Thesis (PhD)--Stellenbosch University, 2015. / ENGLISH ASTRACT: The very high strength, enhanced ductility and long-term durability of ultra-high performance
concrete (UHPC) makes it an ideal material to be used for building structures in the future.
The non-heat treated UHPC requires less quality control than heat treated UHPC, which
makes it more relevant to be applied in South Africa. This research focuses on developing
non-heat treated UHPC with locally available materials, with the exception of short, straight,
high strength steel fibre.
While UHPC mix design guidelines have been proposed, ingredient materials available
locally, but which do not necessarily comply with recommended property ranges, may be
compensated for by particular strategies. The local ingredient materials are compared based
on their mineralogy, specific surface area, particle size and grading by researchers who
successful developed non-heat treat UHPC. The majority of local materials were found not
that ideal for UHPC. Under such circumstances, following the general UHPC mix design, it is
difficult to reach the same designated strength as those achieved by the other researchers.
One of the problems for non-heat treated UHPC is its large shrinkage caused by very low
water to cement ratio. A new mix design philosophy is developed for UHPC by making use of
steel fibre to improve its compressive strength. Instead of avoiding the large shrinkage, this
method uses shrinkage to improve the bond between steel fibre and matrix through the
mechanism of shrinkage induced clamping pressure. Subsequently, the mechanism of
bridging effect of steel fibre is used to confine shrinkage evolvement in UHPC. Through such
a mix design philosophy, the steel fibres are pre-stressed inside UHPC so that it both
improves the compressive strength and ductility. A UHPC strength of 168 MPa is achieve in
this research.
After the UHPC has successfully been developed, factors that can affect UHPC strength are
tested. It is found that the environmental temperature of UHPC, cement composition and specimen cover during the moulded period significantly influence UHPC strength by
approximately 24%. It is also found that after two days of de-moulding, the UHPC exposed to
the air, achieved similar strength as that cured in water, which is helpful for future industrial
application.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/96699 |
| Date | 03 1900 |
| Creators | Zang, Jin |
| Contributors | Van Zijl, G. P. A. G., Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | xvii, 157 pages : illustrations |
| Rights | Stellenbosch University |
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