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 CO 2 emissions from raw materials extraction to PCE fabrication. On this basis, and depending on their chemical composition and country-specific electricity grid CO 2 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 CO 2 footprint. The average total CO 2 emissions of the three kinds of PCEs vary between 2.98 ± 0.54 kg CO 2 /kg (MPEG), 2.48 ± 0.48 kg CO 2 /kg (HPEG), and 2.40 ± 0.47 kg CO 2 /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 CO 2 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 CO 2 balance of a standard concrete (CO 2 footprint ∼ 300 kg CO 2 /m3) varies between approx. 3 and 22 kg CO 2 /m3 in Europe, with ready-mix type PCEs contributing more than precast concrete PCEs. Furthermore, it is demonstrated that the CO 2 footprint of PCE superplasticizers can be reduced by almost 80% if predominantly renewable energy is used in the chemical industry. [Display omitted] • CO 2 footprint of PCE superplasticizers (MPEG/HPEG/IPEG) used in concrete studied. • Total CO 2 emission dependent on PCE chemistry/composition and producing country. • Highest CO 2 emission for MPEG PCE: methacrylic acid and EO major contributors. • Thermal energy generation and grid electricity responsible for most of CO 2 emission. • Utilizing renewable energy can reduce CO 2 footprint of PCE significantly. [ABSTRACT FROM AUTHOR]