Scholarly article on topic 'Durability of Mortars Containing Ground Granulated Blast-furnace Slag in Acid and Sulphate Environment'

Durability of Mortars Containing Ground Granulated Blast-furnace Slag in Acid and Sulphate Environment Academic research paper on "Agriculture, forestry, and fisheries"

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Abstract of research paper on Agriculture, forestry, and fisheries, author of scientific article — Paweł Łukowski, Ali Salih

Abstract The paper deals with corrosion resistance of cement mortars with various amounts of ground granulated blast-furnace slag (GGBS). The mortars were tested in the environment containing acids and sulphates corresponding to the aggressive factors acting on concrete in agricultural areas. The strength development of the composites with GGBS is slower; however, the losses in their strength and mass, as well as linear changes, after storing in the aggressive environment, are lesser than for those containing only Portland cement. This can be attributed, most likely, to the favourable changes in the hardened paste microstructure, caused by GGBS presence. The addition makes the structure of the hardened cement paste more compacted, diminishing the porosity and improving the tightness The long-term tests confirm that cement composites containing GGBS can be rational substitutes for ordinary cement concrete in the aforementioned field. However, the subject of the presented research were mortars; the conclusion shall be verified by concrete testing, planned as the next step of the project.

Academic research paper on topic "Durability of Mortars Containing Ground Granulated Blast-furnace Slag in Acid and Sulphate Environment"

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Procedía Engineering 108 (2015) 47 - 54

Procedía Engineering

www.elsevier.com/locate/procedia

7th Scientific-Technical Conference Material Problems in Civil Engineering (MATBUD'2015)

Durability of mortars containing ground granulated blast-furnace slag in acid and sulphate environment

Pawel Lukowskia'*, Ali Salihb

"Warsaw University of Technology, Faculty of Civil Engineering, al. Armii Ludowej 16, 00-637 Warsaw, Poland bCasey Enterprises, Coolishall, Gorey, Co. Wexford, Ireland

Abstract

The paper deals with corrosion resistance of cement mortars with various amounts of ground granulated blast-furnace slag (GGBS). The mortars were tested in the environment containing acids and sulphates corresponding to the aggressive factors acting on concrete in agricultural areas. The strength development of the composites with GGBS is slower; however, the losses in their strength and mass, as well as linear changes, after storing in the aggressive environment, are lesser than for those containing only Portland cement. This can be attributed, most likely, to the favourable changes in the hardened paste microstructure, caused by GGBS presence. The addition makes the structure of the hardened cement paste more compacted, diminishing the porosity and improving the tightness The long-term tests confirm that cement composites containing GGBS can be rational substitutes for ordinary cement concrete in the aforementioned field. However, the subject of the presented research were mortars; the conclusion shall be verified by concrete testing, planned as the next step of the project.

© 2015 The Authors. 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 underresponsibilityof organizing committee of the 7th Scientific-Technical Conference Material Problems in Civil Engineering Keywords: cement; durability; ground granulated blast-furnace slag; mortar

* Corresponding author. Tel.: +48 22 234 64 81; fax: +48 22 825 75 47. E-mail address: P.Lukowski@il.pw.edu.pl

1877-7058 © 2015 The Authors. 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 organizing committee of the 7th Scientific-Technical Conference Material Problems in Civil Engineering doi:10.1016/j.proeng.2015.06.118

1. Introduction

Ground granulated blast-furnace slag (GGBS) is one of the concrete additions. According to the European Standard EN 206:2013 "Concrete" [1], GGBS is type II addition, together with fly ash and silica fume. It belongs to the group of latent hydraulic materials; EN 206 recommends k value of 0.6 for GGBS used with cements CEM I and CEM II/A. The blast-furnace slag is also important constituent of Portland-composite cements CEM II, blastfurnace cements CEM III, slag-pozzolan cements CEM V and composite cements CEM VI [2].

GGB S is formed by rapid cooling of the liquid slag, which is produced during smelting of the iron ore in the blast furnace. After grinding, it forms fine powder; the grinding process, increasing the specific area of the material, is of favour for its hydraulic activity. The slag is, therefore, the waste material from the production of the iron. According to Neville [3], there is about 300 kg of the slag produced together with 1000 kg of the pig iron.

The main components of the blast-furnace slag are calcium oxide CaO (30-50 %), silicon dioxide SiO2 (28-40 %), aluminum oxide Al2O3 (6-24 %) and magnesium oxide MgO (1-18 %). The slag shows hydraulic ability after activation by such substances like lime (also this produced during Portland cement hydration), sodium hydroxide, sodium carbonate, water glass, gypsum, and others. As reported by Deja [4], the mineral additions usually have a positive influence on the durability of the binders. This effect can also be attributed to ground granulated blastfurnace slag [5, 6], including exploitation in the chemically aggressive environment [7] as well as combined action of freeze and de-icing salts [8].

It is commonly accepted that good quality GGBS should be mainly constituted by the glass phase [9]. According to EN 15167-1:2007 [10], the content of the glass phase in the blast-furnace slag should be at least two third (by mass). The amount of this phase depends on the way and rate of cooling; usually its content is above 80 % by mass. Giergiczny [11] defines the crystalline components of the slag as melilite, merwinite, monticellite and others. The minimum requirements for the ground granulated blast-furnace slag are given in the European Standard EN 151671 (Table 1).

Table 1. Requirements for the ground granulated blast-furnace slag acc. to EN 15167-1.

Property Test method acc. to Requirement

Content of magnesium oxide, mass % EN 196-2 < 18

Content of sulphides, mass % EN 196-2 < 2.0

Content of sulphates, mass % EN 196-2 < 2.5

Loss on ignition, corrected for oxidation of sulfide, mass % EN 196-2 < 3.0

Content of chlorides, mass % EN 196-2 < 0.10

Content of moisture, mass % EN 15167-1 App. A < 1.0

Fineness, m2/kg EN 196-6 > 275

Initial setting time EN 196-3 for combination (by mass) of 50 % of GGBS with 50 % of test cement shall not be more than twice as long as that of the test cement on its own

Activity index EN 196-1 after 7 days > 45 % at 28 days > 70 %

In Ireland, the ground granulated blast-furnace slag is largely used as the concrete addition for industrial and engineering objects. However, until now the Irish Department of Agriculture, Food and Forestry specification for farm concrete [12] does not include GGBS. Its use has been considered for the updated specification, now being

drawn up towards the concrete durability improvement [13, 14]. The main concern when considering the farm objects are tanks, channels and other structures coming into contact with silage acid, which consists mainly of acetic and lactic acid and has pH value from the range 2.5-4.5 [15] as well as sulphate containing environment [16]. The aim of the presented investigation was to verify the possibility of making concrete, exploited in the agricultural areas, more durable without increasing of its material cost. The proposed way is using the significant amount of the granulated blast-furnace slag as the substitute of part of the Portland cement. The research was performed together by Department of Building Materials Engineering of Warsaw University of Technology (Warsaw, Poland), Casey Enterprises (Gorey, Ireland) and Ecocem Ireland Ltd. (Dublin, Ireland).

2. Materials and methods

First stage of the project covered investigation carried out on the mortars with mixed binder, containing ordinary Portland cement CEM I 42.5R (OPC) and ground granulated blast-furnace slag (GGBS) (Table 2) in various proportions: GGBS constituted 0, 30, 50 and 70 % of the binder, respectively. The binder to aggregate (river sand) ratio was 1:3 and water/cement ratio was 0.5. The subject of the testing was the resistance of the mortars against chemical attack, typical for the agricultural areas. The results of this investigation are presented in the paper.

Table 2. Chemical composition of Portland cement and GGBS used in the tests.

Chemical component Content in Portland Cement, mass % Content in GGBS, mass %

SiO2 18.8 35.3

Al2Û3 5.0 14.1

Fe2O3 3.3 13.2

CaO 63.3 40.0

MgO 1.5 8.2

K2O 0.4 0.4

Na2O 0.2 0.8

TiO2 0.2 0.8

P2O5 < 0.9 < 0.1

MnO - 0.5

SO3 3.4 0.05-2.4

The beams 4 x 4 x 16 cm were prepared from the tested mortar mixes for the strength and mass changes determination. For the linear changes measuring, the beams 2 x 2 x 16 cm were prepared. Three specimens were used for in every single test, except the compressive strength, where six specimens (after bending) were used each time. The specimens were cured in water for 28 days and then stored in three environments:

• tap water,

• 10 % (by mass) water solution of magnesium sulphate, MgSO4,

• artificial silage acid (Table 3).

Table 3. Composition of simulated silage acid used in the test.

Component Mass concentration, %

Lactic acid 1.5

Acetic acid 0.5

Formaldehyde 0.3

pH value 3.5-4

The following properties of the mortars were determined:

• compressive strength according to EN 196-1:2005 [17] - for the specimens stored in every environment,

• mass loss using gravimetric method (weighing of the samples in the dry conditions) - for the specimens stored in sulphate and silage acid solutions,

• linear changes according to prENV 196-X [18] - additionally for the specimens stored in sulphate solution.

The tests were performed after specified time of storage: 0 days (initial), 28 days, 56 days, 120 days and 150 days.

3. Results and discussion

The addition of ground granulated blast-furnace slag causes slowdown in the development of the compressive strength of the mortar (Fig. 1). The slowdown increases with increasing content of GGBS, which is in agreement with literature data by Ganesh and Kumar [19].

The corrosion resistance of the mortars with GGBS, however, is improved. The unmodified mortar (containing only ordinary Portland cement), when stored in magnesium sulphate solution or in silage acid, initially continues to develop its strength, but with time the strength starts to decrease. The mortars containing blast-furnaced slag show an opposite behaviour as their strength continues to grow. After 5 months of exposition on the aggressive environment, the compressive strength of the mortars, containing 30 and 50 % of GGBS in the mixed binder, is equal to that of unmodified mortar (Figs. 2 and 3).

The mass changes of the specimens stored in the sulphate solution and silage acid are clearly lesser in the case of the mortars with GGBS. After long period of exposition, the most favourable situation is observed for the mortar containing 50 % of the slag in the mixed binder (Figs. 4 and 5). The same findings can be drawn up when considering the linear changes of the mortar stored in MgSO4 solution; the long-term expansion is the least in the case of the mortar with 50 % of the slag (Fig. 6).

Fig. 4. Changes of mass of the mortars with various content of GGBS stored in sulphate solution.

Fig. 5. Changes of mass of the mortars with various content of GGBS stored in silage acid.

Fig. 6. Linear changes of the mortars with various content of GGBS stored in sulphate solution.

The visual observation of the specimens exposed to the action of the sulphate solution also reveals that they are in better shape when contain GGBS, without or with only small number of stains, cracks and other defects. The particularly good condition can be attributed to the specimens of mortars containing 30 and 50 % of ground granulated blast-furnace slag in the mixed binder (Fig. 7).

Fig. 7. Visual inspection of the mortars with various content of GGBS: a) 0 %, b) 30 %, c) 50 %, d) 70 %, stored in sulphate solution.

The reason for this behaviour is the modification of the composite structure, suggested by Gao et al. [20]. The

addition of ground granulated blast-furnace slag acts similarly to the fly ashes, but this influence can be more intensive. According to Jamrozy [21], the presence of GGBS makes the structure of the hardened cement paste more compacted, diminishing the porosity and improving the tightness. These findings confirm that use of GGBS in the cement composites, exploited in the agricultural areas, can be rational from the technical point of view.

4. Summary and conclusion

The research carried out on the cement mortars containing addition of ground granulated blast-furnace slag confirms that they have improved durability as compared to unmodified mortars. The strength development of the composites with GGBS is slower; however, the losses in their strength and mass, as well as linear changes, after storing in sulphate and silage acid environment, are lesser than for those containing only Portland cement. Taking into consideration the relatively low material cost of the slag and chemical aggressiveness of the environment in the agricultural areas, we can recommend the use of GGBS as the farm concrete component. The subject of the presented stage of research were mortars, therefore, the conclusion shall be verified by concrete testing, which is planned as the next step of the project.

Acknowledgements

The presented research is partially supported by the Faculty of Civil Engineering of Warsaw University of Technology.

References

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