Springbox equipment

It consists of a steel box containing a cubical sample of material, with an edge dimension of 170 mm, to which a repeated load is applied over the full upper surface. One pair of the box sides is fully restrained and the other is restrained through elastic springs, giving a wall stiffness of 10-20 kN/mm. The above arrangement simulates the lateral support of the material within the compacted layer. 

The material to be tested is compacted with a vibrating hammer the assembly provides means to introduce water to the sample or drain the water from its underside. 

Loading takes the form of repeated vertical load applications of controlled magnitude at a frequency of at least 1 Hz and no greater than 5 Hz. The load capacity is equivalent to a vertical stress of at least 150 kPa. 

Measurements of both vertical and horizontal (spring restrained) deflection can be made, with two measurement transducers for each measure. In the case of vertical deflection measurement, the equipment allows the transducers to make direct contact with the specimen, 

The stiffness modulus of the material can be calculated from the averaged deflections measured over a series of loading patterns (Highways Agency 2009b). 

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The Springbox equipment (see Figures 1.12 and 1.13) is a new device for laboratory testing of unbound granular and some weak hydraulically bound mixtures (Edwards et al. 2005). The Springbox uses the standard Nottingham Asphalt Tester loading frame and software. 

Figure 1.13 Springbox equipment. (Courtesy of Cooper Research Technology Ltd.)...

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