Blast Furnace Slag Content Research Articles

The Compressive Strength and Microstructure of Alkali-Activated Binary Cements Developed by Combining Ceramic Sanitaryware with Fly Ash or Blast Furnace Slag

The properties of a binder developed by the alkali-activation of a single waste material can improve when it is blended with different industrial by-products. This research aimed to investigate the influence of blast furnace slag (BFS) and fly ash (FA) (0–50 wt %) on the microstructure and compressive strength of alkali-activated ceramic sanitaryware (CSW). 4 wt % Ca(OH)2 was added to the CSW/FA blended samples and, given the high calcium content of BFS, the influence of BFS was analyzed with and without adding Ca(OH)2. Mortars were used to assess the compressive strength of the blended cements, and their microstructure was investigated in pastes by X-ray diffraction, thermogravimetry, and field emission scanning electron microscopy. All the samples were cured at 20 °C for 28 and 90 days and at 65 °C for 7 days. The results show that the partial replacement of CSW with BFS or FA allowed CSW to be activated at 20 °C. The CSW/BFS systems exhibited better mechanical properties than the CSW/FA blended mortars, so that maximum strength values of 54.3 MPa and 29.4 MPa were obtained in the samples prepared with 50 wt % BFS and FA, respectively, cured at 20 °C for 90 days.

Effect of MgO/Al2O3 ratio on the structure and properties of blast furnace slags: A molecular dynamics simulation

SiO2-Al2O3-CaO-MgO is the most significant slag system in the blast furnace ironmaking process and it is very important to investigate the microstructure and viscosity of the system. In this paper, molecular dynamics simulations were carried out to explore the effects of MgO/Al2O3 ratio on structure and properties of the system. Based on the self-diffusion coefficients, the viscosities were calculated by Einstein-Stokes equation and compared with the experimental value and the Factsage value. The results showed that with the increase of MgO/Al2O3 ratio, the stability of [SiO4]4− and [AlO4]5− tetrahedron became weaken and the relative proportions of bridge and non-bridge oxygen showed a decrease. And due to the increase of MgO, more Mg2+ ions are used as network modifiers to reduce the degree of polymerization of the system, resulting in a decrease in the viscosity, which is consistent with experimental results. Finally, based on the present study, in the case of increasing Al2O3 content of blast furnace slag, the fluidity of slag could be adjusted by controlling MgO/Al2O3 ratio, thereby providing a basis for stable operation of blast furnace ironmaking.

Changes in Heavy Metal Content of Blast Furnace Slag Cement According to Blast Furnace Slag Content

Changes in Heavy Metal Content of Blast Furnace Slag Cement According to Blast Furnace Slag Content

Mechanical and Hydraulic Behaviors of Eco-Friendly Pervious Concrete Incorporating Fly Ash and Blast Furnace Slag

Eco-friendly pervious concretes containing fly ash (FA) and blast furnace slag (BFS) were prepared in this study. The compressive strength and hydraulic behaviors were investigated to explore the effect of replacement content of FA and BFS. Rheological tests of cementitious pastes were first conducted and the results showed that FA could increase the apparent viscosity and BFS did not change the rheology performance. Compared to traditional concretes, FA and BFS both decreased the compressive strength of pervious concrete at 28 d, while pervious concrete incorporated with FA and/or BFS presented comparable strength at 60 d. Compared to the control concrete mix, at the same replacement rate, FA changed the compressive strength more obviously than BFS. FA and BFS both decreased the effective porosity and permeability coefficient of pervious concrete. However, when the replacement rate (30%) was the same, concretes with ternary blends presented obviously larger porosity than binary blends. The relationships between porosity and permeability, and strength were also established.

Original behavior of pore water radiolysis in cement-based materials containing sulfide: Coupling between experiments and simulations

Blended cements with high content of blast furnace slag (CEM III/C) can be used for nuclear waste conditioning because of their low hydration heat as compared to ordinary Portland cements (CEM I). They however contain some sulfide, an impurity whose role needs to be investigated. Indeed, they can have an effect on the radiolytic H2 production under irradiation. To study the impact of sulfide species on H2 production, gamma irradiation, at a dose rate of 356 Gy h−1, was performed during 6 months in a closed system without O2 on a cement paste made with CEM III/C. At short time, the radiolytic H2 production rate is higher than that measured using CEM I. On the basis of reaction data collected in the literature on sulfur species, radiolysis simulations performed for both systems confirm this behavior. Moreover, they suggest that the sulfide concentration, initially imposed in pore solution by the slag is of the order of 180 mM, and is responsible for this H2 production. For the first two irradiation months, the following phenomena are then evidenced in CEM III/C: 1) conversion of sulfide into polysulfide anions; 2) pH increase; 3) production of H2 due to the H•+ H2S reaction having a very high rate constant. Nevertheless, in the medium term, the residual sulfide concentration is not sufficient any more for this mechanism to occur. It imposes a reducing environment, leading to a very efficient recombination of H2 in pore solution. The resulting equilibrium state is reinforced by the high liquid saturation level in the cement paste porosity. Therefore, even if the presence of sulfide species in blended cements momentarily increases the H2 production rate, it strongly reduces it at long times.

Effect of curing time on granulated blast-furnace slag cement mortars carbonation

Currently, ground granulated blast-furnace slag cements use in cement-based materials is being increasing because perform well in marine and other aggressive environments. However, mortars and concretes made of this type of cement exhibit high carbonation rates, particularly in badly cured cement-based materials and when high blast-furnace slag contents are used. Concrete reinforcement remains passive but can be corroded if the pore solution pH drops as a result of the carbonation process promoting the reinforced concrete structure failure during its service life. Results show the very sensitive response to wet-curing time of slag mortars with regard to the natural carbonation resistance. Then, a minimum period of 3–7 days of wet curing is required in order to guarantee the usual projected service life in reinforced concrete structures. In this work, estimation models of carbonation depth and carbon dioxide diffusion coefficient in ground granulated blast-furnace slag mortars as a function of the curing period and the amount of ground granulated blast-furnace slag are proposed. This information will be useful to material and civil engineers in designing cement-based materials and planning the required curing time depending on their ground granulated blast-furnace slag content.

Effect of chemical and thermal activation on the microstructural and mechanical properties of more sustainable UHPC

This paper investigates the influence of the content of blast furnace slag (BFS) on the microstructural and mechanical properties of non-activated and activated ultra-high performance concrete (UHPC). Three volume-substitution rates of cement with BFS were explored (30% for UHPC2, 50% for UHPC3 and 80% for UHPC4) and two activation methods, chemical and thermal, were tested. Results show that with 30% of BFS, heterogeneous nucleation prevailed over dilution, accelerating the hydration reaction of cement and increasing the amount of C-S-H formed. C-S-H decreased the porosity of UHPC2 by 18% and 20% respectively at 3 and 90 days. The compressive strengths of UHPC1 (without BFS) and UHPC2 were very similar. For high BFS contents, the dilution effect prevailed and there was less portlandite, which decreased the amount of hydrated products, particularly at early age. As a result, the porosity of UHPC3 and UHPC4 was more than twofold higher than that of UHPC1.To boost the hydration reaction of blended UHPC with a high BFS content, KOH was added. The use of [KOH]3 significantly increased the amount of hydrated products, reducing the porosity of UHPC4 1.6-fold at 3 days and increasing its compressive strength by 42% at the same age. However, this activation mode was not enough to ensure the required compressive strength of UHPC1. Thermal activation at 90 °C for 2 days was therefore tested. Results showed the acceleration of the reaction of solid components, which increased the consumption of portlandite and hence the development of hydrated products. This resulted in improving the packing density of blended UHPC, decreasing its porosity and enhancing its compressive strength. In comparison with reference concrete at 90 days, the compressive strength of UHPC3-T increased by 7% and that of UHPC4 was 12.5% lower.

One-part geopolymer cement from slag and pretreated paper sludge

Abstract The aim of this study was the valorization of paper sludge waste from paper industry in designing one-part geopolymer cement using ground granulated blast furnace slag as main precursor. The effects of increasing the amount of paper sludge pretreated with a constant amount of sodium hydroxide (2% of slag) on mechanical strength, heat evolution, setting time and durability were analyzed. The reaction products were characterized using X-ray diffraction and thermogravimetric analysis. The findings showed that paper sludge can successfully be used as a secondary source of calcium carbonate in the one-part (“just add water”) geopolymer. The compressive strength of the cured geopolymer increased with increasing the amount of paper sludge, and the non-reacted sludge acted as a filler. The maximum strength (42 MPa, 28 d) was reached at 18 wt-% paper sludge addition. The main reaction products were calcium aluminate silicate hydrate and hydrotalcite-like cementitious gels. From the perspective of its blast-furnace slag content, strength properties, water absorption and setting time, the one-part geopolymer cement could be classified as a CEM IIIC and Type 32.5N class cement under the European standard EN-197.

Thermodynamic modelling of short and long term hydration of ternary binders. Influence of Portland cement composition and blast furnace slag content

Ternary blends are currently used to improve the properties of Portland cement (PC). In this paper, thermodynamic modelling has been used to analyze the influence of the PC composition on the hydrates formed, in binary and ternary blends with blast furnace slag (BFS), and limestone filler (LF) or fly ash (FA) in order to complement experimental results. Thermodynamic modelling shows that contents of 40–50% of BFS can be optimal in ternary blends with low LF or FA content, and modelling also shows the significant effect of the composition of the PC used in the hydration process of the blends.

Estimation of the content of ground granulated blast furnace slag and different pozzolanas in hardened concrete

Methods for estimating the content of ground granulated blast furnace slag (GGBFS), fly ash and other pozzolanas in hardened concrete were investigated including a selective dissolution procedure, a method based on scanning electron microscopy (SEM) combined with image analysis and a XRF method. The results reveal that the content of GGBFS in concrete can be estimated with all methods. The accuracy of the selective dissolution method can be increased by consideration of the dissolution behaviour of the respective aggregate. SEM investigations combined with image analysis additionally enable the estimation of the content of pozzolanas like fly ash or calcined clay.

Use of fly ash from fluidized bed boilers in clinker-slag-ash based binders

The study presents the state of knowledge regarding physical and chemical properties, as well as trends for application of fly ashes from combustion in fluidized bed boilers in building materials. Clinker - slag - ash based binders were tested that contained up to 40 mass % of fly ashes from combustion in fluidized bed boilers. It was demonstrated that fluidized bed combustion fly ashes (FBC fly ash), apart from granular blast furnace slag, could be the ingredient of low clinker Portland cements (ca. 20% by mass). These cements, compared to CEM I Portland cement, have higher water demand and durability in the corrosive environment, and a lower compressive strength value. Based on test results of binders with various content of blast furnace slag and fly ash, the clinker - slag - ash based binder was singled out, which demonstrated the higher durability in the corrosive environment. It was found that production of clinker - slag - ash based binders was possible in the strength class 32.5 even with 30% by mass of FBC fly ash content.

Ternary Blends of High Aluminate Cement, Fly ash and Blast-furnace slag for Sewerage Lining Mortar

High aluminate cement (HAC), fly ash (FA) and blast-furnace slag (BFS) have been treated sustainable materials for the use of cement products for wastewater infrastructure due to their capabilities of corrosion resistance. The purpose of this study is to optimize a ternary blend of above mentioned materials for a special type of mortar for sewerage lining. By the using of Taguchi method, four control parameters including water/cementitious material ratio, mix water content, fly ash content and blast-furnace slag content were considered in nine trial mix designs in this study. By evaluating target properties including (1) maximization of compressive strength, (2) maximization of electricity resistance and (3) minimization of water absorption rate, the best possible levels for each control parameter were determined and the optimal mix proportions were verified. Through the implementation of the study, a practical and completed idea for designing corrosion resistive mortar comprising HAC, FA and BSF is provided.

The efficiency of plasticizing surfactants in alkali-activated cement mortars and concretes

Functionality of mortar and concrete mixes is regulated by surfactants, which act as plasticizers. The molecular structure of these admixtures can be changed during hydration of alkali-activated cements (AAC). The objective was to determine the chemical nature of plasticizers effective for property modification of mortars and concretes based on AACs with changing content of granulated blast furnace slag from 0 to 100 %. The admixtures without ester links become more effective than polyesters when content of alkaline component increase. The admixtures effective in high alkaline medium were used in dry mixes for anchoring (consistency of mortar 150 mm by Vicat cone; 1 d tensile strength in bending / compressive strength of mortar 6.6 /30.6 MPa) and in ready-mixed concretes (consistency class changed from S1 to S3, S4 with consistency safety during 60 min; 3 d compressive strength of modified concrete was not less than the reference one without admixtures).

Self-healing of self-compacting concretes made with blast furnace slag cements activated by crystalline admixture

Test samples were examined using a specific crystalline admixture, AR glass fibre and three types of cements with percentages of blast furnace slag (BFS) of 55%, 35% and 0%. Test specimens were loaded under compression until 90% of their failure load, in order to generate a network of micro-cracks. These samples were subsequently immersed in lime water to trigger the self-healing mechanism, followed by various tests at 28, 56 and 84 days. As BFS content ratio was increased to 55%, there was a noticeable increase in mechanical recovery and permeation reduction properties, indicating good self-healing.

Mechanical Properties and Durability of Latex‐Modified Fiber‐Reinforced Concrete: A Tunnel Liner Application

This study assessed the mechanical properties and durability of latex‐modified fiber‐reinforced segment concrete (polyolefin‐based macrosynthetic fibers and hybrid fiber‐macrosynthetic fiber and polypropylene fiber) for a tunnel liner application. The tested macrosynthetic fiber‐reinforced concrete has a better strength than steel fiber‐reinforced concrete. The tested concrete with blast furnace slag has a higher chloride ion penetration resistance (less permeable), but its compressive and flexural strengths can be reduced with blast furnace slag content increase. Also, the hybrid fiber‐reinforced concrete has higher compressive strength, flexural strength, chloride ion water permeability resistance, impact resistance, and abrasion resistance than the macrosynthetic fiber‐reinforced concrete. The modified fiber improved the performance of concrete, and the hybrid fiber was found to control the formation of micro‐ and macrocracks more effectively. Therefore, overall performance of the hybrid fiber‐reinforced concrete was found superior to the other fiber‐reinforced concrete mixes tested for this study. The test results also indicated that macrosynthetic fiber could replace the steel fiber as a concrete reinforcement.

Factors affecting properties of high strength geopolymer concrete cured at ambient temperature

This paper experimentally investigates the factors affecting properties of high strength geopolymer concrete using low calcium fly ash and granulated blast-furnace slag. The aim is to produce high strength geopolymer concrete with ambient curing and to study its properties in the fresh and hardened state. Effect of ground granulated blast-furnace slag, alkaline liquid, water-binder ratio and molarity on workability and strength are studied. Ground granulated blast-furnace slag content is varied from 0% to 40% of the total binder with sodium silicate to sodium hydroxide ratio 2.5. The molarity of the solution was 14 M and 16 M. Activator content 30%, 35% and 40% of total binder. Increases in strength were observed in geopolymer concrete with higher ground granulated blast-furnace slag ratio in the mix. Fly ash is replaced by 40% ground granulated blast-furnace slag to achieve compressive strength of 77 MPa.

Mixture design and early age investigations of more sustainable UHPC

This paper deals with the possibility to make the Ultra-High Performance Concrete (UHPC) as an environmentally friendly, through cement replacement with Blast Furnace Slag (BFS) and considering its cost and its early age performance. Thereby, a preliminary investigation is carried out, to design an UHPC with local materials and where Silica Fume (SF) is partially replaced with crushed quartz. The results showed that, from a mixture standpoint: i) the use of high energy mixer is necessary to ensure a homogeneous and workable mixture; ii) the polycarboxylate superplasticizer with chemical structure of acrylic polymer (ACP1) and saturation dosage of 1.8% gives better workability for UHPC, compared to other six superplasticizers; iii) despite its negative effect on slump flow, Grey Silica Fume (silicium) ensures better compressive strength at early age, than Light one (zirconium). Results showed also that for 30% of cement replacement, the nucleation effect of BFS particles prevails and induces an acceleration of setting and hydration reaction of cement. For BFS contents of 50 and 80%, the dilution effect is dominating, which decelerates the setting and hydration reaction and decreases the peak of heat flow. BFS addition also affects the strength development. At 3 days, the strengths of the blended mixtures of UHPC with 50 and 80% of BFS were decreased by 26 and 66% respectively, while in contrast, there was a slight increase in the strength (+3%) with 30% of BFS compared to the reference mixture (UHPC1). For UHPC containing 80% of BFS, the use of chemical activator of potassium hydroxide, with a concentration of [KOH]3, causes slag’s dissolution and reaction, which in turn improves the compressive strength by 42% and 11%, at 3 and 7 days, respectively.

Ground granulated blast furnace slag effect on the durability of ternary cementitious system exposed to combined attack of chloride and sulfate

This paper presents a study on the durability of the ternary cementitious system (TCS) containing ordinary Portland cement, calcium aluminate cement and calcium sulfate with different content of ground granulated blast furnace slag (GGBS) when subjected to 5% NaCl, 5% Na2SO4, and 5% NaCl–5% Na2SO4 attacks. The results showed that the partial replacement of TCS by GGBS increased bound chloride, enhanced compressive strength, and decreased apparent porosity. Besides, the presence of chloride mitigated sulfate attack. The presence of sulfate decreased the contents of free and total chloride, and limited the formation of Friedel’s salt.

Kinetic characterizations of biomass char CO2-gasification reaction within granulated blast furnace slag

The reactions of biomass char CO2-gasification within granulated blast furnace slag (BFS) were systematically conducted by the non-isothermal program using a thermogravimetric analyzer. At the same time during reaction proceeded, the conversion of biomass char CO2-gasification reaction increased with the increasing heating rate. However, at the same temperature during reaction proceeded, the conversion of biomass char CO2-gasification reaction decreased with the increasing heating rate. The granulated BFS could be used as a catalyst in the biomass char CO2-gasification reaction and its catalytic effect became more obvious with the increasing content of BFS in the mixture. The A4 model (nuclei production (m = 4) model) selected through the novel two-step method firstly proposed in the study was the best match with all the gasification reactions. The activation energy was from 52.75 kJ/mol to 64.42 kJ/mol and was lower with the increase of heating rate and the content of BFS in the mixture. The kinetic equations of biomass char CO2-gasification reaction within granulated BFS were developed through the selected model and calculated kinetic parameters.

Prediction of electromagnetic transmission properties using dielectric property modeling of foamed concrete containing BFS

In this paper, we propose a formula for modeling dielectric properties for evaluating the electromagnetic transmission of foamed concrete (FC) widely used as building materials. This includes the effective permittivity and loss tangent according to the foam content of FC mixes containing blast furnace slag (BFS), as well as the content of the BFS, by modifying the dielectric modeling formula for porous foam materials. The difference between the permittivity calculated using the proposed modeling formula and the actual measured permittivity ranges from 0.2% to 2.6%. The calculated result and the measured value are approximately the same. The transmission properties of FC were calculated using the calculated dielectric property values. FC samples containing BFS were fabricated using different foam and BFS content, and their transmission properties were measured, the results of which coincided well with the simulation results. Therefore, the accuracy of the proposed dielectric property modeling of FC containing BFS was verified.