Lime Hemp Research Articles

Analysis of the thermal performances of uninsulated and bio-based insulated compressed earth blocks walls: from the material to the wall scale

The lively international debate on the future of the built environment has placed emphasis on the possibilities offered by bio and geo-based building materials. Among these, raw earth-based materials offer several advantages associated to their reusability and low embodied energy.Nowadays, several companies are basing their production lines on prefabricated raw earth products, as is the case of compressed earth blocks (from now on CEBs). CEBs are commercialized for the construction of massive vertical envelopes, characterized by a high thermal inertia. Nevertheless, in order to compete with conventional building materials, it is also necessary to guarantee a high thermal resistance.In this work, this issue was solved by the design and testing of full-scale uninsulated and bio-based thermal insulated CEB walls. In this way, the thermal performance of CEB walls can be increased to meet the high energy requirements currently adopted in European Countries. Furthermore, the choice of bio-based insulations represents the main novelty of the study, aimed at finding hygrothermal compatible solutions at a low environmental cost.More in detail, this work reports the results of the thermal and physical material characterization of CEBs and of two innovative bio-based thermal insulations (lime hemp and sugarcane bagasse panels), and compare them with measurements made on full-scale uninsulated and insulated CEB walls. For this purpose, the walls are tested inside a double-room climatic chamber where they are subjected to variable temperatures on their two faces, reproducing typical indoor and outdoor conditions during summer and winter conditions in a continental climate.Results show the enhancement of thermal performances of compressed earth blocks walls when thin layers of bio-based thermal insulations are added. The thermal resistance of weakly bio-based insulated CEB walls is found to be nine times (for the sugarcane bagasse insulated CEB wall) and four times (for the lime hemp insulated CEB wall) higher than that of uninsulated CEB walls. Moreover, the addition of the insulation layers enhances the time lag and the decrement factor values of CEBs walls.

Exploring the integration of bio-based thermal insulations in compressed earth blocks walls

The growing concern about the environmental impact of contemporary construction has posed emphasis on the possibilities offered by bio-based and raw earth construction. The front challenge for the establishment of earth-based technologies in contemporary building markets is the guarantee of high structural and energy performances, while maintaining a low environmental impact. This work focuses on the performance analysis of compressed earth blocks (from now on CEBs) which are currently commercialized for the construction of massive vertical envelopes, with high thermal inertia. However, to obtain an acceptable comfort and an optimized thermal behavior, CEBs walls must also reach a high thermal resistance. This issue can be overcame by the design of insulated CEB stratigraphies using bio-based thermal insulations presenting hygrothermal properties compatible with raw earth-based materials. In this way, the thermal performance of CEBs walls can be increased, while preserving their hygroscopic behavior. In this spirit, this work reports the results of the experimental characterization of three materials: CEB, lime hemp and sugarcane bagasse bio-based insulation panels. It includes their composition, their main physical (dry density, porosity, capillary water absorption), thermal (specific heat capacity, thermal conductivity) and hygrometric (sorption isotherm, water vapor permeability) properties. Finally, these experimental data are used for the implementation of several numerical simulations at a wall scale in a reference climate to estimate the hygrothermal performances of both uninsulated and bio-insulated CEB walls. The simulations allow for a better comprehension of CEBs’ behavior in view of their combination with the chosen bio-based thermal insulations, and give insights into possible moisture-related issues as mold growth or increase of U-value.

Compared Environmental Lifecycle Performances of Earth-Based Walls to Drive Building Envelope Design

Raw earth has useful applications in contemporary buildings as a sustainable and circular construction material. The present study aims to assess the environmental performance of several earth-based wall systems with similar thermal performance, through a life cycle thinking approach. In particular, a life cycle assessment is developed for (a) unstabilized rammed earth (produced in situ), (b) compressed earth blocks (prefabricated in the factory), (c) stabilized rammed earth and (d) light earth, all combined with biobased (natural fibers, e.g., lime hemp, cork) and/or conventional materials for building insulation. Results show benefits in terms of avoided carbon emission, water footprint and embodied energy throughout the production chain and highlight limits and potential improvements. In addition, the CO2 offset by crops is also estimated based on carbon embedded in natural fibers. In particular, light earth wall systems are the most suitable to minimize environmental impacts, while massive constructive technologies (as unstabilized rammed earth) show a higher dynamic thermal performance for intended use in Mediterranean climates.

Lime Hemp Concrete with Unfired Binders vs. Conventional Building Materials: A Comparative Assessment of Energy Requirements and CO2 Emissions

This work assesses the energy requirements and CO2 emissions of a building made of Lime Hemp Concrete (LHC) with alternative unfired binders as lime replacement, compared to buildings made of standard LHC, and several conventional building materials. The assessment is based on ISO 14040, which deals with Life Cycle Assessment (LCA), and examines two aspects: energy, including pre-use phase Embodied Energy (EE), and use phase Operational Energy (OE); and CO2 emissions, including pre-use phase Embodied Carbon (EC), and use phase Operational Carbon (OC). The EE and EC calculations are based on published databases, while OE and OC were obtained with EnergyPlus simulations. The assessment refers to a specific case study in an arid region, with extreme diurnal and seasonal fluctuations of temperature and relative humidity. Using LHC with 100% unfired binder as lime replacement was shown to save up to 90% of the total energy consumption and CO2 emissions, as compared to conventional building materials. The findings of this research clearly demonstrate the high potential of LHC with unfired binders as lime replacement, which possesses the lowest energy requirements and CO2 emissions, illustrating the potential for a building with significantly low environmental impact over its life cycle, i.e., when calculating both EE and EC, and OE and OC.

Effect of variability of hemp shiv on the setting of lime hemp concrete

Lime hemp concrete (LHC) is one of the most environmentally friendly alternatives to traditional building materials, which is normally used as an insulation material. The lime hemp concrete is made up of hemp shiv and aerial (or hydraulic) lime and has the ability to offer better thermal and acoustic performances. However, it is reported that the shiv/matrix reaction does not always meet the expectations, thus the properties of hemp concrete may be affected by certain characteristics, such as origin, retting time, harvest time, etc. of the used hemp. During this work, the authors have studied the influence of variability of hemp shiv on the setting of LHC. The results depicted that the soluble components (e.g., organic acids, simple sugars, etc.) from hemp shiv had a significant impact on the setting and hardening of mortars. This study also proved that hemp containing more soluble components tends to involve a longer setting time and hinders long-term carbonation reaction of binders. Furthermore, the experimental results also showed that water treatment can effectively remove these soluble agents from hemp shiv and improve the compatibility between shiv and binder in the composite.

Thermal performance of alternative binders lime hemp concrete (LHC) building: comparison with conventional building materials

ABSTRACT This research aims to estimate the operational energy (OE) savings of a full-scale building, made of lime hemp concrete (LHC) with alternative binders partly replacing lime, compared to buildings made of conventional materials, e.g. Autoclaved Aerated Concrete (AAC), Hollow Concrete Blocks (HCB), and Expanded Polystyrene (ESP). The thermal performance of small size (1 m × 1 m) different materials test cells was experimentally studied. Experimental results were compared to simulated values obtained by EnergyPlus. Monitored and simulated indoor temperatures were found to be in good agreement. Subsequently, the thermal performance and energy consumption of full-scale buildings (10 m × 10 m × 2.9 m) were simulated by EnergyPlus with a great degree of confidence. In up-scaled building simulations, LHC presented the best thermal performance and consequently the lowest energy consumption, reaching ∼7 kWh/m2/year, nearly Zero Energy Building standards, 90% lower as compared to HCB which obtained the highest energy consumption. Dynamic external window shading was shown to have a significant impact on cooling energy savings. This research clearly shows the high potential of using LHC with alternative binders as a partial replacement for lime, as it has advantages in terms of energy savings, and their equivalent CO2 emissions.

The ILHWLAD-MCDM Framework for the Evaluation of Concrete Materials under an Intuitionistic Linguistic Fuzzy Environment

Concrete, one of the sources of energy consumption and carbon emissions, is widely used in the construction industry. The selection of concrete materials raises the question of energy sustainability and turns it into a complex multicriteria decision-making (MCDM) issue. To address this, we present an MCDM framework based on the intuitionistic linguistic hybrid weighted logarithmic averaging distance (ILHWLAD). To begin with, the intuitionistic linguistic numbers are used to deal with the uncertainty and fuzziness of the decision-making process. In addition, in view of the significance and the ordered position of the input arguments, an intuitionistic linguistic hybrid weighted logarithmic averaging distance (ILHWLAD) operator is defined. We, then, initiate the criteria system and present the MCDM framework based on the ILHWLAD to select the finest concrete. A case study involving four alternative materials, namely, autoclaved aerated concrete (AAC), hollow concrete blocks (HCB), expanded polystyrene (EPS), and lime hemp concrete (LHC), is presented to verify the scientificity of the framework.

Thermal performance of real-life in-situ cast lime hemp walls in Flanders

In order to meet the energy performance regulations for new buildings and to improve the energy performance of the existing building stock, a high amount of insulation materials will be needed in the coming years. Meanwhile, the demand for renewable materials and materials with a low environmental impact is increasing. In previous research, the ecological and hygrothermal potential of lime hemp as a building material has been shown. Besides incorporating a large share of renewable and fast-growing hemp shives, lime hemp combines thermal insulating properties and a high thermal inertia with a good moisture regulating behaviour. However, despite the growing interest in the material and promising lab results, the thermal performance in real conditions is still uncertain. Due to the lack of validated data for in-situ cast walls, rather conservative λ-values for lime hemp are currently compulsory used in energy performance certification calculations in Flanders, the Flemish region of Belgium.In this paper, the results of a case study analysis of four real-life lime hemp projects are presented. The thermal performance of four dwellings with in-situ cast lime hemp walls (both new construction and renovation) is determined by in-situ measurements of the U-value. The measurements show that the in-situ U-value of the lime hemp walls is significantly better than the U-value that is calculated with the λ-value that is currently accepted by the Flemish Energy Agency. However, drying of lime is a slow process, resulting in initially higher U-values that gradually decrease in the first months after lime hemp application. Once dried, in-situ cast lime hemp walls can meet the Flemish energy performance requirements.

Alternative unfired binders as lime replacement in hemp concrete

The objective of this research was to develop sustainable building materials based on lime hemp concrete (LHC) by replacing some or all of the lime with different dosages of alternative unfired binders, namely, clay, limestone or basalt. The compressive strength, thermal properties and water resistance of mixtures of lime and the unfired binders, with and without hemp, were investigated. In general, for mixtures without hemp, replacing 50% of the lime with an alternative binder resulted in a reduction in the compressive strength. However, when hemp was added, an optimal content of alternative binder was found, up to which a higher content of alternative binder led to improved properties (compressive strength and water resistance), but beyond which there was impairment of the properties. In summary, the higher the content of the alternative binder, the greater the LHC strength, while the density remains the same; however, at too low a lime content (here 10% of the binder material) there was not enough lime to facilitate the formation of a continuous binding matrix within the sample, leading to a reduction in strength. Finally, the thermal properties of LHC were almost not affected by the replacement of the lime with an alternative binder.

The thermal performance of lime hemp concrete (LHC) with alternative binders

This research studied the influence of replacing the lime with alternative unfired binders on the thermal performance of Lime-Hemp Concrete (LHC), and compared it to conventional building materials, e.g., Autoclaved Aerated Concrete (AAC), Hollow Concrete Blocks (HCB), and Expanded Polystyrene (EPS). This was done by monitoring the internal temperature and relative humidity (RH) of test cells built with LHC and conventional materials, under real-time measured outdoor conditions, during summer and winter. It was found that all LHC cells with and without the alternative binders presented similar behavior, in terms of temperature as well as relative humidity. This means that LHC with alternative binders requires similar quantities of operational carbon (OC) and operational energy (OE) as LHC with 100% lime; however, its embodied carbon (EC) and embodied energy (EE) are relatively lower so in total it requires less energy and is responsible for less CO2 emissions. As for the comparison with conventional building materials, AAC performs slightly better than LHC in the winter, but LHC performs better in the summer, while both AAC and LHC demonstrate better performance than HCB and EPS, in terms of temperature as well as relative humidity. It can be concluded that since LHC possesses relatively lower EC and EE as compared to conventional building materials, it has advantages in terms of energy savings, as well as CO2 emissions.

A novel anisotropic analytical model for effective thermal conductivity tensor of dry lime-hemp concrete with preferred spatial distributions

This article develops a novel mathematical model using multi-scale homogenization approach to model the effective thermal conductivity tensors of a hemp shiv particle and lime hemp concrete (LHC). This bio-based material is an environmentally-friendly material that is used more and more in building construction. The thermal conductivity of lime hemp concrete which is generally either cast or sprayed, cannot be expressed as a scalar due to its anisotropic microstructure. The paper develops a novel model to predicting effective thermal conductivity tensor of lime-hemp concrete that takes into account the anisotropy and the size of hemp shiv, the preferred spatial distributions due to fabrication process and the imperfect particle-binding interfaces. Two probability density functions are used for modeling the particle size distributions of hemp shiv and the preferred alignment distribution of hemp particles. A good agreement is obtained between the model and experimental data provided in the literature. The presented analytical solutions offer a suitable tool for a fast optimization of the thermal conductivity of hemp concrete. Such promising future is very useful for the building design, in particular in three-dimensional (3D) simulation models.

A multi-scale homogenization approach for the effective thermal conductivity of dry lime–hemp concrete

Lime–hemp concrete is an environmentally friendly material that is used more and more in building construction. This study develops a multi-scale homogenization approach to model the effective thermal conductivity of this bio-based material. The developed model dedicated to non-compacted and compacted hemp concrete takes into account the shape and the orientations of pores of hemp particles as well as imperfect particle-binding interfaces. Unknown properties of the solid phase of hemp particles and binding, and that of the particle-binding interface are calibrated by inverse analysis using available experimental data. The model is then used to carry out a sensitivity analysis to study the effect of the porosities of hemp particles and binding, the volume fraction of hemp particles, density and temperature on the overall thermal conductivity of hemp concrete. Analytical solution proposed can be used for a fast estimation and optimization of the thermal conductivity of hemp concrete, which is very useful for the building design.

Study of lime hemp concrete (LHC) – Mix design, casting process and mechanical behaviour

This paper deals with the mechanical behaviour of lime hemp composites. LHC blocks have been produced by compression in a rigid die at a relatively high compression pressure. This process allows the production of LHC with a high proportion of hemp shiv. New mechanical parameters are proposed to compare experimental results of this study with those found in published literature. This paper shows that a high compaction pressure enhances the compressive strength and can offset a reduction of binder. Consequently, a new formula is proposed to predict the strength of LHC which depends on both the binder content and the compaction state of the shiv particles. The study leads to recommendations for the mix design of such composites.

Effect of Hemp’S Soluble Components on the Physical Properties of Hemp Concrete

Lime hemp concrete is a sustainable building material made with hemp shiv and lime. In this research, pozzolans are added to the lime binder. Hemp shiv contains water soluble constituents including pectic polysaccharides which can dissolve in the mixing water. Sugars and pectins are known to retard clinker hydration in portland cement. This research studies whether the hemp soluble components impact lime-pozzolan paste reactions thus affecting the properties of hemp concrete with lime-pozzolan binder. Physical tests and microstructural analyses were undertaken to determine how the water soluble hemp constituents influence the hydration reactions responsible for setting and hardening of lime-pozzolan pastes. The effect of hemp particles on a lime-pozzolan binder was also investigated using microstructural analysis. Physical testing evidenced that the hemp’s soluble constituents do not alter ultimate strength however, they delay pozzolanic reaction retarding setting and early strength development. The microstructural analysis of lime-pozzolan pastes agreed with the above, evidencing that the hemp delays the formation of hydrates, in particular calcium silica hydrates. The halt of the pozzolanic reaction by the hemp particles was clear at the hemp interface, where few hydrates were evident. This suggests that the properties of the hemp particles including their high suction (which removes water at the interface) and their high porosity (which assists CO2 diffusion) contribute to the halt of the pozzolanic reaction.

Influence of liquid absorption coefficient on hygrothermal behaviour of an existing brick wall with Lime–Hemp plaster

The study of the hygrothermal parameters and performance of permeable materials is being expanded; however, there is a lack of guidelines or regulation regarding the level of liquid water migrations associated with existing materials. Even if some existing recommendations demand the installation of materials that are increasingly permeable to vapour, the liquid water absorption coefficient is often neglected. This study analyses the influence of six material parameters, such as the liquid absorption coefficient and vapour diffusion resistance, on the hygrothermal behaviour of an existing brick wall insulated on the inside surface with a Lime–Hemp plaster. A specific methodology is developed combining hygrothermal simulations, sensitivity analysis and an experimental planning method. This reproducible methodology allows recommendations to be proposed to help designers choose an appropriate combination of material parameters. The paper demonstrates that the water liquid absorption coefficients of brick and of insulation have a greater influence than the vapour diffusion resistance of those materials in the studied cases. Water liquid absorption coefficient should thus be one of the parameters systematically considered in the hygrothermal analyses of wall components.

Moisture transfer and thermal properties of hemp–lime concretes

Lime–hemp concrete is a low-embodied energy, carbon-negative, sustainable construction material made with a lime-based binder and hemp aggregate. This work investigates moisture and thermal properties of hemp concretes made with hydrated lime and pozzolans, and those including hydraulic lime and cement. The paper concludes that the type of binder influences capillary action of hemp concrete and that increasing the hydraulicity of the binder, as well as adding a water retainer, reduces capillary absorption. The impact of the binder type on permeability is less evident, and the results indicate that the large interparticular spaces between hemp particles (macropores) contribute to permeability to a greater extent than micropores (which are influenced by the hydraulicity of the binder).Finally, the binder type did not have a statistically significant impact on either thermal conductivity or specific heat capacity. A trend however suggests that increasing the binder’s hydraulic content reduces thermal conductivity and increases heat capacity; and that the presence of water retainers enhances both conductivity and heat capacity.

Moisture transport properties of lime–hemp concrete determined over the complete moisture range

To determine the durability of a lime hemp concrete (LHC) wall and its resistance to driving rain, moisture conditions inside the wall have to be modelled. As model input, moisture transport properties were determined. Two LHC mixes were studied. Cup tests provided moisture diffusivity results at relative humidity (RH) values up to 95%. Capillary water uptake tests provided results for the interval 95-100% RH by means of curve fitting and the simulation tool JAM-KAP. A mix containing more lime showed higher moisture diffusivity at relative humidity >95%. (c) 2014 IAgrE. Published by Elsevier Ltd. All rights reserved.

Experimental investigation on the mechanical performance of starch–hemp composite materials

An experimental investigation was conducted in order to study the mechanical performance of starch–hemp composite materials. The starch–hemp composite material is 100% natural fibers and a durable material. The optimization of the binder solution has been based on the dynamical viscosity and the surface tension. The starch–hemp composite material specimens with five hemp/starch ratios, 6, 8, 10, 12 and 14, were manufactured by using the optimal binder. The density of the specimen decreases rapidly during the drying process. The duration of the drying time is between 30 and 40days. The density value is more lightweight than that of the lime hemp concrete. The experimental results show that the tensile strength varies from 0.03 to 0.08MPa, the elasticity modulus varies from 1.47 to 2.16MPa and the Poisson ratio varies from 0.08 to 0.12 when the hemp/starch ratio goes from 6 to 14. This type of natural fibers composite material shows a special property, great displacement. The appearance and propagation of the crack were shown and discussed in this paper.

Study of lime hemp composite precasting by compaction of fresh mix — An instrumented die to measure friction and stress state

This paper deals with the processing of lime hemp composite blocks by compaction. A rigid compression die has been developed to reach relatively high compression pressure. This has been fitted with force and strain transducers to measure the stress state during compaction. It provides some means of understanding the effect of mix design and stress level on the compressibility and homogeneity of hardened composites. It is shown that moisture globally increases both friction and packing compressibility. Proper moisture content and paste-to-shiv mass ratio (P/S) can be chosen to reduce the heterogeneity. The combination of friction at wall level and stress transmission is the most detrimental for a moisture content of 20% and a P/S=1.

Moisture fixation and thermal properties of lime–hemp concrete

Lime–hemp concrete (LHC) is a sustainable building material that combines hemp shiv and building limes. Moisture fixation and thermal properties of LHC were determined so as to gain knowledge about the material’s behaviour in a cold, wet climate. Sorption isotherms were produced over the whole moisture range for two LHC mixes by means of glass jar tests and a pressure plate apparatus. Thermal properties were determined for the mixes at different relative humidities using a transient plane source method. The results showed relatively low thermal conductivity and a steep sorption isotherm in the interval between 95% and 100% RH.