Which characteristic is NOT considered in the mix design?

In the context of mix design, resistance to chemical attacks is not typically one of the primary characteristics considered. Mix design often focuses on factors that directly relate to the mechanical and structural performance of the material under load and environmental conditions. For instance, permanent deformation resistance is crucial as it indicates how well the material can withstand traffic loads without significant deformation over time. Durability is also a key consideration, reflecting the material's ability to withstand environmental factors such as moisture, frost, and wear. Flexibility plays a significant role, particularly in materials used in applications where movement or bending might occur.

While resistance to chemical attacks can be important for certain specific applications, such as in environments exposed to aggressive substances, it does not generally influence the basic parameters of the mix design process aimed at achieving optimal structural performance. Hence, this characteristic is less prioritized when establishing the overall design mix compared to the others listed.