Strength development and microstructural characterization of eco-cement paste with high-volume fly ash

• Locally and abundantly available fly ash could be used to replace up to 80 % of cement in eco-cement pastes. • Long-term strength development, shrinkage behavior, and microstructure of eco-cement pastes were characterized. • Analysis of both economic and environmental impacts was performed to promote sustainable development. • The chemical reaction mechanism of a blended cement-fly ash system has been clarified to gain a piece of full knowledge. • Utilization of high-volume fly ash brings many advantages in technical, environmental, and economical features. Manufacturing cement is one of the construction activities that produces a large amount of CO 2 emissions. Replacing cement with by-products such as fly ash (FA) is one approach for sustainable development. In this research, a more significant amount of cement was replaced by FA to prepare an eco-cement paste. The amount of FA ranged from 0 to 80 % with an interval of 20 %. The mechanical behaviors of eco-cement pastes were assessed via compressive strength and drying shrinkage. Then, the microstructural investigations, including scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR), were used to explain the mechanical properties. Results indicate that the increase in FA amount resulted in a significant reduction in compressive strength. However, the strength gain showed an increment trend with an increase in FA amount. From 7 to 120 days, the strength gain increased from 25.7 to 86.3 % when FA content ranged from 0 to 80 %. The increment in FA amount leads to a considerable reduction in the drying shrinkage of cement pastes. There are strong correlations expressed by exponential functions between drying shrinkage and curing period with a high coefficient of determination for all pastes. The higher strength gain obtained in the paste with FA inclusion is explained by the higher cement hydration and pozzolanic reaction, which is detected by SEM investigation. This is because with FA incorporation, cement is diluted, and FA particles play as nucleation sites for product formation of cement hydration. SEM, XRD, and FTIR results could explain and validate the results obtained from the compressive strength and drying shrinkage tests. The chemical reaction mechanism of cement-FA paste has also been presented. The replacement of cement with FA not only has a benefit in reducing environmental impacts but also gives an advantage regarding economic features by decreasing total material cost. This study provides a systematic assessment of the application of eco-cement paste with a high-volume FA. It can be stated that it is possible to utilize up to 80 % cement replacement by FA. Utilizing FA with high volume brings many advantages in terms of technical, environmental, and economic features.