MECHANICAL PROPERTIES AND DURABILITY OF GEOPOLYMER STABILIZATED EARTH BLOCKS Soênia Marques Timóteo de Sousa1, Carlos Maviael de Carvalho2, Sandro Marden Torres3, Normando Perazzo Barbosa4, Kelly Cristiane Gomes5, Khosrow Ghavami6 1 Instituto Federal de Educação Tecnológica, Juazeiro do Norte, Ceará, Brasil
[email protected] 2,3,4,5 Universidade Federal da Paraíba, João Pessoa, Paraíba, Brasil
[email protected],
[email protected] [email protected],
[email protected] 6 Pontifícia Universidade Católica do Rio de Janeiro, Brasil
[email protected] … Tema6: Researchon Materials and Technologies for Contemporary Architecture and Conservation Key words: compressed earth blocks, geopolymers, durability, earth stabilization.
Abstract Stabilization is a common practice to improve the properties of earth used in the different ways in the field of construction. Nowadays, the most utilized products to stabilize the earth are lime, Portland cement and bituminous emulsions. In the last decades, geopolímers appeared as an alternative binder, being used also to produce concrete. Geopolimers are synthetic material made by alkaline activation of solid particles rich in silica and alumina. For good activation, it is necessary that these materials are in the amorphous form, as in metakaolin, slag and fly-ash. The earth clay fraction is composed by aluminum-silicates. So both the desirable materials are available, even if the great part of them is in the crystalline form. This work presents the first results about compressed earth stabilized by geopolymers. The geopolymeric binder was composed by metakaolin activated by sodium silicate and sodium hydroxide. Three percentages of geopolymers were used. Earth compressed prism of 4 cm x 4 cm x 16 cm were produced, using a pressure of 2 MPa, that is almost the same used in the production of earth blocks by manual presses. Tensile and compression strength were obtained. Tests of durability were also made. Results show the potentiality of this binder: using 6% of the geopolymer the compressed earth attaints appropriate properties for compressed earth blocks. Using higher percentage, compression strength can reach more than 15 MPa.
1.INTRODUCTION While technological development has reached a high level during XXI century, it also ended up producing a very high environmental cost: aggression against biodiversity, air, soil and water pollution, deforestation, burning, extinction of plant, animal and mineral reserves. Within the policy of sustainability, various studies on energy-efficient materials, which produce a reduced amount of air pollution and preserve the mineral and plant resources, are in progress. Third of humanity lives in houses made with earth. In almost all regions of warm and dry climate, the earth has been the most widely used building material. The demand for housing in developing countries is very large. Offers of industrial materials such as cement, clay bricks, concrete, and financial capabilities can´t take account these demands immediately. Surge as a viable alternative to meet the demand for housing, the use of local materials and techniques, like the earth. The earth is the material of construction offers the following advantages: regulates the ambient humidity, acoustically efficient, thermal comfort is higher, demolished material can be recycled for construction of new buildings; allows a construction site that does not generate debris, doesn't produce pollution of environmental, it doesn’t need to be calcined,
doesn´t use energy and materials such as wood and fossil fuels, avoid deforestation, land can be removed, in local , at no cost, or purchased in local approximates at low cost. There are several techniques of Earth Constructions buildings, like, adobe, rammed earth blocks and compacted.
For each type of soil you need a specific type of binder stabilization. Sandy soils can be stabilized with cement. Clay soils are used with cement contents less than 6%, and recommended the use of lime as a stabilizer. A well-graded soil, 4% cement has lead to good results for mechanical strength. Other blocks were produced with asphalt emulsion and fibers. The content of 2% emulsion gives bricks made from soil-fiber acquires resistance to water. Fiber percentages above 2%, it makes difficult to mix with clay soils. 6% lime improves the durability of bricks made with clay soils (Sousa et al, 2000, p.423). In Brazil, PUC-Rio, studies were made of materials with less environmental impact as bamboo, vegetable fibers as reinforcement in cementious matrices (Ghavami, 2001 p. 445-461), and use of these materials in low-cost housing (Ghavami e Toledo Filho pp.1-19). At the Federal University of Paraíba (UFPB), raw earth was studied in the form of compressed blocks and adobe bricks, (Sousa et al., 2000, pp. 413-424) and of wall panels with these blocks (Sousa et al., 1996). The experience of implementation of construction technology of pressed blocks of raw earth, which was widely accepted by the poor community in the state of Paraiba, has shown the feasibility of using this material (Barbosa et al, 1996 pp. 263-276).
Another material that is being studied in Brazil, since the late of the 90’s, is the geopolymer. The first studies addressed the geopolymers, geopolymer mortars and cements. At UFPB, the study was initiated with the geopolymer work exploring sources of aluminosilicates from Paraíba (Gomes, 2008, 154p.), other studies on this subject have been conducted. Geopolymers are employed in the production of fire-resistant components, building structures and the immobilisation of toxic and / or radioactive wastes. Their use in concrete has been introduced with success in the industry. They have good thermal stability and are easy to handle. This material can also be used for environmentally friendly building homes,it produces no pollution because it does not require calcination, acquires high resistance to low temperature, around 45˚C, which corresponds to the sintering temperature of the material to solar energy. Thus, one can reduce energy consumption and promote environmental sustainability, as compared with Portland cement, geopolymer is considered less aggressive to the environment, including making use of agro-industrial waste. The state of Paraiba has mineral resources to provide for the formation of aluminosilicatos geopolymers. Among them, bentonite, kaolin, clays, soils and lateritic concretions are preeminent. 2.MATERIALS AND METHODS The materials used in this study were as follows:Kaolin, Sodium silicate (Na2OSiO3), Sodium hydroxide (NaOH), commercial and Portland Cement CP II – F-32, commercial. The characterization was performed at the Laboratory of Structures and Materials Testing (LABEME) and Rapid Solidification Laboratory (LSR). 2.1 Soil The characterization of the soil in its natural state is indicated on the grading curve of Fig.1 and Tab.1.
Exceeding percentage (%)
100 90 80 70 60 50 40 30 20 10 0 0,001
0,010
0,100
1,000
10,000
100,000
Grain diameter (mm)
Fig.1 - Granulometric curve
In the grading curve, it is observed that the soil is not completely within the particle size range recommended by CRATerre-EAG(Le Centre International Construction La TerreEcole d'Architecturede Grenoble), for the manufacture of pressed blocks (Rigassi, 1995 pp.22 ). Table 1 - Characteristics of the soil Granulometryof natural soil (%) Gravelabove4.8mm Sand(50 µmto 4.8mm) Silt(5µm to50 µm) Clay (
