Isothermal and solution calorimetry to assess the effect of superplasticizers and mineral admixtures on cement hydration

Abstract

The heat of hydration evolution of eight paste mixtures of various water to binder ratio and containing various pozzolanic (silica fume, fly ash) and latent hydraulic (granulated blast furnace slag) admixtures have been studied by means of isothermal calorimetry during the first 7 days of the hydration process and by means of solution calorimetry for up to 120 days. The results of early heat of hydration values obtained by both methods are comparable in case of the samples without mineral admixtures; the values obtained for samples containing fly ash and granulated blast furnace slag differ though. The results from isothermal calorimetry show an acceleration of the hydration process by the presence of the fine particles of silica fume and retarding action of other mineral admixtures and superplasticizer. The influence of the presence of mineral admixtures on higher heat development (expressed as joules per gram of cement in mixture) becomes apparent after 20 h in case of fly ash without superplasticizer and after 48 h for sample containing fly ash and superplasticizer. In case of samples containing slag and superplasticizer the delay observed was 40 h. The results obtained by solution calorimetry provide a good complement to the ones of isothermal calorimetry, as the solution calorimetry enables to study the contribution of the mineral admixtures to the hydration heat development at later ages of the hydration process, which is otherwise hard to obtain by different method

Heat of hydration of low-clinker cements

“…Addition of fly ash more distinctly retards the acceleratory period of cement hydration than slag, this tendency is especially clear for the high substitution rate of fly ashes. This retarding effect of the mineral additions on the cement hydration has been already reported [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35].…”

“…It has been observed in these tests that the evolved heat decreases as slag content increases, but at the same time the heat evolved increases with the fineness of the slag or clinker in the blended cements. Simultaneously, mixtures containing GBFS do not generate higher heat initially, but they generate heat higher than the OPC pastes in the later period [24]. The tests performed at different temperature showed that higher curing temperature increased the reactivity of the slag and a decreased reactivity with an increase in the percentage of slag replacement.…”

“…The hydration heat of blended cements has been investigated by several authors . The hydration of blended cements with different substitution rates of GGBFS has been studied, inter alia, by Roy and Idorn [11], De Schutter [12,13], Escalante et al [14], Saeki and Monteiro [15], Pane and Hansen [16], Binici et al [17], Meinhard and Lackner [18], Ježo et al [19], Chen et al [20], Merzouki et al [21], Hana et al [22], Gruyaert et al [23] and Siler [24]. It has been observed in these tests that the evolved heat decreases as slag content increases, but at the same time the heat evolved increases with the fineness of the slag or clinker in the blended cements.…”

Calorimetry in testing waste materials from the brown coal combustion

“…Subsequently, the heat evolution was monitored for the mixtures composed of 25 % fly ash and 75 % cement CEM I samples. The calorimetric measurements appeared again as a convenient, rapid method of the hydraulic activity assessment, used in case of mineral additives and different modifying agents for a couple of years [15][16][17][18][19][20].…”

Performance of Portland cement pastes containing nano-silica and different types of silica

“…Besides these effects, the reduction in particle size by grinding can boost the effect of heterogeneous nucleation, due to the inclusion of new nucleation sites for deposition of the hydrated products [8][9][10][11][12]. Grinding can also be responsible for promoting partial amorphization and significant increase in specific surface area [5][6][13][14][15][16][17][18].…”