The filler effect: The influence of filler content and type on the hydration rate of tricalcium silicate

Abstract

The partial replacement of ordinary portland cement (OPC) by fine mineral fillers accelerates the rate of hydration reactions. This acceleration, known as the filler effect, has been attributed to enhanced heterogeneous nucleation of C-S-H on the extra surface provided by fillers. This study isolates the cause of the filler effect by examining how the composition and replacement levels of two filler agents influence the hydration of tricalcium silicate (T1-Ca 3 SiO 5 ; C 3 S), a polymorph of the major phase in ordinary portland cement (OPC). For a unit increase in surface area of the filler, C 3 S reaction rates increase far less than expected. This is because the agglomeration of fine filler particles can render up to 65% of their surface area unavailable for C-S-H nucleation. By analysis of mixtures with equal surface areas, it is hypothesized that limestone is a superior filler as compared to quartz due to the sorption of its aqueous CO 3 2À ions by the C-S-H-which in turn releases OH À species to increase the driving force for C-S-H growth. This hypothesis is supported by kinetic data of C 3 S hydration occurring in the presence of CO 3 2À and SO 4 2À ions provisioned by readily soluble salts. Contrary to prior investigations, these results suggest that differences in heterogeneous nucleation of the C-S-H on filler particle surfaces, caused due to differences in their interfacial properties, have little if any effect on C 3 S hydration kinetics. K E Y W O R D S C 3 S, filler effect, limestone, nucleation, quartz Correspondence

Influence of size‐classified and slightly soluble mineral additives on hydration of tricalcium silicate

“…In general, replacements of C 3 S with fillers observably accelerates hydration rates: the main heat flow rate peak (or the main hydration peak) occurs sooner; and the slope of the acceleration regime is steeper compared to the control (ie, plain C 3 S) paste. This is, expectedly, due to increased C‐S‐H precipitation on the additional nucleation sites provided by the filler particulates and is in agreement with prior studies . In terms of filler performance, silica fume and quartz appear to have similar filler effects—although it should be noted that the SSAs of the two fillers are different, and that silica fume particulates are strongly affected by agglomeration .…”

“…The area matched pastes were prepared by ‘matching’ their SSA solid to that of [C 3 S + 30% coarse limestone] and [C 3 S + 30% fine limestone] pastes, for which the SSA solid values are 789.32 m 2 kg −1 , and 589.84 m 2 kg −1 , respectively. The amount of filler required for area matching was calculated in accordance with prior studies . The uncertainty in the measured heat flow rate at the main hydration peak is ±2%…”

“…In the first stage, the profiles were processed, using a simple analytical model, to extract three distinct calorimetric parameters: inverse of time to the main hydration peak [h −1 ]; heat flow rate at the main hydration peak [mW g C3S −1 ]; and slope of the acceleration regime [mW g C3S −1 h −1 ]. Each of these parameters is an indicator of change in C 3 S hydration kinetics; higher and lower values compared to the plain binary system entail relatively superior and inferior dynamics of C 3 S hydration, respectively . In the second stage, the pBNG modeling platform (described in section 3.0) was used to reproduce the experimentally measured heat evolution profiles of all pastes.…”

“…Additional [C 3 S + filler] pastes were prepared by adjusting the replacement level of C 3 S by the filler (ie, quartz, rutile, and corundum) so as to match the total SSA of [C 3 S + 30% limestone] pastes. This area matching was done for each size‐class of the PSDs; the amount of powders required for area matching were calculated in accordance with procedures described in prior studies . These pastes with equivalent total SSAs will be hereon referred to as area matched .…”

Estudio de las reacciones de hidratación temprana en el hormigón proyectado

“…En particular, el método de estudio se ha aplicado para comparar el mezclado manual con la proyección así como analizar el "efecto filler" de la adición de caliza ultra fina, es decir, la aceleración de la hidratación del cemento debida a la presencia de la caliza [10][11][12][13][14].…”