The values of IDT strength may be used to evaluate the relative quality of bituminous mixtures in conjunction with laboratory mix design testing and for estimating the potential for rutting or cracking. The results can also be used to determine the potential for field pavement moisture damage when results are obtained on both moisture-conditioned and unconditioned specimens.

1.1 This test method covers procedures for preparing and testing laboratory-fabricated or field-recovered cores of bituminous mixtures to determine the Indirect Tensile (IDT) Strength.

1.2 The within-laboratory repeatability standard deviation, for the recommended rate of loading (50 mm/min) and test temperature (25ºC), has been determined to be 80 kPa for 101.6 mm diameter specimens, based on 28 labs using either 2 or 4 test replicates with 11 different mix samples. Additional data is provided in Table 1 for the user’s information. The between-laboratory reproducibility of this test method is being determined and will be available on or before August 2012. Therefore, this test method should not be used for acceptance or rejection of materials for purchasing purposes.

1.3 The values stated in SI units are to be regarded as standard.

1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

Source of Data	Number of Replicates	Specimen Diameter (mm)	Loading Rate (mm/min)	Test Temperature (°C)	Average Strength (kPa)	Standard Deviation Strength (kPa)	d2s (2.83×SE) (kPa)	Standard Deviation Strength (% mean)	d2s (2.83×SE) (% mean)
Anderson and McGennisA	3	150	12.5	-10	2870	200	566	7.0	19.8
N CHRP Report 530B	3	150	12.5	-10	-	-	-	9	22–32
(4 aggregate types; 4 binders)	2	150	12.5	-10	-	-	-	11
(nom max size: 9.5 mm to 25 mm)
Solaimanian and KennedyCdry	4	100	50	25	-	103	292	–	–
moisture-conditioned			50	25	-	83	234	–	–
(9 labs; 3 aggregate types; 2 binders)
Test Method D4867/D4867M (dry or conditioned)	2	100	50	25	-	55	159	–	–
(19 labs; 5 mixtures)
Suggested Single Lab Precision			50	25		80

^A R. M. Anderson and R. B. McGennis, “Ruggedness Evaluation of AASHTO TP7 and TP9,” Phase I, FHWA HIPT (Task J), Federal Highway Administration, November 1998.

^B W. Christensen and R. F. Bonaquist, “Evaluation of Indirect Tensile Test (IDT) Procedures for Low-Temperature Performance of Hot Mix Asphalt,” NCHRP Report 530.

^C Solaimanian and T. W. Kennedy, “Precision of the Moisture Susceptibility Test Method TEX-531-C,” Project Summary Report 4909-S, November 2000.