Influence of Alkalis on Porosity Percolation in Hydrating Cement Pastes.
Influence of Alkalis on Porosity Percolation in
Hydrating Cement Pastes.
Bentz, D. P.
Cement and Concrete Composites, Vol. 28, No. 5,
427-432, May 2006.
cements; cement pastes; porosity; percolation;
acceleration; alkalis; hydration; temperature;
Loss-on-ignition (LOI) measurements and low temperature
calorimetry (LTC) are used to study the properties of
hydrating cement pastes with various quantities of
alkalis. In addition to the well-known acceleration of
early age hydration and .retardation. of later age
hydration, the alkalis are observed to have a
significant effect on the percolation of the porosity in
the hydrating systems, as assessed using the LTC
technique. At equivalent degrees of hydration, the
capillary pores in cement pastes with sufficient added
alkalis may depercolate while those in lower alkali
cement pastes remain percolated. A simple
microstructural model is applied to examine the
potential effects of hydration product morphology
(random, needles, and plates or laths) on pore space
percolation. The model suggests that the observed
experimental results could be consistent with the higher
alkali levels modifying the morphology of the C.S.H gel
to produce more lath-like hydration products, as has
been observed by others previously using electron
microscopy. Potential implications for the transport
properties and durability of these materials are