R. Cerny et al., The effects of thermal load and frost cycles on the water transport in twohigh-performance concretes, CEM CONCR R, 31(8), 2001, pp. 1129-1140
Moisture diffusivity of two high-performance concretes used in concrete con
tainment buildings of nuclear power plants is measured as a function of tem
perature up to 80 degreesC, and the effects of high-temperature exposure up
to 800 degreesC and freeze/thaw cycles on its value are analyzed. The temp
eratures in the range of 0-80 degreesC are found to have a moderate effect
on the moisture diffusivities of both concretes, the typical increase being
about 100-200% over the whole region. The high temperature exposure result
s in a much more significant increase of moisture diffusivity, up to three
orders of magnitude, and the freeze/thaw exposure of 400 cycles to an incre
ase up to one order of magnitude. As the main reason for the mentioned mois
ture diffusivity increase, the crack formation is identified. Both thermal
decomposition accompanied by release of substantial amount of gaseous subst
ances and water freezing in the porous system can damage the internal micro
structure of the matrix due to the significant pressure increase in the por
ous body. The magnitude of changes of moisture diffusivity is found to be a
ffected by the quality of aggregates rather than by the quality of cement.
High quality quartzitic aggregates with very low porosity and very good mec
hanical properties perform much better than other more porous siliceous agg
regates such as opal, and than the calcareous aggregates such as chalk. (C)
2001 Elsevier Science Ltd. All rights reserved.