Abstract
D.Ing. (Civil Engineering)
Polypropylene (PP) fibre is one of the most widely used fibres for reinforcing concrete. Due to
its unique material properties such as economic production cost, relatively high melting point and
alkaline resistance, PP fibres in concrete are found to increase the toughness, provide restrained
plastic and drying shrinkage cracking resistance, increase impact resistance and flexural loading
capacity (especially during the post-crack stage) of concrete structures and components.
The wettability of PP fibre surfaces is poor due to the hydrophobic surface nature of
polypropylene. The bonding between the PP fibre and the concrete matrix is recognized as poor
and currently the PP fibre / concrete interfacial bonding depends upon interlocking and keying
(mechanical bonding). As the interfacial bond strength between the PP fibre and the concrete is
much smaller than the tensile strength of PP fibre and concrete, in order to fully explore the
reinforcing effect of PP fibres in concrete, further improvement of interfacial bonding is necessary.
In this investigation, the research work was conducted on the surface oxyfluorinated PP fibre
newly developed by the Atomic Energy Corporation of South Africa Limited. Examining the
feasibility of using this fibre in concrete, as well as evaluating its superiority over unmodified PP
fibres, is the key task of this investigation. This new type of oxyfluorinated PP fibre shows a large
increase in interfacial bond strength compared to the unmodified PP fibres. The surface free
energy concept and Lewis acid-base interfacial interaction theory were innovatively used to
examine the interfacial bonding between the PP fibre and the concrete matrix. The purpose of this
study was to develop the background of such oxyfluorinated PP fibres, to establish the mechanism
of the increase in interfacial bonding and to investigate the basic properties of the concrete
incorporating oxyfluorinated PP fibres. The experimental results on the properties of
oxyfluorinated PP fibre reinforced concrete compared with those of unmodified PP fibre
reinforced concrete and plain concrete are presented, with some field test results focused on the
improvement in shrinkage cracking control capacity.
It is concluded in this investigation that the surface oxyfluorinated PP fibres possess significantly
increased PP fibre / concrete interfacial bonding due to the chemical bond arising from the acid base
interfacial interaction and the intimate interfacial contact arising from the improved fibre
surface wettability. When combining oxyfluorinated pp fibre with concrete, a general
improvement in the physical and mechanical properties of fibrous concrete compared to that
created with unmodified PP fibres, is obtained.