ASTM C348
Understanding ASTM C348 Standard Test Method for Flexural Strength of Hydraulic-Cement Mortars
Introduction
The ASTM Standard Test Method C 348 is a crucial procedure in assessing the flexural strength of hydraulic-cement mortars. This test method provides a standardized approach to evaluate the performance characteristics of cement-based materials, particularly their ability to resist bending or flexing under load. This article delves into the details of the standard and outlines the test method.
Scope and Significance
Scope: ASTM C 348 primarily focuses on determining the flexural strength of hydraulic-cement mortars.
Significance: The test is vital for research and reference purposes, offering insights into the structural integrity and durability of cementitious materials under bending stresses.
Test Method Summary
Mortar Composition: The test mortar comprises 1 part cement and 2.75 parts sand by mass. Water-cement ratios are specified for Portland and air-entraining Portland cements, while other cements use sufficient water to achieve a specified flow.
Prism Preparation: Mortar prisms measuring 40x40x160 mm are moulded in two layers and cured for a day in moulds before testing.
Testing: The prisms undergo a center-point loading test to determine the flexural strength.
Apparatus and Materials
Weights and Measuring Devices: Must conform to ASTM C 1005 standards.
Mixer, Bowl, and Paddle: As per Practice C 305.
Flow Table and Mould: In accordance with C 230/C 230M.
Specimen Moulds: Triple-gang moulds for 40x40x160-mm prisms.
Tamper and Tamper Guide: For uniform compaction of mortar.
Trowel: For smoothing and shaping the mortar in the mould.
Flexure Testing Device: For applying a centre-point load on prisms.
Compression Testing Machine: Hydraulic type as per C 109/C 109M.
Graded Standard Sand: Conforming to Specification C 778.
Procedure
Mortar Preparation: Follow Test Method C 109/C 109M for standard mortar proportioning, consistency, and mixing; Test Method C 1437 for flow determination.
Moulding Process: After the flow test, remix mortar for 15 seconds. Mould specimens within 2 minutes and 30 seconds of mixing, compacting mortar in moulds with tamper strokes.
Specimen Storage: Store specimens according to Test Method C 109/C 109M guidelines.
Flexural Strength Testing: Test specimens immediately after removal from storage within specified time tolerances (24 hours to 28 days). Ensure correct specimen alignment in the testing device and apply load at a specified rate.
Calculation of Results
The flexural strength (Sf) is calculated using the formula Sf = 0.0028 P, where P is the maximum load applied during the test.
Precision, Bias, and Retests
Precision: Specifies the expected variability in test results within a single laboratory and between different laboratories.
Bias: There is no statement on bias due to the absence of an accepted reference material.
Retests: If results are significantly divergent or if specimens are faulty, retests are recommended.
Conclusion
ASTM C348 is an essential standard for assessing the flexural strength of hydraulic-cement mortars. Its rigorous procedure and detailed specifications ensure consistent and reliable testing, contributing to our understanding of the material properties of hydraulic cement. This test method plays a pivotal role in construction material quality control, research, and development.