Search

Highlights • The effect of MK based materials on the steam cured high performance concrete is investigated. • The XRD and TG analysis were applied to quantify the content of CH and AFt after curing. • The MK based admixtures remarkably refines the ITZ and optimize the pore structure of concrete after heat treatment. Abstract High performance pipe piles are widely used in precast industry. In order to improve the production efficiency and performances of the products, steam curing and mineral admixtures are usually applied. This paper evaluates the performances of HPC pipe piles produced with metakaolin-based admixtures. Quantitative phase composition analysis shows that the addition of 10 wt% metakaolin reduces the portlandite content by up to 57.1%, while increases the content of ettringite to some extent. The addition of metakaolin or metakaolin-slag/limestone blends improves the mechanical properties, especially the hybrid usage of metakaolin and limestone filler. Pore structure and microscope analyze confirm the remarkably-refined pore characteristics caused by the addition of metakaolin-based admixtures, in which case the gel pores accounts up to 85% of the total pores. Those remarkably improved properties caused by the addition of metakaolin-based admixtures indicate a promising future for their applications in producing high performance pipe piles with further modified properties. [ABSTRACT FROM AUTHOR]

• PVA modification has adverse effect on the compressive strength of ECC. • Nanomaterials act on the early stage of ECC toughness improvement. • Modified PVA act on the whole cycle of ECC toughness improvement. Nanomaterial modification and fiber reinforcement are both effective modifications for concrete toughening. In this study, the cement matrix was reinforced by a combination of nanomaterials and surface-modified polyvinyl alcohol (PVA). The modification of PVA involves the treatment of interface weakening, which is based on the enhancement of the slip effect. The workability and static mechanical properties of engineered cementitious composites (ECCs) were studied, and the micromorphology of the fiber and matrix after bending failure was observed through scanning electron microscopy. Different nanomaterial contents and concentrations of PVA were designed in the experiment, the purpose of which is to investigate the mechanism of the effect of multiple superposed on the toughening effect of ECCs. The research demonstrated that the direct addition of traditional PVA fiber and nanomaterials adversely affects the workability of ECCs, but it can be improved by fiber modification and ultrasonic dispersion of nanomaterials. An experimental study on the compressive properties showed that, with the increase in PVA fiber modification concentration, the compressive strength decreased, but the addition of nano-CaCO 3 improved the strength of the matrix, thereby compensating for the strength loss. Four-point bending and tensile tests demonstrated that both PVA fiber modification and the addition of nano-CaCO 3 affected the flexural properties of ECCs to some extent. PVA fibers modified with 1% and 2% nano-CaCO 3 at vinyl acetate ethylene concentrations of 25% and 50% can improve the toughness of ECCs. Nano-CaCO 3 can improve the toughness of ECCs by improving the compactness of the matrix structure and fiber interface, while PVA fiber can supplement the defects of the matrix structure by bridging and sliding and have a positive superposition effect on the toughness of the material after proper treatment. [ABSTRACT FROM AUTHOR]