Ultra-rapid hardening of cement by accelerated carbonation – Past, present and future

The ancient Greeks and Egyptians may have unwittingly employed accelerated carbonation with the polishing technique that they used to achieve seamless crack-free linings in lime-based pipe and stucco work. However, it was not until the advent of Portland cement in the mid-19th century that carbonation with gaseous CO2at atmospheric pressure was proposed as a means of accelerating the setting and hardening of mortar and concrete. In the 1970s the first attempts were made to achieve a more thorough scientific understanding of the process, most notably in the USA by Berger and colleagues, but also by researchers in the USSR, Israel and Sweden. The authors’ own development of a carbonation process to accelerate the hardening of precast concrete dates from over 30 years ago, when lowering atmospheric emissions of CO2 by sequestration was not yet an issue. But today, with global cement production increasing relentlessly at around 8% per annum to a current total of 4 Gtonnes and releasing a similar mass of CO2, emission reduction is now a pressing concern in the cement and concrete sector. This paper will report on current commercial operations involving accelerated carbonation of concrete and will look forward to challenges and opportunities in a low-carbon future