Soil blocks are widely used for construction, especially in less economically developed countries. Addition of agricultural waste fibres has been shown to improve the properties of these blocks, ...however unlike most composites the fibres are not bound to the soil matrix. Therefore, the reinforcement mechanisms are different and not well characterised. This article investigates these mechanisms through a series of experimental studies to inform the development of better guidance for practitioners, and hence improve housing for low-income communities. The microstructural characteristics were investigated using scanning electron microscopy, computerised tomography scan, optical microscope analysis and pull out testing. It was established that fibres in the soil matrix are randomly distributed with gaps between the fibres and soil matrix due to fibre shrinkage during drying of the blocks. It also found that natural fibres in soil matrix can either be pulled-out or rupture under load depending on the depth of fibres embedment in the soil matrix.
While urban wastewater infrastructure is aging and no longer adequate, climate change and sustainability are urging the transition from pollution management to resource recovery. Lacking ...evidence-based quantitative evaluation of the potential benefits and consequences of resource recovery from wastewater hinders the negotiation amongst stakeholders and slows down the transition. This study proposes mathematical formulations for technical, environmental, economic, and social key performance indicators (KPIs) that can be used to quantify the benefits and the risks of resource recovery. The proposed formulations are derived from the literature and validated with stakeholders. Each KPI is mathematically formulated at treatment train level by considering: (1) the characteristics of individual unit processes (UPs) in the treatment train (TT), (2) the context in which the TT is installed, and (3) the resources to be recovered. The mathematical formulations of the KPIs proposed in this study enable a transparent, consistent and informative evaluation of existing treatment trains, as well as support the (computer aided) design of new ones. This could aid the transition from urban wastewater treatment to resource recovery from urban wastewater.
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•Quantitative and consistent indicators for evaluating resource recovery is lacking.•We assemble a set of social, economic, environmental and technical indicators.•The indicators incorporate process, context, resource and legal characteristics.•The incorporation of characteristics is built on mathematical formulations.•The indicators also support model-based studies of resource recovery.
In the context of circular economy, wastewater can be used to address some of the 21st century's challenges regarding the transition to renewable resources for water, energy, and nutrients. Despite ...all the research, development, and experience with resource recovery from urban wastewater, its implementation is still limited. The transition from treatment to resource recovery is complex due to the difficulty of selecting unit processes from a large number of candidate processes considering the operational limitations of each process, and sustainability objectives. Presently, a multi-criteria decision support tool that deals with the difficulty of unit process selection for resource recovery from wastewater has not been developed. Therefore, this paper presents the conceptual framework of a decision support tool to find the optimum treatment train consisting of compatible unit processes which can recover water, energy and/or nutrients from a specified influent composition. The framework presents the relationship between the user input, the knowledge library of technologies and a weighted multi-objective nonlinear programming model to aid process selection. The model presented here shows, not only how the processes are selected, but also the four-dimensional sustainability impact of the generated treatment train while considering the weight provided by the user. Thus, this study presents a reproducible framework which can support private and public decision-makers in transparent evidence-based decision making and eventually the systematic implementation of resource recovery from urban wastewater.
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•The framework of a tool to generate wastewater resource recovery trains is presented.•The trains consist of compatible processes, recovering multiple resources.•Processes are selected by a weighted multi objective nonlinear programming model.•The model optimises economic, environmental, technical and social objectives.•4D sustainability gives objective, transparent options promoting resource recovery.
•Natural fibre inclusion in soil blocks positively affects mechanical properties.•Fibre reinforced soil blocks have improved resistance against wearing and erosion.•0.5% fibre content by weight is ...recommended to practitioners for use.•Correlations between properties do not follow those for binder stabilised blocks.•The importance of soil type vs. fibre type depends on the property of interest.
This study investigates the properties of soil blocks stabilised with fibres from agricultural waste. Laboratory experiments including density, water absorption, shrinkage, compressive strength, tensile strength, wearing and erosion were conducted on soil blocks made with two soil types and enhanced with three fibre types at 0.25–1wt.%. It was found that the physical, mechanical and durability properties of the blocks were generally improved and a recommendation of 0.5wt.% fibre content and high clayey soil are made. Many assumptions about relationships between properties established for binder stabilised blocks are found to be inappropriate for fibre reinforced blocks.
•Most fibres will produce increasing block strength with increasing fibre length.•Some fibres have an optimal aspect ratio when used in soil blocks.•Natural fibres continue to hold blocks together ...after failure of the soil matrix.•The effect of fibre aspect ratio is similar in magnitude to effect of fibre content.
Inclusion of fibres in soil blocks has been shown to enhance strength development. This study investigates the effect of aspect ratio of coconut, bagasse and oil palm fibres on the mechanical properties of soil blocks. Experiments were conducted on soil blocks with fibre aspect ratios (25–125) to determine the compressive and tensile strength of the blocks. Blocks with coconut and oil palm fibres showed increasing strength with increase aspect ratio, while bagasse fibres showed an initial increase followed by a decline at higher aspect ratio. The study concludes that generally longer aspect ratios produce better mechanical properties of soil blocks.
•Influence of Moisture Content on the Mechanical Properties of Jute Fibre.•Physical testing of Jute Reinforced Compressed Earth Cylinders.•Scanning Electron Microscopy of Jute Fibres.
This paper ...presents an experimental investigation into the influence of fibre moisture content on the mechanical properties of Jute Fibre Reinforced Compressed Earth Composites (JRCECs). The addition of 0.5% by weight of jute fibre at natural moisture content increased the tensile and compressive strength by approximately 3 and 2 times respectively, when compared to unreinforced samples. The results indicate that soaking and drying jute fibre causes a reduction in the mechanical properties of the fibre and the JRCEC. It was found that jute fibres at natural moisture content should be incorporated in JRCECs to achieve optimum compressive and tensile strength.
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•Design and manufacture of a manual compressed earth block (CEB) machine.•Physical and numerical testing of un-stabilised CEBs with different geometries.•Macro finite element analysis ...for un-stabilised CEBs using a Solid65 material model.•Sensitivity analysis of numerical model to account for block imperfections.
This paper presents a parametric investigation into the influence of geometry on the compressive and flexural strength of un-stabilised compressed earth blocks (CEBs). Three CEBs with dissimilar geometric properties were manufactured and subjected to physical testing and Finite Element Analysis (FEA) using ANSYS Workbench 19.1. The compressive and flexural strength of the CEBs were shown to be dependent on their geometric properties and ranged from 3.74 to 6.73 MPa and 0.63–1.31 MPa respectively. A modified Solid65 element command was utilised within the FEA and was shown to successfully replicate the non-linear elasto-plastic behaviour observed in physical testing.
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