‘Buffer’ effects of natural zeolites in blended cements

Author(s): R. Snellings
Paper category: Conference
Book title: Concrete Repair, Rehabilitation and Retrofitting III (ICCRRR)
Editor(s): M.G. Alexander, H.-D. Beushausen, F. Dehn, P. Moyo
Print ISBN: 978-0-415-89952-9
Publisher: Taylor & Francis Group
Pages: 504- 505
Total Pages: 2
Language: English

Abstract: 
One of the primary sources of natural supplementary cementitious materials are natural zeolite deposits. Natural zeolites present interesting potential both in terms of pozzolan reactivity and availability. Additionally to being consumed in the pozzolanic reaction, the unreacted zeolite fraction interacts with the cement pore solution and the internal cement environment as a water regulator and cation exchanger.
Zeolites can reversibly adsorb and release large amounts of water up to 20% of their weight or more. The uptake of water depends on the availability of water in the surrounding environment. The initial expansion of the zeolite lattice parameters as observed by in situ XRD measurements during the hydration of blended cements show that zeolites respond to the introduction of liquid water by adsorbing water into the zeolite microporous framework. In this manner, the effective water/cement ratio and the macroporosity of the system are reduced. Subsequently, the water contained in the zeolites will be released when the latter are consumed in the pozzolanic reaction or when the availability of water in the binder starts to drop. In this respect, zeolites can be considered as water carriers that gradually liberate their water over the hydration period to promote the completion of the hydration reactions.
Natural zeolites also thoroughly affect the pore solution chemistry of blended cements. Chemical analysis (AAS and ICP-OES) of the pore solutions in a range of zeolite blended cements show that the addition of zeolites generally increases alkali, Si and Al levels and decreases Ca concentrations in the pore solution. It was observed that the evolution of the pore solution is considerably affected by the zeolite type. The alkali concentration in the contact fluid is affected by the extra-framework cation content and the cation exchange characteristics of the zeolite. Most common natural zeolites (i.e. heulandite- clinoptilolite, mordenite, phillipsite, chabazite) selectively take up K and release Na and Ca to the pore solution.

Online publication: 2014
Publication Type: abstract_only
Public price (Euros): 0.00