Increasing the rate of construction material consumption has caused significant environmental problems in recent decades, especially the production of ordinary Portland cement (OPC), which has been associated with 8% of the world’s human CO2 emissions and is considered the leading binder of concrete. This study aims to investigate the effects of substituting conventional concrete (CC) material with green concrete (GC) in the non-structural concrete works of a residential building in New Borg El-Arab City, Egypt. It attempts to establish what the effects are of using GC on cement, natural aggregates, and CO2 emissions in the design phase. By using a design-based solution (DBS), we began with redesign, reduce, reselect, reuse, and recycle strategies to find an optimal solution for applying recycle aggregate concrete (RAC) as a replacement material in selected building parts, such as the internal floor, external sidewalk, entrance steps, and wall boundary. AutoCAD software and 3Dmax were used to modify the original design and obtain two design references with four different scenarios. Comparative analyses were applied to investigate the effects of different concrete materials. The results show a reduction of about 19.4% in cement consumption in terms of the total concrete of the building and a 44.5% reduction in CO2 emissions due to the reduction of cement in specific building parts. In addition, this solution decreased natural coarse aggregate (NCA) consumption by 23.7% in the final concrete. This study recommends that GC materials close the loop of cementitious material consumption to reduce environmental impacts and achieve sustainability in the Egyptian building sector.

<p>Concrete is considered the most anthropogenic material used in the construction sector worldwide. It is associated with consuming massive amounts of energy and the depletion of natural resources, based on the increasing Egyptian urban expansion by establishing new cities to face the population growth challenges and achieve the national development strategy. The importance of applying the Circular Economy (CE) for concrete materials in the building sector became a robust key for reducing conventional concrete (CC) materials and addressing the building materials' future challenges. This study investigates the benefits of Green Concrete (GC) materials and their potential for supporting the principles of achieving circularity for concrete materials in the Egyptian building sector. Furthermore, develop a conceptual framework for using GC from the building scale perspective in two new Egyptian cities. The study attempts to answer how GC materials help achieve a circular economy and the potential benefits of integrating different CE strategies for using GC in the Egyptian building sector. The evidence-based solutions (EBS) methodology was used for collecting and analyzing data for assessing the environmental impacts based on reducing the natural resources consumption, recycling, and reusing waste products in the Egyptian building sector. Case studies are used to provide in-depth insights into the practicalities of GC. Applying the before-and-after (BAA) technique for two building models highlights the challenges and opportunities for substituting CC with GC to assess the interactive factors for achieving CE and applying sustainability. The results showed valuable insights into the potential for using GC to support the CE and have a strong ability to reduce natural resources consumption and construction waste stream, which leads to close the loop and achieving circularity in the Egyptian building sector, and recommended that Design for Recycling (DfR) strategy is the most need for improving the using of GC in the building sectors.</p> <p>Keywords, Green Concrete, Circular Economy, Evidence-based Solutions, Egyptian building sector</p>

<p> </p><p><em>Abstract </em></p><p>The challenges posed by the growth of urbanization in Egypt and the development of new cities play an essential role in applying the circular economy (CE) in the construction materials sector and the priorities for promoting sustainable construction activities in the future. Therefore, the construction sector has many adverse environmental impacts on energy and natural resources consumption. Starting from materials production, operation until disposal to landfills. Consequently, the industry is considered one of the most consumers of non-renewable resources and producer of CO2 emissions. On the other hand, applying Nature-based solutions (NbS) to enhance sustainability by protecting the ecosystems and maintaining economic benefits plays a vital role, especially for new Egyptian cities. The research aims to investigate the role of applying NbS for achieving CE in construction materials and eliminate its negative impact in the scope of three factors:  green building materials, waste management systems, renewable energy use. The current research attempts to answer how NbS can improve the CE and reduce environmental impacts of the construction materials sector. Therefore, the SOWT analysis investigated the strengths, opportunities, weaknesses, and threats of using the NbS strategies for three different construction sites in Egypt. Furthermore, the survey questionnaire was applied to identify the interactions between the parameters derived from 40 participants such as consultants, architecture engineers, civil engineers, site engineers, project managers and review the previous research efforts. As a result, a conceptual framework was created for the construction materials considering reduce, reuse, recycle, recovery, and disposal, to identify the impact of the implementation of NbS on achieving sustainable development strategies in the Egyptian construction sector. The result showed that the NbS could effectively promote the construction sector and achieve environmental and economic benefits, which consequently help the transition to CE. Therefore, there is the necessity for developing new sustainable policies and cooperation between public and private sectors to support the investments of sustainable strategies in the construction materials market and increase Egyptian society's awareness of the benefits of NbS in economic, environmental, and social aspects.</p><p> Keywords, Nature-based solution, Construction materials, Circular Economy, Egypt </p>