Potential use of nano calcium carbonate in polypropylene fiber reinforced recycled aggregate concrete: Microstructures and properties evaluation

Abstract

Fiber materials and nanomaterials are often added to recycled aggregate concrete (RAC) to compensate for the adverse effects caused by recycled concrete aggregate (RCA). Polypropylene fiber (PPF) and nano-CaCO3 (NC) are considered having great potentials to improve the engineering properties of RAC due to their high yield, large reserve, and low price. Based on this, the current study recommended adding NC as an extra material to PPF-reinforced recycled aggregate concrete to compensate for its performance inadequacies. To fully expose the joint reinforcing effect, the microstructures and attributes were evaluated, including compressive strength, tensile strength, flexural strength, resistance to chloride ion permeability, drying shrinkage, scanning electron microscope (SEM), X-ray diffraction (XRD), thermogravimetry (TG), and hydration heat. The results showed that 1 wt.% NC contributes to overall improve the mechanical properties and durability performance of RAC incorporated with 0.133 vol.% 12 mm-length PPF. NC promotes the hydration degree of RAC-based cementitious materials and enhance the microstructural density and interfacial bonding capacity between PPF and RAC mortar. In addition, NC can improve the hydration rate and hydration heat of cement-based materials in the early stage, and participates in the chemical reaction of hydration in the later stage, promoting more occurrences of hydration reactions to the more productions of hydrates. Therefore, the comprehensive adoption of NC and PPF is capable of improving the performance enhancement of RAC for durable buildings.