• Xu, Yi
• Karadelis, John
• Yougui, Lin

Abstract

Beams were rested on (a): rubber foundation (RF) and (b): cement stabilized aggregate foundation (CF), as the last part of the “Green” Pavement Overlays research programme.<br/>The composite beams on a rubber pad foundation exhibited a load-drop after cracking of the base. Plain ordinary Portland cement concrete (OPCC) beams exhibited a peak load and failed soon after. Steel Fibre Reinforced Concrete (SFRC) beams exhibited much higher load bearing capacity than their OPCC counterparts. The augmented load was attributed mainly to the reaction of the foundation.<br/>Parmerter’s theory combined with Winkler’s foundation model are suitable for modelling OPCC beams on elastic foundations but not suitable for SFRC beams. Nevertheless, the load bearing capacity of OPCC beams can be predicted by the above.<br/>The elastic solid foundation model is most suitable for modelling SFRC beams on elastic foundations. Finite Element Analysis is recommended to assist tests in establishing the load-CMOD (Cracked Mouth Opening Displacement) relationship. Modelling load-CMOD using this method, was in good agreement with experimental results.<br/>Regarding SFRC-on-OPCC beams, a method for calculating the cracking load of OPCC base and the particular load value for crack entry into the SFRC overlay, was proposed and verified experimentally. This method combines Parmerter’s cracked beam theory and the principle of equivalent flexural rigidity.<br/>Shear conditions were set up to study the reflective cracking caused by rocking and pumping effects over weak supports as part of the Green Overlays research programme.<br/>The behaviour of specimens on the foundation resembled closely those under single-notch-shear-beam-tests in earlier studies by the same authors and confirmed that the overlaid steel fibre reinforced, polymer enriched, bonded material succeeded in keeping cracking under control.<br/>The notch tip displacement was effectively controlled by the fibre bridging capacity in the overlay.<br/>A good agreement was obtained between measured and predicted results. The finite element method depicted well the real behaviour of beams, with hairline cracks appearing, propagating and resembling closely, laboratory performance. Numerical analysis continued to predict the generation and spreading of cracks well beyond laboratory limitations. These cracks propagated towards the loading position, while gradually more fine cracks appeared in the vicinity of the notch.<br/>It was shown that, increasing overlay thickness can effectively reduce the susceptibility to shear failure and reflective cracking and minimise differential displacement at underlying joints, or cracks.<br/>It has been established that the fibre bridging effect in conjunction with the enhanced mechanical properties of polymeric overlays, have a significant advantage over its plain concrete rival in controlling the deformation and stress concentration at a crack tip.

Topics

• impedance spectroscopy
• theory
• crack
• steel
• composite
• cement
• susceptibility
• finite element analysis
• rubber