S u m m a ry
In this paper is discussed the issue of effective usage of superplasticizers concerning predicting rheological properties of cement binder mixtures, that is mortars and concrete mixtures. The influence o f superplasticizers on rheological properties o f the cement binder mixtures, depending on the properties of the cement, type, amount and properties o f mineral additions and temperature is determined and explained.
In chapter 1 rheological properties o f cement binder mixtures are characterized and the methods of their measurement are analysed. It was found out that rheological properties of mixes with superplasticizers are well described by Bingham’s model determined by two rheological parameters: yield value t 0 and plastic viscosity t |pi or corresponding parameters g and h. The measurement o f rheological parameters of the mixture should best be performed using rheometers, as it was done for this dissertation. It was also demonstrated analytically and experimentally that the nature of influence of basic factors on rheological parameters of fresh mortars and fresh concretes is similar, and tests of mortars can be used for predicting rheological parameters of concrete mixtures. Relations between rheological parameters of fresh mortar and concrete are expressed with mathematical relationships.
In the chapter 2 superplasticizers properties are characterized, as well as its mechanism and basic factors influencing the effects of their action are determined. It was found out that the influence o f superplasticizers depends on the following factors and interactions taking place between them: type, quantity, physical and chemical properties and delay in adding the superplasticizer; type, specific surface and chemical and physical composition of the cement;
type, physical and chemical properties and quantity of applied mineral additions, water to cement ratio, mix temperature and time.
In the chapter 3 investigations of superplasticizer influence on rheological properties of cement binder mixtures, available in professional literature, were analysed. On this basis generalizations o f relations were formulated, among other things: influence of w/c, influence
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of type, quantity and time of adding the superplasticizer on rheological parameters of fresh mortars and concretes and their changes with time.
In the chapters 4, 5, 6, being the principal part of this dissertation, the analysis of the results of exhaustive and systematic own tests of the influence o f cement, type and quantity of mineral additions and temperature on rheological parameters o f mixes with SNF, SMF, PC and PE superplasticizers is presented. Due to the necessity of eliminating the influence of alterations in aggregate grading on rheological properties o f mixtures and to reduce the labour consumption needed for the tests, own tests were carried out for mortars made of standardized sand in accordance with PN EN 196 - 1, but of different w/c. These tests were designed for a wide range o f factor variability in a way enabling statistical assessment of significance as well as putting the factors and their influence on rheological parameters of mixtures into a hierarchy. In the tests some specially prepared laboratory cements were used, limiting the influence of variability o f cement composition elements other than those tested.
In the chapter 4 the analysis of the results of tests of cement specific surface influence as well as C3A, Na2 0e and S 03 contents in cement on rheological effects of SNF, SMF, PC and PE superplasticizers action is presented. It was found out that due to the properties of the cement, the influence of these superplasticizers on rheological parameters of mortars depends mainly on C3A contents in the cement, and, successively, on cement specific surface, Na2Oe contents in the cement and interaction of these factors. In tested range of variability of cement properties no considerable influence of variable SO3 content in cement (2.5 - 3.5%) on rheological properties of mortars or superplasticizer action effects were observed.
As a result of increased C3A contents in the cement g and h parameters of mortars with superplasticizers increase, range of increase of these parameters with time increases as well.
The intensity of these increase depends on cement specific surface, Na2Oe content in the cement and the type o f superplasticizer. When the content of C3A in cement increases, it is necessary to add more superplasticizer to obtain a mortar with determined g parameter. The consequence in case of mixtures of low w/c ratio is usually increasing h parameter. Due to that with determined value of g parameter, mortars with cements o f higher C3A content are characterized with higher shear resistance. On the other hand though, using cements rich in C3A it is easier to obtain stable mixtures of high fluidity, especially self-compacting mixtures.
The nature of the influence of cement specific surface on rheological parameters of mortars with superplasticizers depends on C3A content in cement. With a certain addition of superplasticizer increasing cement specific surface of low C3A content results in insignificant reduction, and in case o f cements of high C3A content in increase o f g parameter o f mortars.
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Value of h parameter o f these mortars decreases with increasing cement specific surface.
Superplasticizer action effects decay faster when cement specific surface increases.
The nature o f influence o f Na20e content in cement on rheological parameters o f mortars depends on the type of superplasticizer. In the case of mortars with addition of SNF and SMF superplasticizers, mortars o f cements containing 0.7% Na2Oe reveal the lowest value of g parameter and the lowest range of increase of this parameter with time. In the case of mortars with addition of PC and PE superplasticizers the increase of Na2Oe content in cement causes increase in g parameter, reduction in h parameter and increase in range of changes of these parameters with time.
Basing on the analysis of dependencies obtained in the tests mathematical models were elaborated, describing the influence of cement specific surface, C3A, Na2Oe and S 0 3 content in cement on rheological properties of different w/c mortars with addition of superplasticizers o f different physical-chemical properties (chapters 4.4). These models are characterized with high estimators of matching and significance. Their accuracy was checked in control tests, stating good conformity of rheological parameter values, calculated on the basis of the model and measured in experiments. Due to wide range of factorial space in which the models were created, they show great utilization possibilities and may be applied to choose the cement - superplasticizer system that is the best for given conditions.
In the chapter 5 an analysis of results of tests of influence of fly ash, granulated ground blast furnace slag as well as condensed silica fume on rheological parameters o f mortars with PC and PE superplasticizers is present. It was demonstrated that rheological results o f PC and PE superplasticizer action on cement mortars and on mortars, in which a part o f cement was substituted with mineral addition, differ significantly, and true assessment of compatibility of cement and superplasticizer should be carried out taking into consideration the presence of mineral additions. The influence of PC and PE superplasticizers on rheological properties of mortars with mineral additions depends on the type and the quantity o f the addition, C3A and Na2Oe content in cement, superplasticizer properties and interactions between these factors.
The nature of the impact of particular additions on rheological parameters o f mortars with PC and PE superplasticizer addition was determined, stating that it is often different from the influence of the influence of these additions rheological parameters of mixes without and with addition of SNF and SMF.
In the chapter 6 the analysis of results of the investigation into the influence of temperature on rheological parameters of mortars with different superplasticizers is presented.
It was found out that the nature and the range of the influence of temperature on rheological
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parameters of mixes and their changes with time depends on w/c, type and quantity of superplasticizer added, cement type, C3A content in cement, cement specific surface, Na2Oe content in cement and interactions of these factors.
It was demonstrated that in the case of using cements of 2% C3A content and cements with additions, as well as when the addition o f superplasticizer and/or w/c is high, rheological parameters of mortars with superplasticizers only slightly depend on temperature. In the case of mortars of CEM I cements of higher C3A content, especially when w/c is low, increase of temperature causes increase o f g parameter and increase in range of increasing g parameter with time. Alterations in h parameter of mortars caused by temperature depend on the type of superplasticizer; however, they do not show unequivocal tendencies. Influence of temperature on h parameter of mortars increases considerably when w/c decreases. In case of PC and PE superplasticizers the intensity o f temperature influence decreases as the length of their side chains increases. Basing on performed tests it was found out that mortars with addition of PC and PE can show the maximum of g parameter in different temperatures, depending on C3A content in cement and length o f side chains o f polymers contained in the superplasticizer.
In the chapter 7 is presented the summary and final conclusions o f the paper. The most important obtained relationships of superplasticizer influence on rheological properties of mixes in cement binders, depending on cement properties, properties o f mineral additions and temperature are indicated. The possibility of practical application of relationships developed in the dissertation, occurring in concrete technology also is brought to attention.
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