Why use ASTM D8329:
The compressive strength of any cured cementitious material is heavily dependent on the water/cement ratio during hydration. If the water/cement ratio is too high, the compressive strength of the cured concrete will be extremely weak. For example, a cementitious material may achieve a compressive strength of 80MPa at an optimum water/cement ratio of 0.3, but at a water/cement ratio of 0.8 the compressive strength drops below 25MPa (see Figure 3*).
Pre-existing concrete Compressive Strength test standards (designed for testing dry mix concrete products) allow for the water/cement ratio to be determined in the lab to achieve optimum results. This is understandable since the cement content is known and the quantity of water added to a conventional dry mix is normally controlled on site. This of course is not possible with GCCMs and so pre-existing test methods provide scope to publish misleadingly high compressive and strength values by using unrepresentative water/cement ratios. Performance values can be increased by more than 10 times in some cases.
ASTM D8329 is, therefore, the only standard that should be used for GCCM compressive strengths because it measures the water/cementitious materials ratio to give a strength that represents field performance.
The compressive strength of a GCCM can be used as an indication of other key GCCM physical properties for erosion control applications such as abrasion resistance, flexural strength, freeze-thaw durability and chemical resistance. In the opinion of Concrete Canvas Limited, GCCMs with low compressive strengths (<40MPa) are unsuitable for erosion control applications.
This has also been recognised in ASTM D8364 ‘Standard Specification for GCCM Materials’, as the performance properties of GCCMs table requires even the lowest grade GCCMs to have a minimum 28-day Compressive Strength of more than 40MPa when tested to ASTM D8329.