Increasing Slag Content Research Articles

Effect of ground granulated blast furnace slag (GGBFS) on RCCP durability

Having recorded a profile of success in mass concrete applications such as in dam building, roller compacted concrete has recently stimulated a growing interest in road pavement construction as a novel application. The present study was designed to investigate the effects of ground granulated blast furnace slag (GGBFS) used in concrete mixtures on durability properties of roller compacted concrete pavements as water absorption, permeability and freeze-thaw cycles. For this purpose, eight principal concrete mixes were designed containing four blast furnace slag levels (0, 20, 40, and 60% relative to the weight of the cementitious materials) and two cementitious material levels (12 and 15% relative to the aggregate weight) at an optimum moisture content. Results showed that the moisture content required for the concrete to reach its maximum compaction increased with increasing slag content. Moreover, cracking and porosity declined with increasing slag content up to a certain level beyond which both took a rising trend. This was evidenced by the minimum and maximum levels of concrete cracks and porosity for slag contents of 40% and 60%, respectively, compared to the levels observed in plain concrete lacking GGBFS. Concrete permeability was also observed to decline with the experimental concrete mix designs containing 20 and 40% GGBFS but increased for a GGBFS content of 60%. Finally, increasing cementitious materials from 12 to 15% was observed to reduce concrete permeability. The highest destructive effect due to 150 and 300 freeze-thaw cycles was observed with mix designs having a GGBFS content of 40%; however, mix designs containing a GGBFS of 60% exhibited relatively improved resistance against the effects of freeze-thaw cycles.

Chloride ingress and steel corrosion in geopolymer concrete based on long term tests

Alkali activated binders (geopolymer) is an emerging technology to produce concrete without the use of any Ordinary Portland Cement (OPC) by alkali activation of alumino-silicate source materials such as fly ash and/or slag. Limited knowledge on durability issues like corrosion behaviour of reinforced geopolymer concrete impedes the usage of this technology in structural applications.This study explored the chloride permeability and initiation of chloride induced corrosion of geopolymer concrete in accelerated chloride environment using longer test period. Corrosion initiation was also monitored in embedded rebar in 2% chloride contaminated concrete. Corrosion state of the rebar was monitored using non-destructive test method using Cu/CuSO4 reference electrode.The results showed that the apparent chloride diffusion coefficient of blended fly ash and slag geopolymer concrete is lower than that of OPC concrete. The diffusion coefficient also decreased with the increase of slag content in the binder. Blended fly ash and slag geopolymer concrete also exhibited higher aging factor than OPC concrete indicating improved resistance to chloride ingress with time. The study also showed that the embedded rebar in fly ash and slag based geopolymer concrete has higher protection against corrosion than a rebar in OPC concrete even when the concrete is contaminated with significant levels of chloride.

The effect of slag on the properties of magnesium potassium phosphate cement

Magnesium potassium phosphate cement (MKPC) incorporated with slag was prepared from the byproduct boron-containing magnesium oxide (B-MgO) from the production of Li2CO3 from salt lakes. The influence of the slag content on the setting time, compressive strength, water resistance and seawater corrosion resistance of MKPC was investigated. The composition and microstructure of MKPC were also studied in detail. The results demonstrate that the setting time of MKPC increases with increasing slag content. The compressive strength at 3h and 28d of MKPC specimens with 20wt% slag can reach approximately 35MPa and 60MPa, respectively. Moreover, slag significantly improves the water resistance and the seawater corrosion resistance of MKPC. The properties of MKPC incorporated with 20wt% slag indicated that it met the requirements for rapid repairing materials.

Effect of by-product steel slag on the engineering properties of clay soils

Clay soils, mainly if they contain swelling minerals such as smectite or illite, may cause severe damage to structures, especially when these soils are subjected to wetting and drying conditions. High expansion and reduction in shear strength and foundation bearing capacity will take place due to the increase in water content of these soils. The engineering properties of these kinds of soils can be improved by using additives and chemical stabilizers. In this work, by-product steel slag was used to improve the engineering properties of clay soils. Lab and field experimental programs were developed to investigate the effect of adding different percentages of steel slag on plasticity, swelling, compressibility, shear strength, compaction, and California bearing ratio (CBR) of the treated materials. The results of tests on the clay soil showed that as steel slag content increased, the soil dry density, plasticity, swelling potential, and cohesion intercept decreased and the angle of internal friction increased. For the CBR, the results of the tests showed an increase in the CBR value with the increase in slag content.

Evaluation of compressive strength development and carbonation depth of high volume slag-blended concrete

Compressive strength development and carbonation are critical topics for using high volume slag concrete rationally. The objective of this study is to present a numerical procedure that evaluates compressive strength and carbonation depth of high volume slag concrete. This numerical procedure consists of a blended hydration model and a carbonation reaction model. The amount of carbonatable materials, such as calcium hydroxide (CH) and calcium silicate hydrate (CSH), is calculated using the blended hydration model. Compressive strength development of cement-slag blends is evaluated from CSH content. By considering the effects of material properties and environmental conditions, the carbonation reaction model analyzes the diffusivity of carbon dioxide and the carbonation depth of concrete. The results of the analysis show that regarding compressive strength, the contribution of slag mixes prepared at a lower water to binder ratio was greater than the contribution of slag mixes prepared at a higher water to binder ratio. Regarding carbonation, with an increase in slag content or reducing the initial curing period, carbonation depth increases. The results of this study are useful for optimum mixing proportional design and carbonation durability design of concrete incorporating a high volume slag.

Improved fire resistance by using slag cements

Concrete is a composite material that mainly consists of mineral aggregates bound by the matrix of hardened cement paste. Composition and microstructure of hardened cement paste have important influences on the properties of concrete exposed to high temperatures. An extensive experimental study was carried out to analyse the post-heating characteristics of concretes subjected to temperatures up to 800 °C. Major parameters of our study were the slag content of cement (0, 16, 25, 41 or 66 m%) and the value of maximum annealing temperature. Our results indicated that (1) the number and size of surface cracks as well as compressive strength decreased by the increasing slag content of cements due to elevated temperature; (2) the most intensive surface cracking was observed by using Portland cement without addition of slag. The increasing slag content of cement increased the relative post-heating compressive strength. Tendencies of surface cracking and reduction of compressive strength were in agreement, i.e. the more surface cracks, the more strength reduction.

Influence of slag weight fraction on mechanical, thermal and tribological properties of polymer based friction materials

This paper aimed to study the influence of blast furnace slags on mechanical, thermal and tribological properties of friction materials elaborated by the dry heat-press molding method. Physical, mechanical and thermal properties were analyzed and tribological behavior was studied for varying the extent of doping (13–43wt.%). The results indicate that the hardness decreases from 63.6 HRL to 57.0 HRL with increasing slag content from 0 to 43wt.%. But density is opposite for the doped samples. The impact strength gradually increases from 3.59kJ/m2 to 3.70kJ/m2 when the content of slag increases from 0 to 43wt.%. Doping was also found to increase the friction coefficients but decrease wear rates, mass-loss and heat release. The sample S4 has a more superior and stable friction coefficient than others because of the transfer layers formed on the surface of friction materials.

Drying Shrinkage of Slag Blended Fly Ash Geopolymer Concrete Cured at Room Temperature

Recent studies have shown that blending of ground granulated blast furnace slag (GGBFS) with low-calcium fly ash can have significant effects on the setting and early strength development of geopolymers cured at room temperature. This paper presents the shrinkage behaviour of geopolymer concrete mixtures in which class F fly ash was replaced with 10% or 20% GGBFS and the sodium silicate to sodium hydroxide (SS/SH) ratio was either 1.5 or 2.5. Shrinkage of 4 geopolymer and 1 ordinary Portland cement (OPC) concrete mixtures cured at room temperature were studied. Comparisons are made between the shrinkage behaviours of geopolymer concretes with different mixture proportions and those of the OPC concrete. It was found that shrinkage decreased with the increase of slag content and decrease of SS/SH ratio in geopolymer concrete cured at room temperature. The shrinkage of geopolymer concrete up to the age of 180 days was found to be comparable to that of OPC concrete of similar compressive strength. Thus, shrinkage of geopolymer concrete could be reduced to values within the limit recommended in the Australian Standards for normal OPC concrete.

INVESTIGATION ON THE EFFECT OF SLAG AND LIMESTONE POWDER ADDITION IN ALKALI ACTIVATED METAKAOLIN

Alkali activated material has recently attracted gr eat attention as an environmentally friendly buildi ng material. Generally, it exhibits higher mechanical properties and better du rability when compared with Portland cement based m aterials. In this article, mixed alkali activated systems consisting of N-A-S- H and C-A-S-H hydrated gels were produced, using me takaolin as a dominated starting material and granulated blast furnace slag as an additional calcium and silicate source. Lime stone powder was then added into the blended metakaolin-slag system as a filler . The influences of slag and limestone powder on se tting times, strength development and microstructure were analyzed. The r esults indicate that, with the increasing slag cont ent, the setting time decreases; the compressive strength firstly increas es and then decreases after the slag replacement ex ceeds a critical value. Additionally, an optimum content for limestone powd er in the metakaolin-slag blends is around 15%. The FTIR spectra and XRD pattern present the changes in reaction products wh en slag was added, and the scanning electron micros cope results showed a denser matrix of the geopolymeric system when compa red to reference sample. However, no significant ch anges of reaction products were detected when limestone powder was in corporated, which indicates that the limestone powd er only works as a nonreactive phase in the alkali activated system.

Preparation of CaO-Al2O3-SiO2 system glass from molten blast furnace slag

To use the potential heat of molten blast furnace slag completely, a CaO-Al2O3-SiO2 system glass (MSG) was prepared from the molten industrial slag. The corresponding method proposed in this study utilized both slag and its potential heat, improving the production rate and avoiding the environmental pollution. Using appropriate techniques, an MSG with uniform color and superior performances was produced. Based on the experimental results and phase diagram, the chemical composition of MSG by mass is obtained as follows: CaO 27%–33%, SiO2 42%–51%, Al2O3 11%–14%, MgO 6%–8%, and Na2O+K2O 1%–4%. Thermodynamic processes of MSG preparation were analyzed, and the phases and microstructures of MSG were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that alkali metal oxides serve as the fluxes, calcium oxide serves as the stabilizer, and alumina reinforces the Si-O network. XRD and SEM analyses show that, the prepared MSG displays the glass-feature patterns, the melting process is more complete, and the melt viscosity is lowered with an increase in calcium oxide content; however, a continuous increase in slag content induces the crystallization of glass, leading to the formation of glass subphase. The optimum content of molten slag in MSG is 67.37wt%. With respect to bending strength and acid/alkali resistance, the performance of MSG is better than that of ordinary marble.

Transport and removal of bacteriophages MS2 and PhiX174 in steel slag-amended soils: column experiments and transport model analyses

The aim of this study was to investigate the removal of bacteriophages MS2 and PhiX174 in soils amended with converter furnace steel slag. Column experiments were performed to examine the bacteriophage removal in slag-amended (slag content: 0%, 25%, and 50%) loam soils. For comparison, column experiments were also conducted with Escherichia coli. In addition, chloride (Cl) was used as a conservative tracer to determine transport characteristics. Results showed mass recoveries of Cl of 98.6±3.5%, indicating that the experiments were conducted successfully. The mass recovery of MS2 was 86.7% in no slag (100% soil), decreasing to 0% in slag contents of 25% and 50%. The mass recovery of PhiX174 decreased from 87.8% to 51.5% with increasing slag content from 0% to 50%. In the case of E. coli, the mass recoveries decreased from 47.0% to 10.5% with increasing slag content from 0% to 50%. In the transport models analyses, the HYDRUS-1D code was used to quantify the sorption parameters from breakthrough curves. For the 100% soil column, a one-site kinetic sorption model was fitted to the data, whereas a two-site kinetic sorption model was fitted for slag-amended (25% and 50% slag) soil data. Results demonstrate that the addition of steel slag to soil enhances the removal of bacteriophages due to the presence of FeO in the steel slag. However, CaO could not contribute to the bacteriophage removal in our experimental conditions because the effluent pH (7.7–8.9) in slag-amended (25% and 50% slag) soils was not high enough to promote the bacteriophage inactivation.

Modeling the service life of slag concrete exposed to chlorides

This paper focuses on the service life of slag concrete, where the time to corrosion initiation for a given chloride threshold value of 0.3% by mass of cement and different surface chloride concentrations (Cs), (1%, 3%, and 5%) was calculated using the error function solution to Fick’s second law of diffusion as a service life model, where the chloride diffusion coefficients of different OPC/slag mixes were collected from literature.To gain improved understanding of the above-mentioned aspect, this research presents an experimental investigation to elucidate the impacts of local by-product water cooled slag (WCS) on the microstructure of OPC cement paste mixes using thermo-gravimetric analysis and de-sorption approaches.A partial replacement of OPC with 50% WCS in OPC paste mixes resulted in an increase in the amount of calcium silicate hydrate (CSH) by 57%, a decrease in the amount of calcium hydroxide (CH) by 66%, and a decrease in the amount of capillary pores by 57%, compared to those in the pure OPC matrix. In addition, the research results demonstrate that increasing Cs from 1% to 5% resulted in dramatically decreasing the service life of OPC/slag concrete, where the amount of decreasing reaches about 71%. Also, the service life of concrete increases with increasing slag content.

Use of Pb blast furnace slag as a partial substitute for fine aggregate in cement mortar

The technical properties of cement mortars containing natural fine aggregate that is replaced by lead blast furnace slag at 25 and 35% level were assessed at fixed water-to-cement (W/C) ratio and at fixed flow table value. The leachabilities of some toxic elements from the cement mortars were also assessed to test the environmental suitability of the slag for use in preparation of cement mortar. At fixed W/C ratio, the strength of the mortar decreased with increase of the slag content. On the other hand, at fixed consistency, strength increased with increasing slag content in the mortar composition. The concentrations of some toxic elements in the leachates collected from the mortars containing slag were slightly higher than for the control mortar, but the concentrations in the leachates remained within the regulatory limits for recycling in construction applications. For most elements, leaching from a mortar containing 35% of slag was similar to that from a mortar containing 25% of slag. Therefore, 35% of natural sand can be beneficially replaced with Pb slag to produce cement mortar without affecting the mechanical and leaching properties studied in this work.

Synthesis of inorganic polymers using fly ash and primary lead slag

The present work reports on the synthesis and properties of inorganic polymers (“geopolymers”) made of 100% fly ash from lignite's combustion, 100% primary lead slag and mixtures of the two. In the inorganic polymers with both fly ash and lead slag the main crystalline phases detected are wüstite, magnetite, sodium zinc silicate, quartz, anorthite, and gehlenite; litharge partially dissolves. FTIR analysis in these samples revealed that the main peaks and bands of end members also exist, along with a new amorphous reaction product. In terms of microstructure, both fly ash and lead slag dissolve and contribute in the binding phase whereas the larger particles act as aggregates. For an increasing lead slag in the composition, the binding phase is changing in chemistry and reaches PbO values higher than 50wt.% for the 100% lead slag inorganic polymer. Regarding the properties of fly ash and lead slag inorganic polymers, compressive strength is higher than 35MPa in all cases and water absorption diminishes as the lead slag content increases. A comparison of leaching results before and after polymerisation reveals that pH is an important factor as Pb is immobilised in the binding phase, unlike Zn and As.

Effect of Slag Content on Physical and Mechanical Properties of Lightweight Aggregate Concrete Small Hollow Blocks

This paper introduced a method of saving materials and energy through making small hollow blocks with the slag admixture in the lightweight aggregate concrete. Through orthogonal design, this paper took slag content, water binder ratio and admixture dosage into consideration and focused on influence of slag content on the physical and mechanical properties of lightweight aggregate concrete small hollow blocks. The results show that: when water binder ratio ，admixture dosage and curing system keep a fixed level, during the range of slag content 30%-40%, with the increase in slag content, the compressive and bending strength of small hollow block increased first and then decreased; water content and absorption and relative water moisture content decreased first and then increased; frost resistance increased then decreased; softening coefficient first increased and then decreased. When the slag content is 35%, the physical and mechanical properties of lightweight aggregate concrete small hollow block are the best, and all the indexes of physical and mechanical properties can meet the standard requirements non-bearing lightweight aggregate concrete hollow block. The curing system significantly affected the strength of the lightweight aggregate concrete small hollow block, and the block strength cured under the standard condition was higher than those under natural condition.

Effects of granulated blast furnace slag and superplasticizer type on the fresh properties and compressive strength of self-compacting concrete

Abstract This paper presents the results of an experimental investigation carried out to study the effect of granulated blast furnace slag and two types of superplasticizers on the properties of self-compacting concrete (SCC). In control SCC, cement was replaced with 10%, 15%, 20%, and 25% of blast furnace slag. Two types of superplasticizers: polycarboxylate based superplasticizer and naphthalene sulphonate based superplasticizers were used. Tests were conducted for slump flow, the modified slump test, V-Funnel, J-Ring, U-Box, and compressive strength. The results showed that polycarboxylate based superplasticizer concrete mixes give more workability and higher compressive strength, at all ages, than those with naphthalene sulphonate based superplasticizer. Inclusion of blast furnace slag by substitution to cement was found to be very beneficial to fresh self-compacting concrete. An improvement of workability was observed up to 20% of slag content with an optimum content of 15%. Workability retention of about 45 min with 15% and 20% of slag content was obtained using a polycarboxylate based superplasticizer; compressive strength decreased with the increase in slag content, as occurs for vibrated concrete, although at later ages the differences were small.

Effects of Mineral Admixtures on the Chloride Permeability of Hydraulic Concrete

The chloride permeability of concrete with slag or (20wt%, 30wt%, and 40wt% of binder) and binary slag and fly ash (the ratio of slag and fly ash 5:5, 4:6 and 6:4) was investigated in this study. The results show that the chloride permeability of concrete decreases firstly and increases latterly with the increasing of fly ash content. However, the permeability of concrete with slag decreases sharply with the slag content increases. Especially the content of slag is 40 wt%, the permeability is only 15.4% of the control concrete. The permeability of concrete using binary admixture of slag and fly ash is less than that of fly ash concrete and more than that of slag concrete.

Effect of copper slag as a fine aggregate on the properties of cement mortars and concrete

An experimental investigation was conducted to study the effect of using copper slag as a fine aggregate on the properties of cement mortars and concrete. Various mortar and concrete mixtures were prepared with different proportions of copper slag ranging from 0% (for the control mixture) to 100% as fine aggregates replacement. Cement mortar mixtures were evaluated for compressive strength, whereas concrete mixtures were evaluated for workability, density, compressive strength, tensile strength, flexural strength and durability. The results obtained for cement mortars revealed that all mixtures with different copper slag proportions yielded comparable or higher compressive strength than that of the control mixture. Also, there was more than 70% improvement in the compressive strength of mortars with 50% copper slag substitution in comparison with the control mixture. The results obtained for concrete indicated that there is a slight increase in density of nearly 5% as copper slag content increases, whereas the workability increased significantly as copper slag percentage increased compared with the control mixture. A substitution of up to 40–50% copper slag as a sand replacement yielded comparable strength to that of the control mixture. However, addition of more copper slag resulted in strength reduction due to the increase in the free water content in the mix. Also, the results demonstrated that surface water absorption decreased as copper slag content increases up to 50% replacement. Beyond that, the absorption rate increased rapidly and the percentage volume of the permeable voids was comparable to the control mixture. Therefore, it is recommended that up to 40–50% (by weight of sand) of copper slag can be used as a replacement for fine aggregates in order to obtain a concrete with good strength and durability requirements.

Composition and microstructure of 20-year-old ordinary Portland cement–ground granulated blast-furnace slag blends containing 0 to 100% slag

The morphology of outer-product (Op) C–S–H in 20-year-old slag–cement pastes appeared in most blends to be finer than at younger ages. The Ca/Si and Ca/(Si + Al) ratios of the Op C–S–H decreased with increasing slag content, and the Al/Si ratio increased. The Ca/Si ratio of C–S–H in the slag-containing pastes was lower at 20 years than at 14 months and the amount of Ca(OH) 2 was reduced indicating that additional slag must have reacted. The mean aluminosilicate chain length of the C–S–H was very long in all the samples and would be expected to have increased with age. The TEM-EDX and NMR data are consistent with nanostructural models for C–S–H. The Mg/Al ratio of the Mg–Al layered double hydroxide phase (LDH) was lower at 20 years than at 14 months in all cases except for the neat slag paste; aluminium hydroxide-based structure might be interstratified with those of the Mg–Al LDH.

Effect of slag on the rheology of fresh self-compacted concrete

The building industry is turning increasingly to the use of self-compacting concrete (SCC) in order to improve many aspects of building construction as SCC offers several advantages in technical, economic, and environmental terms. Fresh self-compacting concrete (SCC) flows into place and around obstructions under its own weight to fill the formwork completely and self-compact without any segregation and blocking. SCC mixes generally have a much higher content of fine fillers. The use of supplementary cementitious materials is well accepted because of the improvement in concrete properties and also for environmental and economical reasons. The present paper is an effort to quantify the influence of Algerian slag on the properties of fresh and hardened self-compacting concrete. The workability-related fresh properties of SCC were observed through slump flow time and diameter, V-Funnel flow time, J-Ring test, U-Box filling height and GTM sieve stability test. The only hardened property that was included in this study was the compressive strength. An optimum slag content of 15% seems to give a good SCC mixture with workability retention of about 60 min. A decrease in compressive strength with increase of slag content was obtained, but this decrease in compressive strength is less important at late ages (56 and 90 days after mixing).