INVESTIGATION OF INFLUENCE OF NANO-REINFORCEMENT ON THE MECHANICAL PROPERTIES OF COMPOSITE MATERIALS

Olga Kononova,Andrejs Krasnikovs,Genadijs Sahmenko,Rimvydas Stonys,Renars Vitols

doi:10.3846/13923730.2015.1106578

Abstract

The present work studies the possibility to decrease the formation of micro and nano cracks around short fibres in fibre-reinforced concrete (FRC) composite with the help of nano-reinforcement, which is carbon nanotubes, or micro reinforcement, which is carbon short fibres and nano-fillers. Tensile and bending strength of FRC depends on the spatial distribution of fibres inside a material, type of fibre and cement matrix, as well as an effective micromechanical work of each fibre while pulling out of the concrete matrix. Shrinkage stresses, acting in the matrix in the vicinity of a fibre, lead to the formation of micro-cracks. Such micro-cracks were observed experimentally and were investigated numerically performing broad modelling based on the finite element method (FEM). The investigation was focused on the micromechanical behaviour of a single steel fibre in a cement matrix. Numerical modelling results demonstrated a high level of shrinkage overstresses around steel fibres in concrete. The role of nano and micro admixtures, nanotubes, short carbon fibres as well as the role of water/cement ratio in a high performance concrete matrix, changing (increasing or decreasing) the friction force between the matrix and the steel fibre, were investigated experimentally by way of performing a single fibre pull-out tests. The high scatters of experimental results were obtained in performed pull-out tests. At the same time, for the same series of samples, a positive role of micro and nano admixtures and carbon nanotubes in the increase of pull-out force was recognised.

Highlights

Obtained circumferential and longitudinal stresses are high compared to the tensile strength of concrete, which varies in the range from 2.5 MPa to 6 MPa
It is possible to see that for every level of shrinkage exists a crack length, at which a crack has a tendency to stop (Fig. 5c)
That high-strength concrete (HS) and normal strength concrete (NS) compositions with carbon nanotubes are characterised by a little decrease in compressive strength values, changing in the range of 5–18%, comparing to samples without nanotubes

Summary

Introduction

Last few decades have been associated with the investigation of novel concrete types: high strength, high performance and ultra-high performance concretes (UHPC) and their appearance on the market (Schmidt, Fehling 2005). Such materials combine the increasing compressive strength with relatively weak load-bearing capacity under tensile loads. Fibre pull-out from a concrete matrix has a main role in the mechanical behaviour of FRC in the post-cracking stage. In order to detect the formation of micro-cracks in the contact zone of the fibre-cement matrix, three types of concrete matrixes were investigated, namely a low strength, a normal strength and a high strength matrix (data on the matrixes is provided below).

Numerical investigation of shrinkage overstresses around steel fibres

Modification of the concrete structure

Experimental investigation

Experimental results and discussions

Conclusions