AASHTO T255 ASTM C566

Summary

This video provides an overview of the AASHTO T255 and ASTM C566 standards for determining the total evaporable moisture content of aggregates by drying. The procedure involves obtaining a representative sample, drying it under controlled conditions, and measuring its mass loss to calculate moisture content. The method ensures accurate and uniform results critical for concrete batch production. It also highlights potential risks like particle explosions when using rapid heating methods and explains how to calculate total evaporable moisture and surface moisture for aggregates.

Takeaways

• 😀 Determining the moisture content of aggregates is crucial for maintaining consistent quality in batch-to-batch concrete production.
• 😀 The standard methods for testing total evaporable moisture of aggregates are ASTM T255 and ASMC 566.
• 😀 The moisture content must be adjusted when there is a change in the total evaporable moisture of the aggregates.
• 😀 The sample for testing should be dried until further heating results in less than a 1% additional mass loss.
• 😀 Larger particles take longer to dry compared to smaller particles, and rapid heating may cause explosions in some cases.
• 😀 Microwaving aggregates may lead to explosions due to certain minerals in the aggregate.
• 😀 Quick-drying methods using denatured alcohol and fire can expedite the process, but caution should be exercised.
• 😀 Sample sizes for testing vary based on the nominal maximum aggregate size, as listed in Table 1 of the standards.
• 😀 A scale accurate to 0.1% of the sample mass is necessary for the procedure, along with a suitable container and heat source.
• 😀 After drying, successive readings are taken to ensure the sample has dried sufficiently, with readings showing less than 1% additional loss in mass.
• 😀 The total evaporable moisture content is calculated by comparing the initial and final mass of the sample, and the surface moisture is derived by subtracting absorption from the evaporable moisture.

Q & A

What is the purpose of determining the total evaporable moisture content in aggregates?

Determining the total evaporable moisture content is crucial for maintaining quality and uniformity in batch-to-batch concrete production. It ensures that the designed batch weights are adjusted correctly when there is a change in the moisture content of the aggregates.

What does the method ASHTO T255 measure and how reliable is it?

ASHTO T255 measures the total evaporable moisture content of aggregates by drying. It is generally more reliable than the sample can be made to represent the aggregate supply. However, the method does not have a time specification for drying, instead, drying continues until further heating causes less than a 1% additional loss in mass.

Why is drying the sample important and what factors need to be considered during the process?

Drying the sample ensures that the moisture content is accurately measured. Factors to consider include avoiding overheating or scorching the aggregate, stirring the sample evenly if using a hot plate, and ensuring no material loss during the stirring process.

What is the risk of rapid heating or using microwaves in drying the sample?

Rapid heating can cause aggregate particles to explode, and using microwaves can present a risk of explosion due to the presence of certain minerals within the aggregate. Caution is necessary when using these methods.

What precautions should be taken when using denatured alcohol and fire in the drying process?

When using denatured alcohol and fire, caution must be exercised to prevent accidents and ensure safety. These methods can expedite the drying process, but their impact on the accuracy of results, especially for larger particles, is still unclear.

What sample size is required for the total evaporable moisture test?

The sample size for the test varies depending on the nominal maximum aggregate size. ASHTO T255 Table 1 provides the exact sample sizes for normal weight aggregates.

How should the scale be used in the moisture test?

The scale should be accurate to at least 0.1% of the sample mass. This precision is necessary to determine the mass of the sample before and after drying accurately.

What is the significance of the 1% additional loss in mass during drying?

The 1% additional loss in mass during successive drying readings indicates that the sample has been sufficiently dried. If the loss falls below 1%, the sample is considered adequately dry for accurate measurement.

How do you calculate the total evaporable moisture content from the test results?

The total evaporable moisture content is calculated using the formula: P = [(W - D) / W] * 100, where P is the moisture content in percent, W is the weight of the original sample in grams, and D is the weight of the dry sample in grams.

What is the difference between total evaporable moisture and surface moisture?

Total evaporable moisture refers to the moisture content that can be evaporated from the aggregate by drying, while surface moisture is the difference between total evaporable moisture and the absorption capacity of the aggregate.