POSSIBLE USE OF THE SLAG AGGREGATE IN FIBRE REINFORCED CONCRETE. Aneta RAINOVÁ, Karel ŠEPS, Vladimíra VYTLAČILOVÁ

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1 POSSIBLE USE OF THE SLAG AGGREGATE IN FIBRE REINFORCED CONCRETE Aneta RAINOVÁ, Karel ŠEPS, Vladimíra VYTLAČILOVÁ Czech Technical University in Prague, Faculty of Civil Engineering, Department of Concrete and Masonry Structures, Thákurova 7, , Prague 6, Abstract The aim of this article is to present results of preliminary study of experimental program, which is focused on production of concrete with full replacement of natural aggregate by crushed slag aggregate and with fibre reinforcement. The need to reuse waste products or by-products becomes more and more important at present and leads to efforts to search new ways of waste materials reusing and new possibilities in combinations of typical construction materials and waste or secondary products of primary production or recycling. In scope of experimental program, which is aimed at utilization of slag aggregate available on Czech market in recycling plant of construction and demolition waste. The first objective was to collect information about production of this material. Further, basic mechanical-physical properties of slag aggregate with different origin were investigated, and test specimens with full replacement of natural aggregate by granulated slag aggregate and polypropylene fibres were prepared. Resulting properties were compared with properties of concretes with substitution by other different recycled materials from construction site, which were also investigated at the department of authors. Obtained data and results will be used in application and during optimization of concrete mixture composition with the use in earth structures. Keyword: Granulated slag aggregate, fibre reinforced concrete, mechanical and physical properties 1. INTRODUCTION As a waste material, slag is a by-product manufactured in industry during thermal and combustion processes. Basic types of slag are divided into blast furnace slag and basic oxygen furnace slag (Fig. 1 and 2), these types are generally called crystalline slag; they are generated by slow solidification of meltage during manufacturing of pig iron or steel [1]. Chemical composition and temperature during manufacturing determinates structure of the slag, what further influences other properties. Slag aggregate - the main objective of this article, is then manufactured by crushing and separation of crystalline slag and other byproducts of metallurgical industry. Granulated slag aggregate is currently utilized mainly in earthworks of linear transport communications [2, 3], as backfill in retaining structures, backfill of roads and pipeline structures, in motorway rugs and groundwork layers, for terrain modification works, during manufacturing of burnt brick products, and also for revitalization of depleted mines. Beside granulated slag aggregate, which is not yet so widely used, slag in generally utilized mostly in a form of finely ground blast furnace slag, which is used as active and filler admixture to concrete. Granulated slag aggregate origins from fast cooling of fluid blast furnace slag in water. Granulated slag aggregate prepared by further processing of blast furnace slag exhibits latently hydraulic properties, which are widely exploited in combination with concrete. European metallurgical industry [4] manufactures 45 million tons of slag per year according to present statistics. According to information base of Arcelor Mittal [5], tons of granulated slag aggregate is produced in the Czech Republic per year. Approximately 30% of the whole amount of slag is used in the form of granulate into groundwork of roads and 60% is used as finely ground form of slag during manufacturing of cement [4]. A 300kg of produced slag origins from 1 manufactured ton of pig iron [6]. Utilization of finely ground slag is a well established method of reusing of this metallurgical by-product, namely in concrete and cement industry. Production of granulated slag aggregate still requires more forms of

2 utilization, next to reusing in groundwork of roads. Current standards [7] allow utilization of artificial and recycled aggregate in concrete, but designations for recycled aggregates are not included in standard in this time. Further it is necessary to prove pertinence of aggregate for utilization in concrete mixture. In order to exploit granulated slag aggregate as convenient as finely ground slag, the main objective of authors is manufacturing of concrete with slag aggregate and other possible recycled materials. When granulated slag aggregate is used, it is necessary to focus on slag composition, which further influences properties of concrete mixture, and on mechanical and physical properties of slag aggregate (density, bulk density, fraction, grain curve, resistance to crushing, amount of voids, absorption etc.) and possible influence of typical aggregate properties on concrete (alkali-silica reaction, chlorides, sulphates). From the view of chemical composition, slag consists of 30-50% CaO, 28-40% SiO2, 8-24% Al2O3 and 1-18% MgO. Composition depends on quality of manufactured cast iron or steel. Composition of slag is then very close to composition of cement. Granulated slag with more than 90% content of amorphous phase is appropriate for alkaline activation. Recent research is aimed at possible exploitation and utilization of granulated slag aggregate, while it is not so widely used in construction industry because of heavy metals content. Durability of concrete with addition of finely granulated slag was investigated in [8]. Mechanical characteristics of concrete with slag aggregate and physical characteristics of slag aggregate, that are also objective of this article, were investigated in [9, 10]. According to findings of authors, durability of concrete with slag aggregate after affecting by moisture, freezing and leaching is slightly lower, but satisfactory compared to ordinary concrete [9]. The same properties were studied in [10], where also compressive strength, tensile strength and Young s modulus were tested. Authors also refer, that concrete with slag aggregate was even more durable in normal weather conditions than ordinary concrete. Further, the possible danger of slag volume changes in dependence on chemical composition was proved for example in [11]. The range of volume changes is connected to amount of CaO and MgO in slag. The aim to use slag aggregate as only one used aggregate in concrete mixture was introduced in [12], where was showed, that volume changes typical for slag aggregate can have positive effect on shrinkage of these concretes. Generally, in case of both blast furnace slag and basic oxygen slag, it is possible to reuse these materials in concrete mixture, if its concordance with standards is proved. It is necessary to focus on chemical composition (silica analysis) and expansion parameters, mainly in case of basic oxygen slag. Slag also provides many positive properties incorporated in concrete, namely latently hydraulic properties of blast furnace slag. Basic oxygen slag has higher strength; in case of blast furnace slag it is possible to exploit its beneficially lower self weight. Slag aggregate can be delivered in dry form of granulate from repositories (Fig. 3) or hydrated from dumps. Different fractions of aggregate are depicted in Fig. 1 and 2. 10cm 10cm Fig. 1 Fractions of blast furnace slag 0/8 mm a 0/32 mm [13]

3 10cm 10cm Fig. 2 Fractions of blast furnace slag 8/16 mm a 16/32 mm [13] Fig. 3 Repository of slag aggregate 2. EXPERIMENTAL WORK The objective of experimental research is targeted on determination of mechanical physical properties of fibre reinforced concrete with full replacement of natural aggregate by basic oxygen furnace slag and blast furnace slag. The results are compared with results found out by another experimental programme and with fibre reinforced concrete with crushed bricks and recycled aggregate. The process of the design of fibre reinforced concrete with full replacement of natural aggregate by slag aggregate is primarily focused on economical, ecological and secondary effects on simple technological procedure, easy processing and usability in construction industry. The experiments have been carried out in laboratory of Faculty of Civil Engineering of CTU in Prague. 2.1 Properties of slag aggregate In first phase there slag aggregate from two sources was used for producing of fibre reinforced concrete. The first aggregate (SK 1) was from DESTRO company and its blast furnace slag cooled by air, wide fraction 0/32 united with combination of furnace slag, crushed bricks and recycled concrete also wide fraction 0/32. Company AZS 98 provided experimental programme with the second slag aggregate; its combination of basic oxygen furnace slag of fractions 0/16 and 16/32. Gradation, water absorption, specific weight and bulk density of slag aggregates were tested. You can see all measured values in graph 1 5 (it is mean value of three measurements). The measurements of

4 characteristics were in accordance with standards specific weight and water absorption (ČSN ), bulk densities with and without compacting and void content (ČSN EN ), sieve analysis (ČSN EN 933-1). The suitability of used slag aggregates was evaluated by the control test in recycle centre because of additional characteristic. The results proved that slag aggregate is convenient for production of concrete. Chart 1 Sieve analysis plot for individual types of slag aggregates (Curves A32, B32 and C32 show boundary between good, usable and unsuitable composition of grain) Chart 2, 3 Specific weight of slag aggregate (left), Water absorption of slag aggregate (right)

5 Chart 4, 5 Chart 4,5: Bulk density of loose aggregates(left), bulk density of packed aggregates(right) 2.2 Production of specimens Two sets of samples (S1 and S2) were prepared; each contained six standard 150 mm cubes. The rest of sets were taken from literature. Sample S3 from Spain research institute, Italian (S4) research institute and previous study from Faculty of Civil Engineering of CTU (B3, C3). A description of the composition of the test samples is shown in table 1. Table 1 Components of specimens of individual sets Set Aggregate Binder Fibres S1 Slag aggregate 1 S2 Slag aggregate 2 CEM II/B-M(S-LL) 32,5R S3 Slag aggregate 9 CEM I 42,5 R S4 Slag aggregate 10 CEM II A/L 42,5 R B3 Recycled concrete 15 CEM II/B-M(S-LL) 32,5R C3 Crushed bricks 15 Forta Ferro 1% volume Without fibres Forta Ferro 1% volume The first set of fibre reinforced concrete contained 1504 kg (S1) the second set contained 2041 kg (S2) of slag aggregate in cubic metre. There were used fibres FORTA-FERRO in all sets of this experimental study on the basis of previous experience with their use in produce of fibre reinforced concrete. FORTA-FERRO is an easy to finish, colour blended fibre, made of 100% virgin copolymer/ polypropylene consisting of a twisted bundle nonfibrillating monofilament and a fibrillating network fibre, yielding a high-performance concrete reinforcement system. FORTA-FERRO is used to reduce plastic and hardened concrete shrinkage, improve impact strength, and increase fatigue resistance and concrete toughness. This extra heavy-duty fibre offers maximum long-term durability, structural enhancements, and effective secondary/temperature crack control by incorporating a truly unique synergistic fibre system of long length design. FORTA-FERRO is noncorrosive, non-magnetic, and 100% alkali proof [14]. The dosage of fibres was determined on the basis of previous experiments as 1% of volume content (9,1 kg/m 3 ) to provide noticeable influence of fibres on the structure of fibre reinforced concrete with recycled aggregate. The cement contents were in sets S1 and S2 determined on the base of previous experimental study 300 kg/m3. The same dosage of Portland composed cement was used in sets B3, C3. The set S3 contain 310 kg/m3 and set S4 317 kg/m3 of cement. Consistency, good workability and current moisture of aggregate have been taken into consideration during setting of amount of water. Individual water-cement ratios were 0,53 (series S1), 0,6 (S2), 0,66 (C3), 0,48 (B3), 0,6 (S3) a 0,52 (S4).

6 The composition of mixes produced during experimental programme, carried out at Faculty of Civil Engineering of CTU, were modified so that is no need to add any other ingredients and good workability and low price of mix have been maintained. All ingredients of fibre reinforced concrete mixture were dosed by weight. The composition of samples and descriptions of experiment studies of series S3, S4, B3 and C3, listed here for comparison is described in more detail in [9], [10], [15]. 2.3 Experimental tests Measurement of basic mechanical-physical properties was carried out according to relevant standards for plain concrete. Specific weight of the fresh concrete has been determined (according to ČSN EN ). Test of cube compressive strength of the hardened concrete was carried out (according to ČSN EN ), tensile splitting strength test of cube (according to ČSN EN ), flexural strength test of prism (according to ČSN EN ) and determined of specific weight of hardened concrete (according to ČSN EN ). The compressive strength and splitting strength test were tested on the standard 150 mm cubes. The tests have been carried out at 28 (sets S1 S4) and 90 days (sets B3 and C3) old specimens respectively. 3. RESULTS AND DISCUSSION The results of the measured characteristics are given in charts 6-8 there are averages of the three measured values of specific weight of hardened concrete, compressive and tensile splitting strengths. The specific weight of concrete with a full replacement of natural aggregate by slag aggregate is very variable and depends on both the type of slag and the resource of the slag. In general the basic oxygen furnace slag has higher specific weight than blast furnace slag. Chart 6 Specific weight of hardened fibre reinforced concrete Chart 7, 8 The compressive strength (left) tensile splitting strength (right), measured on the 150 mm cubes

7 The compressive strength of this concrete is comparable with the concretes with recycled aggregate. the dependence of compressive strength on the specific weight of used slag aggregate was proofed. The high compressive strength In a S4 set is not only due to the high specific weight of slag aggregate but also due to the quality of the cement. As for the tensile splitting strength, it can be concluded that the values are comparable with concretes with other recycled aggregates. The values of tensile splitting strength depend on specific weight of aggregate too. 4. CONCLUSION Resultant values of mechanical characteristics of granulated slag aggregate were assessed in conformity with standards and suitability of slag aggregate as a replacement of natural aggregate in concrete with fibre reinforcement was proved [7]. Composition of concrete mixture was designed with regard to costs of manufacturing, hence special additions modifying properties of concrete were not included and also lower amount of cement in the mixture was chosen with regard to ecological aspects of project. Measurements of density showed expected lower density of concrete with replacement of natural aggregate by blast furnace slag aggregate. This can be beneficially utilized in case of demand to lower self weight of final product. Density of fibre concrete with oxygen furnace slag is comparable to density of ordinary concrete. Mechanical characteristic of designed slag aggregate concrete are comparable to concretes with full replacement of natural aggregate by recycled materials and mechanical characteristics are sufficient for applications in building structures. Findings from preliminary study of experimental program in first part showed convenience of slag aggregate utilization for manufacturing of fibre concrete. This fact verified the assumptions, that intended orientation of experiments in second part is appropriate. Within the scope of following research, mechanical characteristics of slag aggregate and fibre concrete with slag aggregate will be further monitored with focus on optimization of individual components and typical properties of fibre concrete, e.g. ductility. ACKNOWLEDGEMENT The experimental work is supported by project GAČR 104/10/1128 Identification of material characteristics cementious fibre composites with full applications recycled aggregate, which is gratefully acknowledged. LITERATURE [1] TP 138: Užití struskového kameniva do PK [2] SHERWOOD, P. Alternative materials in road construction. 2nd edition. London: Thomas Telford Ltd, [3] ČSN : Návrh a provádění zemního tělesa pozemních komunikací , TP 93: Návrh a provádění staveb pozemních komunikací s využitím popílků a popelů. [4] downloaded 2nd January 2012 [5] downloaded 5th January 2012 [6] NEWILLE, A. M. Properties of concrete. New York: Wiley, [7] ČSN EN 206-1: Beton - Část 1: Specifikace, vlastnosti, výroba a shoda [8] YÜKSEL, I., TURHAN, B., ÖZKAN, O. Durability of concrete incorporating non-ground blast furnace slag and bottom ash as fine aggregate. In Building and Environment 42, 2007, pp

8 [9] MANSO, J.M., POLANCO, J.A., LOSAÑEZ, M., GONZÁLEZ, J.J. Durability of concrete made with EAF slag as aggregate. Cement and Concrete Composites 28, 2006, pp [10] PELLEGRINO, C., GADDO, V. Mechanical and durability characteristics of concrete containing EAF slag as aggregate. Cement and Concrete Composites 31, 2009, pp [11] WANG, G.: Determination of the expansion force of coarse steel slag aggregate. Construction and Building Materials 24, 2010, pp [12] CHUNLIN, L., KUNPEG, Z., DEPENG, CH. Possibility of Concrete Prepared with Steel Slag as Fine and Coarse Aggregates: A Preliminary Study. Procedia Engineering 24, 2011, pp: [13] downloaded 3nd January 2012 [14] downloaded 22th June 2011 [15] VYTLAČILOVÁ, V., ŠEPS, K. Vliv popílku v cementovláknových kompozitech s využitím recyklovaného kameniva. Praha: CEMC, WASTE FORUM 3, 09/2011, s , ISSN