[LAB IN YOUR GRASP] CHARACTERIZATION TEST : "NORMAL CONSISTENCY TEST OF BINDER (CEMENT & FLY ASH)"

Summary

In this video, researchers Adlizie and Panglima from the Geopolymer Research Consortium LBE Green Concrete demonstrate a unique lab testing process for cement and fly ash as a binder. The test, based on ASTM C187-16, focuses on determining the minimum water-to-binder ratio using a trial-and-error method. By substituting 30% of cement with fly ash, the test reveals the impact of fly ash on water consumption in concrete mixtures. The video guides viewers through each step, showing the preparation, mixing, and Vicat test procedure, ultimately highlighting the influence of fly ash on normal consistency.

Takeaways

• 😀 Fly ash is a pozzolanic material that contains reactive alumina silicate and calcium, which can enhance the strength and durability of concrete.
• 😀 Fly ash reacts with cement and water to produce calcium hydroxyde, calcium silicate hydrate (C-S-H), and calcium aluminate hydrate (C-A-H), improving the concrete's properties over time.
• 😀 Fly ash can substitute cement as a binder in concrete, increasing compressive strength and reducing permeability in the long term.
• 😀 The normal consistency test is conducted to determine the water-to-binder ratio (w/b) required for proper hydration and paste consistency in concrete.
• 😀 In the test, fly ash substitutes 30% of the cement by weight, resulting in a total specimen weight of 300 grams (210 grams of cement and 90 grams of fly ash).
• 😀 The water content in the first trial starts at 30% of the binder weight, equal to 90 grams of water.
• 😀 After mixing the cement, fly ash, and water, the paste is formed and tested using a Vicat apparatus to check the consistency.
• 😀 The Vicat test involves the use of a steel bar, which is lowered into the paste to measure the consistency based on the depth of penetration.
• 😀 The target consistency for this test is a 10 ± 1 mm penetration, with adjustments made to the water-to-binder ratio to achieve this result.
• 😀 Results showed that using fly ash increased the water consumption, with a final result of 30.5% water content compared to the pure cement test, which had 29%.

Q & A

What is the role of fly ash in the geopolymer concrete mix?

Fly ash is a pozzolanic material that reacts with cement and water to generate calcium hydroxyde, which then produces calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H). This reaction improves the compressive strength and reduces the permeability of concrete in the long term.

What is the purpose of the normal consistency test demonstrated in the video?

The normal consistency test aims to determine the minimum amount of water needed for the binder (cement and fly ash mixture) to achieve a standard consistency, specifically to find the water-to-binder ratio (w/b) that results in a 10 ± 1 mm descent of the Vicat bar.

How does the water-to-binder ratio impact the test results?

The water-to-binder ratio is crucial because it influences the consistency and the ability of the paste to flow under the Vicat bar. If the ratio is too high or low, the resulting consistency may not meet the required 10 ± 1 mm descent, thus affecting the final results.

What is the significance of fly ash in the context of this test?

Fly ash serves as a partial substitute for cement in the binder. In this test, fly ash replaces 30% of the cement weight, which increases the water consumption required for the mixture to achieve the desired consistency.

What equipment is used in the normal consistency test?

The equipment includes a digital scale (0.01 mg accuracy), water and beaker glass, an iron bowl, a paste mixer, a plastic spoon, a Vicat ring, acrylic plates, latex gloves, and a Vicat test apparatus.

How is the paste prepared for the test?

The paste is prepared by mixing cement and fly ash in the correct proportion (30% fly ash by weight). Water is added based on the initial water-to-binder ratio, and the mixture is stirred and mixed using a spoon and a paste mixer.

Why is the Vicat steel bar lowered onto the paste in the test?

The Vicat steel bar is lowered onto the paste to measure the penetration depth, which is an indicator of the paste’s consistency. The descent of the bar is used to determine if the desired consistency has been achieved.

What is the significance of achieving a 10 ± 1 mm descent in the Vicat test?

Achieving a 10 ± 1 mm descent ensures that the binder mixture has the right consistency for further testing and use in the concrete mix. A deviation from this target could suggest an incorrect water-to-binder ratio.

How does the water content in the test vary with the addition of fly ash?

The addition of fly ash increases the water consumption required to achieve the correct consistency. In this test, fly ash substitution led to a 1.5% increase in water content compared to pure cement.

What happens if the desired 10 ± 1 mm descent is not achieved?

If the desired descent is not achieved, a linear regression analysis is performed on the results to determine the correct water-to-binder ratio that will meet the target of 10 ± 1 mm descent.