Cementos con material calcáreo: Formación de thaumasita por ataque de sulfatos

Abstract

In recent times, the risk of sulfate attack in limestone filler cements (CPF) due to the formation of thaumasite has been reported. This paper presents the results of mortars containing 0 and 20% of calcareous material in Na2SO4 solution and the results in cement pastes with lime (0 and 18%) in a combined solution of Na2SO4 and MgSO4 at temperatures of 5 and 20 °C. To predict the conditions leading to the formation of thaumasite, the survey on profiles was conducted through the DRX technique. Results show that thaumasite is formed when the attack produces ettringite cracking and massive deposition of gypsum, this producing CSH instability. This process is facilitated by the presence of lime, which increases the penetration of aggressive ions due to the increase in the effective w/c ratio in the paste or mortar. Finally, low temperatures also speed up the attack.