The acceleration of the carbonation of cementitious grout has been investigated using high pressures of carbon dioxide. Solid grout samples can be fully carbonated within several days but it is necessary to periodically dry the samples to remove built up water which saturates pores and prevents access of carbon dioxide gas to reaction sites. Periodic drying causes some physical damage to the specimens, including fracturing due to dehydration and shrinkage. Nevertheless, up to 60% of the carbonation capacity of hand-size specimens can be achieved without dehydration damage in less than 24 hours with a single pressurization of carbon dioxide. As such, high pressure carbonation holds promise as a means to rapidly carbonate hand-size grout specimens in order to study the changes that carbonation has on macroscale properties of concretes and grout.
Reactions between solid grout and carbon dioxide gas occur via three sequential diffusion controlled reactions: 1) an initial rapid uptake of carbon dioxide gas into arid diffusion through thin alkaline water films which coat the pores and particles of the cementitious grout; 2) a slower second-stage reaction during which the carbon dioxide must diffuse from the water films into the solid grout matrix; and 3) a final stage which occurs once the interconnected pore network becomes blocked with water released during the carbonation. For grout samples subjected to extreme conditions of drying before reaction with carbon dioxide (continuous vacuum (10 -3 torr) for two months), carbonation proceeds very slowly due to the lack of water to catalyse the reaction. For these experimental runs, there is no evidence of reaction autocatalysis with progressive carbonation. Autocatalysis would be expected due to the build up of water as a result of carbonation.