The Use of Nanoparticle Admixtures to Improve the Performance of Concrete

Konstantin Sobolev, Ismael Flores-Vivian, Vyatcheslav Falikman, The Use of Nanoparticle

Admixtures to Improve the Performance of Concrete, The 4th International fib Congress, Mumbai, February 10-14, 2014.

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THE USE OF NANOPARTICLE ADMIXTURES TO

IMPROVE THE PERFORMANCE OF CONCRETE

Konstantin Sobolev, Ismael Flores Vivian

Department of Civil Engineering and Mechanics, University of Wisconsin-Milwaukee,

3200 N Cramer Street, Milwaukee, WI, 53211, USA

Vyatcheslav Falikman

Department of Binders and Concrete Technologies, Moscow State University of Civil Engineering,

26 Yaroslavskoe Shosse, Moscow, 129337, Russia

Abstract

Processes occurring at the nanoscale ultimately affect the engineering properties and long-term

performance of concrete. Concrete can be nano-engineered by incorporating nano-sized objects to control material behavior and add novel properties, or by grafting molecules onto cement particles,

cement phases, aggregates, and additives to provide surface functionality.

The nanoparticle is the elementary building block in nano-materials and is comprised of cluster of

atoms with a size of 1-100 nm. Nanoparticles have been used to enhance the mechanical

performance of materials, including metals, polymers, ceramic, and concrete composites. Nanosilica (nanoparticles of silicon dioxide, nano-SiO2) is effective admixture improving the

workability and strength of high-performance and self-compacting concrete. This article reviews

the beneficial effects of the nanoparticles on the improvement of concrete performance.

Keywords: Cement, Composites, Concrete, Nanoparticles, Nano-SiO2, Nanotechnology, Strength

1. Introduction

The majority of nano-research in construction has investigated the structure of cement-based

materials and fracture mechanisms in composites (Trtik and Bartos, 2001). With new advanced

equipment, it is possible to observe the structure at its atomic level and even measure the strength, hardness and other basic properties of the micro- and nano-scopic phases of materials.

Considerable progress over recent years has been achieved by the employment of nano-scale

characterization to understand nano-scale processes in cementitious materials The application of atomic force microscopy (AFM) for investigating the “amorphous” calcium silicate hydrate (C-S-

H) gel discovered that at nanoscale this product has a highly ordered structure (Plassard et al.,

2004). Better understanding the structure at nano-level helps to influence the important processes

related to production and use of construction materials—strength development, fracture, corrosion and developing new functionalities. Façade and interior applications require new finishing

materials with self-cleaning properties, discoloration resistance, anti-graffiti, and high-scratch

resistance. Self-cleaning tiles, window glass, and paints were developed using the TiO2 photocatalyst technology which is based on the decomposition of organic pollutants under

ultraviolet (UV) light (Cassar et al., 2003).

Nano-chemistry with its “bottom-up” possibilities offers new products that can be effectively

applied in concrete technology. One example is related to the development of new

superplasticizers for concrete, such as the polycarboxylic ether polymers (PCE) targeting the extended slump retention of concrete mixtures. It was proposed that, when nanoparticles are

incorporated into conventional building materials, such materials can possess advanced or smart



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properties required for the construction of high-rise, long-span or intelligent civil and

infrastructure systems (Trtik and Bartos, 2001; Sobolev et al., 2005). Nano-SiO2 (Fig. 1) has proved to be a very effective additive to composites to improve strength, flexibility, and durability.

The particle size and specific surface area scale related to concrete materials reflect the general

trend to use finer materials (Fig. 2). For decades, major developments in concrete performance

were achieved with the application of super-fine particles such as fly ash, silica fume, and now, nanosilica.

Figure 1: Spherical nano-SiO2 particles of uniform distribution observed under a transmision electron

microscope (Flores et al 2010)

Specific Surface Area, m2/kg

0.01

1

100

10,000

1 10 100 1,000 10,000 100,000 1,000,000 10,000,000

Particle Size, nm

Nanosilica

Precipitated Silica Silica Fume

Finely Ground Mineral Additives

Portland Cement

Fly Ash

Natural Sand

Coarse Aggregates

Metakaolin

Aggregate Fines

Conventional Concrete

High-Strength/High-Performance Concrete

Nano-Engineered Concrete

1,000,000

1,000

100,000

10

0.1

Figure 2: Particle size and specific surface area related to concrete materials (Sobolev et al., 2005)

2. Properties of Concrete with Nanoparticles

As defined by Sanchez and Sobolev (2010), concrete can be nano-engineered by the incorporation

of nano-sized (less than 100 nm) building blocks or objects (e.g., nanoparticles and nanotubes) to

https://www.researchgate.net/publication/224890925_Performance_of_Cement_Systems_with_Nano-_SiO2_Particles_Produced_Using_Sol-Gel_Method?el=1_x_8&enrichId=rgreq-0d2b7136-65ad-4c1d-b775-87e1e57f57e8&enrichSource=Y292ZXJQYWdlOzI2MjcyODY5OTtBUzoxMDMwODA3NzUzODkxOTFAMTQwMTU4Nzc4MDUwOA==



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control material behavior and add novel properties, or by the grafting of molecules onto cement

particles, cement phases, aggregates, and additives (including nano-sized additives) to provide surface functionality, which can be adjusted to promote specific interfacial interactions.”

Nano-binder with a nano-dispersed cement component used to fill the gaps between the particles of mineral additives was proposed (Sobolev et al., 2005). The nano-sized cementitious component

can be obtained by the colloidal milling of portland cement (the top-down approach) or by the self-

assembly using mechano-chemically induced topo-chemical reactions (the bottom-up approach).

The addition of small amounts of calcium silicate hydrate (C-S-H) to portland cement and

tricalcium silicate (C3S) pastes was investigated by Thomas et al. (2009). It was demonstrated that nano-C-S-H particles cause a significant acceleration of the early hydration. It was proposed that

C-S-H provides nucleation sites for the precipitation of hydration products out of the pore solution.

The most of the experimental work on particle incorporation into cementitious systems was

conducted using nano-SiO2 (Fig. 1).

The accelerating effect of 5% nano-SiO2 on the hydration of C3S (alite, Ca3SiO5) was reported by

Björnström et al. (2004). The increased rates of C3S dissolution and subsequent accelerated

formation of C-S-H gel were revealed with diffuse reflectance infrared Fourier transform (DR-FTIR) spectroscopy and differential scanning calorimetry (DSC). The DSC results suggest that the

addition of colloidal silica (CS) mostly affects the initial silica polymerization rates rather than the

amount of ultimate product (Björnström et al., 2004). Qing et al. (2007) investigated the effect of nano-SiO2 (NS) addition at a dosage of 1-5% on

microstructure and strength of superplasticized cement pastes with 13% of ground granulated blast

furnace slag (BFS). It was demonstrated that the addition of nano-SiO2, even at small dosages, reduces the amount of calcium hydroxide (CH) formed at the aggregate’s interface and reduces the

size of CH crystals, thereby improving the aggregate’s interfacial transition zone (ITZ), Fig. 3.

The “bottom-up” sol-gel synthesis of nano-SiO2 (Table 1) and the effects of this material on the

performance of cement systems were reported by Flores et al (2010). The sol-gel process involves

the formation of a colloidal suspension (sol) and gelation of the sol to form a network in a

continuous liquid phase (gel). Usually, trymethylethoxysilane or tetraethoxysilane (TMOS/TEOS) is applied as a precursor for synthesizing nanosilica. The sol-gel formation process can be

simplified to few stages:

1. Hydrolysis of the precursor;

2. Condensation and polymerization of monomers to form the particles;

3. Growth of particles; 4. Agglomeration of particles, followed by the formation of networks and gel structure;

5. Drying (optional) to remove the solvents and thermal treatment (optional) to remove the

surface functional groups and obtain the desired crystal structure.

There are a number of parameters that affect the process, including pH, temperature, concentration

of reagents, H2O/Si molar ratio (between 7 and 25), and type of catalyst. When precisely executed, this process is capable of producing perfectly spherical nanoparticles of SiO2 within the size range

of 1–100 nm. The chemical reaction of nanosilica synthesis can be summarized as:

The design and properties of nano-SiO2 are summarized in Table 1 and Fig. 4. The addition of 0.25% nano-SiO2 improved the compressive strength of standard mortars by 17% and 10% (vs.

reference, NPC) at the age of 1 day and 28 days, respectively. The performance of mortars with

commercial nanosilica, cembinder 8 (CB-8) and silica fume (SF), was over-performed by developed sol-gel nano-SiO2 materials 3B3 and 3A3 synthesized at a molar ratio of

TEOS/Etanol/H2O of 1/6/24 (Fig. 5).

The distribution of nano-SiO2 particles within the cement paste is an important factor governing

the performance; therefore, the disagglomeration of nanoparticles is essential to obtain the



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composite materials. The application of PCE superplasticizers, ultrasonification and high-speed

mixing were proven to be an effective method to distribute nano-SiO2.

Figure 3: The interaction between nano-SiO2 (NS) and Ca(OH)2 at the interface between paste and aggregate

with time determined by X-Ray diffraction as compared with silica fume (SF) Qing et al. (2007)

Li (2004) performed a laboratory study of superplasticized high-strength concrete incorporating

50% of class F fly ash and 4% of nano-SiO2. It was demonstrated that the pozzolanic reaction of

nano-SiO2 is very quick, reaching 70% of its ultimate value within three days. The addition of 4%

nano-SiO2 to fly ash systems accelerated the pozzolanic reaction of fly ash. It was concluded that



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the use of nano-SiO2 increases both the early-age (with 81% higher 3-day strength) and the

ultimate strength of high-volume fly ash concrete.

Table 1. Design and properties of nano-SiO2 (Flores et al 2010).

Specimen Type*

Molar Ratio TEOS/Etanol/ H2O

Reaction Time, hours

Particle Size (TEM), nm

Surface Area (BET), m2/kg

1B3 1/ 24 / 6 3 15-65 116,000

2B3 1/ 6 / 6 3 30, 60-70 145,000

3B3 1/ 6 / 24 3 15-20 133,000

4B3 1/ 24 / 24 3 5 163,000

1A3 1/ 24 / 6 3 5 510,100

2A3 1/ 6 / 6 3 <10 263,500

3A3 1/ 6 / 24 3 <10, 17 337,100

4A3 1/ 24 / 24 3 5 382,200

* BET- Brunauer–Emmett–Teller (BET) theory; TEM- Transmission Electron Microscope

* Sample coding:

a) b)

Figure 4: The morphology of nano-SiO2 (by transmision electron microscope) synthesized using

sol-gel method at a molar ratio of TEOS/Etanol/H2O of 1/6/24 with pH=2 (a) and pH=9 (b) (Flores et al 2010)

Figure 5: Compressive strength of investigated mortars at different ages (Flores et al 2010).

First number denotes molar ratio combination as per as experimental matrix

ABC Last number corresponds to the reaction time in hours

Letter – denotes reaction media: A- for acid and B- for base



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Porro et al. (2005) investigated the effect of the size of SiO2 nanoparticles used at different dosages

on the performance of portland cement pastes. It was demonstrated that the compressive strength of the cement pastes increased with the reduction of the particle size (Fig. 6). This improvement

was attributed to the formation of larger C-S-H silicate chains in mixtures with nano-SiO2.

Strength increase, % Strength increase, %

Dosage, % Dosage, %

Figure 6: The effect of nanosilica type and dosage on the flexural (left) and compressive (right) strength (%

increase) of cement pastes (Porro et al. 2005)

Collepardi et al. (2002) studied the performance of low-heat self-compacting concrete (SCC)

produced with 1-2% of nano-SiO2. It was reported that the addition of nanosilica makes the

concrete mixture more cohesive and reduces bleeding and segregation. The best performance was

demonstrated by concrete with ground fly ash, 2% nanosilica, and 1.5% of superplasticizer. This concrete had the highest compressive strength of 55 MPa at the age of 28 days and the desired

behavior in fresh state: low bleeding, cohesiveness, higher slump flow, and very little slump loss.

3. Developing New Functionalities

The photocatalytic particles were applied in white cement-based concrete introducing self-cleaning

and air-purification features (Cassar et al., 2003). Architectural concrete needs to maintain the

aesthetic characteristics such as color over the entire service life, even in highly polluted urban environments; however, different pollutants adhere to the concrete surface and alter the

appearance. The application of photocatalytic materials is a solution for destroying the organic

pollutants and removing inorganic matter from the surface of architectural concrete. One of the

most popular photocatalytic materials used in cement is the nano-sized anatase polymorph of TiO2.

Under solar radiation, nitrogen oxide (NO) in the air is oxidized and converted to nitrate. The cement matrix entraps the NO2 and the nitrate salts are formed in alkaline environment. The

complete process can be described by the following reaction (Cassar et al., 2003):

NO + OH- → NO2 + H

+

NO2 + OH- → (NO3)ads + H

+

Accelerated 8-hour irradiation tests (with the wavelength more than 290 nm stimulating intensive solar light) of samples with 5% of nano-TiO2 treated with phenanthroquinone solution in methanol

(at a density of 0.1 mg/cm2, resulting in homogeneous yellow color) almost completely restored

the original reflectance spectra of the samples and turned their color back to white. Such treatment

corresponds with approximately one month of sunlight exposure. It was reported that the photocatalytic nano-TiO2 embedded into cement matrix is effective for NOx abatement (Fig. 7).

0

20

40

60

80

100

120

140

0 2 4 6 8 10 12 14

Flexural Strength in Portland Cement Pastes

with Nanosilica Aditions

100-1000 nm20 nm5 nm

% in

cre

ase

% adition

0

10

20

30

40

50

60

70

0 2 4 6 8 10 12 14

Compression Strength in Portalnd Cement Pastes

with Nanosilica Adition

100-1000 nm20 nm5 nm

% in

cre

ase

% adition



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Figure 7: The photocatalytic effect of TiO2 - cement composite:

left, in the dark and right, under UV light (Cassar et al., 2003)

4. Future Developments

Vast progress in concrete science is expected in coming years by the adaptation of new knowledge

generated from the rapidly growing field of nanotechnology. Development of the following

concrete-related nanomaterials is on the way or can be anticipated (Sobolev et al., 2005):

Catalysts for the low-temperature synthesis of clinker and accelerated hydration of

conventional cements;

Grinding aids for superfine grinding and mechano-chemical activation of cements;

Binders reinforced with nano-particles, nano-rods, nano-tubes (including single walled

nanotubes, SWNTs), nano-dampers, nano-nets, graphenes, or nano-springs;

Binders with enhanced/nanoengineered internal bond between the hydration products;

Binders modified by nano-sized polymer particles and their emulsions, or polymeric nano-

films;

Bio-materials (including those imitating the structure and behavior of mollusk shells);

Cement-based composites reinforced with new fibers containing nanotubes, as well as fibers

covered with nano-layers (e.g., to enhance the bond, corrosion resistance, or introduce new

properties such as electrical conductivity);

Next-generation superplasticizers for “total workability control” and supreme water reduction;

Cement-based materials with supreme strength, ductility, and toughness;

Binders with controlled internal moisture supply to avoid/reduce micro-cracking;

Cement-based materials with engineered nano- and micro- structures exhibiting supreme

durability;

Eco-binders modified by nanoparticles and produced with substantially reduced volumes of

portland cement component (down to 10-15%);

Eco-binders with nanoparticles based on the alternative systems (MgO, phosphate,

geopolymers, gypsum);

Self-healing materials and repair technologies using nano-tubes and chemical admixtures;

Materials with self-cleaning/air-purifying features based on photocatalyst technology;

Materials with controlled electrical conductivity, deformative properties, non-shrinking and

low thermal expansion;

Smart materials, such as temperature-, moisture-, stress-sensing or responding materials.

Mechano-chemistry and nano-catalysts could change the face of modern cement industry by

significantly reducing clinkering temperature and even realizing the possibility of cold-sintering clinker minerals in mechano-chemical reactors.



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5. Conclusions

Portland cement, one of the largest commodities consumed by humankind, has significant, but not completely explored potential. Better understanding and precise engineering of an extremely

complex structure of cement-based materials at the nanolevel will result in a new generation of

concrete that is stronger and more durable, with desired stress-strain behavior and possibly possessing the range of newly introduced “smart” properties, such as electrical conductivity,

temperature-, moisture-, and stress-sensing abilities.

Nanoparticles, such as silicon dioxide, were found to be a very effective additive to polymers and

concrete, a development recently realized in high-performance and self-compacting concrete with

improved workability and strength. Nano-binders and nano-engineered cement with nano-sized cementitious component or other nano-sized particles are the next ground-breaking development.

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The Use of Nanoparticle Admixtures to Improve the Performance of Concrete