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Additives such as nano-silica and fly ash are widely used in cement and concrete materials to improve the rheology of fresh cement and concrete and the performance of hardened materials and increase the sustainability of the cement and concrete industry by reducing the usage of Portland cement. Therefore, it is important to study the effect of these additives on the rheological behavior of fresh cement. In this paper, we study the pulsating Poiseuille flow of fresh cement in a horizontal pipe by considering two different additives and when they are combined (nano-silica, fly ash, combined nano-silica, and fly ash). To model the fresh cement suspension, we used a modified form of the power-law model to demonstrate the dependency of the cement viscosity on the shear rate and volume fraction of cement and the additive particles. The convection–diffusion equation was used to solve for the volume fraction. After solving the equations in the dimensionless forms, we conducted a parametric study to analyze the effects of nano-silica, fly ash, and combined nano-silica and fly ash additives on the velocity and volume fraction profiles of the cement suspension. According to the parametric study presented here, larger nano-silica content results in lower centerline velocity of the cement suspension and larger non-uniformity of the volume fraction. Compared to nano-silica, fly ash exhibits an opposite effect on the velocity. Larger fly ash content results in higher centerline velocity, while the effect of the fly ash on the volume fraction is not obvious. For cement suspension containing combined nano-silica and fly ash additives, nano-silica plays a dominant role in the flow behavior of the suspension. The findings of the study can help the design and operation of the pulsating flow of fresh cement mortars and concrete in the 3D printing industry.
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Design and instrumentation of a novel centrifuge container for fly-ash run-out experiments
Debris flow, landslides and material run-outs have significant environmental and economic consequences for numerous industries. High-quality experimental data with controlled boundary conditions can help validate and calibrate the predictive capabilities of mechanistic and semi-empirical numerical models. A novel centrifuge container to model dewatering and run-outs induced by a rapid loss of confinement is presented. The design features a pair of vertical doors opened in-flight to simulate failure of the containing structure. Illustrative centrifuge results investigating the run-out characteristics of a fully saturated, densely deposited class-F fly ash are presented. Modified soil moisture probes to monitor the distributions and time-varying fly-ash water content throughout the testing are explored. Furthermore, the successful use of depth-sensing cameras to reconstruct progressive deformations of the material front at various time scales is demonstrated. Combined water content, pore pressure and deformation measurements provide insight into the material behaviour during the run-out, revealing two time scales at which the deformations occur. However, discrepancies between water contents inferred from the dielectric measurements and electrical conductivities highlight the need for independent verification of the bulk material water content when using the modified probes. Overall, the potential of these innovative instrumentation techniques to complement traditional geotechnical instrumentation is shown.
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- Award ID(s):
- 1520581
- PAR ID:
- 10398667
- Date Published:
- Journal Name:
- International Journal of Physical Modelling in Geotechnics
- ISSN:
- 1346-213X
- Page Range / eLocation ID:
- 1 to 21
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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To promote the sustainable development of eco-efficient calcium sulfoaluminate (CSA) cements through the partial replacement of the CSA clinker with supplementary cementitious waste products, the effects of coal fly ashes on the early-age and mature-age properties of a calcium sulfoaluminate (CSA)-based cement paste were investigated. The impacts of both Class C and Class F fly ashes on the rheological properties, hydration kinetics, and compressive strength development of CSA cement paste were studied. Rheology-based workability parameters, representing the rate of loss of flowability, the rate of hardening, and the placement limit, were characterized for the pastes prepared with fixed water-to-cement (w/c) and fixed water-to-binder (w/b) ratios. The results indicate a slight improvement in the workability of the CSA paste by fly ash addition at a fixed w/b ratio. The isothermal calorimetry studies show a higher heat of hydration for the Class C fly ash-modified systems compared to the Class F-modified systems. The results show that fly ash accelerates the hydration of the calcium sulfoaluminate cement pastes, chiefly due to the filler effects, rather than the pozzolanic effects. In general, ettringite is stabilized more by the addition of Class F fly ash than Class C fly ash. Both fly ashes reduced the 1-day compressive strength, but increased the 28-day strength of the CSA cement paste; meanwhile, the Class C modified pastes show a higher strength than Class F, which is attributed to the higher degree of reaction and potentially more cohesive binding C-S-H-based gels formed in the Class C fly ash modified systems. The results provide insights that support that fly ash can be employed to improve the performance of calcium sulfoaluminate cement pastes, while also enhancing cost effectiveness and sustainability.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1680/jphmg.21.00044
