In recent years, there has been great interest in reducing the cement content of concrete, due t... more In recent years, there has been great interest in reducing the cement content of concrete, due to the high energy and carbon dioxide footprints of cement production. There are numerous (waste) materials that can be substituted for cement in the concrete mixture proportions, including fly ash, slag, silica fume, metakaolin, waste glass, etc. However, a more abundant material substitute would be limestone powder, created from the same limestone that is currently heavily employed in cement production as the primary source of calcium oxide. This technical note presents an approach to replacing not only cement powder, but effectively cement paste consisting of the cement and water, with appropriately sized limestone powder(s). Such an approach effectively extends the conventional utilization of centimeter-sized coarse aggregates (rocks) and millimeter-sized fine aggregates (sand) that occupy between 65 % and 75 % of the volume of a concrete structure to include micro-aggregates ranging between about 1 µm and 100 µm in size. Here, to demonstrate the feasibility of this approach, demonstration mixtures of pastes, mortars, and concretes are each formulated with limestone powder replacement for a significant portion of their cement paste component, achieving cement reductions of up to 28 % in concrete, for example. For these mixture modifications, the water-to-cement mass ratio (w/c) is maintained at or above 0.4 to provide sufficient water to react with all of the cement, so that none of this most costly component of cement-based materials goes to waste. Meanwhile, the water-to-solids ratio (w/s) is reduced to a value in the range of 0.22 to 0.40 in order to maximize the limestone powder replacement level, while still providing sufficient flow and rheology, by using reasonable dosages of high range water reducing admixtures. The fresh, early age, and long term performance properties of these high volume limestone powder (HVLP) mixtures are contrasted with a w/c=0.4 ordinary portland cement (OPC) paste or mortar, or a w/c=0.5 OPC concrete reference, respectively. In general, the properties and performance of these more sustainable mixtures are similar or even superior to those of the corresponding reference mixture, suggesting that these new paradigm HVLP concretes could be readily substituted for existing conventional OPC mixtures. The reduced shrinkage (autogenous and drying) of the mortars with limestone powder replacement, due to their reduced paste content, is highlighted because of its likelihood to reduce concrete cracking. However, beyond measurements of electrical resistivity, this study has not specifically focused on durability issues and additional research on this topic is recommended as these new mixtures are reduced to (field) practice.
Design, Production and Placement of Self-Consolidating Concrete, 2010
Concretes for self-compacting concrete (SCC) applications have to combine a high fluidity and flu... more Concretes for self-compacting concrete (SCC) applications have to combine a high fluidity and fluidity retention with high segregation resistance. This optimal rheological behaviour is obtained by combining a suitable aggregate grading curve with correct rheological properties of the suspending matrix (i.e. the cement paste). It is shown in this paper how these rheological properties can be influenced by polycarboxylate-based superplasticizers. Furthermore it is shown that relatively easy tests can be used to access the rheological properties of both the fresh cement paste and the concrete quantitatively. It is demonstrated that a new superplasticizer leads to an improved robustness in the formulation of SCC.
ABSTRACT For chemical, cosmetic, pharmaceutical, and food industries the rheological properties o... more ABSTRACT For chemical, cosmetic, pharmaceutical, and food industries the rheological properties of a product represent an important quality factor. Unfortunately such features are often difficult to estimate, in particular in a continuous production process. In this work, we present an ultrasound (US) Doppler method suitable for in-line rheological assessment of highly filled opaque suspensions. The velocity profile developed by highly filled and opaque polyurethane based adhesives and sealants flowing in a pipe was measured through a proprietary US board. The high resolution profile was then fitted to the power law model and the wall shear rate (WSR), a reliable rheological indicator in high shear-thinning suspensions, was obtained. The accuracy of the method was evaluated comparing the measured WSR to reference values obtained from off-line laboratory rheometry. The error from 78 measurements at flow rates between 1 and 35 ml/s featured a mean +3.6% bias and a standard deviation below 12%. Moreover, measurements are only minimally affected by the variation of several US parameters over a wide range of values demonstrating the robusness of the technique.
The imbibition kinetics of a millimeter-sized aggregate of 300 nm diameter colloidal particles by... more The imbibition kinetics of a millimeter-sized aggregate of 300 nm diameter colloidal particles by a wetting pure solvent is studied. Three successive regimes are observed. First, the imbibition proceeds by compressing the air inside the aggregate. Next, the solvent stops when the pressure of the compressed air is equal to the excess of capillary pressure at the meniscus of the wetting solvent in the porous aggregate. The interface is pinned and the aggregate slowly degases up to the point where the pressure of the entrapped air stops decreasing and is controlled by the capillary pressure. Finally, the imbibition starts again at a constant excess of pressure, smaller than the capillary pressure but larger than the one of the atmosphere. This last stage leads to the complete infiltration of the aggregate.
In recent years, there has been great interest in reducing the cement content of concrete, due t... more In recent years, there has been great interest in reducing the cement content of concrete, due to the high energy and carbon dioxide footprints of cement production. There are numerous (waste) materials that can be substituted for cement in the concrete mixture proportions, including fly ash, slag, silica fume, metakaolin, waste glass, etc. However, a more abundant material substitute would be limestone powder, created from the same limestone that is currently heavily employed in cement production as the primary source of calcium oxide. This technical note presents an approach to replacing not only cement powder, but effectively cement paste consisting of the cement and water, with appropriately sized limestone powder(s). Such an approach effectively extends the conventional utilization of centimeter-sized coarse aggregates (rocks) and millimeter-sized fine aggregates (sand) that occupy between 65 % and 75 % of the volume of a concrete structure to include micro-aggregates ranging between about 1 µm and 100 µm in size. Here, to demonstrate the feasibility of this approach, demonstration mixtures of pastes, mortars, and concretes are each formulated with limestone powder replacement for a significant portion of their cement paste component, achieving cement reductions of up to 28 % in concrete, for example. For these mixture modifications, the water-to-cement mass ratio (w/c) is maintained at or above 0.4 to provide sufficient water to react with all of the cement, so that none of this most costly component of cement-based materials goes to waste. Meanwhile, the water-to-solids ratio (w/s) is reduced to a value in the range of 0.22 to 0.40 in order to maximize the limestone powder replacement level, while still providing sufficient flow and rheology, by using reasonable dosages of high range water reducing admixtures. The fresh, early age, and long term performance properties of these high volume limestone powder (HVLP) mixtures are contrasted with a w/c=0.4 ordinary portland cement (OPC) paste or mortar, or a w/c=0.5 OPC concrete reference, respectively. In general, the properties and performance of these more sustainable mixtures are similar or even superior to those of the corresponding reference mixture, suggesting that these new paradigm HVLP concretes could be readily substituted for existing conventional OPC mixtures. The reduced shrinkage (autogenous and drying) of the mortars with limestone powder replacement, due to their reduced paste content, is highlighted because of its likelihood to reduce concrete cracking. However, beyond measurements of electrical resistivity, this study has not specifically focused on durability issues and additional research on this topic is recommended as these new mixtures are reduced to (field) practice.
Design, Production and Placement of Self-Consolidating Concrete, 2010
Concretes for self-compacting concrete (SCC) applications have to combine a high fluidity and flu... more Concretes for self-compacting concrete (SCC) applications have to combine a high fluidity and fluidity retention with high segregation resistance. This optimal rheological behaviour is obtained by combining a suitable aggregate grading curve with correct rheological properties of the suspending matrix (i.e. the cement paste). It is shown in this paper how these rheological properties can be influenced by polycarboxylate-based superplasticizers. Furthermore it is shown that relatively easy tests can be used to access the rheological properties of both the fresh cement paste and the concrete quantitatively. It is demonstrated that a new superplasticizer leads to an improved robustness in the formulation of SCC.
ABSTRACT For chemical, cosmetic, pharmaceutical, and food industries the rheological properties o... more ABSTRACT For chemical, cosmetic, pharmaceutical, and food industries the rheological properties of a product represent an important quality factor. Unfortunately such features are often difficult to estimate, in particular in a continuous production process. In this work, we present an ultrasound (US) Doppler method suitable for in-line rheological assessment of highly filled opaque suspensions. The velocity profile developed by highly filled and opaque polyurethane based adhesives and sealants flowing in a pipe was measured through a proprietary US board. The high resolution profile was then fitted to the power law model and the wall shear rate (WSR), a reliable rheological indicator in high shear-thinning suspensions, was obtained. The accuracy of the method was evaluated comparing the measured WSR to reference values obtained from off-line laboratory rheometry. The error from 78 measurements at flow rates between 1 and 35 ml/s featured a mean +3.6% bias and a standard deviation below 12%. Moreover, measurements are only minimally affected by the variation of several US parameters over a wide range of values demonstrating the robusness of the technique.
The imbibition kinetics of a millimeter-sized aggregate of 300 nm diameter colloidal particles by... more The imbibition kinetics of a millimeter-sized aggregate of 300 nm diameter colloidal particles by a wetting pure solvent is studied. Three successive regimes are observed. First, the imbibition proceeds by compressing the air inside the aggregate. Next, the solvent stops when the pressure of the compressed air is equal to the excess of capillary pressure at the meniscus of the wetting solvent in the porous aggregate. The interface is pinned and the aggregate slowly degases up to the point where the pressure of the entrapped air stops decreasing and is controlled by the capillary pressure. Finally, the imbibition starts again at a constant excess of pressure, smaller than the capillary pressure but larger than the one of the atmosphere. This last stage leads to the complete infiltration of the aggregate.
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