INFLUENCE OF METAKAOLINITE AND STONE FLOUR ON THE PROPERTIES OF SELF-COMPACTING CONCRETE

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1 Journal Journal of Chemical of Chemical Technology and and Metallurgy, 48, 2, 48, 2013, 2, INFLUENCE OF METAKAOLINITE AND STONE FLOUR ON THE PROPERTIES OF SELF-COMPACTING CONCRETE E. Todorova 1, G. Chernev 1, P. Markov 2 1 University of Chemical Technology and Metallurgy 8 Kl. Ohridski, 1756 Sofia, Bulgaria georgi_chernev@yahoo.com 2 Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, Akad. G. Bonchev str., 1113, Sofia, Bulgaria Received 11 January 2012 Accepted 20 December 2012 ABSTRACT Self-compacting concrete is the new generation composites, characterized with high filling and passing ability, as well as high resistance to segregation. The flexibility and spreading without external vibrations make these materials prefered for producing tense elements. Powder additives and chemical admixtures play an important role for structural behavior and potential abilities of this type of concrete. The aim of the present study was the manifacture and characterization of mixture for self-compacting concrete with participation of powder additives (metakaolinite and stone flour) and super plasticizers (Viscocrete 5370 and Viscocrete 5800). The influence of chemical admixtures and powder additives on concrete properties were made by the different methods: sorption ability; SЕМ; FTIR and ζ potential. Physical and mechanical properties as compressive strength; spreading and fluidity were measured. Using SEM and FTIR analyses were observed structure behavior of prepared samples. FTIR spectra showed characteristic peaks of the used components, without chemical interactions between them. SEM images showed evenly distribution of the fine fraction in concrete mixture. Tendency of decreasing sorption ability with increasing ph of the media is observed. Higher sorption ability showed mixtures with addition of chemical admixture Viscocrete With increasing amount of chemical admixture decreases ζ - potential of cement paste. Mixtures, containing metakaolinite showed higher values of strength pressure, spreading ability and fluidity. Keywords: self-compacting concrete, metakaolinite, stone flour. INTRODUCTION Self-compacting concrete (SCC) are new generation composite materials, which are characterized with high filling and passing ability and resistance against segregation [1]. They can fill complicate constructions and encapsulate reinforced bars without vibrations [2, 3]. Self-compacting concrete shows high performance, high toughness and exclusive elasticity of concrete constructions and equipment. These properties made SCC more prefered than conventional concrete. They are using for elaboration of beams, tense elements and products with 196 special geometrical forms. Self-compacting concrete are spreading free and reach difficult places. The products have perfect smooth surfaces. The only disadvantage is the higher price compared with the conventional concrete [4]. Researchers have set some guidelines for mixture proportioning of SCC, which include: reducing the volume ratio of aggregate/cementitious material; increasing the paste volume and water-cement ratio (w/c); carefully controlling the maximum coarse aggregate particle size and total volume; using various viscosity enhancing admixtures [5, 6].

2 E. Todorova, G. Chernev, P. Markov This type of concrete has not problems with rusty spots in the areas of reinforcing or corrosion of cement stone. This is because the water cannot penetrate inside. Water plays an important role for behavior of SCC. If the water is more than this in recipe, the concrete will spread and will be with reduced toughness [7]. To achieve high plasticity and to avoid segregation, it has to limit maximum size of the grains of big additive material, the amount of aggregates, their type and granulation. The small size allows decreasing amount of cement and water [8]. The shape of grains play an important role. Usually rounded grains contribute less shrinkage of composite. Powder fillers contribute compact structure [9]. This provides long-term stability and resistance against external influences. This minimized the costs for maintenance and corrections during exploitation period [10]. For manufacture of SCC were used different aggregates: gravel and fluvial sand, crushed quartz porphyry, crushed muschelkalk and crushed sand with a ratio of particles smaller than 4 mm in size that amounted to about 50 mass % [11]. The fine aggregate content is fixed at 40 percent of the mortar volume and the water /powder ratio is assumed to be by volume, depending on the properties of the powder and the superplasticizer dosage [12]. The production of SCC commonly used supplementary cementing materials (SCM), such as fly ash, slag and/or silica fume (SF), glass filler and quartzite filer. The fly ash can be metakaolinite, stone flour and ash from TPP. Silica fume is considered as one of the most effective and widely used SCM. Silica fume increases the strength pressure and concrete permeability. But workability is reduced, which made this additives inappropriate [13]. Metakaolinite (MK) is a pozzolanic material, obtained by dehydroxylation of kaolinite crystals [14]. In recent years metakaolinite was applied as mineral admixture for preparation of SCC. MK leads to improved mechanical properties and durability of the concrete. The particle size of MK is much fine than cement and prevent, the aggregation. Furthermore SCC with participation of metakaolinite showed enhanced viscosity and workability [15, 16]. Lime stone powder or stone flour (SF) is widely applied for preparation of SCC. When high volumes of SF are added to SCC mixture, the required selfcompacting properties are achieved at a lower water/ (cement +filler) ratio.the strength after 28 days is also increased, due to filler effect resulting in improved fineparticle packing with SF particles. Partial substitution of cement with SF, leads to increasing slump flow, viscosity, and compressive strength at early ages. Also SF reduce, the amount of used cement, which respectively influence at the price of prepared concrete [17-19]. The high level of consistence (workability) and stability required the usage of chemical admixtures within the concrete. The advent of superplasticizers and further developments in admixture technology made the production of SCC easier and a variety of materials may be used. These admixtures influence the ζ - potential of cement-water composition, retard the initial hydration of cement particles, forming protective layer around them [20, 21]. Super plasticizers ensure high strength toughness, hardness and resistance of the fabricate concrete. Most using admixtures are sulfonated naphthalene formaldehyde resins, sulfonated melamine formaldehyde resins, polyacrylates and complex admixtures on their base [22]. Modern superplasticizers (based on polycarboxylic ethers) promote good workability. Viscosity modifiers (or segregation controlling admixtures) can be added to increase the resistance to segregation, while still maintaining high fluidity, allowing concrete to flow through narrow spaces [23]. Viscosity-modifying admixtures (VMA) are typically high molecular mass soluble polymers. Mixed with water, their viscosity increased. These admixtures are effective in stabilizing the rheology of the fresh concrete and preventing segregation of the coarse aggregates. One of the most effective VMAs is welan gum, a natural polysaccharide which increases viscosity and maintain the stability of mixture. Welan gum is a very expensive material, which makes it inappropriate for fabrication of SCC [10]. Many different methods have been developed for characterization the properties of SCC. For determination of different workability aspects have to use combination of methods. Useful and applied methods are: Slump flow test, V-funnel test, L-box, J-ring, Penetration test, Orimet test and Sieve test [24]. The purpose of the present study was the preparation and structural characterization of mixtures for selfcompacting concrete with participation of metakaolinite and stone flour, as coarse aggregates and super plasticizers. 197

3 Journal of Chemical Technology and Metallurgy, 48, 2, 2013 EXPERIMENTAL Concrete mixture for self-compacting concrete varying nature and amount of powder additives and super plasticizers were prepared. All components and their amount are shown in Tables 1 and 2. The cement used for the fabrication of the test specimens was CEM II B-M 42.5 R. The limestone aggregates included two gravels with fraction 4-8 mm and 4-16 mm and sand of 0-2 mm. The amount of mixing water was considered with EN Powder materials used were metakaolinite and stone flour. Particles smaller than 0,125 mm contribute to the powder content. The superplasticizers were of polycarboxylate type Viscocrete 5370 and Viscocrete Their content varies between 0, 9 mass % and 1,5 mass %. The influence of studied chemical admixtures on the properties of cement in the present work was studied with the following methods: Sorption ability; SЕМ; Table 1. Prescription mixtures of concrete mixtures with participation metakaolinite. Concrete mixture C1M C2M C3M C4M C5M Cement- Titan CEM II B-M 42.5 R, kg Sand 0-5mm, kg Crushed stone, fraction 4-8, kg Crushed stone, fraction 4-16, kg Metakaolinite, kg Water, L 200/205,9 200/207,7 200/208,8 247,8/253,7 247,8/253,7 W/C 0,34 0,34 0,34 0,42 0,42 W/C 0,35 0,35 0,35 0,43 0,43 Chemical admixture, % SVC % 1,25% Chemical admixture, % SVC % 1,25% 1,5% Table 2. Prescription mixtures of concrete mixtures with participation stone flour. Concrete mixture C1B C2B C3B C4B C5B C6B C7B C8B Cement Titan CEM II B-M 42.5 R, kg Sand 0-5mm, kg Crushed stone, fraction 4-8, kg Crushed stone, fraction 4-16, kg Stone flour, kg Water, L / 175/ 166,9/ 168/ 175/ 166,9/ 166,9/ 180,9 182,1 172,8 173,9 180,9 172,2 172,8 W/C 0,33 0,3 0,3 0,28 0,28 0,3 0,28 0,28 W/C 0,31 0,31 0,29 0,29 0,31 0,29 0,29 Chemical admixture SVC 5800, % 0,9 1 1,1 1,2 Chemical admixture SVC 5370, % 0,9 1 1,1 1,2 198

4 E. Todorova, G. Chernev, P. Markov Тable 3. Spreading of concrete mixture with participation of metakaolinite. Concrete mixture C1M C2M C3M C4M C5M Speading, mm Fluidity (Pl = H2/H1) Тable 4. Spreading of concrete mixture with participation of stone flour. Concrete mixture Spreading, mm Fluidity (Pl = H2/H1) C1B C2B C3B C4B C5B C6B C7B C8B FTIR and ζ potential. Basic physical and mechanical properties as: compressive strength; spreading and fluidity were measured too. Fig. 1. Adsorption of chemical admixture Viscocrete 5370 of Portland cement by different рн of the system. Fig. 2. Adsorption of chemical admixture Viscocrete 5800 of Portland cement by different рн of the system. RESULTS AND DISCUSSION The sorption ability of the used chemical mixture at different ph on the media was investigated. From the results (Figs. 1, 2) can be concluded, that with ph increasing the sorption ability of admixture on cement particles decrease. Viscocrete 5370 (Fig.1) showed higher sorption ability. From the literature is known, that Portland cement has positive ζ potential 0, 5 mv. The increasing of the amount of superplasticizer leads to reduction of ζ -potential, at sorption amount of the polymer from 38 mg/g cement, ζ -potential reaches to -9 mv. From spectra obtained with FTIR analysis showed characteristic peaks of components, without chemical interaction between them (FTIR spectra are not shown). The results of spreading and fluidity of prepared mixtures are shown on Tables 3 and 4. The appropriate mixture for self-compacting concrete is mixture with metakaolinite and 1,25 % Viscocrete 5370, where the spreading is 590 mm. For mixtures with stone flour, most appropriate is mixture with 1,2 % Viscocrete 5800 and Viscocrete The spreading reached 580 and 600 mm. Passing ability and blocking properties of SCC can be measured using L-box. This test gives information regarding the concrete horizontal segregation resistance. Passing ability can be defined using the equation: PL = H2/H1, where H2 and H1 (mm) are the middle (medium) depth of concrete mixture in horizontal and vertical part of box, respectively. Results from tests for fluidity of concrete mixture with L-box confirm the results from spreading, that the appropriate mixture is this with participation 199

5 Journal of Chemical Technology and Metallurgy, 48, 2, 2013 Fig. 3. Variation zeta-potential of cement paste with variation amount of chemical admixture Viscocrete Fig. 4. Influence of the amount of chemical admixture on strength indicators of concrete mixtures with metakaolinite. of metakaolinite and 1,25 % Viscocrete 5370, where the value of Pl is 0,92. From the studied mixtures with stone flour, best results showed these with 1,2 % Viscocrete 5370 and Viscocrete 5800, where the value are 0,88 and 0,8. From the results for strength pressure (Figs. 4 and 5) of concrete mixture with metakaolinite and Viscocrete 5370, the highest values showed samples with admixture 1,25 % and 1,5 %, where the strength reaches 71 and 76,7 МРа. Mixtures with stone flour and 1,2 % Viscocrete 5370 and Viscocrete 5800, showed strength indicators to 65,1 and 63,3 MPa. It can be concluded from the SЕМ micrographs, that the fine fraction is evenly distributed in the volume, which due to chemical admixture Viscocrete It helps for good wetting of the particles. CONCLUSIONS It was studied the influence of two super plasticizers and coarse aggregates (metakaolinite and stone flour) on the properties of cement paste and self-compacting concrete. Sorption ability and zeta-potential of cement Fig. 5. Influence of the amount of chemical admixture on strength indicators of concrete mixtures with stone flour. Fig. 6. SЕМ images of C4B (left) and C2M (right) mixture. paste, and strength pressure, spread and fluidity of concrete mixtures were determined. The results obtained for sorption ability of chemical admixtures proved, that higher degree of sorption showed mixtures with Viscocrete рн of the system leads to lower sorption ability of cement particles. Zeta potential of cement paste becomes lower with ph increasing. Tests for mechanical and physical properties of self-compacting concrete established, that the best appropriate mixtures were these with metakaolinite and 1,25 % Viscocrete 5370, with stone flour and admixture of 1,2 % Viscocrete 5370 and Viscocrete The strength pressure reaches 71 МРа, 65,1 МРа and 63,3 МРа, respectively. SЕМ 200

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