Mechanical Properties and Durability of Ultra High Strength Concrete Incorporating Multi-Walled Carbon Nanotubes.

Liulei Lu,Dong Ouyang,Weiting Xu

doi:10.3390/ma9060419

Abstract

In this work, the effect of the addition of multi-walled carbon nanotubes (MWCNTs) on the mechanical properties and durability of ultra high strength concrete (UHSC) is reported. First, the MWCNTs were dispersed by a nano sand-mill in the presence of a surfactant in water. The UHSC specimens were prepared with various amounts of MWCNTs, ranging from 0% to 0.15% by weight of cement (bwoc). Results indicated that use of an optimal percentage of MWCNTs (0.05% bwoc) caused a 4.63% increase in compressive strength and a 24.0% decrease in chloride diffusion coefficient of UHSC at 28 days curing. Moreover, the addition of MWCNTs also improved the flexural strength and deformation ability. Furthermore, a field-emission scanning electron microscopy (FE-SEM) was used to observe the dispersion of MWCNTs in the cement matrix and morphology of the hardened cement paste containing MWCNTs. FE-SEM observation revealed that MWCNTs were well dispersed in the matrix and no agglomerate was found and the reinforcing effect of MWCNTs on UHSC was thought to be pulling out and microcrack bridging of MWCNTs, which transferred the load in tension.

Highlights

Concrete, a quasi-brittle construction material commonly used in the world, has a relatively high compressive strength, but low flexural and tensile strengths [1]
CNT10 samples decreased by of22.8%, 24.0%, 8.8% compared towith thatincreasing of CNT00, results indicate that the addition of multi-walled carbon nanotubes (MWCNTs) significantly affected the chloride permeability of content of MWCNTs. These results indicate that the addition of MWCNTs significantly affected the chloride permeability of ultra high strength concrete (UHSC)
Microfibers generally require a few micrometers of crack opening for developing a noticeable crack bridging stress [30]. These results show that MWCNTs act as bridges across microcracks that cannot be achieved by conventional microfibers and guarantee the load transfer under tension [23], which is helpful to improve the deformation ability and durability

Summary

Introduction

A quasi-brittle construction material commonly used in the world, has a relatively high compressive strength, but low flexural and tensile strengths [1]. Cracks are one of the main hidden defects in concrete structures; they cause brittle fracture, shorten the service life, and lower the durability [2,3,4,5]. After the microcracks coalesce into macrocracks, traditional microfibers (e.g., steel fiber or polypropylene fiber) mitigate their unstable propagation by providing effective bridging, strength, toughness, and ductility [9,10,11,12,13,14]. These microfibers cannot stop or prevent the initiation of microcracks in a concrete matrix [15,16]

Methods

Results

Conclusion