Mechanical properties and internal mechanisms characterization of calcined clay geopolymer concrete

  • Aminu Bature Shinkafi

    Student thesis: Doctoral ThesisDoctor of Philosophy


    Calcined clay is presently receiving attention as a promising aluminosilicate source that has the potential of extending the application of geopolymers because of its global abundance and low-embodied energy. However, rheological, mechanical and durability performances of calcined clay based geopolymers depend substantially on the calcination process, mineralogy of the clay, type and proportion of chemical activator, etc. Until recently, lateritic clay was considered to be an unsuitable precursor for geopolymers due to its large iron composition. Specifically, the limited research and development interest in the past into this globally available geological material, was due to the reported harmful action of some ferrous compounds (Fe++) that blocked the development of the geopolymeric reaction. Other reasons are the dubious role of iron oxide goethite (FeO(OH)) reported in the scientific literature, and the limitation of some analytical techniques (such as Nuclear Magnetic Resonance spectroscopy (NMR)) in analysing the geopolymeric molecular structures caused by the large iron composition of the lateritic clay. It is against this backdrop that this research focused on studying the technical viability of utilizing flash calcined lateritic clay to produce sealed cured geopolymer concrete. This was achieved by determining the peak strength formulation based on a mass and molar oxide compositional ratios range that produced structural grade concrete using four types of liquid activators. Specifically, the effect of variation in selected mix proportion parameters (activator dosage, paste volume, molar oxide composition and free water content) on performance of the calcined clay geopolymers was studied. The study also involved benchmarking the behaviour of the calcined clay geopolymer mortar against that of alkali activated slag and conventional Portland cement mortars, to determine the similarities and differences between these binder systems. This data laid the foundations for the development of the mix design for the low purity kaolin geopolymer concrete. The study further explored the viability of using the calcined lateritic clay as the main pozzolan for a ternary, semi-dry hydraulically bounded mixture to substitute the scarce GGBS used for that application.

    The rheological behaviour and mechanical properties of the calcined clay based geopolymer concretes were studied. Other properties of the calcined clay geopolymer concrete that had been studied were: setting times, consistency, chloride permeability, and freeze-thaw resistance; as well as internal mechanism analysis that included X-Ray Diffraction (XRD), Scan Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR). The results showed that structural grade concrete obtained by activating the calcined clay with 45% potassium silicate solution achieved a peak strength of 40 MPa after three days and had the best workability. The results further showed that the binding phase of the peak strength concrete was poly ferro-sialate (-Fe-Si-O-Al), and sealed curing was found to enhance the performance of the calcined lateritic clay based geopolymer concrete by preventing atmospheric carbonation. Likewise, the XRD revealed albite and sanidine mineral frameworks for the geopolymer concretes. These are the geopolymeric frameworks that have Si:Al of 3 and are similar to Na-Poly(sialate-disiloxo) and K-Poly(sialate-disiloxo) respectively. Furthermore, the ternary binder composition – Calcined Clay (CC 40%) / Basic Oxide Slag (BOS 50%) / By-Pass Dust (BPD 10%) activated with 15% water content satisfied the strength requirement for Hydraulic Road Binder HRB10 (the 28 days compressive strength of standardized mortars higher than 10 MPa). Additionally, the geopolymer concrete also exhibited excellent freeze-thaw resistance: such that the mass and compressive strength of the samples were greater than 70% of the 28 days old specimens after 300 freezing and defrosting cycles in an aqueous environment.
    Date of AwardOct 2020
    Original languageEnglish
    Awarding Institution
    • Coventry University
    SupervisorMark Tyrer (Supervisor), Morteza Khorami (Supervisor) & Eshmaiel Ganjian (Supervisor)


    • Calcined clay
    • geopolymer
    • mechanical properties
    • freeze-thaw resistance
    • microstructure
    • phase characterization
    • FTIR spectroscopy
    • life cycle analysis (LCA)

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