Related Experiment Video
Updated: Jul 15, 2025
08:16
A Bending Test for Determining the Atterberg Plastic Limit in Soils
Published on: June 28, 2016
20.4K
Shrinkage behavior of compacted bentonite considering physicochemical effects
Zhaoyang Song1, Zhihong Zhang1, Youqian Lu2
1Key Laboratory of Urban Security and Disaster Engineering of Ministry of Education, Beijing University of Technology, Beijing, China.
The Science of the Total Environment
|October 4, 2023
Summary
This study reveals how salt concentration affects bentonite clay shrinkage, crucial for environmental engineering. Higher salinity reduces swelling and alters pore structure during drying, impacting barrier performance.
Area of Science:
- Geotechnical Engineering
- Environmental Science
- Materials Science
Background:
- Bentonite's shrinkage behavior is critical for buffer barrier efficiency in environmental geotechnical applications.
- Physicochemical effects, particularly pore water salinity, significantly influence bentonite's properties.
Purpose of the Study:
- To investigate the shrinkage behavior of Na-bentonite under varying salt concentrations.
- To analyze the impact of pore water salinity on moisture distribution and microstructural evolution during drying.
Main Methods:
- Shrinkage experiments on Na-bentonite specimens prepared with different salt solution concentrations.
- Nuclear Magnetic Resonance (NMR) and Scanning Electron Microscopy (SEM) for moisture and structural analysis.
Main Results:
- Increased pore water salinity decreased swelling deformation and porosity during saturation.
- Drying-induced shrinkage was anisotropic (axial strain > radial strain).
- Higher salinity led to pore water accumulation in smaller pores and a more aggregated microstructure.
Conclusions:
- Pore water salinity influences bentonite's shrinkage and microstructure, with effects diminishing upon water evaporation.
- The study provides a theoretical framework using an effective stress-based constitutive relationship to describe saline bentonite shrinkage.
Related Concept Videos
01:27Shrinkage in Concrete
113
Shrinkage in concrete is primarily due to water loss from evaporation, hydration of cement, or carbonation, leading to a reduction in volume. The volumetric contraction results in volumetric strain in concrete. However, in practice, shrinkage is measured as linear strain, which is one-third of the volumetric strain.
When concrete is still in its plastic state, it can undergo a decrease in volume by about 1% of its absolute volume. This decrease is known as plastic shrinkage. It arises either...
When concrete is still in its plastic state, it can undergo a decrease in volume by about 1% of its absolute volume. This decrease is known as plastic shrinkage. It arises either...
113
01:21Drying Shrinkage
83
When hardened concrete is exposed to air with a relative humidity of less than 100 percent, it begins to lose the free water within its capillaries. As this water evaporates, the water initially adsorbed onto the calcium silicate hydrates migrates towards these now empty spaces and eventually evaporates as well. Over time, as more water leaves, the volume of the concrete decreases, a phenomenon known as drying shrinkage.
A portion of this drying shrinkage can be reversed; if the concrete is...
A portion of this drying shrinkage can be reversed; if the concrete is...
83
01:26Unsoundness of Aggregate due to Volume Change
118
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...
118
01:24Carbonation Shrinkage
152
Atmospheric CO2 penetrates the concrete's pores and, in the presence of moisture, forms carbonic acid, which then reacts with calcium hydroxide in the hydrated cement, forming calcium carbonate. This process reduces the concrete's volume and is termed carbonation shrinkage.
The concrete's permeability is slightly reduced as calcium carbonate produced during the reaction fills its pores. Furthermore, its strength is slightly enhanced as the water released during the reaction...
The concrete's permeability is slightly reduced as calcium carbonate produced during the reaction fills its pores. Furthermore, its strength is slightly enhanced as the water released during the reaction...
152
01:23Pore Size Distribution
155
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.
Adequate...
Adequate...
155
01:20Porosity and Absorption of Aggregate
303
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...
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...
303