This paper studies the effectiveness of alkaline activation of low-calcium fly ash on the improvement of residual granitic soils to be used on rammed-earth construction. Different liquid:solid ratios, alkali concentrations and Na2O : ash ratios were tested. Effect of calcium hidroxide, sodium chloride and concrete superplasticiser is also reported. Compressive strength up to 7 days at 60ºC was determined. Results show that, in terms of mechanical strength, there is an optimum value for the activator:solids ratio and the alkali concentration, and that a decrease in the Na2O:ash ratio results in strength increase. No improvement was observed with the sodium chloride or the superplasticiser, while the calcium produced only a short term increase in strength. SEM/EDS analysis were used to analyse microstructural development, showing that strength is fairly related to the Si:Al and Na:Si ratios. Research highlights  Low calcium fly ash activated with a sodium-based solution.  No significant improvement with sodium chloride or superplasticiser.  There is an optimum liquid : solid ratio and alkali concentration for strength development.  An alkali : ash ratio reduction results in a significant strength increase.  Microstructure is significantly affected and can be related to strength variation.

Building in unstabilised rammed earth results in low environmental impact. However, northern Portugal has not historical tradition with this technique, and thus the suitability of the local granitic residual soils is unknown. This paper presents an experimental investigation, where this possibility is assessed. The results showed that these soils are unsuitable, and that rammed earth construction is only feasible if these soils go through a stabilising process. The alkaline activation of fly ash was investigated as an environmentally friendly stabilisation technique, and it proved to be capable of improving the performance of rammed earth. Highlights:-The strength of unstabilised rammed earth built with granite residual soils is low.-Stabilization is required to build rammed earth with granite residual soils.-The alkaline activation of fly ash was tested as stabilisation technique.-The alkaline activation improves the strength and durability of rammed earth.

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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.