evaluation of pozzolan activity of peat in portland … · 2018. 8. 15. · according to the...

EVALUATION OF POZZOLAN ACTIVITY OF PEAT IN PORTLAND CEMENT

D. C. Oliveira1; C. D. Roveri1; R. F. Grillo2; K. F. Grillo2; C. M. Cruz1, S. C. Maestrelli1 (1) Federal University of Alfenas, Rodovia José Aurélio Vilela, 11999, Cidade Universitária,

BR 267, km 533, CEP: 37715- 400, Poços de Caldas – MG, Brazil. (2) Federal Institute - Sul de Minas, Avenida Maria da Conceição Santos, 900, Parque

Real, CEP: 37550-000, Pouso Alegre - MG, Brazil. [email protected]

Abstract

Cement is one of the most used materials in the world; the pozzolanic type was

investigated in this work. Peat is an organic compound whose chemical composition is

similar to the pozzolans. This work aims to evaluate the pozzolanic potential of peat

when it is added to the cement in 5, 10, 15 and 20%wt. X-Rays fluorescence and

diffraction tests were performed for the characterization of the cements and peat; as

well as physical tests and mechanical resistance. For cold crushing strength of

compositions, there is a reduction of 70% in the mechanical resistance when compared

to pure cements, corroborated by their chemical and physical properties. Peat

presented no pozzolanic activity. For the content of 5% of peat added it is possible to

identify the hydration products; for the addition of 20% of peat the microstructure

changes drastically, presenting areas that did not go through the hydration process.

Keywords: cement, peat, hydration, mechanical properties.

Introduction

Pozzolanic Portland cement is a homogeneous mixture of Portland cement and

a pozzolanic material of fine granulometry, in levels that vary from 15 to 50% [1, 2].

Pozzolan is a siliceous or fireclay material which does not present cementitious value;

however, when it is finely divided in water presence, it reacts chemically with calcium

hydroxide that was liberated in hydration process of cement, at room temperature and

produces compounds with cementitious characteristics [1, 2]. The advantages of this

type of cement are its low heat of hydration, resistance to aggressive environment and

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inhibition of the reaction between cement alkalis and aggregates considered as

reactive. As a disadvantage, it presents slower hardening process, but may present

superior resistance in advanced ages when compared to regular Portland cement.

From physicochemical point of view, peat is a porous material, highly polar and with

great capacity of adsorption of transition metals and polar organic molecules [3], whose

average element composition is 35 to 49% carbon, 43 to 59% oxygen, 0.6 to 1.9%

nitrogen and a level of hydrogen inferior to 6%, besides many functional groups. Being

a material originated from decomposition of vegetal materials in areas with high water

presence, it presents high levels of organic material, above 70% [4, 5, 6].

Materials and methods

The materials used in this paper were: Portland cement type CP II E 32 from

manufacturers Cauê, Holcim and Lafarge and peat supplied by Togni S/A Materiais

Refratários, located in Poços de Caldas, Minas Gerais.

The characterization of the cements was made through qualitative phase

analysis through Rietveld Method using X-Ray Diffractometer D2 PHASER, performed

at Bruker, Atibaia, São Paulo. Both physical and mechanical characterization were

realized at ABCP (Associação Brasileira de Cimento Portland), São Paulo. The results

were made according to the standard ABNT NBR 7215/1996.

For peat characterization, it was performed a semiquantitative chemical analysis

by X-Ray Fluorescence at Togni S/A Materiais Refratários in Poços de Caldas,

equipment Axios PW 4400/40 DY 1686 (Panalytical). Real density was determined

through Helium pycnometry at DEMa – UFSCar, with 5 replicates, through the

equipment Micrometrics AccuPyc 1330 with gas equilibrium rate of 5.0x10-3 psig/min.

It was also performed X-Ray diffraction for peat at Federal University of Alfenas –

Campus de Alfenas, at Crystallography Laboratory, with angular scan from 15 to 75

degrees, step of 0.1; phase identification was made using the program Match!. The

sample sent to XRD analysis was previously prepared with addition of oxygenated

water (volume 10).

The mechanical tests of the compositions were realized according to the

standard ABNT NBR 7215/1996. The peat level to be added in the mortar was

substituted in the cement paste indicated by the standard (624 g). The preparation of


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the mortars and cold crushing strength tests were performed at Instituto Federal do

Sul de Minas, Campi Pouso Alegre and Poços de Caldas.

In order to evaluate porosity, 6 specimens after 28 days of curing were used for

each composition. Initially, the samples were dried in drying kiln for 24 hours

(approximate temperature of 100°C). Then the samples were dried for obtaining dry

weight and immersed in water for 24 hours. Next, the values of immerse and wet weight

were obtained for each of the samples evaluated. The procedure was realized

according to the standard ABNT NBR 9778/1987, apparent porosity was calculated in

percentage. For data evaluation it was performed a variance analysis, Anava, using

the software Sisvar at a significance level of 5%.

In order to analyze peat influence in the microstructure originating from the

hydration process it was performed a scanning electronic microscopy (SEM) in the

specimens evaluated after 91 days of curing, with peat levels of 5 and 20%. The

analysis was performed in the microscopy laboratory at UNESP Campus Rio Claro,

using a microscope JSM-6010LA brand Jeol. For observation and analysis of the

sample with 20% peat addition and Lafarge cement, it was necessary to metalize the

sample, using the equipment JEE-420, also brand Jeol.

Results and discussion

Characterization of cements

With X-Ray diffraction using Rietveld method, it was possible to determine the

different crystalline structures for tricalcium silicate (alite) and tricalcium aluminate

present in the three cements in study (Table 1). Table 2 shows the physical

characterization of the three cements and Figure 1 shows the mechanical behavior at

ages 3, 7 and 28 days of pure cements, without peat addition.


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Table 1: Results of quantification of the three cements.

Components Value (wt%) Cauê Holcim Lafarge Alite (M3) 30.00 27.73 32.31 Alite (M1) 18.15 16.26 18.67

Calcite 12.99 18.41 14.61 Belite (β) 10.61 8.64 9.36

Ferrite 4.87 8.18 7.42 Aluminate (orthorhombic) 4.83 1.06 0.26

Aluminate (cubic) 3.73 3.94 3.15 Portlandite 3.53 1.98 2.33 Periclase 1.83 0.44 0.26

Quartz 0.54 2.28 1.86

Table 2: Physical characterization of the three cements.

Tests Standard Results Limits of

NBR 11578/91

Cauê Holcim Lafarge

Fineness at sieve 75 µm (%) NBR 11579/91 4.3 4.4 2.2 ≤ 10

Water for normal consistency paste (%) NBR NM 43/03 28.2 25.0 29.0 -

Initial set (h:min) NBR NM 65/03 5:05 3:45 4:05 ≥ 1h Final set (h:min) NBR NM 65/03 6:30 5:00 5:45 ≤ 10h

Blaine air permeability (m²/kg) NBR NM 76/98 357 385 360 ≥ 380

Bulk density (g/cm³) NBR NM 23/01 2.99 3.00 2.98 -

Expandability (mm) NBR NM 11582/91 0.0 0.5 0.0 ≤ 5.0

Fig.1. Mechanical resistance (MPa) for pure cements, without peat addition.


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According to Tables 1 and 2 and Fig. 1, the values of mechanical resistance

corroborate the effect of chemical composition as well as the physical characteristics

in the final properties presented by the three cements: cement Cauê has good

mechanical resistance due to its high levels of alite and aluminate and presents lower

mechanical resistance for advanced ages among the three cements as a result of its

higher levels of alkalis and portlandite. As for cement Holcim, the initial resistance is

higher when compared to the other cements, due to its higher permeability and good

levels of alite and aluminate while the resistance in advance ages is good due to the

high level of belite and low level of alkalis. Cement Lafarge contains the lowest value

of mechanical resistance in initial ages when compared to the other two cements, as

a result of its lower permeability, low level of aluminate and higher level of alkalis;

however, it has the highest value of mechanical resistance after 28 days, due to its

good amount of belite. It is worth emphasizing that all the cements evaluated in this

study present values of chemical, physical and mechanical properties in conformity

with the values established by the standard ABNT NBR 11578/1991.

Characterization of peat

The real density found for peat was 1.87 g/cm³, being this value relatively low

when compared to other materials found in the region. In Table 3 is shown the result

of quantitative chemical analysis by X-Ray fluorescence.

Table 3: Quantitative chemical analysis of peat.

Composition and Properties Level (%)

Loss on ignition 32.81 Al2O3 34.36 SiO2 27.79 TiO2 1.62

Fe2O3 2.00 CaO 0.13 MgO 0.16 Na2O 0.02 K2O 0.88

Cr2O3 0.10 P2O5 0.21 ZrO2 0.02


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The chemical demands established by the standard ABNT NBR 12653/1992

indicate that the sum of alumina, silica and iron oxide are superior to 50% for class E

of pozzolans. Thus, peat meets these requisites as the sum of these compounds

correspond to 64.15% of peat composition. As for the maximum percentage of alkalis

available as Na2O, the level presented by peat is a lot inferior to the maximum value

established by the standard, which is 1.5%. However, the loss on ignition is greater

than 30% (which is related to the presence of high levels of organic material), value a

lot higher than the one established by the standard, that is maximum 6%. Figure 2

shows the X-Ray diffractograms for peat.

Fig.2. Phase identification of peat. (using the software Match!).

By analyzing the diffractogram, the minerals present in peat are gibbsite,

montmorillonite, kaolinite and quartz. The diffractogram obtained is typical of a

crystalline material, however, it presents amorphous phases. The higher the value of

amorphous silica, the more reactive the material will be, resulting in good pozzolanic

properties [7]. The peat analyzed presents silica level inferior to 30% and it is not in a

totally amorphous state, which may negatively affect its pozzolanic activity.

Compressive strength

When the values obtained for each composition of all three cements are

compared to reference values (0% peat addition), it can be seen that for ages 7, 14


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and 28 days the values obtained are inferior to reference cements for all compositions

and are inversely proportional to the level of added peat; that is, the higher the level of

peat addition, the lower the mechanical resistance of the cements, as can be

evidenced in Figure 3 [1, 8, 9].

Mechanical resistance of pozzolanic cements is a sum of the resistances

generated by clinker cementitious products and the resistances of the compounds

generated by the pozzolanic reaction [8]. As the level of peat addition increases, the

amount of cement used is lower, which lowers the resistance generated by the

cementitious materials; in addition, peat act poorly as pozzolan and the tendency is

that resistance values lower [10], what can be seen in the values of the compositions

with 20% peat addition, where the mechanical resistance obtained is a lot lower.

As pozzolanic reactions have a slow rate, cold crushing strength tests were

performed after 91 days of curing, as registered in the standard, in order to confirm the

loss in the resistance value. What is expected, when there is addition of pozzolans to

the cement, is that at 91 days of curing the values of mechanical resistance were

superior to the values of reference found for 28 days of hydration (for the type of

cement used, values above 40 MPa are expected), however this is not observed. There

is an increase of resistance at 91 days when compared to the value found after 28

days, due to the continuing process of cement hydration.

Table 4 indicates the loss of mechanical resistance presented for each of the

cements in the ages evaluated, considering the values of lower (5%) and higher (20%)

peat addition. It can be seen that for all three manufacturers of cement, independently

of age, the loss of resistance presented with the increase of peat addition is practically

the same, around 70%. The reduction in the values of mechanical resistance may be

justified by the low quantity of silica present in peat, and by not being in a totally

crystalline state [9], what may directly affect the pozzolanic activity.

Table 4: Loss of mechanical resistance presented by the compositions.

Cement Loss of mechanical resistance (%) 7 days 14 days 28 days 91 days

Cauê 68.31 66.98 70.24 72.92 Holcim 72.99 69.50 70.60 73.40 Lafarge 71.19 75.64 75.65 76.97


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Fig.3. Mechanical resistance for peat compositions for each cement: (a) Cauê, (b)Holcim and (c) Lafarge, by age.

Figure 4 shows the result obtained for apparent porosity for each composition

studied. By applying variance analysis (Anava), for the manufacturers Cauê and

Holcim the value-p is superior to the significance level used (5%); it is then accepted

that all treatments (peat levels) are statistically equal, not influencing the apparent

porosity of the material. For Lafarge cement, however, value-p is lower than 5%,

meaning that this treatment is statistically different. With a Scott-Knott it was possible

to identify which treatments were different: 5 and 10% addition are equal and 15 and

20% are different, what may have contributed to the loss of mechanical resistance.

Generally, peat does not significantly affect the porosity of cement and peat

compositions and does not affect mechanical resistance.


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Fig.4. Apparent porosity (%) for each of the cements as a function of peat addition.

Microstructure

The product responsible for the mechanical resistance acquired by cement is

C-S-H, that is a gel amorphous that guarantees cohesion between the other phases

present. Calcium hydroxide has a format of crystalline hexagonal plates and ettringite

is crystalline, with acicular morphology (needles) [11, 12].

Figure 5 presents the microstructure for all three cements, for the compositions

with 5% peat addition. It can be seen that there is formation of hydration products for

all cements, and the influence of peat in the microstructure is still small. The phases

generated in the hydration process responsible for mechanical resistance (C-S-H and

ettringite) were more easily identified in cements Holcim and Lafarge, what justifies the

higher mechanical resistance obtained for these cements in comparison to cement

Cauê, in which the phase ettringite was not identified. It can also be seen that,

according to Figure 5(b), cement Holcim presents low level of calcium hydroxide, not

being possible its location. Figure 6 shows the microstructure for all three cements with

20% peat addition. For Cauê cement is even more difficult the identification of the

phases formed during hydration, being observed the presence of calcium hydroxide

while for Lafarge cement is still possible to identify phases as ettringite, besides

calcium hydroxide. For cements Cauê and Holcim it was not possible to identify the

presence of C-S-H microstructure, what may also justify the loss of resistance when

compared to pure cement. Such factors indicate that peat negatively affects the


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mechanical resistance of cement. Besides acting as inert material, it still complicates

the hydration process and formation of phases that guarantee higher mechanical

resistance of the product (ettringite and C-S-H).

Fig. 5. SEM for composition with 5% peat addition, increasing x3000, for cements (a)

Cauê, (b) Holcim and (c) Lafarge.

Fig. 6. SEM for the composition of 20% peat, increasing x3000, for cements (a) Cauê, (b) Holcim and (c) Lafarge.


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Greater cohesion of Lafarge cement (Figure 7(b)), when compared to Cauê

cement (Figure 7(a)) results in higher values of mechanical resistance when compared

to the other two cements, however it still presents crystals of Ca(OH)2 that negatively

affect the value of mechanical resistance, what can be one of the reasons for the

reduction of mechanical resistance when compared to the cement without peat

addition, proving that peat does not act as pozzolan and does not react with calcium

hydroxide.

Fig. 7. Microstructures with 20% peat addition for (a) cement Cauê and (b) cement

Lafarge. Conclusions

For all three cements in study there is reduction in the value of mechanic

resistance with the addition of peat, even for advanced ages (91 days of curing). Such

reduction may not have been affected by the porosity, since it remained practically

constant for all compositions evaluated. Scanning electron microscopy corroborates

the results of mechanic resistance found. For the composition with 5% peat addition it

is possible to identify the phases resultant of hydration both for the microstructure and

the chemical composition presented. As for when 20% peat is added, there is a drastic

change in microstructure for all three cements, presenting areas where the hydration

process did not occur. Thus, it is proved that peat does not have pozzolanic activity,

acting as inert material whose carbon quantity, due to organic material, negatively

affects the hydration reaction, since there is reduction of mechanical resistance with

the increase of peat addition in the mixture, independently of curing age.


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Acknowledgments The authors would like to thank Togni S/A Materiais Refratários, ABCP and IF de Pouso Alegre for the realization of tests presents in this research, and to

FAPEMIG for the financial support.

References [1] MEHTA, P. K .; MONTEIRO, P. J. M. Concrete: microstructure, properties and materials. 3.ed. São Paulo: Ibracon Publisher, Brazil, 2008. [2] NEVILLE, A. M .; BROOKS, J.J. Concrete technology. 2.ed. São Paulo: Bookman Publisher Ltda., Brazil, 2010. [3] KAZEMIAN, S. et al. Influence of Peat Characteristics on Cementation and Pozzolanic Reactions in the Dry Mixing Method. Arabian Journal for Science and Engineering, v. 36, p. 1189–1202, 2011. [4] GROVER, S. P. P.; BALDOCK, J. A. The link between peat hydrology and decomposition: Beyond von Post. Journal of Hydrology, Australia, v.479, p.130-138, 2013. [5] WONG, L. S. et al. Comparative measurement of compaction impact of clay stabilized with cement, peat ash and silica sand. Measurement, Malaysia, v. 94, p. 498–504, 2016. [6] KALANTARI, B.; PRASAD, A.; HUAT, B. B. K. Cement and Silica Fume Treated Columns to Improve Peat Ground. Arabian Journal for Science and Engineering, Malaysia, v. 38, p. 805–816, 2013. [7] SALES, F. A. Study of the pozzolanic activity of soda-lime, colorless and amber glass microparticles, and their influence on the performance of Portland cement composites. 161f. Thesis (Doctorate in Structural Engineering) - Federal University of Minas Gerais, Belo Horizonte, Brazil, 2014. [8] ZAMPIERI, V. A. Portland cement added with pozzolans from calcined clays: manufacturing, hydration and mechanical performance. 251f. Thesis (Doctorate in Mineralogy and Petrology) - University of São Paulo, São Paulo, Brazil, 1993. [9] KOPANITSA, N. et al. Additives for Cement Compositions Based on Modified Peat. Advanced Materials in Technology and Construction, Russia, 6f, 2016. [10] ISLAM, S. M. et al. Effect of Peat on Physicomechanical Properties of Cemented Brick. The Scientific World Journal, Malaysia, v. 2014, p. 1-8, 2014. [11] RIDI, F.; FRATINI, E.; BAGLIONI, P. Fractal structure evolution during cement hydration by differential scanning calorimetry: effect of organics additives. The Journal of Physical Chemistry, v.117, p. 25478-25487, 2013. [12] ROSTAMI, V.; SHAO, Y.; BOYD, A. J.; HE, Z. Microstructure of cement paste subject to early carbonation curing. Cement and Concrete Research, v.42, p.186-193, 2012.


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Keywords: cement, peat, hydration, mechanical properties.IntroductionMaterials and methodsResults and discussionConclusionsAcknowledgmentsReferences

evaluation of pozzolan activity of peat in portland … · 2018. 8. 15. · according to the...

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