Self-sensing concrete with nanomaterials - Nanotechnology in Eco-efficient Construction - page 53

tive concrete. This enables resistivity measurements to be carried out and
may be used to analyse variations of strain or stress in structural compo-
nents, thus making possible the early evaluation of damage without the
need to embed sensors. Conduction concrete also has a wide application in
the electromagnetic shielding of vital equipment and de-icing of airfi elds
and highways (Yehia and Tuan, 1999).
The addition of short CF to concrete creates continuous conductive
pathways which transmit current, playing a fundamental role in the electri-
cal transport process. The enhanced electrical conductivity of concrete with
CF also decreases shrinkage and cracking, so improving durability and
resistance to freezing. In addition, it does not require a large quantity of
water. The addition of NCB reduces cost by improving electrical conductiv-
ity and the toughness of the aggregate interface within the concrete matrix.
It also provides a fi ller effect which enhances the density of the matrix (Cai
and Chung, 2007). Due to the extremely small size of NCB compared to
traditional carbon fi bre, it penetrates the matrix in carbon fi bre reinforced
composites. This connects the conductive pathways to form conductive
networks which further improve electrical conductivity (Li et al. , 2006,
2008). Initial and evolving strain in concrete may cause damage which
breaks conductive pathways or networks, resulting in a change of electric
resistance. The combined use of NCB and short CF provides conductive
concrete with effective mechanical properties.
Damage to cement-based material may change its electric resistance, as
manifested in elastic tension, plastic deformation and cracking. Concrete
components with coarse aggregate are often subjected to differences in
loading (e.g., compression, tension and bending), and may also experience
various stages of load-deformation, including pre- and post-cracking behav-
iour. Studies on strain sensing in carbon fi bre reinforced geopolymer con-
crete under conditions of bending and compression have been reported.
However, studies on concrete beams with diphasic electrical conduction
admixtures for diagnosis of damage caused by bending are still very rare.
There are several problems in the study of conductive concrete beams. The
electric characteristics must be suitable for a particular application without
degradation of the workability of fresh concrete or detriment to the
mechanical behaviours of hardened concrete.
Based on investigations into the effect of NCB and CF on the workability,
compression strength and fl exural strength of concrete, a large number of
concrete beams reinforced with conductive material were investigated
experimentally to study the damage and FCR under varied loading levels.
The purpose of this work was to analyse the effect of NCB or CF, and
especially the hybrid use of NCB and short CF, as diphasic conductive
materials on the FCR of concrete beams. It was also concerned with the
relationship between FCR, strain and degree of damage in concrete beams

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