THE POSSIBILITY OF USING BLAST FURNACE SLAG AS CONCRETE AGGREGATE

Problem deponovanja otpadnog industrijskog materijala jedan je od najvećih u većini razvijenijih zemalja svijeta. Problem deponovanja posebno je naglašen ako se uzme u obzir da većina industrijski otpadnih čvrstih materijala zagađuje tlo i/ili vodu, a nerijetko i vazduh. Običan beton obično sadrži oko 12% cementa i 80% masenog agregata. To znači da na globalnom nivou, za proizvodnju betona, potrošimo godišnje od 10 do 11 milijardi tona agregata. Rukovanje, prerada i transport za tako velike količine agregata troše znatne količine energije i negativno utiču na ekologiju [1]. S druge strane, redovni izvori agregata su u velikoj mjeri iscrpljeni dok se u međuvremenu proizvedeni otpad iz industrije značajno širi [2] Imajući u vidu gore rečeno, upotreba industrijskog otpadnog materijala u građevinske svrhe je posebno značajna. Otpad (npr. zgura, leteći pepeo, blokovi keramike i mermera) igra važnu ulogu u održivom razvoju građevinske industrije [3]. U svijetu se povećava potražnja i interesovanje za agregate iz netradicionalnih izvora kao što su industrijski nusprodukti i reciklirani otpad pri gradnji i rušenju [1]. Mnogi istraživači pokušavaju da prouče GBFS (granulirana zgura visoke peći) u proteklim godinama kako bi procijenili njene osobine i njeno ponašanje [4]. Naravno, neophodno je obezbijediti ekonomski isplativu i ekološki prihvatljivu gradnju. Gvožđe se ne može pripremiti u visokoj peći bez proizvodnje njegovog suvog proizvoda, tj. zgure visoke peći. Korištenje ovog agregata u betonu zamjenom prirodnih agregata predstavlja obećavajući koncept jer


INTRODUCTION
The problem of waste disposal is one of the greatest in most developed countries in the world.It is especially pronounced considering the fact that most industrial solid waste materials contaminate soil and/or water, often the air as well.Common concrete usually contains about 12 % of cement and 80% of mass aggregate.It means that globally 10-11 billion tons of aggregates are used annually for concrete manufacturing.Operating, processing and transportation of huge quantities of aggregate consume considerable amounts of energy and have negative effect on environment [1].On the other hand, traditional sources of aggregate are largely exhausted, while the amount of produced industrial waste significantly increases [2].
Bearing in mind the above statements, the use of industrial waste for construction purposes is especially significant.Waste (e.g.slag, fly ash, ceramic and marble blocks) plays a significant role in sustainable development of construction industry [3].The demand for interest in non-traditional aggregates such as industrial by-products and recycled waste from building and demolition increasingly spreads worldwide [1].Many researchers studied GBFS (granulated blast furnace slag) in the previous years in order to assess its properties and behaviour [4].Normally, it is necessary to provide economically profitable and ecologically acceptable construction.
This paper discusses the possibility of using industrial waste produced in base iron manufacturing in Zenica, Bosnia and Herzegovina.
Metallurgical slag is a by-product obtained in the process of base iron and steel manufacturing.In its appearance, mode of cooling and mineralogy, slag is similar to magma, from which silicate eruptive rocks originate such as basalt, diabase, andesite, dacite, syenite etc. which are appreciated materials in construction.
The slag, deposited nearby Iron Works in Zenica occupies a large area; it is supposed that 9,226,000 m 3 or about 19 million tons of material were deposited in landfill Rača in the period 1956-1992, including slag with natural and sudden cooling with the content of metal substance, fireproof materials, ash, slag, casting sand and other waste materials obtained in technological processes in the metallurgical complex.Thus in Iron Works Arceromittal Zenica, 185,000 tons of waste slag were processed in 2011, while in coming years the annual increase of 239,800 tons is assumed.
This paper considers the possibility of using blast furnace slag as concrete aggregate.The presented results of investigation are in accordance with European standards EN 12620:2002+A1:2008, and some characteristics of slag are compared to natural aggregates.

THE PROCESS OF OBTAINING SLAG
As it was previously said, metallurgical slag is a byproduct obtained by manufacturing base iron.In the process of base iron manufacturing, the raw materials (iron ore, coke, and limestone) are continually inserted through the blast-furnace top, while base iron and slag are removed from the bottom.By sudden cooling, liquid slag that floats in melted iron granulates into clinkershaped grains.From the blast furnace, liquid slag directly enters granulation chamber, under sprayed water where slag granulation is carried out.Granulated slag and water are removed to slag pool.From the pool, granulated slag is transported to customers.Slika 1. Proces proizvodnje zgure visoke peći [7] Figure 1.Manufacturing process of blast furnace slag [7] Postoje dva oblika zgure: bazična i kisela.Bazična zgura sadrži najmanje 50% bazičnih oksida CaO i Al2O3 a ostatak je najvećim dijelom SiO2.Kisela zgura sadrži znatno manje od 50% bazičnih oksida CaO i Al2O3 a prevladava SiO2.Zgura visoke peći bogata vapnom (bazična zgura), upotrebljava se u proizvodnji cementa.

THE USE OF SLAG WORLDWIDE
The use of slag for different purposes began long time ago.Today, slag is used as additive (filler) in cement in all countries worldwide.
On the other hand, high density of blast furnace slag makes it suitable material for hydro-technical structures.Namely, in Germany and the Netherlands about 400,000 tons of blast furnace slag is used as a material for covering slopes.Besides, slag is perfect for regulation of eroded watercourses.
Due to the fact that the characteristics of slag depend on its origins, the possibility of using domestic slag as concrete aggregate should be confirmed by numerous tests [8].
One of the recent domains of application of slag is its use as concrete aggregate.According to the available data, the use of slag as concrete aggregate is completely justified.Certain countries such as Japan advanced in this field so much that they have standards related to application of slag as concrete aggregate.In European countries which apply European standards, the assessment of slag characteristics is made according to the standards for aggregate EN 12620:2002+A1:2008 -Concrete Aggregates or EN 13450:2003 -Aggregate for railway ballast or EN 13242:2002 Aggregates for unbound and hydraulically bound materials for application in civil engineering, road construction, etc.The concrete manufactured with slag as aggregate would be considerably heavier in comparison with the concrete made of natural aggregates, thus the possibility for wide application of such concrete is promising.
Slag is often used in road construction as a material for stabilisation of soil.Besides surface layers, granulated blast furnace slag is used as a binder at stabilisation of deeper layers, in cases of poor loading capacity of soil where construction is planned.According to statistical data, the slag in unbound mixtures for lower road layers is the most frequent one, or as aggregate in asphalt mixtures.
Besides using slag in civil engineering, it is also often used as soil fertilizer today.This refers to blast furnace slag with great percentage of calcium and magnesium oxides used as a replacement for lime.Besides these examples, slag can be used in other sectors such as purification of water, production of cement clinker or return to blast furnace for re-manufacturing of base iron.
kind of slag is used, which is cooled suddenly by pouring water.Its granulation is 0-4 mm, and the desired granulation can be obtained by grinding.Figures 1 and 2 show the slag obtained by sudden cooling in air, which is grinded into fractions that can be used for concrete manufacturing and the slag separation plant.
Slag processing in technological sense includes:  Two-stage grinding  Three-sage magnet separation  Multi-stage filtering  Separate depositing of certain fractionsaggregates  Classifying separate metal components and transport to steel-works, blast furnace and agglomeration.
The testing of slag pH was not carried out, although this datum would be very interesting for doubt about corrosive effect of slag on reinforcement.Volume stability of slag due to the change of humidity was examined by using manual (non-standard) method, and the results showed that slag volume did not change.

PREPARATION OF CONCRETE SAMPLES WITH SLAG AGGREGATE
In addition to testing physical-mechanical and chemical properties of slag, the authors of the paper decided to prepare concrete samples with slag aggregate in order to compare the strength of slag aggregate concrete with the strength of dolomite aggregate concrete.Figure 5 shows cumulative curve of sieving slag aggregate.
Five test samples were done for each recipe.Two samples were tested after 7 days, while the remaining 3 after 28 days.Further increase of concrete strength was not tested later.
The used amount of 330 km/m 3 of cement was sufficient for preparation of concrete with strength that corresponded to class C25/30 concrete, when all four fractions of dolomite aggregate were used.The cement from Lukavac (CEM II/B-M (V-W) 42.N) was used for preparation of concrete samples.Chemical composition of the obtained cement is shown in Table 9.

Rezultati ispitivanja
It should be mentioned that during preparation of recipe, significant slump, up to 20 mm, occurred when all four slag fractions were used, thus workability of concrete in steel samples was hard to achieve.On the other hand, the use of dolomite aggregate reduced slump and workability improved.Figure 6 shows the procedure of concrete sample preparation.As it can be seen in Figure 6, the cubes 15x15x15cm were prepared.Na osnovu rezultata dobijenih prilikom ispitivanja uzoraka betona spravljenih sa zgurom iz željezare Zenica, a imajući u vidu kratak period ispitivanja i ograničena sredstva, ustanovljeno je sljedeće:  Fizičko-mehaničke karakteristike zgure zadovoljavaju uslove definisane u evropskim normama za ovu vrstu materijala, naročito kada je u pitanju krupna frakcija zgure.Važno je napomenuti da materijal nije štetan za okolinu ili ljudsko zdravlje.

CONCLUSIONS
Based on the results obtained by testing slag concrete samples obtained from Iron Works Zenica, and bearing in mind a short period of investigation and limited finances, the following was found:  Physical-chemical properties of slag fulfil the conditions defined by European standards for this kind of material, especially related to larger slag fractions.It is important to notify that the material is harmless for human health and environment.
 Radioactivity of slag, change of volume, percentage of chlorides or sulphates is within permissive boundaries.
 The prepared concrete samples have values of strength under pressure that correspond to the concrete category C25/30.It should be noted that this concrete has considerably larger mass in comparison with concrete manufactured with dolomite aggregate.Therefore slag aggregate concrete is mostly used for hydro-technical structures, structure foundations, sustaining walls and other places where larger volume of concrete mass is desirable.
 Since slag is a material with strong abrasive resistance, the use of this material as concrete aggregate for traffic surfaces is desirable.
 Blast furnace slag can be used for concrete that is resistant to high temperatures.
 Workability of concrete manufactured from slag aggregate is hard to achieve, and the slump increases.These problems can be solved easily by adding additives for concrete in order to increase its workability, and hence reduce its slump.
 As it can be seen from sieving curves of this slag aggregate, the small fractions (fillers) are missing.This lack of 0-0.25 fractions can cause a series of negative consequences in concrete.The consequences may be poor workability, higher water absorption etc.
with concrete manufactured with dolomite aggregate.Application of other recipes is possible, but additional investigation is necessary.The use of this by-product contributes to the environmental protection process and reduced use of aggregates from natural sources.

Table 3 -
-Contents of small particles; Los Angeles coefficient; Table4-Index of grain shape;

Table 5 -
Aggregate density and water absorption;

Table 6 -
Contents of chlorides and sulphates;

Table 7 -
Testing of radiation)

Table 6 .
Contents of chlorides and sulphates

Table 8 .
): 1. Recipe I with four fractions of slag aggregate (although they do not fit into boundary curves EMPA and Fuller) 2. Recipe II with three fractions of slag aggregate and one fraction of dolomite aggregate Composition of concrete mixes

Table 10 -
Test results for concrete cube samples 15x15x15cm -Recipe I, Table 11 -Test results for concrete cube samples 15x15x15cm -Recipe II)