Ceramics-Silikáty 54, (2) 144 - 151 (2010)

This study has examined the effect of fly ash used as replacement addition (in the quantities of 0-40 mass %) to the Ordinary Portland cement (OPC) (type CEM I 42,5R) on the setting time in the system of paste, compressive strength development (w/s = 0.475-0.5, t = 20°C) and on drying shrinkage of cement mortars (t = 20°C, RH ≥ 55 %). Enlarged addition of fly ash affects extension of setting time and also affects reducing of the water, needed to achieve normal consistency. The increased addition significantly improves resistance to drying shrinkage throughout the measurement period. On the other side, increased amount of added fly ash reduces early strengths of cement mortars. In the later hydration stages, when pozzolanic reaction takes place, the strength difference between samples made with and without addition of fly ash decreases. The effect of the pozzolanic reaction, determined by using TG/DTA, can be observed after 60 days of hydration. A detailed chemical (X-ray diffraction), thermogravimetric and morphological (scanning electron microscope (SEM)) analyses of the hydrated samples of mortars are presented.