Journal of Materials Science and Engineering A 7 (9-10) (2017) 241-245 doi: 10.17265/2161-6213/2017.9-10.002

Nano and Microstructural Characterization of Phases

and Interfaces of Portlant Cement Mortar Using High

Resolution Microscopy

Matheus de Faria e Oliveira Barreto1 and Paulo Roberto Gomes Brandão2

1. Department of Civil Engineering, University of the State of Minas Gerais, Divinópolis/Minas Gerais 35501-170, Brazil

2. Department of Mining Engineering, Federal University of Minas Gerais, Belo Horizonte/Minas Gerais 31270-901, Brazil

Abstract: This paper proposes to go a little further on the microstructural characterization of surfaces and interfaces of Portland cement mortars. Using scanning electron microscope high-resolution (SEM-FEG), will be used to clarify the micro and nanometric details of cementitious material in Portland cement mortars. The technique of sample preparation is relatively simple compared to other devices and allows the analysis of samples in a natural state which ensures ideal conditions for the characterization of the material. In photomicrographs using high resolution scanning electron microscope (SEM-FEG), increases of about 80 thousand times with great quality were possible, in this paper, we can see above, photomicrographs with an increase of up to 50 thousand times, which enables the visualization of nanopores in mortar matrix. Photomicrographs made in SEM-FEG dual FIB 3D and SEM-FEG Quanta confirm the predominance of euhedral crystals of ettringite in the block-ceramic mortar, characterized by their morphology of hexagonal crystals acicular interface region, and we can also check the lamellar morphology characteristic of portlandite. Photomicrographs made with the SEM-FEG Dual-FIB and SEM-FEG Quanta have confirmed the predominance of euhedral crystals of ettringite in the block-ceramic mortar interface region, characterized by their morphology of hexagonal acicular crystals. Also, the typical morphologies of portlandite, calcite and CSH (calcium silicate hydrate) have been observed with great detail. Key words: Nano and microstructural characterization, mortar, scanning electron microscopy, interfaces and surfaces, cementitious materials.

1. Introduction

The need for research and characterization of

materials aimed to the construction industry has been

growing due to the need for proper selection of

materials, based on the performance of the system

under study, as well as the increasingly constant

shortage of raw materials and market demand for

products with adequate performance and durability.

Only the evaluation of mechanical properties such as

tensile strength of the mortar is not enough to ensure

proper performance of mortar coating systems,

especially in Portland cement mortars that have micro-

and nano-structures still little explored. Thus, this

Corresponding author: Matheus de Faria e Oliveira Barreto,

Ph.D., professor, research fields: civil engineering and civil construction, building materials and cement materials, quality management, planning and certification.

paper proposes to contribute on the microstructural

characterization of surfaces and interfaces of Portland

cement mortars used for coating in construction

works.

2. Portland Cement Mortar

The mortar used in construction is commonly

composed of washed river sand and the natural

binders are generally Portland cement and hydrated

lime [1]. Examples of cement mortar: mortar

roughcast (due to strength gain in the short term) and

mortar cemented floors (due to the requirement of

mechanical and wear resistance). Examples of cement

and lime mortar are: mortar coating (plaster) for

roofing and walls (due to the fact of cement mortars,

though more resistant, have a worse workability, the

addition of lime helps to make them more plastic and

D DAVID PUBLISHING

Nano and Microstructural Characterization of Phases and Interfaces of Portlant Cement Mortar Using High Resolution Microscopy

242

of smooth finishing).

2.1 Microstructure of Portland Cement Mortars

Kinetics of Hydration of Portland Cement

The cement paste and concrete themselves are very

complex heterogeneous materials with different

structures ranging from nanoscale to macroscopic

scale. They consist of amorphous and crystalline

phases and pores [2].

The mixture of cement particles in water triggers a

series of chemical reactions that occur at different

speeds and are influenced by each other, leading to

physical, chemical and mechanical changes within the

system. The products of these reactions—stable

hydrated compounds—adhere to each other giving the

cement adhesive and cohesive properties [3].

The microstructure of the hydrated cement-based

material consists of: solid phase (essentially C-S-H,

CH, Aft, AFm, unhydrated and inert cement particles

and aggregates); pores (with different shapes,

dimensions and connectivity), and liquid and gas

phases (inside the pores). The hydrated C-S-H

compounds are the most important binding phase

since they establish van der Waals bonds that ensure

the agglomeration of solid phases and determine their

cohesion and adhesion [4].

3. Materials and Methods

The scanning electron microscopy, high-resolution

(SEM-FEG) was used to clarify the micro and

nanometric details of cementitious material in

Portland cement mortars. Special emphasis was given

to the CSH phase of hydrated cement, due to its

extremely fine fabric, at the nanoscale, and its

predominantly amorphous structure.

3.1 Microstructure of Portland Cement Mortars

Equipment Used for the Characterization

Two high resolution SEM-FEG instruments

belonging to UFMG’s Microscopy Center have been

used, which are listed below:

(a) Scanning electron microscope with FEG (field

emission gun), FEI brand, Quanta 200 FEG model,

called hereafter as SEM-FEG Quanta, with resolution

of 1.6 nm at 30 kV in high vacuum.

(b) Dual beam scanning microscope with ion gun

and electron FEG, FEI brand, Dual-FIB Quanta 3D

model, called hereafter as SEM-FEG Dual-FIB, with

resolution (electron beam) of 0.8 nm at 30 kV in high

vacuum.

All the photomicrographs shown in this work were

obtained with SEI (secondary electrons image).

3.2 Preparation of the Samples of Portland Cement

Mortar

Three panels of masonry were built and mortar was

applied over them with roughcast trait (1:3) of Portland

cement and washed river sand: on top of these, three

different coatings were further applied, one for each

panel: (a) a plaster cladding with stroke (1:6) of

Portland cement and washed river sand; (b) a mortar

coating (1:1:4) of cement, lime and sand; (c) a mortar

lining with a stroke (1:2:8) of cement, lime and sand.

For sample preparation, approximately 12 cm 12

cm pieces of the panels contain the complete system,

ceramic block, roughcast mortar and mortar coatings.

After the removal, the 12 cm 12 cm samples were

fragmented and reduced to approximately 6.5 cm.

Sample fracture was used instead of cutting hard, not

to interfere with the sample surfaces.

After that, the fragmented samples were prepared

for analysis in the two scanning electron microscopes.

Three sample preparation techniques were used,

regarding the deposition of a conducting film: (ⅰ) 5

nm-thich carbon film (Fig. 1); (ⅱ) 10 nm gold thin

layer (Fig. 2). The third technique consisted of not

using any kind of coating (Fig. 3), and analyzing the

samples under low vacuum in the SEM. This

technique was used to obtain unbiased chemical

microanalyses by the EDS (energy-dispersive (X-ray)

spectrometer), due to the absence of carbon or gold

Fig. 1 Mort

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243

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Nano and Microstructural Characterization of Phases and Interfaces of Portlant Cement Mortar Using High Resolution Microscopy

245

In addition, the relatively large prism on the upper part

of the photo is probably calcite.

5. Conclusions

Using high-resolution scanning electron microscope

(SEM-FEG) proved extremely important in the

characterization of cementitious materials, as in the

case of this study, Portland cement mortars. The

technique of sample preparation is relatively simple

compared to other methods and allows the analysis of

samples in a natural state which ensures ideal

conditions for the characterization of the material.

Moreover, the quality of the photomicrographs is

substantially better than with the conventional SEMs,

which combined with the chemical microanalysis by

EDS, allows a substantial advance in the research and

characterization of cementitious materials.

In observations using high resolution scanning

electron microscope (SEM-FEG), magnifications of

about 80,000 with great quality have been possible,

in this work. Even the visualization of nanopores in

mortar matrix could be done, as proved in some

cases.

Photomicrographs made with the SEM-FEG

Dual-FIB and SEM-FEG Quanta have confirmed the

predominance of euhedral crystals of ettringite in the

block-ceramic mortar interface region, characterized

by their morphology of hexagonal acicular crystals.

Also, the typical morphologies of portlandite, calcite

and CSH have been observed with great detail and

quality in other samples of the mortars studied.

Acknowledgments

The authors are grateful to the following institutions

and offices: the UFMG (Federal University of Minas

Gerais), the School of Engineering and the

Post-Graduate Program in Metallurgical, Materials

and Mining Engineering, and to CAPES/PROEX for

financial support and the scholarship to Barretom, M.

F. O. The co-author Brandão, P. R. G. also

acknowledges CNPQ for a research grant.

References

[1] FIORITO, A. J. S. I. 1994. Manual de argamassas e revestimentos; estudos e procedimentos de execução. 1.ed. São Paulo: Editora Pini, 221.

[2] DAVYDOV, Denis. 2010. “Visco-elasto-plastické vlastnosti cementové pasty.” Ph.D. thesis, Ceské Vysoké Ucení Technické V Praze, Praha, leden, 196.

[3] COSTA, C., ALMEIDA DE CARVALHO, P., BORDADO, J. C., and NUNES, A. 2009. “Estudo de Argamassas de Base Cimentícia por Microscopia Electrónica de Varrimento.” Ciência & Tecnologia dos Materiais 21: 31-5.

[4] BARRETO, M. F. O. 2014. Caracterização micro-nanoestrutural e química de argamassas de cimento Portland, Tese de Doutorado, Belo Horizonte-Brasil, 248.