This paper investigates the effects of incorporating dispersed fibrous reinforcement in hydraulically bound granular 0/16-mm mixtures. The evaluated fibrous reinforcement comprised a mixture of polypropylene and alkali-resistant glass fibers in a 1:2 weight ratio. The fibrous reinforcement was added to the mixtures in amounts of 0.05% and 0.10% by weight. The prepared mixtures utilized 1% of CEM II/B-V 32.5 R Portland cement together with 3.5%, 7%, and 14% of fly ash, characterized by a high content of reactive calcium oxide. It was found that the fibrous additives had only a small effect on the maximum dry densities and virtually none on the optimum moisture contents of the mixtures. The use of the fiber mix significantly improved the compressive strength of the reinforced samples resulting after 42 days of curing, with a performance comparable to a reference mixture bound with 8% of Portland cement. The addition of fibrous reinforcement increased the indirect tensile strength of the mixtures by up to 300%, resulting in a performance similar to that of a reference mixture with 5% of Portland cement. It was found that the use of this particular fibrous reinforcement significantly improved the performance of predominantly fly-ash-bound granular mixtures, allowing the reduction in cement content used in this type of material.

It is increasingly important to find solutions for the problem of the aluminium anodising industry which generates a large amount of acid and alkaline wastewater, composed of high amounts of phosphates, sulphates, nitrates and aluminium. The sulphate removal trough ettringite precipitation is a simple process and involves a low-cost operating. The ettringite can be also formed during the cement hydration in soil-cement mixtures which causes several damages such as expansion. However, the effect of ettringite on the compressive strength, tensile strength and microstructure have few studies. This paper presents a novel experimental study on the influence of the industrial effluent treatment ettringite in resistance and microstructure of soil-cement mixtures. Experimental tests were performed using natural soil, soil mixed with 5% and 6% of cement and soil mixed with 5% and 6% of cement and ettringite for each material. The resistance of the materials was evaluated by unconfined compressive strength and indirect tensile strength, after 3, 7 and 14 days of cure. Additionally, several characterization tests and microstructure analysis were performed. Regarding the experimental results, the compressive strength and tensile strength decreases about 75% and 85%, respectively, when ettringite was added in soil-cement mixtures. The microstructure of natural soil, soil-cement and soil-cement-ettringite mixtures shows that the addition of cement and ettringite, simultaneously, increases the ettringite crystal formation mainly because the cement functions as a source of sulfate ions contributing with the formation of more crystals. Experimental results indicate that the incorporation of ettringite in soil-cement mixtures is not suitable for geotechnical applications.