Strategies for robust renovation of residential buildings in Switzerland.

Building renovation is urgently required to reduce the environmental impact associated with the building stock. Typically, building renovation is performed by envelope insulation and/or changing the fossil-based heating system. The goal of this paper is to provide strategies for robust renovation considering uncertainties on the future evolution of climate, energy grid, and user behaviors, amongst others by applying life cycle assessment and life cycle cost analysis. The study includes identifying optimal renovation options for the envelope and heating systems for building representatives from all construction periods that are currently in need of renovation in Switzerland. The findings emphasize the paramount importance of heating system replacements across all construction periods. Notably, when incorporating bio-based insulation materials, a balance emerges between environmental impact reduction and low energy operation costs. This facilitates robust, equitable, and low-carbon transformations in Switzerland and similar Northern European contexts while avoiding a carbon spike due to the embodied carbon of the renovation.

Multi-objective robust optimization using adaptive surrogate models for problems with mixed continuous-categorical parameters.

Explicitly accounting for uncertainties is paramount to the safety of engineering structures. Optimization which is often carried out at the early stage of the structural design offers an ideal framework for this task. When the uncertainties are mainly affecting the objective function, robust design optimization is traditionally considered. This work further assumes the existence of multiple and competing objective functions that need to be dealt with simultaneously. The optimization problem is formulated by considering quantiles of the objective functions which allows for the combination of both optimality and robustness in a single metric. By introducing the concept of common random numbers, the resulting nested optimization problem may be solved using a general-purpose solver, herein the non-dominated sorting genetic algorithm (NSGA-II). The computational cost of such an approach is however a serious hurdle to its application in real-world problems. We therefore propose a surrogate-assisted approach using Kriging as an inexpensive approximation of the associated computational model. The proposed approach consists of sequentially carrying out NSGA-II while using an adaptively built Kriging model to estimate the quantiles. Finally, the methodology is adapted to account for mixed categorical-continuous parameters as the applications involve the selection of qualitative design parameters as well. The methodology is first applied to two analytical examples showing its efficiency. The third application relates to the selection of optimal renovation scenarios of a building considering both its life cycle cost and environmental impact. It shows that when it comes to renovation, the heating system replacement should be the priority.

Material Diets for Climate-Neutral Construction.

The climate crisis is urging us to act fast. Buildings are a key leverage point in reducing greenhouse gas (GHG) emissions, but the embodied emissions related to their construction often remain the hidden challenge of any ambitious policy. Therefore, in this paper, we explored material GHG neutralization where herbaceous biobased insulation materials with negative net-global warming potentials (GWPs) were used to compensate for building elements that necessarily release GHGs. Different material diets, as well as different building typologies, were modeled to assess the consequences in terms of biobased insulation requirements to reach climate neutrality. Our results show that climate-neutral construction can be built with sufficient energy performance to fulfill current standards and with building component thicknesses within a range of 1.05-0.58 m when timber- and bamboo-based construction is chosen. Concrete-based ones require insulation sizes that are too large and heavy to be supported by the dimensioned structures or accepted by urban regulations. Moreover, a time horizon of 20 years is more appropriate for assessing the contribution of material shifts to biobased materials in the transition period before 2050. This paper demonstrates that this is technically feasible and that climate neutrality in the construction sector just depends on the future that we choose.

Tracking the Environmental Consequences of Circular Economy over Space and Time: The Case of Close- and Open-Loop Recovery of Postconsumer Glass.

With the increasing globalization of waste-derived raw materials, region-oriented circular economy measures that stimulate resource recovery can cause far-reaching ripple effects in geographically dispersed markets, with unintended environmental effects. Identifying, quantifying, and characterizing these implications in a multiregional economic system remains challenging. This Policy Analysis aims to track these market-mediated environmental consequences over space and time with high material resolution. It explores a novel avenue of coupling consequential life cycle assessment and a time-series multiregional material-product chains model. The model is applied to two measures to recover postconsumer glass waste in the province of Quebec (Canada): improving closed-loop bottle-to-bottle resource recovery systems and deploying open-loop system for the marketing of glass powder as a supplementary cementitious material. Their environmental consequence trajectories (2030-2050) across a seven-industry and six-region competing symbiosis are examined. In both cases, cost-based optimized results highlight widespread adjustments in eastern North America trade patterns that are expanding over time in response to the coevolution of symbiotic industries. Between 55% and 94% of the environmental benefits are felt beyond Quebec borders. This information can help decision makers better anticipate the in- and cross-border scope of their measures and coordinate across jurisdictions to maximize overall environmental benefits.

Dataset of service life data for 100 building elements and technical systems including their descriptive statistics and fitting to lognormal distribution.

This article presents the descriptive statistics of service life data of building elements, gathered through an international, European and Swiss literature review of LCA, LCC and other sources called "Real-Estate Management sources" that include building owners, banks, insurances, associations of tenants and owners, etc. Furthermore, the properties of the fitted lognormal distribution are given. The data are structured, using a hybrid decomposition (functional decomposition, according to the eBKP-H - SN506511 and material decomposition, as well). These data and the derived statistical distributions were used in a research study, in order to quantify the uncertainty and sensitivity of the LCA and LCC output, due to the variability of the building elements' service lives.

Dynamic Assessment of Construction Materials in Urban Building Stocks: A Critical Review.

There is a lack of understanding on the different types of dynamics of building stocks, in real life and in models. Moreover, there is now a particular interest in the embodied impacts of construction materials, since with the increasing efficiency of buildings operation, embodied impacts gain more importance in the overall building life cycle. This critical review wants to advance the understanding of the type of dynamics, methods, and tools used. The well-known IPAT equation is adapted for building stocks and three dynamics are defined: spatial, evolutionary temporal, and spatial-cohort dynamic. A framework is defined that can help researchers choose a method, tool, and dynamics of input parameters depending on their research goal, case study, and data. Moreover, generally valid conclusions are drawn, including MFA is useful to model spatially dynamic material flows; GIS is needed to include spatial dynamics. Retrofit, compared to construction and demolition, is understudied and usually analyzed through top-down methods. Material intensity and emission intensity are rarely modeled in a dynamic way. Overall, scholars seem to perform increasingly data intensive and complex studies tailored to a specific case study. However, there are big differences in the quality depending on the dynamic of input parameters.

Designing Reinforced Concrete Beams Containing Supplementary Cementitious Materials.

If supplementary cementitious materials (SCMs) are used as binders, the environmental impact produced by cement-based composites can be reduced. Following the substitution strategy to increase sustainability, several studies have been carried out with the aim of measuring the mechanical properties of different concrete systems, in which a portion of Portland cement was substituted with SCMs, such as fly ashes. On the other hand, studies on the structural behavior of reinforced concrete (RC) elements made with SCMs are very scarce. For this reason, in this paper, a new procedure is introduced with the aim of fulfil a new limit state of sustainability, in accordance with the serviceability and ultimate limit states required by building codes. Although the environmental impact of concrete decreases with the reduction of cement content, the proposed approach shows that the carbon dioxide emission of an RC beam is not a monotonic function of the substitution rate of cement with SCMs. On the contrary, there are favorable values of such substitution rates, which fall within a well-defined range.

Lime as an Anti-Plasticizer for Self-Compacting Clay Concrete.

This paper focuses on the modification of clay properties with inorganic additives to deflocculate and flocculate inorganic soil for the development of a material that would be as easy to use as the current concrete products, but with a much lower environmental impact. Considering that the rheological behaviour of clays is controlled by their surface charge, we first introduce potential determining ions to deflocculate the clay particles and to reduce the yield stress of the earth material. Their efficiency is characterized using zeta potential measurements and rheological tests. We then achieve the flocculation of clay particles by using natural minerals that slowly dissolve in the interstitial liquid and ultimately precipitate calcium silicate hydrate (C-S-H). The precipitation products are identified by X-ray diffraction and the consequences of this delayed precipitation are followed by oscillatory rheometric measurements. Finally, it is suggested that in this process, C-S-H precipitation is not used as a binding vector but as an anti-plasticizer that removes the inorganic dispersant additives.

Flow properties of MK-based geopolymer pastes. A comparative study with standard Portland cement pastes.

Geopolymers are presented in many studies as alternatives to ordinary Portland cement. Previous studies have focused on their chemical and mechanical properties, their microstructures and their potential applications, but very few have focussed on their rheological behaviour. Our work highlights the fundamental differences in the flow properties, which exist between geopolymers made from metakaolin and Ordinary Portland Cement (OPC). We show that colloidal interactions between metakaolin particles are negligible and that hydrodynamic effects control the rheological behaviour. Metakaolin-based geopolymers can then be described as Newtonian fluids with the viscosity controlled mainly by the high viscosity of the suspending alkaline silicate solution and not by the contribution of direct contacts between metakaolin grains. This fundamental difference between geopolymers and OPC implies that developments made in cement technology to improve rheological behaviour such as plasticizers will not be efficient for geopolymers and that new research directions need to be explored.