Renewable bio-based materials are emerging technologies within the construction industry, providing inventive solutions for reducing material waste and the carbon footprint of an inherently carbon-intensive sector. Previously they have been commonly investigated in isolation and there are a significant lack of case studies demonstrating the performance of bio-based materials in entire external wall designs. This study evaluates the thermal and hygric performance of five novel bio-based external wall systems, featuring highly innovative combinations of insulation, structural and fa & ccedil;ade materials. Large scale wall panels were designed, constructed and tested within a bespoke Large Environmental Chamber (LEC) to determine thermal performance and hygric behaviour using the heat flow method. Hygrothermal simulations with WUFI (R) Pro were conducted to assess condensation and mould risks. Insulation materials used were wood fibre, mycelium, sheep's wool and blown-in cellulose. Structural options were timber, Cross Laminated Timber (CLT) and also light-gauge steel, while facades were bio-based-polymeric composite material or bio-based treated timber cladding. Thermal transmittance and conductance were calculated along with time series analysis of temperature and relative humidity. The U-values of the five walls ranged from 0.13 W/m2K to 0.22 W/m2K and modelling simulations were in broad agreement with the practical results, with four of the five walls fulfilling an 0.18 W/m2K benchmark value based upon building regulations. The significance of the study is in the demonstration of the feasibility of a range of bio-based external wall designs, combining emerging material technologies, innovative design and building physics to contribute to the development of bio-based construction.

Bio-based insulation materials can have a significant impact in achieving net zero target in the construction sector. However, they face challenges due to lack of data on environmental performances and professional perception, hindering their proliferation. This study aims to combine scenario-based and dynamic analyses of environmental performances to provide comprehensive environmental information on bio-based thermal insulation materials. The goal is to empower professionals with robust information, facilitating informed decisions and promoting the selection of bio-based materials. Data on manufacturing, use, recyclability, and technical performance of eleven commercially available natural insulation materials were collected from the literature to create a Life Cycle Inventory (LCI). For each material, a scenario-based life cycle assessment (LCA) was conducted by modelling variation in manufacturing, transportation, end-of-life and material properties, using the UK as the primary case study. Materials were compared to three non-bio-based insulation materials by ranking the thirteen environmental impact categories in EN 15804(2013) + A2(2019) to give an exhaustive overview of their potential benefits and burdens. Additionally, a dynamic LCIA was performed to implement in the analysis both short-and long-term emissions, exploring the impact of biogenic carbon. The scenario analysis highlighted that recycled cotton and hemp fibre insulation have the lowest impact across all impact categories, attributed to their sustainable manufacturing processes and minimal impacts at the end-of-life stage. The dynamic LCIA demonstrated that recycled textile insulation has the lowest impact both in the short-term (prior to waste disposal) and the long-term (post-waste disposal), regardless of the chosen end-of-life scenario. Furthermore, it indicated that cotton and hemp fibre have a negligible impact on global temperature changes, achieving a net-zero effect in the short-term and close-to-zero impact in the long-term. The novelty of this paper lies in its comprehensive investigation of the environmental impacts of bio-based thermal insulation materials, employing multiple tools to enhance generalizability. These results will support decision-making by providing data ranges to help practitioners identify the most environmentally friendly insulation materials. Additionally, they offer insights into how similar products compare within that range, driving progress in the built environment towards net-zero emissions. Whilst the full dataset and evaluation methods are illustrated through a UK-based case study, this method can be adapted for specific scenarios and projects, due to the transparency of data and methods. This research significantly influences the built environment and promotes net-zero targets within the sector.

Circular economy principles can be applied to the construction sector to reduce use of resources, energy consumption and wastes. Bio-based construction materials are particularly suitable to circular building design. Advantages of bio-based materials include: (1) a renewable supply chain, (2) often fast-growing, (3) recyclable or used as fertilisers/compost and (4) can sequester carbon. In this paper, the design of three circular bio-based wall panels is presented. The three panels were designed to be disassembled, and innovative bio-based materials, such as mycelium, sheep’s wool and cellulose were implemented in the walls. The wall assemblies were tested in a large environmental chamber to assess whether the panels achieved high insulating performances. Monitoring results showed that the three panels have excellent thermal properties. In parallel, life cycle assessment (LCA) of the bio-based construction materials applied in the three panels was undertaken to assess the sustainability and circularity of the selected materials. LCA results showed that some of the materials, such as sheep’s wool and flax, do have a low carbon footprint. However, there are uncertainties around the carbon footprint of other bio-based materials (e.g. fungi-based products), as information on the manufacturing process and associated emissions are not always available. This paper provides an overview of the applicability, advantages and challenges of innovative and sustainable technologies in buildings to achieve net-zero targets and to apply circular economy model of construction in buildings.

The need for the construction industry to reduce both operational and embodied carbon emissions is urgent. Traditional insulation materials, while effective, require energy-intensive processes and non-renewable resources, making them unsustainable. Mycelium-based composites (MBCs) offer a sustainable alternative with low embodied carbon, biodegradability, and non-toxicity, and studies show promising thermal performance. However, accurate measurement of λ is crucial to ensure effectiveness, requiring an understanding of the factors influencing these measurements. This paper reviews the thermal conductivity of MBCs, covering 19 studies reporting λ values from 0.026 W/mK to 0.18 W/mK. Measurement techniques and their uncertainties are reviewed, as well as additional factors affecting λ , including moisture content, density, temperature, substrate, fungal species, and growth conditions. The influence of the fungal-skin layer and the anisotropic nature of MBCs is discussed. Standardised measurement protocols and thorough methodological reporting are emphasised to ensure comparability. By optimising intrinsic parameters like species-substrate combinations and growth conditions, MBC thermal performance can be improved. This paper informs on MBC thermal characterization, promoting broader adoption in the construction industry and advancing sustainable practices. Consequently, this review aims to guide future research and applications, aiding in reducing both operational and embodied carbon emissions. Keywords Mycelium , insulation , natural building materials , thermal conductivity

A growing awareness of the environmental impact of construction materials is leading to development of more sustainable building products, with particular attention focussed on bio-based resources and circularity. In recent years the market share of bio-based building products has grown significantly, supported by research on materials such as wood fibre, hemp, and straw bale. At the same time there has been growing awareness of the potential for greater circularity in construction, prolonging the life of existing products and materials, thus minimising embodied carbon emissions of future projects, as well as reducing reliance on primary resources and impact on landfill. This paper presents results of an investigation into the thermal and hygric characteristics of three novel insulation prototypes developed from bio-based or waste-stream materials. The experimental development and characterisation of insulation using maize pith, recycled bedding (polyester duvet) materials, and wheat straw insulating prototypes are presented. Hygric and thermal performance are compared to a mineral wool insulation product. As part of this work a series of large-scale thermal conductivity and hygric investigations were also conducted in which the performance of each insulation product with a timber framed wall was studied under steady state and variable environmental conditions. This work was part of a larger international research project aimed at developing insulating materials from bio-based and waste streams and will support market development of novel materials and products into mainstream construction.

This study developed a novel gypsum plaster comprised of high energy storage phase change material (PCM) loaded granules to reduce the amount of energy used in buildings. Changes in the mechanical and thermal properties of gypsum plasters are reported and compared with PCM-loaded cement mortars. Analysis of the energy consumption through simulation showed the amount of PCM-loaded granules and their location in the building material have a significant impact on the effectiveness of the PCM composites. The maximum energy savings of 293.8 kWh were achieved when PCMs granules were incorporated to cement blocks. However, maximum thermal comfort was achieved with PCM gypsum plaster.

Construction projects using emerging bio-based materials have been realized over the past ten to fifteen years within Europe. Bio-based buildings utilize properties of natural materials to regulate internal environments, particularly fluctuations in temperature and relative humidity. Despite individual exemplar projects demonstrating functional performance and long-term operational cost savings, there hasn't been a proliferation of commercial or domestic bio-based projects. With a growing shift towards circular economy construction, bio-based buildings could be readily adopted to meet this development. This study evaluates barriers faced by bio-based materials, making the upscaling of production and a breakthrough into mainstream construction challenging. Evaluation was achieved through senior professionals with experience in bio-based construction participating in semi-structured interviews based on core categories of finance, knowledge, and policy. Challenges include the upscaling of production by manufacturers of emerging materials, inconsistencies in life cycle assessment, material certification and accreditation, vested interests in the construction industry, and concerns regarding initial costs, availability, and knowledge of products. Potential solutions for upscaling bio-based construction are identified and include increased case studies, positive legislation, regional economic regeneration, the wellness agenda, long-term economic sustainability, and engagement with established construction companies. This insight has informed the procurement process, material evaluation, and adoption of policy.

Low-cost housing is urgently needed in low- and middle-income countries. Concrete is often too costly and raw material production, including aggregate extraction, is known to be harmful to the environment. In this paper the use of an agricultural waste, corncob, as a potential lightweight replacement of sand in cement materials has been studied. Corncob granules were added to the mix in percentages of 5%, 10%, 15% and 20% by volume. The corncob granules were used in their natural state as well as following coating with either cement slurry or gum Arabic. The effect of sand replacement was determined through flexural and compressive testing of materials, while the chemical composition was evaluated using Thermogravimetric Analysis (TGA) and X-Ray Diffraction (XRD). The porosity of the mixes was also determined using a mercury inclusion porosimeter (MIP). The results showed that while the early age strength (7 days) was extremely low, the late age’s strengths improved drastically between 10% up to 3500% in 28 days.

To reduce the significant carbon emissions associated with construction materials, there is growing recognition of the potential for bio-based resources, including materials derived from agricultural crops such as straw, hemp and flax. The biogenic carbon stored with plant based materials can significantly reduce carbon emissions compared to other products. Uses of bio-based materials are however generally limited to non-structural, in particular as insulation, but in contrast to many other solutions straw bales can also be used structurally in low-rise construction. Despite the use of straw bales for over 100 years there is still relatively little known about their compression performance, and there are no recognised guides or standards to support structural engineers. This paper describes an experimental study into the load carrying capacity of straw bale wall assemblies. In keeping with practice in the UK, and different to previous North American studies, the wall plates do not directly bear onto the plaster coats. The aim of the paper is to characterise and compare the vertical load carrying performance of straw bale walls without and with plaster coatings, and study the effect of wall height, plaster use, and load eccentricity on compressive resistance. A series of wall assemblies were built from stacking 1 m long wheat straw bales. Wall assembly heights varied with the number of bale courses: one, two, three and four bales high. In total results from 29 tests are presented. Key findings of the study concern the influence of load eccentricity, use of plaster and wall geometry on compression performance. In the absence of national guidance, the results of this experimental study will support structural engineers designing loadbearing straw bale walls.

Chemical treatments can remove waxes and sugar components from the surface of bio-fibres, increasing their compatibility with mineral binders. This paper investigates the effects of alkali solutions treatments on miscanthus shives. For 8, 24, and 48 h, fibres were immersed in NaOH solutions at 1.5, 2.5, and 5.0% concentrations, with and without a 2.5% sodium silicate solution, having a silica modulus (SiO2/Na2O) of 2.0. SEM and Fourier Transform Infrared Spectroscopy (ATR-FTIR) were used to investigate the effect of different treatments on the microstructure and surface chemistry of miscanthus. The SEM results show that the morphologies of miscanthus fibres were significantly altered in the case of 5.0% NaOH treatment, with a weakening of the inner cell structures in some locations. Furthermore, the ATR-FTIR patterns of raw and treated shives were analysed, suggesting that treating miscanthus with 2.5% NaOH and 2.5% sodium silicate results in the required chemical modifications while retaining the cellular structure of miscanthus fibres. For all treatments, the absorbance was reduced by 31 to 77% at 450 cm−1 and 48–80% at 1035 cm−1.

To improve the early age strength of miscanthus-based composites, alkali-activated binders (ground granulated blast furnace slag and fly ash: AASF) were investigated against Portland cement. The impact of miscanthus content on strength development was assessed at three levels of aggregate to precursor binder mass ratio (0.27, 0.43 and 0.76). For the same aggregate to binder ratio, AASF mixes developed compressive strengths exceeding 1.3 MPa at 5% strain, seven times higher than those obtained with Portland cement, with the bulk density values measured in the range of 910-1070 kg/m(3). However, these values for vegetal concretes remain lower than nonvegetal concretes of similar apparent densities such as those made with polystyrene aggregates. The analysis of the microstructure of AASF composites indicates a strong interfacial transition zone, showing microstructural features that suggest the achievement of a complete reaction.

This paper initially reports on development of lightweight aggregates impregnated with phase change material (LWA-PCM), for application in mortars, plasters and other building materials. This is followed by a study into the development and characterisation of prototype cement mortars using the LWA-PCMs. The work has developed methodologies for efficiently impregnating and hosting phase change materials (PCMs) into lightweight aggregates (LWAs), including aerated concrete particles (ACG) and perlite. PCMs can store and release energy within a given temperature range, moderating thermal fluctuations, resulting in the reduction of energy lost in buildings and increasing thermal comfort. Three commercial PCMs, with melting points between 18 degrees C and 25 degrees C, were used in this study. Methods, including vacuum impregnation and immersion, and conditions for optimal absorption of the PCMs into ACG, were developed and evaluated experimentally. Different coating materials, to limit leakage of PCMs from the aggregates, were also trialled as part of this study. Compared to immersion, vacuum impregnation resulted in an increased absorption by up to 15.6 % depending on the type and viscosity of the PCMs. The impregnated aggregates were incorporated into cement mortar mixes, at replacement rates between 10% and 50% (by volume). The effects of PCM impregnated particles on both the mechanical and thermal properties of the cement mortars have been evaluated. Increasing the amount of PCM loaded particles decreased both the flexural and compressive strengths of the cement mortars, by up to 38% and 49% respectively. However, the volumetric heat capacity of the materials increased by nearly 60%. This paper presents a new approach for the design of PCM-loaded aggregate particles, with the potential to be incorporated into different construction materials to improve the energy efficiency and resilience of buildings.

The environmental burdens attributable to buildings remain relatively high. The built environment is responsible for more than one-third of the global energy consumption and nearly 40% of global CO2 emissions. In the context of increasing the sustainability of the built environment, bio-based building materials have gained a growing interest for their application in building envelopes. Miscanthus giganteus (elephant grass) is a perennial, cost effective and sustainable source of fibres for the development of bio-composites. This experimental study evaluates mechanical and acoustic properties of miscanthus - lime composites for their potential use in renovations and new-build houses, in South West England. The impact of binder to aggregate mass ratio and density on compressive strength is investigated. Moreover, the effect of aggregate particle size on the acoustic performance of miscanthus - lime composites is presented. It is shown that the initial fresh density has little effect on compressive strength compared with that of binder content. The acoustic tests results show that the use of small size particles improves the acoustic performance of miscanthus - lime composites with recorded high transmission loss and sound absorption coefficient values.

The incorporation of bio-aggregates such as miscanthus in mineral binder matrices can produce lightweight insulation materials. Bio-aggregate lightweight concretes show peculiar microstructure compared to standard mineral aggregate concretes. This paper evaluates the chemical and mineralogical interactions between miscanthus particles and blends of mineral binders that include hydrated lime (CL90s), natural hydraulic lime (NHL3.5), formulated lime (FLA3.5) and mineral additions such as ground granulated blast furnace slag (GGBS), fly ash (FA) and Portland cement (Ce). The properties and the influence of ternary binder blends made of 75%CL90s, 15%NHL3.5 and 10% mineral additions (GGBS/FA/Ce) on the morphology of the interfacial zone were investigated. It was observed that carbonation of samples proceeds from the outer shell to the inner core of samples leaving a physically identifiable hardened shell (external 1–2 cm) and a softer inner core. In all samples, the X-ray diffraction results show that there is a reduction in peak intensities and broadening of Ca(OH)2 peaks whereas peaks of CaCO3 sharpen and increase in intensity. The mineralogical changes in the binding matrix depend on the type of mineral addition. Thermogravimetric analysis shows that the addition of 10% Portland cement results in the highest levels of carbonation (1.1–1.4%) and hydration (8.6–17.1%). However, also fly ash incorporation was found to be beneficial in terms of reaction processes, and its use can have positive environmental impacts due to its low embodied carbon. FTIR results show that the chemical composition of miscanthus surface changes in contact with all binders, with effects on the structures of both hemicellulose and lignin.

This paper presents findings from a research project that aimed to develop the use of wheat straw bales as non-load bearing building insulation with a new prototype insulation product. Demands for more sustainable construction products, with lower net carbon emissions and improved thermal performance, have grown in recent years. There is an increasing recognition that bio-based insulation materials, including hemp, wood fibre and straw, can provide more sustainable alternatives to current insulation products. Straw bales, produced as an agricultural co-product from cereal production, can be used directly in construction. However, both the bale sizes and orientation of straw fibres in these agricultural bales are sub-optimal for most construction uses, and have become a barrier to wider adoption. This paper reports on the technical development and characterisation of a prototype insulating product produced from wheat straw, in which both the bale size and straw fibre orientation has been produced to optimise insulation performance. Thermal conductivity and hygric performance studies are presented for the prototype bales, characterising improvement in performance from optimising straw fibre orientation. Optimising orientation of the straw fibres in bales has successfully reduced thermal conductivity, compared to conventional agricultural bales, by 38%, allowing similar reductions in insulation thickness for an equivalent performance. Furthermore, by optimising the orientation of the straw fibres a reduction in water vapour permeability, moisture buffering, and moisture infiltration by as much as 76%. This research will support opportunities for greater uptake of a novel bio-based insulation materials into mainstream construction.

Alkali activation is a novel method of soil stabilisation, which could be used for the production of compressed blocks as walling materials. Given that much of the fundamental research into the chemical behaviour of this process has been done for small specimens, there is a knowledge gap over the potential effects of increasing specimen size. In this study, blocks were made from a mix of soil, sand and sodium hydroxide solution using a manual block press. Their phase composition and microstructure were investigated using powder X-ray diffraction and scanning electron microscopy; drying behaviour and compressive strength were also measured. No major microstructural or phase differences were found between the central and edge regions of the blocks. Longer curing time had little effect on phase formation and microstructure, but resulted in increased compressive strength. There are no fundamental chemical issues obstructing the scale-up of this stabilisation method, but further research should focus on the measurement of properties in line with building standards and eliminating hazards in the manufacturing process.

To assess the potential benefits and impacts of circular bio-based buildings, life cycle assessment (LCA) is a valuable method to identify systems or elements that have negative effects on the environment during the whole building life. To achieve low carbon buildings, LCA should be performed during the early design stage of buildings, to influence the choice more environmentally led solutions. In this paper, LCA was used during the early design stage of a circular bio-based wall panel prototype to guide the decision-making process for the improvement of the panel’s design. A cradle-to-cradle life cycle assessment was performed to compare the circular wall panel against other prefabricated wall panels, assembled using common construction materials and techniques. Results indicated that a circular design and some bio-based materials are not always synonymous with low environmental impacts. The first iteration of the circular panel had a GWP100 of 231.1 kgCO2e/m2 in the base case with one life cycle. This compared to 116 kgCO2e/m2 and 181 kgCO2e/m2 for the timber and steel frame panels respectively. The LCA was able to identify materials and components which contribute most significantly to the panels environmental impact. The identification of highly impacting materials in the initial panel design, LCA was used to guide the re-design of the circular bio-based panel. From investigating alternative materials for the insulation, cladding and internal substrate the environmental impact of the new design of the circular panel was lowered to 122 kgCO2e/m2. This research demonstrates how LCA can be used in the design process to reduce carbon emissions in circular buildings by using bio-based materials.

Energy retrofits aim to improve the thermal performance of buildings' external envelopes. With buildings of traditional construction there exists the risk that these improvements may lead to interstitial condensation and moisture accumulation. For historic timber-framed buildings, this potentially exposes the embedded historic timbers to conditions favouring fungal decay and insect infestation. Hygrothermal digital simulations can assess this risk, but these have limitations, especially regarding the study of historic and traditional materials, due to a lack of accurate material data. The research presented in this paper therefore uses the monitoring of physical test panels to examine the performance of four different infill solutions. These are, traditional wattle and daub, a composite of wood fibre and wood wool boards, expanded cork board, and hempcrete. The article focuses on the design and construction of the test cell and presents initial results from the first year of monitoring, following the initial drying phase. These showed no evidence of interstitial condensation in any of the panel build-ups, with increases in moisture content correlating directly with climatic measurements of wind-driven rain. Infill materials with low moisture permeability were seen to produce higher moisture contents at the interface with the external render due to the concentration of moisture at this point. Those panels finished in the more moisture permeable lime-hemp plaster, overall present lower moisture contents, with reduced drying times. The use of perimeter, non-moisture permeable, sealants would appear to potentially trap moisture at the junction between infill and historic timber-frame. The monitoring work is ongoing.