Bulletin of the Transilvania University of Brașov Vol. x (xx) – 2016 [606566]

Bulletin of the Transilvania University of Brașov • Vol. x (xx) – 2016
Series I: Engineering Sciences

EVALUATING ADHERENCE TO THE
SUBSTRATE OF FIBER REINFORCED
PLASTER MORTARS

A. MUSTEA1 D. MANEA2 R. MUNTEAN3 O. MIRON 4

Abstract: Due to the constant evolution of the consumer market, new
building materials appear continuously. One such product is the new
developed composite plaster mortar. The main purpose of the current research
is to evaluate the adh erence to the support layer of plaster mortars reinforced
with polypropylene synthetic fibers. In this experimental study, sets of 2 samples of each recipe were materialized on the substrate of solid bricks. It is
intended an analysis of the mechanical characteristics of the material, in order
to indicate a specific amount of fibers in the matrix and to recommend some proper application areas.

Key words: polypropylene; synthetic fibers; adherence; plaster mortar;
composite; reinforcement;

1. Introduction
The present paper starts from the idea that
the advantages of fibers introduced in mortars should all be
harnessed.
At present, in our domestic market, one
can find only a limited range of fiber
reinforced composite mortars, mainly used
in many precast components, in horizontal floors, blankets or similar elements, and less in plasters, where the research seems to be less directed. [1]

2. Objectives

In this study, the influence of different
doses of fiber reinforcement upon the adhesion of plaster mortars is investigated.
This new developed composite material is

1 Technical University of Cluj-Napoca , str. Memorandumului, nr. 28 , Cluj-Napoca, 400114, Romania.
2 Technical University of Cluj-Napoca , str. Memorandumului, nr. 28 , Cluj-Napoca, 400114, Romania .
3 Transilvania University of Bra șov, str. Turnului, nr. 5, Brașov, 500152, Romania.
4 Technical University of Cluj-Napoca , str. Memorandumului, nr. 28 , Cluj-Napoca, 400114, Romania. obtained through a simple technology, by
the addition of the required mass of
polypropylene fibers and mixing about five
minutes, to achieve a proper dispersal.
The evaluation of the adherence to the
substrate of these plaster mortars it is studied by comparing results of various
fiber doses (1,00 kg/m
3, 1,50 kg/m3, 2,00
kg/m3 and 3,00 kg/m3). Also, the influence
of reinforcement upon tensile strength characteristics is discussed.
For the fabrication of the mortars to be
tested, 12 mm long synthetic fibers (PP)
were used, along with six different recipes
and two control recipes (with no reinforcemet).
Table 1 shows several physical and
mechanical characteristics of different
types of fibers, including polypropylene.

Bulletin of the Transilvania University of Brașov • Vol. x (xx) – 2016
Series I: Engineering Sciences

Different fiber properties [2][3][4] Table 1
Fiber type Diameter
D
[µ] Density
ρ
[kg/m³] Tensile
strength
Rt
[kN/mm²] Elasticity
module
E
[kN/mm²] Elongation
at break
[%]
Steel 5÷800 7850 1,0÷3,0 210 3÷4
Glass 9÷15 2500 1,0-4,0 70÷80 1,5÷3,5
Polypropylene (PP) 10÷200 900 0,5÷0,8 35÷50 20÷25
Carbon (PAN-IM) 8÷9 1780÷1820 2,41÷2,93 228÷276 1,0
Carbon (PAN-UHM) 7÷10 1860 1,72 517 0,3÷0,4
Kevlar 12 1479 2,80÷3,79 131 2,2÷2,8
Polyester 20÷200 950 0,7÷0,9 8,4 11÷13
Polyethylene 20÷200 950 0,70 0,14÷0,42 10
Mineral wool 10 2700 0,5÷0,8 70÷120 0,6
Asbestos 0,02÷20 3200 0,5÷3,0 80÷150 0,5÷2,0
Polycrystalline alumina 500÷770 3900 0,65 245 –
Sisal 10÷50 1500 0,80 – 3
Cotton – 1500 0,4÷0,7 5,0 3÷10

3.1. Material and Methods

For the mineral cement matrix, river sand,
without impurities, dug in the sorting station, of grain size 0÷4mm was used together with lime hydrated according to EN 459/1/CL80-S,
clean water and Portland cement CEM II/B-M
(S-LL) 42,5N of initially common strength; its main components are the Portland clinker (K) between 65 – 79% and a mixed admixture of grain slag (S) and limestone (LL), forming 21
– 35% of the composition, according to SR EN
197-1:2002. [1] [5]
In this test, the pattern of fibers used was
Edifiber3® Multi, a multifilament fiber type, available on our domestic market, manufactured from 100% pure high density
polypropylene by a conventional extrusion
process, having a diameter of approx. 10μm, a tensile strength of 480N/mm² and a melting temperature of 165°C, according to data sheet of the product [6], properties that fit the general
physical and mechanical characteristics of
polypropylene fibers, listed in Table 1 above.

3.2. Establishing the formulae and testing
specimens

The specimens were manually cast in
according to eight mortar formulae in the Laboratory of the Faculty of Civil Engineering,
department of Building materials, Cluj-
Napoca.
For testing tensile strength capabilities,

standard 40x40x160 mm patterns were used (Fig. 1) and for evaluating the adherence to the
substrate, a plaster layer of 10 mm thick was
applied to the surface of a brick (Fig. 2) in order to prepare two circular specimens of diameter 50 mm.

Fig. 1. Standard metallic patterns

A. MUSTEA et al .: Evaluating adherence to the substrate of fiber reinforced plaster mortars 3

Fig. 2. Preparing the brick for plastering

After the grout has hardened, a round
metallic pull-off tester (Figure 3) was bonded on the surface of each sample, in order to facilitate attaching the testing device to the
specimens.

Fig. 3. Metallic pull-off testers

The specimens were kept up to 7 days in the
wet air box at (20±4) °C and humidity over 90%, and then were moved to a (65±5)% humidity room, at the same constant
temperature of (20±4) °C. [1]
Tensile strength was investigated with the

Fruhling-Michaelis device (Figure 4.a) at 3, 7 and 28 days, while adhesion to the substrate was tested with a Controls Pull-Off device
(Figure 4.b) only after 28 days.

Fig. 4. a) Tensile strength testing device and b) Adherence testing device
The calculation relationships applied to
the results in case of the adherence was

݂௧ൌଷ∗ ி∗௟
ଶ∗௕య (1)

and

݂௨ൌிೠ
஺ (2)

regarding the tensile strength.
There are detailed in table 2 the plaster formulae, as follows: R1-M.P. is a market
available material, while R2-M.R.
represents an own formulae mortar, none of which is reinforced.
The next Rf3, Rf4, Rf5, Rf6, Rf7 and Rf9
are reinforced composite mortars with various dosages of polypropylene fibers, as
mentioned above.
As the unit of measurement, the recipes
are relative to 1 cubic meter.

Bulletin of the Transilvania University of Brașov • Vol. x (xx) – 2016
Series I: Engineering Sciences
The plaster mortars formulae Table 2
Crt.
no. Mortar
type Formulae (volumes)
R1 M.P. [1m3] 1500 kg – dry material [6,67l] 10,00 kg – dry material
280 l – wate r 1,87 l – wate r
R2 M.R. [1m3] 171 kg – cement 42,5
[7,00l] 1,197 kg – cement 42,5
260 kg – hydrated lime 1,82 k g – hydrated lime
1500 kg – san d 10,50 kg – san d
water – for 9cm consist. 2,50 l – wate r
Rf3 M.P. +
F.PP
1,0kg/m3 [1m3] 1500 kg – dry material
[7,33l] 11,00 kg – dry material
280 l – wate r 2,053 l – wate r
1,0 kg – PP fibers 7,33 gr – PP fibers
Rf4 M.R. +
F.PP
1,0kg/m3 [1m3] 171 kg – cement 42,5
[7,00l] 1,197 kg – cement 42,5
260 kg – hydrated lime 1,82 kg – hydrated lime
1500 kg – san d 10,50 kg – san d
water – for 9cm consist. 2,50 l – wate r
1,0 kg – PP fibers 7 gr – PP fibers
Rf5 M.P. +
F.PP
1,5kg/m3 [1m3] 1500 kg – dry material
[7,33l] 11,00 kg – dry material
280l – wate r 2,053 l – wate r
1,5 kg – PP fibers 11 gr – PP fibers
Rf6 M.R. +
F.PP
1,5kg/m3 [1m3] 171 kg – cement 42,5
[7,00l] 1,197 kg – cement 42,5
260 kg – hydrated lime 1,82 kg – hydrated lime
1500 kg – san d 10,50 kg – san d
water – for 9cm consist. 2,50 l – wate r
1,5 kg – PP fibers 10,5 gr – PP fibers
Rf7 M.R. +
F.PP
2,0kg/m3 [1m3] 171 kg – cement 42,5
[11,0l] 1,881 kg – cement 42,5
260 kg – hydrated lime 2,86 kg – hydrated lime
1500 kg – san d 16,50 kg – san d
water – for 9cm consist. 3,925 l – wate r
2,0 kg – PP fibers 22 gr – PP fibers
Rf9 M.P. +
F.PP
3,0kg/m3 [1m3] 1500 kg – dry material
[7,33l] 11,00 kg – dry material
280 l – drinking wate r 2 , 0 5 3 l – drinking wate r
3,0 kg – PP fibers 22 gr – PP fibers

In Figure 5 below the samples can be
observed after plastering the brick:

Fig. 5. The brick after plastering

It can be seen in Figure 6 the pattern and
the three specimens after casting:

Fig. 6. The specimens after casting

A. MUSTEA et al .: Evaluating adherence to the substrate of fiber reinforced plaster mortars 5

4. Results and Discussions

The experimental results have highlighted
the influence of the PP fiber reinforcement
upon the mechanical characteristics of cement
based composite mortars, in both a commercially available mortar and a mortar designed by the author, as seen in Table 3. [1]
Recording of the results Table 3

Crt.
no. Mortar type Age
[days] Adherence
to the substrate
fu [N/mm2] Flexural
tensile strength
ft [N/mm2]
R1 M.P. 3 – 0,48
7 – 0,70
28 0,011 1,28
R2 M.R. 3 – 0,51
7 – 0,73
28 0,031 1,25
Rf3 M.P. + F.PP
1,0kg/m3 3 – 0,61
7 – 0,75
28 0,010 1,30
Rf4 M.R. + F.PP
1,0kg/m3 3 – 0,47
7 – 0,67
28 0,017 1,20
Rf5 M.P. + F.PP
1,5kg/m3 3 – 0,55
7 – 0,70
28 0,038 1,27
Rf6 M.R. + F.PP
1,5kg/m3 3 – 0,83
7 – 1,00
28 0,015 0,83
Rf7 M.R. + F.PP
2,0kg/m3 3 – 0,51
7 – 0,64
28 0,009 0,95
Rf9 M.P. + F.PP
3,0kg/m3 3 – 0,60
7 – 0,91
28 0,013 0,93

The composition was homogenized and
applied by hand, the s ubstrate being wetted
in advance.
In case of tensile strength, improvements
in mechanical characteristics can be achieved by a mechanized mixing and proper compacting process.
Similarly, in case of adherence, mixing
and manner of application plays a significant role. On manual application, the mortar is
projected with a certain force over the
masonry, and also when applied with the grout pump, it hits the substrate at a constant speed. By implementing this force, a physical connection is achieved (creating a
"particular" contact), along with chemical

Bulletin of the Transilvania University of Brașov • Vol. x (xx) – 2016 • Series I
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bonds that appear during hardening of the
material.
On the screen capture of the device in
Figure 7 it can distinguished the amount of force applied to the sample (on the left, in
kN) and the calculated resistance value (on
the right, in MPa). The “blank space” is to be considered “zero” value.
For an objective discuss ion of the results, a
graphical analysis of the data is listed in the
chart below (Figure 8).

Fig. 7. Screenshot of the recorded values

Fig. 8. Comparative results for the adherence to substrare and flexural tensile strength

5. Conclusions
Fiber orientation is an important yet
difficult to control factor because of the random dispersion of the fibers in the matrix. This fact occurs mainly in thicker

sections [7], where the material thickness
exceeds the length of the fibers, allowing
orientation in all 3 directions (x, y, z).
Concerning the tensile strength, the
results are significantly similar and it was appreciated that they may be increased, in
0,48
0,010,51
0,0310,61
0,0100,47
0,0170,55
0,0380,68
0,0150,51
0,0090,60
0,0130,700,73 0,75
0,670,700,83
0,640,911,281,251,30
1,201,27 1,26
0,950,93
0,000,200,400,600,801,001,201,40Aherence to subtrate fu[N/mm2]and Tensile strength ft[N/mm2]
3 days 7 days 28 days

A. MUSTEA et al .: Evaluating adherence to the substrate of fiber reinforced plaster mortars 7
favor of composite mortar, by indicating an
optimal dosage of 0,90 ÷ 1,00 kg/m3 for the
polypropylene fibers (avoiding excessive agglomeration of the matrix), by performing an appropriate mixing and compacting.
These conditions above are essential for
removing air from the mass of material in order to obtain a homogeneous composite as more compact and less porous. Regarding adhesion to the substrate, it is
concluded that this characteristic depends
more on the matrix and less on the reinforcement, because the aforesaid does not penetrate into support layer.

If the matrix adheres well to the substrate,
then no separation from support layer occurs, but a split in the material structure (Figure 9).

Fig. 9. Breaking of the matrix structure
Therefore, the pullout efforts are being
transferred to the composite and by default to the fibers, whose role is now decisive.

Different manners of breaking can
distinguished in Figure 10.a and Figure 10.b. Factors that directly influence these physical and mechanical behaviors were mentioned above.
Fig. 10. a) Separation from the substrate

Bulletin of the Transilvania University of Brașov • Vol. x (xx) – 2016 • Series I
8

Fig. 10. a) Various manners of breaking

In terms of aplication area, this new
composite mortar can be successfully used as interior plaster for churches, preparing base layer for painting and successfully replacing hemp fibers. Also, the mortar can be used for
restoration and consolidation of monuments
and other old buildings. For future research, 6 to 8 mm long polypropylene fibers will be used together with mechanized mixing, performing multiple
measurements on the same recipe, so that the
average of the measured results to be most relevant.

References

1. Mustea, A., Manea, D.L.: Influence of
Polypropylene Fibers upon the
Mechanical Characteristics of
Reinforced Composite Mortars. I n :
Proceedings of the 10th International
Conference Interdisciplinarity in Engineering, Tîrgu-Mureș, 2016.
2. Netea, A.G., Manea, D.L.: Chimie și
materiale de construc ții. Cluj.
Mediamira, 2005.
3. Orbán, Y.A.: Cercetări privind studiul
comportării materialelor compozite
prin metode complexe . In: Proiect de
cercetare științifică,
Technical University
of Cluj-Napoca, Cluj, 2015.
4. Jereghi, P.: Adaosuri și aditivi în
betoane , Curs, cap. 5. Available at:

https://materialedeconstructie.files.wordp
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5. Structo® Plus: Cimentul Structo Plus .
Available at: http://www.holcim.ro/ro/produse-si-
servicii/produse/ciment/structor-
plus.html. Accessed: 12.09.2016.
6. Edifiber3® Multi: Fișă tehnică –
Armătură de polipropilen ă în dispersie
pentru armarea betoanelor și
mortarelor . Available at:
http://www.edilcom.ro/,
SC Edilcom
SRL, Negresti Oas Str.Tur Nr.262(334). Accessed: 08.07.2015.
7. Muntean, R.M.: Aplicații practice ale
betonului armat dispers cu fibre din
polipropilen ă, ISBN 978-606-19-0719-9,
Brașov, 2015, p. 65.