Results

 The project is currently under way and the newest findings have been compiled in the 2014 interim technical report, which has been communicated to the project’s sponsors.

After the project’s conclusion and after we resolve all the issues regarding possible patents and other intellectual property, we will publish the final findings in this website.

We also expect to communicate some of the results in peer reviewed academic journals and academic conferences.

 

Below we have included a short summary of the findings so far (Autumn 2014) :

 

Characterisation and Selection of Carbon Nanotubes (Work Package 4)

Within Work package 4, Glonatech proceeded with the synthesis oflong pristine multi-wall carbon nanotubes (MWCNTs)with 98% purity, employing proprietary catalysts and methodologies based on chemical vapor deposition. The nanotubes were distributed to the academic partners [Democritus University of Thrace (DUTH), University of Ioannina and National Technical University of Athens (NTUA)] for parallel comparative study.

A new grade of MWCNTs nanotubes was also developed (95%, long)) which was tested successfully by DUTH and subsequently sent to the other universities. In order to achieve this, focus was given on the modification of Glonatech’s pilot reactor that now allows not only increase in the production capacity and reduction in cost but also decrease in the bulk density of the nanotubes. The latter enables more effective dispersion of MWCNTs in various solvents and matrices, including cement. The reactor’s modification also permits the tailoring of other MWCNTs characteristics such as grain size and length.

The academic partners also received functionalized and short nanotubes by Glonatech, based on the 95% grade, for comparative studies on their sensing capabilities and effect on cement’s mechanical properties improvement.

Structural characterization of carbon nanotubes was carried out with various techniques, including electron microscopy (SEM, TEM), Raman spectroscopy, thermogravimetric analysis (TGA), atomic force microscopy (AFM) and Fourier transform infrared spectroscopy(FTIR).

 

  CNT's as sensors and corrosion performance evaluation (Work Package 2)

The modification of cement-based materials with carbon-based nano-inclusions will lead to the development of innovative products possessing multi-functionality and smartness. The groundbreaking and innovative scientific achievements of the proposed work cover broad spectrum accomplishments in basic and applied research, as well as in the development of new products.

The research program has two directions:

  • The use of nanomodified mortar as sensor of corrosion of rebars
  • The measurement of corrosion of rebars in nanomodified mortar

The measurements establish that the nanomodiefied mortar can used as  sensor for corrosion of rebars. Also the measurement show that the mortar with CNTs for 0.1 up to 0.3 % driping in 3,5 % NaClhas inhibiting effect of corrosion of rebars.

 

 CNT's and CNF's: dispersion, compressive strength, flexural and fracture toughness and self-sending abilities (Work packages 2 &4)

High strength multifunctional cementitious nanocomposites reinforced with carbon fibers at the nanoscale were developed exhibiting remarkably improved mechanical, fracture and self sensing properties. Cement pastes and mortars were reinforced with various percentages of well dispersed multiwall carbon nanotubes (MWCNTs) and carbon nanofibers (CNFs). Dispersion of the nanotubes and nanofibers was achieved following the dispersion method developed by Konsta-Gdoutos et al. According to themethod, constant energy is applied to the nanoscale fiber/superplasticizer suspensions by a 500W cup-horn high intensity ultrasonic processor. The sonicator is operated at an amplitude of 50% so as to deliver energy of 1900-2100 J/min, at cycles of 20 s in order to prevent overheating of the suspensions. After sonication, ordinary Portland cement and sand were added into the CNT/CNF suspensions at a water to cement ratio (w/c) 0.5 and at a sand to cement ratio (s/c) 3.

The flexural and compressive strength, flexural and fracture toughness and Young`s modulus of the nanoreinforced mortars were experimentally investigated and compared with similarly processed reference cement based mixes without the nanoscale fiber reinforcement.  The nanocomposites’ fracture properties were evaluated in three-point bending andalso determined using the two parameter fracture model (TPFM). The excellent reinforcing capability of MWCNTs and CNFs is demonstrated by a significant improvement in flexural strength (86.7% and 106% respectively) (Fig.1), flexural toughness (56% and 111.5% respectively), Young`s modulus (100%,) and fracture toughness (70% and 89% respectively).

The self sensing ability of the nanocomposites was examined by piezoresistivity experiments, conducted by measuring the nanocomposites’ electrical resistance using the four-pole method under simultaneous cyclic compressive loading (Fig.2). Results confirm that CNT and CNF reinforced mortars exhibit an increased change in resistivity, up to 10.6%, which is indicative of the amplified sensitivity of the material in strain sensing (Fig.3).

  

Cement-based Materials – Modification – Quality Control (Work Package 1)

W.P.1 had two main objectives: (a) develop a methodology based on appropriate selection of materials and processes for optimal modification of cement-based materials using carbon nano-inclusions of various volume fractions, and (b) use of traditional as well as develop innovative methodologies for the quality control of the produced new materials. To uniformly disperse the nano-inclusions in the aqueous solution we applied a sonication method using different types of dispersant agents (surfactants/plasticizers). The factors under investigation were sonication time of the suspensions, dispersing agent/nano-inclusion ratio, nano-inclusion concentration and type of dispersing agent. Finally, we studied the effect of the admixtures on the physical properties of the nanomodified mortars. The quality of the dispersion of the nano-inclusions in suspensions was analyzed with conventional methods (UV-vis spectroscopy, Dynamic Light Scattering (DLS), laser particle size analyzer (Cilas)) and the innovative dielectric spectroscopy technique developed for the purpose of this project. Based on the obtained results it was concluded that the use of surfactants provide best dispersion quality, however it results in deterioration of the physical properties due to increase of the air content of the cement mortars (even in conjunction with defoamer). On the other hand plasticizers can provide adequate dispersion quality without significant alteration of the physical properties.

Based on the results the suggested protocol for optimum dispersion and improvement in the physical properties is:

 

Sonication time

90 min

Sonication power

120 W

Dispersing agent

SuperplasticizerViscocrete 300

Workability improvement

Superplasticizer Viscocrete 600

Viscocrete300/ nano-inclusion ratio

1.5/1

Water/cement ratio

0.5

 

 

Mechanical behavior of CNTs/CNFs cement based materials and sensing capability under loading (Work Package 3)

The main objective of W.P.3 was the determination of the effect of the nano-inclusions on the mechanical behavior (compressive strength, bending strength, dynamic elastic modulus and fracture toughness), the monitoring of the fracture process by means of advanced electrical (resistivity measurements), thermal (lock-in, impedance and ultrasonic IR thermography) and acoustic (acoustic emission, ultrasonics) non-destructive techniques and the determination of the optimum dispersion conditions for mechanical response and sensing capability. Based on the obtained results the electrical percolation was determined at 0.53 wt. % CNTs. This level of reinforcement resulted at the same time in a clear enhancement in fracture toughness, while the acoustic emission activity was 6 times higher compared to plain mortars.

Impact of nano-modification on the multi-functionality and smartness of lab scale and on the environmental response of lab scale components (Work Packages 7 & 8)

The purpose of W.P.7 & W.P.8 is to study the impact of nano-modification on the multi-functionality, smartness and environmental response of lab scale components. A common NDE platform will be developed under this task for monitoring the structural integrity deterioration and durability of the modified materials in real time. The realization of the NDE platform is underway. This along with the study of the environmental response will be conducted after the delivery of the equipment that has been purchased for the purpose of this project.

Thermal & electrical modelling of CNTs / cement composites (Work Package 5&6)

In the framework of NSC project, NIKI developed software related to a state-of-the-art multi-scale material modelling technology that optimizes design process of smart, multi-functional materials and structures. The produced software is used to predict thermal and electrical behavior of nano-composite materials by coupling micro and macro-scale analyses results.

  

Definition of composite structure:

  • 3D model design in Abaqus/CAE
  • Homogeneous macroscopic model
  • RVE (Representative Volume Element)

of the microstructure consisting of CNT and cement solid bodies

Macro-scaleanalysis:

  • Mesh generation in Abaqus/CAE
  • Abaqus/Standard solver
  • Post-processing Abaqus/CAE
  • Thermal boundary conditions:

Temperature differenceDΤ=5 0C

  • Electrical boundary conditions: Electric Potential differenceDV=20 Volt

    Micro-scaleanalysis:

    • Abaqus/Standard  solver
    • Post-processing Abaqus/CAE
    • Periodic temperature boundary conditions in thermal analysis:
    • Periodic electric potential boundary conditions in electricalanalysis:

 Project results:

  • Effective thermal conductivity of CNT/cement composite: keff=HFL/(DΤ/L)
  • Simulation tool for the prediction of effective thermal conductivity
  • Effective electrical conductivity of CNT/cement composite: σeff= ECD/EPG
  • Software for the analytical prediction of composite electrical conductivity as a function of CNTs content
  • Percolation threshold region prediction