Papers by Keyword: UHTCC

Abstract: One of the most complex issues that govern the design of a hypersonic vehicle is aerodynamic heating which is much more severe for an air-breathing vehicle as it operates within the atmosphere for longer durations. Due to the detrimental impact of aerodynamic heating on the vehicle structure, it is imperative to develop a robust thermal protection system that can protect the vehicle from high temperatures. However, the development of sophisticated TPS for slender components is impractical and, therefore, requires a hot structure system that can operate at substantial aerothermal loads. The aim of this study is to predict the impact of aero-heating on a UHTCC-based hot structure system of a hypersonic cruise vehicle through uncoupled thermo-structural analysis of the control surface. Validation of numerical methods implemented is done through literature comparison and grid independency tests.

Abstract: UHTCC (Ultra High Toughness Cementitious Composite) is a new type of material which is widely used in this study. It is a kind of cement-based material with very good toughness. It is effective to improve the performance of damaged reinforced concrete and improve its durability. UHTCC is widely used in the reinforcement of concrete structures. There is no clear and effective method for calculating it. There is an approximate formula for the crack width of ordinary concrete. The concept of an average crack spacing is used in the derivation of the formula. The limit of UHTCC for cracks can be measured by the concept of average crack spacing. According to the obtained crack width limit, the reinforcement effect of UHTCC can be shown.

Abstract: Ultra High Toughness Cementitous Composites (UHTCC) is a unique class of the ultra-ductile fiber reinforced cementitious composites. To meet the increasingly high requirements for materials in the construction, nanoSiO₂, polyvinyl alcohol (PVA) and steel (ST) fibers were added into UHTCC to improve the mechanical property and control the crack width. Multiple effects of nanosilica and hybrid fibers on the flexural properties of UHTCC under three-point bending are evaluated. The results show that nanoSiO₂ can increase flexural strength of UHTCC while equivalent deformability is guaranteed. When the addition of nanoSiO₂ is 5%, the highest flexural strength is 15.77MPa. Moreover, hybrid steel-PVA fibers effectively mitigate negative influence from nanoSiO₂ which induce the wider cracks of UHTCC as the stronger matrix. Comparing with mono fiber composites, hybrid fibers composites exhibit remarkably higher flexural strength and slightly lower deformation. The best performance are 24.85MPa and 2.34% at maximum volume of hybrid fibers.

Abstract: In order to research ultra high toughness cementitious composites (UHTCC) economic rationality, this paper chooses the ultra high toughness cementitious composites thermal insulation wall as the research object, uses the study of life cycle method. Establish full life-cycle model with basic life-cycle economic evaluation principle. Evaluate its economic rationality. The results show that ultra high toughness cementitious composites facade has a longer life cycle than ordinary concrete wall. And their local repair costs are all the same, but their maintain frequencies are different. UHTCC facades facing layer does not require maintenance. The calculated models of the two walls are different.

Abstract: Ultra high toughness cementitious composites (UHTCC) demonstrates the properties of non-linear and hardening under load. Its tensile strain may reach over 3%, whereas its average fracture width is only about 60m which shows excellent ability in controlling crack. Tunnel lining is usually made of moulded concrete. One way it endure all the pressures from surrounding rock to guarantee tunnel stability, on the other hand also has low permeability to resist groundwater seepage, while UHTCC has the special advantages in this respect. By analyzing the pressures applied to tunnel lining in one tunnel section, discussion of how UHTCC is applied to lining is done, and some related questions about its application are explained by calculation.

Abstract: The flexural behavior of reinforced concrete (RC) members strengthened with postpoured Ultra High Toughness Cementitious Composites (UHTCC) was investigated in this paper. The flexural behavior, failure mode and crack propagation during loading process of composite specimens were studied, and their structural behavior was also compared to that of original members. The experimental results showed that post-poured UHTCC materials enhanced flexural bearing capacity and toughness of existing concrete members. And introducing UHTCC material into strengthening enabled the composite specimens sustain the loading at a larger deflection without failure. It also revealed that post-poured UHTCC layer dispersed larger cracks in upper concrete into multiple tightly-spaced fine cracks, which prolonged the appearance of harm surface cracks and improved the durability of existing structures.

Abstract: For studying the effectiveness of externally pouring Ultra High Toughness Cementitious Composites (UHTCC) in improving the flexural behaviors of existing reinforced concrete beams, four-point bending tests were conducted up to failure on seven RC beams and strengthening beams. The flexural strength, failure mode and crack propagation of composite beams were investigated. The results showed that pouring UHTCC on the bending surface of reinforced concrete beams properly to improve the ductility and load capacity of composite beams. It was also found that UHTCC layer restricted the development of cracks in upper concrete and dispersed them into multiple fine cracks effectively. Compared with post-poured concrete, UHTCC was more suitable for working together with reinforcement. The load-deflection plots obtained from three-dimensional finite-element models (FEMs) analyses were compared with those obtained from the experimental results, which showed close correlation.

Abstract: This paper presents an experimental study on the flexural fatigue characteristics of Ultra-High Toughness Cementitious Composites (UHTCC), in contrast with plain concrete and Steel Fiber Reinforced Concrete (SFRC) which have similar compressive strength. The results show that UHTCC improves fatigue life and exhibits a bi-linear fatigue stress-life relationship. The deflection ability, failure characteristics of UHTCC were investigated in the tests. It was observed that, similar to static loading situation, multiple cracks were formed under fatigue loading, while the number of cracks decreased with the degradation of stress levels. For this reason, the deformability is much weaker at lower fatigue stress levels than that at higher stress levels. Moreover, the failure section is divided into three different districts, and the proportion of fiber rupture to fiber pullout is different under different stress levels.

Abstract: This paper presents research work relating to design method and mechanical properties of functionally-graded composite (FGC) beams, in which a kind of strain hardening material UHTCC is used as a replacement for the concrete material that surrounds the longitudinal reinforcements. According to mechanical models of materials and a series of assumptions, a simplified design method of such FGC beams is proposed. On the basis of superposition, the determination and the influencing factors of the thickness of UHTCC layer in FGC beams is discussed. Compared with theoretical and experimental results, simplified method shows conservation and guarantees the safety of structures. During the whole flexural loading process, it is found that the opening of cracks in flexural members can be greatly restricted by the introduction of UHTCC. The possibility of steel corrosion therefore can be evidently reduced.