The state of earthen housing worldwide: how development affects attitudes and adoption

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

Circular economy strategies for concrete: Implementation and integration

Concrete is the world's most widely-used anthropogenic material, and Circular Economy strategies will be key to addressing the myriad challenges that face its use today and into the future. Despite a rapid growth of research interest in developing Circular Economy strategies for concrete, this has mostly focussed on technical and environmental issues at the material and product scale. Holistic approaches considering wider social and political aspects as well as system-scale perspectives have been relatively neglected. This article uses a narrative review to investigate three outstanding questions to help address this gap: how concrete's material, product and system-scale attributes influence the interpretation of Circular Economy principles; how the full range of Circular Economy strategies can be implemented for concrete; and what the likely implementation issues will be when integrating different Circular Economy strategies (such as design for durability, component reuse and material recycling). From a product-scale perspective, it is argued that greater specificity is needed around the growing diversity of concrete materials and products in Circular Economy discourse - their properties are often distinct and hence specific strategies are not necessarily universally applicable. At the same time, a solely product-centric Circular Economy perspective is insufficient for concrete, and only joint consideration of structural and systemic perspectives will yield satisfactory solutions. ‘Soft’ perspectives of social, political and legal aspects cannot be viewed simply as an added bonus, but are essential to reconciling the ‘hard’ issues of technical, environmental and economic aspects that dominate discussions. Whilst concrete can and should have a key role in a Circular Economy, its success will require more than just extensions of linear economy thinking

Advances in alkali-activation of clay minerals

To future-proof alkali-activation technology, there is a need to look beyond well-established precursors such as fly ash and blast furnace slag, due to resource competition, geographical distribution and technical limitations. Clay minerals are abundant and diverse aluminosilicate resources available around the world. However, due to the mineralogical complexity amongst the most common 1:1 (kaolinite, halloysite) and 2:1 (montmorillonite, illite) clay minerals, and practical issues such as workability, their use has been more limited. Recent advances have improved understanding both of pre-activation treatments (thermal, mechanical, chemical), and of the factors influencing clay reactivity, phase assemblages and properties of final products. This opens new opportunities for the exploitation of these resources to produce sustainable cements. A one-size-fits-all approach for processing and activating clay minerals is not viable. Instead, activation routes need to be tailored according to the clay mineralogy to achieve the binder properties required for key applications

Discussion of “Earth concrete. Stabilization revisited”

Using metrics is an informative approach to compare the effectiveness of cement use in material systems, but does not necessarily consider all factors needed to determine which system is most sustainable. To make a fair comparison, it is necessary to consider the functions cement performs in each system. In this discussion, suggestions are given for how to assess the use of cement as a binding agent in stabilised earth construction. Consideration of structural requirements and durability, life cycle analysis and moisture buffering shows that the effectiveness of cement use depends on more than just embodied carbon and dry compressive strength

Complete re-utilization of waste concretes–Valorisation pathways and research needs

Global demand for buildings and infrastructure is extremely high as provision of shelter, sanitation and healthcare are paramount to safeguard the world's growing population. Concrete is a preferred construction material to meet this demand, but its production is leading to overexploitation of natural gravel and sand, causing an environmental crisis in regions where these materials are extracted unsustainably. Waste concrete is available globally, particularly in regions with fast growth of the built environment, and those struck by coordinated attacks, earthquakes or severe weather events. Waste concrete has mainly been used for producing recycled aggregates; however, its full recycling is still not practiced. Alternative uses include applications as fine recycled aggregates, supplementary cementitious materials, filler, and feedstocks for clinker production. These technologies still face challenges concerning their adoption and eco-efficiency. Restricted knowledge and operational barriers have also prevented implementation of beneficiation technologies for complete re-recycling of waste concretes, particularly the fine fractions produced during crushing. Despite these issues, it is recognised that the complete utilization of waste concrete offers unique opportunities for supply chain security, reducing natural resources consumption and enabling to move towards a Circular Economy. Harmonizing current practices for the treatment of waste concrete and the by-products generated during their processing, is a first step toward policy and standards development to enable their widespread use. This critical discussion addresses challenges and opportunities, as well as facilitation strategies needed to progress the complete re-utilization of waste concrete as a valuable resource for creating sustainable future infrastructure

Report of RILEM TC 267-TRM phase 3: validation of the R3 reactivity test across a wide range of materials

RILEM TC 267 TRM– “Tests for Reactivity of Supplementary Cementitious Materials” recommends the Rapid Reliable Relevant (R3) test as a method for determining the chemical reactivity of supplementary cementitious materials (SCMs) in Portland cement blends. In this paper, the R3 test was applied to 52 materials from a wide range of conventional and alternative SCMs with the aim to validate such test. An excellent correlation was found between the cumulative heat release and the bound water determined following the R3 test method. Comparison of the R3 test results to mortar compressive strength development showed that all conventional SCMs (e.g. blast furnace slag and fly ashes) followed the same trend, with the notable exception of very reactive calcined kaolinitic clays. It is discussed, through an in-depth statistical regression analysis of the R3 reactivity test results and the 28 days relative compressive strengths, how reactivity threshold values for classification of the chemical reactivity of SCMs could be proposed based on the R3 test results

Report of RILEM TC 267-TRM phase 2: optimization and testing of the robustness of the R3 reactivity tests for supplementary cementitious materials

The results of phase 1 of an interlaboratory test, coordinated by the RILEM TC 267-TRM “Tests for Reactivity of Supplementary Cementitious Materials” showed that the R3 (rapid, relevant, reliable) test method, by measurement of heat release or bound water, provided the most reliable and relevant determination of the chemical reactivity of supplementary cementitious materials (SCMs), compared to other test methods. The phase 2 work, described in this paper aimed to improve the robustness of the test procedure and to develop precision statements for the consolidated test procedure. The effect of the pre-mixing and mixing conditions, and the impact of the mix design on the test method robustness were assessed and fixed for optimal conditions to carry out the R3 heat release test. The effect of the drying step was evaluated to define the R3 bound water test procedure in more detail. Finally, the robustness of the consolidated final test methods was determined by an interlaboratory study to define the precision statements