Microconcrete with partial replacement of Portland cement by fly ash and hydrated lime addition

• Microconcrete with high Portland cement (OPC) replacement has been developed.
• Fly ash (FA) or fly ash-hydrated lime mixtures have been used as replacing materials.
• Addition of hydrated lime (HL) increased the extension of pozzolanic reaction of FA.
• Best mechanical behavior was found for 50/50/10 OPC/FA/HL mixtures.
• The last mixture 50/50/10 showed the presence of portlandite after 360 days.

The reduction in Portland cement consumption means lower CO2 emissions. Partial replacement of Portland cement by pozzolans such as fly ash has its limitations due to the quantity of calcium hydroxide generated in the mix. In this work we have studied the contribution of the addition of hydrated lime to Portland cement + fly ash systems. We have also studied several levels of cement replacement, ranging from 15% to 75%.The best mechanical results were obtained replacing 50% of Portland cement by the same amount of fly ash plus the addition of hydrated lime (20% respect to the amount of fly ash). In these systems, an acid-base self-neutralization of the matrix has occurred through a pozzolanic reaction of fly ash with portlandite liberated in the hydration of Portland cement and the added hydrated lime. It has been identified for these mixtures a significant amount of hydrated gehlenite, typical reaction product from rich-alumina pozzolans.