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Öğe Blended cements containing high volume of natural zeolites: Properties, hydration and paste microstructure(ELSEVIER SCI LTD, 2012) Uzal, B.; Turanli, L.In this study, properties and hydration characteristics as well as paste microstructure of blended cements containing 55% by weight zeolitic tuff composed mainly of clinoptilolite mineral were investigated. Free Ca(OH)(2) content, crystalline hydration products and decomposition of zeolite crystal structure, pore size distribution and microstructural architecture of hydrated cement pastes were examined. Superplasticizer requirement and compressive strength development of blended cement mortars were also determined. The blended cements containing high volume of natural zeolites were characterized with the following properties: (i) no free Ca(OH)(2) in hardened pastes at the end of 28 days of hydration, (ii) less proportion of the pores larger than 50 nm when compared to portland cement paste, (iii) complete decomposition of crystal structure of zeolite at the end of 28 days oil. hydration, (iv) presence of tetra calcium aluminate hydrate as a crystalline product of pozzolanic reaction, (v) more compatibility with the melamine-based superplasticizer when compared to the naphthalene based product, and (vi) similar 28 days compressive strength of mortars to that of reference portland cement. (C) 2011 Elsevier Ltd. All rights reserved.Öğe Characteristics of calcined natural zeolites for use in high-performance pozzolan blended cements(ELSEVIER SCI LTD, 2014) Kucukyildirim, E.; Uzal, B.Two natural zeolites with different characteristics were calcined at various temperatures in order to improve the benefits provided by their use in blended cements as cement replacement material. Natural zeolites were firstly characterized for their crystallinity by X-ray diffraction analysis, specific surface area by nitrogen absorption, and pozzolanic activity by electrical conductivity method, before and after the calcination. In order to assess the performance of calcined natural zeolite as cement replacement material, blended Portland cement pastes and mortars with raw and calcined zeolites were tested for their water requirement, free lime content, pore size distribution and compressive strength. The experimental results indicated that calcined zeolites are more desirable with lower water requirement and higher strength performance as cement replacement material than the raw zeolites. Blended cement with calcined natural zeolite showed higher compressive strength performance, when compared to that with the raw zeolite due to decreased porosity and refined pore structure of the hardened cementitious system. (C) 2014 Elsevier Ltd. All rights reserved.Öğe Evaluation of natural zeolite as a viscosity-modifying agent for cement-based grouts(PERGAMON-ELSEVIER SCIENCE LTD, 2008) Sahmaran, M.; Ozkan, N.; Keskin, S. B.; Uzal, B.; Yaman, I. Oe.; Erdem, T. K.The effects of natural zeolite on the theological and workability properties of the grout mixtures were studied. Setting times of grouts were also determined as part of the experimental study. For comparison, grout mixtures were also prepared with a commercially available viscosity modifying admixture (VMA). The experimental results show that addition of natural zeolite modifies both the rheological and workability properties of grouts. For a constant superplasticizer (SP) content, an increase in the zeolite amount significantly increases the yield stress, the apparent and plastic viscosity, and reduces the fluidity and deformability. Moreover, an increase in the amount of SP causes a significant reduction in both the yield stress and plastic viscosity of the grouts. It was also observed that, grouts prepared with natural zeolite addition have a pseudo-plastic behavior, and shear-thinning behavior increases with an increase in the zeolite amount. Therefore, it has been shown that using natural zeolite as a VMA it is possible to obtain grouts that have satisfactory theological properties, especially if natural zeolite is used in combination with a superplasticizer. (c) 2008 Elsevier Ltd. All rights reserved.Öğe Pozzolanic activity of clinoptilolite: A comparative study with silica fume, fly ash and a non-zeolitic natural pozzolan(PERGAMON-ELSEVIER SCIENCE LTD, 2010) Uzal, B.; Turanli, L.; Yucel, H.; Goncuoglu, M. C.; Culfaz, A.Pozzolanic activity of clinoptilolite, the most common natural zeolite mineral, was studied in comparison to silica fume, fly ash and a non-zeolitic natural pozzolan. Chemical, mineralogical and physical characterizations of the materials were considered in comparative evaluations. Pozzolanic activity of the natural zeolite was evaluated with various test methods including electrical conductivity of lime-pozzolan suspensions; and free lime content, compressive strength and pore size distribution of hardened lime-pozzolan pastes. The results showed that the clinoptilolite possessed a high lime-pozzolan reactivity that was comparable to silica fume and was higher than fly ash and a non-zeolitic natural pozzolan. The high reactivity of the clinoptilolite is attributable to its specific surface area and reactive SiO(2) content. Relatively poor strength contribution of clinoptilolite in spite of high pozzolanic activity can be attributable to larger pore size distribution of the hardened zeolite-lime product compared to the lime-fly ash system. (C) 2009 Elsevier Ltd. All rights reserved.
