7.1 : Tensile Strength Considerations of Concrete

Considering the tensile strength of concrete involves recognizing that the theoretical strength of cement paste can be up to a thousand times higher than what is observed in practical applications. This significant discrepancy is largely attributed to the presence of microscopic cracks within the concrete. These cracks tend to amplify stress at their tips when a load is applied, a phenomenon explained by Griffith's theory of brittle fracture.

The dimensions and shape of a concrete specimen also play critical roles in its overall strength. Larger specimens are more susceptible to failure because they are more likely to contain numerous critical cracks. These internal cracks not only determine the likelihood of failure but also influence where failure is most likely to occur. The highest stress concentrations are found at the tips of these cracks, with their impact further influenced by how the cracks are oriented relative to the direction of the applied load.

When it comes to failure paths, they typically manifest along the interfaces between the cement paste and the larger aggregates within the concrete mix. In some cases, these paths may cut through the aggregates themselves. Understanding these dynamics is crucial for improving the design and formulation of concrete to enhance its structural integrity and durability under tensile stress.