a b s t r a c tA sandy clay from the northeast region of Portugal has been reinforced with polypropylene fibres and cement, and seismic wave velocity measurements and uniaxial compression strength tests were performed. Results showed that the fibre induce variations on the wave's velocity that cannot be related to real changes in the material stiffness. Therefore, care should be used when using this technique in fibre reinforced soils. The addition of fibres resulted in an increase of compression strength of the mixtures, for every cement content. Regarding the stiffness, the fibres proved to be increasingly effective with an increase in cementation, especially at the early stages of the stressestrain curve, when the secant deformability modulus increases with fibre content. However, no influence of the discrete reinforcement was detected on the peak and post-peak stages of the loading process. Fibre length showed also to be influential on strength and stiffness.

19The improvement of geotechnical properties is often achieved by the addition of traditional 20 binders, such as cement or lime. However, the use of such binders implies a considerable 21 financial and environmental cost that needs to be mitigated. An unconventional solution, similar 22 to cement in terms of performance but more environmentally friendly, consists in the use of 23 binders made from alkaline activated industrial residues. The technique consists on the 24 activation of raw materials (such as fly ash or blast furnace slag) rich in Si, Al, or even Ca, with 25 high pH alkaline solutions. The present work was developed aiming the possible stabilization, 26 using different fly ash contents, of a clayey soil with sand. The activator solution was composed 27 of sodium hydroxide and sodium silicate. The extended experimental campaign included 28 unconfined compressive strength (UCS), California Bearing Ratio (CBR), pulse velocity tests 29 and triaxial tests to assess the geomechanical improvement induced by the new binder. As a 30 mean of comparison, the experimental campaign included also the stabilization of the same soil 31 with either cement or lime. The obtained data indicates that the use of alkaline activation as a 32 soil stabilization technique provides competitive geomechanical results, when compared with 33 those obtained with traditional binders.34 35

Cristelo N et al., Influence of fibre reinforcement on the post-cracking behaviour of a cement-stabilised sandy-clay subjected to indirect tensile stress, Construction and Building Materials, Elsevier, 138: 163-173, 2017. 2 3 Influence of fibre reinforcement on the post-cracking 4 behaviour of a cement-stabilised Sandy-Clay subjected to 5 indirect tensile stress 6 7 8 a,22 23 24 25Cristelo N et al., Influence of fibre reinforcement on the post-cracking behaviour of a cement-stabilised sandy-clay subjected to indirect tensile stress, Construction and Building Materials, Elsevier, 138: 163-173, 2017. Abstract 26 27 An experimental campaign was carried out to determine the influence of polypropylene fibre 28 content and length on the post-cracking response of a Sandy-Clay stabilised with different 29 cement contents. Three main sets of specimens were prepared: cement-stabilised specimens 30 with two cement contents (5% and 10%); fibre-reinforced specimens with three fibre contents 31 (0.1%, 0.2% and 0.3%) and cement-fibre-reinforced specimens combining the mentioned fibre 32 and cement contents. Tensile tests on the fibres and indirect tensile tests and triaxial 33 compression tests on the prepared specimens were conducted. Results show that the post-34 cracking behaviour is strongly affected by the combination of fibre and cement content as well 35 as fibre length. Pull-out was the governing failure mode. Post-peak tension loss rate increased 36 with fibre content, as a result of the loss of influence of the fibres on the post-peak behaviour. 37On the contrary, an increase in fibre content resulted in higher pre-peak strength gain rates and 38 higher peak stresses. 39 40 41 Cement stabilisationCristelo N et al., Influence of fibre reinforcement on the post-cracking behaviour of a cement-stabilised sandy-clay subjected to indirect tensile stress, Construction and Building Materials, Elsevier, 138: 163-173, 2017. 4 complex material in terms of tensile strength, especially on the post-peak stress segment of the 70 load-displacement curve. This structural response has not yet been fully characterised, and is 71 thus the main subject of the present paper. 72 73 In general, the fibres are responsible for an increase of the compressive and shear strength, 74 especially at the post-peak and residual (post-cracking) stages, and the extent of such 75 improvement is intrinsically dependent of several factors, such as: fibre properties, geometry 76 and content; fibre distribution and orientation within the matrix; existence and magnitude of 77 artificial cementation (using, for instance, Portland cement or lime); and fibre-soil bonding 78 (stress-slip behaviour).79 80 The present paper aims a thorough characterisation of the tensile stress post-peak response of a 81 polypropylene fibre reinforced sandy-clay. It is part of an extensive research programme 82 designed to understand the mechanical response of a very common Portuguese soil, when 83 reinforced with fibres, as well as the potential need for additional chem...

The paper addresses several options to improve the reaction kinetics of alkali activated low calcium fly ash binders for soil stabilisation in road platforms. For that purpose, an experimental program was established to assess the strength evolution, with time, of different binders, based on ash, lime, sodium chloride and alkali solutions, applied in the stabilisation of a silty sand. The tests included unconfined compression strength tests, triaxial tests and seismic wave measurements performed at different curing periods. The results were compared with a binder made of Portland cement and a commercial additive specifically designed for soil stabilization in road applications. The activated ash mixtures with lime were the most performing producing a significant increase in the reactions development and, consequently, in the strength gain rate. The sodium chloride significantly improved the lime and lime-ash mixtures, but provided only a slight improvement in the activated ash mixtures.

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