During the cement
hydration process, water reacts with Portland
cement to form calcium-silicate-hydrate
(CSH). A by-product of this reaction is the
formation of calcium hydroxide, or lime.
This lime is the weak link in concrete, and
it reduces the effect of the CSH. When KAOROCK™ is
present in the hydration process, it reacts
with the free lime to form additional CSH
material, thereby making the concrete stronger
and more durable (see equations below).
Portland Cement + Water = Cementitious Materials + Lime
Lime + KAOROCK™ = Additional Cementitous Materials
A recent, independent laboratory study
of mortar pastes demonstrates
the ability for KAOROCK™ to react with the free lime at
early stages in the curing process (See Figure ‘a’ below).
For the control, pastes were made without any pozzolanic material,
and then KAOROCK™ and silica fume replaced a portion of
the Portland cement (8% and 15%). The pastes containing KAOROCK™ showed
higher heats of evolution than the control mix or silica fume.
Silica fume reduced both the rate of heat evolution and the total
heat evolved, likely due to the removal of cement from the system.
Further, silica fume rate curves follow the same general profile
as the control, with the first peak, corresponding to the CSH
hydration, reaching higher than the second peak (C3A). This reflects
dilution of the cement hydration and indicates that there is
little secondary reaction occurring at these early ages.
