Pozzolana characterisation and properties of mortar containing calcined marine clay

Abstract

The production of cement is highly associated with the emission of carbon dioxide into the atmosphere which has generally lead to the use of pozzolanic material to partially replace cement in construction industries with the motive of reducing the emission. The use of high-grade kaolinite as pozzolanic materials in construction industries has long been established. However, the high cost and depletion of high-grade material has led to the use of low-grade kaolinite material in cement production. This research aims to explore the use of a low-grade kaoline – marine clay, as a potential pozzolanic material through a series of experimental studies. These studies are done to assess the characteristics of marine clay; examine its pozzolanic reactivity and the effect of calcination: this study also investigates the properties of mortar containing the calcined marine clay. The characterisation process was done based on its index properties, which included its natural moisture content, liquid limit, plastic limit, and plasticity index. The microstructure was determined via the particle size analysis (PSA), the x-ray fluorescence analysis (XRF), the thermogravimetric analysis (TGA), the differential thermal analysis (DTA), and the x-ray diffraction (XRD) test. The reactivity of marine clay was studied through its conductivity. The effect of calcination ranging from 600 - 1000°C on marine clay was done to examine the response of its embedded chloride and sulphate content and loss on ignition. Finally, the properties of mortar containing calcined marine clay were investigated via the compressive strength, strength activity index, and microstructure. The characterization result indicated that the marine clay had fulfilled the basic properties of a pozzolanic material - where it belongs to the kaoline group with over 40% kaoline content. The conductivity test has indicated that marine clay that was calcined at 700°C for 1-hour yielded the highest pozzolanic reactivity, measured based on the loss in conductivity due to the formation of C-S-H. A decrease in compressive strength was recorded with the replacement level increased from 5% to 30%; the control specimen consistently exhibited the highest compressive strength. This is attributed to the dilution effect and the ease at which marine clay absorbs water from the mix to yield a more porous blend. Nevertheless, marine clay has achieved the strength activity index requirement for pozzolanic materials. Lastly, the scanning electron microscopy, XRD, TGA, and DTA results had conclusively justified the use of marine clay as a potential pozzolanic material, which was proven through the consumption of portlandite for C-S-H formation. As such, even though marine clay has a bad reputation due to its instability and presence of undesirable organic material, it was still thermally activated to produce a good pozzolana. The results of this study are expected to provide valuable insights into the existing literature on the application of low-grade kaoline as a potential pozzolanic material.