properties of steel slag

Fistri, M., Strineka, A., Roskovic, R.: Lastnosti agregata iz jeklarske lindre in asfaltnega betona iz jeklarske lindre

Properties of steel slag aggregate and steel slag asphalt concrete

mr.sc. Mladen Fistri, dipl.ing. dr.sc. Andrea Strineka, dipl.ing. dr.sc. Ruica Roskovic, dipl.ing.

Institute IGH, Laboratory IGH, Zagreb, Croatia

Abstract

Ferrous slags (blast furnace slag, steel slag, ferro-alloy, etc.) are the industrial by-products from a greatest interest to the pavement construction industry, given their wide avail-ability and scope of uses. Above that, the production of aggregate from slag instead from rock would decrease the amount of raw material extraction and enable further environmental benefit since less industrial by-products would be disposed in landfills.

Until the regulations for construction products according to EU Directives didnt get in force in Croatia, there were no technical requirements or specifications for the evaluation of possible use of the slag aggregates in road construction. Therefore there is no much experience in Croatia in the application of the slag aggregate in bituminous mixtures and the practical application is rather in the research phase.

In this paper testing results of one type of steel slag aggregate produced in Croatia are presented, as well as results of the asphalt produced from 75 % of steel slag aggregate and 25 % of limestone rock aggregate. Analysis of results showed that the asphalt produced with the steel slag aggregate has good resistance to permanent deformation, high stability with good flow properties and high stiffness modulus.

Povzetek

elezne lindre (plavna lindra, jeklarska lindra, elezova zlitina itd.) so industrijski stranski proizvodi, ki so zelo zanimivi za gradnjo zgornjega ustroja, ker so zelo dostopni in imajo iroko podroje uporabe. Poleg tega bi proizvodnja agregata iz lindre namesto iz kamna zmanj-ala obseg pridobivanja surovin in omogoila dodatne okoljske koristi, ker bi se na odlagaliih zmanjala koliina industrijskih stranskih proizvodov.

Do uveljavitve predpisov o gradbenih proizvodih v skladu z direktivami EU na Hrvakem ni bilo tehninih zahtev ali specifikacij za oceno morebitne uporabe agregatov iz lindre pri gradnji cest. Zato na Hrvakem ni veliko izkuenj pri uporabi agregata iz lindre v bitumenskih zmeseh, praktina uporaba pa je e v fazi raziskav.

V tem prispevku so predstavljeni rezultati preskuanja vrste agregata iz jeklarske lindre, proizvedenega na Hrvakem, in rezultati asfalta, izdelanega iz 75 odstotkov agregata iz jeklarske lindre in 25 odstotkov agregata iz apnenca. Analiza rezultatov je pokazala, da ima asfalt, izde-lan iz agregata jeklarske lindre, dobro odpornost na stalne deformacije, visoko stabilnost z dobrimi prometnimi lastnostmi in modulom visoke togosti.

Fistri, M., Strineka, A., Roskovic, R.: Properties of steel slab aggregate and steel slag asphalt concrete

10. SLOVENSKI KONGRES O CESTAH IN PROMETU, Portoro, 20. 22. oktobra 2010

1 Introduction Ferrous slags are the industrial by-

products coming from metallurgical process of iron production (blast furnace slag) or steel production (steel slag) which is, because of its favourable physical and mechanical proper-ties, almost fully used in various branches of industry. If slag is used as raw material, it is no longer necessary to store it on industrial waste landfill sites, and lesser quantities of mineral raw materials need to be extracted.

Slags are mostly used in the manufacture of building materials, such as the road con-struction aggregate, concrete, railway ballast, cement, mineral wool, etc. It is interesting to note that even the old Romans used slag from furnaces in the construction of Roman roads in the Sussex District in England [1]. In the USA slag is used from the first half of the 19th century as road construction material, from the second half of the 19th century as railway ballast and in cement industry, and from the beginning of the 20th century as aggregate for bituminous mixtures [2].

Nowadays, according to the US Geologi-cal Survey data [3], 11.6 million tons of blast furnace slag was manufactured in the US in 2006. 35.7 % of this quantity was used in cement industry, and 34.3 % in road construc-tion. In the same year, out of the total of 8.7 million tons of steel slag produced, 8.2 % was used in cement industry, and as many as 63.1 % in the production of road construction materials.

As per data [4] provided by the European slag association (EUROSLAG), about 25 million tons of blast furnace slag was pro-duced in Europe in 2004. Out of this quantity 64.0 % was used in cement industry, and 32.6 % in the production of road construction materials. In the same year 15 million tons of steel slag was produced. Only 1 % of that quantity was used in cement industry, while 45 % was used in road construction (em-bankments, loose base courses, asphalt lay-

ers). The possibility of using water cooled

steel slag to obtain a sized aggregate, suitable for asphalt wearing course production, is studied in this paper. For that purpose, suit-ability of slag as aggregate was tested in laboratory and the asphalt mix type AC 11, with 75% of slag and 25% of stone aggregate, was designed. According to this mix design asphalt plant was adjusted and, finally, the asphalt was produced and placed as wearing course at a test section.

2 Test results 2.1 Test results of steel slag

aggregate To assess whether slag is suitable for use

as aggregate in asphalt mixes, the laboratory conducted slag testing in accordance with HRN EN 13043, Aggregates for bituminous mixtures and surface treatments for roads, airfields and other trafficked areas [5].

This standard defines requirements for aggregate, and hence for slag, with categories according to individual aggregate properties.

Test results for slag as aggregate, and relevant categories for individual properties, are presented in Tables 1 to 10. Tests shown in Tables 1 to 9 were conducted in the Stone & Aggregate Laboratory of Institute IGH, while the testing shown in Table 10 was made in the Stone & Aggregate Laboratory of Slovenian National Building and Civil Engi-neering Institute. 2.1.1 Geometrical properties of

steel slag aggregate Although requirements and categories

for aggregate grading and fines content are specified in HRN EN 13043, these properties (although tested) were not analyzed in this paper as they are dominantly dependent on the technological process of crushing, screen-ing, and dedusting.

Table 1. Particle shape of aggregates flakiness index, EN 933-3 [5] and shape index, EN 933-4 [6]

Overall flakiness index Category Shape index Category Aggregate size (mm) FI FI SI SI

4/8 4 FI10 1 SI15

8/16 2 FI10 3 SI15



Table 2. Determination of the flow coefficient of fine aggregates, EN 933-6 [7]

Aggregate size (mm)

Flow coefficient of aggregates Ecs (s)

Category Ecs

0/4 18 Ecs38

2.1.2 Physical properties of steel slag aggregate

Table 3. Determination of resistance to wear (micro Deval), EN 1097-1 [8]

Micro-Deval koeficijent

Mean value Category Aggregate size/

/test type Particle size

fractions DEM DEM DEM

7,8 8/16 mm/ /wet

10/11,2 mm: 30-40 %

11,2/14 mm: 70-30 % 7,3

8 10DEM

Table 4. Resistance to fragmentation by the Los Angeles test method, EN 1097-2 [9]

Los Angeles coefficient Category Aggregate size (mm) Particle size fractions

LA LA 10/11,2 mm: 30 %

8/16 11,2/14 mm:70 %

13 LA15

Table 5. Particle density and water absorption, EN 1097-6 (Pyknometer method) [10]

Particle density (Mg/m3)

Water absorption (%) Aggregate size (mm)

ssd rd a 24WA 0/4 3,49 3,41 3,69 2,2 4/8 3,65 3,59 3,82 1,7

8/16 3,73 3,68 3,88 1,5

Table 6. Determination of the polished stone value, EN 1097-8 [11]

Mean polished stone value PSV

Category PSV

70 PSV68

2.1.3 Thermal and weathering properties of steel slag aggregate

Table 7. Determination of resistance to freezing and thawing according to EN 1367-1 [12] and by mag-nesium sulfate test according to EN 1367-2 [13]

Magnesium sulphate crystallization method Freeze thaw test method Particle size

fraction Mean value Category Mass loss Category

(mm) MS MS (%) F 8/16 1 MS18 0,4 F1



Table 8. Determination of resistance to thermal shock, EN 1367-5 [14]

Change in resistance to fragmentation by Los Angeles test method Particle size

fraction (mm) Mass loss LA1 before heating

LA2 after thermal

shock

Loss in strength (VLA= LA2-LA1)

10-14 mm 0,4 % 12,8 14,1 1,3

Table 9. Determination of the affinity between aggregate (slag) and bitumen, EN 12697-11 [21]

Degree of bitumen coverage (%) Particle size fraction (mm)

after 6 h after 24 h 8/11 95 90

2.1.3 Chemical properties of steel slag aggregate

Table 10. Volume stability of steel slag aggregate, EN 1744-1, 19.3 [15]

Type of steel slag Expansion (% v/v) Category of volume stability

V Steel slag cooled by water 2,2 V3,5

2.2 Test results of asphalt with steel slag aggregates

Test of the asphalt mix samples was conducted and initial mix design was devel-oped in the Asphalt Laboratory of INSTI-TUTE IGH for the asphalt mix type AC 11 with steel slag. The following constituents were used in the asphalt mix production: water-cooled steel slag, crushed rock aggre-gate of carbonate composition and sedimen-tary origin from Tounj Quarry (0/4 mm

aggregate size), and "Japra" mineral filler of carbonate composition. The road-construction bitumen type 50/70 was used as binder. Proportions of individual mineral components in the designed asphalt type AB 11 (slag) are shown in Table 11. The designed proportion of bitumen was 5,3 [%(m/m)].

The asphalt plant was adjusted for pro-duction with these materials, and the asphalt mix was produced based on the mix design. This asphalt mix was placed at the test section in August 2009.

Table 11. Mineral material fractions in the design asphalt mix

Mineral material Fraction Quantity in mix [% (m/m)] JAPRA filler 3,1 TOUNJ 0 - 4 25,5

TROSKA 0 - 4 25,5 TROSKA 4 - 8 26,4 TROSKA 8 - 11 19,5

2.2.1 Testing of asphalt mix-tures

The asphalt mix samples taken at the as-phalt plant during production were submitted to the following laboratory testing:

soluble binder content (EN 12697-1) [16];

particle size distribution (EN 12697-2) [17];

maximum density (EN 12697-5) [18]; bulk density of bituminous specimens

(EN 12697-6) [19]; air voids content, voids in the mineral

aggregate, voids in the mineral aggreg-



gate filled with binder (EN 12697-8) [20];

water sensitivity (EN 12697-12 - Method A Indirect tensile strength) [22];

indirect tensile strength (EN 12697-23) [24];

stiffness (EN 12697-26 Annex C) [25];

stability and flow (EN 12697-34) [27]. Test results for asphalt mixtures are

shown in Tables 12 to 15.

!"#$

Figure 1. Particle size distribution of sampled mineral mixture

Table 12. Typical properties of steel slag asphalt mix

Soluble binder content [% (m/m)] 5,1 Bulk density of bituminous specimens [kg/m] 2723 Maximum density [kg/m] 2894 Void content [% (v/v)] 5,9 Voids in the mineral aggregate [% (v/v)] 19,5 Voids in the mineral aggreggate filled with binder [% (v/v)] 69,7

Test specimens for determination of wa-ter susceptibility of bituminous specimens were prepared using Marshall compactor (EN 12697-30) with 2 x 35 blows.

Half of total number of specimens were conditioned for 72 hours in temperature

chamber at 25 C, while the remaining specimens were stored in water for 72 hours at the temperature of 40 C. The tensile strength was determined at 25 C.

Table 13. Test results of water sensitivity

Indirect tensile strength of dry specimens

Indirect tensile strength of wet specimens Indirect tensile strength ratio

[MPa] [MPa] [%] 1,6 1,3 80,0

The indirect tensile strength testing was conducted at two testing temperatures: 25 C and 5 C. Test specimens for this testing were

prepared by 2 x 50 blows, using Marshall compactor.



Table 14. Test results of indirect tensile strenght and stiffness modulus

Indirect tensile strength at 5 C Indirect tensile strength at 25 C Stiffness modulus

[MPa] [MPa] [MPa] 4,0 1,8 7128

The stiffness modulus was determined by testing indirect tensile strength according to HRN EN 12697-26. For this testing, six specimens were prepared for each mix using Marshall compactor (2 x 50 blows). The testing was conducted at 20 C. The asphalt mix test results are presented in Tables 12 to 15.

The water susceptibility testing of bitu-men specimens was conducted according to EN 12697-12 by tensile strength measure-ment. Twelve specimens were prepared for

testing with 2 x 35 blows using Marshall compactor. Out of the total of twelve samples, six were stored for 72 hours in temperature chamber at 25 C, while the remaining six specimens were stored in water for 72 hours at the temperature of 40 C. The tensile strength was determined at 25 C.

The indirect tensile strength testing was conducted at two testing temperatures: 25 C and 5 C. Twelve specimens were prepared for this testing by 2 x 50 blows, using Mar-shall compactor.

Figure 2 Testing head for indirect tensile strength test

Figure 3 Apparatus for stiffness modulus test

Determination of the stability, flow and the Marshall Quotient of Marshall specimens, was performed according to EN 12697-34.

Table 15. Marshall test

Property Unit AB 11 (slag) Stability kN 15,2

Flow mm 2,5 Marshall quotient kN/mm 6,1



2.2.2 Testing properties of the placed asphalt layer

In the IGH Asphalt laboratory the fol-lowing tests of the placed asphalt layer were conducted:

resistance to permanent deformation by wheel - tracking test [23];

compaction degree; thickness [28].

To enable the above testing, 200 and 100 mm samples were extracted by drilling from the wearing course at the test section. Wheel tracking was performed on samples 200 mm in dia. using the Procedure B at ambient air and at the temperature of 60C. The test result

is the rutting depth after the test specimen was subjected to 20,000 passes of wheels.

Test conditions for wheel tracking: wheel load: 700 N; total distance of travel of tyre wheel

across the surface of test specimen: 230 mm;

frequency of loading: 26,5 cycles per minute;

test temperature: 60 C; number of load cycles: 10 000.

The compaction degree and thickness testing was performed on specimens 100 mm in diameter. Test results obtained in this testing are shown in Tables 16 and 17.

Table 16. Wheel tracking test results

PROPERTY AB 11 (SLAG) Mean wheel-tracking slope, WTSAIR mm/1000 cycles 0,09 Mean proportional rut depth, PRDAIR % 5,7 Mean rut depth, RDAIR mm 2,7

rut depth vs. number of passes

0

0,5

1

1,5

2

2,5

3

3,5

4

4,5

5

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000 12000 13000 14000 15000 16000 17000 18000 19000 20000

Number of passes

Rut d

epth

[m

m]

AB 11 (SLAG)

Figure 2 Wheel tracking test results

Table 17. Results obtained by testing compaction degree and thickness of the placed asphalt layer

PROPERTY AC 11 (SLAG) Bulk density (kg/m3) 2676 Compaction degree (%) 98,2 Layer thickness (mm) 45,4



3 Analysis of results 3.1 Results obtained by steel

slag aggregate testing After analysis of laboratory test results

for the pre-crushed water cooled steel slag, it was established that:

geometrical properties with respect to shape index and flatness index meet criteria for highest categories (FI10 ; SI 15),

resistance of slag to wear in wet state complies with requirements for the highest category (MDE10),

crushing resistance by Los Angeles method meet requirements for the highest category (LA15) and, after the heat shock, the decrease in strength is low, i.e. 1.3 (the value determined dur-ing the testing is 14.1 and is suitable for the highest category),

polishing stone value is also adequate for the highest category (PSV68),

density values are high, which was to be expected considering the origin of the aggregate,

on the tested fractions, the water ab-sorption was higher than 1 %,

mass losses during testing by the mag-nesium sulphate method and the freez-ing/thawing method are very small, and the results obtained meet the highest-category requirements for the durability of aggregates,

the volume of slag is stable and, ac-cording to the expansion value, the slag meets the highest volume stability re-quirements,

the adhesion of bitumen binder, tested by method A, is 95 % after 6 hours, and 90 % after 24 hours.

3.2 Results obtained by test-ing asphalt containing the steel slag aggregate

According to HRN EN 13108 - 1 (Bitu-minous mixes - Material specifications - Part 1: Asphalt concrete), the mix AC 11 with steel slag can be classified, based on some of the tested properties, into the following cate-gories as shown in Table 18:

Table 18. Categories for mix AC 11 with steel slag

Test property Category Total number of categories for selected property according to

EN 13108 - 1 Water sensitivity expressed by indirect tensile strength ratio ITSR80 2 of 5

Stiffness Smin7000 6 of 14

Maximum wheel tracking slope WTSAIR 0,10 4 of 12

Maximum proportional rut depth PRDAIR 5,0 5 of 8

4 Conclusion The results obtained by aggregate testing

shows that the aggregate produced from water-cooled steel slag meets criteria for the use in asphalt mixes. When compared with aggregates produced from igneous rocks of silicate composition that are used in asphalt mixes on motorways and roads belonging to highest traffic load categories, it can be concluded that most properties of the slag submitted to this testing are equally good. The resistance to polishing is even much better when compared to silicate rocks. Only the water absorption value is somewhat higher

when compared to silicate rocks that are used for aggregate production.

The test results of the asphalt mix and placed asphalt layer shows that asphalt pro-duced with steel slag aggregate has good resistance to permanent deformation, high stability with good flow properties and high stiffness modulus. Samples also show high stabilities, with good flow properties. The higher stability and stiffness modulus of steel slag asphalt mix can be used to design thinner asphalt layers. Because good resistance to polishing of steel slag particles, it can be expected that asphalt with steel slag will have very good skid resistance value (SRV), once



the bitumen film will be removed from its surface.

References

[1] Emery, J.: Steel Slag Utilization in Asphalt Mixes, National Slag Association, MF 186-1, www.nationalslagassoc.org

[2] Lewis, D.W.: Properties and Uses of Iron and Steel Slags. National Slag Association, MF 182-6, www.nationalslagassoc.org

[3] van Oss, H. G.: Slag Iron and Steel, U.S. Geological Survey 2007 Minerals Yearbook, minerals.usgs.gov

[4] The European Slag Association: Legal Status of Slags, EUROSLAG, Position paper, www.euroslag.org

[5] EN 13043 Aggregates for bituminous mixtures and surface treatments for roads, air-fields and other trafficked areas

[6] EN 933-4:2008 Tests for geometrical proper-ties of aggregates -- Part 4: Determination of particle shape -- Shape index

[7] EN 933-6:2006 Tests for geometrical proper-ties of aggregates -- Part 6: Assessment of sur-face characteristics -- Flow coefficient of ag-gregates

[8] EN 1097-1:2004 Tests for mechanical and physical properties of aggregates -- Part 1: De-termination of the resistance to wear (micro-Deval)

[9] EN 1097-2:2007 Tests for mechanical and physical properties of aggregates -- Part 2: Methods for the determination of resistance to fragmentation

[10] EN 1097-6:2007 Tests for mechanical and physical properties of aggregates -- Part 6: Determination of particle density and water absorption

[11] EN 1097-8:2009 Tests for mechanical and physical properties of aggregates -- Part 8: Determination of the polished stone value

[12] EN 1367-1:2008 Tests for thermal and weathering properties of aggregates -- Part 1: Determination of resistance to freezing and thawing

[13] EN 1367-2:2004 Tests for thermal and weathering properties of aggregates -- Part 2: Magnesium sulfate test

[14] EN 1367-5:2004 Tests for thermal and weathering properties of aggregates -- Part 5: Determination of resistance to thermal shock

[15] EN 1744-1:2004 Tests for chemical properties of aggregates -- Part 1: Chemical analysis

[16] EN 12697-1:2007 Bituminous mixtures -- Test methods for hot mix asphalt -- Part 1: Soluble binder content

[17] EN 12697-2:2008 Bituminous mixtures -- Test method for hot mix asphalt -- Part 2: De-termination of particle size distribution

[18] EN 12697-5:2009 Bituminous mixtures -- Test methods for hot mix asphalt -- Part 5: Determination of the maximum density

[19] EN 12697-6:2008 Bituminous mixtures -- Test methods for hot mix asphalt -- Part 6: Determination of bulk density of bituminous specimens

[20] EN 12697-8:2003 Bituminous mixtures -- Test methods for hot mix asphalt -- Part 8: Determination of void characteristics of bitu-minous specimens

[21] EN 12697-11:2008 Bituminous mixtures -- Test methods for hot mix asphalt -- Part 11: Determination of the affinity between aggre-gate and bitumen

[22] EN 12697-12:2008 Bituminous mixtures -- Test methods for hot mix asphalt -- Part 12: Determination of the water sensitivity of bitu-minous specimens

[23] EN 12697-22:2008 Bituminous mixtures -- Test methods for hot mix asphalt -- Part 22: Wheel tracking

[24] EN 12697-23:2004 Bituminous mixtures -- Test methods for hot mix asphalt -- Part 23: Determination of the indirect tensile strength of bituminous specimens

[25] EN 12697-26:2008 Bituminous mixtures -- Test methods for hot mix asphalt -- Part 26: Stiffness

[26] EN 12697-30:2008 Bituminous mixtures -- Test methods for hot mix asphalt -- Part 30: Specimen preparation by impact compactor

[27] EN 12697-34:2008 Bituminous mixtures -- Test methods for hot mix asphalt -- Part 34: Marshall test

[28] EN 12697-36:2003 Bituminous mixtures -- Test methods for hot mix asphalt -- Part 36: Determination of the thickness of a bituminous pavement

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