Abstract
The effect of ZnO has already been studied for Portland cement, but the study of its impact on hybrid pastes is scarce. Thus, in this investigation, the influence of ZnO addition on hydration, compressive strength, microstructure, and structure of hybrid pastes is presented. The analyses were made by setting time tests, compressive strength tests, X-ray diffraction, Fourier-transform infrared spectroscopy, thermogravimetric analysis with differential scanning calorimetry, and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. The results indicate that the setting time of the cements was delayed up to 39 min with additions of 3 wt% ZnO. Alternatively, the higher values of compressive strength were observed when 0.5 wt% ZnO was added to the cements for all curing days. In addition, no important differences in the microstructure of samples with different additions of ZnO were observed after 28 days of curing. It is expected that the use of ZnO contributes to the delay of the setting time and the increase of the compressive strength without negatively modifying the microstructure of hybrid pastes.
Highlights
Portland cement (PC) has been effectively replaced by supplementary cementitious materials (SCM), such as slag, fly ash, silica fume, and natural or artificial pozzolans such as metakaolin, leading to significant improvements of cement properties mainly in mechanical and durability properties [1,2,3,4,5,6,7,8,9]
The results indicated that the hybrid cements have similar mechanical properties than Ordinary Portland Cement (OPC), resulting in a dense matrix of hydration products similar to those generated by cements and geopolymers [36]
The above confirms that the addition of sodium silicate inhibits the formation of OPC hydration products, as could be observed in the results obtained by X-ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR), where the phases and vibrations of the bonds associated with the anhydrous compounds of the OPC were observed, and the phases and vibrations of the OH bonds associated with calcium hydroxide (CH) were not identified
Summary
Portland cement (PC) has been effectively replaced by supplementary cementitious materials (SCM), such as slag, fly ash, silica fume, and natural or artificial pozzolans such as metakaolin, leading to significant improvements of cement properties mainly in mechanical and durability properties [1,2,3,4,5,6,7,8,9]. The combination of traditional alkali activation precursors with PC is commonly referred to as hybrid alkali cements [26,27] This type of cements combines some of the advantages of traditional PC, such as setting at ambient temperature with the development of high early-age mechanical strength and low heat of hydration by the use of alkaline activation of blast furnace slag and fly ash. These materials may pose problems of availability and uniformity, which can be resolved with the use of clays in their place [28,29]. The results are explained in terms of changes in important variables, such as setting time, compressive strength, and microstructural and structural evolution
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