부산대학교 도서관

Response Surface Methodology with a three factor, two level (2³) face centered, central composite design showed that the optimum paste mix design with the water-to-binder at 36.0%, fly ash (FA)-to-binder at 29.5% and nano-iron oxide (NI)-to-binder at 0.78% produced a spread percentage of the fresh paste at 107.0% and, at the same time, compressive strengths of the hardened paste at 22.1, 60.4 and 79.8 MPa after 3, 28 and 90 days of curing, respectively. FA began to play a significant role for the compressive strength after 28 days of curing, whereas NI did after 90 days of curing, indicative of time-dependent contribution of FA and NI to the development of compressive strength. These were further supported by the SEM microstructure analysis. Such a delayed involvement of FA and NI in the cement chemistry should be taken into consideration with care when translating laboratory research results typically based on a 28-day strength to field practice where a shorter curing is typically provided for cost reasons. [ABSTRACT FROM AUTHOR]