Hellenic Ministry of Education and Religious Affairs

Athens, Greece

Hellenic Ministry of Education and Religious Affairs

Athens, Greece

Time filter

Source Type

Miltiadou-Fezans A.,Hellenic Ministry of Education and Religious Affairs | Tassios T.P.,National Technical University of Athens
Materials and Structures/Materiaux et Constructions | Year: 2013

Besides its sufficient penetrability and fluidity, a hydraulic grout in order to be injectable should also exhibit an appropriate stability, i.e. to be able to keep its homogeneity during the injection process, up to its setting. The paper is part of a broader attempt to establish a rational methodology for the design of hydraulic grouts for strengthening of masonry historical buildings, based on their discrete injectability characteristics. The first and second part of this holistic methodology regarding the penetrability and fluidity were published elsewhere. This paper deals with stability, the third basic injectability characteristic. The most prevailing parameters shaping stability characteristics, are water content and percentage of ultrafine materials. After a brief literature survey, an oversimplified predictive model of bleeding is firstly proposed and then its validity is confirmed using the results of an experimental study. The role of superplasticizers is also discussed. In both cases, with and without superplasticizer, semi-empirical formulae are proposed, that may be useful for the design of a grout composition. Finally, the paper presents experimental results demonstrating the role of water and superplasticizer content in the appearance of segregation; some empirical formulae are also proposed for the estimation of the critical water content initiating segregation. Résumé: En sus des exigences de pénétrabilité et de fluidité, un coulis hydraulique doit également avoir une stabilité satisfaisante pour pouvoir être injectable. Il doit ainsi pouvoir conserver son homogé néité durant tout le processus d'injection. Cet article fait partie d'une tentative plus générale destinée à établir une méthodologie rationnelle permettant la formulation des coulis hydrauliques par l'intermédiaire d'une analyse de leurs propriétés d'injectabilité. Les deux premières parties de cette méthode portant respectivement sur les caractéristiques de pénétrabilité et de fluidité ont été publiées par ailleurs. Le présent article est consacré à la stabilité, troisième propriété essentielle caractérisant l'injectabilité. Les paramètres essentiels influençant les caractéristiques de stabilité sont la teneur en eau et le pourcentage en éléments ultra fins. Après une brève analyse bibliographique, un modèle simplifié de prédiction de l'exsudation est proposé puis validé à l'aide des résultats d'une analyse expérimentale. Le rôle des superplastifiants est également discuté. Des formules semi empiriques considérant l'éventuelle présence de superplastifiant et constituant une aide dans la formulation des coulis hydrauliques sont ensuite proposées. Cet article présente enfin des résultats expérimentaux montrant le rôle de l'eau et de la teneur en superplastifiant dans l'apparition de ségrégation. Quelques formules empiriques fournissant une estimation de la teneur en eau critique provoquant une initialisation du phénomène de ségrégation sont également proposées. © 2013 RILEM.


Miltiadou-Fezans A.,Hellenic Ministry of Education and Religious Affairs | Tassios T.P.,National Technical University of Athens
Materials and Structures/Materiaux et Constructions | Year: 2013

Design of hydraulic grouts for strengthening of masonry historical buildings seems to follow rather empirical procedures, with all the related uncertainties, both in terms of economy and efficiency. This paper is part of a broader attempt to establish a rational methodology for the design of such grouts, based on their discrete injectability characteristics, i.e. (i) Penetrability, (ii) Fluidity and (iii) Stability. This paper deals with penetrability and constitutes the first part of this holistic methodology. The second part regarding the fluidity and the third regarding the stability are separately published. Grouting is intended to fill voids, fissures and open joints of the masonry as a system, producing a "dendrite" (a three-dimensional skeleton), directly contributing to the strength of the masonry as a whole. However, to do so, the grout should be able to pass through the "narrowest" possible width of such discontinuities, in order to reach the maximum possible internal volume of masonry and open joints, avoiding most of possible blockages. In the specific case of three-leaf masonries, the most decisive result of the grouting is expected to be the strengthening of the bond along the interfaces between the external layers and the infill; the rather small voids, as well as pre-existing fissures along these interfaces have to be penetrated. In this paper the penetrability of hydraulic grouts is discussed, and relationships between two characteristic diameters of the grains of the solid phase of the grout and the nominal minimum width of fissures and voids of the structure to be injected are proposed. Furthermore the beneficial role of replacing part of the cement or hydraulic lime with ultrafine materials in order to improve penetrability is presented, and related criteria are proposed. © 2013 RILEM.

Loading Hellenic Ministry of Education and Religious Affairs collaborators
Loading Hellenic Ministry of Education and Religious Affairs collaborators