using the SGC tend to have non-uniform air void distribution both along their diameter
and along height. SGC-compacted specimens have higher air void content at the top and
bottom edges, and in sections adjacent to the mold walls, as compared to the interior
portion of the specimens. Finally, fully lubricated end plates were found to minimize end
restraint on the specimen. Increasing the number of gages used to measure axial strain
decreases the number of test specimens necessary.
Load Level
Since the interpretation of the complex modulus is based on the assumption of
linear viscoelasticity of the mixture, it is necessary to maintain a fairly low strain level
during testing to avoid any nonlinear effects. Maintaining a stress level that results in a
strain response that is close to linear is critical to achieve a test that is reproducible.
The concept of material linearity is based upon two principles. The first principle,
proportionality, is described with Equation 2-9.
(C a(t)) = C (at)) (2-9)
It implies that if a stress is increased by any factor then the strain will also increase
by the same factor. This allows the shape of the stress/strain relationship to be more
easily mapped out across the linear range.
The principle of superposition is the other condition that describes linearity.
Equation 2-10 describes this concept.
(oa, (t) +,2 (t -t))=)) = s(0-2 (t- 1)) (Eq. 2-10)
This implies that if it is known how the material will behave under a single loading
condition that it will be known how it would behave under multiple loads. Figure 2-2
and 2-3 show graphically the concept proportionality and superposition. The