Effects of Sodium Hexametaphosphate Addition on the Dispersion and Hydration of Pure Calcium Aluminate Cement.

Benjun Cheng,Can Yao,Haijun Zhang,Xueyin Liu,Shaowei Zhang,Jian Xiong

doi:10.3390/ma13225229

Abstract

The effects of sodium hexametaphosphate (SHMP) addition on the dispersion and hydration of calcium aluminate cement were investigated, and the relevant mechanisms discussed. The content of SHMP and the adsorption capacity of SHMP on the surface of cement particles were estimated using plasma adsorption spectroscopy and the residual concentration method. The rheological behavior of hydrate, ζ-potential value of cement particles, phase transformation and the microstructure of the samples were determined by coaxial cylinder rheometer, zeta probe, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicate that SHMP readily reacted with Ca2+, forming complexes [Ca2(PO3)6]2− ions which were subsequently adsorbed onto the surfaces of cement particles. When the content of SHMP was 0.05%, the adsorption ratio reached 99%. However, it decreased to 89% upon further increasing the addition of SHMP to 0.4%. The complexes [Ca2(PO3)6]2− adsorbed onto the surfaces of cement particles inhibited the concentration of Ca2+ and changed ζ-potential, resulting in enhanced electrostatic repulsive force between the cement particles and reduced viscosity of cement-water slurry. The experimental results indicate that the complexes [Ca2(PO3)6]2− covering the surfaces of cement particles led to a delayed hydration reaction, i.e., they extended the hydration time of the cement particles, and that the optimal addition of SHMP was found to be about 0.2%.

Highlights

Superplasticizers around the world can be divided into several distinct types based on different chemicals; they have a similar function, that is, to reduce the water content of concrete without loss of workability [1,2,3]
Based on the residual concentration method, the concentrations of P element determined by ICAP can be used tox estimate the amounts of sodium hexametaphosphate (SHMP) in the filtrate and adsorbed onto the44 of surfaces of
At the beginning of the experiment, the cement particles sank to the bottom, and the

Summary

Introduction

Superplasticizers around the world can be divided into several distinct types based on different chemicals; they have a similar function, that is, to reduce the water content of concrete without loss of workability [1,2,3]. Most of these chemicals are high molecular weight organic compounds, some are synthetic and others are derived from natural products. Because of the addition of water-reducing agent, the surface of cement particles forms an adsorption film, which affects the hydration speed of cement, makes the growth of cement stone crystal more perfect, reduces the capillary gap of water evaporation, and makes the network structure more compact, which improves the hardness and structural densification of cement mortar [9,10,11]

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