It is generally very difficult to produce high-performance concrete having
concurrently high strength, high durability, high workability and high dimensional
stability. This is because low water content is required to achieve high strength
and high durability, high water content and large paste volume are required to
achieve high workability, and low cement content and small cement paste volume
are required to achieve high dimensional stability. One way of overcoming such
conflicts is to add fillers to increase the packing density of concrete so that the
amounts of water and paste needed to fill voids could be reduced. In this study,
the use of fillers to improve the packing density and performance of concrete is
investigated by measuring the packing density and overall performance of cement
paste and concrete mix samples with different types and amounts of fillers added.
The packing density results revealed that finer fillers are more effective in
improving the packing density for releasing more excess water (water in excess of
that needed to fill voids) to lubricate the solid particles. Moreover, triple blending
of two fillers of different fineness with cement can better increase the packing
density than double blending of just one filler with cement. On the other hand, the
workability, strength and dimensional stability results showed that the addition of
condensed silica fume, fly ash microsphere or superfine cement could improve the
overall workability-strength performance of cement paste through increasing the
packing density of the cementitious materials, while the addition of condensed
silica fume, fly ash or limestone fine coeuld improve the overall dimensional
stability-strength performance of concrete through decreasing the cement content
or cement paste volume. Hence, the incorporation of fillers to improve the
packing density opens up the possibility of using ultra-low W/CM ratio and
ultralow paste volume to produce an ultrahigh-performance concrete.
However, despite increases in packing density and excess water, the
addition of fillers does not always improve the workability. Generally, the
addition of fillers would more significantly increase the workability at low W/CM
ratio and less significantly increase or even decrease the workability at high
W/CM ratio. In-depth analysis indicated that both the excess water and solid
surface area have great effects on the rheology. In this regard, a parameter called
water film thickness (WFT), which is defined as the average thickness of water
films coating the solid particles and may be determined as the excess water to
solid surface area ratio, is proven to be the key factor governing the rheology.
Therefore, it should be the WFT rather than the packing density that should be
maximized in the mix design of high-performance concrete. The addition of fillers
would increase both the excess water and solid surface area. If the proportional
increase in excess water is larger than the proportional increase in solid surface
area, the WFT would increase, but if otherwise, the WFT would decrease. To
increase the WFT, a filler that can significantly increase the packing density
without excessively increasing the solid surface area is the best choice. / published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy
| Identifer | oai:union.ndltd.org:HKU/oai:hub.hku.hk:10722/167231 |
| Date | January 2012 |
| Creators | Chen, Jiajian., 陈嘉健. |
| Contributors | Kwan, AKH, Ho, JCM |
| Publisher | The University of Hong Kong (Pokfulam, Hong Kong) |
| Source Sets | Hong Kong University Theses |
| Language | English |
| Detected Language | English |
| Type | PG_Thesis |
| Source | http://hub.hku.hk/bib/B48199552 |
| Rights | The author retains all proprietary rights, (such as patent rights) and the right to use in future works., Creative Commons: Attribution 3.0 Hong Kong License |
| Relation | HKU Theses Online (HKUTO) |
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