In all continents, soil is used for construction of low-cost shelters and the current world population statistics indicate that approximately 30% of the population still lives in earthen structures (United Nations, 2011). It is expected that the earthen structures in developing countries will continue to exist in the next decades due to prevalence of poor socio-economic conditions, especially among rural communities. The earthen construction possesses some shortcomings and its technical know-how has not been systematically established for the sustainable future applications. The demerits include poor mechanical properties such as low compressive and tensile strength, low resistance to water ingress, low resistance to swell and shrinkage. Hence issues pertaining to desiccating cracking arise.
Earthen construction is vulnerable to natural phenomena such as earthquakes and floods. Several reports have shown that unreinforced earthen structures suffer severe damage compared to reinforced structures (Morris et al., 2010). It can be hypothetically established that undesirable performance of the earthen construction during natural or manmade disasters is due to poor mechanical properties of the materials. This can be addressed by employing proper material improvement techniques such as fiber inclusions.
3
Therefore, it can be anticipated that improved material properties and good construction methods, could enhance performance of earthen structures during earthquakes or other loading conditions. Nevertheless, the design guidelines for low-cost earthen structures cannot be published unless thorough knowledge of material behaviour in different and extreme environments is acquired. Therefore, research focus on the potential application of low cost reinforcement of materials for earthen structures is fundamental to the establishment of the guidelines for earthen construction.
Earthen construction for dwelling units is currently at the verge of being abandoned especially in Africa due to lack of proper construction guidelines. Macroeconomics statistics have shown that most of rural communities in the sub Saharan Africa are living below poverty line and cannot afford cement or lime, the situation that has led to the development of non-resilient infrastructure. Therefore, it is imperative to investigate the mechanical properties of the potential low-cost and sustainable materials that enhance resilience and durability to low-cost earthen construction.
The biggest obstacle in earthen construction particularly in developed countries is lack of trust and confidence by the engineers, reluctance and apprehension of some clients and builders on the earthen construction methods. In Africa, engineers acknowledge the potential of earthen construction. The earthen construction industry can be promoted not only by introducing advanced techniques but also by the systematic establishment of its technical know-how. It is therefore imperative to establish well-documented design and construction guidelines for earthen structures that are supported by the scientific evidence on the performance and behaviour of the earthen materials in various environments.
Natural fiber inclusion is the best technique to achieve resilience of the low-cost earthen construction. Although natural fibers are more attractive in this regard, they have limitations such as moisture absorption which could cause dimensional changes and result in the composite with weak interfacial adhesion and low durability (Buitrago et al., 2015). Therefore, investigations are required to find possible ways of enhancing durability and fiber-matrix interfacial shear properties of natural fiber soil composites in order to achieve desired mechanical properties and long term mechanical performance.
4
The modification of the fiber surface through physical and chemical methods reduces the hydrophilic nature of the natural fibers and decreases the rate of biodegradation in natural settings (Ahmad et al., 2010a; Chand, 2000). Coating fibers with acrylic butadiene styrene (ABS) asphalt emulsion, rosin–alcohol mixture, paints, bituminous materials, a water soluble acrylic and polystyrene can improve composite long term performance (Prabakar and Sridhar, 2002). However, using synthetic materials is not cost effective and ecologically green approach to addressing shortcomings of natural fibers. In order to maintain the cost-effectiveness of using natural fibers for soil reinforcement, investigations that focus on application of natural based additives to improve fiber-matrix adhesion and ultimately the performance of natural fiber soil composites are paramount.
Besides fiber soil reinforcement, utilisation of industrial waste products in the developed countries can play a major role in achieving more resilient earthen construction. In most of the developed countries such as South Africa, the high production of industrial wastes poses challenges in waste management due to high quantities of waste disposal. Fly ash, a waste product from coal burning has shown positive effects on improving mechanical and durability properties of soil. The use of fly ash is more attractive as it is cheap and produced in abundance in the developed countries. Fly ash stabilised soils exhibit high stiffness and brittle behaviour (Abtahi et al., 2010a; Aqeel Al Adili et al., 2012a; Basha et al., 2005; Ghavami et al., 1999a; Tang et al., 2007). Therefore, incorporating fiber reinforcements within soil could be an effective and reliable technique to improve ductility of the soil. Natural fiber-fly ash soil stabilisation could be best techniques to ensure the balance of cost-effectiveness and environmental friendliness in construction. The level of strength improvements of fiber-lime fly ash stabilisation with construction uncertainties such as pre-loading is a problem worthy of investigations.