RCC2 - Life cycle assessment of heatable formwork for CO₂-reduced and climate-neutral concrete

Experimental development of innovative formulations of CO₂-reduced concrete and heated formwork to support early strength development in wintry temperatures.

Short Description

Motivation and Research Question

Clinker-reduced concrete mixtures have lower CO2 emissions than standard concretes. The delayed early strength development of CO2-reduced concrete - reduced carbon concrete (RCC) - due to the lower binder content poses a challenge, particularly at low outside temperatures. This lack of energy at the beginning of the hardening phase can be compensated for by a.o. heatable formwork. Yet heating the formwork with electricity does consume energy, further contributing to CO2 emissions. Therefore, the life cycle assessment of heatable formwork to support CO2-reduced concretes is key to evaluating the sustainability of innovative RCC formulations. The following research question can be addressed as follows: How can the life cycle assessment of heatable formwork to support CO2-reduced concretes be evaluated and to what extent does this influence the sustainability of innovative concrete mix designs?

Current Situation/Status Quo

The previous research project RCC – Reduced Carbon Concrete (GZ 2020-0.657.535), which was co-initiated by the City of Vienna, Department 20 (Energy Planning) in 2020, aimed to research the use of CO2-reduced concrete on construction sites. During this research project further research questions were formulated, including the role of innovative formwork for improved construction site practice with delayed early strength of the fresh concrete.

Generally, CO2-reduction in concrete can be achieved by

reducing clinker or CO2 in the cement,
reducing the CO2-content in the cementitious additions,
changing the production process,
optimizing transport routes.

Project Content and Objectives

The aim of this continuation of the research project, also initiated by the Municipal Department 20 of the City of Vienna and funded by the FFG, is to contribute to the establishment of CO2-reduced – and even climate-neutral – concrete as the new state of the art and to enable the year-round use of these concretes. This was tested on the construction site with the support of a prototype of heated formwork which was developed by Doka GmbH (internal project name: IHF Intelligent Heated Formwork) in combination with Doka's component temperature monitoring system (Concremote). In order to evaluate climate-dependent influences, two series of tests were carried out – one in summer and one in winter. The summer test provided reference values for the success-sensitive winter test. The summer test series was successfully completed in October 2022 with the support of the City of Vienna, Department 20 and with considerable in-kind contribution from the participating consortium partners. This final report documents the implementation and the findings of the crucial winter test series with heatable formwork.

Methodical Approach

12 concrete elements, 6 of them in a heatable moulds and 6 in a conventional moulds, were produced, stored in cooling containers at an ambient temperature of -5 °C and then subjected to a test concept. The test was carried out in six modular cold storages to ensure controlled conditions independent of weather and external temperature fluctuations. This allowed for the creation of the least favorable climate scenario for the region, with constantly low average temperatures below 0 °C. The wall elements remained in the (heated) formwork until stripping strength was reached. The slab elements were heated on one side and post-treated according to normative specifications. Due to the constantly low ambient temperatures in the modular storages, appropriate measures had to be taken during the protection period and after the protection period had been reached in accordance with normative specifications.

Results

The results from the winter experiment are promising: the heatable formwork from Doka is able to provide adequate support for the early strength development of concrete elements even at sub-zero temperatures. Ultimately, after 28 days the required strength was achieved for all concrete elements. Thus, heatable formwork is able to decisively support the hydration of binder-reduced concrete with lower heat development at low outside temperatures, enabling compensation for the delayed early strength development as well as to ensure the energy-optimized protection of the young concrete at temperatures below 3 °C according to ÖN B 4710-1 and ONR 23339 respectively. Even at constant ambient temperatures of -5 °C, temperatures of well over 10 °C (double-sided formwork (walls)) or around 10 °C (single-sided formwork (ceilings)) could be maintained in the concrete elements in the heated formwork. In particular, the heatable formwork enables an equivalent early strength development for CO2-reduced concrete even at temperatures below 0 °C, even under the most difficult environmental conditions. The energy input required for the heatable formwork reduces the recipe-related CO2 savings for the CO2-reduced concrete mixture by around half and for the CO2-reduced concrete mixture including technical carbon by only around a seventh.
The CO2 footprint of the electrically heated formwork reduces the CO2-reduction of the concrete mixtures in the present winter test by about 10% of the total "embedded carbon" ( the global warming potential (GWP)) in relation to the regional reference concrete.

Conclusion & Outlook

The results from the experiment create an important perspective for the industry-wide use of CO2-reduced and climate-neutral concrete. This means the possibility of establishing climate protection targets with performance concrete as the new state of the art without a minimum binder content. Based on the average monthly temperatures below 5 °C in recent decades, the selective use of heated formwork on approx. 40-50 days a year appears to be appropriate for the Vienna metropolitan region.

In particular, the CO2-reduced concrete mixtures with the addition of technical carbon are potentially capable of making concrete climate-neutral in terms of its carbon footprint, even when using heated formwork, as the heating of the formwork only reduces the CO2-reduction by a fraction.

The research project did not have the task of carrying out the necessary concrete technology tests for the addition of large quantities of technical carbon. These investigations are essential and are already beingcarried out in many places. In any case, with the life cycle assessment of heatable formwork for CO2-reduced concrete, the goal of decarbonizing concrete for construction practice is now within reach.

Project Partners

Project management

Architekt DI Thomas Matthias Romm - forschen planen bauen ZT

Contact Address

Architekt DI Thomas Matthias Romm
forschen planen bauen ZT
Löwengasse 47a/7
A-1030 Vienna
Tel.: +43 (650) 984 84 88
E-mail: thomas.romm@romm.at
Web: www.romm.at