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the cement-perlite matrix and the oxide which adds nucleation sites for the hydration process. The shorter relaxation time of
the samples containing TiO 2 in the hardening period suggests that the introduction of the oxide results in a denser pore
structure with smaller crystallites.
In comparison to the PC and the CP+PC samples, the EP+PC and EP+PC+TiO 2 ones show significantly increased T 1 in values
due to the increased amount of water in the mixture (see Table 1). Also the initial period is characterized by almost stable T 1
values and an abrupt starting of the acceleration period. This behaviour is probably related to the porous structure of the EP
which tends to adsorb a high percentage of water that is stored inside and is going to react with the cement gel during the
acceleration period. Comparing to the pure PC, the acceleration period of the EP+PC sample is severely prolonged. The
addition of the oxide (PC+EP+TiO 2 ) reduces the acceleration period duration while the hydration graph stabilizes the step
like form. This resembles the corresponding influence of the TiO 2 in the PC+TiO 2 and CP+PC+TiO 2 samples. On the other
side, the T 1 fin values of both the EP+PC and EP+PC+TiO 2 samples remain bigger than that of the unmodified PC. This is
related to the bigger size of the pores introduced by the expanded perlite in the modified cement matrix which is also
responsible for the light concrete properties on the one side and the deterioration of the mechanical strength on the other.
T 1
(msec)
100
10
PC
PC+TiO 2
Fig. 1. The spin-lattice relaxation time of the
unmodified PC and the modified with TiO 2 cement
samples, for various hydration time periods. Vertical
lines separate the characteristic three regions (initial,
acceleration, hardening) of the cement hydration
kinetics for the unmodified sample.
1
0.1 1 10 100 1000
Hydration Time (Hours)
The photoinduced properties of the cementitious samples, were tested by the degradation of methyl orange (MO) azo-dye
pollutant solution. 28 days after their preparation, the samples were immersed into a bath of 0.5-0.6 10 -4 M dye aqueous
solution and UV irradiated for 9 hours. The light activation of the TiO 2 nanoparticulate additives, resulted in an approximate
30% net pollutant degradation, taking into account the physical adsorption of the dye inside the porous cementitious samples.
It is very interesting that all the perlite modified samples presented better oxidizing effect than the reference PC sample. This
is probably related to the high porosity of perlite which permits the formation of the highly drastic hydroxyl radicals upon the
surface of the modified concrete materials, after UV irradiation [3]. A project that will monitor the ageing of the
photoinduced process is under way.
References
[1] L. Cassar, MRS Bulletin, May 2004, p.1
[2] ] M. Lackhoff, X. Prieto, N. Nestle, F. Dehn and R. Niessner, Appl. Catal. B 43 (2003) 205.
[3] A.I. Kontos, A.G. Kontos, D.S. Tsoukleris, G.D. Vlachos, and P. Falaras,Thin Solid Films, 515 (2007) 7370.
[4] L.-H Yu, H. Ou, and L.-L. Lee, Cem. Concr. Res. 33 (2003) 73-76.
[5] Isocon, A.E., (http://www.isocon.gr/greek/products/perlomin.html)
[6] G. Papavassiliou, F. Milia, R. Rumm, E. Laganas, O. Jarh, A. Sepe, R. Blinc and M.M. Pintar, J. Am. Ceram. Soc. 76
(1993) 2109.
[7] G. Papavassiliou, M. Fardis, E. Laganas, A. Leventis, A. Hassanien, and F. Milia, A. Papageorgiou and E. Chaniotaki, J.
Appl. Phys. 82 (1999) 450.
209