Rheological behavior and CO2 footprint of cements binder exhibiting ultra-low clinker content

In order to reduce the CO2 footprint of cement it is necessary to decrease the clinker content significantly, i.e. well below 50 %. To probe into such systems, the use of alternative raw materials like GGBFS (Ground Granulated Blast Furnace Slag) in the mixtures has to be considered; slag content can vary and its introduction allows to strongly decrease clinker content. Studies have shown that GGBFS could potentially reduce the carbon footprint in a typical concrete mix design by ~ 22 %.

In our work, we have identified the suitable PCE superplasticizers for cement composite exhibiting ultra-low clinker content. The results suggest that for such binders of extremely low clinker content fundamentally different PCE structures are required, and that the behavior of PCEs established on OPC cannot simply be applied to those slag dominated binders. At the same time, those novel binders stand out because of their extremely low CO2 footprint. A rough assessment produces the values
as follows (kg CO2-equ./to binder) : OPC 825; slag 100; blended cement (60:40 GGBS: clinker) 390; blended cement (70 GGBS:30 clinker) 320; and finally blended cement (85 GGBS:15 OPC) 210. This suggests that by using such ecologically optimized binders a massive reduction in CO2 emission of up to 75 % is possible.

Apart from the drastically lower CO2 footprint of the novel eco binder also the CO2 emission associated with the use of the PCE admixture needs to be considered. For PCEs, depending on their individual structural composition, the values vary between 3.000 and 5.000 kg CO2-equ./to PCE. Bearing in mind that PCEs typically are applied at dosages well below 1 % by weight of binder, their CO2 contribution amounts to ~ 10 – 25 kg CO2 equ./to binder. Here, an advantage of the slag rich binder is that it generally requires up to 50 % lower PCE dosages to achieve comparable workability as in OPC.

The investigations demonstrate that “green cements” of ultra-low CO2 footprint (as low as 200 kg CO2-eqn./to) are already possible.

Co-Authors / Mitautoren:

Dr. Laurent Frouin, Dr. Mohend Chaouche, Dr. Roberta Alfani

x

Related articles:

Issue 02/2020 Concrete technology

Measures to reduce CO2 emissions

More than 6 % of the worldwide carbon dioxide (CO2) emissions caused by humans are associated with the production of cement and concrete. It is a known fact that a purposeful substitution of the...

more
Issue 07/2014

Concrete products based on a binder matrix produced with low CO2 emissions

Cement production is characterized by process temperatures in excess of 1.300?°C and substantial CO2 emissions; about 60?% of these emissions are attributable to limestone neutralization [1]. These...

more
Issue 10/2021

Admixtures enable massive CO2 reduction in concrete

The German federal government‘s decision to achieve climate neutrality in Germany by 2045 has further increased the pressure, also in the construction industry, to take comprehensive measures to...

more
Issue 05/2024

Performance and durability of clinker-reduced concretes using specially designed additives

Following the announcement of global climate targets to reduce carbon emissions, clinker-reduced concretes (also known as eco-concretes) are becoming increasingly important in the construction...

more
Issue 02/2021

PCE-based superplasticizers for composite cements containing calcined clay

Global cement production currently amounts to about 4.4 billion tons per year. Unfortunately, this comes with a huge CO2 emission which represents approximately 7?% of total anthropogenic CO2 output....

more