ASTM C265
Overview of ASTM C265 - Standard Test Method for Water-Extractable Sulfate in Hydrated Hydraulic Cement Mortar
Introduction to ASTM C265
The ASTM C265 standard outlines the method for measuring water-extractable sulfur trioxide (SO3) in hardened hydraulic cement mortar. This test is crucial in determining the unreacted, available sulfate remaining in the mortar, which is key to understanding the chemical composition and potential performance of the cement.
Scope
ASTM C 265 is designed to measure the water-extractable SO3 in hardened hydraulic cement mortar. It's particularly important in identifying excess soluble sulfate ions, which could impact the durability of the cement. This test method is applicable for compliance checks in Specification C 595 for cements where optimized SO3 exceeds table limits and provides valuable information for other hydraulic cements, as specified in Specifications C 150 and C 1157.
Safety Concerns
This standard emphasizes safety due to the caustic nature of fresh hydraulic cement mixtures, which can cause chemical burns upon prolonged exposure.
Apparatus and Materials
Sieve: A 2.36-mm (No.8) sieve as per Specification E 11.
Mixer, Bowl, and Paddle: As specified in Practice C 305.
Polyethylene Containers: Watertight bags or sheets for sample storage.
Mortar and Pestle: For sample pulverization.
Water Bath: Controlled at 23.0 ± 0.15 °C.
Mixing Water: Conforming to Type II of Specification D 1193.
Graded Sand: As per Specification C 778.
Test Procedure
Preparation of Test Mortar: The mortar is proportioned and mixed following the guidelines of Test Method C 109/C 109M, using a water-cementitious material ratio of 0.5.
Storage of Test Mortar: The mixed mortar is stored in polyethylene containers in a water bath maintained at a specified temperature.
Preparation of Cement Extract: After specific time intervals (24 hours, 3 days, 7 days), the mortar is removed, pulverized, and mixed with water. This mixture is then mechanically stirred and filtered.
Analysis of the Extract: The filtrate is analyzed using the sulfur trioxide determination section of Test Methods C 114, including a reagent blank test.
Calculation and Reporting
The SO3 content is calculated to the nearest 0.01 g/L of solution, and the results from two determinations are averaged. The age of the test specimens is also reported.
Precision and Bias
The within-laboratory standard deviation for 24-hour testing is 0.077 g/L SO3.
The between-laboratory standard deviation for the same period is 0.137 g/L SO3.
Since no reference samples are available, no conclusive statement can be made about the bias of this test method.
Significance
This test method is essential for assessing the quality of hydraulic cement, particularly in determining the sulfate levels that could affect the material's durability and suitability for various applications. It helps in ensuring that the cement conforms to specific standards and performs as expected in construction projects.
Testing Method Overview
Mortar Preparation: Following specified proportions and mixing guidelines to ensure consistency.
Storage: Using polyethylene containers and a controlled water bath for precise temperature maintenance.
Sample Processing: Pulverizing and stirring the mortar sample with water at specific intervals for analysis.
Analysis: Filtering the slurry and analyzing the clear extract for SO3 content using established chemical methods.
Calculation: Using the formula to calculate the SO3 concentration in the solution.
Reporting: Averaging results from duplicate tests and noting the age of the test specimens.
The ASTM C 265 test method plays a vital role in quality control processes within the cement industry, ensuring the production of durable and reliable cement products.