Earthen techniques have been historically used in construction of housing in Africa, Asia and Latin America. In the past two decades the interest in earthen material has grown considerably, leading to the development of sustainable materials such as compressed earth blocks (CEB), compressed stabilized earth blocks (CSEB) and interlocking stabilized soil blocks (ISSB). Scientific publications from various countries and context have examined the physical aspects of these earthen building materials, but so far, the results are not well connected to housing practices for and by low-income households with their self-organizing skills. This research sought to close this gap by documenting the housing projects where earth blocks are applied in participatory social housing. The study provides an overview of relevant practical examples from the three world regions (Africa, Asia and Latin America), with their cultural and climatic differences, and an analysis of similarities and possibilities. Based on the lessons learned from these examples, recommendations are made on further research on sustainable building materials within social housing practices, which can benefit the scientific community. We propose to set up a worldwide database of housing projects where earthen techniques have been applied responsibly. We conclude and recommend that more high-quality pilot projects with CSEB and ISSB are needed to get a broader picture on the potential of these materials for social housing, and the necessary support for local communities wishing to be involved in these sustainable housing practices.@en

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.@en

Building with unfired earth (mud) is an ancient practice that is regaining popularity due to the rising concern about the impact of the construction sector on climate. However, the low image of earthen materials is a major barrier to its acceptance in India, and is caused due to its poor water resistance performance. This research focuses on developing a low-cost, water resistant and desirable earthen building material for rural housing in India. This thesis contributes toward a better understanding of water ingress and water resistance in unstabilised and biologically stabilised earthen materials, especially cow-dung stabilised earthen blocks. Moreover, it addresses the three key aspects identified for rural earthen housing in India; 1. Affordability, by using inexpensive techniques and binder; 2. Durability, by enhancing the water resistance in both unstabilised and cow-dung stabilised earthen material, and 3. Desirability, by producing Compressed Earth Blocks of a good finish and aesthetic and using a widely acceptable stabiliser. The research work is expected not only to provide scientific insights that facilitate understanding and adoption of earthen materials but also the knowledge that can be directly applied in the construction of earthen houses.@en

The water-resistance of cow-dung has made it a widely used stabiliser in traditional earthen structures in several Asian and African countries. Multiple studies have shown an improvement in water-resistance with the addition of cow-dung, but none provides insight into this behaviour. The present study investigates the water-resistance behaviour of cow-dung stabilised earthen blocks through an extensive experimental programme to identify and characterise the components of cow-dung responsible for its water-resistance. Fresh cow-dung was collected and separated into fibres (>63 μm), medium-sized microbial aggregates (1-63 μm) and small-sized microbial aggregates (0.5-7 μm). Each component was mixed with soil and samples were prepared at different water contents (optimum water content corresponding to the highest dry density and water content higher than optimum) and compacted with 2.5 MPa force to prepare compressed blocks. The water-resistance of these blocks was evaluated through the immersion and modified drip/rain test. It was found that the small-sized microbial aggregates are almost entirely responsible for water-resistance behaviour of cow-dung stabilised earthen blocks. Small-sized microbial aggregates were further characterised by gas chromatography, mercury intrusion porosimetry, N2- BET surface area, zeta potential measurement and electron microscopy. The results indicate that the small-sized microbial aggregates are composed of clay-sized negatively charged particles that are rich in fatty acids. The hydrophobicity of these particles is hypothesised to be responsible for water-resistance behaviour. These insights are further used to produce stabilised blocks that performed at least 30 times better than the unstabilised blocks in both water-resistance tests. The study concludes with practical recommendations for the use of wet cow-dung over dry cow-dung and a reduction of fibre content to increase the water-resistance of earthen blocks. @en

Housing is a cross-cutting issue that is crucial to achieving several of the Sustainable Development Goals. Earthen housing is found across the globe, particularly in developing countries, but there is a lack of up-to-date information about its distribution and trends. This knowledge gap is a barrier to developing more effective research and policy for earthen housing. In this study, national demographic datasets were used to investigate the distribution, trends and attitudes towards earthen housing worldwide. Data was collected and analysed for the most populous 26 countries, which make up >75% of the global population. Globally, earthen housing is in decline relative to non-earthen housing, driven by demographic changes and negative perceptions of earthen materials in developing countries. The proportion of households living in earthen dwellings worldwide is estimated to be 8–10%, and the average across developing countries to be 20–25%. There is a negative correlation between countries’ level of development and prevalence of earthen housing. Whilst data is more sparse for highly developed countries, the development of standards and commercial interest suggests more favourable attitudes to earthen housing. A focus is encouraged on high-quality earthen dwellings which can help meet housing needs in both developing and developed countries.

@en

There is an enormous demand for rural housing in India that needs to be catered for within a short span of time. Building with earth (mud) is proposed as an economical and environmental friendly alternative due to the rising costs of conventional building materials. However, the construction of earthen houses has significantly declined in India and thus it is necessary to evaluate if they can make a valuable contribution to contemporary housing shortage. Therefore, an informal survey was conducted in India to understand factors favouring or limiting the construction and daily use of earthen houses. The outcome of the survey suggests that ‘Image’ is the key barrier against a wide acceptance of traditional earthen houses which are linked to poverty. While modern earthen construction is desired, it is expensive for low-income households. The role of earth in addressing the contemporary housing shortage is analysed and suggestions are given for the implementation of modern earthen technologies for low-cost affordable rural housing. Initiatives by middle-high income households, entrepreneurs and government can trigger a widespread interest in earthen construction. Successful demonstration of durable earthen structures at diverse locations and contexts can act as catalysts for change of the image of earth and make it a desirable material for low-cost housing in rural India.

@en

With rapid industrialisation and the increase in popularity of concrete and brick constructions, a decline in earth houses has been observed especially in the rural areas of India. A survey was carried out in five regions of India to understand the technical and social factors favouring/limiting the construction and everyday use of earth houses. As an outcome of the survey, a low societal image of earth houses and durability issues, such as termite infestation and poor resistance to rain water, were the main reasons behind the choice of low-income households in favour of modern building materials over earth construction.@en

Starch is a natural polymer which is commonly used as a cooking ingredient. The renewability and bio-degradability of starch has made it an interesting material for industrial applications, such as production of bioplastic. This paper introduces the application of corn starch in the production of a novel construction material, named CoRncrete. CoRncrete is formed by mixing corn starch with sand and water. The mixture appears to be self-compacting when wet. The mixture is poured in a mould and then heated in a microwave or an oven. This heating causes a gelatinisation process which results in a hardened material having compressive strength up to 26 MPa. The factors affecting the strength of hardened CoRncrete such as water content, sand aggregate size and heating procedure have been studied. The degradation and sustainability aspects of CoRncrete are elucidated and limitations in the potential application of this material are discussed.

@en

Given the increasing scarcity of resources, a transition from the traditional linear “make-take-waste” production scenario to a circular model is essential to be able to meet the needs of future generations. In the circular economy concept1 products are designed in such a way that their components fit as nutrients in either the biological cycle – biodegradable after use, recycled, and regrown by nature itself – or the technical cycle of industrial non-renewable materials whose finite stocks need to be secured by high-level recycling.@en