Lilkov V., Petrov O., Tzvetanova Y.
Clay Minerals, June 2011, Vol. 46; N. 2, p. 225-232
DOI: 10.1180/claymin.2011.046.2.225© 2011 Mineralogical Society of Great Britain and Ireland
Abstract
Rheological, porosimetric, and SEM studies of cements with additionsof natural zeolites (chabazite, mordenite and clinoptilolite)were investigated. The addition of 5% zeolite to cement pasteshad a plastifying effect. The increase in the rheological parametersof aqueous cement–zeolite suspensions began after additionsof more than 10% zeolite. At a water/solid ratio (w/s) = 0.5all compositions exhibited similar rheological behaviour for yieldstress and maximum shear stress values. At lower w/s valuesthe rheology depended on the zeolite used, decreasing in theorder Sl (clinoptilolite, Niny Hrabovec deposit, Slovakia),M (mordenite, Philipines), Bp (clinoptilolite, Beli Plast deposit,Bulgaria), NM (clinoptilolite, Saint Cloud deposit, New Mexico)and Ch (chabazite, Nasm Yan deposit, Korea).
After 28 days of hydration the mixtures containing 10% Bp clinoptilolite, mordenite, and Sl clinoptilolite (up to 30%) had unchanged specific pore volumes but additions of 10% and 30% of chabazite and NM clinoptilolite and of 30% mordenite and Bp clinoptilolite lead to increases in the total specific pore volume compared to the neat cement paste. Between the 28th and 180th days of hydration the specificvolume of the pores in all the cement-zeolite pastes decreaseddue to the filling of the pores with products from the pozzolanicreaction between the zeolites and the hydration products ofthe cement.
The pozzolanic reaction between zeolite and the hydration products of cement is enhanced by the zeolite content in the samples and depends on the Si/Al ratio (clinoptilolite (Si/Al >4.5), mordenite (Si/Al >5), chabazite (Si/Al surface area (clinoptilolite from Slovakia has the smallest crystallites and, hence, the greatest reactive surface area).
