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Related Concept Videos

Unsoundness of Aggregate due to Volume Change01:26

Unsoundness of Aggregate due to Volume Change

Unsoundness in aggregates due to volume changes is primarily caused by the physical alterations aggregates undergo, such as freezing and thawing, thermal changes, and wetting and drying. Unsound aggregates, when subjected to these changes, result in volume change upon disintegration. This, in turn, contributes to the deterioration of concrete, including scaling, pop-outs, and cracking. Particular types of aggregates, such as porous flints, cherts, and those containing clay minerals, are...
Porosity and Absorption of Aggregate01:20

Porosity and Absorption of Aggregate

Aggregates contain pores of varying sizes; while some are completely enclosed within the particles, others open onto the surface, allowing water to penetrate. The porosity of aggregates is a major factor contributing to the overall porosity of concrete, given that aggregates constitute about three-quarters of concrete's volume.
When all pores in an aggregate are filled with water, the aggregate is considered saturated and surface-dry. If left in dry air, water will evaporate until the aggregate...
Maximum Size of Aggregate01:12

Maximum Size of Aggregate

The maximum size of aggregate is defined as the aperture of the sieve retaining 15 percent or more of the particles present in the aggregate sample. The aggregate's maximum size impacts the concrete's water requirement, workability, and strength. Larger aggregates reduce the surface area needing cement paste coverage, which can lower water needs, thereby allowing a decrease in the water-to-cement ratio when the desired workability and richness of the mix are to be maintained, which can result...
Toughness and Hardness of Aggregate01:22

Toughness and Hardness of Aggregate

Toughness and hardness are critical properties of aggregate materials used in concrete, particularly on pavement surfaces and industrial flooring subjected to heavy loads. Toughness is defined as the aggregate's resistance to failure by impact and is measured by the aggregate impact value (AIV). For this, the aggregate impact value test is performed, wherein the impact is delivered by a standard hammer, which falls freely under its own weight onto the aggregates. The aggregates fragment in the...
The Availability Heuristic01:08

The Availability Heuristic

A heuristic is a general problem-solving framework (Tversky & Kahneman, 1974). You can think of these as mental shortcuts that are used to solve problems. Different types of heuristics are used in different types of situations, and the impulse to use a heuristic occurs when one of five conditions is met (Pratkanis, 1989):
Deleterious Substances in Aggregate01:25

Deleterious Substances in Aggregate

Deleterious substances in aggregates can be detrimental to the quality and durability of concrete. These substances include organic impurities like loam, which interfere with cement hydration and are usually present in the sand. These prevent a good bond between aggregate and cement paste. Organic impurities can be detected using the colorimetric test, where the darkness of a solution after agitation indicates the level of organic content.
Another type of impurity is clay and fine material that...

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Visualizing Field Data Collection Procedures of Exposure and Biomarker Assessments for the Household Air Pollution Intervention Network Trial in India
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Some limitations of aggregate exposure metrics.

Louis Anthony Cox1, Douglas A Popken

  • 1Cox Associates, Inc., 503 Franklin Street, Denver, CO 80218, USA. tony@cox-associates.com

Risk Analysis : an Official Publication of the Society for Risk Analysis
|May 22, 2007
PubMed
Summary

Aggregate exposure metrics for complex mixtures can be misleading. Relying solely on these metrics may lead to ineffective risk management decisions, especially when component potencies vary.

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Area of Science:

  • Environmental Health
  • Toxicology
  • Risk Assessment

Background:

  • Aggregate exposure metrics, like sums or weighted averages, are common in assessing complex mixtures (e.g., asbestos-associated dusts).
  • These metrics inform decisions on allowed exposure levels and ambient concentrations, impacting health protection and remediation efforts.

Purpose of the Study:

  • To evaluate the reliability of aggregate exposure metrics in risk assessments of complex mixtures.
  • To determine if aggregate metrics can guide rational risk management when mixture components have varying potencies and compositions.

Main Methods:

  • Theoretical analysis of aggregate exposure metrics under varying component potencies and compositions.
  • Case study in El Dorado Hills, California, comparing aggregate risk estimates with component-specific risk estimates.

Main Results:

  • Aggregate exposure metrics can be unreliable and potentially "worse than useless" when mixture components differ significantly in potency and composition.
  • In the El Dorado Hills case study, aggregate metrics yielded risk estimates approximately 25 times higher than component-specific estimates, with uncertain validity.

Conclusions:

  • Aggregate exposure metrics alone are insufficient for effective risk management of complex mixtures with heterogeneous components.
  • Risk assessment and management strategies should consider the specific potencies and compositions of individual mixture components for accurate health protection.