Determining the mechanical properties of soils treated with cementitious binders by the splitting tensile test (“Brazilian test”)

The principle of the splitting tensile test consists mainly in performing a diametral compression test on a specimen of compacted treated soil after a given curing time.

The splitting tensile test, also known as “Brazilian test”, is a laboratory test to determine the indirect tensile strength (Rit) of soils treated with cementitious binders. The test is performed as specified in European standard EN 13286-42. From the indirect tensile strength found it is possible to deduce tensile strength, which is more difficult to measure.

As suggested in BRRC’s code of good practice for soil treatment with lime and/or cementious binders (R81/10), the value of indirect tensile strenghth, Rit, can be used to check the frost resistance of treated soils. When treated soil is used as a (sub)base layer, it may be exposed to frost action and must, therefore, have adequate frost resistance. To assess whether a treated soil resists frost action, is has been empirically established that indirect tensile strength Rit as determined after sixty days of curing, or at the age which corresponds with the presumed date of first appearance of frost on site, must be higher than 0.25 MPa.

When using specific equipment in the form of strain transducers, this test also makes it possible to determine the modulus of elasticity and Poisson’s ratio of treated soils. The procedure is decribed in standard EN 13286-43. The modulus of elasticity, E, and Poisson’s ratio, ν, are required as inputs in calculations for structural pavement design. Knowing the behaviour and deformability of treated soils through the indirect tensile test, it becomes possible to make savings by more accurate structural design. Although this practice is still uncommon en Belgium, examples outside our borders have demonstrated the practical interest of design calculations based on the modulus of elasticity and Poisson’s ratio of treated soils.

When soil treatment is considered for an application in a (sub)base layer, indirect tensile tests should be made both in the mix design study and in checking the performance of the treated soil layer after construction.

The mix design study will indicate whether treatment is advisable or not, as well as the appropriate rate of spread of binder. Tests performed on specimens after different curing times (generally twenty-eight, sixty and ninety days) allow predictions of the long-term behaviour of the material. Design calculations make it possible to define the thickness of soil layer to be treated as well as the thickness of the whole structure.

The behaviour of the mixture of in-place treated soil needs to be checked by manufacturing specimens to the Normal Proctor optimum in the laboratory. Indirect tensile strength is then determined on three specimens after sixty days of curing at 20 °C. The average Rit value obtained on the three specimens should be higher than 0.25 MPa.

BRRC has the following apparatus for indirect tensile tests by the procedure described in standard EN 13286-42:

  • a computer-controlled press of 250 kN;
  • three force transducers: 10 kN, 50 kN and 250 kN;
  • three strain transducers – range = 10 mm;
  • the necessary moulds for manufacturing specimens (Ø = 5 cm, h = 5 cm and Ø = 10 cm, h = 10 cm).

In addition, the following items are necessary for tests to determine the modulus of elasticity and Poisson’s ratio as specified in standard EN 13286-43:

  • one extensometer for specimens Ø = 5 cm, h = 5 cm;
  • one extensometer for specimens Ø =10 cm, h = 10 cm;
  • four strain transducers – range = 2 mm.