Sustainable Construction through Utilization of Optimization Tools and Experimental Methods—An Editorial

1. Introduction

It is widely recognized that the adverse impacts of the construction industry on economic, social, and environmental sustainability are staggering. With growing global awareness of the importance of the above, the construction industry has been forced to explore innovative techniques to ensure that its processes and products are sustainable. Here, optimization-based engineering can pave the way for sustainable construction practices in various areas from the utilization of natural resources and the organization of business processes and production through the reduction of energy demands, costs, and environmental footprints all the way to ensuring health and safety conditions, among other areas.

For the engineering problem at hand, optimization can identify the best solution in the set of all possible solutions. In this way, optimization lies at the very core of the basic mission of engineering, i.e., to develop new, better, more-efficient, and sustainable systems and improve the functioning of existing ones. The potential of optimization to determine the best solution without actually testing all possible solutions comes from the use of advanced mathematical methods and is only realized after performing iterative numerical calculations that follow clearly defined logical procedures or computational algorithms implemented in computer software and after consuming the necessary processor time.

This Special Issue is dedicated to the latest developments in the field of sustainable construction through the utilization of optimization tools and experimental methods. On the one hand, this Special Issue aims to publish influential and innovative articles that deal with the challenges of construction sustainability through the use of optimization tools that involve either exact mathematical programming or meta/hyper/bio-heuristics, alternative hybrid approaches, or multi-criteria decision-making techniques. On the other hand, field or laboratory research on materials, products, structures, objects, or operations often provides key data for developing optimization models. Therefore, research engaging with experimental methods to address current issues associated with sustainable construction is also covered by this volume. Moreover, scientific works combining optimization tools and experimental methods to reach synergistic effects in favor of sustainable construction are included within this Special Issue as well.

2. Key Insights of This Volume

This thematic volume consists of eleven original articles. The paper by Rogulj et al. (Contribution 1) deals with flat-roof renovation planning on public buildings using fuzzy multi-criteria analysis. The study establishes the priority of the renovation of the flat roofs of public buildings, employing the multi-criteria method PROMETHEE II in fuzzy logic form. The proposed approach demonstrates the ability to transform the uncertain and vague information received from an expert into a fuzzy number. This makes it possible to obtain an objective outcome, remove the criteria conflict, and enable the ranking of alternatives, as well as mutual comparison. Based on the defined goals and criteria, the roofs are evaluated and ranked according to the priority for renovation. The suggested approach is validated on an actual example. Accordingly, it is argued that when it comes to flat roof renovation decision-making, a multi-criteria approach can support and assist building owners or facility managers in making informed decisions based on a set of indicators beyond just cost or aesthetics. The article also states that this can lead to more-informed decisions involving the full range of factors affecting the performance, durability, and sustainability of a flat roof system.

The study by Premrov and Kozem Šilih (Contribution 2) presents a numerical analysis of the racking behavior of multi-story timber-framed buildings considering the load-bearing function of double-skin façade elements (DSF). Based on the research performed, the use of the DSF elements as load-bearing structural elements to increase the racking load-bearing capacity of the whole structure proves to be reasonable. It is claimed that the development of racking-resistant timber DSF elements can open new perspectives in designing contemporary multi-story timber buildings located in seismic areas with strong winds and with a strong asymmetrical position of the transparent glass areas. However, this may decrease the energy demand for heating and provides more daylight, contributing to better living comfort within the building. The paper indicates the potentially beneficial socioeconomic effects of the research outcomes, as they can encourage the construction of multi-story timber buildings, which enable better use of forested areas and contribute to reducing the impact of buildings on the environment.

The article by Bekdaş et al. (Contribution 3) addresses the optimal dimensions of post-tensioned concrete cylindrical walls using harmony search and ensemble learning with SHapley Additive exPlanations (SHAP) methodology. The research is motivated by the fact that the optimal design of prestressed concrete cylindrical walls has a rather beneficial effect on the economic and environmental aspects of construction. Here, the unit costs of concrete and steel, the specific weight of the stored fluid, and the height of the cylindrical wall are the input parameters, whereas the optimum thicknesses of the wall with and without post-tensioning are the output variables. Founded on this database, advanced ensemble learning techniques like the extreme gradient boosting, light gradient boosting machine, categorical gradient boosting, and random forest algorithms are trained, while the impacts of various input features on the predictions of distinct machine learning models are analyzed via the SHAP approach. The paper infers that the gained predictive equations could be included in the engineering design process to facilitate structural optimization.

The research by Jelušič and Žula (Contribution 4) addresses the sustainable design of circular reinforced concrete column sections via multi-objective optimization. With this purpose, a mixed-integer nonlinear programming optimization model is developed, incorporating the requirements of Eurocodes for structural design. This model is created in MATLAB software, where a genetic algorithm (GA) is used for optimization. On these bases, parametric structural optimization is conducted separately for various combinations of applied loads and the objective functions of material costs and CO₂ emissions generated during the production of reinforced concrete. Multi-objective optimization is executed to identify a range of structural design solutions that offer optimal balances between economic and environmental objectives, i.e., minimum material cost and CO₂ emissions. The article highlights that the model is developed in a general form and can provide the optimal solution for various structural design parameters, including different concrete strength properties.

The investigation by Jelušič et al. (Contribution 5) reveals the potential of using waste materials in flexible pavement structures identified via and optimization design approach. The novelty of this work is the optimization model, which may provide an optimal pavement structure design and is able to consider various material properties affected by the inclusion of waste materials, both in terms of minimum construction cost and CO₂ emissions. GA is used to minimize construction cost and CO₂ emissions in accordance with pavement design guidelines. In order to show the effects of the material properties of the asphalt, base layer, sub-base layer, and subgrade, as affected by the inclusion of waste materials, a parametric study is conducted to establish the optimal design of flexible pavement structures. The paper points out that by applying the proposed optimization model, engineers can aim for a pavement structure that is both structurally sound and environmentally sustainable while minimizing construction costs.

The contribution by Galjanić et al. (Contribution 6) tackles the identification of key factors for project performance within a multi-stakeholder environment, the definition of a performance measurement framework for construction investments, and the constitution of a link between performance measurement and project performance prediction. Here, the performance management fields are derived from formerly executed, comprehensive bibliographical research analysis and multiple case-studies that consider predefined performance measures, including their outcomes in selected construction investment projects. The suggested framework for creating a pattern from which to predict the project success is based on actual construction investment projects and is thoroughly analyzed using a multiple-case-study method followed by semi-structured interviews with identified stakeholders. The study draws attention to the significance of multi-stakeholder factors on performance measurement and project success, even if the contractor is a single company.

The work by Ruá et al. (Contribution 7) evaluates the viability of different roof rehabilitation systems and identifies the best one based on a multi-criteria analysis, which comprises environmental, economic, and performance factors. Simulation tools are applied to assess the energy savings, payback periods, and environmental effects for a selected building in the survey area. The obtained results are mapped to a neighborhood level. The research outcomes highlight the value of considering parameters like weight, cost, and user preferences when choosing appropriate solutions for refurbishment. In addition to assessing the potential energy savings and carbon emission reductions in the area, the findings also emphasize the importance of roof refurbishments for extending a building’s life span, thus contributing to sustainable construction.

The report by Roux et al. (Contribution 8) concentrates on geopolymer (GP) compositions designed for structural use with the objective of minimizing the environmental impact. A life cycle assessment model for metakaolin– and potassium–silicate-solution-based GP mortars is developed. The model is applied to optimize the GP matrix as well as the granular skeleton, beginning from an existing formulation, throughout the decrease in greenhouse gas (GHG) emissions. The findings demonstrate that 3D-printed GP formulations do not yet constitute a mature technology, and their short-term applications are not inevitably environmentally favorable. Despite that, GPs contain the potential to reduce GHG emissions with conceivable innovations. The material designed shows adequate extrudability and buildability such that it could be utilized in high-performance applications owing to its high compressive strength. Regardless of its low share of aggregates, the dealt material holds an environmental value since it contains a substantial portion of earth that is broadly at hand and frequently also treated as waste.

The text by Simón-Portela et al. (Contribution 9) deals with the optimization of glulam roof structures, aiming to enhance sustainable construction. The study assesses the impact of glulam strength classes on the design of roof structures made of timber double-tapered beams and purlins, taking into account the requirements of Eurocode 5. A GA-based tool is developed for the purpose of optimization, and based on the results, various equations are suggested to identify the optimal geometry of structural elements, including their spatial configuration given the roof length, span, snow load, and strength class. In addition, a general equation is derived to anticipate the optimal volume needed for the roof structure, bearing in mind various strength classes, which may promote the efficient usage of resources and economic benefits while meeting structural and safety requirements.

The writing by Pennacchia et al. (Contribution 10) gives a catalog of optimized and sustainable solutions for strengthening the energy efficiency of the most-common types of roofs that distinguish the national residential building’s heritage, focusing particularly on the principles of standardization and prefabrication. The methodological approach includes the identification, study, and classification of roofings according to their construction period. Standardized optimal solutions are identified in terms of the essential energy retrofitting of deteriorated residential building stock. The performance assessments of the obtained results allowed for the implementation of a matrix, which may be a valuable support for designers in selecting optimal solutions for the building heritage in question based on energy efficiency and sustainability criteria.

Finally, the treatise by Villar-García et al. (Contribution 11) concerns both the static and kinetic friction coefficients of chestnut timber. The purpose of the research is to spread the application of Castanea sativa in the design of structures involving frictional forces, encouraging construction sustainability with the use of less-exploited materials, which entails the diversification of the species utilized in construction, thereby mitigating the demand for those more commonly exploited. The experimental program considers the orthotropic nature of material by assessing different wood orientations, engaging both wooden frictional pairs and wood against a steel plate. The effect of the moisture content is also taken into account in this study. The outcomes of the experimental program form a comprehensive database that is useful as an input for engineering optimizations, which may then be reflected in the more-prudent use of the considered natural resource.

3. Conclusions

The present Special Issue of Sustainability addresses various pressing topics related to sustainable construction and demonstrates diverse optimization, multi-criteria decision-making, and experimental approaches that represent the best available solutions to actual engineering problems occurring in the field. Established authors of reputable research institutions from all over the world—from Croatia, the Czech Republic, France, Italy, the Republic of Korea, Slovenia, Spain, Turkey, and the USA—responded to the invitation and contributed their studies, giving the content of this Special Issue its particular value. From the foundation built by the contributing authors, this Special Issue is intended to promote and disseminate the knowledge required to advance sustainable construction practices.