IR-SPECTROSCOPIC INVESTIGATION OF GEOPOLYMER AND CSH-PHASE STABILITY ON HEATING TEMPERATURE IN POST-FIRED BUILDING MATERIALS.

Hardened cement pastes were prepared using CEM I 52,5 N, CEM III/B 42,5 and CEM I 52,5 N with the addition of 50 wt% granulated blast furnace slag (H). IR spectra indicated the destruction of Si-O chains of the CSH-phase in 600°C heated with respect to unheated samples. Series of CEM I 42,5 N hardened cement pastes were heated in 100°C steps up to 800°C. IR spectra indicated a certain variation in the density of states (DOS) of asymmetric Si-O vibrations up to 300°C, followed by a linear decrease in the DOSPM (DOS peak maximum) up to 800°C. This effect is explained by the destruction of the Si-O chain units of the CSH phases. A direct relation of the DOSPM behavior with the stagnation of compressive strength up to 300°C, followed by a linear decrease up to 800°C was proved using mortars prepared based on CEM I 42,5 R with the addition of 20 wt% fly ash. For concrete samples a similar decrease in DOSPM was observed. Alkali activated metakaolin (AAMK) and granulated blast furnace slag (AAH), aged over 6 years show compressive strength of about 60 and 100 MPa for AAH and 35 for AAMK. Heating at 800°C revealed a loss of strength by about 50-80% for AAH but only 20% for MK. For AAH the loss in strength during thermal stress is related to similar effects in the IR spectra also described for breakdown of CSH-phases obtained for CEM-related samples. For AAMK weakening is related to crack formation along Si enriched zones. [ABSTRACT FROM AUTHOR]