Abstract:
Volcanic pozzolans are vitreous or poorly crystallized materials rich in SiO2 and Al2O3 that react with the portlandite generated during cement hydration to yield hydrated calcium silicates and aluminates with low solubility and good cementitious properties (pozzolanic reaction). The purpose of the present study was to analyze the reaction between calcium hydroxide and two natural, partially crystalline pozzolans found in Cuba, characterize the C-S-H gels produced and determine the relationship between pozzolan composition and structure and its capacity to fix calcium. The findings of the XRD and FTIR analyses conducted with this aim included a gradual decline of the zeolite (heulandite and faujasite) peaks on the diffractograms with reaction time, and changes in the IR absorption bands attributed to the zeolites, along with the appearance of new bands indicative of the formation of the CSH gel. Although the amount of Ca fixed by the two pozzolans after 90 days was similar, the reaction rate was faster in the Los Congos material. The gel forming in the Carolinas sample had Al in its composition, with Q3 (1Al) and Q2 (1Al) units whose content increased with time. The presence of Fe in the Los Congos sample hampered the analysis of the gel formed, although the presence of Al in its composition could be inferred from the 27Al MAS NMR data. The thermodynamic data showed that C-S-H gel was formed in both cases. © 2005 Elsevier B.V. All rights reserved.
