Effects of the combined usage of nanomaterials and steel fibres on the workability, compressive strength, and microstructure of ultra-high performance concrete

Kunhong Huang,Ronghui Wang,Yuan Feng,Jianhe Xie,Rui Rao

doi:10.1515/ntrev-2021-0029

Abstract

Abstract Using nanomaterials to enhance concrete performance is of particular interest to meet the safety and functionality requirements of engineering structures. However, there are few comprehensive comparisons of the effects of different nanomaterials on the properties of ultra-high performance concretes (UHPCs) with a compressive strength of more than 150 MPa. The aim of the present study was to assess the coupling effects of nanomaterials and steel fibres on the workability and compressive performance of UHPC. Three types of nanomaterials, nano-SiO2 (NS), nano-calcium carbonate (NC), and carbon nanofibre (CNF), were each added into UHPC mixes by quantity substitution of the binder; two types of steel fibres were investigated; and two mixing methods were used for casting the UHPC. In addition, the effect of curing age (7 or 28 days) on the compressive performance of the mixtures was considered. Comprehensive studies were conducted on the effects of these test variables on the fluidity, compressive strength, failure mode, and microstructure. The results show that the combination of these nanomaterials and steel fibres can provide good synergetic effects on the compressive performance of UHPC and that the addition of CNF results in a greater enhancement than the addition of NS or NC. The addition of NS, not CNF or NC, has a considerable negative influence on the fluidity of the UHPC paste. It is suggested that reducing the agglomeration of the nanomaterials would further improve the performance of the resulting UHPC.

Highlights

With continued modernisation, the requirements for the safety and functionality of engineering structures are increasing rapidly [1]
The following conclusions can be made: (1) The combination of nanomaterials and steel fibres can provide good synergetic effects on the mechanical performance of ultra-high performance concretes (UHPCs), i.e. the nanomaterials and steel fibres are mainly responsible for matrix reinforcement and anti-cracking, respectively
(2) The addition of nano-calcium carbonate (NC) or carbon nanofibre (CNF) has a slight influence on the fluidity of the UHPC paste, while adding NS into UHPC can cause a great reduction in the mixture fluidity

Summary

Introduction

The requirements for the safety and functionality of engineering structures are increasing rapidly [1]. To meet these requirements, the development of ultra-high performance concretes (UHPCs) has accelerated in the last two decades [2]. UHPC is defined as a cementitious material that is reinforced by fibre and that has compressive and tensile strengths greater than 150 and 5 MPa, respectively [3]. Compared with normal-strength and high-strength concretes, UHPC has many advantages, including an ultrahigh compressive strength and excellent durability [4]. The advantages of using higher-strength concrete in structures include reducing member sizes and building dead loads, offering an attractive alternative to traditional concrete

Objectives

Methods

Results

Conclusion