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No-slump concrete (NSLC) is one of the commercial types of concrete that is known as a type of concrete with almost zero flowability. No-slump concrete is normally used for typical applications, like pavements construction and massive dam structures. The specific feature of a no-slump concrete is its high shape holding ability. No fixed formwork is required for the construction. The main disadvantage of this type of concrete is that a great amount of energy is required for a proper compaction. Self-compacting concrete (SCC) is another commercial type of concrete that is known as a type of concrete that flows and fills the formwork under its own weight without applying any external energy. Although SCC is a relatively recent development, it has demonstrated substantial economic and environmental benefits in terms of faster construction, reduction of required manpower, better surface finishing, easier and vibration-free placing and reduced noise level. Therefore, SCC has recently found a wide use for different applications and structural configurations. However in comparison with NSLC, its demolding time for preserving its shape is much longer and fixed formworks are required for the construction. The first objective of this research project is to study the possibility of developing a self-compacting no-slump concrete (SCNSLC), which does not need compaction and also has a high shape holding ability shortly after placing in the formwork. The second objective is to develop a model, which can predict the rheological behaviour of a mixture based on the properties and proportion of the mix components. The study starts with a comprehensive study of mechanisms that govern the rheological behaviour of concrete in the dormant period, i.e. when the hydration effect is still ignorable. A fresh concrete mixture is considered as a two-phase system, paste and aggregates. The paste itself is divided into two components, the “void paste” and the “excess paste”. The void paste is the part of the paste which fills the void space between the aggregates in a compacted state. The excess paste is the rest of the paste used to form a nominal layer with an average constant thickness around every single aggregate particle. The void paste tries to keep the aggregate particles in their positions, while the excess paste tries to push the aggregate particles apart and promote their mobility. With respect to the dominant mechanism, mixtures are divided into three main classes: Class 1: High Excess Paste volume mixtures, where the excess paste effect is dominant. For these mixtures the capacity to deform is maximal. Class 2: Intermediate Excess Paste volume mixtures, where the effect of the void paste becomes significant and gradually increases with decreasing excess paste volume. The capacity of the intermediate excess paste volume mixtures to deform is lower than the high excess paste volume mixtures. Class 3: Low Excess Paste volume mixtures, where the void paste effect is dominant and the excess paste does not significantly affect the rheological behavior. For these mixtures the capacity to deform is minimal. Mix design The shape holding ability of mixtures is characterized by the shape preservation factor 0<SPF?1. The SPF shows the ability of a mixture to preserve its shape in the slump test after demolding. The SPF is the ratio of the cross sectional area of a 3D sample after and before demolding. A SPF is about 1 for a mixture which shows almost no deformation, i.e. a no-slump concrete mixture (NSLC). For a conventional self-compacting concrete mixture (SCC), with a spread diameter?~600 mm, the SPF is less than about 0.4. In this thesis it is found that the maximum SPF for mixtures that can compact under their own weight is about 0.7. A mixture with SPF?0.7 is denoted a Self-Compacting High Shape Preserving Concrete (SCHSPC). A mix design method is proposed for mixtures with a shape holding ability ranging from no-slump concrete mixtures (NSLC) with the shape preservation factor SPF?1 to conventional self-compacting concrete mixtures (SCC) with a shape preservation factor SPF?0.4. First the volume of the excess paste with a certain consistency is determined for a required shape preservation factor SPF. Then the volume of the total paste, i.e. the void paste plus the excess paste, and the volume of the aggregate are determined to obtain a required packing density of aggregate. In the next step, the quantities of the paste composition, i.e. amount of Portland cement CEM I 52.5, limestone powder, water and superplasticizer, are determined for the required paste consistency. Finally the deformability of the obtained mixture is checked by the slump test (experiment or numerical simulation). Numerical modeling For numerical flow analysis, the particle flow code 2D (PFC2D), ITASCA, is used. This program is based on the principles of a discrete element method (DEM). In this program a material is considered to be built of a finite number of individual elements. The behavior of such a system is described in terms of the movement of elements and the inter-element forces. In this study the correlation between the mix composition and the deformability of the mixtures was studied. The deformability of a mixture is characterized by the spread diameter (D) and the slump value (Hs). The focus is on simulation of rheological behavior of mixtures made with aggregates with a narrow particle size distribution. In the model a mixture is considered as an assembly of a finite number of individual two-phase elements. A two-phase element is defined as an aggregate particle surrounded with an excess paste layer. The force-displacement relation, which is adopted between the elements, is defined according to the interaction diagram, developed in this thesis. The interaction force is related to the inter-element distance, element size, consistency of the paste and the thickness of the excess paste layer. The approach showed to be promising for predicting the deformability of the mixtures made with aggregates with a narrow particle size distribution (Rmax/Rmin?2.0). The deformability of a mixture made with aggregate with a broad particle size distribution is considered to be the same as that of a mixture made with aggregate with a narrow particle size distribution with the same consistency of the paste and the same volume of the excess paste. This assumption is validated for the mixtures made with the aggregate particles with a shape deviation of about 3 % from the spherical shape, specific density between 2500-2600 kg/m3, maximum size of 8 mm, minimum size of 0.125 mm and the maximum fineness modulus of 5.0. The minimum fineness modulus of granular material is limited to 2.0 and 3.5 for aggregates with a narrow particle size distribution and with a broad particle size distribution, respectively. 0.125 mm is the boundary size between the aggregate particles and the powder particles.
Hooman Hoornahad (Wed,) studied this question.