High-ductile engineered geopolymer composites (EGC) prepared by calcined natural clay

An economical and widely available raw material is essential for the application and populari-zation of geopolymer. Due to the vast reserves of natural clay, calcined natural clay is considered a cost-effective geopolymer raw material. The present study aims at developing a high-ductile engineered geopolymer composites (EGC) using calcined natural clay. Firstly, natural clay as a construction waste was ground and calcined, and the calcined natural clay was mixed with ground granulated blast furnaces slag (GGBFS) and polyvinyl alcohol (PVA) fiber to prepare geopolymer composite samples. Then, the mini slump and uniaxial tensile test were conducted on the geopolymer composite samples, and the digital image correlation technology (DIC) was used to further analyze the effect of the slag and fiber contents on the tensile behavior of EGC. Finally, the optimal slag and fiber contents for EGC with highest ductility were proposed. The results showed that the natural clay exhibited a certain reactivity after a thermal activation process due to the presence of a small amount of kaolinite. The tensile properties of geopolymer composites prepared by calcined natural clay were significantly enhanced with increasing fiber content. Meanwhile, the incorporation of slag could enhance the tensile properties, while excessive slag content decreased the tensile properties. The EGC with 10.0% slag content and 2.5% fiber content exhibited the highest ductility, with an ultimate tensile strength of 3.61 MPa and a tensile strain capacity of 6.59%.