

The reinforcement treatment for embankment using the fly ash deposits as the filling material for roadbed was clarified in this paper. Studies have shown that fly ash can be used as the filling material for embankment, but the subgrade bearing capacity from the original fly ash deposits cannot meet the requirements for operating. Fly ash has a good condition to run the dynamic consolidation for meeting the requirements of embankment compaction. The modulus of resilience and the California bearing ratio (CBR) of fly ash is close to that of general filling material for embankment. Fly ash also has the engineering properties of high void ratio and low cohesion. The maximum level of compaction of the fly ash deposits can be 93% and the bear capacity can be about twice over before after the treatment.