Increasing Slag Content Research Articles

Experimental study on static and dynamic mechanical properties of slag concrete

The slag concrete with 15%, 30% and 45% admixtures was prepared by the equal displacement cement method. The quasi-static mechanical properties of slag concrete were studied using a TYE-2000B pressure testing machine, and the dynamic mechanical properties of slag concrete under different strain rates were studied using a Φ100mm split Hopkin, and compared with ordinary concrete. Studies have shown that under quasi-static loading conditions, the compressive strength of slag concrete increases with the increase of slag content. Under dynamic load conditions, the strain rate sensitivity of slag concrete is significant. As the strain rate increases, the peak stress, strength enhancement factor and peak strain of slag concrete are significantly improved. In addition, the amount of slag is in the range of 0% to 45%. As the amount of slag increases, the dynamic compressive strength of the slag concrete increases.

Mechanical property and structural evolution of alkali-activated slag-phosphate mine tailings mortars

The present work studies consolidation of phosphate mine tailings through alkaline activation process with the addition of slag for adjusting the gel structure. As increasing slag contents in the raw materials, more (Na,K)2O–CaO–Al2O3–SiO2–H2O (C-A-S-H) and (Na,K)2O–Al2O3–SiO2–H2O (N-A-S-H) gels were formed in the mine tailings-based mortars. Compressive strength of the mortars increased as increasing the slag contents from 0 to 40%, and then it kept a plateau. Evolution in microstructure of these mortars were characterized through scanning electron microscopy (SEM), X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) measurements. The study provides fundamentals for the co-disposal of phosphate mine tailings with blast furnace slag through alkaline activation process.

Effect of K2O/Na2O on fusion behavior of coal ash with high silicon and aluminum level

Ash fusion temperatures (AFTs) are widely used for evaluation of fusibility of coal ash for combustion and gasification. K2O and Na2O is regarded as the effective component to enhance the ash fusibility for slag tapping. The combination of K2O and Na2O may enhance the flux efficiency. In this work, the effect of K2O/Na2O mass ratio on fusion behavior of coal ash with high silicon and alumina level was evaluated by the height variation of ash cone during heating. The results showed that AFTs and theoretical fusion range (Tliq-Tini) decreased quickly and then increased slowly as the K2O/Na2O mass ratio in the coal ash was reduced. The sub-liquidus phase changed from mullite into feldspar, which was responsible for change of AFTs. Meanwhile, most of K element occurred in leucite (KAlSi2O6) and the rest existed in nepheline (KAlSiO4), but Na almost existed in nepheline (NaAlSiO4). The competition effect between K2O and Na2O on AFTs was reflected by KAlSiO4/NaAlSiO4 in nepheline, so the SiO2-KAlSi2O6-NaAlSi2O6 ternary phase diagram was constructed, which well explained the variation of AFTs caused by K2O/Na2O mass ratio. Meanwhile, the fusion process was divided into two stages based on variation rate of ash cone height. At first stage, the amount of liquidus phase is limited and the viscosity is high, so only a low shrinkage rate of ash cone exhibits. However, at the second stage, high shrinking rate is caused by not only the rapid increase of slag content but also the sharp decrease of viscosity besides, the addition of K2O/Na2O change ash fusion process from “melting-dissolving” into “softening-melting”.

Development of a paste for passive fire protection mainly composed of granulated blast furnace slag

AbstractIn this study, the behavior of granulated blast furnace slag as a component of passive fire protection materials is evaluated. To investigate the performance of blast furnace slag, different replacement levels from 0 to 80 wt% have been analyzed. Different properties, such as physical, mechanical, and insulating capacity and leaching, have been thoroughly analyzed. Pastes made of a combination of granulated blast furnace slag and gypsum can be potentially used as a component in construction materials for passive protection against fire. The results indicate that the mechanical properties diminish when the slag content increases. It was concluded that replacements lower than 60 wt% comply with all the mechanical demands. A slight reduction of the insulating capacity was observed when the slag content was increased. Additionally, no heavy metal leaching problems have been detected.SignificanceThe current research presents the results of a study to reuse granulated blast furnace slag in fire‐resistant pastes with gypsum. Blast furnace slags decrease the thermal diffusivity of the paste at high temperatures, improving its insulating capacity. It facilitates its use in specific and high‐value applications with similar properties to commercial materials and increases the recycling rate with any heavy‐metal leaching problem.

Fly ash and zinc slag blended geopolymer: Immobilization of hazardous materials and development of paving blocks

The potential for practical application of fly ash, zinc slag and their blends for geopolymer synthesis at ambient temperature have been investigated in this paper. Fly ash is an alumino-silicate byproduct suitable for geopolymer reaction, but its low reactivity at ambient condition is the restriction of its bulk utilization. Above limitation can be overcome by blending with zinc slag (ZS). Additionally, ZS contains heavy and toxic metals (Pb, Zn, Cr, Cd, As), which can be stabilize in Al-Si based geopolymer network structure. Isothermal conduction calorimetry (ICC) is used to monitor the geopolymer reaction with time. Slag rich specimens are characterized with higher rate of reaction with augmented peak. The mineralogy and microstructure of the geopolymers have been examined through X-ray diffraction and scanning electron microscope. The detected chief reaction product is N-(C)-A-S-H and C-(N)-A-S-H11(where, N=Na2O, C=CaO, A=Al2O3, S=SiO2 and H=H2O) type hydrated gel. Continual improvement of compressive strength of the geopolymers with increasing slag content is explained with higher degree of reaction, formation of more reaction products and development of compact microstructure. According to toxicity characteristic leaching procedure (TCLP), toxic metals leaching is within permissible limit. Paver blocks using 40−80 wt% ZS has been developed, which meets IS 15,658: 2006 standard and comply with US-EPA specification.

Preparation and Reaction Mechanism Characterization of Alkali-activated Coal Gangue-Slag Materials.

In this paper, slag is used as a calcium source to make alkali-activated coal gangue–slag (AACGS) based material. The reaction mechanism of AACGS materials was discussed in depth by means of XRD, FT-IR, 29Si MAS-NMR (nuclear magnetic resonance) and SEM-EDS (energy dispersive spectrometer). The experimental results show that coal gangue can be used as a raw material for preparing alkali-activated materials. The liquid–solid ratio is the most influential factor on AACGS paste fluidity and strength, followed by slag content. As the modulus of sodium hydroxide increases, the depolymerization process of the reactant precursor is accelerated, but the high sodium hydroxide concentration inhibits the occurrence of the early coal gangue–slag polycondensation reaction, and exerts little effect on the 28 d compressive strength. Ca2+ in the slag promotes exchange with Na+, and the product is converted from N-A-S-H gel to C-(A)-S-H gel, and C-(A)-S-H is formed with higher Ca/Si ratio with the increase of slag content. The slight replacement of coal gangue by slag can greatly improve the reaction process and the strength of AACGS materials.

Physicochemical property and chromium leaching behavior in different environments of glass ceramics prepared from AOD stainless steel slag

Herein, we prepare Cr-containing glass ceramics from argon-oxygen-decarburization stainless steel slag and characterize their physicochemical properties (e.g., Cr stability), revealing the occurrence of a diopside solid solution → akermanite-gehlenite solid solution phase transition with increasing slag content. The properties of all ceramics (slag content = 40–80 wt%) met the requirements of the construction industry for building materials, with the highest flexural strength (137.83 MPa) as well as good acid and alkali resistance achieved at a slag content of 50 wt%. Moreover, the prepared ceramics were subjected to Cr leaching tests, which revealed that (i) Cr leached into aqueous solution was mainly present in the form of Cr3+ and largely precipitated as Cr(OH)3 and (ii) the layered structure of akermanite-gehlenite glass ceramics can partially bind Cr and thus facilitate its effective immobilization.

Expansion of CEM I and slag-blended cement mortars exposed to combined chloride-sulphate environments

This study investigates the effects of specimen curing duration, temperature, and slag composition on expansion of CEM I and composite slag-cement mortars exposed to a combined NaCl and Na2SO4 solution for up to 664 days. Test prisms prepared at 0.5 w/b ratio, were wet-cured for either 7 or 28 days prior to submersion in a combined salt solution at temperatures of 20 or 38 °C, to simulate temperate or warm tropical climates respectively. Equivalent reference specimens were stored in saturated limewater at 20 °C and tested in parallel. Mortar samples were used to investigate expansion and sorptivity, while corresponding paste specimens were prepared, cured and exposed under similar conditions for chemical and microstructural investigation. Such characterisation was performed on specimens immediately prior to exposure to salt solution and after the onset of expansion. The results show significant resistance to sulphate-induced expansion for specimens cured and exposed at 38 °C. For slag blends, the influence of exposure temperature was found to be more pronounced than curing duration. Differences in slag composition and curing duration also played key roles on the expansion resistance of mortar specimens. Expansion was attributed to the formation of ettringite crystals due to the reaction of aluminate phases of the binders with sulphate ions, although Friedel's salt and Kuzel's salt were also formed. The presence of chloride mitigated sulphate expansion of CEM I. For slag blends, it was shown that sulphate expansion was significantly reduced with increasing slag contents.

Fresh and hardened properties of one-part fly ash-based geopolymer binders cured at room temperature: Effect of slag and alkali activators

Geopolymers are considered to be a sustainable and environmentally friendly replacement for ordinary Portland cement as they lead to a reduction in carbon footprint. The dosage and type of precursors and alkali activators have been known to be important parameters affecting the fresh and hardened properties of geopolymers. This study investigates the effect of slag content as well as type and dosage of alkali activators on one-part fly ash-based geopolymers cured at room temperature. Different ratios of fly ash were replaced with slag as a CaO-rich precursor. Setting time and flowability tests were carried out to evaluate the fresh properties, compressive and flexural strength experiments were conducted to determine the mechanical properties of the geopolymers. The mineralogy and microstructure of the samples were evaluated by Optical microscope, X-ray Diffraction (XRD) and Scanning Electron Microscope (SEM-EDS) analysis. The experimental results revealed that the increase of slag content improved the strength and reduced workability. Moreover, some microcracks were observed when over 15% of fly ash was replaced with slag. In terms of activators, the sodium metasilicate anhydrous provided optimum strength and higher flowability compared to the others. Microstructural analysis results showed the presence of more unreacted particles when less than 8% Na2SiO3 content as alkaline activator and also less than 15% slag as replacement was used in the system.

Hydration mechanisms of composite binders containing copper slag at different temperatures

The hydration mechanisms of composite binders containing copper slag at different temperatures (20 °C and 50 °C) were investigated by hydration heat determination, TG/DTG, non-evaporable water content measurement and X-ray diffraction (XRD). The compressive strengths of mortars containing copper slag cured at different temperatures were also determined. In addition to plain cement, quartz powder with a similar particle size and the same replacement ratio as copper slag was selected as the control sample. The results show that the addition of quartz powder has a slight acceleration effect on the hydration of cement, while the addition of copper slag has a strong retarding effect on the hydration of cement. The second exothermic peak of the composite binder containing copper slag is delayed as the copper slag content increases, but this trend weakens at high temperatures. The hydration heat of the composite binder containing copper slag decreases with increasing copper slag addition. Moreover, the hydration heat of the composite binder containing copper slag is higher than that of the composite binder containing an equal mass of quartz powder within 72 h. Copper slag has pozzolanic activity and consumes Ca(OH)2 in hardened paste, although the pozzolanic activity of copper slag is low. However, the pozzolanic activity of copper slag is enhanced at high temperature. Furthermore, the reaction of copper slag does not produce new crystalline products compared to those produced by cement. Moreover, compared to hardened plain cement, the hardened composite binder containing copper slag has a higher non-evaporable water content gain rate. The mortar containing copper slag also has a higher compressive strength gain rate than the mortar containing equal mass quartz powder. Although the compressive strength of mortar containing copper slag is lower than that of plain cement mortar, it is higher than that of mortar containing quartz powder.

Effects and mechanisms of slag reinforced coal gangue geopolymers

This paper uses alkali activators with the modulus of 1.30 to prepare coal gangue geopolymers, thereby studying the reinforcement effects of slag content on coal gangue geopolymers. Besides, XRD, TG-DTG, and SEM are introduced to analyze changes in the microstructure and further explore the change mechanisms. The experimental results show that the compressive strength of coal gangue geopolymers increases with the increase in slag content. Compared to the P.O 42.5 pure cement paste, coal gangue geopolymers can obtain higher early strength. Besides, the 28d compressive strength of coal gangue geopolymers is greater than P.O 42.5 pure cement specimens when the slag content is 20%. The geopolymer products of slag-containing coal gangue geopolymers are C-(A)-S-H and N-A-S-H gels. The two kinds of gels, which are highly compatible, jointly constitute the network-like disordered structure of polymers. The XRD, TG-DTG and SEM results are consistent with the strength analysis results.

Effect of sodium carbonate/sodium silicate activator on the rheology, geopolymerization and strength of fly ash/slag geopolymer pastes

Reactions between the fly ash/slag composite mix and the Na2CO3/Na2SiO3 activator were monitored through Isothermal conduction calorimetry. The resulting products were analyzed with the help of XRF, XRD and FT-IR techniques. In calorimetric response, the composite pastes had more total heat release than the fly ash paste requiring ∼50% less activation energy to yield reaction products. These products were largely amorphous as observed in the XRD patterns. Rheological studies indicated that composite pastes were very stiff above 25 wt% slag addition as its yield stress was almost doubled to fly ash paste. The compressive strength of hardened pastes increased with increasing slag content and activator dosage and decreased with increasing water-binder ratio. The deposition of reaction products onto the fly ash/slag particle surfaces and also the dense microstructures as observed in FESEM supported higher strength of geopolymer pastes at higher activator and slag contents. The developed paste with standard sand at 1:2 ratio produced mortar with a compressive strength of ∼72 MPa.

Determining k-Value with Regard to Freeze-Thaw Resistance of Concretes Containing GGBS.

The European concrete standard EN 206 introduces the k-value concept as one of the three methods allowing the use of granulated blast furnace slag in the design of the freeze-thaw-resistant concrete mix. It is assumed that the freeze-thaw durability of the concrete, whose composition (w/c ratio) has been corrected by adopting a certain k-value, is the same as the freeze-thaw resistance of the reference concrete made with the cement containing no addition (CEM I). This article presents the results of freeze-thaw resistance analysis (modified with the ASTM C666A standard Class XF3) of 24 series of concretes made with a binder containing varied amounts of slag, with a w/b ratio ranging from 0.25 to 0.55. The aim of the study was to estimate the k-value as a parameter defined by the w/b ratio and the slag content in the binder. In this approach, the k-value is determined by trial and error in such a way that the deformation of the concrete specimens containing the slag corresponds to the deformation of the reference concrete. As shown by the analysis, the k-value decreases with increasing slag content in the binder.

Slag hydration and chloride binding in slag cements exposed to a combined chloride-sulphate solution

The effects of curing temperature (20 °C or 38 °C), slag composition and slag content on the hydration and chloride binding characteristics of ground granulated blast-furnace slag (ggbs) – blended cements have been studied. Two slags (CaO/SiO2 = 1.05 or 0.94) were each blended with CEM I 52.5R at 30% and 70% replacement. Paste samples of constant 0.5 w/b ratio were hydrated for 56 days, dried and exposed to either sodium chloride or combined sodium chloride – sodium sulphate solutions. Sodium sulphate concentration was 3 g/L, while chloride concentrations varied from 0.1 to 3.0 M. Post-exposure reaction products were characterised by XRD and thermal analysis. Chloride binding was followed via Friedel’s salt formation, with thermal analysis showing a decrease in Friedel’s salt formation in the presence of sulphate ions. Increasing slag content changed the nature of the chloride binding mechanism significantly. Hydration of slag studied by SEM-BSE image analysis showed that the higher basicity slag was more reactive, with the degree of slag hydration increasing with temperature. An increase in the slag load reduced the degree of slag hydration. Apart from the increase in slag load, the other changes in hydration corresponded well with the chloride binding characteristics of the blends.

The degradation mechanisms of alkali-activated fly ash/slag blend cements exposed to sulphuric acid

In the present work alkali-activated fly ash/slag cements (AACs) are synthesized and exposed to sulphuric acid (pH = 1.0) to investigate their anti-corrosion properties. The mineralogical compositions, pore structure and microstructure of different layers of the corroded samples are examined, along with the compressive strength change. The results show that with fly ash/slag ratio varying from 100/0 to 0/100, the compressive strengths of all of the samples decrease during acid attack; the most anti-corrosion mixture is found in the pure fly ash binder, which retains 83.5% strength after 28 days of exposure. Gypsum is only observed in the surface layer (0–5 mm) of samples. In terms of pore structure, the acid attack results in higher porosities in the corroded layers than their corresponding uncorroded layers. The samples with slag addition show a notably pore structure change. The sulphuric acid attack on the AACs binders has certainly led to the increase of porosity, regardless of the compact level of AACs (slag addition leads to compacter microstructure). The Al/Si atomic ratios in the corroded layer decrease after acid attack, and the reduction ratios become smaller as slag content increases, suggesting a dense matrix is advantage to impede the loss of aluminum from gel structures.

Effect of slag content and activator dosage on the resistance of fly ash geopolymer binders to sulfuric acid attack

Geopolymer (GP) binders are an appealing alternative to Portland cement (PC) binders as they have the potential to reduce the CO2 emissions associated with the cement and concrete industry. However, their durability in aggressive environments needs thorough examination if they are to become a viable alternative to traditional PC materials. This study investigated the effect of increasing slag content and activator dosage on the sulfuric acid resistance of fly ash GP binders. Their performance was also compared with that of neat PC mixes using various physical and microstructural techniques. The results show that increasing the slag content of fly ash GPs decreases porosity, but makes the reaction products more susceptible to sulfuric acid attack. It was also found that increasing the alkaline activator dosage of fly ash GPs has little impact on sulfuric acid resistance. Finally, GP binders displayed superior sulfuric acid resistance than their PC counterparts.

Workability and mechanical properties of alkali-activated fly ash-slag concrete cured at ambient temperature

Alkali-activated fly ash-slag (AAFS) concrete is a new blended alkali-activated concrete that has been increasingly studied over the past decades because of its environmental benefits and superior engineering properties. However, there is still a lack of comprehensive studies on the effect of different factors on the fresh and hardened properties of AAFS concrete. This paper aims to provide a thorough understanding of workability and mechanical properties of AAFS concrete cured at ambient temperature and to obtain the optimal mixtures for engineering application. A series of experiments were carried out to measure workability, setting time, compressive strength, splitting tensile strength, flexural strength and dynamic elastic modulus of AAFS concrete. The results showed that workability and setting time decreased with the increase of slag content and molarity of sodium hydroxide solution (SH). Compressive strength increased with the increase of slag content and molarity of SH as well as the decrease of alkaline activator to binder (AL/B) ratio, but it did not have significant relationship with sodium silicate to sodium hydroxide (SS/SH) ratio. In addition, equations provided by ACI code, Eurocode and previous researchers for ordinary Portland cement concrete overestimated the values of splitting tensile strength, flexural strength and dynamic elastic modulus of AAFS concrete. The optimal mixtures of AAFS concrete were set as slag content of 20–30%, AL/B ratio of 0.4, 10 M of SH, and SS/SH ratio of 1.5–2.5 considering the performance criteria of workability, setting time and compressive strength.

Influence of Granulated Silico-Manganese Slag on Compressive Strength and Microstructure of Ambient Cured Alkali-Activated Fly Ash Binder

This work focuses on gainful utilization of low reactive fly ash at ambient temperature into alkali-activated binder with the addition of another industrial waste silico-manganese (SiMn) slag. Granulated SiMn slag (GSS) percentage was gradually increased into fly ash-based reference batch. The influence of slag on reactivity of the blends was monitored by isothermal conduction calorimetry. Reactivity was improved with increasing slag content. The structural reorganizations of the resultant binder were detected by peak shifting in Fourier transform infrared spectroscopy study. The positional change of the hump in X-ray diffraction analysis was due to structural rearrangement of the binder. The calcium-rich hydrated product formation was increased with slag inclusion. The fly ash-derived geopolymer gel (N–A–S–H) was coexisted with slag activated gel (C–S–H/C–A–S–H), (where N = Na2O, A = Al2O3, C = CaO, S = SiO2, and H = H2O) in the blend matrix. EDX analysis confirmed the variation in Si/Al, Ca/Si, and Na/Al ratios of the binder with the alteration of reaction products. The development of better compressive strength in slag-rich binder attributed with the formation of Ca-rich gel phases.

Drying shrinkage and cracking resistance of concrete made with ternary cementitious components

The compressive strength, free and restrained drying shrinkage and cracking resistance of concrete under drying condition were investigated for ternary cementitious systems containing Portland cement, slag and fly ash. The restrained shrinkage test (ring test) was carried out following ASTM C1581. The results showed that the increased replacement level of slag or fly ash from 0 to 50% led to a gradual decrease in 28d compressive strength of concrete. The free drying shrinkage increased with the increase of slag content, but reduced with the fly ash content. The cracking resistance was well related to the free drying shrinkage of concrete, other factors such as strength also showed certain effects on cracking resistance of concrete. The cracking resistance of concrete was enhanced with the addition of fly ash while weakened with the slag replacement level up to 50%.

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.