Environmental concerns on the impact of sand dredging in India have led to severe restrictions on this activity, with direct impact on concrete construction. At the same time, waste plastic is rarely recycled, and left untreated in open landfill. Work funded by the British Council under the UKIERI (United Kingdom India Educational Research Initiative) programme, has been investigating how recycled plastic might be used as a replacement for sand in concrete, providing a solution to both problems. This paper details 180 day carbonation tests under accelerated conditions in a 4% CO2 environment, comparing concrete with 10% sand replaced by recycled plastic with a plain concrete mix. The accelerated test method is estimated to predict the performance of the material after 25.7 years in service. It is seen that the carbonation depth after 180 days is only 5% greater in the concrete with recycled plastic.