Authors:J. Ninov, I. Doykov, L. Dimova, B. Petrov, and L. Brakalov
The investigation of the kinetics of pozzolanicreactions is an important experimental task that gives characteristic constants for the reaction rate. Using them, one can evaluate the effectiveness of applying
Authors:M. García de Lomas, M. Sánchez de Rojas, and M. Frías
This work presents the relation between the pozzolanic activity, the hydration heat and the compressive strength developed
by blended mortars containing 10 and 35% of a spent fluid catalytic cracking catalyst (FCC).
The results show that, in comparison with 100% Portland cement mortar, a mortar with 10% FCC increases the hydration heat
all over the period of testing. This hydration heat increasing is due to the pozzolanic effect, therefore the resulting compressive
strength is higher than the reference mortar. Whereas, in a mortar with 35% of FCC, the hydration heat is higher than 100%
PC mortar, until 10 h of testing. After this age, the substitution degree predominates over the pozzolanic activity, showing
in this case, lower hydration heat and developing lower compressive strength than 100% PC mortar.
The pozzolanic reaction between natural zeolite tuffs, portlandite and water was investigated over the course of the early
reaction period up to 3 days. Isothermal conduction calorimetry experiments supplemented by TG/DTG and XRD analyses assisted
in the elucidation of the sequence of reaction processes taking place. The calorimetry experiments clearly showed the dependence
of the pozzolanic reaction rate and associated heat release on the fineness of the zeolite tuff. Higher external surface areas
of pozzolans yield higher total heat releases. Also the exchangeable cation content of the zeolites influences the reaction
rate. Release of exchangeable alkalis into solution promotes the pozzolanic reaction by raising the pH and zeolite solubility.
The appearance of an exotherm after approximately 3 h of reaction is more conspicuous when alkali-rich zeolites are reacted.
This exotherm is conceived to be related to a transformation or rupture of initially formed reaction products covering the
zeolite grains. The formation of substantial amounts of ‘stable’ calcium silicate hydrate (C–S–H) and calcium aluminate hydrate
(C–A–H) reaction took place after an induction period of more than 6 h. The openness of the zeolite framework affects the
proneness of the zeolite to dissolution and thus its reactivity. Open framework zeolites such as chabazite were observed to
react much more rapidly than closed framework zeolites such as analcime.
The kinetics of the pozzolanic reaction of enriched kaolin from the “Senovo” deposit (Bulgaria) with lime is the object of
this article. The kaolin contains kaolinite as a major clay mineral as well as admixtures of quartz and illite. The experimental
data of pozzolanic activity at temperatures of 100 and 23 °C are obtained for different reaction times. The reaction degrees
of kaolinite and lime at 100 °C are determined from the pozzolanic activity data using a powder X-ray diffraction analysis.
The kinetic analysis is performed by joint presentation of theoretical and experimental data in dimensionless coordinates
having in mind the influence of particle size distribution on the reaction rate. It is found by the kinetic analysis that
the rate of entire reaction is limited by the rate of chemical reaction on the reaction surface up to degree of reaction near
to 0.4. The rate of penetration of the chemical reaction into the kaolinite particles for this area—from the beginning to
degree of reaction 0.4, is determined to be equal to 2.10−11 m/s.
Authors:G. Baert, S. Hoste, G. De Schutter, and N. De Belie
Four paste mixtures with varying replacement level of the cement content by fly ash have been studied. Due to fly ash, the
acceleration period decreased and a third hydration peak was noticed with isothermal calorimetry. The total heat after 7 days
increased with increasing fly ash content. From 1 to 7 days, thermogravimetry showed a higher chemically bound water and Ca(OH)2-content for the pastes with fly ash. Between 7 and 14 days the calcium hydroxide started to be depleted due to the pozzolanic
reaction. A unique relation was found between calcium hydroxide and total heat development.
Differential thermal analysis and thermogravimetry were used to evaluate the effect of some additives, such as CaSO4, CaCl2 and silica fume amorphous silica from ferrosilicon synthesis on the mechanism and kinetics of reactions occurring in fly
ash-Ca(OH)2 system. The accelerating role of these additives was demonstrated from the data relating to Ca(OH)2 consumption in hydrated pastes, determined by TG measurements.
chemically combined water caused by hydration or pozzolanicreaction of fine SCMs is much lower than that caused by hydration of fine clinker in the first few minutes. For middle fractions (10–30 μm), GBFS shows slightly higher water requirement than Portland
Authors:K. Vessalas, P. Thomas, A. Ray, J. Guerbois, P. Joyce, and J. Haggman
Thermogravimetric (TG) analysis was applied to the characterisation of the pozzolanic reaction in mortars containing the supplementary
cementitious materials (SCMs) pitchstone fines (PF) and fly ash (FA) as partial replacements for Portland cement (PC). TG
analysis was used to determine the proportion of calcium hydroxide (CH) present from the hydration of the PC based on the
dehydroxylation of the CH present in the blended PC-SCM mortars. The consumption of CH indicated that both SCMs underwent
the pozzolanic reaction and that PF was found to compare favourably in its pozzolanic reactivity of FA, the industry and globally
accepted standard artificial pozzolan.
The results of pozzolanic activity determination using DTA-TG method are presented. This feature was characterised by Ca(OH)2 residue determination in cement pastes admixtured with siliceous earth, consuming the calcium ions from hydrolysis of cement
clinker minerals. The rate of pozzolanic reaction was thus estimated. Some results for fly ash containing pastes were also
The kinetics of the pozzolanic reactions of illite clay from the ‘Mirkovo’ deposit with lime is studied using X-ray, DTA/TG,
optical and electron microscopy methods. In parallel, the compressive strength properties of the specimens, stored under appropriate
conditions for up to 6 months, are measured. Illite reacts almost completely with lime for about 3 to 4 months. The reaction
of kaolinite takes place slowly and only about 2/3 of its quantity transform for the 6 months storage period.
The hardened amorphous hydrosilicates and hydroaluminate are formed through the pozzolanic reactions and contribute to the
mechanical properties of the stabilized clay specimens. The maximal compressive strength obtained at the experiments reaches
about 5-6 MPa. At the end of the storage period, the formation of fibrous or prismatic crystallites is observed on the surface
of the particles.