Marshall and indirect tension
- In the Marshall test, a compacted specimen is loaded diametrically at the specified rate; maximum load (stability) and the associated deformation (flow) are recorded.
- In indirect tension, loading a cylindrical specimen creates internal tensile stresses; peak load is used to estimate indirect tensile strength.
- Indirect tension can also support moisture-susceptibility assessment when conditioned specimen groups are compared as required by the method.
Cracking tests
- SCB loads a notched semicircular specimen and examines energy or response associated with crack propagation.
- IDEAL-CT uses a cylindrical specimen and its load-deformation curve to estimate a cracking-resistance index.
Bond between pavement layers
- Interlayer shear or bond tests measure the force needed to slide or separate materials at an interface.
- Core preparation, interface plane, temperature, and loading rate must follow the specified procedure.
Interpretation
- Peak load alone does not tell the whole story: retain the load-displacement curve and calculate the indices defined by the method.
- These tests are complementary. Relate them to composition, air voids, and other performance tests before making mix decisions.
Strength and load-deformation ratio
- Indirect tensile strength: ITS = 2P/(π·t·D), where P is peak load in N, t is specimen thickness, and D is diameter in mm. The result is N/mm², equivalent to MPa.
- Marshall stability: report peak load corrected by the geometric factor required by the method. Flow is the deformation associated with the peak and is reported in mm.
- Marshall quotient: MQ = stability/flow. It is an empirical comparative stiffness index, not a fundamental material property or universal acceptance criterion.
- Results are sensitive to temperature, conditioning, specimen height, and loading rate. Report these with the mean and scatter.
Educational reference guide. Check the current standard, calculation assumptions, and project specification before applying a procedure or acceptance criterion.