Sulfate Attack on Concrete-The Effects of Supplementary Cementitious Materials and Exposure Temperature on External Sulfate Attack (PDF)

The Effects of Supplementary Cementitious Materials and Exposure Temperature on External Sulfate Attack (PDF)

Pdf Summary

The document discusses the effects of supplementary cementitious materials (SCMs) and exposure temperatures on external sulfate attack in concrete. It includes findings from a laboratory testing program designed to assess sulfate resistance under various conditions. Key points from the study include:

1. <strong>Temperature Impact</strong>: Higher temperatures increase the solubility and formation of ettringite and gypsum, enhancing the risk of sulfate attack. Conversely, lower temperatures can promote thaumasite formation, albeit more slowly. Portland limestone cement concretes are highlighted as particularly vulnerable under these conditions.

2. <strong>SCMs Role</strong>: Using SCMs like fly ash, silica fume, and metakaolin improves concrete's resistance to external sulfate attack by reducing Ca(OH)2 content and enhancing the formation of stable aluminate hydrates. This is achieved through dilution and consumption via pozzolanic reactions, reducing the penetrability of the cement matrix.

3. <strong>Laboratory Testing</strong>: The program involved multiple series of mortar bars and cubes exposed to varying temperatures (1°C, 5°C, 10°C, 23°C) and sulfate solutions. The compressive strength of mortar cubes was tested at 5°C, 23°C, and 38°C.

4. <strong>Results</strong>: SCM-blended mortars demonstrated better sulfate resistance than control mortars, with fly ash and metakaolin performing notably well across different temperatures. However, at colder exposures, the sulfate resistance diminished significantly for SCM-blended mortars.

5. <strong>Conclusions</strong>: The study suggests CSA A3001 testing for sulfate-resisting cements might be too stringent, with temperature being a crucial factor. Metakaolin showed improved performance at colder temperatures due to its fine particle size enhancing cement hydration. The results imply that with appropriate SCM use, Portland limestone cement can achieve high sulfate resistance.

Overall, the research underscores the importance of selecting suitable SCMs and understanding environmental exposure conditions to improve the durability of concrete structures against sulfate attacks.

Keywords

supplementary cementitious materials

external sulfate attack

temperature impact

ettringite

gypsum

thaumasite

fly ash

silica fume

metakaolin

Portland limestone cement