Publication detail

The thermal analysis of zinc oxide‑contaminated Portland cement blended with thiocyanates and determination of their effect on hydration and properties

MATĚJKA, L. ŠILER, P. NOVOTNÝ, R. ŠVEC, J. MÁSILKO, J. KOPLÍK, J. ŠOUKAL, F.

Original Title

The thermal analysis of zinc oxide‑contaminated Portland cement blended with thiocyanates and determination of their effect on hydration and properties

Type

journal article in Web of Science

Language

English

Original Abstract

The contamination of cement binders with zinc represents a significant problem due to the negative effects on cement hydration. Zinc compounds cause a drastic increase in setting time due to prolonging the induction period. The currently accepted mechanism behind this effect is the formation of Ca(Zn(OH)3 ) 2 ·2 H 2 O hydrates on the surface of cement grains that deplete Ca 2+ ions from the pore solution and creates a diffusion barrier. Hydration accelerators are commonly employed in the concrete industry to counter long setting time caused by low temperature and contamination by heavy metals. These compounds influence both hydration kinetics and composition of hydration products. The influence of various compounds on the mechanism of cement hydration can be studied using calorimetric methods such as isoperibolic and isothermal calorimetry. The hydration of the material was stopped, and the properties of hydrated cement pastes were studied using differential thermal analysis, X-ray diffraction and scanning electron microscopy. Some setting accelerators have been found to significantly decrease setting time of zinc-contaminated cement. Out of the most used compounds in commercial accelerators, the efficiency of thiocyanates is yet to be determined. The results show that thiocyanates induce a visible change in hydration mechanism of cement to various degrees depending on concentration and on the presence of the specific cation. Alkali thiocyanates drastically retard the hydration of zinc-contaminated OPC. With further retarded hydration of cement, the mechanical properties were negatively impacted. Calcium thiocyanate on the other hand effectively accelerates setting and positively impacts compressive strength at low doses. Main difference between the influence of alkali and calcium thiocyanates on setting is the change in ettringite content. Alkali salt promotes AFm phases at the expense of ettringite content while calcium salt promotes formation of ettringite at early stages of cement hydration.

Keywords

Cement · Zinc · Hydration · Retardation · Accelerators · Thermal analysis

Authors

MATĚJKA, L.; ŠILER, P.; NOVOTNÝ, R.; ŠVEC, J.; MÁSILKO, J.; KOPLÍK, J.; ŠOUKAL, F.

Released

31. 10. 2022

Publisher

Springer

Location

Maďarsko

ISBN

1588-2926

Periodical

Journal of Thermal Analysis and Calorimetry

Number

2022-11-13

State

Hungary

Pages count

29

URL

https://link.springer.com/content/pdf/10.1007/s10973-022-11666-0.pdf

BibTex

@article{BUT179816,
  author="Lukáš {Matějka} and Pavel {Šiler} and Radoslav {Novotný} and Jiří {Švec} and Jiří {Másilko} and Jan {Koplík} and František {Šoukal}",
  title="The thermal analysis of zinc oxide‑contaminated Portland cement
blended with thiocyanates and determination of their effect
on hydration and properties",
  journal="Journal of Thermal Analysis and Calorimetry",
  year="2022",
  number="2022-11-13",
  pages="29",
  doi="10.1007/s10973-022-11666-0",
  issn="1588-2926",
  url="https://link.springer.com/content/pdf/10.1007/s10973-022-11666-0.pdf"
}