During the past few decades, concrete technology has been developing rapidly followed with huge popularity of high-performance concrete (HPC). However, the mix design for HPC still remains a major challenge due to the wide adoption of mineral and chemical admixtures, the effects of which are rather complicated and not yet fully understood. To resolve this issue, this thesis presents a comprehensive experimental study focused on the physical effects of some supplementary cementitious materials (SCM) on the fresh and hardened properties of mortar. Based on the experimental results, some fundamental parameters governing the performance of mortar were investigated.
It has been postulated by some researches that increasing the packing density of the particle system would improve the rheology and strength of concrete. Through adding SCM finer than cement to increase the packing density, the voids between solid particles will be reduced so that more excess water can be released to provide better lubrication. Through adding two kinds of SCMs with different fineness, the packing density will be further enhanced by the successive filling action. In this study, a wet packing method, which is newly developed at the University of Hong Kong, was used to directly measure the packing densities of mortars with binary and ternary blended cementitious materials. The filling effect and successive filling action were both quantified through the packing density results.
The study revealed that the addition of fine SCM will, not only increase the packing density, but also increase the solid surface area, which will have negative effect on the rheology of mortar. To combine the effects of water content, packing density and solid surface area together, we proposed a new parameter called water film thickness (WFT), defined as the average thickness of water films coating the solid particles and evaluated as the excess water to solid surface area ratio. The results demonstrated that the WFT plays a key role in controlling the rheology and strength of mortar. Hence, it is the WFT, rather than the packing density, that should be maximized at given water content in the mix design of HPC. The addition of fine SCM will increase both the excess water content and solid surface area. The effects on the both sides can be quantified by the WFT no matter how complex the cementitious system is. Therefore, the WFT could be used as an effective indicator to adjust the SCM content. Joint addition of fine SCM at different level finer than cement to make a ternary cementitious system can effectively increase the packing density without excessively increasing the solid surface area. As a result, the ternary cementitious system has higher effectiveness than the binary cementitious system in improving the performance of mortar. / published_or_final_version / Civil Engineering / Master / Master of Philosophy
| Identifer | oai:union.ndltd.org:HKU/oai:hub.hku.hk:10722/173879 |
| Date | January 2012 |
| Creators | Li, Yan, 李彦 |
| Contributors | Kwan, AKH |
| 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/B48330097 |
| 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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