The hydration kinetics of a ternary system containing high lime fly ash activated with alkali sulphate rich fly ash has been studied. The effect of low intensive mechanical activation of fly ashes influencing the particle packing and water demand was undertaken. A ternary blend of fly ashes and silica fume was found to show improved bond strength between the binder paste and aggregate rather than the binder paste matrix with progressive hydration after 90 days. Analogous physico-chemical properties of the developed ternary blend with the control cement were revealed. Quick dissolution of K+, Na+ and SO42- into the liquid phase as well as consumption of Ca2+ by silica fume in a high-pH environment were the predominant factors for producing a dense non-expansive hydration product by the ternary blend.
Cracks and interfaces have been recognized as important planes in global behavior of RC structures. In fact, the response of structures, failure modes and even capacity of RC elements can be affected by the stress transfer mechanism across cracks and interfaces. On the other hand, understanding and expressing different kinds of stress transfer mechanisms has a major role in finite element-based analyses. In this paper, dowel action mechanism has been examined analytically and experimentally. In order to simulate the shear transfer by the dowel bar under different loading conditions, the beam on elastic foundation analogy has been extended by proposing a simple elasto-plastic formulation for subgrade springs. Available experimental results and the data obtained from the experimental program have been used to calibrate and develop the model. Verification of the proposed model is carried out by comparing with the corresponding experimental results.
The precipitates in cracks in an actual utility concrete pole exhibiting self healing which had been in service for 34 years in a freezing and thawing environment were analyzed and the mechanism of self healing was discussed. CaCO3 was observed at the surface of the pole, and it was guessed from the condition of precipitation that water accumulated inside the pole had flowed through the crack to the surface. CaCO3 and ettringite were precipitated in the cracks inside the pole. While cracks approximately 200 μm wide were not completely healed, cracks with a smaller width of 50 to 100 μm were blocked up with precipitates. Precipitates were mainly observed near the interface between the matrix and crack, and much less near the interface between the aggregate and crack. The steel inside the concrete was protected against corrosion by self healing of cracks.
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