A comprehensive evaluation of sedimentary zeolites from Turkey as pozzolanic addition of cement- and lime-based binders

The pozzolanic action played by five natural zeolite-rich materials (three clinoptilolite- and one each
mordenite- and analcime-bearing rocks) coming from Turkey, has been examined, evaluating also the
influence of various chemical–physical parameters, such as grain size of the zeolitic materials and nature
of the cation present as extra-framework component of the structure. Pozzolan activity has been estimated
by the official test of the European Standards and by thermogravimetry, finding a good accordance
between the two procedures. Clinoptilolite-rich rocks gave the best results, but performance turned out
to depend on the specific surface area and pre-enrichment in a potassium form. Experimental data analysis
demonstrated that the pozzolanic reaction is kinetically controlled by the diffusion of reactants
through a layer of dense reaction products. Experimental blended cements with the five zeolite-rich rocks
were also prepared and the compressive strengths measured as a function of the curing time. The effectiveness
of the pozzolanic action was monitored by XRD and FTIR analyses. An accurate microstructural
study of the hardened pastes was also carried out and point analysis performed, pointing out that the
zeolite-lime interaction is characterized by two stages: initially zeolite subtracts calcium from the environment
by cation exchange, then it acts as a true pozzolan as soon as its structure breaks down.