Dr. Y. Qian, Department of
Civil Engineering, The University of Hong Kong.
is the most widely used infrastructural material, where 3 billion tons were
consumed globally in 2010. Modern concrete is a complex material consisting not
only cement, aggregates and water, but also chemical admixtures and
supplementary cementitious materials (SCMs) for concrete sustainability.
with conventional vibrating concrete, self-consolidating concrete (SCC) is more
flowable and can consolidate under its own weight. Therefore, it introduces
many advantages in construction applications. These include decreasing labor
work for casting, better quality control and enhancing hardened properties.
However, challenges still remain, such as issues relating to formwork pressure
and multi-layer casting. Each of these issues is closely related to the
property of thixotropy. For SCC, as well as other concrete systems, it is about
balancing sufficient flowability during casting and rate of structural buildup
after placement. For instance, relating to the issue of SCC formwork, it is
ideal for the material to be highly flowable to achieve rapid casting, but then
exhibiting high rate of structural buildup to reduce formwork pressure. This
can reduce the cost of formwork and reduce the risk of formwork failure. It is
apparent that accurately quantifying the two aspects of thixotropy, i.e.
structuration and destructuration, is key to tackling these challenges in field
have been extensively working on defining and quantifying thixotropy since PhD
program. Firstly, I applied creep recovery test to accurately measure the
static yield stress and probe tack test to quantify cohesion. Nanoclay addition
increases both static yield stress and cohesion and thus decreases SCC formwork
pressure, as well as improve static segregation and stability. Secondly, after
accurately measuring both aspects of thixotropy, I tied thixotropy to the
discrepancy between static and dynamic yield stress. The higher the thixotropy,
the higher the discrepancy. I also define an index to effectively quantify thixotropy. Thirdly, results
of thixotropic index indicate that water reducing agents decrease
thixotropy while nanoclay increases it. Finally, with a good balance of water
reducing agents and nanoclay, I have developed mixtures with high flowabiltiy
yet high stability after placement. It is an ideal mixture for 3D printing
cementitous materials. System and material control for successful 3D concrete
printing are also studied.
Qian is currently Assistant Professor at the University of Hong Kong. He worked
as Research Fellow at Singapore Centre for 3D Printing. Before that, he also
worked as postdoctoral Research Fellow at Ghent University in Belgium. He has
obtained his Ph.D. at Columbia University in the City of New York, his M.S. at
Hokkaido University in Japan, and his B.S. at Huazhong University of Science
and Technology in China.
specializes in cement and concrete rheology, especially developing
characterization methods to probe and control the viscoelastic properties of
fresh cementitious systems and design of cementitious systems to improve
processing during construction. He is also interested in nanoparticles, and
sustainable construction materials.
No registration is
enquiries, please contact Ir Dr Simon Wong at 21761412
information, please browse http://st.hkie.org.hk/.
will be issued.
the Best Reporter Award are invited. Report must be submitted to firstname.lastname@example.org within
two weeks after the seminar. The rules of the Best Reporter Award could be
referred to the following link:
information and views expressed by speakers and in their conference materials
do not reflect the official opinion and position of the HKIE. No responsibility
is accepted by the HKIE or their publisher for such information and views
including their accuracy, correctness and veracity.