In soil improvement, the insertion of cement to the soil matrix provides an increase in strength and rigidity of the material, whereas fibre addition provides an increase in ductility, reducing post-peak loss in strength. This research aims to experimentally analyse the mechanical behaviour of unreinforced and fibre-reinforced cemented sands under flexural tensile monotonic loading conditions. In order to do so, an experimental program was planned using silty sand (Arenito Botucatu), early strength Portland cement -CPIII, and polypropylene fibres 24 mm long and 0.023 mm thick. Three different dry unit weights (d) (18, 19 and 19.7 kN/m 3 ), three cement contents (3, 5 and 7%), and two fibre contents (0 and 0.5%) were chosen. Analysing the results, an increase in cement content generates an increase in flexural strength (qf) for all concentrations and the increase in d generated smaller qf gains, especially for lower cement contents. The addition of fibres generated a qf increase for lower d but at higher d there was a reduction in the influence of fibre addition on strength gain. The reduction can be attributed to an entanglement of the fibres in higher compaction strengths, disrupting the formation of cementitious bonds. However, based on a qualitative assessment, there was a noticeable reduction in post-peak strength loss due to fibre insertion. The parameter porosity/volumetric cement content (/Civ 0.28 ) was considered suitable to predict the qf mechanical behaviour of the studied composite.

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The use of industrial residues instead of virgin materials is a good alternative for a more sustainable approach to disposing of and managing waste. Soil improvement with coal fly ash (CFA) is particularly attractive for geotechnical earthworks. This study investigated the strength, stiffness and durability of Osorio sand-CFA-lime blends with a variety of improvements by assessing the impact of varying the lime content, fibres, sodium chloride (NaCl) and dry unit weight. Moreover, to contribute to a more rational dosing methodology, strength, stiffness and durability results were correlated to the porosity/binder index [η/(Biv)0.28]. Durability was assessed by comparing wet-dry (WD) and freeze-thaw (FT) cycles, and WD cycles were found to present better performance than FT cycles. Ranks were established for the different components of the blends according to the WD and FT results. The addition of NaCl alone was more effective in improving unconfined compression strength (qu) results than fibres alone. While fibres significantly decreased stiffness at very small-strain shear modulus (G0), NaCl increased G0. The application of η/(Biv)0.28 demonstrated that not only can it predict mechanical behaviour, but also the long-term performance of Osorio sand-CFA-lime blends with or without the addition of NaCl and fibres.

Palavras-chave: cinza volante, moagem, cal de carbureto, resistência à compressão simples, relação porosidade/teor volumétrico de cal, temperatura de cura.