648 research outputs found
Shear transfer mechanism in reinforced engineered cementitious composite (ECC) beams: Quantification of Vs and Vc
No full textTo enhance the structural and seismic resistance, as well as durability of concrete structures, an ultra ductile fiber reinforced cementitious composites called Engineered Cementitious Composite (ECC), also known as Strain Hardening Cementitious Composite (SHCC), was developed. ECC has a similar compressive and tensile strength to conventional concrete, but it exhibits a pseudo-strain-hardening behaviour under uniaxial tension with excellent crack control ability. The ultimate tensile strain of ECC can reach 3–12%, which is 300–1200 times higher than that of concrete. It is reported that ECC can also exhibit at least twice as high shear carrying capacity compared to traditional concrete, signifying a potential to use ECC material in shear-resistance elements. However, the shear resisting mechanism of reinforced ECC (R/ECC) members is still not clear. In most existing codes and models, the shear strength of reinforced structural members (Vu) is divided into two parts, i.e., shear resistance coming from the matrix (Vc) and from the transverse reinforcement (Vs). To quantify accurately Vc and Vs and also their development throughout the loading, a well-designed testing method consisting of continuous strain quantification along the stirrups, was used in this research. Six steel reinforced beams incorporating different matrix (ECC, concrete and mortar) were tested under four-point bending. The test results indicated that Vc changed continuously with the propagation of shear crack, whereas the stirrups that crossed the critical shear crack, did not always yield at the ultimate shear resistance.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Concrete Structure
Chloride penetration resistance of engineered cementitious composite (ECC) subjected to sustained flexural loading
No full textThis paper presents a research on the chloride penetration behavior of engineered cementitious composites (ECC) under sustained flexural loads. Three load levels, i.e. 30 %, 60 % and 75 % of the ultimate flexural load were used. Chloride diffusion depth and concentration profile were measured 30, 60 and 150 days after the specimen was exposed to NaCl solution and compared with pre-loaded specimens. Influence of the sustained local bending stress and microcracks were investigated. It shows that under sustained loads, the relationship between the surface chloride content and maximum normal tensile stress can be described using an exponential equation. A binary model was developed to explain the correlation among the chloride ion diffusion coefficient, maximum normal tensile stress and exposure time. Changes of capillary pore structure and phase compositions were measured using mercury intrusion porosimeter and X-ray diffraction, respectively. Unlike mortar, the fiber bridging of ECC helps with limiting crack width and thus the diffusion process, and the measured results were used to explain the observed penetration behavior of ECC. It is believed that the current study provides theoretical foundation for the durable design of the ECC/concrete composite structure.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Materials and Environmen
Repair concrete structures with high-early-strength engineered cementitious composites (HES-ECC): Material design and interfacial behavior
No full textAimed at realizing the effective strengthening and durable repair of concrete structures, particularly in emergencies like traffic interruption triggered by broken roads and damaged bridges, nine groups of specimens were designed and tested in this paper to develop the high-early-strength Engineered Cementitious Composites (HES-ECC) featured as both high early-strength and superior long-term-deformability. The high-early-strength effect of sulphoaluminate cement, silica fume, and Portland cement on HES-ECC was compared, as well as their influence on the deformation ability of HES-ECC. Moreover, the interfacial behaviors between HES-ECC and existing concrete structure were clarified, considering the effects of interfacial agents, interfacial treatment methods, and interfacial roughness. The results indicate that HES-ECC with 6% silica fume mixed could obtain both the high early-strength and superior long-term-deformability. The flexural strength at 3 h could reach 66.67% of that at 28d. The compressive strength could reach up to 28.7 MPa at 3 h, and the ultimate tensile strain could remain 4.21% at 28d. Cement paste interfacial agent could enhance the chemical adhesive bonding between HES-ECC and existing concrete while polymer modified interfacial agent was incompatible. The increased roughness of chiseled interface was beneficial to both the bearing capacity and the deformation ability. Interfacial shear performance of the grooved interface was scarcely deteriorated even if the roughness decreased by 54.18% compared with the chiseled interface. The recommended interfacial treatment is chiseled interface combined with grooved interface, as well as a thickness of 1–2 mm cement paste interfacial agent. This study provides valuable and credible experimental data for promoting the application of HES-ECC in repairing existing concrete structures in practice.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Concrete Structure
Influence of fiber orientation on the mechanical responses of engineering cementitious composite (ECC) under various loading conditions
No full textThe mechanical performance of engineered cementitious composite (ECC) depends greatly on fiber orientation and distribution. In this paper, the effect of fiber orientation on ECC's mechanical properties was investigated using two different casting methods: a flow-induced casting was used to enhance the fiber orientation within ECC mixture and compared with the conventional casting. The fiber orientation was quantified using scanning electron microscope (SEM) and image processing. Mechanical tests on the specimens with various fiber orientations were performed. The failure processes of ECC specimens under compression and tensile tests were analyzed using digital image correlation (DIC) technique. The proposed flow-induced casting enhanced the fiber alignment in the flow direction. Consequently, ECC's mechanical properties were significantly improved with more finer cracks under uniaxial loading. In conclusion, the proposed flow-induced casting can be adopted as an effective approach to improve fiber bridging efficiency in ECC.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Materials and Environmen
Fatigue life and cracking characterization of engineered cementitious composites (ECC) under flexural cyclic load
No full textThis paper presents a study on cracking characterization of engineered cementitious composites (ECC) under flexural cyclic load using digital image correlation (DIC) technique. Five stress levels, namely 0.65, 0.75, 0.8, 0.85 and 0.9 of the flexural strength, were applied. Strain map at the side surface was obtained by DIC and used to drive evolution of the midspan deflection, damage pattern, maximum crack width, number of cracks, and crack width distribution with respect to the normalized number of cycles. The stress level was found to have a significant influence on the cracking behavior of ECC under flexural cyclic load. Regardless of the applied stress level, most of the crack widths are in the range between 20 and 80 μm. In the end, a two-dimension Gauss function was used to correlate the crack width distribution with normalized number of cycle and shows satisfactory results.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Materials and Environmen
Effect of crack width and wet-dry cycles on the chloride penetration resistance of engineered cementitious composite (ECC)
No full textThe resistance of cracked ECC against chloride ingress is mainly governed by the accumulated crack width of all the cracks rather than the maximum width of multiple cracks. However, most studies focus on the influence of a single fine crackGreen Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Materials and Environmen
Review and outlook on durability of engineered cementitious composite (ECC)
No full textDurability is important for construction materials especially when they are used for long-term engineering applications. Engineered cementitious composite (ECC) as a relatively new fiber-reinforced cementitious composite material has attracted broad interest from research and construction communities. ECC has strain-hardening behavior and self-healing ability due to its micro-cracking under tensile loading. These advantages make ECC more durable under various environmental conditions comparing to ordinary concrete. This paper presents an up-to-date review on ECC durability studies in the literature, with detailed discussions on ECC high temperature resistance, permeability resistance, frost and salt corrosion resistance, shrinkage resistance, abrasion resistance, fatigue resistance and etc. These durability discussions are closely related to the behaviors of fiber, matrix and fiber-matrix interface of ECC under various environmental conditions. Finally this paper proposes several research directions related to ECC durability based on the research gaps identified from the comprehensive literature review
NEC4 ECC contracting for Dutch inner-city infrastructure projects
No full textThis thesis includes the research performed to investigate how to move away from the current adversarial practices in the Dutch infrastructure sector found in the current way of contracting. Adversarial practices are defined as each party pursuing their own concerns at the other party’s expense. As a result of this, the industry is not performing to its maximum. The objective of this research is therefore to stimulate client-contractor collaboration in Dutch innercity infrastructure projects in order to move away from the adversarial practices. In the way the current UAV-GC is applied in projects, dysfunctional conflicts arise between the client and contractor. This research aims to find opportunities for improvement in the UAV-GC by means of clauses from the NEC4 ECC contract. The NEC4 ECC contract is a relational way of contracting, which is relatively new for the infrastructure sector.Civil Engineering | Construction Management and Engineerin
Investigating self-healing capacity of micro-cracked ECC with different volume of fly ash
No full textCrack is called the intrinsic flaw of concrete that is inevitable for concrete infrastructures during their service life. The presence of crack offer aggressive agent access to pass through, which has a direct impact on durability, therefore resulting in shortened service life. Nevertheless, the influence of crack on the durability can be greatly minimized when crack width is controlled within certain limits. Engineered Cementitious Composite (ECC) is a new class of HPFRCC micro-mechanically designed to achieve high tensile strain capacity of 3-5%, while maintaining very tight crack width. In this paper, we attempt to investigate the self-healing capacity of micro-cracked ECC by capillary water sorption test. Three ECC mix proportions with different volume of fly ash are used in this research. Before water curing the specimens are pre-loaded at 28 days so as to produce micro-cracks. The micro-cracked specimens are then cured under water for another 30 and 60 days, respectively, before water sorption test is conducted. It is found that water absorbed by cracks of the pre-loaded specimens reduces with increasing curing age, which suggests that self-healing products accumulate within the cracks over time. Subsequent ESEM observations also confirm the above findings. Most pronounced self-healing behavior is revealed for the mixture with highest fly ash content, which also shows smallest crack width. The crack width reduces with increasing volume of fly ash, denoting better capacity of crack width control. With excellent crack width control and self-healing behavior, ECC can be an ideal material for durable concrete infrastructure
Flash-memories in Space Applications: Trends and Challenges
No full textNowadays space applications are provided with a processing power absolutely overcoming the one available just a few years ago. Typical mission-critical space system applications include also the issue of solid-state recorder(s). Flash-memories are nonvolatile, shock-resistant and power-economic, but in turn have different drawbacks. A solid-state recorder for space applications should satisfy many different constraints especially because of the issues related to radiations: proper countermeasures are needed, together with EDAC and testing techniques in order to improve the dependability of the whole system. Different and quite often contrasting dimensions need to be explored during the design of a flash-memory based solid- state recorder. In particular, we shall explore the most important flash-memory design dimensions and trade-offs to tackle during the design of flash-based hard disks for space application
- …
