The application of thermal analysis to study the hydration behavior of tricalcium aluminate-gypsum in the presence of polycarboxylate-based superplasticizers
Introduction
The newly developed polycarboxylate-based superplasticizers (PCE) are very efficient in the formulation of modern concrete [1]. The PCE are comb-like copolymers which consist of a negatively charged backbone with carboxylic groups and grafted side chains which are mainly composed of polyethylene oxide units. Their dispersing effect is due to the adsorption of polymers on particle surfaces and then induce electrostatic and/or steric repulsive forces [2]. Through this unique interactions, PCE exhibit superior dispersing force compared to polycondensates [3]. As a side effect, PCE may also lead a undesired retardation phenomena on the setting of the cement paste [4].
Tricalcium aluminate (Ca3Al2O6, C3A) is one of the most reactive components of Portland clinker. The hydration of this mineral presenting in Portland cement leads to the formation of ettringite and monosulphate phase, which plays a vital role in the early hydration and setting behavior of cement paste [5]. Generally, many compatibility problems occurred between PCE and cement, such as early slump loss, poor flow behavior, higher PCE dosage or severe segregation [6], could be attributed to the hydration behavior of C3A. A number of studies on PCE and C3A in cement paste are available. Some studies indicated that the addition of PCE in cement paste would slow down the dissolution rate of the constituents [7], meanwhile the formation of ettringite is retarded [8]. On the contrary, some researchers suggested that early growth rate of ettringite was accelerated in cementitious system. For example, Roncero et al. [9] noted that at the age of 15 min, no ettringite was detected by the XRD analysis of the reference paste whereas it was observed in the pastes with superplasticizer, especially in the PCE paste. Yu et al. [10] studied the impact of PCE on the hydration of C3A-gypsum suspension, and found that the addition of PCE accelerated the depletion of sulfate as well as the C3A dissolution, and led to the precipitation of monosulphate phase. So far, there are still controversies on the effects of PCE on the hydration of clinkers [11].
The aim of the present work is to investigate the detailed influence of PCE on the hydration of the C3A-gypsum system, which is a partial system of ordinary Portland cement, and illustrate the mechanism for these effects. For this purpose, pure C3A was synthesized and the interactions between C3A and PCE were carefully studied. Isothermal calorimeter, complex thermal analysis (TG-DSC) and X-ray diffraction (XRD) are applied to investigate the hydration processes of C3A in the presence of PCE. Gel permeation chromatography (GPC) and scanning electron microscopy (SEM) have been performed to clarify possible morphology changes of the ettringite phase upon PCE addition.
Section snippets
Materials
The pure C3A phase was prepared by a high-temperature calcination of analytically pure CaCO3 and Al2O3 with molar ratio 3:1 at 1350 ℃ for 3 h. Prior to the second calcination, the prepared specimens were crushed and ground in a laboratory mill. The obtained product was re-calcined until X-ray diffraction indicates that no other phases were present. The XRD pattern of synthesized C3A samples is shown in Fig. 1. The obtained C3A powder had a nitrogen BET surface area of 220 ± 10 m2/g.
The PCE used
Isothermal calorimetry of C3A-gypsum
The hydration process of C3A-gypsum paste was monitored by isothermal calorimeter. Fig. 3 shows the comparison of the calorimetric curves of paste samples containing 0, 0.1 and 0.2 wt.% PCE hydrated for 30 h. When anhydrous C3A-gypsum began to contact with water, there was a rapid rate of heat development lasting for a few minutes. Subsequent, the hydration rate increased to a maximum vale and then declined. The initial heat peak could be attributed to rapid dissolution and formation of
Discussion
The addition of PCE to C3A-gypsum system influences the hydration rate and amount of formed hydration products. Additionally, the morphology and size of hydrate crystals were changed.
Conclusions
The initial hydration of C3A-gypsum system and formation of crystalline monosulphate were evidently slowed down by the introduction of PCE. It was found that the retardation is due to adsorption of the PCE on surface of anhydrous mineral as well as hydrated compounds. The PCE adsorbed on the ettringite precursor and stabilized it, thus extending the period of ettringite nucleation, and delaying the formation of monosulphate. Moreover, the precipitate rate of C3AH6 phase in the presence of PCE
CRediT authorship contribution statement
Ming Liu: Methodology, Investigation, Software, Writing - original draft. Yuxin Gao: Conceptualization, Project administration. Lei Zhang: Methodology, Writing - review & editing. Guangming Jiang: Conceptualization, Writing - review & editing. Chao Zeng: Methodology. Peng Wang: Software.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The authors wish to thank the financial support of China West Construction Group Co., Ltd., science and technology research and development foundation (ZJXJ-2019-19). The authors would like to acknowledge the great help from Xiaoqin Liu and Xiaorun Chen.
References (23)
- et al.
Synthesis, characterization and performance of a polycarboxylate superplasticizer with amide structure
Colloid Surf. A
(2014) - et al.
The role of steric repulsive force in the dispersion of cement particles in fresh paste prepared with organic admixture
Cem. Concr. Res.
(1997) - et al.
The application of thermal analysis, XRD and SEM to study the hydration behavior of tricalcium silicate in the presence of a polycarboxylate superplasticizer
Thermochim. Acta
(2015) - et al.
Ettringite formation: a crucial step in cement superplasticizer compatibility
Cem. Concr. Res.
(2003) - et al.
Influence of solution chemistry on the hydration of polished clinker surfaces-a study of different types of polycarboxylic acid-based admixtures
Cem. Concr. Res.
(2002) - et al.
Study of the influence of superplasticizers on the hydration of cement paste using nuclear magnetic resonance and X-ray diffraction techniques
Cem. Concr. Res.
(2002) - et al.
Effects of two retarders on the fluidity of pastes plasticized with aminosulfonic acid-based superplasticizers
Cons. Build Mater.
(2012) - et al.
Fundamental mechanisms for polycarboxylate intercalation into C3A hydrate phases and the role of sulfate present in cement
Cem. Concr. Res.
(2010) Basics of analytical methods used for the investigation of interaction mechanism between cements and superplasticizers
Cem. Concr. Res.
(2011)- et al.
Impact of zeta potential of early cement hydration phases on superplasticizer adsorption
Cem. Concr. Res.
(2007)
Cement hydration and microstructure formation in the presence of water-soluble polymers
Cem. Concr. Res.
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