Reactivity of NO 2 and CO 2 with hardened cement paste containing activated carbon

The development of building materials to reduce the concentration of NO 2 is growing interest in a world where the air quality in urban areas is affected by the car traffic. The main binder in concrete is the cement paste that is partly composed of calcium hydroxide. This alkaline hydrate composing the hardened cement paste shows a high BET surface area (close to 100 m 2 .g −1 ) and can absorb low-concentrations of NO 2 . However, the presence of CO 2 in the atmosphere limits the de-polluting effect of reference cement paste, mainly due to carbonation of the alkaline hydrates (reaction leading to the formation of calcium carbonate). The results established in this paper demonstrate that the addition of activated carbon in the cement paste, because of its very high BET surface area (close to 800 m 2 .g −1 ) and its specific reactivity with NO 2 , can significantly improve and prolong the de-polluting effect in presence of CO 2 and even after complete carbonation of the surface of the cement paste.