Analyzing the Lifecycle of Sustainable Building Materials

The construction industry has been compelled to revise its practices due to the disproportionate extraction of minerals, shifting its focus toward sustainable building materials. Nowadays, the industry strives to achieve sustainability on social, economic, and environmental fronts. This holistic approach is facilitated by the implementation of life-cycle assessments (LCAs), which evaluate the long-term environmental impacts of materials and methods, ensuring they are minimized.

LCA provides a framework for inputting various potential scenarios within the lifecycle of a material, along with identifying key process parameters that need enhancement. As a fundamental model of reality, LCA involves several steps defined by international standards.1 This article examines the LCA of various sustainable building materials, assessing their environmental impacts from production through to disposal.

Plastic Waste
Plastic waste, specifically polyethylene terephthalate (PET), can be incorporated into building materials such as concrete and mortars, offering several benefits, including cost reduction, enhanced properties, increased bio-corrosion resistance, and lower energy consumption in infrastructure.1

The lifecycle of PET waste typically follows one of three routes: landfilling, incineration, or recycling. The first two options pose significant environmental risks, with landfilling leading to soil contamination and incineration causing air pollution. Conversely, PET recycling involves a series of steps, starting with the collection and segregation of PET bottle waste from other debris. Non-plastic elements like labels and caps are then removed, and the bottles are compressed, washed, and chopped into flakes or other forms suitable for recycling and construction use.1

In the construction industry, the life-cycle assessment (LCA) of PET used in structural components such as walls takes into account various end-of-life scenarios. These scenarios often hinge on whether the materials are directly reused or demolished, varying based on user practices.1

Natural Earthen and Bio-based Materials
Building structures using natural materials such as cob, light straw clay, and rammed earth not only creates an ideal indoor atmosphere for residents’ comfort and well-being but also significantly reduces energy consumption. LCA of these natural assemblies shows they can decrease energy use by 32-59 % in hot deserts, 29-55 % in semi-arid regions, 46-73 % in Mediterranean climates, 34-57 % in temperate zones, and 27-50 % in continental climates compared to traditional building methods.2

The operational impacts of these materials largely depend on their thermal properties and the regional climate. However, they greatly surpass traditional materials in terms of environmental benefits. For instance, natural building assemblies can reduce embodied energy consumption by 38-83 %, climate change potential by 60-82 %, air acidification by 57-98 %, and particulate pollution by 27-99 %.2 When combining operational and embodied impacts, the LCA shows that the total environmental load of natural earthen and bio-based assemblies remains lower than that of insulated traditional structures even after 50 years of use.

Despite these advantages, natural materials have not yet gained widespread adoption in the construction industry. This is primarily due to the lack of technical data on their energy performance in various climatic conditions and the absence of comprehensive environmental parameters that would allow for consistent evaluation throughout the entire design phase.

Supplementary Cementitious Materials (SCMs)
Granulated blast furnace slag (GBS), fly ash, plastic powder, and bagasse ash are currently being investigated as sustainable supplementary cementitious materials (SCMs) to partially replace cement, thereby reducing construction costs and enhancing the eco-friendliness of concrete. A life-cycle assessment (LCA) comparing ordinary Portland cement (OPC), ground granulated blast furnace slag (GGBS), and Portland pozzolana cement (PPC) shows that concrete made with OPC has a significantly larger environmental impact and carbon footprint across various metrics.

The LCA for these materials encompasses the extraction of raw materials, energy consumption, transportation by road, and concrete preparation. The preparation phase, in particular, is a major contributor to climate change, primarily due to CO2 emissions that intensify global warming. Additionally, cement manufacturing consumes vast quantities of natural resources, leading to their depletion.3

While derivatives from iron production and thermal power generation are environmentally hazardous, utilizing them as SCMs can mitigate the environmental impact of concrete production. Industrial by-products like GGBS and fly ash, used as binders in concrete, decrease the demand for natural resources and promote environmentally sustainable concrete. Furthermore, they help to reduce the adverse effects of concrete on human health, marine ecosystems, and freshwater sources.3

Cross-laminated Timber (CLT)
CLT has surfaced as a sustainable replacement of steel/concrete in the building sector with a low carbon footprint, high strength-to-weight ratio, easy installation, and aesthetics. It was first employed in structural applications in the early 1990s and those CL-based constructions have not yet completed their service life.4

LCA of CLT buildings reveals a 40 % lower carbon footprint than traditional steel/concrete-based multi-story buildings. Additionally, CLT accounts for only 0.05 to 6.3 tons of CO2 equivalent per m2 floor of greenhouse gas (GHG) emissions. This variation in environmental impact assessments is attributed to a multitude of factors, including local climate, regulatory standards, the behavior of residents, the height and shape of buildings, the electricity mix, the LCA methodology employed, and the data sources used.4

CLT has been conventionally used in residential buildings. Lately, however, it has been combined with reinforced concrete to form composites for structural applications in extensive government projects and commercial infrastructure.4

Challenges and Future Prospects
All materials that initially seem sustainable may not actually be so. For instance, a recent study published in Sustainability compared two optimized geopolymer (GP) mortar formulations designed for three-dimensional (3D) printing with a traditional 3D-printed mortar using Portland cement. While the GP mortars demonstrated promising extrudability, buildability, and compressive strength suitable for high-performance applications, their environmental credentials were less clear.5

However, a life-cycle assessment (LCA) of these materials revealed that the technology for 3D-printed GP is not yet fully developed, and its immediate applications may not necessarily be environmentally beneficial. Despite GPs’ potential to reduce greenhouse gas emissions, their use in GP mortars could actually increase human and environmental risks, deplete natural resources, and elevate fossil fuel consumption.5

The use of LCA has proven to be a robust tool for evaluating the sustainability of building materials. The accuracy and efficiency of LCAs can be further enhanced by incorporating advanced technologies. A novel approach, for example, involves integrating large language models (LLMs) with LCAs. LLMs are sophisticated neural networks trained on extensive textual data through methods such as pre-training and fine-tuning. One study demonstrated this by evaluating bacterial cellulose aggregates as a bio-based alternative building material, showing how sustainable thinking can be embedded into the building design process through the use of LLM-integrated LCAs.6

Such innovative techniques can refine the precision and speed of LCA evaluations, improving our understanding of the ecological impacts of construction materials, methods, and processes. Moreover, LLMs facilitate the organization of data collection and analysis, supporting more informed and sustainable decision-making in the construction industry.6

In conclusion, the detailed methodology of LCA provides a comprehensive and reliable assessment of the environmental impacts of construction materials, delivering crucial insights for designers, policymakers, and businesses to make well-informed choices regarding their practices and materials.1,6