The spalling properties of concrete were investigated in relation to surface moisture content. Changes in the microstructure of concrete, moisture transfer and internal pressure were also investigated from a microscopic aspect.Based on the results of the investigation, experimental research was conducted on the effects of heat and moisture transfer on spalling as well as the causes of vapour pressure (internal stress) surges and spalling. Spalling of highstrength concrete was found to be significantly affected by moisture transfer in the surface region of concrete and moisture transfer was found to be closely related to the temperature profiles resulting from the characteristics of pore structures, which are the main passages for moisture. It was also found that, in the high-strength (80 MPa) concrete used in this study, the probability of spalling and scale of damage could be reduced according to dryness in the surface region (0-30 mm depth).
The effect of ground granulated blast-furnace slag (GGBS) and alkaline activator on the properties of setting, compressive strength, drying shrinkage and resistance of carbonation was assessed to develop high volume slag concrete, the GGBS replacement rate of which was more than 80 percent. The changes in the concrete as the replacement rate of GGBS increases were as follows. Initial and final setting time was delayed by two and a half hours, and the compressive strength development properties of concrete in early and long term age were decreased. Drying shrinkage was satisfactory as below 6×10 -4 in every mixture, and yet showed a tangible trend by replacement rate. Carbonation was materially increased. Setting time and early strength development property, however, were extremely advanced by the addition of the alkaline activator. While drying shrinkage was improved by the alkaline activator, resistance to carbonation was not.
For high strength concrete of 40∼60 MPa, the effects on the early strength and concrete dry shrinkage properties replacing 60∼80% of Ordinary Portland Cement with Blast Furnace Slag Powder and using the Alkali Activator (Modified Alkali Sulfate type) are considered in this study. 1% Alkali Activator to the binder, cumulative heat of hydration for 72 hours was increased approximately 45%, indicating that heat of hydration contributes to the early strength of concrete, and the slump flow of concrete decreased slightly by 3.7∼6.6%, and the 3-and 7-strength was increased by 8∼12%, which that the Alkali Activator (Modified Alkali Sulfate type) is effective for ensuring the early strength when manufacturing High Strength Concrete (60%) of Blast Furnace Slag Powder. Furthermore, the dry shrinkage test, both 40 MPa and 60 MPa specimens had level of length changes in order of BS40 > BS60 > BS60A > BS80A, and the use of the Alkali Activator somewhat improved resistance to dry shrinkage.
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