Volume 29, Issue 4 (July 2001)
Development of New Low-Cost Indirect Tensile Test Equipment for Bituminous Mixtures
In order to design pavements analytically, mechanical properties such as elastic modulus and Poisson's ratio should be known. In addition, fatigue and plasuc deformation life of bituminous mixtures have to be known. Marshall mix design, while abandoned in many developed countries, is still in use in Turkey. The reason for using the Marshall mix design is the lack of knowledge by highway authorities of other mix design methods, and the cost of change.
In order to minimize the cost of change, new low-cost indirect tensile test equipment has been developed that costs about one-tenth that of conventional equipment. The equipment is fully computer controlled and the control program was written by the first author. The load is controlled by a load cell, and the pressure is applied via an electronic pneumatic system. Deformation is measured by two LVDTs. The specimen size is the same as a Marshall specimen for the sake of easy sample preparation. However, if compaction equipment is available, other sample sizes can also be tested using the mold. In order to control the temperature in the cabinet, a digital thermostat that also shows the cabinet temperature on the screen is used. It is possible to apply square, haversinusoidal, and triangular waves to the sample.
Using different granular material gradations and temperatures, fatigue lives were obtained for analytical pavement design. As can be seen from the test results, the fatigue relationship does not have a good linear fit. Fatigue test results were interpreted in a different way using fuzzy set theory, which indicated that fatigue life can be predicted better than using the linear fit.