When aggregate, water and portland cement paste are combined to produce a homogenous substance, that substance takes on new physical properties that are related to but not identical to the physical properties of its components. Thus, several common mechanical laboratory tests are used to characterize the basic mixture and predict mixture properties. Unlike HMA, it is difficult to draw a clean distinction between characterization tests and performance tests. Typically, PCC is characterized by slump, air content and strength. However, these characteristics can also be used as performance predictors for workability, durability and strength respectively. Therefore, this section does not distinguish between mixture characterization tests and performance tests.
Whereas HMA tests are often scale simulations of actual field conditions (such as rut tests), PCC tests are directed more at the basic physical properties of PCC as a material.
The challenge in PCC testing is to develop physical tests that can satisfactorily characterize key PCC performance parameters and the nature of their change throughout the life of a pavement. These key parameters are:
- Workability. This parameter, typically measured by slump, is indicative of fresh concrete rheology.
- Strength. This parameter is related to a rigid pavement’s ability to support loads. Flexural strength is commonly used in design and then correlated to compressive strength for use in field tests.
- Durability. Several tests can be conducted to determine susceptibility to freeze-thaw or chemical attack damage.
- Early age behavior. HIPERPAV, a software program, can be used to predict early-age PCC behavior.
Although there are many different PCC tests, only those typically used on pavement PCC are discussed in this Guide.