Factors Influencing the Hydration, Dimensional Stability, and Strength Development of the OPC-CSA-Anhydrite Ternary System.

Zhenzhen Yang,Dajun Zhou,Baiyun Li,Hansong Ye,Yuelin Li,Qiang Yuan

doi:10.3390/ma14227001

Abstract

Due to the advantages of high early strength and rapid setting, ternary systems consisting of ordinary Portland clinker (OPC), calcium sulphoaluminate (CSA) clinker, and anhydrite have broad application prospects. However, further studies need to be undertaken to find a more optimal mixing proportion of this ternary binder in order to meet basic performance requirements. In this paper, isothermal calorimetric tests, chemical shrinkage tests, drying shrinkage tests, and compressive strength tests were carried out to systematically identify the effect of the OPC/CSA ratio and anhydrite dosage on the hydration, mechanical property development, and dimensional stability of ternary binders. It was found that a higher CSA content leads to a higher cumulative hydration heat, a shorter acceleration period, and a delayed induction period, which can be ascribed to the retardation of C3S at a high aluminate concentration. However, a higher addition of anhydrite can retard the main peak of hydration despite promoting the intermediate peak and improving the hydration reaction rate. The drying shrinkage of blends decreases first along with the CSA proportion and then increases. Moreover, a higher anhydrite content mitigates the drying shrinkage and hinders the strength development. Finally, considering the properties of both the fresh and hardened binder, the ternary blends with 5% anhydrite and OPC/CSA ratios ranging from 3/7 to 2/8 were identified as most suitable for applications that require a high early strength, stable late strength, and small level of shrinkage.

Highlights

Introduction published maps and institutional affilOrdinary Portland cement–calcium sulphoaluminate cement–anhydrite (OPC-CSACS) ternary composite binders have the characteristics of a high early strength, rapid setting [1], and adjustable rheological properties [2], which make them suitable for use in repairing mortars, shrinkage-free grouting materials, cement-based self-leveling screed [3,4,5,6], and 3D printing materials [7].The performances of ordinary Portland clinker (OPC)-CSA-CS systems are governed by the calcium sulfate dosage and OPC/CSA ratio
For single CSA, the addition of 5% CS boosts the compressive strength significantly at all tested age, while the addition of 10% CS plays an opposite role, which is consistent with the results reported in the literature [56]
When the CSA addition is too high, ettringite due to CSA hydration forms a skeleton structure, Overall, the results demonstrate that a CSA content ranging from 60 to 80% is conducive to simultaneously obtaining a higher early and late compressive strength

Summary

Introduction

Ordinary Portland cement–calcium sulphoaluminate cement–anhydrite (OPC-CSACS) ternary composite binders have the characteristics of a high early strength, rapid setting [1], and adjustable rheological properties [2], which make them suitable for use in repairing mortars, shrinkage-free grouting materials, cement-based self-leveling screed [3,4,5,6], and 3D printing materials [7]. The performances of OPC-CSA-CS systems are governed by the calcium sulfate dosage and OPC/CSA ratio. The effect of calcium sulfate on hydration products has been well investigated in neat OPC or CSA systems. In the case of OPC, calcium sulfate reacts with. C3 A to form ettringite, which contributes to early strength development and improves the hydration degree [8].

Methods

Results

Conclusion