The Impact of Polypropylene Fibre Addition on the CBR Value

The classic test for soil or aggregate bearing capacity in road construction is the CBR test. The results of the CBR were determined for gravelly sand and sand with the addition of 1.5% cement, as well as for their mixtures with 18 mm long polypropylene fibres in the amounts of 0.1%, 0.2% and 0.3%. The effect of compaction and time of curing of samples stabilised with hydraulic binder were also determined. The natural soil without cement and fibre additions had relatively high CBR values. The additions of 0.1% and 0.2% polypropylene fibres to the dry mass of the soil resulted in an approximately 2-fold increase in the CBR value for the samples compacted using the standard method. Increasing the amount of fibres to 0.3% caused a reduction in the CBR value to that obtained without fibre addition. For samples compacted using the modified Proctor method, the observations are different. Only the sample with 0.2% fibre addition achieved a slightly higher CBR value. Moreover, the addition of 1.5% cement and the length of treatment increased the CBR values.