A hydration model for cementitious materials was applied to slag blended cement. The original model was found to overestimate the hydration degree of slag, and the influence of the slag ratio on the hydration degree not to be well simulated either. The hydration mechanism of slag was investigated, considering the role of calcium hydroxide as activator and the Ca/Si ratio of C-S-H. It is assumed that for low Ca/Si ratio, the C-S-H inner product has a stronger resistance against ion diffusion and thus influences the hydration process significantly. Accordingly an enhanced model for slag hydration is proposed. Finally, the enhanced model is verified by both hydration degree and heat generation tests.
The purpose of this study is to clarify the effect of stirrups in deep beams by investigating the shear failure mechanism analytically by using the 3-D Rigid-Body-Spring Model analytical tool. The investigation of the analytical results of the internal stress state and 3-D deformations of deep beams were the key objectives of this study. Firstly, the applicability of the analytical tool on deep beams was confirmed by comparison of analytical and experimental results. Then, the stirrup contribution to load carrying capacity of deep beams was investigated and the shear failure mechanism based on the B and D region concept was clarified analytically. To achieve this, analytical results such as stress distribution, 3-D deformations, crack patterns and strain of stirrups were investigated. Three types of stirrup effect were observed in deep beams. In the a/d= 0.5 case, the peak load increase due to the confinement effect of stirrups. In the a/d=1.0 case, the stirrup contributes to the strut action that leads to an increase in load. In the case of a/d < 1.0, the D region is dominant. On the other hand, the peak load increases significantly with increases of stirrup ratio in the case of a/d > 1.5, in which the truss analogy is dominant rather than the strut action.
The microwave absorption characteristics of both powdered and rectangular blocks of an electrically conductive concrete were measured and compared to a normal Portland cement concrete in a multimode cavity. The variables investigated were: irradiation time, sample mass and incident power for the powdered samples and sample orientation, water additions and multiple irradiations for the block samples. The results were quantified in terms of the microwave absorption efficiency (ηa). The absorption efficiency of the electrically conductive concrete was significantly higher than the Portland cement control concrete. For both of the concretes, hot spot formation occurred in the vicinity of the corner of the block. For the electrically conductive concrete this phenomenon took place close to the surface and resulted in combustion of the carbon and disintegration of the concrete. For the normal Portland cement concrete, the hot spot formed below the surface where fracturing, degradation and melting occurred.
Stack migration imaging technology (SMIT), an advanced data processing technique typically used in geophysical exploration, was employed for the detection of small cracks inside concrete structures. Ultrasonic transducers were utilized as both actuator and sensor to generate and receive stress waves in the concrete. The wave field reflected from the damage was synthesized at a common reflective point to highlight the effective signals by using multiple transducers. Two concrete specimens with embedded damage were examined using horizontal stacking technology and diffracting scan pre-stack migration technology, respectively. The dimensions and locations of the damage were successfully imaged. Compared with traditional ultrasonic detection, The experimental results show that SMIT offers better damage visualization and allows damage detection from one side of the specimen.