Mechanical and shrinkage properties of engineered cementitious composites with blended use of high-belite sulphoaluminate cement and ordinary Portland cement

Engineered cementitious composites (ECCs) are often considered potential ideal structure repair materials. However, conventional ordinary Portland cement (OPC)-based ECC generally has the disadvantages of high shrinkage and slow early strength development , which restricts the effectiveness and efficiency of engineered repairs. To solve these problems, this study introduced high-belite sulphoaluminate cement (HBCSA) to replace or partially replace OPC to promote the overall performance of OPC-ECC. XRD , TG, MIP, and SEM analyses were used to examine the resulting changes in microstructure and hydration composition and their effects on the properties of ECCs. Results showed that while HBCSA cement enhanced the early compressive strength (improved from 13.6 MPa to 27.7 MPa at 3 d), the later strength development was postponed by the higher HBCSA substitution rate due to the fly ash's reactivity being reduced by the matrix's decreased alkalinity. HBCSA cement reduced the setting time and drying shrinkage of ECC by virtue of its rapid hydration reaction and the compensatory shrinkage of its hydration product , ettringite . When the HBCSA cement content was increased from 50 % to 100 %, the initial setting time was shortened by 65.9 %–80.6 % and the drying shrinkage at 28 d was decreased by 60.6 %–75.2 % compared to OPC-ECC. Furthermore, while all ECC blends exhibited strain-hardening behaviors, blended cement ECC has superior tensile properties . This study shows that the judicious use of HBCSA cement can effectively compensate for the weaknesses of conventional ECC and make it more adaptable to restoration projects. • Blended cement ECCs provide better mechanical properties and volumetric stability. • The high content of HBCSA cement dramatically reduces setting time and shrinkage. • The hydration property of HBCSA cement alters the shrinkage mechanism of ECC. • The reason for the modification was analyzed by the study of hydration products.