Effects of natural fiber inclusions and pre-compression on the strength properties of lime-fly ash stabilised soil

In this study, the synergic effects of pre-compression and fiber inclusions, on the mechanical behaviour of lime fly ash stabilised soil were investigated. Randomly distributed 25 mm sisal fibers were mixed with stabilised soil at the contents of 0%, 0.25%, 0.5%, 0.75% and 1% by dry mass of the soil. Both fiber composite and unreinforced soil specimens were subjected to the pre-compression stresses equivalent to 10% and 20% of the strength mobilised by the un-precompressed specimens. The pre-compression stresses were applied after 4 h, 8 h and 24 h of accelerated curing at 40 °C, after which the conditioned specimens were allowed to continue curing under constant conditions. The 7 day strength of the fully cured composites was determined by a series of unconfined compression tests. The results revealed that optimum strength of 3.5 MPa was mobilised by un-precompressed specimens at 0.75% fiber content. Pre-compression with 10% UCS showed maximum strength of 2.8 MPa at 0.25% fiber content whereas 20% UCS indicated optimum strength of 3.04 MPa at 0.25% fiber content. In comparison, pre-compressed specimens exhibited lower strength values than un-precompressed specimens. This was attributed to the redistribution of bond strength, evolution of matrix cracking and fiber-matrix interfacial debonding. The maximum strengths of specimens for both pre-compression levels occurred after 24 h of curing. This was due to the progressive strength development that endowed the composite with some resistance to compression that was responsible for matrix cracking and debonding. Fiber inclusions significantly improved ductility of the stabilised soil. The theoretical crack model of damage mechanisms in cementitious fiber composites can predict strength behaviour of composites that were pre-compressed after short period of curing.