Construction and Building Materials 23 (2009) 3332–3336

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Construction and Building Materials

journal homepage: www.elsevier .com/locate /conbui ldmat

Chemical interaction between EVA and Portland cement hydration at early-age

A.M. Betioli a,*, J. Hoppe Filho a, M.A. Cincotto a, P.J.P. Gleize b, R.G. Pileggi a

a Department of Construction Engineering, University of São Paulo, Av. Prof. Almeida Prado No. 83, 05508-900 São Paulo, SP, Brazilb Department of Civil Engineering, Federal University of Santa Catarina, Caixa Postal 476, 88040 900 CEP, Florianópolis, SC, Brazil

a r t i c l e i n f o

Article history:Received 28 November 2008Received in revised form 18 June 2009Accepted 19 June 2009Available online 15 July 2009

Keywords:EVACementChemical interactionThermogravimetry

0950-0618/$ - see front matter � 2009 Elsevier Ltd. Adoi:10.1016/j.conbuildmat.2009.06.033

* Corresponding author. Tel.: +55 11 30915382; faxE-mail address: andreabetioli@gmail.com (A.M. Be

a b s t r a c t

Ethylene/vinyl acetate (EVA) copolymer, as latex or redispersable powder, is added to mortars and con-crete to improve the fracture toughness, impermeability and bond strength to various substrates. Thephysical and chemical interactions were already proved after one day of hydration but during the firsthour just the physical interaction was identified and some evidences of a chemical interaction. Theaim of this paper was to evaluate the chemical interaction between EVA and Portland cement duringthe first hours of hydration in the thermogravimetric analysis. The results confirmed that the EVA hydro-lyses in pH alkaline and consumes calcium ions from the solution, forming an organic salt (calcium ace-tate), reducing the calcium hydroxide content. And, its interaction occurred in the first 15 min ofhydration.

� 2009 Elsevier Ltd. All rights reserved.

1. Introduction

Ethylene/vinyl acetate (EVA) copolymer, as latex or redispersa-ble powder, is added to mortars and concrete to improve the frac-ture toughness, impermeability and bond strength to varioussubstrates [1–6].

The kind of interaction developed between cementitious andpolymeric phases on the same aqueous solution is not clear, andsome controversies exist among researchers, according Silva et al.[5]. The physical interaction occurs in the first minutes of hydra-tion improving the workability and the reduction of water/cementratio at a given consistency, which contributed to a strength in-crease and drying shrinkage decrease. This behavior is due to the‘‘ball bearing” action, the entrained air and the dispersing effectof surfactants, used during the production of this copolymer [4].

The chemical interaction evidences were observed just after oneday of hydration as shown by Georgescu et al. [7] in a system con-taining tricalcium aluminate (C3A), gypsum and poly (vinyl alco-hol–acetate), between 1 and 28 days old and, by Silva et al. [5],in cement paste with EVA, at 28 days old. They observed a chemicalinteraction, where the acetate groups of EVA copolymer undergoalkaline hydrolysis and interact with Ca2+ ions of the pastes to forman organic salt (calcium acetate). The calcium hydroxide content isdecreased, and according to Silva et al. [5], the ettringite crystalsappear to be well formed and many Hadley’s grains were observed.

ll rights reserved.

: +55 11 30915544.tioli).

Notwithstanding, in the first hours of hydration the chemicalinteraction is not cleared, some evidences have been observed bycalorimetric tests [3,8], infrared and soft X-ray transmissionmicroscopy [9,10]. Therefore, the purpose of this work is to evalu-ate the chemical interaction between EVA and hydration cementduring the first hours trough thermogravimetric analysis.

2. Experimental, materials and methods

2.1. Materials

A blended Portland cement with 10% calcareous filler was used, according toBrazilian Standard (CPII F 32). The chemical and physical characteristics are pre-sented in Table 1. The water-redispersable powder is the EVA (vinyl acetate/ethyl-ene copolymer), Vinnapas RE 5010 N, produced by Wacker Polymer SystemsGmbH & Co. KG. Table 2 presents the polymer characteristics. The protective col-loid of EVA is a surfactant used to improve the chemical and mechanical stabilityof polymer latexes, besides optimizing the polymer particles dispersion in cementmixtures.

2.2. Cement pastes

A reference paste (without polymer) and a modified cement pastes were ana-lyzed. The EVA contents in the mixture were 5% and 10% by cement weight. Thewater/cement ratio was kept constant at 0.38, in weight basis. For mixing thepastes, the following procedure was employed on IKA RW 20 DZM.n mixer: homog-enizing of dry-mixture of EVA and cement; dry-mixture following over deionizedwater under 300 rpm, during 3 min; then for more 2 min in the same speed.

2.3. Thermogravimetric analysis (TG/DTG)

The thermogravimetric analysis were made in the Netzsch STA 409 PG equip-ment, using alumina top-opened crucible (mass 184 mg and volume of 0.085 ml),sample mass with 30 mg approximately, N2 gas dynamic atmosphere, heating rate:10 �C/min to 1000 �C.

Table 2Characteristics of EVA.

Solids contenta 98–100%Protective colloida Polyvinyl alcohol (PVA)Particle sizea Max. 4% over 400 lmPredominant particle size redispersiona 0.5–8 lmMinimum film formation temperaturea 4 �CSpecific gravity of the powderb 1.27 g/cm3

Ash contentc 12%

a Information provided by the manufacturer.b Determined by Helium picnometry.c Determined by thermogravimetry at 1000 �C under dynamic N2 atmosphere;

heating rate 10 �C/min.

Table 1Physical and chemical characteristics of the blended Portland cement.

Physical characteristicsSpecific gravity (g/cm3) 2.97% Passing sieve #325 96.8Blaine specific surface area (m2/kg) 330Initial and final setting times (minutes) 185, 285Compressive strength (NBR 7215/96) 28 days (MPa) 40.00

Chemical characteristicsLoss of ignition (%) 5.10Insoluble residue (%) 0.76Aluminum oxide – Al2O3 4.28Silicon dioxide – SiO2 18.44Ferric oxide – Fe2O3 3.04Calcium oxide – CaO 63.38Magnesium oxide – MgO 2.08Sulfur trioxide – SO3 2.92Sodium oxide – Na2O 0.09Potassium oxide – K2O 0.74Carbon dioxide– CO2 4.14Free calcium oxide – CaO (free) 2.43Sodium oxide equivalent – Na2O (0.65 � K2O% + Na2O%) 0.58

Table 3Temperature bands of C–S–H and hydrate aluminates, CH and CaCO3 decomposition.

Time (h) C–S–H and hydrate aluminates (�C) CH (�C) CaCO3 (�C)

0.25 28–360 360–450 450–9980.501234 28–375 375–460 460–99856 28–375 375–485 485–99812 28–380 380–490 490–99824 28–380 380–500 500–998

A.M. Betioli et al. / Construction and Building Materials 23 (2009) 3332–3336 3333

In programmed maturation ages (0.25; 0.5; 1; 2; 3; 4; 5; 6; 12 and 24 h) thepastes were frozen in liquid nitrogen (�180 �C) and manually ground in cruciblewith pestle. Particles diameter between 150 lm and 75 lm were used as analyticalsample. These samples were D-dried in Terroni Fauvel LC 1500 Lyophilizator for24 h.

All weight loss data are expressed in function of ignited sample weight, as sug-gested by Taylor [11]. The non-evaporable water was separated in two groups: C–S–H and aluminate hydrates – ettringite and monosulfoaluminate – and the calciumhydroxide (CH). The temperature bands, according to the hydration time, are indi-cated in Table 3. The calcium hydroxide content was determined using the follow-ing equation:

CHð%Þ ¼ DCHð%Þ �MCH=Mh ð1Þ

100 200 300 400 50

T

86

88

90

92

94

96

98

100

TG /%

0.25h2 h4 h6 h12 h24 h200 300

86

88

90

92

94

96

98

100

TG

/%

0.25h2 h4 h6 h12 h24 h

0.25h2 h4 h6 h12 h24 h

360 380 400 420

T

-0.70

-0.60

-0.50

-0.40

-0.30

-0.20

-0.10

0

DT

G /(

%/m

in)

0.25h2 h4 h6 h12 h24 h-0.70

-0.60

-0.50

-0.40

-0.30

-0.20

-0.10

0

0.25h2 h4 h6 h12 h24 h

0.25h2 h4 h6 h12 h24 h

a

b

Fig. 1. TG curves of reference paste (a). Magnificatio

where CH(%) is the content of Ca(OH)2, DCH(%) is the weight loss during the dehydra-tion of calcium hydroxide, MCH is the molar weight of calcium hydroxide and Mh isthe molar weight of water.

0 600 700 800 900 1000

emperature /°C

700 800

440 460 480 500

emperature /°C

n of DTG curves in CH ranges, 350–500 �C (b).

0

5

10

15

20

0 6 12 18 24Time (h)

Non

-eva

pora

ble

wat

er a

nd C

H (

%)

CH

Non-evaporable water

Fig. 2. Non-evaporable water (C–S–H and aluminate hydrates) and calciumhydroxide (CH) content in the first 24 h.

3334 A.M. Betioli et al. / Construction and Building Materials 23 (2009) 3332–3336

It was opted to analyze the weight loss of CO2 gas released, since the exactstoichiometry of the decomposition reactions of the carbonate phases is notknown.

EVA copolymer contains a vinyl acetate group which suffers hydrolysis whendispersed in an alkaline solution [4,5]. To deduct the polymer weight loss, an errorwould be done if the pure polymer was considered. To prevent it, a hydrolysis sim-ulation was carried out, with EVA in the alkaline solution, extracted from the super-natant of water and cement mixture, for 15 and 60 min. A change in the weight lossby thermogravimetric analysis was observed and no difference was detected be-tween 15 and 60 min of exposition. Then, the EVA in alkaline solution was usedin the weight loss.

100 200 300 400 50

80

85

90

95

100

TG

/% 0.25h2 h4 h6 h12 h24 h

0.25h2 h4 h6 h12 h24 h

0.25h2 h4 h6 h12 h24 h

Fig. 3. TG curves of CH dehydration during hydr

360 380 400 420-0.60

-0.50

-0.40

-0.30

-0.20

-0.10

0

DT

G /(

%/m

in)

0.25h2 h4 h6 h12 h24 h

420

0.25h2 h4 h6 h12 h24 h

0.25h2 h4 h6 h12 h24 h

Fig. 4. DTG amplification curves of CH dehydration during hydration of EVA-modifie

3. Results and discussion

Fig. 1a shows the weight loss of reference paste until 24 h ofhydration. Three distinct regions occurred during the heat of thepastes: until 380 �C, referring to a C–S–H and aluminate hy-drates; calcium hydroxide (CH) dehydration, between 380 �Cand 500 �C and, the decomposition of the carbonate phases upto 500 �C. There was not increase in the weight loss for 2 hhydration. A little increase was observed at 4 h and, more accen-tuated after 6 h.

The dehydration peak of CH (Fig. 1b) changes with hydrationtime, but it keeps between 380 and 550 �C [11].

As shown in Fig. 2, the non-evaporable water (C–S–H and alu-minates hydrates) and the CH content in reference paste increasesafter 2 h of hydration.

EVA did not modify the curve profile (Fig. 3) and the same dis-placement of calcium hydroxide DTG curves was observed (Fig. 4).However, a new peak appeared in DTG curves at 380 �C.

Fig. 5 shows that the EVA has a little effect in non-evaporablewater for 3 h of hydration. After that, the modified pastes have ahigher increase in non-evaporable water content due to the disper-sion effect of surfactants used in EVA production. This admixturereduces the water surface tension and disperses the cement parti-cles, increasing the dissolution rate [8].

EVA copolymer contains a vinyl acetate group that suffershydrolysis in alkaline medium producing polyvinyl alcohol andacetate anion (CH3COO�) [4]. This anion combines with Ca2+, re-leased from cement dissolution (the first step of cement hydration)and forms the calcium acetate (Ca(CH3COO)2) [5,12,13]. This is

0 600 700 800 900 1000

Temperature /°C

ation of EVA-modified pastes with 5% EVA.

440 460 480 500Temperature /°C

d pastes with 5% EVA. The circle shows the calcium acetate peak decomposition.

0

5

10

15

20

0 6 12 18 24Time (h)

Non

-eva

pora

ble

wat

er (

%) 0% EVA

5% EVA

10% EVA

Fig. 5. Non-evaporable water content during 24 h of hydration, by thermogravi-metric analysis, in reference and EVA-modified pastes with 5% and 10% of EVA.

0

4

8

12

16

20

24

28

32

36

0 6 12 18 24Time (h)

% C

aO3 (

%)

0% EVA

5% EVA

10% EVA

Fig. 6. CaCO3 content by thermogravimetric analysis in reference and EVA-modified cement paste with 5% and 10% of EVA.

-5

0

5

10

15

20

0 6 12 18 24

Time (h)

CH

(%)

0% EVA

5% EVA

10% EVA

CH

CH

Fig. 8. Calcium hydroxide (CH) content in reference paste and CH contentestimated in EVA-modified pastes with 5% and 10% of EVA.

A.M. Betioli et al. / Construction and Building Materials 23 (2009) 3332–3336 3335

confirmed due to a new peak at 380 �C observed in Fig. 4 and, dueto the decomposition of the calcium acetate [5] resulting in the for-mation of calcium carbonate (Fig. 6), as shown in followingequation:

CaðCH3COOÞ2calcium acetate

!380—400�CCH3COCH3

acetoneþ CaCO3

calcium carbonateð2Þ

a

Fig. 7. DTG amplification curves in range of CO2 gas released during the de

According to Kasselouri et al. see in Silva et al. [5], the thermaldecomposition of calcium carbonate, formed from calcium acetatedecomposition, occurs at lower temperatures, proved to theenlargement of peak range (Fig. 7), proving the chemical interac-tion theory.

EVA strongly reduces the calcium hydroxide (CH), according toAfridi et al. [14] and Silva et al. [5]) and, this reduction was ob-served in the first 15 min as shown in Fig. 4. The CH content inmodified paste was determined using Eq. (1).

The difference between carbonate (Fig. 6) content released fromEVA-modified and reference pastes was used to calculate the cor-respondent increasing in CaO content as carbonate in modifiedpastes. Assuming that the difference is due to the calcium acetatedecomposition, it could estimate the CH content that was notformed, due to the chemical interaction between EVA and ionsCa2+ in solution; the difference between this content and CH con-tent in reference paste can estimate the CH content remaining, ascan be seen in Fig. 8.

The negative values (Fig. 8) evidence the EVA interaction withhigher ions Ca2+ than those necessary to form CH in referencepaste. Therefore, from these results, the EVA does not allow theCH precipitation for 4.5 and 6 h of hydration for 5% and 10% EVAadded, respectively.

These results showed that the acetate groups of EVA copoly-mer undergo alkaline hydrolysis and interact with Ca2+ ions ofthe pastes to form an organic salt (calcium acetate). This chem-ical interaction probably decreases the EVA flexibility, thus pro-

b

composition (500–1000 �C) of pure (a) and 5% EVA-modified-paste (b).

3336 A.M. Betioli et al. / Construction and Building Materials 23 (2009) 3332–3336

moting the elasticity modulus of cement-based materialsincreases.

4. Conclusions

EVA copolymer reduced the calcium hydroxide in the cementpaste due to the chemical interaction between Ca2+ ions and anionsacetate, released in the EVA alkaline hydrolysis. This interactionwas verified at the first 15 min by the absence of the dehydrationpeak in thermogravimetric analyses until 5 and 6 h in EVA-modi-fied pastes with 5% and 10% EVA, respectively; the new peak ob-served at 380 �C, referred to the first calcium acetatedecomposition and; the increase in CO2 release, due to its calciumcarbonate formed during the decomposition of the calcium acetate.This chemical interaction probably decreases the EVA flexibility,thus promoting the elasticity modulus of cement-based materialsincreases.

Acknowledgments

The authors are thankful to CAPES (Fundação Coordenação deAperfeiçoamento de Pessoal de Nível Superior, Ministério da Edu-cação, Brasil) for the financial support. The authors are thankfulto the Department of Civil Engineering, Federal University of SantaCatarina and the Microstructural Laboratory (LME) of the Depart-ment of Civil Construction Engineering of Escola Politecnica – Uni-versity of São Paulo.

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[3] Su Z. Microstructure of polymer cement concrete. Delft: Delft University Press;1995.

[4] Ohama Y. Polymer-based admixtures. Cem Concr Compos 1998;20:189–212.

[5] Silva DA, Roman HR, Gleize PJP. Evidences of chemical interaction betweenEVA and hydrating Portland cement. Cem Concr Res 2002;32:1383–90.

[6] Gomes CEM, Ferreira OP, Fernandes MR. Influence of vinyl acetate–versaticvinylester copolymer on the microstructure characteristics of cement pastes.Mater Res 2005;8(1):51–6.

[7] Georgescu M, Puri A, Coarna M, Voicu G, Voinitchi D. Thermoanalytical andinfrared spectroscopy investigations of some mineral pastes containingorganic polymers. Cem Concr Res 2002;32:1269–75.

[8] Silva DA. Effects of EVA and HEC polymers on the microstructure of Portlandcement pastes. UFSC/PGMAT Dissertation, Florianopolis – Brazil; 2001 [inPortuguese].

[9] Silva DA, Monteiro PJM. Hydration evolution of C3S–EVA composites analyzedby soft X-ray microscopy. Cem Concr Res 2005;35:351–7.

[10] Silva DA, Monteiro PJM. Analysis of C3A hydration using soft X-raystransmission microscopy: effect of EVA copolymer. Cem Concr Res2005;35:2026–32.

[11] Taylor HFW. Cement chemistry. 2nd ed. Londres: Thomas Telford; 1992.[12] Chandra S, Flodin P. Interactions of polymer and organic admixtures on

Portland cement hydration. Cem Concr Res 1987;17:875–90.[13] Zeng S, Short NR, Page CL. Early-age hydration kinetics of polymer-modified

cement. Adv Cem Res 1996;8:1–9.[14] Afridi MUK, Ohama Y, Iqbal MZ, Demura K. Behavior of Ca(OH)2 in polymer

modified mortars. Int J Cem Compos Lightweight Concr 1989;7(4):235–44.

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