http://www.mdpi.com/journal/sustainability/special_issues/building-materials/ Dear Colleagues, Earth-based technologies for building systems include adobe, cob, straw and compressed earth bricks. Earth architecture and construction when properly executed results in buildings that are economical, energy-saving, environmentally-friendly and more sustainable. Earth-based technologies have been successfully being used for load bearing purposes in some tall structures. Examples include the 175 feet-high Al-Muhdhar Mosque in Tarim – Yemen. It is however not possible to replicate the technology used in such applications throughout the globe. The exaggerated thickness of earth walls which give such buildings thermal mass works only in the hot and dry climate; they would not be appropriate for hot and humid regions. With the latter, in addition to securing thermal comfort for the occupants, the earth-based elements must also resist the combined effect of moisture and temperature. In general, key areas of concern include lack of durability especially as far as resisting hygrothermal loads is concerned and low performance with respect to physical and mechanical properties. There are also significant variations in the performance of earth-based building elements depending on the source of the soil, manufacturing methods and climatic conditions. Such factors have limited the structural use of earth-based technologies around the globe. Although the use of such technologies constitutes a sustainable approach to erecting building, several issues will have to be thoroughly investigated before the number of people using earth-based technologies can reach a critical mass. This special issue will focus on identifying strategies that have been used successfully to address the existing concerns. Papers will address a wide spectrum of topics including but not restricted to 1) defining potential strategies for enhancing the physical and mechanical properties of earth-based technologies for building systems in different parts of the world; 2) Critiquing different experiences with the use of earth-based technologies and the structural challenges that limit their widespread adoption based on selected case studies of earth-based technologies; 3) Identifying strategies for enhancing the durability of earth-based technologies, and ; 4) Addressing quality control concerns in the production and construction processes. Prof. Dr. Charles Kibert Dr. Esther Obonyo Guest Editors{snippet name="submission_info"} http://www.mdpi.com/2071-1050/3/4/596/ The paper is based on findings from research that assesses the potential for enhancing the performance of compressed earth bricks. A set of experiments was carried out to assess the potential for enhancing the bricks’ physical, mechanical and hygrothermal performance through the design of an optimal stabilization strategy. Three different types of bricks were fabricated: soil-cement, soil-cement-lime, and soil-cement-fiber. The different types of bricks did not exhibit significant differences in performances when assessed on the basis of porosity, density, water absorption, and compressive strength. However, upon exposure to elevated moisture and temperature conditions, the soil-cement-fiber bricks had the highest residual strength (87%). The soil-cement and soil-cement-lime bricks had residual strength values of 48.19 and 46.20% respectively. These results suggest that, like any other cement-based material, compressed earth brick properties are affected by hydration-triggered chemical and structural changes occurring in the matrix that would be difficult to isolate using tests that focus on “bulk” changes. The discussion in this paper presents findings from a research effort directed at quantifying the specific changes through an analysis of the microstructure. http://www.mdpi.com/2071-1050/3/4/596/ Wed, 30 Mar 2011 00:00:00 CEST Sustainability 2011-03-30 3 4 Communication 596 604 2071-1050 Optimizing the Physical, Mechanical and Hygrothermal Performance of Compressed Earth Bricks 2011-03-30 doi: 10.3390/su3040596 Esther Obonyo http://www.mdpi.com/2071-1050/3/2/410/ Because of concerns over the construction industry‘s heavy use of cement and the general dissatisfaction with the performance of building envelopes with respect to durability, there is a growing demand for a novel class of ―green‖ binders. Geopolymer binders have re-emerged as binders that can be used as a replacement for Portland cement given their numerous advantages over the latter including lower carbon dioxide emissions, greater chemical and thermal resistance, combined with enhanced mechanical properties at both normal and extreme exposure conditions. The paper focuses on the use of geopolymer binders in building applications. It discusses the various options for starting materials and describes key engineering properties associated with geopolymer compositions that are ideal for structural applications. Specific properties, such as compressive strength, density, pore size distribution, cumulative water absorption, and acid resistance, are comparable to the specifications for structures incorporating conventional binders. This paper presents geopolymer binders, with their three dimensional microstructure, as material for structural elements that can be used to advance the realization of sustainable building systems. http://www.mdpi.com/2071-1050/3/2/410/ Wed, 16 Feb 2011 00:00:00 CET Sustainability 2011-02-16 3 2 Review 410 423 2071-1050 Advancing the Use of Secondary Inputs in Geopolymer Binders for Sustainable Cementitious Composites: A Review 2011-02-16 doi: 10.3390/su3020410 Esther Obonyo Elie Kamseu Uphie C. Melo Cristina Leonelli http://www.mdpi.com/2071-1050/3/1/293/ Lateritic soils are formed in the tropics through weathering processes that favor the formation of iron, aluminum, manganese and titanium oxides. These processes break down silicate minerals into clay minerals such as kaolinite and illite. Iron and aluminum oxides are prominent in lateritic soils, and with the seasonal fluctuation of the water table, these oxides result in the reddish-brown color that is seen in lateritic soils. These soils have served for a long time as major and sub-base materials for the construction of most highways and walls of residential houses in tropical and sub-tropical countries of the world. Civil engineering applications of these lateritic soils are continually being developed with the use of different types of stabilizers. The stabilized soil-based products are as such viewed as environmentally-friendly and low-cost energy materials for sustainable building applications. This work aims at presenting a global view of what has been done in the field of lateritic soil improvement for construction purposes in tropical countries such as Cameroon. This shall be discussed through the presentation of the structure, composition and properties of lateritic soils, the various ways of improving their properties for construction purposes, the properties of products obtained and other prospects. http://www.mdpi.com/2071-1050/3/1/293/ Wed, 19 Jan 2011 00:00:00 CET Sustainability 2011-01-19 3 1 Review 293 305 2071-1050 Laterite Based Stabilized Products for Sustainable Building Applications in Tropical Countries: Review and Prospects for the Case of Cameroon 2011-01-19 doi: 10.3390/su3010293 Patrick N. Lemougna Uphie F. Chinje Melo Elie Kamseu Arlin B. Tchamba http://www.mdpi.com/2071-1050/3/1/69/ Earth building is a sustainable, environmentally friendly and economical method of construction that has been used worldwide for many centuries. For the past three decades, earth has seen a revival as a building material for a modern construction method due to its benefits in terms of low carbon content, low cost and energy involved during construction, as well as the fact that it is a sustainable technology of building. Climate change is influencing precipitation levels and patterns around the world, and as a consequence, flood risk is increasing rapidly. When flooding occurs, earth buildings are exposed to water by submersion, causing an increase in the degree of saturation of the earth structures and therefore a decrease of the suction between particles. This study investigated the effect of cycles of flooding (consecutive events of flooding followed by dry periods) on earth walls. A series of characterization tests were carried out to obtain the physical and mechanical properties of the studied earth material. In a second stage, Flooding Simulation Tests (FST) were performed to explore the earth walls’ response to repeated flooding events. The results obtained for the tested earth wall/samples with reinforced material (straw) reveal hydraulic hysteresis when wall/samples are subject to cycles of wetting and drying. http://www.mdpi.com/2071-1050/3/1/69/ Mon, 27 Dec 2010 00:00:00 CET Sustainability 2010-12-27 3 1 Article 69 81 2071-1050 Flooding Effect on Earth Walls 2010-12-27 doi: 10.3390/su3010069 Gabriela M. Medero Justin H. Kennedy Peter K. Woodward Meysam Banimahd http://www.mdpi.com/2071-1050/2/12/3639/ The discussion in this paper is part of research directed at establishing optimal stabilization strategy for compressed bricks. The deployment context for the use of the compressed bricks was Dar es Salaam (Tanzania) where manually fabricated bricks are increasingly being used in low cost housing units. This discussion specifically focuses on strategies that can be used to counter deterioration due to wind-driven rain erosion. The impact of using cement, lime, fiber and a commercial stabilizing fluid was assessed. Factory-produced bricks were used for benchmarking. The durability of the bricks was assessed using the “modified” Bulletin 5 Spray Test. The different brick specimens were sprayed with water at 2.07 MPa and 4.14 MPa over one-hour time period while measuring the depth of erosion every 15 minutes. Factory-produced bricks hardly eroded at both 2.07 MPa and 4.14 MPa pressure levels. The maximum depth of erosion for Soil-Cement bricks ranged from a maximum of 0.5 mm at 2.07 MPa water pressure to 0.8 mm at 4.14 MPa. The maximum and minimum depths of erosion for Soil-Cement-Lime bricks were 25mm and 17 mm respectively. The inclusion of natural fiber in the bricks resulted in a sharp increase of the erosion depth to a maximum of 40 mm at 2.07 MPa and 55 mm at 4.14 Mpa. As the use of natural fibers and lime enhances some physio-mechanical properties, further research is necessary to determine ways of achieving this goal while maintaining acceptable levels of erosion resistance. http://www.mdpi.com/2071-1050/2/12/3639/ Thu, 25 Nov 2010 00:00:00 CET Sustainability 2010-11-25 2 12 Communication 3639 3649 2071-1050 Durability of Compressed Earth Bricks: Assessing Erosion Resistance Using the Modified Spray Testing 2010-11-25 doi: 10.3390/su2123639 Esther Obonyo Joseph Exelbirt Malarvizhi Baskaran http://www.mdpi.com/2071-1050/2/11/3561/ The research discussed in this paper is a subset of a bigger, NSF funded research project that is directed at investigating the use of sustainable building materials. The deployment context for the research is the hot and humid climate using selected cases from the East African region. The overarching goal for the research is advancing the structural use of earth-based technologies. Significant strides can be made through developing strategies for countering the adverse factors that affect the structural performance of the resulting wall, especially ones related to moisture dynamics. The research was executed in two phases. The first phase was a two-day NSF supported workshop which was held in Tanzania in July 2009. It provided a forum for sharing best practices in earth-based building technologies and developing a research and development roadmap. The priority research areas were broadly classified as optimizing the physio-mechanical properties of earth as a building material and managing socio-cultural impediments. In the second phase of the research, the authors collaborated with researchers from East Africa to conduct experimental work on the optimization of physio-mechanical properties. The specific research issues that have been addressed are: (1) characterizing the chemical reactions that can be linked to deterioration triggered by hygrothermal loads based on the hot and humid context, and; (2) developing a prototype for a simpler, portable, affordable and viable compressed brick production machine. The paper discusses the results from the characterization work that ultimately will be used to design bricks that have specific properties based on an understanding of how different stabilizers affect the hydration process. It also describes a cheaper, portable and more efficient prototype machine that has been developed as part of the follow-up research activities. http://www.mdpi.com/2071-1050/2/11/3561/ Fri, 19 Nov 2010 00:00:00 CET Sustainability 2010-11-19 2 11 Communication 3561 3571 2071-1050 Advancing the Structural Use of Earth-based Bricks: Addressing Key Challenges in the East African Context 2010-11-19 doi: 10.3390/su2113561 Esther Obonyo Derrick Tate Vincent Sika Mang Tia http://www.mdpi.com/2071-1050/2/10/3291/ Raw earth is a construction material unknown to most people. Nowadays, raw-earth constructions are an area of growing interest, both for rescuing the heritage and for a rediscovered environmentally friendly building and eco-sustainability material. However, because raw-earth constructions are a forgotten technique, we find problems of a lack of skilled people at all levels in this area, from designers to masons, as well as problems of how to carry out compatible conservation works on earthen heritage. This paper tries to fill the gap for a peculiar historic earthen building technology, namely cob (or bauge), which is present in Macerata in the center of Italy. Results are presented on regaining possession of the material and constructional aspects and their initial structural resources, and guidelines are given on how to improve the manufacturing process to reuse the cob technique for construction and for how to accurately work on it for a compatible and sustainable conservation. http://www.mdpi.com/2071-1050/2/10/3291/ Thu, 21 Oct 2010 00:00:00 CEST Sustainability 2010-10-21 2 10 Article 3291 3308 2071-1050 Cob Construction in Italy: Some Lessons from the Past 2010-10-21 doi: 10.3390/su2103291 Enrico Quagliarini Alessandro Stazi Erio Pasqualini Evelina Fratalocchi