The objective of this paper was to reproduce the formation of thaumasite due to the reaction of atmospheric SO2 with hydraulic mortars. The research was carried out on mortars made with ordinary Portland cement (OPC), mineralized white Portland cement. Lime and a mixture of lime and pozzolana. Mortars under went sulfation by exposing the samples to 300 ppm SO2 at 25°C and 95% RH for 2 days. Subsequently, half of sulphated samples were kept for 6 and 12 months in a chamber with 0.3 ppm, SO2 as pollutant (0.5 l min-1 flow gas velocity) 5°C and 95% RH. The other halves of the sulphated samples were kept partially immersed in water at 5°C for 4.9 and 14 months. The process of thaumasite formation in hydraulic mortars due to the interaction with atmospheric SO2 was reproduced in all hydraulic mortars kept partially immersed in water at low temperature, except in the lime-pozzolana mixture. Gypsum was in the first reaction product formed as a result of that interaction. Subsequently, gypsum reacted with calcium carbonate and C-S-H gel resulting in the formation of thaumasite. The formation of thaumasite was easier and quicker in sulphated samples kept at low temperature partially immersed in water. Only in OPC mortars was thaumasite formation observed in samples exposed to 0.3 ppm SO2 for 12 months.
Thaumasite formation due to atmospheric SO2 - hydraulic mortar interaction
2003
Abstract
The objective of this paper was to reproduce the formation of thaumasite due to the reaction of atmospheric SO2 with hydraulic mortars. The research was carried out on mortars made with ordinary Portland cement (OPC), mineralized white Portland cement. Lime and a mixture of lime and pozzolana. Mortars under went sulfation by exposing the samples to 300 ppm SO2 at 25°C and 95% RH for 2 days. Subsequently, half of sulphated samples were kept for 6 and 12 months in a chamber with 0.3 ppm, SO2 as pollutant (0.5 l min-1 flow gas velocity) 5°C and 95% RH. The other halves of the sulphated samples were kept partially immersed in water at 5°C for 4.9 and 14 months. The process of thaumasite formation in hydraulic mortars due to the interaction with atmospheric SO2 was reproduced in all hydraulic mortars kept partially immersed in water at low temperature, except in the lime-pozzolana mixture. Gypsum was in the first reaction product formed as a result of that interaction. Subsequently, gypsum reacted with calcium carbonate and C-S-H gel resulting in the formation of thaumasite. The formation of thaumasite was easier and quicker in sulphated samples kept at low temperature partially immersed in water. Only in OPC mortars was thaumasite formation observed in samples exposed to 0.3 ppm SO2 for 12 months.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
