Photo: Concrete sample after it has been tested for Abrasion Resistance by ASTM C 779, Procedure C.
Abrasive wear is a hot topic in the concrete and construction industry. It seems it is a cause for concern on many jobsites whether it be bridges, dams, sewage pipes or roadways. Simply put, abrasive wear of concrete is the abrading of the concrete surface, so instead of that nice, smooth, level surface that is expected from concrete it is riddled with uneven patches, smooth and rough spots and even pop-outs. It is no wonder the industry actively seeks viable solutions to increase abrasion resistance.
Fibres in concrete/cement have been shown to be one of those viable options to help lessen this problem. When fibres are added to concrete a few things happen: In the case of a micro fibre, something really small, it helps to increase the gradation envelope.
Imagine a box filled with soccer balls, there is a lot of space in between each ball, adding a fibre is like adding biscuits, we are decreasing the size of pores and filling in some of these smaller gaps. By doing so, this helps to increase workability and flow ability. Which then allows water to be pulled out of the mix. Anytime water can be pulled out, while still maintaining fresh properties, is generally going to lead to a stronger and more durable concrete – which then will translate to a concrete less susceptible to abrasive wear.
Another benefit to adding fibres is that there is another shape added to the concrete, so not only are pores being filled in, but the fibres are able to get into nooks and crannies that the aggregate would not normally fill. Fibres help hold the cement mix together making the removal of sand and gravel more difficult, resulting in a higher general resistance to abrasion.
The fibres also help to keep the water appropriately dispersed throughout the mix, this decreases the risk of bleed water sitting on top of a concrete slab. [NRMCA, 1994]. Adding fibres to concrete is another piece of the puzzle when dealing with abrasive wear.
NRMCA. (1994). CIP 24 — Synthetic Fibers in Concrete. Concrete in Practice. Retrieved April 7, 2018, from https://www.nrmca.org/aboutconcrete/cips/24p.pdf