Dear Shivang,

pozzolanic effect occurs thanks to amorphous allumino silicates that reacts with hydrate lime , normally from hydrolysis of Portland cement, during hydration of the binder. Low calcium fly ash has higher content of metakaolinite (allumino silicate amorphous formed during burning of coal at high temperature, more than 1300°C) so can react better than high calcium fly ash that are more similar to slag and may produce flash setting due precipitation of calcium alluminate hydrate minerals. So to answer at your doubt , no isn’t ratio Calcium to Silica , but Alumina to Silica that allows good reactivity. There is a mineralogical lack of the necessary compounds to obtain good pozzolanic effect. To make an example think about metakaolin, Microsilica , cocciopesto (laterite or meta clay) and slag or fly ash class C. The most reactive are metakaolin and Microsilica , the last for size , superficial area is obviously one of key points, but mineralogy and shape of particles is also important. Fly ash class F is a glass sphere so the real reactive materia is lower (on the crust) compared to clay mineral like metakaolin or nanomaterial like microsilica . For fly ash C the reactive minerals are even lower so reactivity for pozzolanic effect is lower, but setting time is very faster because calcium aluminates precipitation.

Hoping to be clear and useful.

Best regards

Alex Reggiani

Dear Shivang,

pozzolanic effect occurs thanks to amorphous allumino silicates that reacts with hydrate lime , normally from hydrolysis of Portland cement, during hydration of the binder. Low calcium fly ash has higher content of metakaolinite (allumino silicate amorphous formed during burning of coal at high temperature, more than 1300°C) so can react better than high calcium fly ash that are more similar to slag and may produce flash setting due precipitation of calcium alluminate hydrate minerals. So to answer at your doubt , no isn’t ratio Calcium to Silica , but Alumina to Silica that allows good reactivity. There is a mineralogical lack of the necessary compounds to obtain good pozzolanic effect. To make an example think about metakaolin, Microsilica , cocciopesto (laterite or meta clay) and slag or fly ash class C. The most reactive are metakaolin and Microsilica , the last for size , superficial area is obviously one of key points, but mineralogy and shape of particles is also important. Fly ash class F is a glass sphere so the real reactive materia is lower (on the crust) compared to clay mineral like metakaolin or nanomaterial like microsilica . For fly ash C the reactive minerals are even lower so reactivity for pozzolanic effect is lower, but setting time is very faster because calcium aluminates precipitation.

Hoping to be clear and useful.

Best regards

Alex Reggiani

Hi

Article A New Quantification Method Based on SEM-EDS to Assess Fly A...

Please see the following work, you can find some good information related to your question.

Hope this helps

Regards

Yuvaraj