CHH Cement Composite
A. Cwirzen, K. Habermehl-Cwirzen, L.I. Nasibulina, S.D. Shandakov,
A.G. Nasibulin, E.I. Kauppinen, P.R. Mudimela, and V. Penttala
*
Abstract. The compressive strength and electrical resistivity for hardened pastes
produced from nanomodified Portland SR cement (CHH- Carbon Hedge Hog cement) were studied. The nanomodification included growing of carbon nanotubes
(CNTs) and carbon nanofibers (CNFs) on the cement particles. Pastes having water
to binder ratio of 0.5 were produced. The obtained hardened material was characterized by increased compressive strength in comparison with the reference specimens made from pristine SR cement, which was attributed to reinforcing action of
the CNTs and CNFs. The electrical resistivity of CHH composite was lower by one
order of magnitude in comparison with reference Portland cement paste.
1 Introduction
Carbon nanotubes (CNTs) were first described in 1991 [1] and since that time an
intensive research has been initiated in number of institutes around the world.
CNTs are characterized by high tensile strength and elastic modulus as well as
exceptional electrical and thermal conductivity. CNTs were incorporated into matrixes based on metals, ceramics and to a limited extend into Portland cement [25]. The main problems while incorporating CNTs into any matrix is to obtain their
uniform dispersion and sufficient bond with the binder matrix. Incorporation of
CNTs into Portland cement-based matrixes was done mainly by water dispersion,
[6, 7]. The main drawback of this method is the limitation of the maximum
amount of the CNTs to around 1-1.5% (according to the cement weight, with
water to binder ratio of 0.5). Higher additions usually deteriorate severely workability, [6]. Some solution of this problem was to add surfactants, usually polycarboxylated-based superplasticizers, which facilitated dispersion processes and
enhanced the workability. Another solution is to chemically functionalize CNTs
surfaces with “polar impurities” e.g. OH, COOH end groups [8, 9, 10] or oxidation, [11]. One of the main drawbacks of functionalization in the case of Portland
cement-based binders is strong loss of workability due to absorption of surfactants
A. Cwirzen, K. Habermehl-Cwirzen, and V. Penttala
Helsinki University of Technology, Faculty of Engineering and Architecture
L.I. Nasibulina, S.D. Shandakov, A.G. Nasibulin, E.I. Kauppinen, and P.R. Mudimela
Helsinki University of Technology, NanoMaterials Group, Department of Applied Physics
and Center for New Materials
182
A. Cwirzen et al.
on the functionalized surfaces, [7, 12]. The present paper will describe new type of
Portland cement incorporating in-situ grown CNTs and carbon nano fibers (CNF)
named as CHH cement (Carbon Hedge Hog cement). Basic mechanical and electrical properties of the obtained hydrated matrix will be described.
2 Production of CHH and Experimental Setup
The CHH cement is produced from Portland cement by growing the CNTs/CNFs
from Fe catalyst particles naturally occurring in cement. The processes included in
production of the CHH cement composite are shown schematically in Figure 1.
The CNTs/CNFs were grown using a modified Chemical Vapor Deposition
(CVD) method, [11]. The modification included addition of a screw feeder, which
allowed continuous productions of the CHH cement.
The obtained hybrid material was called Carbon Hedge Hog (CHH) cement. A
SEM image of cement particles with grown CNTs/CNFs is shown in Figure 2.
The amount and morphology of the grown CNTs/CNFs depended on the applied temperatures, which varied from 500 to 700⁰C, on the flow speed of pristine
cement and on the type/amount of the introduced gas. In this paper only results
obtained from CEM I 42.5 N (SR) produced by Finnsementti Oy will be presented. The main chemical phases of that cement were C3S (68%), C2S (13%), C3A
2
(1%) and of C4AF (13%). The specific surface area was 360 m /kg and the bulk
3
density was 3100 kg/m .
Seven mixes were studied in this part of the research. Constant water to binder
ratio of 0.5 was used for all mixes. The amount of added superplasticizer equaled
1.5% as calculated by weight of the binder. Each mix contained CHH produced
under different conditions, which resulted in different amounts of the grown
Fig. 1 Production process for CHH cement composite
CHH Cement Composite
183
Fig. 2 SEM image of CHH cement particle as produced by the modified CVD method
CNTs/CNFs varying from 2 to 20% by weight of produced binder, [13]. The obtained workability varied from fluid to plastic and enabled to fill the formworks
with just light vibration.
The compressive and flexural strengths were determined by using beams hav3
ing dimensions of 10 x 10 x 60 mm . These small sizes of the specimens were
dictated by the small amount of available materials. In order to increase the homogeneity of the mix, and especially to reduce the amount of entrapped air, a special
small volume vacuum mixer was used.
3 Tests Results and Discussion
The studies of the mechanical properties revealed no significant change of the
flexural strength of any of the studied mixes in comparison with the reference
paste. On the other hand, the measured compressive strength, Figure 3, showed a
remarkable increase in the case of mixes C3 and C6. Mixes C1, C2, C4, and C5
revealed lower strength in comparison with the reference pristine cement.
The main reason for these variations is the amount of the CNTs/CNFs present
on the cement particles. The TG studies which results are published elsewhere
[12] have confirmed that conclusion. Furthermore, the recorded electrical resistivity values showed significant differences. The highest conductivity was obtained
for mixes C1 and C2. At the same time, these mixes showed the lowest compressive strength values. On the bases of SEM and TG results, it can be attributed
mainly to the high amount of the CNTs/CNFs, which covered tightly the surface
of the cement particles. As a result, the access of water to cement was significantly
limited with resulted in a lower hydration degree. Furthermore, the morphology
of the grown nanofibers could affect the obtained results. For instance, longer,
more spiral-like shaped and with more surface defects, CNTs/CNFs could be
characterized by better bond with the binder matrix. Additionally bond strength
could be also increased by actual embedment of the catalyst particle into the hydration phases which adds a chemical bond possible otherwise by functionalization of the surfaces.
184
A. Cwirzen et al.
Compressive strength
Resistivity
4.0
10
2.0
0
0.0
C7
20
C6
6.0
C5
30
C4
8.0
C3
40
C2
10.0
C1
50
Electrical resistivity [Mёcm]
12.0
Ref.1
28-day compressive strength [MPa]
60
Fig. 3 28-day compressive strength and electrical resistivity [13]
The SEM studies showed that during hydration processes the CNTs/CNFs were
imbedded into the CSH matrix. Furthermore, as seen in Figure 4, a bridging of
voids occurred. Studies of the resin impregnated and polished specimens’ revealed
that the microstructure was regular for any binder matrix made of Portland cement
at water to binder ratio of 0.5. Interestingly, there was significantly less Portlandite present in the hydrated CHH matrix in comparison with specimens produced
from pristine SR cement as observed on polished section in the SEM using back
scattered electron detector (BSE). These results were also confirmed by XRD
measurements which results were published elsewhere, [11, 12].
Fig. 4 Hydrated CHH binder: a) fractures surface, b) polished surface [13]
CHH Cement Composite
185
4 Conclusions
The CHH cement composite is a new material obtained after hydration of Portland
cement modified with CNTs/CNFs by application of chemical vapor deposition
method. The resulting material is characterized by high amount of incorporated
CNTs/CNFs, which are uniformly distributed thought out the binder matrix and
partly chemically bonded to it through a catalyst particle originating from Portland
cement. It was possible to obtain a composite containing up to 20% of nanofibers.
The mechanical properties of the composite were improved providing that the optimum amount of the nanofibers was grown. The electrical conductivity was increase
by one order of magnitude allowing to classify this materials a semiconductor.
Acknowledgments. The results presented in this paper belong to a research project financed by Finnish Academy of Sciences, which is gratefully acknowledged.
References
1. Iijima, S.: Helical microtubules of graphitic carbon. Nature 354, 56–58 (1991)
2. Gao, L., Jiang, L., Sun, J.: Carbon nanotube-ceramic composites. J. Electroceram,
1751–1755 (2006)
3. Dubios, P.H., Alexandre, M.: Performant Clay/Carbon Nanotube Polymer Nanocomposites. Adv. Eng. Mater. 8, 147–154 (2006)
4. Girifalco, L.A., Hodak, M., Lee, R.S.: Carbon nanotubes, buckyballs, ropes, and a
universal graphitic potential. Phys. Rev. B 62, 13104–13110 (2000)
5. Li, G.Y., Wang, P.M., Xiaohua, Z.: Pressure-sensitive properties and microstructure of carbon nanotube reinforced cement composites. Cement Concrete Comp. 29, 377–382 (2007)
6. Kowald, T.: Influence of surface-modified Carbon Nanotubes on Ultrahigh Performance Concrete. In: Proceedings of International Symposium on Ultra High Performance Concrete, September 2004, pp. 195–203 (2004)
7. Cwirzen, A., Habermehl-Cwirzen, K., Penttala, V.: Surface decoration of carbon nanotubes and mechanical properties of cement/CNT composites. Adv. Cem. Res. 20, 65–
73 (2008)
8. Yao, N., Lordi, V., Ma, S.X.C., Dujardin, E., Krishnan, A., Treacy, M.M.J., Ebbesen,
T.W.: Structure and oxidation patterns of carbon nanotubes. J. Mater. Res. 13, 2432–
2437 (2000)
9. Ebbesen, T.W., Hiura, H., Bisher, M.E., Treacy, M.M.J., Sheeve Keyer, J.L., Haushalter, R.C.: Decoration of Carbon Nanotubes. Adv. Mater. 8, 155–157 (1996)
10. Moisala, A., Nasibulin, A.G., Kaupinen, E.I.: The role of metal nanoparticles in the
catalytic production of single-walled carbon nanotubes – A review. J. Phys-Condens
Mat. 15, 3011–3035 (2003)
11. Cwirzen, A., Habermehl-Cwirzen, K., Shandakov, D., Nasibulina, L.I., Nasibulin, A.G.,
Mudimela, P.R., Kauppinen, E.I., Penttala, V.: Properties of high yield synthesized carbon nano fibers/Portland cement composite. Adv. Cem. Res. (submitted) (2008)
12. Cwirzen, A., Habermehl-Cwirzen, K., Shandakov, D., Nasibulina, L.I., Nasibulin,
A.G., Mudimela, P.R., Kauppinen, E.I., Penttala, V.: CHH cement composites - microstructure and hydration processes. Cement Concrete Res. (submitted) (2008)
13. Cwirzen, A., Habermehl-Cwirzen, K., Shandakov, D., Nasibulina, L.I., Nasibulin,
A.G., Mudimela, P.R., Kauppinen, E.I., Penttala, V.: Mechanical and selected physical
properties of cement pastes produced by using Portland cement modified with multiwalled carbon nanotubes. In: Proc. 8th International Symposium on Utilization of
High-Strength and High-Performance Concrete, Tokyo, Japan (2008)