The use of nanomaterials has become a popular way to improve the performance of cement-based composites. At the same time, ultra-high strength concrete is becoming more widely used. These materials provide superior durability to infrastructure elements, reducing the need for maintenance or early replacement. The performance boost is achieved by producing a denser microstructure and, in the case when nanofibers are used, may reduce the initiation of cracks. Aluminum oxide nanomaterials have the potential to provide a significant increase in compressive strength of cement-based materials. Here, the effect of incorporation of aluminum oxide nanofibers in oil well cement based mortars and composites is reported. The design of ultra-high strength concrete often requires a precisely tuned aggregate gradation, the use of specific cement types and high quantities of silica fume and superplasticizers along with high temperature and curing under elevated pressure. It was demonstrated that the use of small quantities of aluminum oxide nanofibers in an oil well cement based mortar could provide a compressive strength approaching 200 MPa. These levels were achieved at a considerably lower dosage of silica fume. It is envisioned that the high strength matrix is formed due to the reinforcing of calcium silicate hydrate layers which are formed around the nanofibers. This research demonstrated that due to a ‘‘shish kebab” effect the addition of well-dispersed aluminum oxide nanofibers at a very small dosage of 0.25% (by mass of cement) could provide up to 30% increase in compressive strength of cementitious systems, helping to meet the benchmarks for ultra-high strength cement-based composites.

Introduction

Ultra-high strength cement-based composite (UHSCC) materials, including ultra-high-performance fiber reinforced concrete (UHPC), are becoming a popular solution in modern construction practice [1–۵]. These new composite materials tend to provide superior durability and allow thinner structural sections to be used. However, the use of ultra-fine fillers and high quantities of reactive silica materials results in a significant increase in cost compared to conventional concrete. If a cement-based material with similar properties was developed without the need for such high volumes of sub-micron sized and ultra-fine components, the difference in price with conventional concrete could be significantly reduced. The properties of cementitious matrices are often considered as one of the most important features contributing to the performance of the composite. These properties are of even greater importance when ultra-high strength cement-based materials are considered.