Baza Publikacji Pracowników Politechniki Lubelskiej
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Synthetic zeolites that are obtained from the hydrothermal reaction of NaOH with fly ash have a well-defined pore structure
and pozzolanic properties. This work examines the effect of the low-silica (Na-A) and high-silica (ZSM-5) zeolite structure
on the kinetics of alite hydration and mineralogical characteristics of the reaction products. The addition of the Na-A and
ZSM-5 zeolites reduced the rate of heat release during the hydration reaction, which is typical for commonly used pozzo-
lanic additives. The ZSM-5 zeolite had a much higher Si/Al ratio relative to the Na-A zeolite, which translated into a higher
pozzolanic activity and resulted in greater stability of the hydration reaction kinetics. The addition of zeolites caused the
heat of hydration to decrease compared to the reference pastes (the alite reference paste—206 J/g): Na-A 15%—148.9 J/g;
ZSM-5 15%—149.9 J/g. The concentration of calcium ions in the alite solution and the content of active silica were identified
as the most important parameters affecting the kinetic, morphological, and structural characteristics of the C–S–H phase.
The addition of zeolites increased the amount of C–S–H gel phases formed. At the same time, the proportion of portlandite
in the hydration products of the alite–zeolite systems decreased. Pozzolans reduced the ratio of CaO/SiO2 in the C–S–H
phase, which for pastes with the addition of the Na-A ranged from 1.61 to 1.37, and for the ZSM-5 from 1.91 to 0.47. This
ratio decreased with the dosage and the age of alite paste. In summary, this research has shown that synthetic zeolites are a
viable pozzolanic additives.