Study on Utilization of Carboxyl Group Decorated Carbon Nanotubes and Carbonation Reaction for Improving Strengths and Microstructures of Cement Paste.

Xiantong Yan,Qinghua Qin,Waiching Tang,Hongzhi Cui,Xiangming Zhou

doi:10.3390/nano6080153

Abstract

Carbon nanotubes (CNTs) have excellent mechanical properties and can be used to reinforce cement-based materials. On the other hand, the reaction product of carbonation with hydroxides in hydrated cement paste can reduce the porosity of cement-based materials. In this study, a novel method to improve the strength of cement paste was developed through a synergy of carbon nanotubes decorated with carboxyl group and carbonation reactions. The experimental results showed that the carboxyl group (–COOH) of decorated carbon nanotubes and the surfactant can control the morphology of the calcium carbonate crystal of carbonation products in hydrated cement paste. The spindle-like calcium carbonate crystals showed great morphological differences from those observed in the conventional carbonation of cement paste. The spindle-like calcium carbonate crystals can serve as fiber-like reinforcements to reinforce the cement paste. By the synergy of the carbon nanotubes and carbonation reactions, the compressive and flexural strengths of cement paste were significantly improved and increased by 14% and 55%, respectively, when compared to those of plain cement paste.

Highlights

Though cement-based materials are the most extensively used construction material for various types of infrastructure all over the world, their major drawbacks such as low tensile strength, extreme quasi-brittleness, and the uncontrolled propagation of cracks have limited their engineering applications
As a desired reinforcing material, a carbon nanotube (CNT) is a tube-shaped material constructed with one-atom-thick rolled sheets of carbon and it belongs to an allotrope of carbon [2,3,4,5]
CNTs are usually classified as single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) based on the concentric tube number [6]

Summary

Introduction

Though cement-based materials are the most extensively used construction material for various types of infrastructure all over the world, their major drawbacks such as low tensile strength, extreme quasi-brittleness, and the uncontrolled propagation of cracks have limited their engineering applications. Carmen et al [9] systematically studied the effect of CNT dosage, curing age, current intensity, loading rate and maximum stress applied on the strain-sensing properties of CNT-reinforced cement paste. They found that the cement-based CNT sensors showed more sensitive behavior at the age of 28 days, and the best performance as a strain sensor was obtained for the 0.05% CNT composites, reaching values of a gauge factor up to 240 with an R2 Pearson’s coefficient of 0.99. Polycarboxylate superplasticizer (a kind of surfactant), a carboxyl group (–COOH, introduced into cement paste by CNTs), and different pH values of the samples influence the final morphology of the calcium carbonate crystals

Results and Discussion

Carbonation Curing Method

Strength

Microstructure

Conclusions