Blended cements containing high volume of natural zeolites: Properties, hydration and paste microstructure
Highlights
► Blended cements containing high volume of natural zeolite were studied. ► Hydration characteristics and paste microstructure were investigated. ► No free Ca(OH)2 in pastes at the end of 28 days of hydration was observed. ► Crystal structure of zeolite completely decomposed at the end of 28 days of age. ► Similar 28-day compressive strength to that of reference Portland cement was found.
Introduction
Portland cement industry is responsible for approximately 7% of global CO2 emission [1]. Partial replacement of portland cements by one or more additives to obtain blended cements not only provides reduction in CO2 emission and energy saving in cement production but also supplies more durable cementitious systems to construction industry.
The extent of the benefits provided by use of blended cements increases with increasing content of additives in blended portland cements. However, the content of additives in blended portland cements, especially for natural pozzolans, is limited by some factors such as increase in water requirement and decrease in rate of strength development of the cementitious systems. It has been found that the blended cements containing high volume (55% by weight) of natural pozzolans (volcanic tuff) posses lower 28-day compressive strength when compared to the reference portland cement, although they show similar strength values at 91 days of age [2], [3]. Therefore production of high-volume natural pozzolan blended cements which are able to compete against ordinary portland cement requires natural pozzolans exhibiting significantly high strength activity.
Natural zeolites are crystalline aluminosilicates composed of a three dimensional arrangement of silicon–oxygen (SiO4) and aluminum–oxygen (AlO4) tetrahedra [4]. Zeolite group of minerals currently include more than forty naturally occurring species, and is the largest group of silicate minerals [4]. Clinoptilolite, heulandite, analcime, chabazite, and mordenite are the most common types of natural zeolite minerals on the earth. It is known that they show considerable pozzolanic activity despite their distinct crystalline structure. Pozzolanic activity of natural zeolites has been principally attributed to dissolution of zeolitic crystals of three-dimensional framework structure under the attack of OH− ions available in hydrating cementitious system [5], [6], [7], [8], [9], [10]. In a recent study, Uzal et al. [11] reported that the clinoptilolite zeolite possesses a lime reactivity which is comparable to silica fume, and higher than fly ash and a non-zeolitic natural pozzolan. They also concluded that the high reactivity of the clinoptilolite is attributable to its specific surface area for certain grinding method and duration as well as its reactive SiO2 content.
It is known that zeolitic tuffs are used in some countries as a blending component during cement production and as a mineral admixture in concrete mixtures. However the knowledge on the properties and hydration characteristics of blended cements containing natural zeolites is limited. Published the literature contains no report on properties and hydration of blended portland cements containing high volume of natural zeolites, more than 50% by weight. One of the objectives of this study is to fulfill this need.
This paper presents the results of an investigation on blended cements containing 55% by weight clinoptilolite-rich zeolitic tuffs. Zeolitic tuffs obtained from two major deposits in Turkey, Gordes and Bigadic, were finely ground so as to blend with portland cement separately. Blended cements containing 55% zeolitic tuff were obtained, and tested for setting time; Ca(OH)2 content and pore size distributions of the pastes; superplasticizer requirement and compressive strength development of mortars in comparison with the reference portland cement. In addition, the hardened blended cement pastes were examined for the crystalline products of hydration via X-ray diffraction (XRD) analysis and for the microstructural architecture using back-scattered scanning electron microscopy (BS-SEM).
Section snippets
Materials
Chemical composition and physical properties of the ordinary portland cement (PC) used in the study are shown in Table 1.
Normal consistency and setting time
Water-to-cement ratios required for normal consistency and setting time of cements are shown in Table 3. Water demand of GZ55 and BZ55 blended cements for normal consistency was approximately 60% and 40% higher than that of reference PC, respectively. Significantly increased water demand of blended cements when compared to PC is probably due to high capacity of zeolite particles to absorb water. Lower water demand of BZ55 could be attributed to lower BET surface area of BZ when compared to GZ.
Conclusions
Based on the experimental results, the following conclusions can be drawn;
- 1.
Blended cements containing large amount of clinoptilolite tuff demonstrated faster initial and final setting time than the ordinary portland cement. This fact may be related to consistency loss resulted from high water absorption of zeolite particles indicated by high water demand of blended cements for normal consistency, rather than setting of the blended system.
- 2.
In blended cement pastes, Ca(OH)2 formed from hydration of
Acknowledgements
The authors would like to thank Prof. Hayrettin Yücel (Dept. of Chemical Engineering), Prof. M. Cemal Göncüoğlu (Dept. of Geological Engineering) and Prof. Ali Çulfaz (Dept. of Chemical Engineering) at Middle East Technical University for their helpful comments on the characterization of zeolitic tuffs used in the study. This study was funded by The Scientific & Technological Research Council of Turkey under Project No: 104M393. The instrumental analyses in the study were carried out in Middle
References (28)
- et al.
Studies on blended cements containing a high volume of natural pozzolans
Cem Concr Res
(2003) - et al.
Effect of material characteristics on the properties of blended cements containing high volumes of natural pozzolans
Cem Concr Res
(2004) - et al.
Kinetics and mechanism of reaction in the zeolitic tuff-CaO–H2O systems at increased temperature
Cem Concr Res
(1978) - et al.
Natural zeolites as constituents of blended cements
- et al.
Properties of alkali-activated clinoptilolite
Cem Concr Res
(2000) - et al.
A study on the hydration rate of natural zeolite blended cement pastes
Constr Build Mater
(1999) - et al.
The effect of natural zeolites on the hydration of portland cement
Micropor Mesopor Mater
(2003) - et al.
Pozzolanic activity of clinoptilolite: a comparative study with silica fume, fly ash and a non-zeolitic natural pozzolan
Cem Concr Res
(2010) Effect of drying on cement-based materials pore structure as identified by mercury intrusion porosimetry a comparative study between oven-, vacuum-, freeze–drying
Cem Concr Res
(2001)- et al.
The effect of zeolite on the properties and hydration of blended cements
Cem Concr Compos
(2010)
Some advances in understanding the pozzolanic activity of zeolites: the effect of zeolite structure
Cem Concr Compos
Time evolution of a natural clinoptilolite in aqueous medium: conductivity and pH experiments
Micropor Mesopor Mater
Effect of large amounts of natural pozzolan addition on properties of blended cements
Cem Concr Res
Use of natural zeolite as a supplementary cementitious material
Cem Concr Compos
Cited by (85)
Solidification of radioactive spent liquid scintillator wastes: Effect of additives on the leaching of radionuclides
2024, Nuclear Engineering and DesignMechanical, electrochemical (EIS), and microstructural characterization of reinforced concrete incorporating natural volcanic pozzolan
2023, Case Studies in Construction MaterialsEvaluation of zeolite as supplementary cementing material
2023, Materials Today: ProceedingsMechanical performance and feasibility analysis of green concrete prepared with local natural zeolite and waste PET plastic fibers as cement replacements
2022, Case Studies in Construction MaterialsVariation in mineral composition by hydration and carbonation in calcium hydroxide matrix containing zeolite
2022, Journal of Building EngineeringMechanical activation of diabase and its effect on the properties and microstructure of Portland cement
2022, Case Studies in Construction Materials
- 1
At the time of the study, the author was a Ph.D. Candidate at the Department of Civil Engineering, Middle East Technical University, Ankara, Turkey.