J. Szwabowski

Air‐entrainment problem in self‐compacting concrete

Abstract According to the actual state of knowledge and in accordance with the PN‐EN 2006–1 norm, it is recommended to use air‐entrainment as a basic way of assuring frost‐resistance of concrete. In case of self‐compacting concrete (SCC), achieving adequate air‐entrainment is a problematic issue because of one of the side‐effects of the functioning of a new generation of superplasticizers, i.e. excessive air‐entrainment (considerably higher than 2%) in a self‐compacting concrete mix. Thus, in this situation, the dosage of an air‐entraining admixture has to be reduced. It was discovered that the cause of an air‐entrainment effect of superplasticizers is a decrease of the surface tension value of the liquid phase in paste. In the paper, the problem of air‐entrainment is discussed, formed as a result of the functioning of a superplasticizer on the characteristics both of concrete and a mixture, depending on the content. To verify the influence a superplasticizer and an air‐entraining admixture have on concre...

THE INFLUENCE OF SELECTED COMPOSITION FACTORS ON THE RHEOLOGICAL PROPERTIES OF FIBRE REINFORCED FRESH MORTAR

ABSTRACT In the paper the methodology and test results of the investigation are presented and discussed on the influence of fibres on Theological properties of modified standard mortars. The rheological parameters of fibre reinforced fresh mortars (FRFM) - yield value and plastic viscosity were determined. FRFM behaves as a Bingham body, their rheological parameters were determined by using rheometer to pastes and mortars. In the research, an experimental verification of a significance of an influence: W/C ratio, volume fraction of fibres, lengths and kind of materials of fibres on rheological properties of FRFM was investigated. In the paper the results obtained for mixes with polypropylene, steel, carbon and glass fibres are presented. The first step of the procedure was a rheological identification of fiber-mortars, which was completed based on the delimitation of the tension due to an assignment of characteristic dependence - speed of non-dilatational strain, in the form of a curve flow and acceptance of adequate model and rheological equalizations. This equalization is a base to the experimental analyses which influences composition factors of mixtures on the character of their flowing and rheological parameters. The analysis of the results of these measurements permitted on the following qualifications: reliable statistics of rheological parameters from variables, indications of workability forms of mortars with fibres and approximate reliability among rheological parameters of FRFM.

The Influence of the Type of Anti-Foaming Admixture and Superplasticizer on the Properties of Self-Compacting Mortar and Concrete

Abstract To prevent excessive air entrainment, superplasticizers (SPs) should not only be compatible with cement, but also should not create the air-entraining effect in mortar. In order to counteract excessive air entrainment, anti-foaming admixtures (AFAs) can be used to prevent the formation of air bubbles. This paper investigates the influence of the type, amount and time of introduction of AFAs on air-entrainment, rheological properties and workability loss of self-compacting mortar. The research results prove that AFAs decrease air-content in mortar. Mortar containing an AFA does not undergo segregation, as is the case with mortars of a similar degree of fluidity with no AFA and incorporating an SP only. Moreover, mortar with an AFA keeps initial consistency for longer in comparison to mortar with a SP only. The properties of hardened mortar mixes are also investigated. The research results show that AFAs do not have a significant influence on the compressive strength of mortar mixtures. The compres...

Anti-Foaming Admixture (AFA) and its Influences on the Properties of a Fresh Self-Compacting Concrete Mix

Abstract The properties of a concrete mix should secure the self-elimination of needless air bubbles from its volume. What is interesting, these properties are not taken into consideration in commonly used self-compacting tests. On the basis of different tests concerning self-compacting concrete mixes, it has been discovered that too high air content in their volume was a result of a superplasticiser, in spite of meeting the self-compactibility criteria. To decrease too high air volume in SCC, the use of an anti-foaming admixture (AFA) is proposed by the authors. Because of an AFA introduced into a self-compacting mix, air-content in this mix is decreased, mix flow diameter is increased and flow time is decreased. In case of a mix incorporating an AFA, its high flowability does not cause segregation of the mix, which is possible in case of SCC incorporating only a superplasticiser. However, time of introduction of an AFA is essential to get higher flowability degree, but is not important in achieving low ...

INFLUENCE OF CEMENT AND SUPERPLASTICIZER ON RHEOLOGICAL PROPERTIES OF MORTARS

ABSTRACT Effectiveness of superplasticizer is an effect of complex system of factors connected mainly with concrete components properties, concrete composition and concreting conditions. From among these factors the key role for the superplasticizer effectiveness plays interaction of cement and superplasticizer. Selection of cement - superplasticizer system determines also workability of fresh concrete and thus also possibility of performing of HPC. In the paper methodology and results of the investigation into the influence of different superplasticizers on the rheological properties of modified, for the sake of superplasticizer addition and W/C ratio, standard mortars (according PN EN 196—1:1996) with different cements are presented. The rheological parameters of these mortars, yield value and plastic viscosity were determined using a rheometrical methods. In the research program the influence of following factors: chemical origin of superplasticizers (SNF, SMF, PC and PE superplasticizers), cement composition (cements of different C3A, Na2Oeq and SO3 content) and cement specific surface, superplasticizer dosage and W/C ratio were investigated. On the basis of test results the relationships between cement and superplasticizer properties and rheological properties of cement mortars were defined and discussed. These relationships in form of mathematical models can be used in workability shaping process to select optimal cement - superplasticizer system.