WUHAN UNIVERSITY OF SCIENCE AND TECHNOLOGY

Influence of lead nitrate on the early
hydration of high alumina cement
that contains spinel

1 XRD of the high alumina cement (HAC) All authors
1 XRD of the high alumina cement (HAC)
All authors
2 Effect of Pb(NO3)2 on the hydration of cement:(a) rate of heat of hydration over 48 h(b) cumulative heat of hydration over 48 h
2 Effect of Pb(NO3)2 on the hydration of cement:(a) rate of heat of
hydration over 48 h(b) cumulative heat of hydration over 48 h
3 XRD patterns without Pb(NO3)2 (P0) and with 0.5% Pb(NO3)2 (P1) at different hydration times: (a) 1 h(b) 6 h(c) 24 h
3 XRD patterns without Pb(NO3)2 (P0) and with 0.5% Pb(NO3)2 (P1) at different hydration times: (a) 1 h(b) 6 h(c) 24 h
4 The pH of the solution without Pb(NO3)2 (P0) and with 0.5% Pb(NO3)2 (P1) with a liquid-solid ratio of 10:1 at different hydration times
4 The pH of the solution without Pb(NO3)2 (P0) and with 0.5% Pb(NO3)2 (P1) with a liquid-solid ratio of 10:1 at different hydration times
5 DTG and TG curves without Pb(NO3)2 (P0) and with 0.5% Pb(NO3)2 (P1) for 24 h at 20°C
5 DTG and TG curves without Pb(NO3)2 (P0) and with 0.5% Pb(NO3)2 (P1) for 24 h at 20°C
6 SEM and EDS micrographs of samples without Pb(NO3)2 (P0) and with 0.5% Pb(NO3)2 (P1): (a) SEM image of P0 at 24 h(b) SEM image of P1 at 24 h(c) EDS image of P1 at 24 h(d) Element analysis diagram of P1 at 24 h
6 SEM and EDS micrographs of samples without Pb(NO3)2 (P0) and with 0.5% Pb(NO3)2 (P1): (a) SEM image of P0 at 24 h(b) SEM image of P1 at 24 h(c) EDS image of P1 at 24 h(d) Element analysis diagram of P1 at 24 h

The effect of 0.5 wt.% lead nitrate on the early hydration of high alumina cement (HAC) that contains spinel was examined by isothermal calorimetry, XRD, TG-DSC and SEM. Lead nitrate affects the hydration and both the initial setting time and final setting time were extended. Lead nitrate also reduced and delayed the maximum rate peak of hydration of HAC. The pH value of HAC paste was significantly lower in the early stages when compared with the addition of lead nitrate. It was found that an NO3-hydrate phase (Ca4Al2(NO3)2(OH)12 ∙ 4H2O, NO3-AFm) was formed at 6 h. Although the characteristic value of the hydrated calcium aluminate (CAH10) was decreased, the characteristic values of the hydrated dicalcium aluminate (C2AH8) and tricalcium aluminate (C3AH6) were increased significantly. That means that lead nitrate promotes the early generation of NO3-AFm in HAC, which will delay early hydration. However, after 18 h lead nitrate promotes C2AH8 or transformation of the metastable needle-shaped or hexagonal CAH10 into stable cubic C3AH6.

1 Introduction

The heavy metal Pb has a strong tendency to migration and enrichment and is non-biodegradable. It can cause chronic poisoning, carcinogenicity, deformity and mutagenic effects [1]. The solidification/stabilization (S/S) [2-4] procedure was adopted to deal with heavy metal wastes before landfill disposal to reduce the seepage of heavy metals into the environment.

Cement materials, such as ordinary Portland cement (OPC), calcium aluminate cement (CAC), calcium sulfate, etc., are the most adaptable binders currently used for the S/S [5-9]. OPC can reduce the leaching of heavy metals,...

Find out more in

ZKG 12/2018

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ZKG 12/2018

Ressort:  Materials
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TEXT Jingran Wang1,2, Jinhua Zhang1, Xuexin Liu1
1The State Key Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology, Wuhan/China
2The State Key Laboratory of Silicate Materials for Architecture, Wuhan University of Technology, Wuhan/China

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