Biological Stabilisers in Earthen Construction: A Mechanistic Understanding of their Response to Water-Ingress

Earthen construction is re-gaining popularity as an ecological and economical alternative to contemporary building materials. While building with earth offers several benefits, its performance due to water ingress is a concern for its widespread application. This limitation is often solved by adding chemical stabilisers such as Portland cement and hydraulic lime. Chemical stabilisers are a subject of widespread debate as they increase the cost and embodied energy of the structure, and reduce the desirable characteristics of raw or unstabilised earth. This along with perceived environmental performance, renewability, and proven effectiveness in traditional earthen construction has led to a growing interest in biological or organic stabilisers. Although the strengthening mechanism of biological stabilisers is widely covered in scientific studies, discussion regarding the water-resistance is limited. This review aggregates the research from the field of earthen construction and geotechnical engineering and extends it to explain the possible mechanism responsible for the water-resistance behaviour of biologically stabilised earthen materials. This study includes a wide range of traditional and industrial biological stabilisers derived from animals (cow-dung, casein, chitosan), plants (starch, guar gum, cactus mucilage, lignin, tannin) seaweeds (alginate, agar, carrageen) and microbes (xanthan gum, gellan gum). A conceptual model of water-ingress in unstabilised earthen blocks is proposed and the response of biological stabiliser to water ingress and related physico-chemical and physical factors is discussed using the model at microscale (stabiliser interaction with clay, sand) and macroscale (hydraulic conductivity of block). Properties of stabilisers such as hydrophobicity, stability under wet conditions or interaction with cations have a dominant effect on the overall response to water ingress. Key gaps have been identified in the existing knowledge that are necessary to investigate in order to understand the water-resistance behaviour comprehensively. The study concludes with a brief assessment of biological stabilisers based on their performance and feasibility to use in contemporary earthen construction.

An overview of the remaining challenges of the RILEM TC 274-TCE, testing and characterisation of earth-based building materials and elements

Based on the RILEM Technical Committee 274-TCE work, this paper is a discussion of the remaining engineering challenges faced by earthen architecture. The assessment of earth material performances requires the development of appropriate procedures and standards. This is discussed in particular for the characterisation, hygrothermal behaviour, mechanical behaviour, and durability of earth materials. One other important challenge, since one of the main advantages classically put forward, is its ecological performance, is a proper assessment of life cycle assessment of earth materials, elements and buildings. Moreover, the paper develops why the approach to earthen construction must be different compared to the dominant construction materials, to preserve its ability to contribute to the ecological transition in the construction sector. In particular, the needs of using local soils, with an architectural approach coping with the limits of the materials, and developing an architectural optimisation to preserve the earthen materials multifunctionality rather than selecting a sole property to be maximised. Lastly, the findings of the paper can be used to develop a holistic approach to earthen construction to foster the development of new earthen architecture projects.

Raw Earth Construction Perspectives in Italy: An Overview Through the Rehabilitations of Casa Fenu in Villamassargia, Sardinia, and Casa di Teresa in Casalincontrada, Abruzzo

A detailed analysis of the rehabilitation processes of two publicly owned buildings in Sardinia and Abruzzo is taken as a basis for describing the background, difficulties and possible future developments of raw earth as a building material in Italy. Earthen construction techniques, despite a rich tradition and extensive documentation, are still considered outdated, and their use today requires a fortunate confluence of contextual factors. Archival research, literature review and a study of manuals were coupled with an examination of urban plans and public policies, as well as interviews with experts and stakeholders. This multi-approach research shows that there is a strong need to appropriate traditional knowledge so as to translate local skills into viable solutions able to meet today’s needs. The key issue may be investment in training and dissemination. The mindset of the artisan, that of the homo faber (Sennet 2008), needs to be more widely associated with action toward sustainable local development.

Mechanical and durability properties of adobe blocks filled with date palm wastes

Purpose Earthen construction does not meet today’s requirements due to certain limitations such as low water resistance and its high vulnerability to cracking damage. The purpose of this study is to improve the mechanical properties and low durability of adobe blocks by incorporating date palm wastes as a natural reinforcement and lime as a stabilizer. Design/methodology/approach Soil from the region of Biskra in Algeria was mixed with sand and lime in suitable ratios. Then, date palm wastes were added to the previous mixture at different ratios (0.3%, 0.6% and 0.9%) by dry mix weight to manufacture adobes. Cubical and cylindrical specimens were prepared and tested in a laboratory to investigate the curing time, mechanical and durability characteristics of the formulated blocks. In addition, X-ray diffraction and scanning electron microscopy (SEM) tests were used to identify the materials. Findings It has been observed that the addition of lime to the soil is very beneficial for its stabilization, in particular for an optimum of 12%. The presence of date palm waste in the mixture (soil + lime) generated a significant improvement in tensile strength reaching a rate of about 67%. The same observation was made for the tests of resistance to dry abrasion, resistance to erosion, attack by external sulphate and wetting/drying. However, for cases of compressive strength, water absorption and swelling an unfavorable effect was recorded. Originality/value Based on the above-mentioned findings, this paper presents a novel solution to increase the durability of adobe materials using date palm wastes with oven curing at 65°C for about nine days. Adopting such an approach would certainly encourage building durable mud housing on a large scale. This can contribute to solving the acute housing shortage, particularly in poor countries.

NEW PARADIGMS FOR EARTH CONSTRUCTIONS TECHNOLOGIES: SUSTAINABILITY AND CONTROL OF THE CONSTRUCTION PROCESS

The paper presents part of the international research, between Italy and Morocco, on the earth constructions technologies. Although history demonstrates many applications there isn’t a large use nowadays. The aim of this study is therefore to understand why such promising material today is not widely used and applied only for niche situations. Through the analysis of earth construction technologies from those linked to tradition to more contemporary ones, it was possible to understand how the material was adapted locally to different building needs according to the climatic context and the available resources. In addition, the international regulatory framework is also analyzed, in order to understand the current level of development of regulations for the use of earth-based technologies. Morocco is a country with a deep and widespread knowledge of earthen construction, and the contemporary construction regulatory framework provides for its use. Through a Moroccan case study, it was possible to experiment the use of rammed earth masonry as infill, respecting contemporary construction standards. In addition, the application of BIM modeling was tested, in order to make this construction technique meet the requirements of the contemporary building process, making it faster, controlled in terms of performance and economically advantageous. The results of research, including the preparation of an abacus of the earth walls used with 123 elements and the related 17 characteristic information, for a total of 8000 m of earth, demonstrate the ability of this traditional building system to be managed and controlled in a contemporary way.

Experimental characterization of natural fibre–soil interaction: lessons for earthen construction

Earthen construction materials are the subject of renewed interest due to the rising alarm about environmental pollution from the construction industry. Current research efforts are focused on improving the mechanical properties of earthen materials to make them modern and competitive. To increase strength and improve ductility fibres can be added to the soil mixture and if natural fibres are used one achieves stabilisation in an environmentally friendly way. Several previous studies have dealt with the behaviour of this composite material at a macroscopic level and on the general interaction between fibres and soil, but there is little published research on the interfacial mechanical interaction between natural fibre reinforcement and a soil matrix which is key to the former. This paper attempts to fill this gap by presenting and discussing laboratory results from a large campaign of pull-out tests conducted on composite earthen samples. The variables investigated here are the nature of the fibres (i.e. single or collections twisted together) and the use of fibre treatments such as PVA glue and baking soda. In the study both fibre–soil failure and soil-soil failure are investigated and the results lead to conclusions as to appropriate use of fibres to reinforce earthen construction materials.