A PREMIER CONSTRUCTION AGGREGATE

Transcription

1 S T E E L S L A G A PREMIER CONSTRUCTION AGGREGATE

2 STEEL SLAG TERMINOLOGY OPPORTUNITY Service EXPERTISE Service SUPPORT Service AN ENVIRONMENTALLY SAFE AND VALUABLE PRODUCT As early as 350 B.C., the Greek physician, Aristotle, referenced iron-making slags for healing wounds. In the centuries to follow, additional applications for slag would be discovered, such as mosaics and even cannonballs. However, it was not until the early twentieth century, when the modern processes for iron and steel production were developed, that the commercial use of iron making slags became acceptable on a larger scale. In contrast, Steel Slag s commercial introduction took significantly longer, as this product was thought to have little value beyond its use as an iron containing burden feed for the Basic Oxygen Furnace (BOF) steel making process and later as a sinter feed ingredient for the blast furnace iron making process. In recent years, Steel Slag has evolved into the premier construction aggregate for many specialized applications. The National Slag Association s continued promotional and research efforts, since its inception in 1918, have focused on identifying and developing innovative applications for Steel Slag s specific chemical and/or physical requirements. Steel Slag s unique physical and chemical composition often qualifies it as the most viable product for meeting the technical and fiscal requirements of a given market segment. Some of the largescale applications include Hot Mix Asphalt (HMA) aggregate, portland cement, road shoulders, unconfined road base applications, soil remineralization, and ph neutralization of abandoned mines and contaminated sites. The united effort of today s National Slag Association members, which consists not only of slag processors but also steel producers and associate members worldwide, represent continued emphasis on providing value-added quality products to the construction industry well into the new millennium. DEFINITION AND DESCRIPTION OF STEEL SLAG The American Society for Testing Materials (ASTM) defines Steel Slag as a non-metallic product, consisting essentially of calcium silicates and ferrites combined with fused oxides of iron, aluminum, manganese, calcium and magnesium, that is developed simultaneously with steel in basic oxygen, electric arc, or open hearth furnaces. THE PROCESS In the Steel Industry, two main types of slags are produced - Blast Furnace Slag and Steel Slag. Slag is a co-product of the iron and steel-making process. Iron cannot be made in a Blast Furnace without the production of its co-product, Blast Furnace Slag. Similarly, steel cannot be produced in a Basic Oxygen Furnace (B.O.F.) or in an Electric Arc Furnace (EAF) without making its co-product, Steel Slag. Due to their unique physical and chemical properties as well as end use applications, it is important to differentiate Steel Slag from Blast Furnace Slag. This brochure will deal mainly with the Steel Slags currently being produced from EAF and BOF furnaces. To find out more about Blast Furnace Slag, please contact The National Slag Association office to request the brochure entitiled Blast Furnace Slag. Integrated Steel Making (BOF slag) In Integrated Steel Mills, a blast furnace uses coke (carbon) to reduce iron to a high carbon molten iron, called hot metal. This hot metal is then sent to the steel-making shop s Basic Oxygen Furnace (BOF) where it is combined with steel scrap, various metallic elements, additional lime or dolomitic lime fluxes and is injected with oxygen to produce steel. In this process, the BOF uses oxygen to remove carbon and oxidizing reactions to provide heat. Blast of hot air F Slag Steel Slag contains the oxidation products that are fluxed from the iron bath, which remains bound in the hardened aggregate form. BOF slag is generated at a rate of lbs./ton (75-150kg./tonne) of steel produced. Electric Arc Furnace (EAF Slag) In an Electric Arc Furnace (EAF) steel-making operation, steel scrap is melted in an electric arc furnace along with fluxing agents to produce similar products as that of a Basic Oxygen Furnace: steel and Steel Slag. EAF steel is produced at about lbs./ ton (65-80 kg/tonne) of steel produced. In this process the Steel Slag chemistry is based upon the fluxing practices and the impurities from the selected scrap. Typical Steel Slag Chemistries % CONSTITUENT CaO FeO SiO2 MgO MnO AI2O3 P2O5 S Iron Coke Limestone 0 F 900 F 20 F 30 F Gas Blast Furnace Lime Scrap Molten Pig Iron Scrap Lime Flux Oxygen Electric Furnace Basic Oxygen Furnace % BY WEIGHT PHYSICAL PROPERTIES: The physical characteristics, weight, particle size, structural properties, etc.-vary according to the method used in processing the molten slag. Accordingly, end use of the processed materials varies, which helps to explain the unique diversity of slag products.

3 STEEL BITUMINOUSSLAG PAVEMENT BITUMINOUS PAVING Steel Slag has evolved as an ideal aggregate in Hot Mix Asphalt (HMA) surface mixture applications. Where friction is an important safety consideration in pavement design for the motoring public, properties of Steel Slag qualify it as a premier surface aggregate for skid resistant applications. With the development and implementation of Superpave technology throughout the United States as well as the further expansion of Stone Matrix Asphalt (SMA) mixes for severe traffic and axle-loading applications, Steel Slag has earned the distinction as a premium surface aggregate. In addition, Steel Slag continues to be recognized as a standard for use in both Seal Coating and Cold Patching applications. FRICTIONAL PROPERTIES OF STEEL SLAG The frictional properties of Steel Slag have demonstrated outstanding performance in making asphalt pavements skid resistant and maintaining that skid resistance over the life of the pavement. With safety in mind, many road agencies require Steel Slag when skid resistance is of prime concern. The physical properties and surface texture of Steel Slags provide a coefficient of friction in bituminous surface courses higher than most natural aggregates. Steel Slag s unique combination of particle structure and hardness produces a pavement wearing surface where long-term frictional properties are maintained, as aggregate polishing does not occur. CHIP AND SEAL Chip and Seal also known as "Chip Seal" or "Aggregate Seal Coating", is a single or double application of Bituminous Surface Treatment applied to existing pavement surfaces. The primary purpose for Chip and Seal is to achieve a skid resistance on rural pavements and to maximize driving safety for the general public. The use of Chip and Seal is a cost effective way to improve the safety and integrity of a road surface in low traffic environments. A seven-year cycle is recommended to insure road reliability and safety. Adhering to this cycle also helps reduce the need for other more expensive maintenance applications such as "cold patching". Construction begins with the removal of any loose debris from the existing road surface. An asphalt emulsion binder is then sprayed on the pavement at a rate of between gallons per square yard. Immediately after a Steel Slag chip or a combination of Steel Slag chip along with another aggregate is uniformly applied to the surface, a rubber-tired roller is driven over the surface to ensure that the aggregate adheres properly to the asphalt binder and pavement surface. Steel Slag contributes a high coefficient of friction to the roads surface by providing the roughness necessary to attain a skid resistant pavement. Physically, natural aggregates are unable to provide a surface that will resist polishing; therefore, they easily become slippery when wet. Additionally, with its hard, PROBLEM: angular, skid resistant shape and great asphalt binder affinity, Steel Slag is the most advantageous choice of aggregate for Chip and Seal applications. SUPERPAVE Over the past several years, the Hot Mix Asphalt industry has undergone dramatic changes as a result of state and federal agencies attempts at extending the service life of asphalt pavements. A performance based specification system was developed to obtain a closer correlation between Hot Mix Asphalt (HMA) design objectives and actual field service life. This new design criteria, called Superpave, incorporates mix design procedures involving the careful selection and proportioning of materials based upon traffic volume and loading conditions. Historically, the Hot Mix Asphalt industry has been able to meet most Department of Transportation (DOT) highway specification requirements by utilizing a limited number of locally available aggregates. Today, with Superpave s more extensive design criteria, many HMA producers have experienced unforeseen delays and incremental costs in their initial attempt to establish acceptable asphalt mixtures. Through the incorporation of coarse and some fine Steel Slag aggregates, establishing design criteria can be made easier due to steel slag s physical characteristics. SUPERPAVE AGGREGATE BLENDING PRINCIPLES While the effect of aggregate properties on the performance of asphalt mixtures has been well documented, Superpave is the first design method to specify consensus properties to meet specific traffic volume criteria. These consensus properties include coarse aggregate angularity, fine aggregate angularity, flat and elongated particles and clay content. Coarse / Fine Aggregate Angularity This property ensures a high degree of aggregate internal friction and rutting resistance. Course Aggregate Angularity Criteria Traffic, million ESALs <0.3 <1 <3 <10 <30 < Depth from Surface < 100 mm > 100 mm -/55/-/65/50/75/60/85/80 80/75 95/90 95/90 100/ / /100 Note: 85/80 denotes that 85% of the course aggregate has one or more fractured faces and 80% has two or more fractured faces. Fine Aggregate Angularity Criteria Traffic, million ESALs <0.3 <1 <3 <10 <30 < Depth from Surface < 100 mm > 100 mm Source properties are those that DOT s most often use to qualify local sources. They are: 1. Toughness 2. Soundness 3. Deleterious materials Once again, Steel Slag aggregate matches exceptionally well with these criteria. Another significant change with the Superpave Design Criteria involves gradation requirements. The existing 0. power gradation curve has been modified to include control limits and a restricted zone. The restricted zone was established to avoid mixtures having a high proportion of natural sand to total sand, and to avoid gradations that follow the maximum density line (which do not normally have adequate Voids in the Mineral Aggregate (VMA). Rutting results when shear stress exceeds the shear strength of the Cubical Aggregate aggregate mass along the shear plane. Shear Rounded Aggregate strength is primarily dependent upon the resistance of movement, or internal friction provided by the aggregate. The cubical nature of Steel Slag along with its rough texture provides more resistance than rounded, smooth-textured or flat and elongated aggregates. AGGREGATE SHAPES Steel Slag aggregates are a perfect fit for these criteria. With its cubical, rough texture, Steel Slag s physical characteristics are synergistic with the first three criteria. With both a high coarse and fine aggregate angularity, Steel Slag has a high degree of internal friction and therefore a high shear strength and resistance to rutting. Steel Slag s cubical shape ensures little breakdown in handling and construction. Because Steel Slag is a co-product of the steel manufacturing process, no clay exists thus insuring the adhesive bond between the asphalt binder and the Steel Slag aggregate. Asphalt pavements with low shear strength can lead to permanent deformation or rutting of the pavement by repeated wheel loading as seen here. Rutting from Weak Mixture original profile CUBICAL STEEL SLAG weak asphalt layer shear plane AGGREGATE PROPERTIES Regardless of the aggregate type, its processing method, or its mineralogy, aggregates in Hot Mix Asphalt must provide enough shear strength to resist repeated traffic load Before Load applications. When shear plane the aggregate mass is overloaded, a shear plane develops and aggregate particles After Load shift, or shear with respect to each other, resulting in a deformation or a Rut. ROUNDED UNCRUSHED GRAVEL Criteria are percent air voids in loosely compacted fine aggregate. FLAT AND ELONGATED LIMESTONE

4 BY BRUCE DINKHELLER, P.E. Engineer of Project Implementation Illinois Department of Transportation STEEL SLAG PORTLAND CEMENT STONE MATRIX ASPHALT (SMA) Stone Matrix Asphalt (SMA) is a European paving technology developed to prevent rutting from heavy traffic loading. This technology also focuses on providing a durable pavement that is less susceptible to low temperature cracking, while providing a friction coarse to reduce hydroplaning. BACKGROUND Portland Cement is primarily composed of hydraulic calcium silicates, along with some calcium aluminates, calcium aluminoferrites and usually containing one or more form of calcium sulfate (gypsum) as an interground addition. Materials used in the manufacture of portland cement must contain appropriate proportions of calcium oxide, silica, alumina and iron oxide components. gas volumes (air, combustion products, and CO2) that must traverse the kiln are significantly reduced, allowing higher production and lower fuel consumption per ton of clinker. CHEMICAL COMPATIBILITY All of the major components of Portland Cement clinker are present in Steel Slag. Clinker Steel Slag PAVEMENT DEFORMATION PRIOR TO REPLACING WITH STEEL SLAG SMA SMA incorporates a gap-graded, coarse aggregate, which accounts for seventy to eighty percent of the mixture, to form a structural skeleton or matrix in the compacted mix. The rough textured aggregate in this matrix, unlike those in conventional or Superpave mixes, are in close particleto-particle contact. This provides vital internal friction and high shear resistance. Asphalt cement in an SMA mixture, usually polymer modified, is typically between 5-8 percent. Less fine aggregate is used within the SMA mixtures to insure the particle-to-particle contact and increase the Voids to Mineral Aggregate (VMA) percentage. In addition, a fiber of either cellulose or Slag is used to prevent asphalt drain down. The combination of fine aggregate, asphalt and fibers form a mastic that fills the voids between aggregate particles. Air voids in the compacted asphalt mat range from 3-5 percent. The use of Steel Slag aggregate in SMA has proven to be extremely successful. Because of Steel Slag s durability, the particle-to-particle contact of the aggregate does not break down during the manufacturing, lay down or compaction process. Additionally, Steel Slag is a superior aggregate for achieving friction in the pavement riding surface. Due to the increased asphalt content, limited amounts of fine aggregate and high temperature requirements for the mix, placement of SMA mixes can be quite sensitive. However, Steel Slag s thermal characteristics do provide some beneficial contributions to preserving mix temperatures. STEEL SLAG SMA - BISHOP FORD EXPRESSWAY/ CHICAGO THE STEEL SLAG SMA 3/4 CHIP, 1/2 CHIP SMA Slag Bituminous Mixes in Illinois Appropriate use of Stone Matrix Asphalt (SMA) has been successful in Illinois in recent years. Superimposing IDOT's safety skid policies and accepted coarse aggregate physical properties makes Steel Slag coarse aggregate a logical choice for this use. Incumbent Illinois Department of Transportation (IDOT) policies require "high friction aggregates" to be used in bituminous surface courses when certain conditions are met. These aggregates are currently limited to sandstone, crushed gravel, Air Cooled Blast Furnace Slag, and Steel Slag. The public continues to expect more from the construction industry to provide more durable, longer lasting construction products. Success on these projects to date has been based upon the unique combination of Steel Slag (with current beneficiation requirements in place), Superpave liquid asphalt material requirements, and sensitivity to the motorists by paving only at night to minimize travel delays to the public. The Illinois Department of Transportation has successfully specified Steel Slag SMA bituminous mixes on several roadways in the past few years. Some of these roadways include the Bishop Ford Expressway paved by Callaghan Paving, I-55 in Will County paved by Gallagher Asphalt, US 41 in Lake County paved by Curran Contracting and Peter Baker & Sons. The latest in materials, technology and resourcefulness were incorporated into these projects to meet the needs of the motorists for years to come. IDOT intends to continue specifying Steel Slag SMA bituminous mixes for appropriate applications in the future. Finally, as SMA continues to gain wider acceptance for applications susceptible to rutting, Steel Slag will become recognized as the material of choice by SOLUTION specifying agencies. Bruce Dinkheller While iron and steel making slags have been used for decades by some cement companies as a cost effective chemical raw feed additive, in recent years the interest in utilizing these materials has grown dramatically due primarily to increased environmental regulation and market requirements for improved productivity. STEEL SLAG S CONTRIBUTION TO CEMENT MANUFACTURING IMPROVED CLINKER PRODUCTION AND REDUCED CO2 EMISSIONS Steel Slag can provide a significant contribution to improving production capacity, while also reducing CO2 emissions. This beneficial feature of Steel Slag exists because it has previously undergone calcination, eliminating CO2 and most volatile materials. Consequently, while a ton of limestone's yield contribution of cement clinker can be as low as 60%, Steel Slag's yield is 100%. Production increases with moderate addition (8-11%) of Steel Slag can be almost proportionate to the amount utilized. REDUCED ENERGY COSTS Substantial energy savings can be realized when Steel Slag is utilized. The low moisture absorption of Steel Slag (1-6%) can reduce the total raw material moisture contents of the kiln feed. The Steel Slag can also bypass the drying stage all together and be fed directly into the kiln. The fact that Steel Slag has already been calcined, means that the heat of decarbonation is eliminated. This allows a reduction in fuel consumed per ton of clinker produced. The Ca0 Si02 AI203 Fe203 67% 22% 5% 3% With proper proportioning, Steel Slag can reduce or replace all or parts of current raw mix design components such as: Clay Bauxite Mill Scale Sand Fly Ash Shale METHODS OF INTRODUCING STEEL SLAG TO A PORTLAND CEMENT KILN Inter-ground in existing raw mill with other raw mix components. Bypass raw mix drying and grinding and feed directly into the back end of the kiln as received, utilizing conventional material handling equipment. SUMMARY OF BENEFITS Improved production capabilities Reduced environmental emissions Chemical compatability with other materials Economic viability Efficiencies in pre-grinding and drying Substantial energy savings PORTLAND CEMENT MANUFACTURING PROCESS 35-60% 10-20% 1-7% 0-35%

5 TEEL SLAG BASE APPLICATIONS STEEL SLAG AGRICULTURAL APPLICATIONS INTRODUCTION Steel Slag has been used successfully for many years as a construction aggregate. Steel Slag aggregates are typically used within close proximity (50 miles) of the producing steel mill, therefore, restricting availability and application in many parts of North America. Where Steel Slag is available, its use in base applications can be considered, providing that both the material and the application have both been carefully evaluated. STEEL SLAG BASE SHOULDERS GENERAL BASE APPLICATIONS The chemistry of Steel Slag can vary between sources and it is important to understand the properties of the materials when considering its use in base applications. The chemical composition of some Steel Slags causes undesirable levels of expansion. This expansion will be extenuated if a dense graded aggregate is used. Depending upon this level of expansion and the material gradation, confined applications such as bases under pavements and structures may need to be avoided. One of the most common applications for Steel Slag is the construction of unpaved parking lots. This application is particularly suited to Steel Slag with higher expansion levels. Once placed and compacted in accordance with normal construction methods, the Steel Slag will tend to set-up producing a very hard, dense and durable parking lot to support heavy loads. In a similar application, Steel Slag has been used extensively as an unpaved road shoulder material. The cementitious properties of Steel Slag produce a hard, long lasting and durable road shoulder that is less susceptible to the eroding effects of run off water than a shoulder made from other aggregates. Steel Slags have also been used in the construction of berms and embankments. In this application, care needs to be taken in the selection of the slag material if these berms or embankments are capable of applying expansive pressures to buildings or structures, or if there is a possibility of future construction activities that may be affected. OPEN HEARTH STEEL SLAG Open Hearth Furnaces producing Open Hearth Steel Slag as a co-product of the steel making process were closed in the late 1970 s due to technological advances in the production of steel. However, Open Hearth Steel Slags are typically non-expansive and reserves are still being processed into aggregates and have been used successfully in base applications. STEEL SLAG BEING INCORPORATED IN AN AGRICULTURAL APPLICATION Calcium (Ca) Iron (Fe) Magnesium (Mg) Manganese (Mn) Boron (B) Sulfur (S) Zinc (Zn) Molybdenum (Mo) Copper (Cu) Calcium Carbonate Equivalent (CCE). REMINERALIZATION Steel Slag was first utilized for agricultural purposes in Europe before the turn of the twentieth century. Introduction in North America started in 1916, with material produced from United States Steel. Originally, Steel Slag served only as a substitute for agricultural lime (limestone) and super-phosphate. It has since become valued not only for its lime value but its fifteen other trace minerals, some of which were only recently recognized as valuable for agricultural purposes. These include iron, manganese, magnesium, zinc and molybdenum. In addition to being a recognized plant nutrient, molybdenum plays a major role in the metabolism of nitrogen-fixing organisms. As an example it has been found that as little as one-sixtieth ounce per acre of M0O3 (~.0025lbs.) increases yields of clover on molybdenum deficient soils. The molybdenum in Steel Slag readily supplies this requirement. Typical analyses of the important elements in Steel Slag for agricultural purposes are as follows: Element Percent Lbs. / Ton The traditional crops utilizing Steel Slag are corn and soybeans. Other crops such as sugar cane and rice have shown favorable results when incorporating Steel Slag. It has been shown that when Steel Slag is applied on organic or low mineral soils there is a reduction of leaf freckling and significant increases in crop yields in both sugar cane and rice. There continues to be increased usage and interest in the use of Steel Slags for agricultural purposes. Each year larger quantities are applied on North American farmlands with excellent results. As regulatory agencies look for new ways to recycle industrial by products, the use of finely ground Steel Slag as a co-product to the agricultural industry is an example of government working with industry for the betterment of our farmlands and the conservation of our natural resources. 90 STEEL SLAG BASE PARKING LOT

6 TEEL SLAG ENVIRONMENTAL IMPACT ENVIRONMENTAL COMMITMENT In the early 1900 s there were limited markets for Steel Slag; therefore, millions of tons were stockpiled. Through the marketing and research efforts of the National Slag Associations () member companies, Steel Slag has become recognized as a premier construction aggregate for many construction related applications, utilizing over seven million tons annually in North America. STEEL SLAG COALITION In an attempt to provide industry with a comprehensive environmental assessment of Steel Slag, the Steel Slag Coalition (SSC) was formed in This coalition, comprised of iron and steel manufactures and slag processors, hired an independent, nationally renowned, chemical laboratory and risk assessment team to conduct a human and ecological health risk assessment of Steel Slag. The risk assessment scientists analyzed samples from each participating company in accordance with EPA s risk assessment guidelines. The results of this study reinforced that Steel Slag conforms to EPA s stringent requirements and does not pose a threat to human or plant life. Consequently, it should continue to be recommended for a wide variety of construction applications (Further information can be obtained through the office). The National Slag Association and its member companies recognize their responsibility in protecting the environment and conserving the earth s natural resources. For this reason, they will continue to remain committed to researching and recommending responsible end uses for this environmentally safe, man-made resource. ph NEUTRALIZATION FOR ACID MINE DRAINAGE (A CASE STUDY) In an ever increasing environmentally conscious world, government agencies are looking for ways to further clean up our environment from past indiscretions. Steel Slag has become a solution for one of these problems. In the late 1950's in Northern Ontario, Canada, a mining company extracted a moderate amount of pyrite ore and then abandoned the mining site. The pyrite ore contained approximately 39% sulfur. The exposed walls contained massive sulfide zones, which by exposure produced Acid Mine Drainage (AMD). Rehabilitation measures were needed to minimize the infiltration and exiting of surface water into the pit and minimize contact with the sulfide zones in the mine walls. The solution to the problem was to design a new saturated fill to achieve a low oxygen diffusion coefficient that would minimize the flux of oxygen to the sulfide zones and inhibit the generation of Acid Mine Drainage (AMD) at the source. The new fill was a blend of steel slag fines (>1/2") and another steel mill co-product Basic Oxygen Furnace (BOF) sludge. After the mine was filled with the blended Steel Slag products, Ministry of Ontario leachate tests showed that the constituent levels in the leachate from the blended materials were well below quality criteria concentrations. Additionally, both materials were determined to have low sulfide sulfur content, as well as, a low maximum potential acidity (MPA) and had a high neutralizing potential (NP). The results of the static acid base accounting tests are as follows: NATIONAL SLAG ASSOCIATION Sulfide / Sulfur Maximum Acid Potential (MPA) Neutralizing Potential (NP) NP / MPA Ratio Steel Slag Fines BOF Sludge.03%.14% 1.9 (Tonnes Ca CO 3 Eq.) 8 (Tonnes Ca CO 3 Eq.) 8 (Tonnes Ca CO 3 Eq.) 470 (Tonnes Ca CO 3 Eq.) 255:1 59:1 The results of monitoring indicate that the objectives are being met. The saturated conditions of the backfill have been maintained. The ground water levels in the pit have risen significantly and the levels of gaseous oxygen in the fill are low. There has been a general improvement in the quality of the water measured in the monitoring wells surrounding the pit. The ph of the water in the wells near the pit has increased to near neutral values and the conductivity has generally decreased. As environmental problems from past practices confront us, practical solutions become critical to our environmental as well as our economic well being. Steel Slag was the solution in this case study. And it s an exciting prospect that Steel Slags have the potential for helping to eliminate environmental problems in the future.

7 NATIONAL SLAG ASSOCIATION Suite W. Lancaster Avenue Wayne, Pennsylvania Phone: 610/ Fax: 610/ useslag@aol.com Internet: