ASTM C1038

ASTM C1038 overview - Standard Test Method for Expansion of Hydraulic Cement Mortar Bars Stored in Water

Introduction

The ASTM C 1038 standard specifies a test method for determining the expansion of mortar bars made from hydraulic cement, particularly when sulfate is a component of the cement. This test is crucial in the construction industry to ensure the quality and durability of cement products.

Scope and Safety

This method covers the process of measuring the expansion of mortar bars when stored in water, which is indicative of the sulfate content in the cement. High sulfate levels can lead to excessive expansion, compromising the cement's integrity. It's important to note that fresh hydraulic cement mixtures are caustic and can cause chemical burns, thus proper safety measures should be observed.

Apparatus and Materials

• Reference Masses and Mass-Determining Devices: As per Specification C 1005.

• Glass Graduates, Molds, and Length Comparator: Conforming to C 490.

• Moist Cabinet or Room: As per C 511.

• Mixer, Bowl, and Paddle: Conforming to C 305.

• Trowel and Tamper: As per Test Method C 109.

• Mixing Water: Potable or reagent water as per D 1193.

• Graded Sand: Conforming to C 778.

Procedure

1. Preparation of Specimens: Make four test specimens with specified dimensions for each cement, using a mix of cement and graded sand. The effective gage length of these specimens is 250 mm.

2. Molding Test Specimens: Mold the specimens in two layers, ensuring a homogeneous specimen and a smooth surface finish.

3. Initial Storage: Store the specimens in a moist cabinet or room for 22.5 hours, then immerse in water or saturated lime water for at least 30 minutes before initial measurement.

4. Subsequent Storage: Store specimens in saturated lime water, covering them with at least 5 mm of water.

Length Change Measurement

Measure the length change of the specimens at 24 hours and again at 14 days using a length comparator. Additional readings at other intervals can provide more data.

Calculation and Reporting

Calculate the change in length at 24 hours and 14 days to the nearest 0.001% and report the average length change of the four specimens.

Testing Method Overview

1. Specimen Preparation: Create mortar bar specimens using a defined ratio of cement to sand.

2. Molding: Mold specimens in layers, ensuring even compaction and surface smoothness.

3. Initial and Subsequent Storage: Store specimens initially in a moist environment, then in saturated lime water.

4. Measurement: Use a length comparator to measure specimen expansion after 24 hours and 14 days.

5. Calculation: Calculate expansion as a percentage change in length.

6. Reporting: Document average expansion rates for quality assessment.

This ASTM C 1038 test method is a vital tool in the quality control of hydraulic cements, helping to ensure that products used in construction are durable, stable, and safe for their intended applications.