ASTM C191
Overview of ASTM C191 - Test Method for Time of Setting of Hydraulic Cement by Vicat Needle
Introduction
The ASTM C 191 standard outlines methods for determining the time of setting of hydraulic cement using the Vicat needle. This standard features two test methods: Method A using the manually operated standard Vicat apparatus and Method B allowing the use of an automatic Vicat machine.
Scope and Safety
Scope:
This standard aims to establish the time of setting of hydraulic cement using the Vicat needle.
It adheres to SI units as the standard measurement system.
Safety Concerns:
Emphasizes the importance of protective measures due to the caustic nature of fresh hydraulic cement mixtures.
Referenced Documents
Various ASTM standards are referenced, including C 150, C 151, C 183, and others, providing guidelines and specifications for cement testing.
Terminology
The terms used in this test method are defined in accordance with Terminology ASTM C219, ensuring clear understanding and consistency in application.
Summary of Test Method
The test involves preparing a cement paste to normal consistency, then performing periodic penetration tests using a 1-mm Vicat needle. The initial time of setting is determined by the time taken for the needle to achieve a penetration of 25 mm, while the final time is noted when the needle does not leave a complete circular impression on the paste surface.
Significance and Use
This test method is crucial for determining compliance with specification limits for Vicat time of setting. It's important to note that the time of setting determined by this method may not be the same as that measured by other methods or the setting time of mortar or concrete.
Apparatus
The required apparatus includes a Vicat apparatus with a movable rod and needles of specific dimensions, reference masses, and devices for determining mass, glass graduates, non-adsorptive plates, a flat trowel, and a conical ring. For Method B, an automatic Vicat Needle Apparatus is used.
Reagents and Materials
Potable water or reagent water conforming to ASTM D1193 specifications is used for mixing the cement paste.
Sampling and Conditioning
Cement samples should be obtained as per Practice ASTM C183, with specific environmental conditions maintained for the testing area, including temperature and humidity.
Test Procedures
Preparation of Cement Paste:
Mix 650 g of cement with water required for normal consistency as per Test Method ASTM C187.
Molding Test Specimen:
Form the cement paste into a ball and mold it into a conical ring placed on a non-absorptive plate.
Time of Setting Determination:
For Method A, manually perform penetration tests with the Vicat needle. For Method B, use the automatic Vicat apparatus to record penetration measurements.
Calculation
Calculate the Vicat time of setting to the nearest minute for initial and final settings.
Reporting
Report the Vicat times of setting for both initial and final settings, specifying the method used (A or B).
Precision and Bias
Provides standard deviation values for single-operator and multi-laboratory tests.
No bias information is available due to the absence of a suitable reference material.
Conclusion
ASTM C191 is a pivotal standard in the construction industry, providing a reliable means to determine the setting time of hydraulic cement. This test method ensures that cement meets specific time-related criteria, which is essential for its performance in various applications. The use of Vicat needles, both manually and automatically, offers a standardized approach to measure setting time, contributing to consistent quality control in cement usage.