ASTM C807
OVERVIEW OF ASTM C 807 - Standard Test Method for Time of Setting of Hydraulic Cement Mortar by Modified Vicat Needle
Introduction
The ASTM C 807 standard provides a method for determining the setting time of hydraulic cement mortar, a critical factor in construction and building material assessment. This test employs a modified Vicat needle to measure the time it takes for cement mortar to reach a specified level of hardness.
Scope and Safety
Scope:
This method focuses on using the modified Vicat needle to ascertain the setting time of hydraulic cement mortar.
It adheres strictly to SI units.
Safety Concerns:
Emphasizes precautions due to the caustic nature of fresh hydraulic cement.
Recommends protective gear and immediate action in case of skin contact.
Summary of Test Method
The method involves preparing a mortar with specified quantities of cement, water, and standard sand. The consistency of this mortar is first determined using a modified Vicat apparatus. The time of setting is then measured by observing the time required for the modified Vicat needle to achieve a specific penetration depth.
Significance and Use
This test is vital for verifying compliance of cement with specified setting time limits, particularly useful for expansive cements. It helps in ensuring the suitability of cement for various construction purposes.
Apparatus
The test requires specific apparatus like a modified Vicat apparatus, tamper, trowel, mold, mixer, bowl, paddle, scraper, glass graduates, and precise mass determining devices.
Reagents and Materials
Graded standard sand and potable or reagent water (as per ASTM D1193 specifications) are used in this method.
Sampling and Conditioning
Cement samples should be collected as per Practice C183, and the test environment, including materials and equipment, should be maintained at specific temperatures and humidity levels.
Test Procedure
Preparation of Mortar:
Mix cement, water, and standard sand to achieve desired consistency.
Puddle the mortar in a mold using a tamper.
Test for Consistency:
Determine using the modified Vicat apparatus.
The mortar is of correct consistency when the rod settles to a point 20 ± 4 mm below the original surface after 30 seconds.
Test for Time of Setting:
After confirming the mortar's consistency, remold and place it in a moist closet or room.
Use the modified Vicat apparatus to measure needle penetration at regular intervals until a penetration of 10 mm or less is achieved.
Precautions:
Ensure the testing apparatus is on a stable, vibration-free surface.
Maintain the cleanliness of the plunger and guide bearing.
Calculation
Calculate the setting time to the nearest minute using the formula involving times and penetration readings at various intervals.
Reporting
Report the time of setting in minutes, with the nearest one-minute precision.
Precision and Bias
The multilaboratory standard deviation is 15.2 minutes, indicating that results from different labs on the same cement sample should not differ by more than 43 minutes.
No bias information is available due to the absence of a material with an accepted reference value.
Conclusion
The ASTM C807 test method is an essential tool in the field of construction and material science, providing a standardized approach to determine the setting time of hydraulic cement mortar. This method ensures the consistency and reliability of cement used in various applications, affirming its suitability and quality for specific construction needs.