W.W.S. Fung

Adiabatic Temperature Rise of Pulverized Fuel Ash (PFA) Concrete

Owing to the less exothermic pozzolanic reaction of pulverized fuel ash (PFA) compared to cement hydration, the addition of PFA can reduce the heat generation of concrete during its hardening. However, as the water to binder (W/B) ratio would affect the proportions of cement and PFA that could react with water, the conventional practice of determining concrete temperature rise solely based on the cement and PFA contents may not yield accurate estimations. An experimental programme was launched to investigate the adiabatic temperature rise of PFA concrete mixes. Seven concrete mixes without PFA added and 14 concrete mixes with PFA dosages at 20% and 40% were tested with the recently developed semi-adiabatic curing test method. The adiabatic temperature rise was obtained by applying heat loss compensation to the test results. It was found that the incorporation of PFA could suppress the adiabatic temperature rise by 4°C to 14°C. The test results revealed the dependence of adiabatic temperature rise on both PFA dosage and W/B ratio, whose combined effects can be accurately addressed via the prediction formula and design chart developed herein.

Shrinkage of High-strength Concrete and High-flowability Concrete

Throughout the years, a large amount of research on the shrinkage of normal concrete with cube compressive strength up to 60 MPa has been carried out. Relatively, the amount of research on the shrinkage of high-strength concrete and high-flowability concrete is not as much. However, some engineers have raised the concern that as these high-performance concretes tend to contain more cementitious materials or have a larger paste volume, their shrinkage might be larger than that of normal concrete. To address this issue and find out whether the shrinkage of high-performance concretes could be a major problem, a comprehensive testing programme using optical fibre strain gauges to measure the shrinkage strains was launched. The shrinkage measurement lasted over three years and covered normal concrete, high-strength concrete and high-flowability concrete with characteristic cube strength ranging from 35 to 80 MPa, paste volume ranging from 30 - 40%, and slump flow up to 750 mm.

Improving Packing Density of Powder in Cement Paste for Production of High-Performance Concrete

The packing density of the powder in cement paste has great influence on the performance of the concrete. A higher packing density could at the same water/powder ratio increase the amount of excess water for lubricating the cement paste and thereby improve the flowability of the concrete. Alternatively, it would allow the water/powder ratio to be reduced to improve the strength of the concrete without compromising the flowability. Therefore, it is of great interest, especially for production of high-performance concrete, to maximize the packing density of the powder. This study aims to investigate the roles of superplasticizer and fillers in the packing density of the powder in cement paste. Packing density tests were carried out to determine the packing density of cement with various dosages of superplasticizer and different fillers (limestone fine, superfine cement and condensed silica fume) added using a newly developed wet packing method. The results showed that the addition of superplasticizer can significantly improve the packing density of cement while the addition of fillers can further improve the packing density of the powder.

Adiabatic Temperature Rise of Condensed Silica Fume (CSF) Concrete

Condensed silica fume (CSF) is often added into concrete mixes to enhance the properties of concrete. However, the effect of CSF on the heat evolution and temperature rise of concrete is not clearly known. Test results in the literature are insufficient and sometimes contradictory to enable any conclusion to be drawn regarding the role of CSF in heat generation behaviour of concrete. Moreover, since the chemical reactions of cement and CSF both involve water and hence cement and CSF are competing with each other in reacting with water, the water to binder (W/B) ratio may affect the temperature rise characteristics of concrete. This paper reports an experimental study of adiabatic temperature rise of CSF concrete conducted at The University of Hong Kong. Five concrete mixes without CSF and 10 concrete mixes with CSF dosages at 5% and 10% were tested with the recently developed semi-adiabatic curing test method. The adiabatic temperature rise was obtained by applying heat loss compensation to the test results. It was found that the addition of CSF could suppress the adiabatic temperature rise of concrete. At the same time, the strength of concrete could be enhanced. Based on the experimental results, prediction formula and design chart of adiabatic temperature rise of CSF concrete were developed.

Enhancing the Built Environment by Green Roofs

Green roof systems are living vegetation integrated on top of roofs. They could enhance the built environment in a number of ways. Herein, different types of green roof and their structural arrangement and materials design are introduced. Various benefits offered by green roof to the urban habitat are discussed. Finally, examples of applications of green roofs are presented.