Abstract
The effects of elevated temperatures on the properties of high-strength cement paste (HSCP) based on metakaolin (MK), silica fume (SF), and fly ash (FA) were studied in the current experimental research. The resistance of HSCP against elevated temperatures was evaluated as well. The new method is expressed by the total area under each curve of strength, known as “temperature resistance”, is adopted. Results of the HSCP mixtures containing MK, SF, and FA with replacements ratios of 9%, 6% and 15% have shown excellent temperature resistance at all levels of maximum temperatures, respectively. Properties added to HSCP by these supplementary cementitious materials (SCM) such as decreasing the amount of CaO and increasing the amounts of SiO2 and Al2O3 have minimized the harmful effects of the use of pure ordinary Portland cement (OPC) at elevated temperatures. The results have shown also that the grinding fineness of OPC influences the amount of optimum replacement of the used SCM on HSCP at elevated temperatures. Hence, the amount of optimum replacement of MK blended with CEM I 42.5 N was 9% whereas, the amount of optimum replacement of MK blended with CEM I 52.5 N shifted to 3%. Finally, the fineness of cement of 4500 cm2 g−1 has shown a better-elevated temperature resistance compared to the cement with a fineness of 4000 cm2 g−1 in case of using pure OPC.
Highlights
The production of high strength concrete (HSC) has been one of the essential incentive research for engineers and researchers in terms of enhancing the performance and durability of concrete [1]
The particles of the used supplementary cementitious materials (SCM) are very small compared to the ordinary Portland cement (OPC) particles, resulting in high specific surface area, silica fume (SF) that contains hundreds of small spherical particles that together reach the size of one particle of OPC
This could be contributed to the chemical processes occurring in the high-strength cement paste (HSCP) with 0% MK (which contains a high content of Ca(OH)2 compared to mixtures that contain MK)
Summary
The production of high strength concrete (HSC) has been one of the essential incentive research for engineers and researchers in terms of enhancing the performance and durability of concrete [1]. No available studies have investigated the influence of cement fineness on the amount of optimum replacement of SCM at elevated temperatures exposure. The significance of this study is clear since the results testing, comparing, and discussing of the effects of the three SCM, i.e., MK, SF, and FA materials on highstrength cement paste (HSCP) after the exposure to elevated temperatures is presented . The investigated powders are taken from the samples that showed high performance after exposure to elevated temperatures (optimum replacements of SCM), as well as the mixtures of pure OPC (reference) for the comparison. SEM investigations have helped to discover and understand the microstructure properties of hardened cement paste containing different ratios of SCM (reference and optimum mixtures) before and after the exposure to high temperatures. The samples containing different ratios of SCM (reference and optimum) have been investigated under CT equipment to evaluate the distribution and the volume of pores in hardened cement paste
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