). Presumably the better activity of particular components in the CSA 1180 allows to produce more ettringite without disturbing the dissolution of initial material. The ettringite is known as forming an impermeable layer during the early cementhydration
loss during mortar application, to improve the workability of the fresh mortar, as well as to increase the hardened mortar adherence to the substrate [ 3 ].
Still, one of the side effects of cellulose ether's addition is the cementhydration
Calorimetry was applied to an investigation of the early hydration of Portland cement (PC)–calcium aluminate cement (CAC)
pastes. The heat evolution measurements were related to the strength tests on small cylindrical samples and standard mortar
bars. Different heat-evolution profiles were observed, depending on the calcium aluminate cement/Portland cement ratio. The
significant modification of Portland cement heat evolution profile within a few hours after mixing with water was observed
generally in pastes containing up to 25% CAC. On the other hand the CAC hydration acceleration effect was also obtained with
the 10% and 20% addition of Portland cement. As one could expect the compressive and flexural strength development was more
or less changed—reduced in the presence of larger amount of the second component in the mixture, presumably because of the
internal cracks generated by expansive calcium sulfoaluminate formation.
The aim of this work is to compare the influence of addition of waste aluminosilicate catalyst on the initial periods of hydration
of different cements, i.e. calcium aluminate cements of different composition and Portland cement, basing on the calorimetric
studies. Cement pastes containing up to 25 mass% of additive were studied, where the water/(cement+additive) ratio was 0.5.
An attempt was undertaken to explain the mechanism of action of introduced aluminosilicate in the system of hydrating cement,
particularly in the case of calcium aluminate cement pastes.
It was found that the presence of fine-grained additive caused in all studied cases the increase of the amount of released
heat in the first period after the addition of water. In the case of aluminate cements with aluminosilicate addition, a significant
reduction of induction time and faster precipitation of hydration products were observed compared to the reference sample
(without additive). In the experimental conditions, the additive caused the acceleration of aluminate cements hydration, and
the mechanism of its action is probably complex and can encompass: nucleative action of small grains and formation of new
Calorimetry is a good method for studies on cementhydration during its first hours of action when chemical and physical processes occur most intensively. This technique bases on continuous measurements of heat released in
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.
A simple water sorption/retention (WS/WR) test, followed by stepwise static heating, was applied to the study of cement quality and the reactivity of its grain surface.
The physically bound water and hence the specific surface both in the unhydrated and in the hydrated state were estimated
as a function of the hydration time. Rehydration after heating at 220°C and contact with air was different inWS from that inWR samples, which indicates a difference in microstructure. XRD proved the formation of portlandite during the sorption test
and eventual heating at 200°C, and its transformation into carbonates on contact with air, especially on heating at 400°C.
The contents of these compounds were estimated from the mass difference between 400 and 800°C, which was compatible with the
mass change between 220 and 400°C and this indicates surface reactivity. The test may serve for the routine study of cement.
A simple isothermal calorimeter ideal to study hydration of cementitious systems is described together with an ampoule design
to allow addition of water and mixing with the ampoule inside the calorimeter. An overview of dynamic corrections is given,
and the utilisation of the different dynamic corrections on the calorimeter output is discussed. Correction of data on b-hemihydrate
hydration to form gypsum has shown good kinetic agreement with data from synchrotron X-ray diffraction.
The so-called pozzolanic activity of waste catalysts from fluidised cracking was investigated. For this purpose a series of
cement mixtures with this waste material were prepared and subsequently the pastes and mortars were produced. Waste aluminosilicate
catalyst was used both in raw form and after grinding in a ball mill for 60 min. The hydrating mixtures were subjected to
the calorimetric measurements in a non-isothermal/non-adiabatic calorimeter. After an appointed time of curing the hydrating
materials were studied by thermal analysis methods (TG, DTG, DTA). The pozzolanic activity factors were determined, basing
on the compressive strength data. The increased activity of cement — ground pozzolana systems has been thus proved. An accelerated
Ca(OH)2 consumption as well as higher strength were found for materials containing ground waste catalyst, as compared to those, mixed
with the raw one. Thus grinding was also proved to result in mechanical activation in the case of the waste catalyst from