I am looking into the carbonation reaction and currently using concrete containing 20mm and 10mm limestone aggregates. However my samples are limited to 40mm cubes due to the certain aspects of the project. Do the aggregates have any other effects than reducing the degree of the carbonation due to limiting diffusion? My issue is i am interested in techniques such as mapping XRD however, the bulk of the signal comes from the aggregate which masks the process.
Although I've never seen anything published on the topic, I could estimate a slight effect on carbonation rate. Reducing the aggregate size will increase the specific surface area of aggregate, and so there will be slightly more interfacial transition zone. Having said this, I'm not sure the effect will be huge.
A greater concern is that you can't use 20mm aggregate in a 40mm cube, so you're really limited to only 10mm aggregate.
Thanks for both the answers, they are both really useful.
In terms of the aggregate size, I am looking into moving away from atleast the 20mm aggregate
To, Mr. Alex,
Normally, maximum size of coarse aggregate in a concrete member is limited to one fifth of minimum dimension ( thickness)of member, as specified in code like IS 456- 2000. For 40 mm cube size specimen, it will be better to consider maximum aggregate size as 10 mm.
Of course, for the given proportion of concrete mix, lower size of aggregate will give thinner cement paste due to larger surface area as compared to larger size of aggregate. Specific gravity of aggregate also affects mix design. Lime stone aggregates have lower specific gravity as compared to basalt or granite hence larger volume of coarse aggregate will provide thinner paste. Shape of aggregate also affects mix design particularly workability. Carbonation has strong relation with voids available in cement paste hence water cement ratio and shape and size of aggregate must be considered while finding the effect of carbonation. The percentage area of aggregate exposed to carbonation is one most important parameter to determine diffusion of carbonation into concrete. Aggregates will help in reducing carbonation, however bond between cement paste and aggregate will get reduced due to carbonation of cement paste. In this area , more research is needed.
Thanks for recommendation.
Admixtures will also affect carbonation since reduction in water cement ratio is possible in concrete mix. However, air- entraining admixtures may allow more penetration of CO2 hence more carbonation.
Actually carbonation is very long process. There is various effect as per size, shape, texture of aggregate on carbonation. also some reactive aggregate much affect on carbonation. More water absorbed aggregate give much carbonation.
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