A comparative study of natural Tunisian clay types in the formulation of compacted earth blocks

https://doi.org/10.1016/j.jafrearsci.2019.103620Get rights and content

Highlights

  • Tunisian clays from Nabeul, Zeramdine and Gafsa were investigated.

  • An ecofriendly and optimal CEB formulation was sought.

  • Mixtures preparation influences physical and mechanical properties of CEB.

  • Lime use as a binder improves mechanical properties of CEB.

  • Correlation could be established between porosity, shrinkage, packing density and strength of the CEB.

Abstract

This study investigates the physico-chemical, mineralogical and thermal characteristics of three natural Tunisian clays collected from Gafsa (A1), Zeramdine (A2) and Nabeul (A3). The aim was to promote an appropriate formulation of materials and to obtain optimal compacted earth blocks (CEB). Results of mineralogical analysis of clays revealed the dominance of kaolinite (>13.58%), illite (>25.7%), quartz (>18%) and a minor fraction of smectite phases. Chemical analysis of the clays major elements showed a SiO2 content exceeding 50% and a percentage of Al2O3 higher than 18%. Particle size distribution showed that clay fractions varied from 10 to 20%. Plasticity index defined a plastic character while the values of specific surface area were around 60 m2/g. This discrepancy has an effect on the behavior of these clays in CEB, notably their mechanical properties. From this characterization, it appears that all the sampled clays are suitable as raw material for CEB application. The prepared CEB formulations varied according to compaction energy and binder dosages. In this work, lime served as a binder at different rates (4, 6, 8 and 10%) to ameliorate the quality of CEB. Unconfined Compressive Strength values were determined by Static method test. Then bulk density, shrinkage and porosity values of samples were determined. Compressive strength could reach 7 MPa with lime supplementation in sample A1. The static compaction onto the sand-clay mixture achieved a value of density superior to 2 g cm−3 with lime supplementation in sample A1. Overall, the Gafsa clay was the most suitable for CEB preparation. Also, lime improved the compressive strength of the matrix, in addition to its ecological merits.

Introduction

The production process of fired clay bricks has a considerable negative impact on the environment (Oti and Kinutihia, 2012). This implies significant production costs, due to fuel prices and huge CO2 emissions in the nature that contribute to increased greenhouse effects which leads to global warming (Muntohar, 2011). Therefore, the need to produce low-cost and eco-friendly construction materials has become a major concern (Gouny et al., 2013; El Fgaier et al., 2016). Developing new sustainable building materials is a prime consideration in the preservation of the environment (El Fgaier et al., 2016; Gouny et al., 2013). In fact, the harmful impact of building materials on the environment must be reduced throughout their life cycle. New technologies based on optimizing the choice of raw materials play an important role in this approach by using ecological, local and renewable materials. In particular, earth is considered the oldest source of building materials with low acquisition cost. A more ecological alternative to the common fired clay brick is the compressed earth block (CEB) (Oti and Kinutihia, 2012). Interestingly, this building material has attracted much interest and several attempts to optimize its formulation have been made. Morton indicated that CEB could win more than 80% of energy compared with fired clay brick (Morton, 2005).

Tunisia is endowed with an abundance and diversity of geological clay minerals. In this context, some Tunisian clays were the objective of this study. Materials from three Tunisian sites were characterized and tested for CEB formulation at different clay/sand proportions. Also, lime was used as a binder and the mechanical strength of the different matrices were compared.

Section snippets

Materials: geological setting

Three different clay samples were used in this study. The first sample was collected from Djebel Bouamrane “Gafsa” located in Southwest of Tunisia. This clay is red and belongs to the Turonian age and Beida formation. The second clay was obtained from Zeramdine quarry (Jemmel) “Monastir” in the Northeast of Tunisia. It is a white clay of Serravallien-Totonian age and Oum Douil formation. The third one was brought from Djebel Abderrahmane “Nabeul” (situated in Northeast of the country). This

Materials identification and characterization

Samples were characterized by several chemico-physical methods, which allowed us to classify and compare clay characteristics and behaviors. Grain size analysis determines the particle distribution of samples and allows to classify the materials according to their constituent parts (clay, sand, gravel). This test was performed to standard 13 320-1 and using Coulter LS 13 320 Laser device and Fraunhofer 780d optical model. The detection particles size was range from 0.375 μm to 2 mm.

Casagrande

Particle size distribution data

Particle size distribution presents one of the main criteria in manufacturing suitable earth blocks. Fig. 2 a shows the particle size distribution of natural clay, sand as well as the recommendation range deduced from the CEB norms NF XP P13-901 (AFNOR NF XP P13-901, 2001).

Granulometry curve of natural clay was beyond the range because they were much finer. Thus, sand 0/2 mm was added. Data obtained showed that the new granulometry curve of mixture was well positioned on the recommendation

Conclusion

In this paper, three clays sampled from different geographical locations (Djebel Bouamrane Gafsa, Zeramdine quarry and Djebel Abderahmanne Nabeul) were studied. Mineralogical analysis of samples indicated the presence of illite and kaolinite as dominant mineral phases associated with smectite and quartz. The behaviors of clay bricks depended on the nature, type and the amounts of various minerals present and physico-chemical analysis.

Results for manufacturing bricks and Unconfined Compressive

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