Self-sensing concrete with nanomaterials - Nanotechnology in Eco-efficient Construction - page 54

undergoing bending in the pre-cracking region. The relationship between
FCR and the strain of initial geometrical neutral axis (IGNA) was estab-
lished by regression analysis. Based on damage mechanics theory and the
relationship mentioned above, the correlation between the degree of
damage and the FCR was established. The results show that the relationship
between FCR and the strain of the IGNA in concrete beams can be effec-
tively described by the First Order Exponential Decay curve before
cracking.

4.2 Studying conductive admixtures in concrete

4.2.1 Materials

The nano carbon black (Fig. 4.1) used in the experiments was a super-
conductive form of porous agglomerates of carbon particles with an average
size of 60 nm and a density of 0.3-0.5 g/cm 3 . The carbon fi bre used (Fig. 4.2)
in the conductive phase was asphalt base short carbon fi bre with a diameter
of 12-15

m and a length of 6 mm. Its density was 1.55-1.60 g/cm 3 . The
properties of NCB and CF used are shown in Tables 4.1 and 4.2.
In order to analyse the effect of conductive admixtures on the concrete,
plain concrete samples without CF and NCB were prepared as references.
The design mixture of the plain concrete is shown in Table 4.3. The type of
cement used was CEM I 42.5, the W/B was 0.45, and a water reducing agent
(WR) was used in the amount of 1.0% by mass of binder. The 28d compres-
sive strength was 43.6 MPa. The NCB content with a particle size of ca .
30-90 nm (Fig. 4.1) was between 0.1% and 0.4% by mass of binder (0.53-

μ

￿ ￿ ￿ ￿ ￿ ￿

4.1 Nano carbon black and particle size using high resolution fi eld
emission SEM.