Behavioural comparison between fibre and steel reinforcement in paving slabs

Topics Covered

Background
Diagrammatic comparison of behaviour under stress
Comparative benefits

Background

Marshalls have developed their STRUXTM 90/40 concrete fibre reinforced pimple paving slabs to withstand aggressive and repeated loading from vehicle overrun in areas which are prone to this particular hazard. As part of this development, Marshalls have studied and compared the behavioural response of paving reinforced with evenly distributed fibres, such as occur in the STRUXTM 90/40 paving slabs, to that of paving reinforced with steel bars which they have used in vehicular overrun areas in the past.

Diagrammatic comparison of behaviour under stress

The following diagrams show in further detail how the response of the fibre reinforced paving differs from that of the steel reinforcement.

 

When vehicle overrun occurs, the weight of the vehicle is passed to the flag through a very small contact area between the tyre and the surface.

Due to the weight of the vehicle and the relatively small contact areas of the tyres, the vehicle weights are actually being passed through as point loads over a very short period of time.

Fibre reinforced paving

 

Paving reinforced with steel bars

Due to the excessive load, cracking starts to form on the bottom face of the flag, at the point where the concrete is under tension.

Due to the excessive load, cracking starts to form on the bottom face of the flag, at the point where the concrete is under tension.

As further loading occurs, the growth and spread of the crack is significantly delayed by the fibres which reduce the stress at the crack tip, as well as bridging the crack, holding the pieces together.

As further overloading occurs,  the growth and spread of the crack quickly takes place, with the steel reinforcement offering no resistance to crack propagation, passing through the flag to the top face.  Movement and abrasion failure at the face continue to open up the crack, as the failed unit ‘pivots’ about the steel reinforcement.

When the crack eventually passes through the flag to the top face, fibres continue to bridge the failure, having sufficient strength and pull out resistance to continue holding the pieces closely together, critically maintaining the alignment of the failed pieces.  These then continue to perform as a complete flag unit as if no failure has taken place.

As the two, now hinged pieces continue to twist relative to each other, abrasion and crumbling continue to open up the crack face,  particularly at the top and bottom faces.  Subsequent loading leads to further, rotating movement around the exposed reinforcement, leading to further abrasion and spalling,  opening up wide cracks on the top face, creating the presence of potential trip hazards and poor aesthetics.

Comparative benefits

Fibre reinforcement is shown to have the following benefits when compared with steel reinforcement:

          Reinforcement always correctly placed
- resulting in consistent performance

          No sharp protrusions
- leading to improved Health & Safety on site

          No corrosion
- avoids staining or spalling and gives improved aesthetics

          Tighter crack control
– the fibres ‘interfere’ with crack propagation ‘throughout’ the whole body of the flag giving improved post failure performance

          Better performance at crack face-
- gives extended failure times with ‘closer’ cracks – better aesthetics
- gives less hazards and spalling at crack edges – safer performance

 

Protusions from worn steel-reinforced paving flag.

Source: Marshalls

            April 2004

            

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