Mechanical Properties of Recycled Aggregate Concretes Containing Silica Fume and Steel Fibres.

Soheil Jahandari,Mohammad Saberian,Hania Miraki,Maria Rashidi,Leili Mohammadifar,Masoud Mohammadi,Aida Rahmani,Masoumeh Abolhasani,Mostafa Kazemi

doi:10.3390/ma14227065

Abstract

In this study, the impact of steel fibres and Silica Fume (SF) on the mechanical properties of recycled aggregate concretes made of two different types of Recycled Coarse Aggregates (RCA) sourced from both low- and high-strength concretes were evaluated through conducting 60 compressive strength tests. The RCAs were used as replacement levels of 50% and 100% of Natural Coarse Aggregates (NCA). Hook-end steel fibres and SF were also used in the mixtures at the optimised replacement levels of 1% and 8%, respectively. The results showed that the addition of both types of RCA adversely affected the compressive strength of concrete. However, the incorporation of SF led to compressive strength development in both types of concretes. The most significant improvement in terms of comparable concrete strength and peak strain with ordinary concrete at 28 days was observed in the case of using a combination of steel fibres and SF in both recycled aggregate concretes, especially with RCA sourced from high strength concrete. Although using SF slightly increased the elastic modulus of both recycled aggregate concretes, a substantial improvement in strength was observed due to the reinforcement with steel fibre and the coexistence of steel fibre and SF. Moreover, existing models to predict the elastic modulus of both non-fibrous and fibrous concretes are found to underestimate the elastic modulus values. The incorporation of SF changed the compressive stress-strain curves for both types of RCA. The addition of steel fibre and SF remarkably improved the post-peak ductility of recycled aggregates concretes of both types, with the most significant improvement observed in the case of RCA sourced from a low-strength parent concrete. The existing model to estimate the compressive stress-strain curve for steel fibre-reinforced concrete with natural aggregates was found to reasonably predict the compressive stress-strain behaviour for steel fibres-reinforced concrete with recycled aggregate.

Highlights

Concrete is considered the most widely used construction material in the world [1,2,3,4,5,6,7,8,9,10,11,12,13]
The results indicated that the fracture strain of the concretes containing two types of Recycled Coarse Aggregates (RCA) was higher than that of the control concrete containing Natural Coarse Aggregates (NCA)
This may have been due to the fact that the total ITZ of RCA is higher than that of concrete containing NCA

Summary

Introduction

Concrete is considered the most widely used construction material in the world [1,2,3,4,5,6,7,8,9,10,11,12,13]. Most studies have investigated the improvement in the mechanical properties of recycled aggregate concrete containing steel fibres by measuring the compressive, tensile and flexural strengths. To mitigate the weaker performance of RCA and make it more comparable to conventional concrete, multiple approaches have been utilized in previous research, including the addition of supplementary cementitious materials (SCMs) such as fly ash, electric arc furnace slag, ground granulated blast furnace slag, and SF [39] Such SCMs contribute to strength enhancement through eliminating the inferiority of RCA and make it comparable to natural aggregate concrete. The current study aims to evaluate the impacts of steel fibre and SF and their combination on the compressive stress-strain behaviour and elastic modulus of different recycled aggregate concretes. The RCA replacement levels in this study were considered at 50% and 100%, and two different types of RCAs sourced from both low- and high-strength concretes were prepared and tested to investigate the improvement in mechanical properties

Raw Materials

Mixture Proportions

Sample Preparation and Test Methods

Compressive Stress-Strain Behaviour

Conclusions