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Related Concept Videos

Porosity in Cement Paste01:18

Porosity in Cement Paste

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The porosity of concrete is a measure of the void spaces within its structure. These spaces impact its strength and durability significantly. When water and cement interact, a chemical reaction called hydration creates a semi-solid paste. This paste includes combined water, making up approximately 23% of the cement's dry mass, and gel water, which fills minuscule voids known as gel pores, accounting for about 28% of the cement gel volume.
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Gradually Varying Flow01:29

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Gradually varying flow (GVF) in open channels describes situations where water depth changes slowly along the channel due to factors like non-uniform bed slope, channel shape variations, or obstructions. This flow type occurs when the depth adjusts gradually to balance gravitational forces, shear forces, and energy requirements, resulting in a low rate of depth change.Characteristics of Gradually Varying FlowGVF is commonly observed in natural streams, rivers, and canals, where flow depth...
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In concrete, the pore size distribution significantly influences the material's properties. Capillary pores, markedly larger than gel pores, form a vast network within partially hydrated cement paste, reducing the concrete's strength and increasing its permeability. This heightened permeability leads to a greater risk of damage from environmental factors like freeze-thaw cycles and chemical attacks, with the extent of vulnerability also being tied to the water-to-cement ratio.
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Aggregate shape is classified based on the relative sharpness or roundness of the edges and corners. This classification includes categories like rounded, angular, elongated, and flaky, each with specific characteristics. Rounded aggregates, fully shaped by attrition, are typical of river or seashore gravel, while angular aggregates, such as crushed rock, have well-defined edges. Aggregates that are elongated and flaky are less desirable, as they can reduce the workability and strength of...
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Rapidly varying flow (RVF) in open channels is characterized by abrupt changes in flow depth over a short distance, with the rate of depth change relative to distance often approaching unity. These flows are inherently complex due to their transient and multi-dimensional nature, making exact analysis difficult. However, approximate solutions using simplified models provide valuable insights into their behavior.Key Features of Rapidly Varying FlowRVF is commonly observed in scenarios involving...
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In precipitation gravimetry, the precipitating agent should react specifically or selectively with the analyte. While a specific reagent reacts with the analyte alone, a selective reagent can react with a limited number of chemical species.
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Updated: Jan 10, 2026

An Analog Macroscopic Technique for Studying Molecular Hydrodynamic Processes in Dense Gases and Liquids
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Shape evolution of pumice during granular flow.

Carolina Figueiredo1, Ulrich Kueppers1, Luiz Pereira1,2

  • 1Department of Earth and Environmental Sciences, Ludwig-Maximilians-Universität München, Munich, Germany.

Communications Earth & Environment
|November 24, 2025
PubMed
Summary
This summary is machine-generated.

Volcanic ash generation from pumice lapilli during tumbling experiments quickly produced significant ash. Pyroclast shape evolution showed a decelerating rate of change, offering insights into eruption dynamics.

Keywords:
Natural hazardsSedimentologyVolcanology

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Area of Science:

  • Geosciences
  • Volcanology
  • Experimental Petrology

Background:

  • Explosive volcanic eruptions pose significant geo-hazards.
  • Direct observation of energetic eruptive processes is limited.
  • Studying pyroclast textures and deposits is crucial for understanding eruption dynamics and improving hazard assessments.

Purpose of the Study:

  • To investigate ash generation and pyroclast shape evolution during volcanic eruptions.
  • To provide experimental constraints for improving volcanic hazard assessment.
  • To quantify the susceptibility of porous pyroclasts to shape change.

Main Methods:

  • Performed tumbling experiments using pumice lapilli from the Laacher See eruption.
  • Measured volume and four morphological parameters (axial ratio, convexity, form factor, solidity) of 100 clasts before and after each experimental step.
  • Analyzed ash generation and pyroclast shape evolution in terms of effective relaxation timescales.

Main Results:

  • Significant ash generation (up to 48 wt.%) occurred within the first 15 minutes of tumbling.
  • Most pyroclast shape change happened rapidly in the initial experimental stages.
  • Pyroclasts exhibited a decelerating rate of shape change, approaching a time-invariant morphology.

Conclusions:

  • The study quantifies the susceptibility of porous pyroclasts to shape changes.
  • Findings enhance the understanding of transport processes from clast generation to sedimentation.
  • Experimental data provides vital contributions to volcanic hazard assessment by simulating ash formation and clast evolution.