This study was conducted to assess the critical air-void system parameters required to ensure freeze-thaw resistance of ternary concrete containingordinary portland cement (OPC), fly ash (FA) and silica fume (SF). Two methods were used for determination of air void system parameters in hardened concrete specimens: the modified point-count method (ASTM C 457) and the automated technique using a flatbed scanner. It was observed that high slump (associated with high superplasticizer dosage) concrete generally exhibited poor freeze-thaw resistance, regardless of the quality of the air-void system. This was likely a result of reduced capability to provide freeze-thaw protection of the air bubbles created by superplasticizer compared to that of the bubbles formed by air entraining admixture. However, for mixtures with slumps below 190 mm, it was concluded that ternary OPC/FA/SF concrete did not require more stringent air-void system parameters thanconventional concrete. Further, a reasonable agreement between the manual and automatic methods of air-void system characterization was obtained for such parameters as air content, void frequency and spacing factor. Although the results of these two techniques did not match perfectly, the data suggested that the flatbed scanner technique could be efficiently used for the purpose of discerning between freeze-thaw durable and non-durable concrete.
Samenvatting