Ultrafine grinding of fly ash with grinding aids: Impact on particle characteristics of ultrafine fly ash and properties of blended cement containing ultrafine fly ash

• Grinding aid (GA) improves the particle characteristics of ultrafine fly ash (UFFA).
• Pozzolanic reaction degree and activity index of UFFA are also improved by GA.
• Properties of blended cement containing UFFA with GA are better than without GA.
• UFFA with GA improves the hydration process and microstructure of blended cement.

This paper presents the ultrafine grinding performance of fly ash with grinding aids (GA) and effect of GA on the particle characteristics, pozzolanic reaction degree of ultrafine fly ash (UFFA) and properties of blended cement containing UFFA. The experimental results indicate that GA can improve the particle characteristics of ground fly ash. The specific surface area of UFFA with 0.05 wt% GA is higher by 104 m2/kg than control sample. The particle size distribution of UFFA with GA becomes narrow and particle content of less than 16 μm is obviously increased. Additionally, the fluidity and loose bulk density of UFFA have also been improved. For pozzolanic reaction degree, 3-day, 7-day and 28-day hydration degree of UFFA with GA is increased by 1.2%, 2.3% and 4.6%, respectively; and 3-day, 7-day and 28-day activity index of UFFA with GA is also increased by 6%, 8% and 9%, respectively. For properties of blended cement containing UFFA, enhancement effect of UFFA with GA on the strength of blended cement containing 20 wt%, 30 wt% and 40 wt% fly ash are significant, and 3-day strength is increased by 12.6%, 6.6% and 6.6%, respectively, 28-day strength is increased by 6.5%, 9.3% and 10.5%, respectively. In this study, the hydration degree and microstructure of blended cement containing UFFA paste are also analyzed by SEM, XRD, IR and TG-DTA. The studies show that improvements such as hydration degree, products quantity, uniformity and compactness of products structure of blended cement containing UFFA are attributed to finer particle size and better particle size distribution caused by the addition of GA.