RESI DUAL GRANI TI C SOI L I MPROVEMENT FOR RAMMED EARTH CONSTRUCTI ON MELHORAMENTO DE SOLOS RESI DUAI S GRANÍ TI COS A UTI LI ZAR NA CONSTRUÇÃO EM TAI PA Cristelo, Nuno; Trás-os-Montes e Alto Douro University, Vila Real, Portugal, ncristel@utad.pt Roma, Ricardo; Trás-os-Montes e Alto Douro University, Vila Real, Portugal, ricardoroma1@hotmail.com Fernandes, Lisete; Trás-os-Montes e Alto Douro University, Vila Real, Portugal, ume@utad.pt Miranda, Tiago; University of Minho, Guimarães, Portugal, tmiranda@civil.uminho.pt Oliveira, Daniel; University of Minho, Guimarães, Portugal, danvco@civil.uminho.pt Silva, Rui; University of Minho, Guimarães, Portugal, ruisilva@civil.uminho.pt ABSTRACT This paper describes the research developed to evaluate the performance of stabilised residual granitic soil from the north region of Portugal. It is part of a research project designed to investigate the possibility of using this soil for rammed earth construction. Since its reduced plasticity makes the use of lime less effective, and the increasing environmental concerns with cement production can no longer be ignored, the study was focused on binders made from alkaline activation of low calcium fly ash. Therefore, the aim of this work was to determine, through a parametric analysis using laboratory tests, the optimum fly ash – based alkaline activated binder for improving granitic soil, in terms of mechanical strength. Identification of the key parameters allowed the characterisation of the most effective mixtures, which will be later used in the construction of large rammed earth wall panels that will be tested according to proper specifications. RESUMO O presente artigo descreve parte do trabalho de investigação realizado com o intuito de avaliar o desempenho de solos residuais graníticos da região Norte, depois de estabilizados. O referido trabalho de investigação insere-se num projeto mais abrangente destinado à aplicação deste tipo de solos em construções em terra, concretamente na construção em taipa. Uma vez que a fraca atividade destes materiais com fração argilosa reduzida e à base de caulinite limita a eficácia da cal no seu melhoramento, e tendo em conta as crescentes preocupações ambientais relacionadas com a produção de cimento, foi utilizado um agente estabilizante obtido através da ativação alcalina de cinzas volantes. O objetivo consistiu assim na determinação da mistura mais vantajosa, em termos de resistência mecânica, sendo que os parâmetros agora determinados serão utilizados na construção e análise de painéis em taipa. 1 - I NTRODUCTI ON Soil is certainly one of the most ancient building materials. The most common earth construction techniques are rammed-earth and adobe masonry (Houben and Guillaud, 1994). Adobes are bricks prepared with moist earth (to which straw is added sometimes) by simply moulding it in a wooden frame and drying it out in the sun. Then the masonry is prepared by ‘gluing’ the adobes with earth mortar. A rammed earth wall is made by compacting thin layers of packed earth using a rammer. The development of modern construction materials gradually made the application of earth as a construction material less and less attractive, which had more to do with social than with technical disadvantages. Inclusively, this trend had a significant influence on the lack of production of specific regulation codes. However, the recent growing concern with a meaningful and sustainable development is a serious motivation for seeking environmentally friendly construction materials. Also, a curious change of mentality occurred, since what was until recently a social embarrassment is now seen as a very modern material, capable of producing comfortable and visually impressive buildings. Rammed earth walls are relatively thick (0.5 to 0.9 m), and the dwellings are usually one or two stories high, in order to limit the compression stresses. That is because these walls have a reduced compressive strength when compared with other building materials, which currently causes serious limitations in terms of architectural and structural design. One of the major techniques used to overcome the problems created by under-performing soils is the mixing with a cementitious binder. Usually these binders are cement and/or lime, which glue the soil particles together through chemical reactions. In the case of cement, the reactions are mainly hydraulic, while with lime they are pozzolanic. This means that cement needs only water to react and increase in strength; while lime needs water and a pozzolanic material, like soil. Both binders share the fact that their reactions with water depend largely on their specific surface. Moreover, although the type of