Abstract
Calcined Hwangtoh (HT) clay is a very promising supplementary cementitious material (SCM). In this work, the development of the mechanical properties and microstructures of HT-blended cement paste was studied after substituting the binder with HT powder calcined at 800 °C. The water-to-binder (w/b) ratios of the paste used were 0.2 and 0.5, and the quantities of HT powder added to the mixture were 0, 10, and 20%. The compressive strength test indicates that the addition of the HT powder increases the compressive strength of the paste after seven days of curing, and the highest compressive strength is obtained with the 10% HT substitution, regardless of whether the w/b ratio is 0.5 or 0.2. X-ray fluorescence (XRF), X-ray diffraction (XRD), inductively coupled plasma mass spectrometry (ICP-MS), isothermal calorimetry, thermogravimetric analysis (TGA), and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) analysis show that the HT powder not only has a physical effect (i.e., nucleation effect and dilution effect) on cement hydration but also has a chemical effect (i.e., chemical reaction of HT). The results of scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) analysis show that the paste has more ettringite during the early stage, and the microstructure is refined after the addition of the HT powder. In addition, the relationships between chemically bound water, hydration heat, and compressive strength are presented.
Highlights
Cement is currently the most manufactured product on earth and has made tremendous contributions to human development
According to a report by Malhotra [1], the annual global greenhouse gas (GHG) emissions produced by ordinary Portland cement (OPC) are estimated to be close to
In order to reduce the amount of cement used, supplementary cementitious materials (SCMs) are attracting increasing attention
Summary
Cement is currently the most manufactured product on earth and has made tremendous contributions to human development. There is a global increase in the use of SCMs, such as fly ash, ground granulated blast furnace slag, silica fume, and metakaolin This is because concrete mixtures can be rendered more economical and Materials 2019, 12, 458; doi:10.3390/ma12030458 www.mdpi.com/journal/materials. Materials 2019, 12, 458 environmentally friendly by using SCMs, which can reduce the permeability, increase the strength, or improve other properties of concrete through filler effects and pozzolanic reactions [4,5,6]. The report mentions that the partial replacement of clinker with calcined clay could effectively reduce the environmental pollution caused by the manufacture of cement. In their study [15], when HT was calcined at 800 ◦ C and used as a substitute for part of the cement clinker, the mechanical properties were significantly improved compared with the OPC samples.
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