Characterization of Calcium Silicate Hydrate Gels with Different Calcium to Silica Ratios and Polymer Modifications.

Amirhossein Madadi,Jianqiang Wei

doi:10.3390/gels8020075

Abstract

Calcium silicate hydrate (CSH) gels, the main binding phases of hydrated cement, are the most widely utilized synthetic materials. To understand the influences of composition and polymers on the reaction kinetics and phase formation, CSH gels with varying Ca/Si ratios and amounts of poly (acrylamide-co-acrylic acid) partial sodium salt (PAAm-co-PAA) were synthesized via a direct method. The CSH gels were characterized through isothermal calorimetry, thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and Raman spectroscopy at different ages. By increasing the Ca/Si ratio from 0.8 to 1.0, the formation of CSH was enhanced with a 5.4% lower activation energy, whereas the incorporation of PAAm-co-PAA increased the temperature sensitivity of the reactions with an 83.3% higher activation energy. In the presence of PAAm-co-PAA, the reaction rate was retarded at an early age and the negative impact faded over time. The results of an XRD analysis indicated the formation of tobermorite as the main phase of the CSH gels, while the addition of PAAm-co-PAA resulted in a postponed calcium hydroxide consumption and CSH formation, which was confirmed by the decreased FTIR intensity of the C=O bond, Si–O stretching and Si–O bonds. The increased Raman vibrations of Si–O–Si bending Q2, Ca–O bonds, O–Si–O and asymmetric bending vibrations of SiO4 tetrahedra in the presence of PAAm-co-PAA indicate the intercalation of the polymeric phase and internal deformation of CSH gels.

Highlights

Portland cement, which serves as a binding phase of concrete, is the most widely employed synthetic material
The reaction rate and formation of Calcium silicate hydrate (CSH) gels at different calcium to silicate (Ca/Si) ratios and the incorporation of a polymer were investigated by isothermal calorimetry, thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and Raman spectrometry
The data at 96 h showed that the elevated Ca/Si ratio resulted in slightly lower activation energy of the reactions, while the addition of PAAm-co-PAA significantly increased the temperature sensitivity of the CSH reaction with higher activation energy

Summary

Introduction

Portland cement, which serves as a binding phase of concrete, is the most widely employed synthetic material. Besides its excellent characteristics such as high strength and cost-effectivity, some inherent mechanical shortcomings, such as a high brittleness, low toughness, and high susceptibility toward cracking, impede a greater diversity for such material in industrial applications [1]. This remains an intractable problem that shortens the lifetime of structures and costs billions of dollars for maintenance each year [2]. Improving the toughness and durability of cementitious materials is a route to overcome such mechanical shortcomings and to enhance the sustainability of infrastructures [5,6]

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Conclusion