CO2 emission of polycarboxylate superplasticizers (PCEs) used in concrete

At an annual production of -15 million tons, polycarboxylate (PCE) based superplasticizers (cement dispersants) present the most widely used concrete admixture. In this paper, their carbon footprint was quantified considering the three most common kinds of PCE polymers, namely methacrylate ester (MPEG), methallyl ether (HPEG) and isoprenol ether (IPEG) based PCEs produced in four major manufacturing countries: EU-27, US, Japan and China. A cradle-to-gate approach was applied to estimate CO2 emissions from raw materials extraction to PCE fabrication. On this basis, and depending on their chemical composition and country-specific electricity grid CO2 emission factors, their carbon footprints were calculated. The results show a strong dependence on the kind of PCE, their structural design as well as the producing country. For all PCEs, the main components ethylene oxide, unsaturated acids (methacrylic/acrylic acid) and NaOH were found to be mainly responsible for the entire CO2 footprint. The average total CO2 emissions of the three kinds of PCEs vary between 2.98 +/- 0.54 kg CO2/kg (MPEG), 2.48 +/- 0.48 kg CO2/kg (HPEG), and 2.40 +/- 0.47 kg CO2/kg (IPEG). Evidently, MPEG PCEs reveal the highest footprint which is owed to methacrylic acid whereas HPEG and IPEG PCEs contain acrylic acid. The range of total CO2 emissions is caused by significant differences in the carbon footprints of the electrical grids in various countries. An impact study revealed that at common field dosages the contribution of PCEs to the CO2 balance of a standard concrete (CO2 footprint - 300 kg CO2/m3) varies between approx. 3 and 22 kg CO2/m3 in Europe, with ready-mix type PCEs contributing more than precast concrete PCEs. Furthermore, it is demonstrated that the CO2 footprint of PCE superplasticizers can be reduced by almost 80% if predominantly renewable energy is used in the chemical industry.