Properties of Fiber-Reinforced Cement Concretes for Lower Layers of Rigid Pavements on Recycled Aggregates

A series of concretes on recycled aggregates for the construction of lower layers of rigid pavements have been developed, that incorporate micro- and macro- polypropylene fibre and glass fibre. Fibre was added to three base compositions containing different aggregates, i.e. river gravel, quartz sand and coarse and fine size recycled concrete aggregate. All the mixtures used a cement with a high slag content at a dosage of 300 kg/m³ and were designed for an S1 consistency. The inclusion of fibre significantly affected the fresh concrete's water demand, which demonstrated an increase in the w/c by 7 – 15 %. Mechanical testing on the 28th day showed that neither polypropylene fibre improved the compressive strength and even caused a slight reduction (0.3 – 5 %), which was a result primarily attributed to the associated increase in the w/c ratio. The macrofibre also reduced the flexural strength by 5 – 6 %; the microfibre provided only a marginal increase in the flexural strength (1 – 4 %). In contrast, the alkali-resistant glass fibre was the only type to enhance both the compressive and flexural strength, increasing them by 4 – 12 % and 9 %, respectively. All the fibre-reinforced mixtures achieved a frost resistance grade of at least F100. The research concluded that for stiff mixtures made with recycled aggregates, the tested polypropylene fibres are inefficient, whereas the alkali-resistant glass fibre presents a viable option for performance enhancement.