Climate mitigation models require a high level of technical accuracy to accurately reflect Circular Economy (CE) measures. Current climate mitigation models have to significantly progress technologically to address these CE technical aspects. This is the scope of the CO2NSTRUCT Horizon project. A framework for adding CE measures to the well-known open energy systems model JRC-EU-TIMES is proposed by the project. The framework focuses on the application of CE measures to the value chain of six carbon-intensive construction materials (i.e., cement, steel, brick, glass, wood, and insulation materials) and will include supplementary elements for the JRC-EU-TIMES model, taking into account citizen behavior toward CE and climate mitigation. Hence, one of the key goals of CO2NSTRUCT is to establish a technique for measuring citizen behavior on CE measures of the six construction materials and update the JRC-EU-TIMES model based on the corresponding findings. In light of this, it will be investigated how individuals perceive and act in relation to circular economy and climate change challenges. To identify gaps and opportunities in citizen behavior connected to climate change mitigation through a circular economy, the first stage in this activity has been to perform a literature assessment relevant to the project's themes. Following, the results of the literature review are utilized to construct a questionnaire focusing on citizens’ perceptions and behavior on circular construction materials and their contribution to CO2 reduction. The questionnaire is developed through a co-creation process involving all the partners of the CO2NSTRUCT project. The questionnaire will be utilized within a quantitative survey that will be conducted in nine European countries (project partners, plus Poland and Romania), involving 500 participants in each. The survey is expected to take place during the autumn of 2023.