Awe-inspiring gorges and valleys are nature’s testimony to the undeniable strength of water. Primarily in technical hydraulic engineering, but also in traffic zones with high loads or hard rolling bodies, concrete surfaces experience considerable and at times extremely abrasive forces. The mechanisms of damage thereby depend centrally on the type of burden.
Whether the surface is exposed to rolling, rubbing or percussive influences differentiates the possible patterns of damage as well as any preventive measures substantially.
Over the course of decades and even centuries, exposure to abrasion can yield the most varied experiences with damage patterns. Above all the difference between rolling loads in roadway traffic, heavy traffic including steel wheels or exposure to water, with or without the additional transport of sediment, must be considered. In traffic zones the intensity, weight and the type of wheels are decisive for the overall load. In the case of abrasion by water, it is the velocity of flow, the quantity and type of sediment that are crucial.
In order to boost concrete’s abrasion resistance, in most cases provision for hard surfaces is the proper dimensioning approach. If, however, handling the exposure involves percussive or bumping impact, then in addition the adsorptive capacity of the surface plays a role, which can stand in contradiction to surface hardness. The most critical basic principle in the concept is the expert installation of the concrete (prevention of a rising up of fines to the surface due to excessive vibration) and excellent curing, so that the desired concrete properties can emerge above all in areas close to the surface. Furthermore, the surface should offer the lowest resistance possible to abrasive attack. Surfaces that are as level as possible provide the smallest potential for attack.
Ascertaining damage patterns is rather straightforward, and is carried out by assessing the abrasion of the surface, the condition of the cement laitance skin and of aggregates near to the surface.
Concrete with enhanced or high abrasion resistance should demonstrate a target compressive strength of approximately 50 MPa. The surface can be considerably enhanced against grinding abrasion through the use of micro silica and/or surface hardener scattered on the surface. In order to boost resistance against percussive or striking impact, the toughness and flexural strength of the concrete must be improved. This can be achieved with the use of fiber reinforcements in the mix. Improving the general working capacity of concrete can be accomplished by mixing in synthetic polymers to strengthen the hardened cement paste matrix, which furthermore enhances adhesion (entanglement) with aggregates. Finally there must be additional differentiation between transport distances and areas that are built to facilitate the dissipation of energy. In these areas, the use of high strength, steel fiber reinforced concrete with a strength above 80 MPa and corresponding flexural strength is recommended. In construction the design of edges must be given particular attention. Whether this concerns dilatation joints in roadway surfaces or tearing edges in hydraulic construction, these must usually be handled specially; construction in concrete alone is normally insufficient. Special joint profiles must be incorporated, often made of steel.
Conditions for better abrasion resistance
The abrasion resistance of the hydrated cement is lower than that of the aggregate, particularly with a porous cement matrix (high water content). However, as the w/c-ratio decreases, the porosity of the hydrated cement decreases as well and the bond with the aggregate improves.
Curing is essential to ensure the concrete’s surface, the area subject to abrasion, has achieved it’s full potential.