Pavel Šiler

Influence of superplasticizers on the course of Portland cement hydration

A multicell isoperibolic — semiadiabatic calorimeter was used for the measurement of temperature and the determination of the hydration heat evolution at earlier period of cement pastes setting and hardening. The measurements were aimed at the determination of the effect of superplasticizers (SPs) on the course of the Portland cement hydration. Commercial polycarboxylate SP was added to the mixtures and the heat effect was measured. With the increasing content of SP, the hydration temperature increased up to a certain value and then decreased. In case of a sufficient amount of water in the mixture to achieve complete hydration of cement, samples with the highest values of the maximum hydration temperature reached the highest values of the released total heat. If there is not a sufficient amount of water to achieve complete hydration, the samples with the highest values of the maximum hydration temperature reach the lowest values of the released total heat.

Calorimetric determination of the effect of additives on cement hydration process

Possibilities of a multicell isoperibolic-semiadiabatic calorimeter application for the measurement of hydration heat and maximum temperature reached in mixtures of various compositions during their setting and early stages of hardening are presented. Measurements were aimed to determine the impact of selected components’ content on the course of ordinary Portland cement (OPC) hydration. The following components were selected for the determination of the hydration behaviour in mixtures: very finely ground granulated blast furnace slag (GBFS), silica fume (microsilica, SF), finely ground quartz sand (FGQ), and calcined bauxite (CB). A commercial polycarboxylate type superplasticizer was also added to the selected mixtures. All maximum temperatures measured for selected mineral components were lower than that reached for cement. The maximum temperature increased with the decreasing amount of components in the mixture for all components except for silica fume. For all components, except for CB, the values of total released heat were higher than those for pure Portland cement samples.

The Influence of Particle Size of Cement and Different Additives on the Properties of Portland Cement Pastes

The consumption of concrete as a building material is still increasing over the world. Concrete production is closely associated with CO2 and other greenhouse gases emissions. The reduction of these emissions can be achieved by a higher utilization of secondary raw materials in cement mixtures. Particle size is an important factor for more effective use of these materials. This work is focused on the calorimetric determination of the effect of particle size of cement, finely ground granulated blast furnace slag (GBFS), high-temperature fly ash (FA) and fluidized fly ash (FFA) on the Portland cement hydration. Effect of particle size on the hydration of pure cement pastes and pastes with the addition of secondary raw materials is monitored by isoperibolic calorimetry. Other part of this work is aimed on the mechanical properties of resulting materials. The flexural strength and compressive strength were observed after 1, 7 and 28 days of curing.