Scholarly article on topic 'Influence of Aggregate Granulometry on Air Content in Concrete Mixture and Freezing - Thawing Resistance of Concrete'

Influence of Aggregate Granulometry on Air Content in Concrete Mixture and Freezing - Thawing Resistance of Concrete Academic research paper on "Civil engineering"

CC BY-NC-ND
0
0
Share paper
Academic journal
Procedia Engineering
OECD Field of science
Keywords
{concrete / aggregate / durability / "freezing - thawing resistance" / porosity / "air content" / absopbtion}

Abstract of research paper on Civil engineering, author of scientific article — Laurynas Zarauskas, Gintautas Skripkiūnas, Giedrius Girskas

Abstract Concrete frost resistance is one of the main factors that effects its durability. This is particularly important in the harsh climate regions where the water in concrete pores gets multiple freeze-thaw cycles. Concrete frost resistance can be increased by changing the coarse aggregate content by volume in the concrete mixture, as it is changing and concrete porosity. It was found that coarse aggregate volume concentration increase has a negative effect on predicted freezing - thawing resistance of concrete. It was found the correlation between a closed porosity of concrete, coarse aggregate volumetric concentration, air content in the concrete mixture and the predicted frost resistance of concrete. After statistical processing of test results it was found significant dependencies between coarse aggregate volumetric concentration in concrete, its closed porosity and predicted concrete freezing – thawing resistance and durability of concrete.

Academic research paper on topic "Influence of Aggregate Granulometry on Air Content in Concrete Mixture and Freezing - Thawing Resistance of Concrete"

CrossMark

Available online at www.sciencedirect.com

ScienceDirect

Procedía Engineering 172 (2017) 1278 - 1285

Procedía Engineering

www.elsevier.com/locate/procedia

Modern Building Materials, Structures and Techniques, MBMST 2016

Influence of aggregate granulometry on air content in concrete mixture and freezing - thawing resistance of concrete

Laurynas Zarauskasa, Gintautas Skripkiunasb, Giedrius Girskasc

a-cDepartment of Building Materials, Faculty of Civil Engineering, Vilnius Gediminas Technical University, Sauletekio ave. 11, LT-10223 Vilnius, Lithuania eInstutite of Buildings Materials and Products, Vilnius Gediminas Technical university, Sauletekio 11, LT-10223 Vilnius, Lithuania

Abstract

Concrete frost resistance is one of the main factors that effects its durability. This is particularly important in the harsh climate regions where the water in concrete pores gets multiple freeze-thaw cycles. Concrete frost resistance can be increased by changing the coarse aggregate content by volume in the concrete mixture, as it is changing and concrete porosity. It was found that coarse aggregate volume concentration increase has a negative effect on predicted freezing - thawing resistance of concrete. It was found the correlation between a closed porosity of concrete, coarse aggregate volumetric concentration, air content in the concrete mixture and the predicted frost resistance of concrete. After statistical processing of test results it was found significant dependencies between coarse aggregate volumetric concentration in concrete, its closed porosity and predicted concrete freezing - thawing resistance and durability of concrete.

© 2017Publishedby ElsevierLtd. This is anopenaccess article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of the organizing committee of MBMST 2016

Keywords: concrete, aggregate, durability, freezing - thawing resistance, porosity, air content, absopbtion.

Introduction

Concrete, as it is known today, is a construction material consisting of primarily rocks of limited maximum size that meet certain characteristics related to their mechanical, chemical, and granulometric properties and which are merged by a binding paste formed by a binder (cement) and water." [1]

E-mail a^^re55/laurynas.zarauskas@vgtu.lt;gintautas.skripkiunas@vgtu.lt;giedrius.girskas@vgtu.lt

1877-7058 © 2017 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license

(http://creativecommons.org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of the organizing committee of MBMST 2016

doi: 10.1016/j.proeng.2017.02.153

Hardened cement paste, cement mortar or concrete is porous materials which in can penetrate gas or liquids. Materials can be influenced by porosity in different ways. Total porosity volume, size of pores, pore distribution in material, bigest pore size, shape and bond between, have influence to concrete strength and elasticity. Durability of concrete depends on freezig - thawing resistance and can be controled by different pore volume and spacing between them [2;3].

Cement stone strength and durability depend ragely on the input of cement and water and cement and water ratio (W/C). Increasing this ratio concrete quality decreasing [4]. Pores existing in cement stone can be divided into three main groups: capillary pores, pores of the gell, air pores [5].

Capillary pores in cement stone arise after evaporation of water excess from the production of concrete mix. In most cases, the production of mixtures provide more water than necessary to occur chemical reactions. Capillary pores are open and easy fill up with water. The ammount of water in cement stone is main factor causing the destructive effects of freezing. The higher capillary pore volume and size, the lower is resistance to freezing [4]. Ammount of capillary pores in hardened cement stone depends on W/C ratio [6;7].

T. C. Powers opinion, the cement stone freezing - thawing resistance is increasing, reducing in W/C ratio 0,4 and less [8]. R. Feldman found that water content in capillary pores completely frozen when temperature drops below -13 °C and the temperature interval of 0 °C to -13 °C is ice formation in capillary pores period [9].

Pores of the gel does not effect the freezing - thawing resistance of cement stone because they are very small. The size is 1.5 to 2.0 nm [4;6;10;11]. Gel pores have no significant effect on concrete strength and conductivity because they are very small and have no free water [13].

Closed/air pores are forming by including air from environment and hardening cement stone contraction. Air inclusion promotes some special additives and contraction occurs naturally. Included air pores and contraction pores form closed porosity which improves freeze resistance. Air pores formated by included air, unlike capillary pores, increasing conglomerate freezing - thawing resistance. In water absorption air pores remains dry because they are closed. Air pore fineness, is another feature that infuences the cement stone frost resistance. Cement with the same quantity of air, the smaller the air pores are, more numerous and smaller distances between them. In this case water, infulenced with ice pressure have to penetrate to the air pore. When the average distance between the air pores are less 200 ^m cement stone is frost resistant [4;6;13;14].

Main decay, cracking and reason for the crumbling is that the water which turn into ice, the volume increases. Water density is 1 g/cm3, adn the ice is 0,917 g/cm3. Ice holds 9 % greater volume than water. Ice crystals depressing hardened cement stone pore and capillary walls, expanding the product and may disrupt it [15;16].

Cement stone degradation due to frost is the most common cement stone products destruction in case. The cyclically-cooled and reheated, the water saturated cement stone as well as other mineral solid body can be degraded

There are concrete forst resistance criteria KF - it is a closed porosity of Pu (included air + contraction pores) and open porosity Pa (capillary pores) ratio: KF = Pu / 0,09 Pa. Air critical mass is about 3 %. Thus, if the concrete or mortar mixture compacted in semi finished product included air is more than 3 % it can be expected that the product will be frost reisistant. The required amount of entrained air further depends upon the composition of the conrete mix, cement content, W/C ratio, aggregate size, distribution of entrained air and pore size and so on [18].

Cement stone frost resistance reduces the open and capillarie pores, which are formed be evaporation of the free water in cement stone. Such capillary pores and amount of them depend on the W/C ratio. The more water was added in to cement stone mixture, the more remains unbound water, after evaporation formed open porosity [17].

D. Nagrockiene and others, used different coarse aggregate concrentations. They found the dependencies between coarse aggregate volumetric concentration and air void in hardened concrete. The concrete with bigger ammount of coarse aggregate have lowest closed porosity and lowest freezing-thawing resistance [19].

Of the coarse aggregate and hod interoperability is currently no consensus. Traditinional opinion argues that the total aggregate surface area should be minimal, it means that concrete mixtures should be designed with the maximum amount of coarse aggregate. Gumuliauskas et. al. indicates that the coarse aggregate in the mixtures should be not at a maximum [20]. G. Skripkiunas and others believes that the focus in designing strong concrete is to the distribution of coarse aggregate in concrete and stress concrentation around coarse aggregates [21].

M. Dauksys with others conducted the research to determine a predicted frost resistance of concrete by concrete porosity parameters. In research as fine aggregate used 0/1; 0/2 and 0/4 sand and coarse aggregate 4/16 fraction

gravel. The concrete samples acording to the volumetric cooling forecasted freezing and thawing cycles it appears that only a fine grained concete (obtained without the use of coease aggregate) withstood the expected number of cycles. Concrete with coarse aggregate according to its porosity parameters set nuber of cycles did not withstood [22].

Materials and test methods

The concrete mix was made of water, cement, sand and coarse aggregate gravel and crushed gravel. Concrete compositions differed by the amount of gravel and sand. Portland cement produced in AB "Akmenes cementas", specimens were made of CEM I 42.5 N class Portland cement complying with LST EN 197-1:2000 standard requirements. Gravel and crushed gravel was used 4/16 mm fraction, sand 0/4 mm.

Table 1. Properties of sand 0/4, gravel 4/16 and crushed gravel 4/16.

Sand Gravel Crushed gravel

Property value value value

Density, kg/m3 2620 2600 2610

Bulk density, kg/m3:

normal state 1660 1525 1410

compacted state 1875 1725 1600

Porosity, %:

normal state 36.6 41.3 46

compacted state 28.4 33.7 38.6

Coarseness module 2.94

Two different concrete composition with different fine aggregate and coarse aggregate concentrations where investigated. First one was made of gravel, sand, water and cement, second one: crushed gravel, sand water and cement. Concrete composition and technological properties are presented in Tables 2, 3.

Table 2. Concrete composition and technological properties with gravel.

Materials for 1 m3 concrete, kg Concrete mix

No. 9st Cement Gravel Sand Water Density kg/m3 Air content, % Slump, cm

1.1 0.52 368 1356 516 187 2427 0 3.5

1.2 0.48 367 1248 615 187 2417 0.24 4.5

1.3 0.44 367 1143 709 187 2406 0.61 4

1.4 0.4 368 1044 809 184 2405 0.79 3.2

1.5 0.36 361 927 911 182 2381 1.73 2.8

1.6 0.31 360 815 1020 182 2377 1.82 1.8

1.7 0.23 358 611 1207 181 2357 2.53 0.8

1.8 0.16 356 404 1396 180 2336 3.28 0

1.9 0.08 349 197 1558 177 2281 5.4 0

1.10 0 347 0 1751 178 2276 5.43 0

Table 3. Concrete composition and technological properties with crushed gravel.

Materials for 1m3 concrete, kg Concrete mix

No. 9st Cement Crushed gravel Sand Water Density kg/m3 Air content, % Slump, cm

2.1 0.54 355 1418 449 193 2415 0.03 16

2.2 0.47 356 1221 639 193 2409 0.13 13.5

2.3 0.43 355 1114 744 192 2405 0.27 11.5

2.4 0.39 353 1010 844 192 2399 0.41 9

2.5 0.34 350 899 937 190 2376 1.31 7

2.6 0.3 346 791 1030 188 2355 2.14 3.5

2.7 0.22 340 583 1209 185 2317 3.58 1.5

2.8 0.15 345 394 1356 187 2282 4.68 0.5

2.9 0.08 345 197 1509 187 2238 6.2 0

2.10 0 347 0 1663 188 2198 7.52 0

The concentration of coarse aggregate ¡p in concrete was derived from the equation:

9 st =— (1)

where: St - coarse aggregate content in concrete; pst - coarse aggregate density.

The total porosity of concrete was determined by concrete density, whereas open porosity was determined by the total water saturation. Concrete slump and density were tested according to EN 12350-2, EN 12350-6. Entrained air content was calculated from fresh concrete density and constituent materials densities:

^m PSm

Wst ■ St 100

Pst I 1 +

.W» 100

where: C, Sm , St, V - cement, sand, coarse aggregate and water contents in concrete; pc, psm, pst, pv - cement, sand, coarse aggregate and water densities.

Concrete specimens were made 100 x 100 x 100 mm, which were compacted on laboratory vibration table. After one day curing in forms specimens were removed from formwork and cured 27 days in water. Later, these samples were split into cubes 50x50x50 mm for water absorbtion kinetics, density and specific gravity determination tests. Specific gravity of concrete was determined by pycnometer method.

All samples were tested at the same time, so the environmental impact of all was the same.

Experimental results

Tested specimens kinetics of water absorption is presented in figures 1 and 2. Highest water absorption was reached for specimens without coarse aggregate. Increasing coarse aggregate volume concentration water absorption decreased. Water absorption kinetics in first one hour shown that the specimens with gravel coarse aggregate reached 86 % whereas crushed gravel coarse aggregate reached 72 % of total absorption.

Test results of the porosity of concrete specimens with different amount of coarse aggregate concentration shown in figs. 3 and 4. Increasing concentration of coarse aggregate the amount of closed porosity is decreasing. When 9st reaches 0.54 the concrete almost have no closed pores and it is less frost resistance.

How we can see from data shown in figures 3 and 4 using crushed gravel coarse aggregate total porosity of concrete is higher than using gravel coarse aggregate. Influence of absorption by increasing coarse aggregate concentration have a larger impact to concrete with crushed gravel coarse aggregate. The total porosity is decreasing from 19.74 % with 0 coarse aggregate to 13.33 % with ^st - 0.54 than using gravel coarse aggregate the total porosity with 9st-0 is 16.95 and ^st-0.52 is 10.37 %. We can see that crushed gravel have a more significant effect to porosity parametersand air content changes than gravel coarse aggregate.

< 2 1 0

0,52 0,44 0,23 0

Duration, min

Fig. 1. Function of absorption and duration with gravel coarse aggregate.

0,54 0,43 0,22 0

Duration, min

Fig 2. Function of absorption and duration with crushed gravel coarse aggregate.

20 ^ 18

$ 16 ' «

^ 12 10 8

'-•A

• Pa

0,1 0,2 0,3 0,4 0,5 0,6 Coarse aggregate volume concentration

20 ^ 18

£ 16 si

2 14 o

P12 10 8

"••■•A

•■«......• •

0 0,1 0,2 0,3 0,4 0,5 0,6 Coarse aggregate volume concentration

Fig. 3. Function of porosity and coarse aggregate volume concentration (gravel).

Fig. 4. Function of porosity and coarse aggregate volume concentration (crushed gravel)..

Increasing coarse aggregate volume concentration the total porosity is reducing while open porosity almost remain constant.

Statistical processing of test results by using a linear function model between air content in concrete mixes and closed porosity with gravel and crushed gravel coarse aggregate (fig. 5). Using gravel coarse aggregate the correlation of the function r=0.987 and determination coefficient R2= 0.974. Processing empirical data was produced closed porosity prediction equation for concrete:

P„ = 0.965 ■ A

Where: Pu is closed concrete porosity, %; A is entrained air content in concrete mix, %.

• Gravel ■ Crushed gravel

1 2 3 4 5 6 7 Entrained air, %

Fig. 5. Function of closed porosity and air content in concrete mix with gravel and crushed gravel coarse aggregate.

The work revealed the significantly correlation between closed porosity and air content in concrete using crushed gravel coarse aggregate which correlation coefficient r=0.997, determination coefficient R2= 0.996. It can be concluded that is no difference between using gravel or crushed gravel coarse aggregate.

Relationship between coarse aggregate volume concentration and frost resistance criteria Kf is shown in fig. 6. Statistical processing test results with gravel have been found correlation coefficient r=0.993, determination coefficient R2= 0.98. With crushed gravel the correlation coefficient r=0.974, determination coefficient R2= 0.979. Test results scattering is shown in figure 6. Using both coarse aggregate types frost resistance criteria (KF) can be predicted with linear function:

KF = 5.88 - 12 ■ 9st (4)

Coarse aggregate volumetric concentration

Fig. 6. Function of frost resistance criteria and different coarse aggregate volume concentration.

Test results have shown that frost resistance factor depends on closed porosity of concrete by linear function. Statistical processing of test results by using linear function model produced a function of closed porosity and frost resistance factor for concrete. Have been found correlation coefficient r=0.998, determination coefficient R2= 0.997. Frost resistance factor can be calculated knowing closed concrete porosity or entrained air content in concrete mix by equation:

KF = 0.96 ■ Pu + 0.1 = 0.93 ■ A (5)

The equation valid for concrete with about 300 l cement paste content or about 350 kg cement for 1m3 concrete mix with plastic consistency.

Closed porosity, %

Fig. 7. Function of frost resistance criterion and closed porosity of concrete.

Where is significant dependence between coarse aggregate volume concentration in concrete mix and frost resistance factor, less is used coarse aggregate concentration the higher is frost resistance criterion of concrete.

It was found that coarse aggregate particle form had no significant impact on the quantity of air in concrete mixture and its freezing - thawing resistance. Coarse aggregate concentration determine the concrete frost resistance criterion KF, which can be predicted from water absorption rate of hardened concrete or entrained air content in concrete mixture.

Conclusions

1. Coarse aggregate particle form have no significant impact on the quantity of entrained air in concrete mixture therefore and its freezing - thawing resistance.

2. Coarse aggregate concentration in concrete determine the concrete freezing - thawing resistance criterion KF, which can by predicted from water absorption rate of hardened concrete or entrained air content in concrete mixture.

3. After statistical processing of test results it was found significant dependencies between coarse aggregate volumetric concentration in concrete, its closed porosity and predicted concrete freezing - thawing resistance and durability of concrete.

References

[1] F. Cánovas, M. Hormigón., Ed. Colegio de Ingenieros de Caminos, Canales y Puertos, 1989, p. 334.

[2] P.W. Brown, D. Shi, J. Skalny, Porosity/Permeability Relationships, Material Science of Concrete II, 1991, pp. 83-110.

[3] N. Hearn, R.D. Hooton, R.H. Mills, Pore structure and permeability, Significance of tests and properties of concrete and concrete making materials, American Society for Testing and Materials, 1994.

[4] K.A. Kallipi, Pore structure of cement-based materials, Testing, interpretation and requirements, Modern concrete technology series 12 (2006)

[5] P.K. Mehta, P.J. Monteiro, Concrete structure, properties and materials, Prentice-Hall, Inc., Englewood Cliff, New Jersey, Second Edition, 1993, p.548.

[6] G. Skripkiünas, Building conglomerate structure and properties. Kaunas: Vitae Litera, 2007, p. 335 (in Lithuanian).

[7] I. Soroka, Portland Cement Paste and Concrete, Macmillan. London, UK, 1979, p. 88.

[8] T.C. Powers, The air requirements of frost-resistant concrete, Proceedingsof the Highway Research Board, Portland Cement Association, Bulletin 33 (1949) 1- 28.

[9] R. Feldman, Length change - adsorption relation relations for the water - porous glass system to -40 °C, Canadian Journal of Chemistry (48)2

(1970)287-292.

[10] H.F.W. Taylor, Cement Chemistry, London Vol. 2 (1997), p. 480.

[11] S. Rostam, Durable concrete structures-design guide, Comite Euro-International du Beton, London: Thomas Telford, 1992.

[12] H. Romberg, Zementsteinporen und betoneigenschaften, beton-Information 5 (1978) 50-55.

[13] E.K. Attiogbe, Predicting freeze-thaw durability of concrete - a new approach, ACI Materials Journal 93(5) (1996) 457-464.

[14] E.K. Attiogbe, Volume fraction of protected paste and mean spacing of air voids, ACI Materials Journal 94(6) (1997) 588-591.

[15] H. Cai, X. Liu, Freeze-thaw durability of concrete: ice formation process in pores, Cement and Concrete Research 28(9) (1998) 1281-1287.

[16] B. Zuber, J. Marchand, Modeling the deterioration of hydrated cement systems exposed to frost action, Part 1: description of the mathematical model, Cement and Concrete Research 30 (2000) 1929-1939.

[17] B. Vektaris, V. Vilkas, Concrete sustainability, Concrete sulphate and alkaline corrosion, frost resistance and carbonation, Studies and preventive measures, Kaunas: Technologija, 2006, p.163 (in Lithuanian).

[18] A.E. Sheikin, L.M. Dobshic,Cement concrete and high frost resistance, Stroyizdat, Len. Dep, N., 1989, p. 128 (in Russian).

[19] D. Nagrockiene, G. Skripkiunas, G. Girskas, Predicting frost resistance of concrete with different coarse aggregate concentration by porosity parameters, Mater. Sci. 17(2) (2011) 203-207.

[20] A. Gumuliauskas, G. Abromavicius, Filler influence the concrete structure of parts of the strength of concrete and reinforced concrete: conference, Kaunas: Technologija, 2001, pp. 41-45 (in Lithuanian).

[21] G. Skripkiunas, V. Vaitkevicius, R. Sciukas, Coarse aggregates influence the strength of the concrete, Of concrete and reinforced concrete: conference, Kaunas: Technologija, 2000, pp. 89-94 (in Lithuanian).

[22] M. Dauksys, E. Ivanauskas, S. Juociunas, D. Pupeikis, L. Seduikyte, The Assessment of Prediction Methodology of Concrete Freezing and Thawing Resistance Mater, Sci. 18(4) (2012) 403-409.