AASHTO T21 ASTM C40

Summary

The video explains the ASHTTO T-21 and ASMC40 methods for testing organic impurities in fine aggregates used in concrete. It covers the two testing procedures, one using a 3% sodium hydroxide solution and a glass color standard, and the other using a potassium bromate solution in sulfuric acid. The process involves preparing the sample, adding the solutions, and observing color changes to determine organic contamination levels. If impurities are found, additional tests may be needed. The video also mentions that there are no significant differences between ASHTTO T-21 and ASMC40.

Takeaways

• 🧪 ASHTTO T-21 and ASMC40 are standard test methods for detecting organic impurities in fine aggregate used for concrete.
• ⚠️ The test involves hazardous materials such as 3% sodium hydroxide, potassium dichromate, and concentrated sulfuric acid.
• 👷 Users of these chemicals are responsible for their proper handling and safety.
• 🔬 The main purpose of the test is to determine if harmful amounts of organic matter are present in the fine aggregate.
• 🧴 There are two methods: using 3% sodium hydroxide solution with a glass color standard or using potassium dichromate in concentrated sulfuric acid.
• ⏱ When using potassium dichromate, the reference standard color solution must be prepared no longer than 2 hours before the test; this is not required for the sodium hydroxide method.
• 🥽 The test requires a colorless glass bottle with a watertight cap, capacity 240–470 ml, and thickness 1.5–2.5 inches.
• ⚖️ Sample collection should follow ASHTTO T2 or ASMC D75, with a sample weight of approximately 450 g (1 lb).
• 🧪 To perform the sodium hydroxide method, fill the bottle with sample and solution to specific marks, cap, shake, and let sit for 24 hours before color comparison.
• 🎨 The final test involves comparing the liquid color to a glass color standard; if the color is darker than standard number three, further tests like ASHTTO T71 may be needed.
• ✅ There are no significant differences between ASHTTO T-21 and ASMC40 methods.

Q & A

What is the main purpose of the ASHTTO T-21 and ASMC40 test methods?

The main purpose of the ASHTTO T-21 and ASMC40 test methods is to determine if there are harmful amounts of organic matter present in fine aggregate for concrete.

What hazardous materials are involved in performing this test?

The hazardous materials involved include 3% sodium hydroxide solution, potassium dichromate, and concentrated sulfuric acid.

What should users be responsible for when using hazardous materials in this test?

Users are responsible for the proper use and handling of hazardous materials during the test.

What are the two methods for performing the organic impurities test in fine aggregate?

The two methods are using 3% sodium hydroxide solution with a glass color standard, or producing a standard color solution by dissolving reagent grade potassium dichromate in concentrated sulfuric acid.

How is the standard color solution prepared using potassium dichromate?

The standard color solution is prepared by dissolving 0.25 g of reagent grade potassium dichromate in 100 ml of concentrated sulfuric acid.

How long in advance must the standard color solution be prepared when using potassium dichromate?

The standard color solution must be prepared no more than 2 hours before the test.

Is there a time limitation for preparing the 3% sodium hydroxide solution?

No, there is no time limitation for preparing the 3% sodium hydroxide solution.

What is the required capacity of the colorless glass bottle used for the test?

The colorless glass bottle must have a capacity of 240 to 470 ml (8 to 16 fluid ounces).

What should the thickness of the glass bottle be?

The thickness of the glass bottle must be at least 1 and 1/2 inches but not more than 2 and 1/2 inches.

How should the sample be prepared before performing the test?

The sample should be obtained in accordance with ASHTTO T2 or ASM D75, weighing approximately 450 g or one pound.

What should be done after adding the 3% sodium hydroxide solution to the sample?

After adding the solution, the bottle should be capped and shaken vigorously, and then the sample should sit for 24 hours before comparing the color to the glass color standard.

What should be done if the liquid turns darker than the standard color?

If the liquid turns darker than the number three glass color standard or darker than the standard color solution, additional tests, such as ASHTTO T71, may be necessary to assess the effect of organic impurities on mortar strength.

Are there any significant differences between ASHTTO T-21 and ASMC40?

No, there are no significant differences between ASHTTO T-21 and ASMC40.