Showing papers on "Ground granulated blast-furnace slag published in 2002"

Characterisation of chloride transport and reinforcement corrosion in concrete under cyclic wetting and drying by electrical resistivity

Abstract: Concrete prisms were made with four cement types including cements with fly ash and/or blast furnace slag and three waterto- cement (w/c) ratios. Chloride penetration and corrosion of rebars were stimulated by subjecting prisms to cyclic loading with salt solution and drying. Concrete resistivity, steel potentials and corrosion rates were measured up to one year of age. Chloride penetration profiles were determined after salt loading. It was found that the resistivity of a particular concrete reflects its properties with regard to chloride penetration, corrosion initiation (probability of corrosion) and corrosion propagation (corrosion rate). Blending the cement with blast furnace slag, fly ash or both is beneficial with regard to delaying the onset of corrosion and subsequently limiting its severity under simulated de-icing salt load. The fly ash cement shows increased resistivity compared to Portland cement from eight weeks. Cement with a high percentage of slag develops a significantly higher resistivity after one week

Durability of ternary blend concrete with silica fume and blast-furnace slag: laboratory and outdoor exposure site studies

Abstract: In September 1998, a site investigation assessing the durability performance of ternary blend concretes was initiated by an academic-government-industry consortium. Different concretes were cast in the field to assess durability performance in an outdoor exposure setting as well as with standard lab tests. Resistances to the following deterioration mechanisms were assessed: alkali-silica reactivity, chloride ion ingress, and deicer salt scaling. Compressive strength was also measured at various ages. This paper describes this project in detail and presents field observations and lab findings up to 2 years later.

A Comparative Evaluation of Various Additives Used in the Stabilization of Expansive Soils

Abstract: This paper investigates the effectiveness of using cement by-pass dust, copper slag, granulated blast furnace slag, and slag-cement in reducing the swelling potential and plasticity of expansive soils. The soil used in this study was brought from Al-Khod (a town located in Northern Oman) where structural damage was observed. The first stage of the experimental program dealt with the determination of the chemical, mineralogical, and geotechnical characteristics of the untreated soil. The soil was then mixed with the stabilizers at 3, 6, and 9% of the dry weight of the soil. The treated samples were subjected to liquid limit, plastic limit, swell percent, and swell pressure tests. Furthermore, the cation exchange capacity, exchangeable cations (Na+, Ca++, Mg++, and K+), and pH of the treated samples were also measured. The study showed that copper slag caused a significant increase in the swelling potential of the treated samples. Other stabilizers reduced the swelling potential and plasticity at varying degrees. The study further indicated that cation exchange capacity and the amount of sodium and calcium cations are good indicators of the effectiveness of chemical stabilizers used in soil stabilization.

Monitoring electrical resistance of concretes containing alternative cementitious materials to assess their resistance to chloride penetration

Abstract: Chloride ion penetration into concrete and the resulting deterioration (cracking and spalling due to the corrosion of reinforcement) is a major concern of engineers and owners of bridges and marine structures. Several publications have reported the excellent performance of concrete containing alternative cementitious materials (ACMs), such as pulverised fuel ash (PFA), ground granulated blast furnace slag (GGBS), microsilica (MS) and metakaolin (MK) in marine environment and highway structures. The resistance offered by these concretes has been related to the low mobility of chloride ions due to either the reduction in the number of interconnected pores as a result of the pozzolanic reaction of the ACMs or the chemical binding with the cement hydrates. However, the secondary reaction products are formed slowly in Portland cement concrete containing ACMs and as a result it is likely that the resistance offered to the penetration of chloride ions also increases slowly with time. In order to monitor the continuous behaviour of concretes containing these ACMs in a chloride exposure regime, an investigation was carried out, the results of which are reported in this paper. Ten different concrete mixes were subjected to a cyclic ponding regime with 0.55 M sodium chloride solution and the changes in concrete were monitored by measuring the changes in resistance between pairs of stainless steel electrodes embedded in the concrete at different depths from the exposed surface. The test was continued for nearly one year. The results indicated that, although the resistance of concrete decreased initially due to the penetration of chlorides, in the longer term the resistance of concretes containing ACMs outperformed the control concrete made with ordinary Portland cement (OPC). Drilled dust samples extracted after different durations of ponding were tested for the chloride content, which confirmed that the increase in resistance of the ACMs was due to the combined effects of the reduction in the penetration of chlorides and the continuous hydration activity of the ACMs.

The mineralogy and microstructure of three composite cements with high replacement levels

Abstract: The hydration products of three high replacement, composite cement pastes, i.e. Portland cement mixed with 75% and 90% ground, granulated blast furnace slag (BFS) and 75% pulverised fuel ash (PFA), are reported and compared with those from a 100% ordinary Portland cement (OPC) paste. The samples were cured in air under the same temperature and humidity conditions and tested at various times for up to six months. The hydration products were identified by means of X-ray diffraction (XRD) and their microstructure by scanning electron microscopy (SEM). Although the observed hydration products were mostly as expected, due to the high replacement levels, the degree to which these phases was present was unusual. In particular the calcium hydroxide initially formed in the BFS-cement systems was totally consumed within six months, indicating the important pozzolanic behaviour of BFS at such high replacement levels.

Low shrinkage, high strength cellular lightweight concrete

Abstract: An economical structural cellular lightweight concrete with a density of from about 45 lb/ft3 to about 90 lb/ft3 and a strength from about 1,000 psi to about 6,000 psi after 28 days of curing at room temperature and with minimal shrinkage on drying, is described. The concrete comprises cement, lightweight aggregate with a density from about 25 lb/ft3 to about 60 lb/ft3, fiber, superplastizer, gas and/or foaming agents, and a shrinkage reducing agent. The concrete can be manufactured using facilities for conventional concrete even with a portion of Portland cement replaced by industrial by-products or recycled materials such as blast furnace slag, coal fly ash and recycled glasses. The preferred procedure for making the lightweight concrete is also described. The products made with the lightweight concrete have much better ductility and construction capabilities than conventional concrete products.

Early age creep and stress relaxation of concrete containing blended cements

Abstract: The main objective is to investigate key properties that influence the stress development in concrete at early ages and the effect of using blended cements. Mineral additives and amount by weight of total binder used in the blended cements are fly ash (25%), ground granulated blast furnace slag (25%), and silica fume (10%). The properties investigated include tensile creep, elastic modulus, split tensile strength, and autogenous shrinkage. The relaxation modulus used for stress prediction was obtained from the creep data fitted using a log-power creep function. These findings show that tensile creep and stress relaxation are important properties of Portland cement concrete. These properties however are reduced in concretes containing blended cements. Blended cements affect the early age strength and elastic modulus moderately but significantly alter the autogenous deformation. Water/cement ratio (w/c), type and dosage of mineral additives were found to influence the magnitude of autogenous deformation. This deformation was found to be significant in low water-cement ratio concretes and should be included in early age stress calculations.

Use of Copper Slag and Cement By-Pass Dust as Cementitious Materials

Abstract: Copper slag (CS) and cement by-pass dust (CBPD) are by-products of the production of copper and cement, respectively. In the Sultanate of Oman, large quantities of copper slag (60,000 tons/year) and cement by-pass dust (25,000 tons/year) are produced every year, most of which is not effectively utilized and disposed on-site without any reuse. The main objective of this research is to investigate the potential use of copper slag and cement by-pass dust in concrete as partial replacements for Portland cement. The physical and chemical properties of both slag and cement by-pass dust were determined. Mortar samples were prepared using different proportions of slag, cement by-pass dust and lime, which was used as an activating material. Proportions up to 15% of Portland cement replacement were used. In addition, a control mixture containing 100% Portland cement was prepared for comparison. Results obtained indicated that the increase in the proportions of copper slag and cement by-pass dust alone resulted in a decrease in the compressive strength of mortars compared with the control mix. The highest compressive strength was achieved in samples containing 5% CBPD + 95% cement, which was 41.7 MPa after 90 days. The optimum copper slag and cement by-pass dust to be used is 5%. In addition, it was determined that using cement bypass dust as an activating material will work better than using lime. Additional studies should investigate the strength and durability when copper slag and cement by-pass dust are used in concrete mixes.

Influence of magnesia on sintering characteristics of iron ore

Abstract: The MgO in blast furnace slag provides an optimum condition in terms of both good flowability and desulphurisation. The mode of its addition to the blast furnace changed from, initially, as raw flux in the form of dolomite, to via sinter, with the argument that raw flux demands energy for its decomposition inside the blast furnace. Thus, the decomposition reaction was diverted from the blast furnace to the sintering bed, and the energy source for decomposition was changed from costly blast furnace coke to a relatively cheap coke breeze. Now olivine/dunite/serpentine is being used as a source of MgO, where energy for decomposition is not required; this also provides a source of SiO2, which eliminates need for the addition of quartzite. The effect of MgO on blast furnace slag is fairly well established, but its effect on sintering and sinter quality is unclear. Operating results of the sinter plants show that, with an increase of MgO, the sintering rate, the fuel rate, and sinter strength and reduci...

Slag—iron and steel

Abstract: In the making of crude or pig iron in a blast furnace, iron oxide ores are stripped of oxygen and other impurities by means of high-temperature reactions with carbon reducing agents and fluxes. Most of the impurities and fluxing agents combine to form a liquid silicate melt called iron or blast furnace slag, which floats above the liquid crude iron and which is tapped (removed) from the blast furnace separately from the iron. The crude iron is then transferred to a steel furnace, where the iron’s residual carbon content of about 4% is reduced, generally to below 0.5%, and other impurities are removed; this process involves lime and silicate fluxes and the formation of steel slag. Steel furnaces, particularly electric arc furnaces (EAF), also may be fed with scrap iron and steel, but again the impurities are removed by fluxing agents that form a slag. Apart from the original furnace feedstock impurities, slags (especially steel slags) also may contain significant amounts of entrained free metal. The physical attributes of slags when solidified—glassy, metallic, or stony; hard and compact or vesicular—depend mainly on how the material was cooled. The cooling method also largely determines how a particular slag may be used. Slags have been used for construction purposes, especially for road surfaces, since Roman times, but with the advent of the industrial revolution, iron and steel production rose dramatically, and the volume of slag produced soon far outpaced consumption of slag. The result was a growth of unattractive slag piles on industrial land. By the mid-19th century, new uses for slags had been found, particularly as an aggregate in hydraulic cement concrete and, for some slags, as a cementitious material in its own right. Consumption remained modest, however, until the 20th century, when slag was found to be an excellent aggregate for asphaltic concrete (asphalt) road paving. This and other new uses, together with a rapidly increased use of hydraulic cement concrete worldwide, led to the consumption of most existing slag piles and current slag consumption roughly keeps pace with new slag production. Ferrous slags are now properly recognized as useful coproducts of the iron and steel industry, not waste products. Notwithstanding their utility, most slags have very low unit values compared to pig iron and steel products. Iron and steel companies, accordingly, consider the slag they produce to be a nuisance and contract with outside slag processing companies to get rid of it; the slag processing company may also be responsible for cooling the slag. Although the financial arrangements vary, typically the processing company receives the cooled slag for free, crushes it to various marketable sizes, uses screens and magnetic separators to recover entrained metal from the slag (this metal to be returned to the furnace for a low charge), sells the slag on the open market, and pays a small percentage of the net slag sales revenues or profits to the iron or steel company. Blast furnace slags are of three main types. The first, aircooled blast furnace slag, is formed by allowing the molten slag to cool relatively slowly under ambient conditions; final cooling

Carbonation aspects of alkali activated slag mortars and concretes

Abstract: The studies on the alkali activated slag cementitious materials have been carried out at the University of Mining and Metallurgy for over 28 years. In this work the results concerning the corrosion resistance in carbonate atmosphere are presented. Particularly those containing the effect of CO 2 on the depth of carbonation and compressive strength changes. In first part of investigations carbonation of slag mortars activated by sodium carbonate and water glass was measured. In second part, samples of 27 years old alkali- activated slag concrete cut from real industrial construction were analysed. The samples were subjected to the compressive strength test, the estimation of the depth of carbonation, the analysis of uncombined sodium ions in the hardened alkali activated slag cementitious material and to the investigations of microstructure and phase composition by means of XRD, mercury porosimetry and Environmental Scanning Electron Microscopy.

Durability of plain and blended cements in marine environments

Abstract: This study was conducted to investigate the durability of two plain cements (Type I and Type V) and three blended cements prepared with fly ash (FA), silica fume (SF) and blast furnace slag (BFS), in marine environments. Cement paste, mortar and reinforced concrete specimens were exposed to sea water for a period of 2 years. In addition to inspecting the specimens visually, the performance of both plain and blended cements was evaluated by measuring the strength development, reduction in compressive strength, expansion, weight change, reinforcement corrosion and conducting chemical and mineralogical analyses. The visual inspection and compressive strength results indicated that the sulphate attack was somewhat hindered in plain and blended cements despite the high sulphate concentration in the marine environments. The data on reinforcement corrosion confirmed the superior performance of silica fume cement in sea water, followed by blast furnace slag and fly ash cements. The corrosion resistance of Type I ...

Optimization of ternary cementitious mortar blends using factorial experimental plans

Abstract: Producing cements incorporating high-volume replacement of ordinary portland cement (OPC) by recycled industrial by-products is perceived as the most promising venture for the cement and concrete industry to meet its environmental obligations. However, the two-component (binary) cements thus produced are often associated with shortcomings such as the need for extended moist-curing, increased use of chemical admixtures, low early age strength, increased cracking tendency due to drying shrinkage, and de-icing salt scaling problems. There is need for research to investigate whether high-volume replacement multi-component (ternary and quaternary) cements could be optimized with synergistic effects allowing component ingredients to compensate for any mutual shortcomings. This study uses factorial experimental plans to investigate the performance of OPC-silica fume (SF)-class F fly ash (FA) and OPC-SF-ground granulated blast furnace slag (GBFS) ternary cementitious blends. Response surfaces for the superplasticizer requirement to achieve a constant flow, setting time, drying shrinkage up to 112 days, compressive strength at 1, 7, 28 and 56 days, and for the sulfate expansion up to 9-months were obtained for up to 20%, 60%, and 60% replacement levels of OPC by SF, FA and GBFS, respectively. A multiparametric optimization is used to establish response surfaces for a desirability function, which is used to rate ternary cementitious blends. Results indicate that when rheological, mechanical, durability and cost requirements are combined; the use of costly mineral admixtures such as silica fume is not economic in ternary OPC-SF-FA or OPC-SF-GBFS blends beyond levels of about 3 to 5% Moreover, it is shown that the major hurdle for high-volume replacement of OPC with class F fly ash is compromising the early age performance. Results also indicate that a good quality high-fineness GBFS can be used at replacement levels of OPC up to 60% without major disadvantages.

A Fundamental Study on the Steel Slag Aggregate for Concrete

Abstract: Compared with the blast furnace slag, steel slag has the expansibility due to the reaction with water and free CaO. Therefore it is specified in Standard Specification for Concrete in Korea that steel slag aggregate must not be used in concrete. So it is unusual to use steel slag aggregate in concrete. In this study steel slag aggregate processed by several aging process was comparatively satisfied with fundamental properties as concrete aggregate, which are specific gravity, absorption, unit weight, percentage of solids and abrasion value etc. Chemical analysis is also observed to understand the effect of aging process in steel slag aggregate. When the strength is measured, it is found that the concrete replacing crushed stone with unstable steel slag aggregate had a little problem.

Early-Age Creep and Shrinkage of Blended Cement Concrete

Abstract: This paper reports a study on the early-age creep and shrinkage of concrete with and without silica fume (SF), ground granulated blast-furnace slag (GGBS), and combinations. Test parameters were water-binder ratio, aggregate content, partial replacement of cement by SF, GGBS, or both, as well as test conditions. The stress-strength ratios at loading were fixed at 30% of the 3-day compressive strength and 20% of the 3-day tensile strength for compressive and tensile creep, respectively. The test environment was controlled at a temperature of 30 deg C and a relative humidity of 65. The compressive and tensile creep together with drying and autogenous shrinkage were determined over 4 months of loading. Results obtained for plain, double-blended, and triple-blended concrete were assessed and compared to provide guidelines on the use of SF and GGBS in concrete structures subjected to early-age creep and shrinkage.

New applications for iron and steelmaking slag

Abstract: Iron and steelmaking slag is a by-product of the iron and steelmaking process. Slag has traditionally been used as a component of cement and construction aggregate. NKK has led the industry in promoting the effective use of slag. In this paper, fine concrete aggregate, known as Sandy-S, and slag sand-capping material are introduced as new applications of granulated blast furnace slag. Other innovative uses of steelmaking slag are introduced: large carbonated slag blocks, called Marine Blocks, produced by injecting carbon dioxide into slag compact, and potassium silicate fertilizer produced by adding a potassium source to steelmaking slag.