Papers by Author: Shi Lang Xu

Abstract: This research focuses on mechanical performances of UHTCC-FGC beams under monotonic and fatigue loading. Three UHTCC-FGC beams are tested, including two monotonic beams and one fatigue beam. The stress level of fatigue beam is set as 0.85. The constant ratio of minimum stress to maximum stress is set to 0.2 to avoid any impact and slip between the loading machine and the specimens during testing. The specimen is subjected to sinusoidal cyclic loading at 1 frequency. During the experiments, the fatigue life, deformability and loading capacity of UHTCC-FGC beams are measured and recorded. Meanwhile，the development of cracks and the failure pattern of UHTCC-FGC beams during the test are observed at the same time.

Abstract: Advancement in the study of carbon nanotube has enabled its application in civil engineering as constitutive materials or additives. In this study, the availability of applying multi-walled carbon nanotube to improve the characteristics of cement composites was investigated with experiments on more than 30 specimens. The multi-walled carbon nanotubes (MWCNTs) were effectively dispersed in the water with surfactant, which can keep stable for over 3 months. Specimens with MWCNTs of 0.025%, 0.05% and 0.1% of cement (by weight) were tested with a loading machine and then analyzed with a SEM. It was found that the compressive strength of the samples increased with the increasing MWCNTs, it can improve the 7-day compressive strength by 22% . Microscopic analysis (SEM) revealed that carbon nanotubes were surrounded with hydration products. The bridging and debonding of carbon nanotubes in cement pastes was observed as well.

Abstract: In this article, through the seismic experimental analysis for six frame joints of ultra-high toughness cementitious composites, the load-carrying capacity, hysteretic behavior, energy dissipation and ductility of new joints are studied under different axial compressive ratio and the stirrups space. The experimental results show that the UHTCC joints have higher anti-cracking capacity and shear ductility. The UHTCC can reduce or even eliminate the amount of shear stirrups of the joint core. According to the analysis for the experiments, a theoretical calculating formula of shearing capacity is presented, whose calculating results agree well with the experimental results.

Abstract: A new class of high performance fiber reinforced cementitious composites called Ultra High Toughness Cementitious Composites (UHTCC) is developed in the last few years. It is a pseudo strain hardening material with maximum tensile strain capacity more than 3%, yet the fiber volume fraction no more than 2%. The multiple cracking patterns accompanying pseudo strain hardening behavior are obtained which implies high ductility, energy absorption capacity, and toughness. A remarkable characteristic distinguish it from conventional high performance fiber reinforced concrete is the maximum crack width of multiple cracks which is about 60µm under ultimate tensile load. Such micro-cracks are often small enough to prevent the intrusion of aggressive agents. From a durability point of view this composite can be considered as an effectively uncracked material. The performances of this new material, including the apparent density, the uniaxial tensile property, and the drying shrinkage performance, are experimental studied in this paper.

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.