82 research outputs found
A Micromechanics-based Elastic Constitutive Model for Particle-Reinforced Composites Containing Weakened Interfaces and Microcracks
No full text??? ??????????????? ???????????? ????????????(particle-reinforced composites)??? ????????? ???????????? ????????? Lee and Pyo(2007)??? ?????? ????????? ??????????????? ????????? ??????????????? ???????????? ??????????????? Karihaloo and Fu(1989)??? ???????????? ??????????????? ????????????, ??????????????? ????????????(imperfect interface)??? ?????? ??? ??????????????? ???????????? ??????????????????(constitutive model)??? ??????????????? ???????????????. ????????? ????????????????????? ????????? ????????? ????????????????????? ??????????????? ????????? ????????? ???????????? ?????? ?????? ?????? ???????????? ??????-????????? ????????? ??????????????? ???????????????. ??????, ????????? ?????? ??????????????? ??? ?????????????????? ????????? ????????? ????????? ????????? ???????????? ???????????????
Investigation of ultra high performance concrete (UHPC) from multiple perspectives: Air permeability, lightweightness and cementless binder
No full textDepartment of Urban and Environmental Engineering (Urban Infrastructure Engineering)clos
Experimental Study on Sound Absorption Performance of Surface-Perforated Mortar for Mitigating Railway Noise
No full textDepartment of Urban and Environmental Engineering (Urban Infrastructure Engineering)This study proposes the surface-perforated mortar (SPM) to mitigate railway noise. As one of the most emerging noise problems, railway noise deteriorates the quality of human lives. This study investigates the sound absorption performance of SPM, and it is compared to that of porous concrete, which has been adopted as a potential solution for railway noise. The effects of hole size, depth, and surface porosity on the sound absorption performance of SPM are examined using an in-situ sound absorption test, and the results explain the sound absorption mechanism of SPM. Based on these understandings, two methods to improve the sound absorption of SPM without strength degradation are proposed: (i) a combination of different depths of the holes and (ii) an application of sound-absorbing filler into the holes. The improvements show that the sound absorption performance of the SPMs is more than double that of the porous concrete with 25% design porosity.
The study also utilizes aluminum powder to generate micropores to enhance sound absorption in the lower frequency range. Even though SPM has macro-sized holes on its surface and micro-sized pores on the inside, no significant synergistic effect on sound absorption has been observed between macro-sized holes and micro-sized pores in SPM due to the minimal amount of micro-sized pores in the cement-based matrix. Therefore, the micropore was generated using aluminum powder, and the sound absorption was then compared to that of SPM without aluminum powder. The sound absorption test shows that incorporating micro-pores enhances the synergistic effect and increases SPM sound absorption by 133%. The results also show that both frequency range and peak sound absorption values can be controlled using different combinations of depth and porosity. The effects of aluminum powder dosage, hole size, hole depth, and SPM porosity are also studied to provide SPM design guidelines.ope
High Performance Concrete
No full textThe innovations in construction materials that have been made due to the development of different varieties of concrete have led to innovations in structural applications and design. This Special Issue mainly focuses on state-of-the-art research progress in high-performance concrete, including the effect and characteristics of fibers on the properties of high-performance concrete, the CO2 curing efficiency of high-performance cement composites, and the effect of nano materials when used in ultra-high-performance concrete. This Special Issue also contains two comprehensive review articles covering the following topics: the role of supplementary cementitious materials in ultra-high-performance concrete and recent progress in nanomaterials in cement-based materials. Readers working towards conducting research on innovative construction materials will be exposed to findings related to this topic in this Special Issue
High Performance Concrete
No full textThe innovations in construction materials that have been made due to the development of different varieties of concrete have led to innovations in structural applications and design. This Special Issue mainly focuses on state-of-the-art research progress in high-performance concrete, including the effect and characteristics of fibers on the properties of high-performance concrete, the CO2 curing efficiency of high-performance cement composites, and the effect of nano materials when used in ultra-high-performance concrete. This Special Issue also contains two comprehensive review articles covering the following topics: the role of supplementary cementitious materials in ultra-high-performance concrete and recent progress in nanomaterials in cement-based materials. Readers working towards conducting research on innovative construction materials will be exposed to findings related to this topic in this Special Issue
Characteristics of Ultra High Performance Concrete Subjected to Dynamic Loading.
No full textUltra High Performance Concrete (UHPC) is among the most promising cementitious materials developed to date. It has the potential to be a viable solution for improving the resilience and sustainability of the built infrastructure because of its high strength, durability and energy absorption capacity. Pilot studies have shown that its impact resistance is particularly impressive, yet there is hardly any information about its dynamic behavior.
The experimental effort focuses on investigating the strain rate sensitivity of UHPC as a function of fiber type (straight or twisted), characteristics and volume fraction. Low strain rate tests are conducted using a hydraulic actuator, whereas high strain rate tests are conducted using a new device that employs suddenly released elastic strain energy to apply an impact pulse. Developed and optimized through computational modeling, the new device permits accurate and practical testing of UHPC specimens in direct tension, under high strain rate, and can capture both hardening and post peak responses. It is compact compared to existing test methods and permits the use of specimens that are similar in size and geometry to the specimens tested with the hydraulic actuator.
A key experimental observation is that UHPC becomes significantly more energy dissipative in tension under increasing strain rates, which highlights the material’s potential for use in impact- and blast-resistant applications. Although specimens with twisted steel fibers show somewhat better mechanical properties than specimens with straight fibers due to the untwisting mechanism, comparable benefits could be obtained by using straight fibers with higher aspect ratios. Crack propagation studies show that crack speed increases asymptotically as notch tip strain rate increases.
The analytical portion of the study focuses on the source of strength enhancement for concrete materials under high rate tensile loadings, a topic of current controversy in the literature. Dynamic fracture models considering crack velocity dependency prove that strain rate sensitivity is strongly associated with the characteristics of dynamic crack growth, especially the asymptotic nature of crack speed versus strain rate and inertial effects at the crack boundaries. The theoretical observations are corroborated with experimental data in the literature and new data produced by this work.PhDCivil EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/107173/1/shpyo_1.pd
Experimental Investigation of Multi-mode Fiber Laser Cutting of Cement Mortar
No full textThis study successfully applied multi-mode laser cutting with the variation of the laser cutting speed to cement mortar for the first time. The effects of the amount of silica sand in the cement mortar on laser cutting are tested and analyzed. The kerf width and penetration depth of the specimens after laser cutting are investigated. As the laser cutting speed increases, the penetration depth decreases for both cement paste and cement mortar, whereas the kerf width becomes saturated and increases, respectively, for cement paste and cement mortar. Cross sections of the specimens are compared with illustrations. Top-view images of the cement mortar with indicators of the physical characteristics, such as re-solidification, burning, and cracks are examined, and the possible causes of these characteristics are explained. The optical absorption rates of cement-based materials are quantified at wide ranges of wavelength to compare the absorption rates in accordance with the materials compositions. The chemical composition variation before and after laser cutting is also compared by EDX (Energy Dispersive X-Ray) analysis. In addition to these observations, material removal mechanisms for cement mortar are proposed
Micromechanical analysis of aligned and randomly oriented whisker-/ short fiber-reinforced composites
No full textThis paper presents a micromechanical approach for predicting the elastic and multi-level damage response of aligned and randomly oriented whisker-/ short fiber-reinforced composites. Based on a combination of Eshelby's micromechanics and the evolutionary imperfect interface approach, the effective elastic moduli of the composites are derived explicitly. The modified Eshelby's tensor for spheroidal inclusions with slightly weakened interface [Qu (1993b)] is extended in the present study to model whiskers or short fibers having mild or severe imperfect interfaces. Aligned and random orientations of spheroidal reinforcements are considered. A multi-level damage model in accordance with the Weibull's probabilistic function is then incorporated into the micromechanical framework to describe the sequential, progressive imperfect interfaces in the composites. Numerical examples corresponding to uniaxial tensile loadings are solved to illustrate the potential of the proposed micromechanical framework for predicting the elastic and multi-level damage response of the composites. Furthermore, comparisons between the present predictions and experimental data in the literature are made to further highlight the capability of the proposed micromechanical framework
Ultra high performance concrete (UHPC) sleeper: Structural design and performance
No full textBoth structural and material performance of railway sleepers are critical to ensure the safety of railway track structures. In this study, for the first time, ultra high performance concrete (UHPC) is adopted to the post-tensioning type of sleeper to prolong design life and reduce the maintenance of sleepers. A structural design is carried out to fully utilize the material benefits of UHPC, including superior compressive strength and tensile ductility, and reviewed the critical sections of the sleeper based on strain compatibility analysis. Sixteen UHPC sleepers were fabricated using the developed UHPC mixture, incorporating coarser aggregates and ground granulated blast furnace slag, to perform structural verification tests according to the European standard, including bending strength tests under static, dynamic, and fatigue loading. The series of structural tests conducted on the UHPC sleepers show that the ductile characteristic of UHPC reinforced with steel fibers resulted in stable structural behavior and outstanding crack resistance capabilities even after the initial cracks developed. This experimental study may provide new insight into the structural applications of UHPC under railway loading conditions
Effect of steel fiber content on structural and electrical properties of ultra high performance concrete (UHPC) sleepers
No full textThis experimental research investigates the structural and electrical responses of ultra-high performance concrete (UHPC) railway sleepers with three different levels of steel fiber content. The UHPC sleepers used in this research were fabricated using a conventional concrete sleeper manufacturing process including the post -tensioning method. They were then evaluated via static bending tests at the rail-seat section and via electrical insulation performance tests. Test results indicate that UHPC sleepers with all three levels of steel fiber content sufficiently meet international requirements. The results from the first cracking load and the load when a crack width becomes 0.05 mm indicate that an amount of steel fiber greater than 1% is required to effectively control early-stage crack development in UHPC sleepers. In addition, the relationship between fiber volume fraction and normalized strength highlights that the material characteristics of UHPC, especially its tensile capacities, correlate strongly with the structural behavior of UHPC sleepers
- …
