1
Nano-core effect in nano-engineered cementitious composites
Baoguo Han
1, *
, Liqing Zhang
1
, Shuzhu Zeng
1
, Sufen Dong
1
, Xun Yu
2,3
, Rongwei Yang
4
, Jinping Ou
1, 5
Abstract
Nanoscale impact can bring big changes in micro-meso-macroscale behaviors of the composites.
addition of nano fillers makes cementitious materials stronger, more durable and
multifunctional/smart. This paper aims at investigating the underlying mechanism for understanding
and controlling the nano-engineered cementitious composites. The nano-core effect is proposed
through integrating core-effect with nano effect, and is proved by experimental evidences for the
cementitious composites with different nano fillers. The nano-core effect is closely relative to the
intrinsic properties of nano fillers, composition and processing of the cementitious composites. The
behaviors of the nano-engineered cementitious composites are governed by nano-core effect zone,
i.e. nano-core-shell element. It is therefore concluded that the nano-core effect is fundamental for
design, fabrication and application of the nano-engineered cementitious composites.
Key words: A. Reinforced cement/plaster; A. Smart materials; B. Physical properties; B.
Microstructures
1 Introduction
Cementitious composites are the most widely used materials for infrastructures because they are
resistant to water, easily formed into various shapes and sizes, cheap and readily available
everywhere. Twice as much cementitious composites are used in infrastructures around the world
© 2017. This manuscript version is made available under the Elsevier user license
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than the total of all other building materials, including wood, steel, plastic and aluminum. In the
foreseeable future, cementitious composites will continue to play an important role in infrastructure
construction. However, the development of cementitious composites is encountering enormous
problems and challenges. Firstly, cement manufacturing has a direct and visible impact on the
world’s resources, energy consumption and environment. Making one ton of cement requires about
2 tons of raw material (limestone and shale), consumes about 4 GJ of energy in electricity, process
heat, and transport (the energy equivalent to 131 cubic meters of natural gas), produces
approximately one ton of CO
2
produces about 3 kg of NO
X
(an air contaminant that contributes to
ground-level smog), and produces about 0.4 kg of PM10 (an airborne particulate matter that is
harmful to the respiratory tract when inhaled). Secondly, increasing attention has been paid on the
security of infrastructures since cementitious composites are brittle material and usually work with
cracks. Thirdly, the durability of infrastructures is a very important issue, in particular during the
process of their design and application. Fourthly, cementitious composites are complex composites
in nature. Fifthly, the multifunctional and smart cementitious composites are required since
traditional cementitious composites that just serve as structural materials cannot meet the
requirement of the safety, longevity and function of advanced engineering infrastructures.
Nanotechnology is an emerging field related to the understanding and control of matters at
nanoscale. Nanomaterials have remarkable properties and functions which can endow cementitious
composites high-performances (including high mechanical property and durability) and
multifunctionality/intelligence. Therefore, applications and advances of nanotechnology and
nanomaterials have injected new vitality into cementitious composites [
1-5]. Nano nonmetallic
oxide and metallic oxide similar to cementitious composition are first used to enhance/modify
cementitious materials. The big gains in mechanical, durable and functional properties were
achieved. An addition of 1.5% nano-sillica (NS) increased the 3d compressive and flexural
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strengths by 45.6% and 18.4%, respectively [
6]. Meanwhile, the addition of NS can increase the
freeze-thaw resistance, chloride penetration and permeability, abrasion resistance and fire resistance
of cementitious composites [7-10]. The fracture toughness of cementitious composites can be
enhanced by 400% when nano-ZrO
2
is used as fillers [11]. An addition of 5% nano-Al
2
O
3
can
increase the elasticity modulus of cementitious composites by 143% [12]. The electrical resistance
of cementitious composites can be decreased by 45% with 5% nano-Fe
2
O
3
[12]. Nano-TiO
2
can
endow cementitious materials with the photocatalytic effect to decompose both organic pollutants
and oxides such as NO, NO
2
and SO
2
[
13]. Moreover, extensive research endeavors demonstrated
the potential of various nano carbon materials including carbon nanotubes (CNTs), carbon
nanofibers (CNFs), and graphene for enhancing/modifying cementitious materials [14-22]. The
observed best performance enhancement of cementitious with CNTs or CNFs include a 300%
increase in compressive strength, a 34.28% increase in tensile strength, a 269% increase in flexural
strength, a 270% increase in fracture toughness, a 14% increase in fracture energy, an over 600%
improvement in Vickers’s hardness at the early ages of hydration, a 2200% increase in deflection, a
130% increase in ductility, an over 430% improvement in resilience and a 227% increase in
Young’s modulus [17]. Only 0.03% of graphene can improve the tensile, flexural and compressive
strength of cementitious composites by 78.6%, 60.7% and 38.9%, respectively [17]. The presence
of CNTs obviously enhances the transport property and durability of cementitious materials [
19].
Graphene significantly improves the moisture transport performance and acid resistance of the
composites at 0.05 vol. % of dosage [17]. The electrical resistivity reduction extent of cementitious
materials with 1.52 vol. % of CNTs/nano carbon black composite filler is 99.9% [23]. The thermal
conductivity of CNTs cementitious composites is 85% greater than that of cementitious composites
without CNTs [24]. The damping capacity of cementitious composites with 2% CNTs is 1.6 times
than that of cementitious composites without CNTs [
25]. An addition of 0.6 wt. % CNTs into
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cementitious materials can lead to a 27% decrease in electromagnetic wave reflectivity at a
frequency of 2.9 GHz [17]. Additionally, the composites with CNTs, CNFs or graphene feature
smart self-sensing (e.g. sensing stress, strain, crack, damage, temperature, and smoke), self-heating
and steel cathodic protection performances. Nano fillers not only can enhance/modify the above
mentioned performances of cementitious composites in hardened state, but also have strong impact
on the rheology and workability of fresh cementitious composites [
24].
Although a lot of researches have been done on the behaviors of cementitious composites with nano
fillers, the modification mechanism of nano fillers to the performances of cementitious materials
remains elusive. Therefore, this paper will perform a fundamental research into the nano and
micro-scale phenomena that govern the behaviors of cementitious composites with nano fillers. The
nano-core effect in nano-engineered cementitious composites is firstly proposed, and it was proved
by experimental evidences of cementitious composites with different nano fillers. The factors
affecting nano-core effect are comprehensively analyzed. Finally, the concept of nano-core effect
zone is proposed to link the nano-core effect to the behaviors of the nano-engineered cementitious
composites.
2 Materials and methods
2.1 Materials
In this study,
Portland cement (P·O 42.5R conforming to the requirement of Chinese standard)
produced by Dalian Onoda Cement Co. Ltd. in China was used. Standard sand produced by Xiamen
Ai Si Ou Standard Sand Co. Ltd., China was used as aggregate. Nano fillers include NS, Nano-TiO
2
,
Nano-ZrO
2
, CNFs, and multi-layer graphene (MLG). NS with mean particle size of 12 nm produced
by Tokuyama in Japan was applied. Nano-TiO
2
with mean particle size of 20 nm was purchased
from Nanjing Haitai Nanomaterials Co., Ltd. in China. Nano-ZrO
2
(average diameter 20 nm,
Nanjing Haitai Nanomaterials Co. Ltd. in China ) was used. CNFs (trade name PR-24-XT-HHT,
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average diameter 100 nm, length on the order of 50-200 μm) were procured from Pyrograf Products,
Inc. an affiliate Applied Science, USA. The water reducing agent is polycarboxylate superplasticizer
used to disperse nano fillers.
2.2 Methods
The process of fabricating nano-engineered cementitious composites is as follows: 1) Water,
superplasticizer and nano fillers were mixed by glass bar and then sonicated to form a suspension; 2)
Cement and aggregate were put into the suspension slowly in stir pan and mixed by agitator; 3) The
mixture was poured into the oiled mould and the mould was put on the electric vibrator in order to
eliminate bubbles; 4) All nano-engineered cementitious composites were cured at temperature of
20°C in 95% relative humidity for 24 h before demold. Then specimens were cured in water at
20±1°C until the curing age
[6, 19]. Three test specimens were fabricated for each cementitious
material.
Field Emission Scanning Electron Microscope (Nova Nano SEM 450, American FEI Ltd.) was used
to observe the microstructures.
Thermogravimetry (TG) analysis was performed using a METTLER
TOLEDO STARe system to get the hydration degree of cement [26]. The condition of TG analysis
was under nitrogen atmosphere at a heating rate of 10 ºC/min up to 1000°C. X-Ray diffraction
(XRD) (Bruker D8 Advance, Bruker German) was applied for studing the tendency of crystal of
calcium hydroxide
[27]. The quasi-steady-state method is applied to test thermal conductivity with
ZKY-BRDR Quasi Steady State Specific Heat/Thermal Conductivity Coefficient Tester (Cheng Du
Century Science and Technology Co., Ltd., China) in this experiment.
3 Results and discussion
3.1 Description of the nano-core effect
The nano-core effect means the combination of nano effect and core effect caused by nano fillers
incorporated into cementitious composites. Due to the ultra high specific surface area and great