Journal of Colloid and Interface Science 455 (2015) 16–23

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Journal of Colloid and Interface Science

www.elsevier .com/locate / jc is

Analysis of main parameters affecting substrate/mortar contact areathrough tridimensional laser scanner

http://dx.doi.org/10.1016/j.jcis.2015.05.0280021-9797/� 2015 Elsevier Inc. All rights reserved.

⇑ Corresponding author. Fax: +55 5133084054.E-mail addresses: carimstolz@yahoo.com.br (C.M. Stolz), angela.masuero@ufrgs.

br (A.B. Masuero).

Carina M. Stolz ⇑, Angela B. MasueroDept. of Civil Engineering, Federal University of Rio Grande do Sul, Av. Osvaldo Aranha, 99, 3� andar, 90035-190 Porto Alegre, RS, Brazil

g r a p h i c a l a b s t r a c t

a r t i c l e i n f o

Article history:Received 4 March 2015Accepted 14 May 2015Available online 27 May 2015

Keywords:WettingInterfaceContact areaMortarGranulometric compositionSandLaser 3D scannerApplication energy

a b s t r a c t

This study assesses the influence of the granulometric composition of sand, application energy and thesuperficial tension of substrates on the contact area of rendering mortars. Three substrates with distinctwetting behaviors were selected and mortars were prepared with different sand compositions.Characterization tests were performed on fresh and hardened mortars, as well as the rheological charac-terization. Mortars were applied to substrates with two different energies. The interfacial area was thendigitized with 3D scanner. Results show that variables are all of influence on the interfacial contact in thedevelopment area. Furthermore, 3D laser scanning proved to be a good method to contact areameasurement.

� 2015 Elsevier Inc. All rights reserved.

1. Introduction

In Brazil, most building constructions use rendering mortars.However, poor technological control and the lack of technical

expertise in the production of rendering mortars often producepathological manifestations that may compromise the functionsof renderings: the protection, waterproofing and aesthetic appear-ance of constructions.

In order to mitigate the onset of pathological manifestations,many researchers [1–5] have focused attention on the adhesionof rendering mortars because problems associated with poor adhe-sion often affect the value of constructions. The main concern is

C.M. Stolz, A.B. Masuero / Journal of Colloid and Interface Science 455 (2015) 16–23 17

with microadhesion [6] and macroadhesion [7,8], but there is littleinformation about the behavior of rendering mortars regarding themechanisms that affect adhesion. Microadhesion is created by theabsorption of mortar pastes that come into contact with a poroussubstrate, with the filling of the pores creating a mechanical ‘an-chor’ of the mortar to the substrate [9]. Macroadhesion is charac-terized by the accidental or deliberate filling of protuberancesand indentations found on a surface, which hold mortar projec-tions in place by anchoring them to the surface [9].

Some researchers believe that to maximize the adhesion of themortar to the substrate, large textures need to be created toincrease the actual surface area that can be wetted by a givenadhesive or resin [10]. However, it should be pointed out that thismechanical interlocking depends on the extension of adhesion,which is defined as the ratio between the effective contact surfaceand the total potential area that can be bond [11].

In addition, researchers [12] have published images that indi-cate that increasing the surface texture of a substrate is not enoughif the mortar applied to the surface cannot penetrate the textureand wet the substrate. In this context, the rheological characteris-tics of mortars [13–16] have been investigated in order to under-stand their influence on the phenomenon of adhesion.

In addition to the texture characteristics of substrates, chemicalcharacteristics of surfaces may also influence the development ofthe contact area at the interface between mortar and substrate.

Surface tension is a direct measurement of intermolecularforces as van der Waals forces and hydrogen bonds. The most com-mon attraction forces are van der Waals forces that can be attrib-uted to dispersion and polar forces. When liquid touches solid,opposing forces appear: on the one hand the solid tends to be sur-rounded by liquid molecules, decreasing the potential energy ofsurface molecules. On the other hand, the liquid tends to remaingrouped to reduce its exterior surface. Only when the surfaceenergy of the solid is equal to or greater than the surface tensionof the liquid is disintegration of the liquid possible on the solid sur-face, producing wetting [10].

One way to observe the wettability of a substrate is to measurethe contact angle. This parameter is defined as the angle that liquiddrop shape with the solid surface in the contact zone between thetwo phases. It is considered that a liquid wets a solid when thecontact angle between the droplet and the solid surface is smallerthan 90�. Therefore, it is believed that the higher the contact angle,the less wetting of the surface [10].

Considering all the variables that can be of influence on theinterface contact, this study aims to analyze the influence of mor-tars with different rheology characteristics, modified by the granu-lometric composition of the sand, applied to substrates withdifferent superficial tensions in the interfacial contact area.

Table 1Chemical and physical properties of cement used.

Experiment Method Results

Blaine specific surface NBR NM 76/98 4398.5 cm2/gDensity NBR NM 23/01 2.76 g/cm3

Medium diameter Laser diffraction 16.95 lmFineness sieve #200 NBR 11579/91 0.27%Initial curing period NBR NM 65/02 243.25 minFinal curing period NBR NM 65/02 284.80 minCompressive strength 7 days NBR 7215/96 25.03 MPa

28 days NBR 7215/96 36.20 MPaInsoluble residue NBR NM 22/04 35.84%Sulfur trioxide (SO3) NBR NM 146/04 2.28%Magnesium oxide (MgO) NBR NM 14/04 4.61%Loss on ignition 3.64%

2. Experimental program

2.1. Mortar production

A layer of mortar prepared with a composition of 1:1:6(cement: hydrated lime: dry sand, in volume) was producedaccording to the Brazilian Standard NBR 13276/2005, for a240 mm consistence index (measured in flow table, before subject-ing the mortar to 30 strokes and measure the mean of three diam-eters of resulting circle). During mortar production, the volumecomposition was dosed in mass, for a better production control.The quartz sand used (specific mass 2.50 g/cm3) consisted of threecompositions of sand. All of them, with grains retained in sieves#1.2; 0.6; 0.3 and 0.15 mm. The first composition (CG1, aggregateunit mass 1.51 g/cm3) consists of equal fractions of each sieve, 25%each. The second (CG2, aggregate unit mass 1.48 g/cm3), with 10%,

40%, 40% and 10% of each sieve respectively, and third (CG3, aggre-gate unit mass 1.54 g/cm3) with 40%, 10%, 10% and 40% of eachsieve, respectively.

About sand granulometric compositions utilized, it is possibleto observe that CG2 is uniform, with similar diameters grains pre-dominance, like natural quartz available in the city of study. CG3 isnot uniform with good compacity, the opposite of CG2. Finally, CG1present a continuous granulometric composition, less uniformthan others do. These affirmations can be proved by uniformityindex (UI) calculation, by UI = d60/d10, where d60 and d10 are,respectively, the sieves where cumulative passing percentage ofmass corresponding 60% and 10%. Granulometric composition isconsider uniform when UI < 5, with median uniformity when5 < UI < 15 and no uniform when UI > 15. So, the uniformity indexof all granulometric compositions are: CG1: 3.95 (uniform), CG2:2.48 (uniform) and CG3: 6.28 (median uniformity).

The mortars produced with CG1, CG2 and CG3 were called A61,A62 and A63, respectively.

The cement used was Portland cement type IV (equivalent tothe American IP (MS) grade), and the calcitic lime (specific mass2.37 g/cm3, mean particle size 22.4 lm) complied with the limitsset by Brazilian standards.

The physical and chemical properties of the cement types usedare shown in Table 1.

2.2. Substrate selection

Through preliminary analysis, three non-absorbent substrateswith different wettability ratings were chosen: glass, acrylic, andpolyethylene. These substrates were characterized by measuringthe contact angle of a drop of water projected on their surfaceusing a goniometer.

The contact angle can be measured using a drop of water (orother liquid) analyzer equipment, that makes a picture with ahigh-precision digital camera of surface/liquid interface. This pic-ture enables the contact angle measure with AutoCad software,for example.

2.3. Mortar application

The mortar was applied to the substrates by means of a devicecalled ‘‘drop box’’ from two fixed fall heights of thirty centimetersand one meter. A ‘‘drop box’’ is a simple device that allows users toadjust the height from which the mortar will be dropped onto thesubstrate, therefore controlling the energy applied.

To control the size and thickness of the mortar samples, we pro-duced wood templates of 10 cm � 10 cm with a thickness of 1 cm.The bottom was covered with each of the materials of differentsurface tensions. For each mortar/substrate/energy combination,three blocks were cast.

Table 2Characterization tests of fresh rendering mortars A61 (CG1), A62 (CG2) and A63(CG3).

Mortar Bulk density of freshmortar (kg/m3) – NBR13278/05

Water retentivity(%) – NBR 13277/05

Air content (%)– NBR NM 47/02

A61 1628 97 1.60A62 1609 96 2.25A63 1645 96 1.60

Table 3Characterization tests of hardened rendering mortars, at 28 curing days, A61 (CG1),A62 (CG2) and A63 (CG3).

Mortar Flexuralstrength(MPa) –NBR13279/05

Compressivestrength(MPa) – NBR13279/05

Dynamicelasticitymodulus(GPa) –NBR15630/08

Density ofhardenedmortar(kg/m3) –NBR13280/05

Capillarywaterabsorption(g/dm2 min1/2) – NBR15259/05

A61 0.25 2.27 7.31 1886 15.67A62 0.27 1.84 6.72 1848 18.64A63 0.42 2.35 8.44 1889 14.91

Table 4Apparent viscosity and shear stress values measured at 40 s of test execution.

Mortar Apparent viscosity in 40 s (Pa s) Shear stress (Pa)

A61 8.00 266.54A62 10.46 348.63A63 7.73 257.62

18 C.M. Stolz, A.B. Masuero / Journal of Colloid and Interface Science 455 (2015) 16–23

2.4. Laser scanning of the substrates

After applying on substrates through use of the ‘‘drop box’’, andcured for at least seven days, manual separation of the mortar/sub-strates was performed. This separation was made in easy way,without mortar material loss to surface, do not making damagesin real contact of mortars.

The mortar interface was then digitalized with a Tecnodrilltridimensional laser scanner, model Digimill (3D), with a 50 mmlens and 0.1 mm precision between points.

2.5. Mortar characterization

Characterization tests of the fresh and hardened mortars wereperformed to provide the technological control of mortars and con-cretes, in addition to the characterization of the different rheolog-ical behaviors of the mortars. In fresh state, it was performed bulkdensity, water retentivity and air content characterization, all ofthem according Brazilian standards. In hard state, 28 days beforemortars production, it was performed flexural strength, compres-sive strength, dynamic elasticity modulus, density and capillarywater absorption characterization tests, all according Brazilianstandards.

A Brookfield Rotational Rheometer R/S plus was used for therheological characterization. For these tests a vane type V30 � 15 was used, with a height of 30 mm and a diameter of15 mm, in a standard container for all mortars. This type of vaneis the most suitable for rheological tests on mortar coating suspen-sions and high viscosity materials. The size of the vane was deter-mined in preliminary tests. The rotational rheometer data werethen treated with the Rheo3000 Software.

The routine chosen for mortars analysis consists in four lectureslevels, one each 20 s, reaching a maximum of 100 1/s shear rate(Fig. 1). The objective of this characterization was to take an appar-ent viscosity in a fixed point to compare different mortars.

Complementary, it was made rheological characterization bySqueeze-flow test. The squeeze-flow test was adopted in 2010 asa standardized test method in Brazil, by NBR 15839. This test mea-sures the force required to compress, between two parallel plates,a cylindrical sample along one axis. This force generatesshear-strain and elongation forces in the test specimen.

3. Results and discussions

3.1. Mortar characterization

Tables 2 and 3 present the characterization of fresh and hard-ened mortars (curing time: 28 days), respectively. All of them wereperformed by Brazilian standardization methods, identified on

Fig. 1. Rheometer routine.

tables by respective numbers (NBR – Brazilian Standard and NM– Mercosur Standard).

Table 4 reveals that, in the fresh state, the A61 mortar usingsand with medium aggregate unit mass and low uniformity index(uniform), also had a medium bulk density. A62 using sand withthe lowest aggregate unit mass and lowest uniformity index (mostuniform), also had the lowest bulk density and the A63, using sandwith the highest aggregate unit mass and bigger uniformity index(median uniformity), also had the highest bulk density. These factswere expected and show that porosity in fresh state is related withaggregates packing and uniformity, since as lower aggregate unitmass values and less uniformity indicate greater presence of voidsbetween grains, which makes the mortar lighter and consequentlyless dense.

The air content behavior can also be related with sand packingand uniformity, deduced by aggregate unit mass. A61 and A63,which have better packing and bigger uniformity index, had thesame behavior. A62, on the other hand, which has the worst pack-ing and lowest uniformity index, also had the highest air content inthe fresh state.

Water retentivity had no significant variation. It is probablyassociated with lime proportion, which was the same in all mortarsproduced.

The hardened behavior, presented in Table 5, can also be relatedwith the aggregates packing observed in the fresh characterization.A63, for example, had the best mechanic properties, higher densityand dynamic elasticity modulus, all resulting from the lowerporosity.

3.2. Rheological characterization of the mortars

Fig. 2 presents the squeeze-flow results of the mortars accord-ing to the times and velocities established in the Brazilian standardNBR 15839/10.

Table 5contact angle of a water drop with selected surfaces.

Glass Acrylic Polypropylene

m= 27ºm= 52º

m= 96º

Hydrophilic Intermediary Hydrophobic

Fig. 2. Squeeze-flow behavior of A61, A62 and A63 mortars with 3 mm/s and 0.1 mm/s velocities, in 10 and 60 min and 15 and 65 min, respectively.

C.M. Stolz, A.B. Masuero / Journal of Colloid and Interface Science 455 (2015) 16–23 19

It is possible to see that mortars A61 and A63 have similarbehavior, distinct from A62, that presented more flow resistance.A61 and A63 resulting in bigger plastic stage, where mortar havebigger displacement whit smaller force application, while A62 pre-sented a smaller one, with a premature strain hardened stage,where mortar presented a smaller displacement whit bigger forceapplication. A62 is the most uniform aggregate composition

mortar, and this fact can be related with flow resistance, as moreuniform grains lock himself, not allowing the interparticle bearing.

This fact cannot be observed only in the 15 min time of test exe-cution. It can be related whit smaller velocity of force application,when sand grains have more time to reorganize himself into sus-pension during the A62 compression. It is characterized by oscilla-tions in the graph’s curve. In A62 it was expected, because this

(a) (b)

0 2 4 6 8

10 12

0 50 100 150VI

SCO

SITY

(Pa.

s)

SHEAR RATE(1/s) SHEAR RATE(1/s)

A61 A62 A63

0

100

200

300

400

0 50 100 150

SHEA

R ST

RESS

(Pa)

A61 A62 A63

Fig. 3. Rheological characterization in rotational rheometer: (a) viscosity vs. shear rate (b) shear stress vs. shear rate.

(a) (b) (c)

Non-contact areas

Fig. 4. Images resulting from the 3D scan. The non-contact area points are shown in dark blue and black: (a) 3D image resulting from treatment in Geomagic Studio 10Software; (b) image 2D treated in Geomagic Studio 10 Software; and (c) image treated in Photoshop CS5 Software. (For interpretation of the references to color in this figurelegend, the reader is referred to the web version of this article.)

Table 6Measurement of non-contact areas of A61 (CG1), A62 (CG2) and A63 (CG3) mortarsapplied to the acrylic substrate with fall heights of 30 cm and 100 cm.

Acrylic

Fallheight(cm)

Mortar Non-contactarea (%)

Non-contactarea average(%)

Standarddeviation(%)

Variationcoefficient(%)

30 A61 28.49 26.7 2.44 9.1223.9327.70

A62 39.71 41.21 1.79 4.3440.7343.19

A63 21.9 22.89 2.18 9.5121.3925.39

100 A61 11.79 12.89 2.17 16.8415.3911.49

A62 34.09 34.32 1.64 4.7736.0632.81

A63 14.96 14.45 2.17 15.0716.3412.07

Table 7Measurement of non-contact areas of A61 (CG1), A62 (CG2) and A63 (CG3) mortarsapplied to the polyethylene substrate with fall heights of 30 cm and 100 cm.

Polyethylene

Fallheight(cm)

Mortar Non-contactarea (%)

Non-contactarea average(%)

Standarddeviation(%)

Variationcoefficient(%)

30 A61 28.04 28.23 1.56 5.5226.7729.87

A62 32.34 33.07 1.94 5.8635.2731.61

A63 24.72 24.66 2.94 11.9121.6927.56

100 A61 23.96 24.08 3.14 13.0521.0027.28

A62 32.06 37.49 4.87 12.9938.9141.48

A63 23.46 27.54 3.53 12.8229.6129.54

20 C.M. Stolz, A.B. Masuero / Journal of Colloid and Interface Science 455 (2015) 16–23

mortar was dosed whit less packing sand, so, there were moreempty areas, filled by water, which was ejected during slowestforce application. During faster force application, there are no timeto reorganization of grains, so occurs the grains friction, turningflow more difficult [17].

The longer plastic stage of mortars A61 and A63 than A62, canbe related with higher presence of fine particles in the

composition, which improves workability and decreases viscosity.Despite the fact that A62 has more water in its composition, itsgranulometric composition lacks fine sand, creating segregationand locking the flow by the presence of larger aggregates (1.2 mm).

About squeeze-flow test realized in 60 and 65 min after mortarproduction, it was possible to observe cement hydration and waterloss influence, mainly in A62, mortar whit more water and voids,that can lost water faster than other does.

Table 8Measurement of non-contact areas of A61 (CG1), A62 (CG2) and A63 (CG3) mortarsapplied to the glass substrate with fall heights of 30 cm and 100 cm.

Glass

Fallheight(cm)

Mortar Non-contactarea (%)

Non-contactarea average(%)

Standarddeviation(%)

Variationcoefficient(%)

30 A61 21.63 25.63 3.57 13.9128.4826.77

A62 23.98 31.40 7.35 23.4038.6731.54

A63 23.65 21.62 2.64 12.2218.6322.57

100 A61 23.11 18.02 5.24 29.0518.312.65

A62 20.56 24.04 3.04 12.6325.3926.16

A63 7.74 8.72 1.48 16.987.99

10.42

C.M. Stolz, A.B. Masuero / Journal of Colloid and Interface Science 455 (2015) 16–23 21

In general, it appears that the mortars have short elastic andplastic stages, since the maximum deformation of the test was9 mm and the maximum deformation obtained was about1.5 mm. The test ended, in all cases, when the applied forcereached the maximum standard defined of 1 kN.

The rheometric characterization of mortars is presented inFig. 3. Table 4 presents the apparent viscosity and respective shearstress of all mortars analyzed on second measurement, corre-sponding of 40 s test execution.

Just as in the squeeze-flow test, in rheometric tests A61 and A63mortars presented a similar behavior, with apparent viscosity val-ues of 8.00 and 7.73 Pa s, respectively. This is directly related withgranulometric composition and uniformity index of sand, which inA61 and A63 mortars had a better packing. The presence of somany grains of similar diameters in sand A62, results in the mortarflow being hindered, increasing viscosity and, consequently, shearstrength, resulting in values of 10.46 Pa s and 348.63 Pa of eachproperty, respectively.

In A62 mortar it is possible that ‘‘wall effect’’ are happening,resulting of different diameters grains interaction. The ‘‘wall effect’’is a physical effect that occurs when, in a various diameters gran-ular mixture, the grain one diameter (d1) is not so larger than thesecond grain diameter (d2), so that, when d1 grain enters into amixture of d2 predominance, results in spacing contact interfacebetween two grains classes [18].

3.3. Surface selection

Table 5 presents the chosen surface with their respective con-tact angles. It shows that glass surface can be considered

Table 9Controlled factors and contact area data analysis of variance.

SS DF

Mortar 1877.22 2Fall height (cm) 483.60 1Substrate 520.85 2Mortar ⁄ fall height (cm) 62.05 2Mortar ⁄ substrate 307.99 4Fall height (cm) ⁄ substrate 334.28 2Mortar ⁄ fall height (cm) ⁄ substrate 69.46 4Error 398.67 36

SS: sum of squares; DF: degrees of freedom; MS: mean squares; Fcalc: calculated F-valu

hydrophilic, with a contact angle of 27�, the acrylic surface is anintermediary surface, with a 52� contact angle, and the polyethy-lene surface is hydrophobic, with a 96� contact angle.

3.4. Laser 3D scanning

After cure time, the mortars were separated from the substratesand digitized with a tridimensional laser scanner. The results weretreated with the Geomagic Studio 10 software to generate a tridi-mensional image. This image was saved in the PNG (PortableNetwork Graphics) format and opened with the Photoshop CS5Software, where contact and non-contact areas were quantified.It is important to emphasize that the images were not altered,but only treated to connect scanner 3D points and highlight thenon-contact areas.

One example of the results of these treatments is presented inFig. 4, were dark blue and black points represent the non-contactareas.

The results for the non-contact area measurement of the A61,A62 and A63 mortars are presented in Table 6 for the acrylic sub-strate, Table 7 for the polyethylene substrate, and Table 8 for theglass substrate.

In order to verify the statistical significance of the obtained val-ues, an analysis of variance with 95% confidence was performedwith the Software Statística 7. The results obtained are presentedin Table 9. The graphs of significant interactions are presented inFig. 5.

Fig. 5b shows, as expected, that mortar application with differ-ent energies using different drop heights was of significant influ-ence on the development of contact areas, with lower energyproducing a greater percentage of contact failures. Additionally,Fig. 5d reveals that the mortar A62 is not significantly influencedby the different application energies, which may be related to itsrheological properties (higher viscosity) resulting from its particlesize distribution.

Fig. 5c presents the significance of substrates with differentwettability conditions in relation to the mortar’s contact area.This explains why the hydrophobic substrate, which makes surfacewetting more difficult, increased the percentage of failures in themortar/substrate interface.

Some aspects can be inferred from the graphs presented inFig. 5. Graph ‘‘a’’ shows that the A61 and A63 mortars had a similarperformance, and that the A62 mortar had the worst performancein increasing areas with contact failures. This fact is probablyrelated to the different granulometric compositions of the mortars,with A62 having the lowest amount of fine particles, hampering itsscattering on the substrate.

Finally, graphs ‘‘e’’ and ‘‘f’’ show that on the polyethylene sub-strate (hydrophobic) the difference in applied mortar energy doesnot generate differences in contact area. In this case, it seems thatthe surface tension factor exerted a greater influence on wettingthan energy application. For the acrylic and glass substrates, whichhave lower contact angles, the maximum fall height considerably

MS Fcalc p-factor Significant

938.61 84.756 0.000000 Yes483.60 43.669 0.000000 Yes260.42 23.516 0.000000 Yes

31.02 2.801 0.074002 No77.00 6.953 0.000296 Yes

167.14 15.093 0.000017 Yes17.37 1.568 0.203788 No11.07

e.

Fig. 5. Controlled factors and contact area data analysis of variance: (a) non-contact area vs. mortars, (b) non-contact area vs. fall height, (c) non-contact area vs. substrate, (d)non-contact area vs. fall height vs. mortars, (e) non-contact area vs. substrate vs. fall height, and (f) non-contact area vs. fall height vs. substrate.

22 C.M. Stolz, A.B. Masuero / Journal of Colloid and Interface Science 455 (2015) 16–23

reduced failures at the interface, i.e., in these cases the appliedmortar energy proved to be more relevant.

For a more detailed statistical analysis, an average multivariateanalysis of variables was performed, which is presented inTable 10.

This analysis allows us to draw some conclusions about thebehavior of different mortar coatings when applied to the differentsubstrates with both energies.

The A61 and A63 mortars applied with a low-energy (dropheight of 30 cm) on polyethylene, acrylic and glass substrates,showed no significant difference in contact area, i.e., the surfacetension was not significant. However, when higher energies wereapplied to the same substrates (drop height 100 cm), the differentsurface tensions of the substrates were of influence on the develop-ment of contact failures. The A62 mortar showed significant differ-ences between the two application energies.

Table 10Average multivariate analysis of variables, where ‘‘Yes’’ represent significant interaction and ‘‘No’’ represent insignificant interaction.

Mortar Fall height (cm) Substrate 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

1 A61 30 Polyethylene No No No Yes Yes No Yes No Yes Yes No No No Yes No Yes Yes2 30 Acrylic No No No Yes Yes Yes Yes No Yes Yes No No No No No Yes Yes3 30 Glass No No No Yes Yes Yes Yes Yes Yes Yes No No No No No Yes Yes4 100 Polyethylene No No No Yes Yes Yes Yes Yes Yes Yes No No No No No Yes Yes5 100 Acrylic Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No No6 100 Glass Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes Yes No No Yes No Yes7 A62 30 Polyethylene No Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes Yes Yes Yes8 30 Acrylic Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes Yes Yes9 30 Glass No No Yes Yes Yes Yes No Yes Yes No Yes Yes Yes Yes No Yes Yes

10 100 Polyethylene Yes Yes Yes Yes Yes Yes No No Yes No Yes Yes Yes Yes Yes Yes Yes11 100 Acrylic Yes Yes Yes Yes Yes Yes No Yes No No Yes Yes Yes Yes Yes Yes Yes12 100 Glass No No No No Yes Yes Yes Yes Yes Yes Yes No No No No Yes Yes13 A63 30 Polyethylene No No No No Yes Yes Yes Yes Yes Yes Yes No No No No Yes Yes14 30 Acrylic No No No No Yes No Yes Yes Yes Yes Yes No No No No Yes Yes15 30 Glass Yes No No No Yes No Yes Yes Yes Yes Yes No No No Yes Yes Yes16 100 Polyethylene No No No No Yes Yes Yes Yes No Yes Yes No No Yes Yes Yes Yes17 100 Acrylic Yes Yes Yes Yes No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes18 100 Glass Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes

C.M. Stolz, A.B. Masuero / Journal of Colloid and Interface Science 455 (2015) 16–23 23

4. Concluding remarks

Based on the results, we conclude that the superficial tension ofsubstrates is a property that deserves more attention fromresearchers studying adhesion. This property can be affected bythe substrate composition or mold release agents used in concrete.

Furthermore, the energy of mortar application is a very impor-tant factor for the development on contact in the interfacial area. Inpractice, it is important to standardize as much as possible thisvariable, using mechanized instead of manual application, whichis frequent in most Brazilian works.

Finally, mortar rheology is directly related to hardened behav-ior, and the granulometric composition of sand is an efficientway to diversify the rheological properties of the mortar.

Acknowledgments

The authors appreciate the financial support of CNPq (ConselhoNacional de Desenvolvimento Tecnológico- Brazilian Council ofTechnological Development) and CAPES (Fundação Coordenaçãode Aperfeiçoamento de Pessoal de Nível Superior – BrazilianMinistry of Education).

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