Effect of Natural Zeolite as Partial Replacement of Portland Cement on Concrete Properties

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1 Effect of Natural Zeolite as Partial Replacement of Portland Cement on Concrete Properties Eva Vejmelková 1, Tereza Kulovaná 1, Dana Koňáková 1, Martin Keppert 1, Martin Sedlmajer 2, Robert Černý 1 1 Czech Technical University in Prague, Faculty of Civil Engineering, Czech Republic 2 Brno University of Technology, Faculty of Civil Engineering, Czech Republic Abstract: Natural zeolites are supposed to be an effective Supplementary Cementitious Materials due to its chemical composition and very fine microstructure. In this paper, selected mechanical, thermal and hygric, properties of several concrete mixes containing natural zeolite (clinoptilolite) as partial substitution of Portland cement are presented and compared with reference concrete. However, it is shown that although from both environmental and economic points of view it would be desirable to use highest possible amount of zeolite in concrete production, the extent of Portland cement replacement in concrete mixtures has certain limits. The studied zeolite with high clinoptilolite content is probably not a good choice for HPC concrete. Keywords: natural zeolite, Portland cement, mechanical properties, thermal properties, hygric properties 1. Introduction During production of Portland cement carbon dioxide which is one of the greenhouse gases is emitted to the atmosphere. Approximately 1 tone of CO 2 arises during the production process of 1 tone of Portland cement; about one-half of it originates from decomposition of limestone, which is the main raw material for Portland clinker, and the second half from fuel combustion necessary for cement production [1]. Therefore, with respect to a necessity to decrease the amount of carbon dioxide in atmosphere, alternative materials have a high potential to replace a part of Portland cement in concrete. Certain natural materials were used as supplementary cementitious materials (SCM) since ancient times, due to their pozzolanic properties. In the ancient Rome, fine volcanic pozzolanic ashes were used in a mixture with lime. At present natural pozzolanas are used as SCM for Portland cement concrete mainly in the countries where they are easily available. Natural zeolites are probably the most often used natural SCM; likely the largest importance have natural zeolite rocks as cement blendings in China [2]. The zeolite-admixture is known to reduce the sulfate attack as well as the ASR damage due to the zeolite ionic exchange ability [3]. However, zeolite concrete is a much less frequent subject of investigation as compared for instance with silica fume, metakaolin, fly ash or ground granulated blast furnace slag as SCM. This paper aims to contribute to characterization of a Slovak zeolite containing concrete from the point of view of building materials engineering. Selected mechanical, thermal and hygric properties of several concrete mixes containing natural zeolite as SCM are studied and compared with reference concrete. Since each natural zeolite rock is different an optimum dosage has to be searched individually. 2. Materials The high performance concrete mixtures presented in Table 1 were prepared with Portland cement CEM I 42.5 R as the main binder; its specific surface area was 341 m 2 kg -1. A part of cement was substituted by natural zeolite Zeobau 200 from Nizny Hrabovec quarry (Slovakia) with clinoptilolite as dominant component; its specific surface area was 227 m 2 kg -1. All the fresh concrete mixtures were prepared in a way to obtain a constant consistency (similar slump test - S 2) [4]. The chemical composition of cement and natural zeolite (Table 2) were determined on the instrument IPC JY ACTIVA, sulphates were determined according to Czech Standard [5], loss of drying according to Czech Standard [6] and loss of ignition according to Czech Standard [7]. The measurement of material parameters of hardened concrete mixes was done after 28 days of standard curing. It took place in a conditioned laboratory at the temperature of 22±1 C and 25-30% relative humidity.

2 Table 1. Composition of studied concretes. Component Composition [kgm -3 ] CZ2 ref CZ2 10 CZ2 20 CZ2-40 CZ-60 CEM I 42,5 R - Mokrá Natural zeolites - 35 (10%) 70 (20%) 140 (40%) 210 (60%) ZEOBAU 200 Aggregates 0-4 mm Aggregates 4-8 mm Aggregates 8-16 mm Plasticizer Mapei N Plasticizer Dynamon SX water Table 2. Chemical composition of cement and zeolite. Component Amount [%] Cement Natural zeolite SiO Al 2O Fe 2O CaO MgO K 2O Na 2O TiO P 2O SO Experimental methods 3.1 Basic physical parameters Among the basic properties, the bulk density, matrix density and open porosity using the gravimetric and vacuum saturation method were measured [8]. Each sample was dried in a drier to remove majority of the physically bound water. After that the samples were placed into the desiccator with deaired water. During three hours air was evacuated with vacuum pump from the desiccator. The specimen was then kept under water not less than 24 hours. From the mass of the dry sample m d, the mass of water saturated sample m w, and the mass of the immersed water saturated sample m a and the volume V of the sample was determined from the equation

3 V m w m a, (1) l where ρ l is the density of water. The open porosity ψ 0, the bulk density ρ and the matrix density ρ mat were calculated according to the equations m m w d, (2) 0 V l m d, (3) V m d. (4) mat V 1 0 In the experimental work 5 specimens of 50 x 50 x 50 mm were used. 3.2 Characterization of porous system Characterization of pore structure was performed by mercury intrusion porosimetry. The experiments were carried out using the instruments PASCAL 140 and 440 (Thermo Scientific). The range of applied pressure corresponds to pore diameter from 20 nm to 100 μm. Since the size of the specimens is restricted to the volume of approximately 1 cm 3 and the studied materials contained some aggregates about the same size, the porosimetry measurements were performed on samples without coarse aggregates. In the experimental work 3 specimens of 10 x 10 x 10 mm were used. 3.3 Mechanical paremeters The measurement of compressive and bending strength was done by the electromechanical testing device VEB WPM Leipzig 3000 kn having a stiff loading frame with the capacity of 3000 kn. The tests were performed according to ČSN EN In the experimental investigation of bending strength 3 specimens of 100 x 100 x 400 and in the case of compressive strength 3 specimens mm of 150 x 150 x 150 mm were used. 3.4 Water transport parameters The water sorptivity was measured using a standard experimental setup [8]. The specimen was water and vapor-proof insulated on four lateral sides and the face side was immersed 1-2 mm in the water. Constant water level in tank was achieved by a Mariotte bottle with two capillary tubes. One of them, inside diameter 2 mm, was ducked under the water level, second one, inside diameter 5 mm, was above water level. The automatic balance allowed for recording the increase of mass. The water absorption coefficient A [kgm -2 s -1/2 ] was calculated using the formula i A t, (5) where i [kgm -2 ] is the cumulative water absorption, t is the time from the beginning of the suction experiment. The water absorption coefficient was then used for the calculation of the apparent moisture diffusivity in the form

4 2 A app, w w c 0 (6) where wc is the saturated moisture content [kgm -3 ] and w 0 the initial moisture content [kgm -3 ]. In the experimental work 5 specimens of 150 x 150 x 20 mm were used. 3.5 Water vapor transport parameters Two versions of the common cup method were employed in the measurements of the water vapor diffusion coefficient [9]. In the first one the sealed cup containing silica gel (5 % relative humidity) was placed in a controlled climatic chamber with 50% relative humidity and weighed periodically. In the second one the cup water (97 % relative humidity) was placed in the 50% relative humidity environment. The measurements were done at 20C in a period of two weeks. The steady state values of mass gain or loss were determined by linear regression for the last five readings. The water vapor diffusion coefficient D [m 2 s -1 ] was calculated from the measured data according to the equation D m d R T S M p p, (7) where m the amount of water vapor diffused through the sample [kg], d the sample thickness [m], S the specimen surface [m 2 ], the period of time corresponding to the transport of mass of water vapor m [s], p p the difference between partial water vapor pressure in the air under and above specific specimen surface [Pa], R the universal gas constant, M the molar mass of water, T the absolute temperature [K]. On the basis of the diffusion coefficient D, the water vapor diffusion resistance factor was determined: D a, (8) D where D a is the diffusion coefficient of water vapor in the air. The samples were on four lateral sides water- and water vapor-proof insulated with epoxy resin to ensure the one-dimensional transport. In the experimental work 5 specimens of 150 x 150 x 20 mm were used. 3.6 Thermal parameters Thermal conductivity and specific heat capacity were measured using the commercial device ISOMET 2104 (Applied Precision, Ltd.). The measurement is based on analysis of the temperature response of the analyzed material to heat flow impulses. The heat flow is induced by electrical heating using a resistor heater having a direct thermal contact with the surface of the sample. ]. In the experimental work 3 specimens of 70 x 70 x 70 mm were used. 4. Experimental results 4.1 Basic physical parameters The basic physical parameters of studied materials are shown in Table 3. The bulk density of the analysed concretes decreased with the increasing amount of natural zeolite by 10% when compared the highest substitution level with the reference concrete. The open porosity increased by 60% in the corresponding way. The values of matrix density were almost the same (within a 2% limit) for all studied concretes.

5 Table 3. Basic physical properties of studied concretes. Materials b mat [kg m -3 ] [kg m -3 ] [%] CZ-ref CZ CZ CZ CZ Characterization of porous system The results of mercury intrusion porosimetry are presented in Figure. 1. The measurement revealed that increase of porosity with increasing zeolite content was mostly due to the growing volume of fine pores. Hydration of pozzolanic admixtures in concrete generally cause refinement of pore system but with respect to the strength measurement more likely seems to be explanation that at least part of the added zeolite did not take an active part on the hydration process and remained in the concrete structure in its initial state; i.e. the observed increasing pore volume is due to preserved porous microstructure of the zeolite. 4.3 Mechanical parameters Table 4 shows the mechanical properties of five studied concretes after 28 days. The replacement of Portland cement by natural zeolite caused to significant decrease in compressive strength. For CZ60 the compressive strength was more than two times lower as compared with the reference concrete mixture CZ-ref which was not satisfactory. Fortunately smaller strength difference between control and zeolitecontaining mixtures can be expected at longer time scale [10]. The compressive strength was affected in

6 much higher extent than bending strength. The values of bending strength decreased for material with the highest content of pozzolana admixture up to 30%. Table 4. Mechanical properties of studied concretes (28 days). Materials Bending strength Compressive strength [MPa] [MPa] CZ-ref CZ CZ CZ CZ Water transport parameters The results of water sorptivity measurements are presented in Table 5. They were in a very good qualitative agreement with the open porosity data (Table 3). The liquid water transport parameters systematically increased with the increasing amount of natural zeolite in the mixture. This is a negative trend, in general. The absorption coefficient of CZ-60 was about eight times higher than reference concrete CZ-ref and the value of the apparent moisture diffusivity increased by about 31 times. Table 5. Water transport properties of studied concretes. Materials Absorption coefficient Apparent moisture diffusivity [kgm -2 s -1/2 ] [m 2 s -1 ] CZ-ref E-09 CZ E-09 CZ E-09 CZ E-09 CZ E Water vapor transport parameters The water vapor transport parameters of the studied concretes are shown in Table 6. Table 6. Water vapor transport properties of studied concretes. Materials 5/50% 97/50% D D [s] [m 2 s -1 ] [-] [s] [m 2 s -1 ] [-] CZ-ref 2.45E E E E CZ E E E E CZ E E E E CZ E E E E CZ E E E E

7 The experimental data show that the water vapor diffusion resistance factor of studied materials decreased with increasing amount of natural zeolite in the mixture which was in accordance with the open porosity data in Table 3. The measured data revealed basic information that the values of water vapor diffusion coefficient corresponding to the lower values of relative humidity (5/50 %) were always lower than those for higher relative humidity values (97/50 %). This is in accordance with the previous measurements on many other materials including concrete [11]. The main reason for this finding is coupling of water vapor transport with liquid water transport in a material with higher relative humidity where the capillary condensation takes place in a much higher extent than in the range of lower relative humidity [12]. 4.6 Thermal parameters The thermal properties of studied concretes in dry and saturated state show Table 7 and Table 8. Table 7. Thermal properties of studied concretes in dry state. Materials c [Wm -1 K -1 ] [10 6 Jm -3 K -1 ] CZ-ref CZ CZ CZ CZ The thermal conductivity decreased with the increasing amount of natural zeolites. This is in a qualitative agreement with open porosity results (Table 3). Table 8. Thermal properties of studied concretes in saturated state. Materials c [Wm -1 K -1 ] [10 6 Jm -3 K -1 ] CZ-ref CZ CZ CZ CZ The values of volumetric heat capacity decreased with the increasing amount of zeolites. However, the maximum difference was about 5%, as compared with the reference concrete CZ-ref which was within the error range of the measurement method. The thermal parameters data in Table 8 show that the studied materials in saturated state had systematically higher values of thermal conductivity than in dry state and lower values with higher content of zeolite. This is in a qualitative agreement with the open porosity data in Table 3. The volumetric heat capacity increased with increasing moisture content which was related to the high specific heat capacity of water. 5. Conclusions Natural zeolite can be considered as an environmental friendly admixture with a potential to replace part of Portland cement in concrete in building industry. The tested zeolite featured by significant slowdown of hydration process resulting in negative influence on 28-days strength. The kinetics of hydration could be improved by alkaline ionic exchange [13]. The admixing of zeolite caused increase of porosity which

8 influenced correspondingly the liquid water and water vapor transport properties as well as the thermal conductivity of concrete. 6. Acknowledgement This research has been supported by the Czech Science Foundation, under project No P104/12/ References 1. Hasanbeigi, A. Price, L., Lin, E Emerging energy-efficiency and CO2 emission-reduction technologies for cement and concrete production: A technical review. Renewable and Sustainable Energy Reviews, Vol. 16, Feng, N.-Q., Peng, G.-F Applications of natural zeolite to construction and building materials in China. Construction and Building Materials, vol. 19, Karakurt, C., Topcu, I.B Effect of blended cements produced with natural zeolite and industrial by-products on alkali-silica reaction and sulfate resistance of concrete. Construction and Building Materials, vol. 25, EN 206-1: Concrete - Part 1: Specification, performance, production and conformity. 5. ČSN EN Testing fresh concrete: Slump test. Czech Standardization Institute. Prague ČSN : Basic analysis of silicates - Determination of sulphate sulphur. Czech Standardization Institute. Prague ČSN : Basic analysis of silicates - Determination of loss by drying. Czech Standardization Institute. Prague Roels, S., Carmeliet, J., Hens, H., Adan, O., Brocken, H., Černý, R., Pavlík, Z., Hall, C., Kumaran, K., Pel, L. & Plagge, R Interlaboratory Comparison of Hygric Properties of Porous Building Materials, Journal of Thermal Envelope and Building Science 27: Kumaran, M.K Moisture Diffusivity of Building Materials from Water Absorption Measurements. Journal of Thermal Envelope and Building Science, 22: Yılmaz, B., Ucar, A., Oteyaka, B., Uz, V Properties of zeolitic tuff (clinoptilolite) blended portland cement. Building and Environment, Vol. 42, Kumaran M.K IEA Annex 24 Final Report, Vol. 3, Task 3: Material Properties. KU Leuven, Leuven. 12. Černý R, Rovnaníková P Transport Processes in Concrete. Spon Press, London. 13. Snellings, R., Mertens, G., Hertsens, S., Elsen, J The zeolite lime pozzolanic reaction: Reaction kinetics and products by in situ synchrotron X-ray powder diffraction. Microporous and Mesoporous Materials, Vol. 126,