Award Date

May 2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil and Environmental Engineering and Construction

First Committee Member

Moses Karakouzian

Second Committee Member

Brendan O’Toole

Third Committee Member

Moses Karakouzian

Fourth Committee Member

Brendan O’Toole

Fifth Committee Member

Jeayun Moon

Sixth Committee Member

Pramen Shrestha

Number of Pages

145

Abstract

Cement has been largely used in the construction industry, specifically as a matrix for concrete. Recently, a new generation of cement-based composite that greatly increases mechanical properties is replacing conventional concrete. With periodic advances in the field, researchers considered particles with high-aspect ratios such as Carbon Nanotubes (CNTs) to reinforce cement matrices. Although there is not much literature to draw upon in research, some research on improving the tensile strength of cementitious composite incorporating with CNTs does exist. However, there had been no evidence of investigation into impact strength until this study.

Most papers presented examined the effect of multi-walled carbon nanotubes, but very few investigated single-walled carbon nanotubes (SWCNTs), and none of the research compared SWCNTs with multi-walled carbon nanotubes (MWCNTs), and hybrid CNTs (50% of MWCNTs and 50% SWCNTs) in cementitious composites.

The aim of this research is to assess and compare the effect on tensile and impact strength of cementitious composite of reinforcing cement with functionalized (-COOH) SWCNTs, MWCNTs, and hybrid CNTs. Additionally, the lack of standard mixing and test procedures for nanomaterials with cement is considered.

The first objective of this research was to enhance the effectiveness of CNTs’ dispersion in water with a sonicator and to develop the procedure that can be replicated and perhaps standardized for cementitious nanocomposite. The most important objective of this research was to assess and compare the effect of reinforcing cementitious composite with single-walled, multi-walled, and hybrid carbon nanotubes. This process reveals the best low dosage (less than 1.0%) of MWCNTs and SWCNTs on energy absorption under drop-weight impact test. Among several methods of impact testing, two velocity-based impact tests are classified as low-velocity (quasi-static) and high-velocity (dynamic) tests. The drop-weight test is one of many low-velocity impact tests in which the velocity of the striking body is lower than 10 m/s. The ACI 544.2R-89 report is followed and modified for this specific nanocomposite.

The third objective of this investigation was to measure the tensile splitting strength of the nanocomposites. The splitting tensile test is in compliance with ASTM 496/ 496M-04 standard. However, the specimens are scaled down and the test procedure is modified for this specific class of nanocomposite.

The energy absorption of cementitious composite reinforced with SWCNTs, MWCNTs, and hybrid CNTs was measured and compared. Investigation of cementitious composite incorporating CNTs indicated reduced brittleness throughout, changing diagonal to radial failure mechanism.

Hybrid CNTs’ reinforcement performed outstandingly at decreasing crack propagation and debris spatter of specimens subjected to impact load. Additionally, the impact strength of cementitious nanocomposite incorporating 0.4% hybrid carbon nanotubes by weight of cement increased. However, more experiments should be conducted. Lastly, tensile strength and ductility of hybrid reinforced cementitious nanocomposite improved, and failure mechanism was investigated.

Keywords

Carbon Nanotube; Cement; Failure Mechanism; Impact Toughness; Nanocomposite; Tensile Strength

Disciplines

Civil Engineering | Engineering Science and Materials | Materials Science and Engineering | Mechanical Engineering

Language

English


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