The number immediately following indicates the year of last revision (i.e., ASTM C55-11 is the version of C55 published in 2011). For example, ASTM C55 is the fixed designation for concrete building brick. The letter and first number of an ASTM designation is the fixed designation for that standard. Currently, seven ASTM standards apply to units intended primarily for construction of concrete masonry walls, beams, columns or specialty applications (see Table 1). These requirements include items such specified component materials, compressive strength, permissible variations in dimensions, and finish and appearance criteria. These ASTM standards contain minimum requirements that assure properties necessary for quality performance. This is a relatively inexpensive test that can provide an indication of cured GCCM performance in 24 hours, without the expense and wait for 28-day compressive strength results.The most widely-used standards for specifying concrete masonry units in the United States are published by ASTM International. Concrete Canvas Ltd Quality Control procedure dictates that at 24 hours after curing, a minimum machine direction IFS of 4.0MPa is required.Ģ4-hour IFS can also be used as part of Material Quality Assurance to verify that the material supplied to a project meets the specifications.
This is defined in GCCM Specification Standard ASTM D8364, requiring all GCCM materials to have a minimum IFS of 3.5MPa at 24 hours from hydration. It is therefore important for GCCM manufacturers to report the IFS of their material when tested to ASTM D8058. Poor quality cement blends and high water/cement ratios would be reflected in a lower IFS. A higher IFS is therefore preferable and ASTM D8058 3-point bending tests are used by GCCM manufacturers to check material quality as part of factory production control procedures.Ī higher IFS demonstrates the cementitious material is well constrained in the GCCM and the water/cement ratio is controlled. In terms of field performance, GCCMs with a lower IFS will tend to have a weaker cementitious layer and are more likely to disintegrate over time. By studying the results, ASTM D8058 enables the composite performance of a GCCM to be understood by determining both the Initial Flexural Strength (IFS), which is governed by the cementitious material, and the Final Flexural Strength (FFS), when the geosynthetic components fail. What is ASTM D8058:ĪSTM D8058 uses a constant rate of extension testing machine with a 3-point fixture set up to continuously measure the stress and displacement of a cured GCCM specimen as it is loaded to failure. The internationally recognised standard for flexural strength testing of GCCMs is ASTM D8058 ‘Standard Test Method for Determining the Flexural Strength of a GCCM Using the Three-Point Bending Test’. Broadly speaking, conventional geosynthetics are strong in tension and weak in compression, whereas concrete is strong in compression but weak in tension.įlexural Strength testing of cured GCCMs provides the best overall indication of the in-service performance of a GCCM by compressing one surface while simultaneously extending the other and is considered the standard index test for this class of material. GCCMs behave as composite materials, they combine the benefits of geosynthetics and concrete. This Technical Note 3 focusses on the importance of using ASTM D8058 for determining the flexural strength of GCCMs. It is also critical to ensure the cementitious material is cured at a water/powder ratio that is representative of field (in-service) hydration and not artificially controlled in the laboratory. It is therefore important to test the properties of the cured cementitious material so that the behaviour of the GCCM as a hardened composite can be understood. GCCMs are the only geosynthetic to contain unset cementitious material and pre-existing geosynthetic test standards do not include methods for understanding the performance of the cementitious material contained within a GCCM.
Geosynthetics are typically buried and their performance is often assessed according to their tensile strength, whereas hardened cementitious materials are often exposed and their performance is typically assessed according to their compressive strength, which is typically correlated with other key characteristics such as abrasion resistance, freeze thaw resistance and resistance to chemical attack. GCCMs contain geosynthetic and cementitious materials, both of which possess very different physical properties. Both the uncured (pre-set, soft and flexible) and cured (post-set, hardened and rigid) properties need to be reported to understand the GCCM capabilities in both deployment and in-service respectively.
GCCMs are unlike most geosynthetics as their properties change on hydration from flexible to rigid.