Mineralogical study of polymer modified mortar with silica fume

Construction
and Building

MATERIALS

Construction and Building Materials 20 (2006) 882–887

www.elsevier.com/locate/conbuildmat

Mineralogical study of polymer modified mortar with silica fume
Alessandra E.F.de.S. Almeida *, Eduvaldo P. Sichieri
School of Engineering of Sa˜o Carlos, University of Sa˜o Paulo, Av. Trabalhador Sa˜o Carlense, 400 - CEP: 13566-590, Sa˜o Carlos, Sa˜o Paulo, Brazil
Received 29 September 2004; received in revised form 16 June 2005; accepted 30 June 2005
Available online 6 September 2005

Abstract
Experimental investigation on the effects of styrene acrylic polymer and silica fume on the mineralogical composition of pastes of
high-early-strength portland cement after 28 days of casting are presented in this paper. Thermogravimetry and derivative thermogravimetry were used to study the interaction between polymers and cements, and the extent of pozzolanic reaction of mortars with
silica fume. Differential scanning calorimetry and X-ray diffraction were also used to investigate the cement hydration according to
the additions. The results showed that the addition of silica fume and polymer reduces the portlandite formation due to delaying of
portland cement hydration and pozzolanic reaction.
Ó 2005 Elsevier Ltd. All rights reserved.
Keywords: Silica fume; Polymer; Thermal analysis; X-ray diffraction

1. Introduction
Polymers have been used for improving mechanical
properties, adhesion with substrates, or waterproofing
properties of mortars and concretes. Pozzolanic materials can partially substitute Portland cement in order to
enhance the properties of concrete and mortars such
as durability and mechanical properties.
Polymer modified mortars are known as a popular

construction material because of their excellent performance. The fundamentals about polymer modification
for cement mortar and concrete have been studied for
the past 80 years or more. The cement mortar and concrete made by mixing with the polymer-based admixtures are called polymer-modified mortar (PMM) and
polymer-modified concrete (PMC), respectively [1,2].
Polymeric admixture, or cement modifier, is defined
as an admixture which consists of a polymeric compound that acts as a main ingredient at modifying or
*

Corresponding author. Tel.: +55 16 33 64 5788.
E-mail addresses: ,
(A.E.F.de.S. Almeida).
0950-0618/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.conbuildmat.2005.06.029

improving the properties such as strength, deformation,
adhesion, waterproofing and durability of mortars and
concretes. Polymer latex is a colloidal dispersion of
small polymer particles in water, which is obtained by
the emulsion polymerization of monomers with emulsifiers [3,4].
The physical properties of a latex-modified cement
mortar are affected by those same variables that can affect unmodified Portland cement mortars and concretes,
and by polymer typical properties, such as solids content, pH, density and minimum film formation temperature [3,4]. Acrylic polymers used with Portland cement
are composed mainly of polyacrylates and polymethacrylates, resulting from the polymerization of derivatives
of acrylic acids [4].
The literature agrees that the properties of polymermodified mortar and concrete depend significantly on
the polymer content or polymer–cement ratio, that is,
the mass ratio of the amount of polymer solids in a polymer-based admixture to the amount of cement in a polymer-modified mortar or concrete [1,2,5].
Silica fume or microsilica is an industrial by-product from electric arc furnace producing silicon and

A.E.F.de.S. Almeida, E.P. Sichieri / Construction and Building Materials 20 (2006) 882–887

ferrosilicon alloys. It has been widely used as a concrete and mortar mixture, mainly to improve the
mechanical properties and reduce porosity, due to
pozzolanic activity [6,7].
Finely ground material such as silica fume can increase the water required for a given degree of workability at low water–cement ratio, thus water reducing
admixture (or superplasticizer) is often used to improve
the workability of mortars with silica fume [6].
The correct combination of silica fume, superplasticizer and polymeric emulsions may have the synergistic
effects of these three admixtures, resulting in good performance of construction material to many applications,
for example, a high quality repairing and overlaying
materials for the application of the concrete structures
[8,9].
In the previous work, the author studied the effects
of silica fume and acrylic polymer on the mortar
properties, specifically to fix porcelain tiles [10]. This
work showed the improvement of the adherence
strength of mortars using such additions. For this reason, aim of this work is to study the influence of such
admixtures concerning the hydration of Portland cement by means of the mineralogical study of the
pastes with the same composition used in the mentioned work [10].
The interaction between polymers and cement portland can be investigated through several techniques such
as thermal analysis and X-ray diffraction. Thermogravimetry (TG), derivative thermogravimetry (DTG) and
differential scanning calorimetry (DSC) are considered
important tools for evaluating the nature of hydrated
products according to different stages of cement hydration, in addition to quantifying the different phases
[11–14].
When cement is hydrated, its main components are
transformed into hydration products, mainly calcium
silicate hydrate (C–S–H gel) and portlandite. The hydration can be evaluated by measuring the mass loss of hydrated compounds up to 900 °C. The following peaks
and temperature ranges have been studied when hydrated cement is heated in thermobalance and they are

interpreted as described below [12,13]:
 $100 °C: dehydration of pore water,
 100–300 °C: different stages of C–S–H dehydration,
 $500 °C: dehydroxylation of Ca(OH)2,
 $700 °C: decarbonation of CaCO3.
This study reports the results of investigations in
which methods of thermal analysis, TG, DTG and
DSC, were applied to investigate the effects of polymer
modification on the process of hydration of portland cement by estimating Ca(OH)2 content and calcium hydrate content. X-ray diffraction was carried out to
study the hydrate products of cement [15].

883

2. Materials
2.1. Cement and silica fume
The mortars were prepared using high-early-strength
Portland cement (CPV-ARI Plus according to NBR
5733; and Type III cement according to ASTM C150),
chemical and physical properties of cement are shown
in Tables 1 and 2, respectively, according to the manufacturer. The silica fume used was marketed by Microssilica Brazil, with specific surface area of 27.74 m2/g
obtained by BET test, and 94.3% SiO2 content.
Table 3 shows the chemical properties of the silica fume,
according to the manufacturer.
2.2. Superplasticizer
The superplasticizer marketed by MBT Brazil I.C.
was used, presenting chemical base sulfonated melamine, liquid aspect, density 1.11 g/cm3 (± 0.02), pH:
8.5 ± 16.49% solids content.
2.3. Polymer latex
 Aqueous dispersion of styrene-acrylate copolymer
with 49–51% total solids content; viscosity Brookfield

(RVT 415 °C): 1000–2000 mPas; density: 1.02 g/cm3;
pH value: 4.5–6.5.
 Minimum film-forming temperature: 20 °C.
 Mean size of particles: 0.1 lm.
 Film properties: clear and transparent.
 Stability to ageing: good.
Table 1
The chemical composition of cement
Chemical composition

CPV-ARI-Plus %

Loss on ignition
SiO2
Al2O3
Fe2O3
CaO total
MgO
SO3
Na2O
K2O
CO2
RI
CaO

3.10
18.99
4.32
3.00
64.7

0.68
3.01
0.03
0.85
1.81
0.26
1.63

Table 2
Physical properties of cement
Setting time (min)
Initial
150.78

Blaine surface
area (m2/kg)

Final
226.25

467.9

Compressive strength (MPa)
NBR 7215
1
day

3
days

7
days

28
days

27.87

43.57

48.69

56.16


884

A.E.F.de.S. Almeida, E.P. Sichieri / Construction and Building Materials 20 (2006) 882–887

Table 3
The chemical compositions of silica fume
Chemical composition

%

SiO2
Al2O3
Fe2O3
CaO
MgO

SO3
K2O
Na2O

94.3
0.09
0.10
0.30
0.43
–
0.83
0.27

The experimental conditions were: N2 gas dynamic
atmosphere (40 ml minÀ1); heating rate (10 °C minÀ1);
platinum top-opened crucible. The samples were heated
in the range À25 to 500 °C at a constant rate.
XRD was used to identify the polycrystalline phases
of cement and hardened cement paste by means of the
recognition of the X-ray patterns that are unique for
each of the crystalline phases. The qualitative XRD
investigation was performed in a Carl Zeiss-Jena Universal Diffractometer, URD6 model.

3. Experimental program

4. Results and discussion

Six mixtures were prepared as described in Table 4,
which are the pastes with the same proportions used in
the previous work [10], as explained in the introduction.

The materials were weighed and mixed in a planetarytype mortar mixer. The total quantity of water was
maintained, taking into account the water from the latex. The superplasticizer was also added in the ratio of
1% of the weight of cement.
The preparation for TG, DSC and X-ray diffraction
was carried out using agate crucible, in which the paste
was manually ground until the size of particles was
lower than 0.063 mm. For the prevention of carbonation
and maintenance of relative humidity, all specimens
were stored in the vacuum up to the time when the test
started.
The analyses were performed in the Institute of Chemistry of Sa˜o Carlos, University of Sa˜o Paulo, using a
TGA 2050 Thermogravimetric Analyzer V5.1A equipment. The experimental conditions were: N2 gas dynamic
atmosphere (40 ml minÀ1); heating rate (10 °C minÀ1);
platinum top-opened crucible. The samples were heated
in the range of 20–900 °C at a constant rate. The
Ca(OH)2 was estimated from the weight loss measured
in the TG curve between the initial and final temperature
of the corresponding TG peak.
Differential scanning calorimetry (DSC) has been employed to investigate the combined effect of silica fume
and polymer on heat development in the pastes. A
DSC 2010 differential scanning calorimeter was used.

Figs. 1 and 2 show the TG curves of pastes with silica
fume content of 5% and 10%, respectively (P5 and P6).
It can be seen that TG curves for these pastes consist
of four zones:
$25–123.3 °C: dehydration of pore water,
$123.3–420 °C: dehydration of calcium silicate
hydrates,
$420–480 °C: dehydroxylation of calcium hydroxide,

$480–730 °C: decarbonation of CaCO3.
Figs. 3 and 4 show TG curves of pastes with 5% silica
fume and polymer addition of 5.2% and 10.4% (polymeric solids). Figs. 5 and 6 present TG curves of pastes
with 10% silica fume and polymer addition of 5.2% and
10.4% (polymeric solids). The TG curves obtained in
these tests are typical of hydrated cement pastes containing carbonate phases and polymeric admixtures. As it is
shown, the curves can be divided into five major parts,
according to different reactions:
$25–123.3 °C: dehydration of pore water,
$123.3–345 °C: dehydration of calcium silicate
hydrates,
$345–427 °C: weight loss due to polymer pyrolysis,

Table 4
Mixture proportion of the mortars
Designation
of paste

Silica
fume
content
(%)a

Polymer
latex
content
(%)a

Solids of
polymer

content
(%)a

Water/
cement
ratio

P1
P2
P3
P4
P5
P6

5
5
10
10
5
10

10
20
10
20
0
0

5.2
10.4

5.2
10.4
0
0

0.36
0.31
0.36
0.31
0.36
0.36

a

By weight of cement.

Fig. 1. TG curve of the paste without polymer and 5% of silica fume
P5.


A.E.F.de.S. Almeida, E.P. Sichieri / Construction and Building Materials 20 (2006) 882–887

885

0,02

0,02

TG P6

DTG P6

100

DTG P3

100

TG P3

0,00
95

0,00
95

-0,02

-0,02

-0,04
-0,06

85
-0,08
80

90

TG (%)

TG (%)

90

85

-0,06

80

-0,10
-0,12

75

-0,04

-0,08

75

-0,10

-0,14
70

70
0

100

200

300

400

500

600

700

800

900

0

1000

100

200

300

Temperatureo( C)

500

600
o

700

800

900

-0,12
1000

Temperature ( C)

Fig. 2. TG curve of the paste without polymer and 10% of silica fume
P6.
TG P1

DTG P1

100

400

Fig. 5. TG curve of the paste P3.

0,02

0,01

DTG P4

100

TG P4

0,00

0,00
95

95

90

-0,04

85

-0,06
-0,08

80
-0,10

TG (%)

TG(%)

-0,02

-0,01

90

85

-0,02

80

-0,03

75

75

-0,04

-0,12
0

100

200

300

400

500

600

700

800

900

1000

o

Temperature ( C)

0,02

TG P2
0,00

95

-0,02

TG (%)

90

-0,04
85
-0,06
80
-0,08
75

-0,10

70
100

200

300

400

500

600

100

200

300

400

500

600

700

800

900

1000

Fig. 6. TG curve of the paste P4.

DTG P2

0

0

Temperature (oC)

Fig. 3. TG curve of the paste P1.
100

70

700

800

900

-0,12
1000

Temperature (oC)
Fig. 4. TG curve of the paste P2.

$427–475 °C: dehydroxylation of calcium hydroxide,
$475–711 °C: decarbonation of CaCO3.
The weight loss for each temperature range can be
seen in Table 5. For pastes with polymer addition, the
weight loss related with the dehydroxylation of calcium

hydroxide is lower than pastes with silica fume addition
alone.
Fig. 7 shows the DSC curves obtained for the pastes
studied. From these results, it is clear that pastes with
polymer present different results from the pastes which
do not contain polymer. All curves show an endothermic peak around 480 °C, but they are more intense for
pastes with silica fume alone because of the higher
Ca(OH)2 content. Pastes with silica fume and polymer
presents an exothermic peak around 350 °C, indicating
polymer pyrolysis, as it was found from the TG/DTG
analyses. The pastes modified with polymer presented
higher heat absorption between 100 and 200 °C, suggesting that these pastes contain more free water resulting
from the delaying of hydration, and that these have a
bigger amount of calcium silicate hydrates.
The XRD results show some qualitative differences in

the hydration rate due to the incorporation of silica and
polymer. Figs. 8–10 show the X-ray patterns of the
pastes with 5%, 10% of silica fume, and pastes with polymer. The main compounds observed are Ca(OH)2 in the


6.544
5.175
4.663
1.707
6.289
74.88

S+C

P+S

P

P

C

P

P

S+C
C

P

150

55

60

100

0

5

10

15

20

25

30

35

40

45

50

65

70

75

2θ (degrees)
Fig. 8. XRD patterns of the P1 and P2 pastes after 28 days of
hydration. P, portlandite (Ca(OH)2); CC, calcium carbonate (CaCO3);
E, ettringite (Ca6[Al(OH)6]2 (SO4)3 Æ 26H2O); S, silicates; F, ferrite.

P

P

150

P

S+C
C

P

200

P4

P

250

P+S

S+C

300

S+E+F

350

100

250

P3

P

150

P

S+C
C

P

P

200

S+E+F

S+C

300

P+S

50

100
50
0
0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

2θ (degree)
Fig. 9. XRD patterns of the P3 and P4 pastes after 28 days of
hydration. P, portlandite (Ca(OH)2); CC, calcium carbonate (CaCO3);
E, ettringite (Ca6[Al(OH)6]2(SO4)3 Æ 26H2O); S, silicates; F, ferrite.

-1,1

P+S

250

P
P
P

C

P5
P

150

P

S+C

P

200

C

0
300

Intensity (cps)

-0,5

-1,0

S+C

100
50

P1
P4
P5
P6

S+C

150

-0,4

-0,6

P+S

200

P6

S+E+F

-0,3

250

S+E+F

-0,2

300

E

ntensity (cps)I

-0,1

-0,9

P1

0

0,0

-0,8

S+C

200

S+E+F

250

50

0,1

Heat flux (mW/mg)

0
300

P

Intensity (cps)

50

form of portlandite, a small amount of CaCO3 resulting
from carbonation of Ca(OH)2 and calcium silicate anhydrous. The peak intensity in the region 2h = 18° has been

-0,7

P

24.6–123.3
123.3–344.6
344.6–429.6
429.6–476.5
476.5–713.5
Residue above 850 °C

P

5.695
4.949
2.53
1.912
6.308
77.89

P
P

25.2–123.3
123.3–344.6
344.6–427.3
427.3–474.3
474.3–711.3
Residue above 850 °C

C

5.236
4.767
5.175
2.301
7.357
74.12

S+C
C

26.1–123.3
123.3–333.4
333.4–422.9
422.9–478.8
478.8–713.5
Residue above 850 °C

S+E+F

5.922
5.037
2.665
2.095
7.412
75.04

P

25.9–123.3
123.3–337.9
337.9–429.6
429.6–481
481–711.3
Residue above 850 °C

P2

100

S+C

P4

8.43
5.238
1.876
8.436
75.23

150

P

P3

25.2–123.3
123.3–420.6
420.6–478.8
478.8–729.2
Residue above 850 °C

200

P

P2

7.487
5.75
2.056

5.258
78.9

250

P

P1

28.3–123.3
123.3–416.2
416.7–472.1
472.1–702.3
Residue above 850 °C

Intensity (cps)

P6

Weight loss (%)

Intensity (cps)

P5

Temperature range (°C)

300

P

Table 5
Weight loss of the pastes according to the temperature

P+S

A.E.F.de.S. Almeida, E.P. Sichieri / Construction and Building Materials 20 (2006) 882–887

Intensity (cps)

886

100
50
0
0

-1,2

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

2θ (degree)

-1,3
-50

0

50

100

150

200

250

300 350
o

400

450

500

Temperature ( C)

Fig. 7. DSC curves of the pastes P1, P4, P5 and P6.

550

Fig. 10. XRD patterns of the P5 and P6 pastes after 28 days of
hydration. P, portlandite (Ca(OH)2); CC, calcium carbonate (CaCO3);
E, ettringite (Ca6[Al(OH)6]2(SO4)3 Æ 26H2O); S, silicates; F, ferrite.


A.E.F.de.S. Almeida, E.P. Sichieri / Construction and Building Materials 20 (2006) 882–887

considered as a measure of the quantity of Ca(OH)2 [15].
Therefore, Figs. 8–10 show that 10% of silica fume

replacement and polymer addition resulted in the lowest
peak intensity for the portlandite.
5. Conclusions
From the thermogravimetric investigations performed, showed in the TG and DSC curves, it is possible
to conclude that mineral admixtures and polymeric additions have influenced the cement hydration, mainly when
added simultaneously. Both the pozzolanic reaction and
the delaying of hydration due to polymer addition appear to cause a decreasing on the Ca(OH)2 content.
The qualitative XRD investigation revealed that a
lower intensity of Ca(OH)2 (in the region 2h = 18°)
was obtained in the presence of latex, compared to
pastes without polymer. Similarly, we found a decrease
in the Ca(OH)2 content in the TG analyses for the pastes
with polymer addition. As it can be seen, pastes with
polymer and 10% silica fume content presented the lowest Ca(OH)2 compared with the other pastes.
The additions studied in this work resulted in the decrease of the portlandite (Ca(OH2)) content, which can
justify the improvement of the mortarsÕ performance
studied earlier by the authors.
Acknowledgments
The authors acknowledge the financial support from
FAPESP.

887

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