Critical Grain Size of Fine Aggregates in the View of the Rheology of Mortar

The aim of this research was to investigate the validity of the Krieger-Dougherty model as a quantitative model to predict the viscosity of mortar depending on various aggregate sizes. The Krieger-Dougherty model reportedly predicted the viscosity of a suspension, which includes cement-based materials. Concrete or mortar incorporates natural resources, such as sand and gravel, referred to as aggregates, which can make up as much as 80% of the mixture by volume. Cement paste is a suspending medium at fresh state and then becomes a binder to link the aggregate after its hydration. Both the viscosity of the suspending medium and the characteristics of the aggregates, therefore, control the viscosity of the cement-based materials. In this research, various sizes and gradations of fine aggregate samples were prepared. Workability and rheological properties were measured using fresh-state mortar samples and incorporating the various-sized fine aggregates. Yield stress and viscosity measurements were obtained by using a rheometer. Based on the packing density of each fine aggregate sample, the viscosity of the mortar was predicted with the Krieger-Dougherty model. In addition, further adjustments were made to determine the water absorption of fine aggregates and was transferred from successful experiment to simulation for more accurate prediction. It was also determined that both yield stress and viscosity increase when the fine aggregate mean size decreases throughout the mix. However, when the mean size of the fine aggregates is bigger than 0.7 mm, the yield stress is not affected by the size of the fine aggregate. Additionally, if aggregate grains get smaller up to 0.3 mm, their water absorption is critical to the rheological behavior

Remontée d’un anneau de voussoir : modélisation et analyse paramétrique

Les mortiers de bourrage injectés entre le sol et l’anneau de voussoirs en béton armé d’un tunnel s’apparentent à des fluides à seuils. L’anneau de voussoir peut, en fonction des sollicitations mécaniques qu’il subit, se déplacer au sein de ce fluide. La modélisation d’un tel problème d’écoulement de fluide plastique permet d’estimer les efforts nécessaires à la mise en mouvement du tunnel dans une direction quelconque ou d’évaluer le risque de remontée d’un anneau de voussoir soumis à un effort de type « poussée d’Archimède ». A cette fin, un outil de calcul analytique est développé. L’incidence des paramètres géométriques, rhéologiques et tribologiques sur les risques de mouvement de l’anneau est alors étudiée. Les résultats obtenus sont comparés à ceux provenant d’un calcul par éléments finis

Exploitation de deux outils de rhéométrie pour l'identification de courbe d'écoulement de pâtes de ciment

National audienc

Squeeze flow of sticking viscoplastic fluids: Direct identification of behavior parameters by an equivalent flow curve,

International audienceA squeeze flow analysis method of sticking viscoplastic fluids is developed. This method allows an equivalent flow curve to be extracted from squeeze data. From this equivalent flow curve, rheological properties of viscoplastic fluids can be directly identified. For this, we have calculated an instantaneous average strain rate. This average strain rate is defined by means of a dimensional analysis coupled with energy balance. Furthermore, we consider a Bingham model to describe the squeeze flow of viscoplastic fluids and specify an equivalent stress-strain state at any time. For this purpose, it is assumed that the fluids stick on both plates and the flow field is essentially extensional around the plane of symmetry. The constitutive parameters of the Bingham model are evaluated by confronting squeeze data and analytical solution of the Bingham squeeze force. In particular, we focus on the development of an algorithm which enables the construction of an equivalent flow curve with step-by-step computation. The algorithm, preliminary tested and validated on simulated data of complex fluids in sticking squeeze flow, is applied on experimental squeeze data. It is finally shown that the equivalent flow curves obtained from squeeze data are close to the conventional shear flow curves

Comportamento reológico em squeeze flow de suspensões concentradas de esferas de vidro em silicones de diferentes viscosidades

Squeeze flow é uma das principais técnicas para analisar o comportamento reológico de argamassas. Esses materiais podem ser considerados como suspensões concentradas, reativas e heterogêneas com grande extensão granulométrica, nas quais o comportamento reológico é influenciado pelas quantidades e características de seus constituintes. Para avaliar alguns fenômenos de maneira mais detalhada, é interessante reduzir os fatores que influenciam o fluxo. Assim, este trabalho avalia o comportamento reológico de suspensões concentradas de esferas macroscópicas de vidro em fluidos newtonianos de diferentes viscosidades (silicones: 100, 1.000 e 10.000 cSt) e visa analisar a interação entre as fases líquida e sólida e a ocorrência de segregação. As suspensões com 60% e 70% em volume de sólidos foram submetidas a ensaios de squeeze flow com diferentes velocidades. O aumento da quantidade de fluido altera os principais fenômenos relacionados ao fluxo: com baixo volume de líquido o atrito entre as partículas, a capacidade de lubrificação do fluido e a coesão decorrente da formação de meniscos são predominantes na suspensão, enquanto em suspensões com volume de líquido suficiente para afastar as partículas a viscosidade do fluido, a força de arraste e a  permeabilidade do sistema granular influenciam no comportamento reológico e na ocorrência de separação de fases