THE INFLUENCE OF PROPERTIES AND CONTENT CEMENT PASTE S ON RHEOLOGY OF SELF-COMPACTING HIGH PERFORMANCE CONCRETES

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1 THE INLUENCE O PROPERTIES AND CONTENT CEMENT PASTE S ON RHEOLOGY O SEL-COMPACTING HIGH PERORMANCE CONCRETES Jacek Gołaszewski 1, Aleksandra Kostrzanowska 2 1 Silesian University of Technology, aculty of Civil Engineering, ul. Akademicka 5, Gliwice, Poland. jacek.golaszewski@polsl.pl 2 Silesian University of Technology, aculty of Civil Engineering, ul. Akademicka 5, Gliwice, Poland. aleksandra.kostrzanowska@polsl.pl Abstract. The influence of rheological properties cement paste s expressed by parameters: the slump flow value and the time slump flow value as well and the influence of the paste content in concrete mixture expressed by the ratio of filling the aggregate s crumb pile with paste φ kz on the rheological properties of mixture for self-compacting high performance concrete with a crushed type of coarse aggregates (D max = 16 mm) and its changes with time are presented and discussed in the paper. The researches are included cement pastes and concrete mixtures in the ratio w/b in the range from 0,30 to 0,38 which are made on the basis of portland cement CEM I 42.5 R with the addition of the silica fume S (0; 5; 10 % by the mass of binder) and admixture of superplasticizer (2,5; 3,0; 3,5 % by the mass of binder). Rheological properties of the concrete mixture is also formed by the ratio of filling the aggregate s crumb pile with paste φ kz in the range from 1,2 to 1,4. Rheological parameters are measured using rheometrical test while the technological parameters are measured using technological test. The analysis of results shows that the regression function of the influence of the rheological parameters the cement paste and the ratio φ kz on the rheological parameters of self-compacting high performance concrete mixtures can be formulated as a second degree polynomial. This equation is characterized by high matching estimators and materiality. The conclusion reached is that the rheological properties of cement paste and the paste content in concrete mixture expressed by the ratio φ kz significantly affect the rheological properties of self-compacting high performance concrete mixtures. The analysis of the significant impact shows that among tested factors, the highest influence on the rheological properties of paste and mixture has a w/b ratio, and then the volume of silica fume, time and superplasticizer volume. Keywords:. self-compacting high performance concrete, rheology, rheological properties, concrete, cement paste. 1. Introduction The most important characteristic of self-compacting concrete (SCC) is specific rheological properties of fresh concrete mixture. Such properties, by which means high flowability and the viscosity of the mixture of conditional stability, or lack of segregation of aggregates and give of cement paste. Rheological properties of mixtures are formed by the choice of composition and proportion of careful selection of components. Next they are staying checked with self-compacting tests, introduced in (E- NARC 2005). Most used optimization methods of selfcompacting mixture composition are based on experimental trials, consisting of successive approximations to the composition in order to obtain self-compacting mixture. The most commonly used methods for designing self-compacting concrete design algorithm includes designs 3 or 2 stages (Su et al. 2001, Nielsson and Wallevik 2003, Li et al. 2005, Li 2007). They consist in designing the composition of the cement paste or mortar either cement paste and mortar so that as a consequence of a mixture of these mixture was characterized by the appropriate rheological properties that allowing for the meeting of the conditions self-compactibility. Empirical design methods in system design: the paste mortar a mixture in many cases be simplified to the scheme design: mortar a mixture (ig 1), or paste a mixture. Rheological properties of mortar or paste are examined, as well as if necessary corrected so that they fulfil guidelines around (ENARC 2005).In this way, mortar or paste designed in conjunction with the appropriate content and type of aggregate should give the guarantee of obtaining the selfcompacting mixture. Examinations concerning methods of designing self-compacting high performance concrete are being conducted by authors. Based on the researches will be possible to obtain the reply, which of the methods according to the scheme: paste-mixture or mortar-mixture 71

2 are more precise and useful in the designing of the composition of the self-compacting mixture. At this time the influence of rheological properties cement paste s on rheological properties mixture s, taking into account different paste content in the mixture are presents in paper. This design method consists in choosing the composition of the paste to the rheological properties of the paste and the strength of concrete, aggregates selecting the appropriate due to the strength properties and complying with the recommendations of the selection of particle size and degree of aggregate fill cavities paste, as expressed in the ratio of filling the aggregate s crumb pile with paste φ kz ( ig.2) (Czopowski 2009). ig 1. Outline of designing SCC according to the Japanese method in the scheme mortar-mixture (Li 2007) ig 2. The main factors determining the rheological properties of the mixture according to (Czopowski 2009) Table 1. Levels of variable factors for the investigated pastes and mixtures for self-compacting high performance concrete Water/binder ratio, w/b Superplasticizer, SP Silica fume, S Type Volume, % mass of binder Type Volume, % mass of binder 0,30 0,34 0,38 SP 1 2,5 3,0 3,5 S

3 The influence of rheological properties cement paste s expressed by parameters: the slump flow value and the time of slump flow value and the influence of the paste content in concrete mixture expressed by the ratio of filling the aggregate s crumb pile with paste φ kz on the rheological properties of mixture for self-compacting high performance concrete with a crushed type of coarse aggregates (D max = 16 mm) and its changes with time are presented and discussed in the paper. The of influence factors of mixture composition on the rheological properties of cement paste and concrete mixtures is also presented in the report. 2. Methodology of research 2.1. The variable factors in the research and study plan The influence of rheological properties of the cement paste and content of paste in concrete mixtures on the rheological properties of self-compacting high performance concrete mixtures are presented in paper. Rheological properties are shaped by changes in the composition of paste and self-compacting mixture. or pastes and mixtures of 3 factors variables were adopted on 3 levels of variability (Table 1). The ratio of filling the aggregate s crumb pile with paste φkz are adopted on 3 levels of variation in the range 1,2 1,4. Moments of SP dosage (together with water), temperature (200C) and the type of aggregate was adopted in the researches as constant factors. The levels of factors were selected on the basis of the analysis of literature data (ENARC 2005, Yin et al. 2005, De Schutter et al. 2008, Sri Ravindrarajah et al. 2003, Gesog lu et al. 2009, Domone 2006, Pereira de Oliveira et al. 2006), so that the contents of tested mixtures corresponded with the compound of its typical configurations of the variability of self-compacting high performance concrete used in practice. In the research the selective multifactorial determined plan of stellar points was applied. This plan allows you to perform tests of statistical analysis of the influence of various factors, and clinical variables in determining the regression model, depending on the influence of rheological parameters of the paste and the ratio of filling the aggregate s crumb pile with paste φkz on the rheological parameters self-compacting high performance concrete Properties of materials and compositions of mixtures The properties of cement and silica fume are presented in Table 2. In the researchs, superplasticizer based on polyether with a density 1,07 g/cm 3 and a concentration of 32,0 % was used. Superplasticizer was dosed by weight, changing the volume of water in the batched water. The aggregates natural sand of 0-2 mm and broken syenite of coarse aggregate with a maximum size of 16 mm was used. The amount of cement in the mixtures fluctuated depending on the w/s ratio and with the φ kz ratio in the range from 487 to 576 kg/m 3, the amount of S in the range of 0 to 62 kg/m 3, while the volume of aggregate in the range of 920 to 1100 kg/m Method of measurement of paste and mixture rheological parameters In spite of the lack of regulations about selfcompacting high performance concrete, however, managed to develop a series of methods to assess workability (rheological properties), understood as the flowability and the ability to self-leveling compound, and ability to fulfill the form and reinforcement under the weight. Detail the methods are presented in (ENARC 2005). The ability to flow and the viscosity of the mixture are most often examined with slump test. Rheological properties of the mixture were assessed with slump test formed in the shape of the Abramsa cone. The test measured the slump time up to 50 cm (Tm) and the value of the maximum diameter (Dm). The test also provides some information on the possible segregation, which is assessed visually. Mixtures were prepared in a mixer with forced action. The time of mixing was 5 minutes, first for 1 min. was mixed dry ingredients, then added water with superplasticizer. Measurement of the rheological parameters was performed after 20 and 60 minutes from finishing mixing ingredients up. Between measurements the mixture was being stored in the mixter under the cover. Before the second measurement the mixture was being mix for 3 min. Rheological properties of the paste was measured slump test. This test is the technological characteristics of the susceptibility of the paste flow. It is being made on the steel measuring plate about dimensions 700 x 700 mm, which were marked with circles coaxially with a diameter d1 = 250 mm and d2 = 50 mm. Diameter d2 is the central location of the ring, the same as for the determination of the consistency of gypsum pastes Sothard s ring. However the diameter d1 is treated as a measurement of the diameter of the paste slump time (Tp). Pastes were prepared in a mixer. The time of mixing up was 3 min. rotation speed equal to 140 rev/min. Measurement of the rheological parameters was performed after 20 and 60 minutes from finishing mixing ingredients up. Between measurements the paste was being kept under the cover and mixing for 1 min. immediately before the next measurement. Table 2. The chemical composition and specific surface of the components used Components SiO 2 Composition [%] CaO Al 2 O 3 e 2 O 3 MgO Na 2 O SO 3 K 2 O Specific surface [m 2 /kg] CEM I 42,5 R 21,6 64,4 4,5 2,2 1,25 0,4 3,1 0, Silica fume 92,8 0,7 0,6 0,3 1,32 0,3 0,8 0,

4 3. Test results and discussion The results presented in Table 3 and igures 3 and 4. In considering the results of regression analysis identified the following features: 1. the ratio of filling the aggregate s crumb pile with paste φ kz slump flow of paste value D p slump flow of mixture value D m ; 2. the ratio of filling the aggregate s crumb pile with paste φ kz time slump flow of paste value T p time slump flow of mixture value T m ; In igure 3 a surface graph of the relation of rheological parameters (diameter and time slump) of mixture from the rheological parameters (diameter and time slump) of paste and the ratio of filling the aggregate s crumb pile with paste φ kz was described. Dependence shows that with increasing slump flow and increasing the ratio φ kz increases the flow diameter of the concrete mixture. As well as that a decrease in the slump time of the paste and the increasing ratio φ kz reduces the time slump of concrete mixture. The regression function of the influence of the rheological parameters of paste and the ratio of filling the aggregate s crumb pile with paste φ kz on the rheological parameters of self-compacting high performance concrete mixtures can be formulated as a second degree polynomial of the form: RP m (φ kz, RP p ) = R + A φ kz + B RP z + AB φ kz RP p + AA φ 2 2 kz + BB RP p (1) where: RP m the rheological parameters of self-compacting high performance concrete mixtures: D m [mm], T m [s]; RP p the rheological parameters of paste: D p [mm], T p [s]; φ kz the ratio of filling the aggregate s crumb pile with paste; R, A, B, AB, AA, BB constant regression related to the properties of components. ig 3. Surface dependence graph: the ratio of filling the aggregate s crumb pile with paste φkz rheological parameter of cement paste Dp, Tp rheological parameter of concrete mixture Dm, Tm Multiple correlation coefficients for the model adopted as shown in igure 3. This equation is characterized by high matching estimators and materiality. The diameter and time flow are assessed on the basis of the equation has been experimentally measured and verified in control tests. The average deviation of the measured values of the diameter and time flow are Table 3. Variance analysis of the factorial research on the influence of the composition of cement paste and self-compacting mixture and time to rheological parameters THE CEMENT PASTE THE CONCRETE MIXTURE Source of variance Slump value, D p [cm] Time slump value, T p [s] Slump value, D m [cm] Time slump value, T m [s] Time 48,82 0, ,15 0, ,03 0, ,04 0,83408 w/b ratio 85,36 0, ,00 0, ,44 0, ,85 0,05792 superplasticizer 1,43 0, ,22 0, ,71 0, ,01 0,33884 Silica fume 67,03 0, ,09 0, ,21 0, ,94 0,

5 calculated at around 20 %, with a maximum deviation does not exceed 40 %.Wide range of space factor for the regression equation provided a satisfactory compatibility and rheological parameters of the mixture calculated on the basis of regression equations and measured experimentally is the possibility of effectively applying it to predict the rheological properties of self-compacting concrete. Based on the variance analysis of the results obtained studies demonstrate the importance of influence factors studied material on the rheological properties of pastes and concrete mixtures. The results of the analysis of statistical of individual factors of influence are shown in Table 3. The analysis of the significant impact shows that among tested factors, the highest influence on the rheological properties of paste has a w/b ratio and the additive of silica fume and then the passage of time. In the examined period the effect of increasing the content of superplasticizer is clearly weaker. As expected, increasing the ratio w/b or additive of superplasticizer or decrease the content of additive of silica fume cause increases the slump flow value and decreases the time slump flow value of paste (ig 4). Rheological properties of paste are changing over time increasing the diameter of slump flow and time slump flow decreases (ig 4). Rheological properties of fresh concrete depend in order on the w/b ratio, the additive of silica fume and admixture of superplasticizer. Generally, according to expectations, the increase in the w/b ratio or amount of superplasticizing additive, or decrease of amount of additive of silica fume cause increases slump flow value and decreases time slump flow value of fresh concrete (ig 4). Rheological properties of the mixture to change with time the diameter slump flow decreases and the time slump flow increases (ig 4), inversely than the change of rheological properties of cement paste with time. This effect is even smaller with the greater the ratio w/b. Scope of changes during the time slump flow also decreases with the increase on w/b ratio and superplasticizer addition and reduction of the amount of additive silica fume. 4. Conclusion Rheological properties of concrete and selfcompacting of high performance concrete depend on the rheological properties of the paste and the ratio of filling the aggregate s crumb pile with paste φ kz. The degree of the relation is developing on the high level of. Based on the measurement of rheological parameters of the paste can predict the rheological properties of the concrete mixture. Accepted regressive model (1) is well describing the relation of rheological parameters self-compacting mixture of high-performance concretes from rheological parameters of paste and the ratio of filling the aggregate s crumb pile with paste φ kz. It may be, after adjusting regression coefficients for the ingredients used, and then used to predict and shape of rheological properties of self-compacting concrete mixture. It was found that due to the composition of the greatest influence on the rheological properties of the mixture has a w/b ratio and then content of silica fume. At the same time, it was found that the effect superplasticizer addition on rheological properties of the mixture in the variation of the test is not statistically significant. On rheological properties of the paste has the greatest impact in turn on the w/b ratio, the content of silica fume and the superplasticizer addition. On rheological properties of cement pastes and selfcompacting mixtures of the impact of time is reversed. It means that with the passage of time the diameter of mixture slump flow is reducing and time slump flow of mixture is growing longer. By contrast, increasing the diameter of the paste slump and time slump flow of the paste decreases with time. Designing a self-compacting mixture on the basis of the rheological parameters of paste should be taken into account this phenomenon. About self-compacting mixture determined primarily by the diameter of the paste slump flow (Dp). Based on the findings set out the scope of variability of parameter rheological pastes because of the possibility of obtaining self-compacting concrete. Pastes for self-compacting high performance concrete should be characterized by the diameter of slump flow value over 320 mm. Obtained slump flow times range from 1 to 10 s are significantly higher than for ordinary concrete pastes to (1 5 s) and allow the mixture to obtain the slump flow time clearly more than 2 s, which qualifies them for the class of viscosity ranges VS 2.That rheological parameters pastes (diameter and time slump flow of pastes) typical for selfcompacting concrete mixtures of high performance concrete can be used in designing and correcting workability self-compacting high performance concretes. 75

6 ig 4. Profiles of the value approximate of rheological parameters of paste and self-compacting concrete 76

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