Abstract
Hybrid cement has become one of the most viable options in the reduction of CO2 emissions to the environment that are generated by the cement industry. This could be explained by the reduction of the content of clinker in the final mixture and substitution of the remaining percentage with supplementary cementitious materials with the help of an alkaline activation. Following that, properties that are provided by an Ordinary Portland Cement and of a geopolymer are mixed in this type of hybrid material and could be achieved at room temperature. Thereafter, the main objective of this research was to synthesize hybrid cements reducing the clinker content of Portland Cement up to 20% and use metakaolin and fly ash as supplementary cementitious materials in different proportions. The mixtures were alkaline activated with a mixture of sodium silicate and sodium hydroxide, calculating the amounts according to the percentage of Na2O that is present in each of the activators. The samples were then characterized using Compressive strength, X-ray diffraction, Fourier Transform Infrared Spectroscopy, and Scanning Electron Microscopy with energy-dispersive X-ray spectroscopy. The results indicated that the hybrid cements have similar mechanical properties than an Ordinary Portland Cement, and they resulted in a dense matrix of hydration products similar to those that are generated by cements and geopolymers.
Highlights
The cement industry is currently facing challenges that are related to the improvement of its manufacturing processes, and to achieving the reduction of the environmental impact generated by the manufacture of Ordinary Portland Cement (OPC)
The precursors used in this investigation were: (a) fly ash from a thermoelectric plant in Nava, Coahuila, Mexico, which was used in a particle size under 75 μm, (b) metakaolin, which was calcined in a kiln at 800 ◦ C for 8 h to achieve the de-hydroxylation of the material and, achieve the disorder between the layers of silica and alumina necessary to increase the reactivity of the material, and (c) clinker from an OPC (Cemex, Monterrey, Mexico), which was ground to a particle size under 75 μm
The results were estimated as the average of four samples for each mixing system, the standard deviation showed a maximum of 2 MPa
Summary
The cement industry is currently facing challenges that are related to the improvement of its manufacturing processes, and to achieving the reduction of the environmental impact generated by the manufacture of Ordinary Portland Cement (OPC) In this process, large emissions of several greenhouse gases into the environment are involved, where CO2 is the most important, and is the main responsible for global warming. It should be noted that eliminating CO2 emissions into the environment from the decomposition of limestone is mainly impossible, since this process is necessary for the manufacture of OPC clinker (CK) These emissions can be reduced while using waste materials as raw material for the clinker or by using final substitute materials for OPC.
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