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Related Concept Videos

Porosity in Cement Paste01:18

Porosity in Cement Paste

207
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.
The balance of water to cement in the mix is...
207
Soundness of Cement01:17

Soundness of Cement

224
The soundness of cement refers to the ability of cement paste to retain its volume after setting. Unsound cement can lead to expansion and structural damage due to the presence of free lime, magnesia, and calcium sulfate. Free lime hydrates very slowly, expanding and causing unsoundness, which is difficult to detect because it intercrystallizes with other compounds. Magnesia also reacts with water, forming crystals that can disrupt the cement's structure. Calcium sulfate can create...
224
Strength of Cement01:20

Strength of Cement

208
Strength tests for cement are not performed directly on neat cement paste due to difficulty in obtaining consistent, reliable specimens. Instead, cement is typically tested in the form of cement-sand mortar.
For compressive strength tests, ASTM C 109-05 standards prescribe a cement-sand mix ratio of 1:2.75 and a water/cement ratio of 0.485 for making 2-inch cubes. These cubes are mixed, cast, and cured in saturated lime water at 23°C until testing. Flexural strength testing, outlined in...
208
Design Example: Managing Concrete Workability01:14

Design Example: Managing Concrete Workability

111
This example deals with managing the workability of concrete for a raft foundation project under hot weather conditions. Workability is crucial for ensuring the concrete is easy to place, compact, and finish. In this scenario, a slump test — a common method to measure the workability of fresh concrete — initially indicated low workability. This was attributed to the rapid water loss from the concrete mix, exacerbated by the high temperatures causing the course aggregates to heat up.
111
Testing Water Quality01:14

Testing Water Quality

166
When the quality of water for concrete preparation is uncertain, its impact on the setting time of cement and compressive strength of mortar is assessed by comparison with de-ionized or distilled water benchmarks. American Society for Testing and Materials (ASTM) C1602 requires the setting times to be within 90 minutes of the control, British Standard (BS) 3146:1980 allows a 30-minute variance in the initial setting, while British Standards European Norm (BS EN) 1008 specifies initial setting...
166
Deleterious Substances in Aggregate01:25

Deleterious Substances in Aggregate

231
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...
231

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Related Experiment Video

Updated: Aug 25, 2025

Production and Analysis of Sporosarcina pasteurii Biocement Bricks Using Custom 3D-Printed Molds for Unconfined Compression Tests
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Experimental Investigation on Red Mud from the Bayer Process for Cemented Paste Backfill.

Jiwei Bian1, Shuai Li1, Qinli Zhang1

  • 1School of Resources and Safety Engineering, Central South University, Yuelu District, Changsha 410083, China.

International Journal of Environmental Research and Public Health
|October 14, 2022
PubMed
Summary

This study demonstrates that adding binders to red mud from the Bayer process significantly enhances its mechanical strength and water resistance for cemented paste backfill (CPB). This method also effectively reduces hazardous substance leaching, offering an eco-friendly utilization solution.

Keywords:
CPBleachingred mudwater resistance

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Area of Science:

  • Materials Science
  • Environmental Engineering
  • Chemical Engineering

Background:

  • Red mud, a byproduct of alumina production via the Bayer process, poses significant disposal challenges due to its environmental impact.
  • Current disposal methods for red mud are often unsustainable and environmentally detrimental.

Purpose of the Study:

  • To investigate the feasibility of utilizing red mud in cemented paste backfill (CPB).
  • To enhance the mechanical properties, water resistance, and environmental behavior of red mud-based CPB using various binders and activators.
  • To introduce and utilize water immersion tests for evaluating CPB water resistance.

Main Methods:

  • Experimental investigation of red mud-based CPB formulations with different binders and activators.
  • Unconfined compressive strength (UCS) testing.
  • Water immersion tests to assess disintegration and softening.
  • Leaching experiments to determine the release of hazardous substances.
  • Softening coefficient determination after 28 days of curing.

Main Results:

  • Unmodified red mud specimens exhibited low UCS (<0.2 MPa) and disintegrated in water.
  • Binders significantly improved the mechanical properties and water resistance of red mud-based CPB, with softening coefficients exceeding 0.7.
  • Binders effectively inhibited the leaching of hazardous substances (Cr(VI), Se, F, As, Pb, V) by over 70% through solidification and stabilization.

Conclusions:

  • The addition of binders is crucial for improving the performance of red mud-based CPB.
  • Red mud-based CPB with binders demonstrates excellent mechanical properties, water resistance, and reduced environmental risk.
  • This approach offers a viable, environmentally friendly, and large-scale utilization strategy for Bayer process red mud.