AUTHOR=Bo Fu , Zhenyun Cheng 

TITLE=Effect of Cr6+ on the Properties of Alkali-Activated Slag Cement

JOURNAL=Frontiers in Materials

VOLUME=8

YEAR=2021

URL=https://www.frontiersin.org/journals/materials/articles/10.3389/fmats.2021.754463

DOI=10.3389/fmats.2021.754463

ISSN=2296-8016

ABSTRACT=<p>In order to investigate the effect of Cr<sup>6+</sup> on the properties of alkali-activated slag cement (AAS), the effects of added dosage of Na<sub>2</sub>Cr<sub>2</sub>O<sub>4</sub> on the setting time and compressive strength of AAS were measured. The leaching concentration of Cr<sup>6+</sup> from AAS cement stone was measured using dual-beam UV-visible spectrophotometry. The effect of Na<sub>2</sub>Cr<sub>2</sub>O<sub>4</sub> on the hydration kinetics of AAS cement was monitored by microcalorimetry and the corresponding kinetic parameters were analyzed. The pore solution from AAS was collected and analyzed using the high pressure press method. The effects of Na<sub>2</sub>Cr<sub>2</sub>O<sub>4</sub> on the hydration products of AAS cement were observed and compared using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The experimental results showed that the AAS hydration process was markedly affected by Na<sub>2</sub>Cr<sub>2</sub>O<sub>4</sub> dosage. The setting time of AAS pastes was increased and the compressive strength of cement stones was reduced with increasing dosage of Na<sub>2</sub>Cr<sub>2</sub>O<sub>4</sub>. With the development of AAS hydration, the leaching concentration of Na<sub>2</sub>Cr<sub>2</sub>O<sub>4</sub> gradually decreased. Na<sub>2</sub>Cr<sub>2</sub>O<sub>4</sub> did not affect the dissolution of slag particles, but impeded the formation of C-S-H gel. The Cr<sup>6+</sup> was immobilized chemically in the form of needle-like CaCrO<sub>4</sub> particles formed by the chemical reaction between Na<sub>2</sub>Cr<sub>2</sub>O<sub>4</sub> and Ca<sup>2+</sup> leaching from the slag.</p>