Raw Slag Research Articles

Fabrication of a cost-effective metal oxide-based adsorbent from industrial waste slag for efficient CO2 separation under flue gas conditions

Efficient and affordable adsorbents for CO2 capture are essential in implementing carbon capture technology to mitigate the negative impact of greenhouse gas emissions. This study focuses on synthesizing new nanoporous adsorbents from industrial waste slag using a simple and cost-effective coprecipitation method. In this method, raw slag was milled for 48 h and used as a benchmark for comparing two newly synthesized adsorbents. Selectivity and pure gas isotherm experiments were conducted for all adsorbents in the 25–65°C temperature range and under harsh industrial conditions of 65°C and 15 % CO2. This study utilized the response surface methodology (RSM) to optimize the CO2 adsorption parameters. Specifically, the optimized adsorption conditions were determined for the 15/85 % CO2/N2 condition, and the optimal values for pressure and temperature were found to be 5 bar and 45°C, resulting in CO2/N2 selectivity of 5.65. The NH3-slag adsorbent was identified as the superior choice based on its selectivity and maximum adsorption capacity. The maximum adsorption capacity and cyclic efficiency were determined to be 4.15 mmol/g and 98.1 %, respectively, at a temperature, pressure, and composition of 45°C, 5 bar, and 15 % CO2. Isotherm and thermodynamic models were employed to further investigate the adsorption process. The isotherm results indicated that the adsorption of CO2 by adsorbents occurred heterogeneously in patch-wise sites. Meanwhile, the thermodynamic parameters showed that the process was exothermic and spontaneous, with ΔH° falling below 20 (kJ/mol), showing physisorption phenomena.

Influence of the chemical composition of leachates on the results of ecotoxicity tests for different slag types

In this study, four ecotoxicological tests on Vibrio fischeri bacteria, Sinapis alba L. (white mustard), Daphnia magna S. (daphnia's) and earthworms were performed for three types of aqueous slag (ladle, blast furnace and converter) leachates with two-grain sizes (<4 mm, <10 mm). Concentrations of toxic elements and concentrations of Cr(VI), Ca, Na, Al, and other ions were determined. The raw slags were analyzed using X-ray fluorescence spectroscopy (XRFS), and major substances were determined by X-ray powder diffraction (XRD). The aqueous slag leachates passed ecotoxicological tests and met the required criteria, showing no toxicity to Vibrio fischeri and complying with white mustard test criteria. According to the results of the ecotoxicity tests with daphnia, the blast furnace slag samples were not ecotoxic, while two other slag samples were found to be entirely compliant. Characterization of the slags showed that the effect of element/ion leachability and slag grain size is essential. Biplot principal component analysis (PCA) showed that grain size does not significantly affect the separation of individuals on the plane. A positive correlation on toxicity was found with pH, conductivity, calcium content, dissolved content, salinity and fluoride concentration, whereas a negative correlation was found with magnesium concentration, dissolved organic carbon and potassium concentration. The effective concentration at 50% inhibition (EC50) value for Vibrio fischeri correlated with the first dimension of bivariate assessment. In summary, it was found that the investigated slags can be effectively reused as they comply with regulations and do not endanger the environment.

Risk assessment for the long-term stability of fly ash-based cementitious material containing arsenic: Dynamic and semidynamic leaching

Fly ash from municipal solid waste incineration (MSWIFA) contains leachable heavy metals (HMs), and the environmental risk of contained HMs is an important concern for its safe treatment and disposal. This paper presents a dynamic leaching test of fly ash-based cementitious materials containing arsenic (FCAC) in three particle sizes based on an innovative simulation of two acid rainfall conditions to investigate the long-term stability of FCAC under acid rain conditions. As well as semi-dynamic leaching test by simulating FCAC in three scenarios. Furthermore, the long-term stability risk of FCAC is evaluated using a sequential extraction procedure (SEP) and the potential risk assessment index. Results showed that the Al3+ in the FCAC dissolved and reacted with the OH− in solution to form Al(OH)3 colloids as the leaching time increased. Moreover, the oxidation of sulfide minerals in the slag produced oxidants, such as H2SO4 and Fe2(SO4)3, which further aggravated the oxidative dissolution of sulfides, thereby resulting in an overall decreasing pH value of the leachate. In addition, due to the varying particle sizes of the FCAC, surface area size, and adsorption site changes, the arsenic leaching process showed three stages of leaching characteristics, namely, initial, rapid, and slow release, with a maximum leaching concentration of 2.42 mg/L, the cumulative release of 133.78 mg/kg, and the cumulative release rate of 2.32%. The SEP test revealed that the reduced state of HMs in the raw slag was lowered substantially, and the acid extractable state and residual state of HMs were increased, which was conducive to lessening the risk of FCAC. Overall, the geological polymerization reaction of MSWIFA is a viable and promising solution to stabilize mining and industrial wastes and repurpose the wastes into construction materials.

Study on the Performance and Mechanism of Cement Solidified Desulfurization Manganese Residue.

Desulfurized manganese residue (DMR) is an industrial solid residue produced by high-temperature and high-pressure desulfurization calcination of electrolytic manganese residue (EMR). DMR not only occupies land resources but also easily causes heavy metal pollution in soil, surface water, and groundwater. Therefore, it is necessary to treat the DMR safely and effectively so that it can be used as a resource. In this paper, Ordinary Portland cement (P.O 42.5) was used as a curing agent to treat DMR harmlessly. The effects of cement content and DMR particle size on flexural strength, compressive strength, and leaching toxicity of a cement-DMR solidified body were studied. The phase composition and microscopic morphology of the solidified body were analyzed by XRD, SEM, and EDS, and the mechanism of cement-DMR solidification was discussed. The results show that the flexural strength and compressive strength of a cement-DMR solidified body can be significantly improved by increasing the cement content to 80 mesh particle size. When the cement content is 30%, the DMR particle size has a great influence on the strength of the solidified body. When the DMR particle size is 4 mesh, the DMR particles will form stress concentration points in the solidified body and reduce its strength. In the DMR leaching solution, the leaching concentration of Mn is 2.8 mg/L, and the solidification rate of Mn in the cement-DMR solidified body with 10% cement content can reach 99.8%. The results of XRD, SEM, and EDS showed that quartz (SiO2) and gypsum dihydrate (CaSO4·2H2O) were the main phases in the raw slag. Quartz and gypsum dihydrate could form ettringite (AFt) in the alkaline environment provided by cement. Mn was finally solidified by MnO2, and Mn could be solidified in C-S-H gel by isomorphic replacement.

Potential of ladle furnace slag as supplementary cementitious material in concrete

This research investigated the suitability of a locally available ladle furnace slag (LFS) as a supplementary cementitious material (SCM) to partially replace cement in concrete. The engineering properties of the LFS blended concrete were evaluated through an extensive experimental program. The SCM was used as (i) raw slag and (ii) sieved (finer than 75 µm) slag to use to produce different strength class concrete, viz., C35 and C40. Mechanical strengths and non-destructive tests were conducted for concrete with 5%, 10%, 15%, 20%, 25%, and 50% LFS replacement by weight of cement for various curing duration. Besides, indirect durability tests such as sorptivity and nitrogen gas permeability tests on LFS blended concretes were performed. Uniaxial compressive strength (UCS) for lower-grade concrete at 5% and 10% LFS levels are always higher relative to the control sample, regardless of the material type and curing period. The ultrasonic pulse velocity (UPV) test on concrete suggests that pulse velocity has a pattern similar to that of the UCS. Nitrogen gas permeability varies by LFS level, temperature, and material fineness. Capillary absorption indicates an evident general trend of increased water absorption with exposure/absorption time and LFS level. These properties for higher-grade concrete are reasonably similar to that of lower-grade concrete, however, the finer material shows better performance in this case.

Facile and scalable synthesis of mesoporous composite materials from coal gasification fine slag for enhanced adsorption of malachite green

The recycling of the solid wastes produced in the industrial process and converting them into functional materials with unique structures are of great significance for the sustainable development of human society. In this study, a facile and scalable synthesis method was designed for the preparation of mesoporous composite materials from waste coal gasification fine slag using K2CO3 as a mild chemical additive to chemically recombine SiO2 and Al2O3. At a fine slag to K2CO3 mass ratio of 1:1, a mesoporous composite material (OMB-KB) mainly composed of faujasite-Na and amicite was obtained, which possessed a uniformly porous and loose structure with a specific surface area of 40.26 m2/g and the pore size range of 2–50 nm. Metals inherited from the raw slag and various chemical groups existed on the surface of OMB-KB, making the materials have unique surface chemical properties. OMB-KB exhibited ultra-high adsorption performance on malachite green (MG), and the adsorption capacity reached 7218.31 mg/g when 0.01 g of OMB-KB and 300 ml of MG solution with a concentration of 300 mg/L were used for the adsorption at 298K. The increase of pH was beneficial to the adsorption of cationic MG, and the removal efficiency reached an excellent state at pH ≥ 6. The good fitting of the pseudo-second-order kinetic model and the Freundlich isotherm model suggested that the adsorption process was dominated by chemisorption. The thermodynamic analysis showed that the adsorption of OMB-KB to MG was endothermic, entropy-increasing and entropy-controlled. The adsorption of MG by the material was realized through the exchange interactions between cations, as well as the electrostatic attraction and van der Waals forces between –OH groups and MG. Meanwhile, the oxygen-containing groups and π-electrons in the carbon layer could also adsorb MG molecules by electrostatic attraction.

The effect of slag chemistry on CO2 binding capacity of C3S-slag (-gypsum) system

In this paper, the authors investigated the correlation between slag chemistry and CO2 binding capacity of the blended system. To simplify the composition of mixture, model paste containing C3S, slag covering the common composition range and gypsum was employed.After accelerated carbonation test, three CO2-binding phases were identified in the system as: carbonated Ca-Al AFm phases, carbonated hydrotalcite-like phase, and calcium carbonate, irrespective of slag chemistry and the addition of gypsum. On the other hand, carbonated Ca-Al AFm phases played a minor role in absorbing CO2, sharing less than 5% of CO2 among all carbonate phases. Hydrotalcite-like phase was able to bind up to ∼10% CO2, depending on the Mg/Al atomic ratio of raw slag. CaCO3, originated from the carbonation of portlandite and C−S−H gel phase, took up more than 85% CO2 after carbonation. Moreover, the carbonation degree of C−S−H gel phase was found to be negatively related with the Al2O3 content and Ca/Si ratio of raw slag.

Optimization of Water Leaching of Chlorides from Aluminum Salt Slag

Aluminum recycling generates large amounts of hazardous wastes, known as salt slags, consisting mainly of oxides, metallic aluminum, and salt fluxes. Water leaching is a common technique used for salt removal, being a decisive operation due to water usage and the need to achieve sufficient salt recovery. In this study, water leaching tests under varied operational conditions (water type, slag particle size, solid content, and leaching time) were carried out in salt slag samples obtained from a Brazilian aluminum scrap melting company. Leaching efficiency was assessed by the % chlorine leached. The optimal leaching condition, defined as the one that resulted in the highest chloride removal from the slag together with appropriate operational conditions (larger viable slag size, lower leaching time, etc.), was identified for a slag size below 2.8 mm, 30 wt% of solids in pulp, and a leaching time of 90 min. The results showed that it was possible to recover more than 92% of the salts initially contained in the raw slag, resulting in a leached material with less than 2.5% salts. The recovered salt characteristics showed potential for recycling and could be re-mixed to the salt flux used for aluminum melting. The possibility of achieving higher efficiencies and lower water consumption during leaching was also discussed, as was a preliminary flowsheet for salt slag treatment.

Conversion of Steel Converter Slag into Anion Removing Agent via Alkali Fusion

Steel converter slag, a by-product of iron- and steel-making plants, was converted into a product containing hydrocalumite-like compound using the alkali fusion method. Most of the crystalline phase in the converter slag was converted into a soluble phase by the fusion method, and could be transformed into a product which included hydrocalumite-type crystals. The ability of the product to remove BO3 −, F−, PO4 3−, AsO2 −, AsO4 3−, SeO3 2− and SeO4 2− from aqueous solution is higher than that of raw slag, especially for BO3 −, AsO2 −, AsO4 3− and SeO3 2−.

Characterization of iron oxide waste scales obtained by rolling mill steel industry

Every year, the steelmaking industry produces millions of tons of slags resulting in pollution to the environment. Among the waste, secondary metals and scales rich in iron oxides are also thrown away. There is a need to treat the steel waste in a reasonably way to protect the environment and proposing new cheap technologies for producing advanced materials. In this study we report the morphological and structural characterization of waste scales generated during roll milling steel process at JSC “Arcelor Mittal Temirtau”. The raw slag and annealed at 1000 °C were measured by X-ray diffraction (XRD), scanning electron microscopy adapted with energy dispersive X-ray (SEM- EDX), magnetometry and Mössbauer Spectroscopy (MS). Fe and O were detected by EDX as main chemical elements and Si, S, Ca, Mg, C and Al as minimal elemental composition. XDR for the raw sample revealed α-Fe2O3 (hematite) and Fe3O4 (magnetite) as principal and secondary phase, respectively; whereas monophasic α-Fe2O3 is detected for the scales annealed at 1000 °C. Magnetometry measurements show the Verwey transition for the raw sample and the Morin transition for the annealed at 1000 °C; those are fingerprints for the presence of magnetite and hematite, respectively. MS measurements for the raw sample consist of 6 small peaks of absorption and a broad two-lines absorption peak in the central part. The doublets are associated to the hyperfine parameters belonging to wustite. Magnetite is related to the hyperfine parameters for two sextets in octahedral Fe2.5+ and tetrahedral Fe3+sites and a small sextet that resembles the Mössbauer parameters of α-Fe2O3. Only a well crystallized and weakly ferromagnetic sextet confirm the presence of α-Fe2O3 phase for the sample annealed at 1000 °C due to thermal oxidation.

Waste-free separation and recovery of copper telluride slag by directional sulfidation-vacuum distillation

Copper telluride slag is a high-value secondary resource generated by copper smelting systems, but it is typically treated using acid and alkaline liquids, which generate toxic waste. Exploring innovative green and efficient methods for tellurium recycling can improve production efficiency and mitigate ecological hazards. In this work, a clean and efficient method for the separation and extraction of tellurium by directional sulfurization-vacuum distillation was proposed. First, the Cu–Te chemical bonds in copper telluride slag were broken by S, which formed Cu–S chemical bonds and elemental Te and achieved the separation effect. Secondly, elemental Te was extracted by vacuum distillation. The feasibility of the method was confirmed by theoretical analysis. The experimental results showed that the optimal temperature of directional sulfidation was 400 °C, while the experimental parameters of distillation were 650 °C for 60 min and the pressure was 10–20 Pa. The tellurium content extracted from the raw slag was 97.60%, and its purity was 96.37%. All the copper in the raw material was enriched in the form of sulfide in the distillation residue. The volatiles could be directly used as crude tellurium products, and the residues could be reused in pyrometallurgical copper smelting processes. Compared with the traditional process, this proposed process is short and greatly eliminates the loss of tellurium due to multiple dispersion. The process does not produce three wastes and is friendly to the environment, as shown by the economic and sustainability evaluation. This research provides a clean and sustainable method for treating copper telluride slag for the metallurgical industry.

Performance of Ladle Furnace Slag in Mortar under Standard and Accelerated Curing

This research preliminarily investigated the suitability of a locally available ladle furnace slag (LFS) as a partial replacement of cement in mortar. The raw material was first characterized to obtain its chemical and physical properties through particle size distribution, X‐ray fluorescence (XRF), X‐ray diffraction (XRD), and scanning electron microscopy (SEM). Later, the raw LFS was classified into two categories: (i) raw LFS and (ii) sieved (passing through #200 sieve) LFS and incorporated in mortars as a partial replacement of cement. Mortar prisms with 5, 10, 15, 20, 25, and 50% LFS (raw and sieved) were prepared and cured under normal temperature (NTC) for 7, 28, and 56 days. Additional mortar prisms (with raw and sieved LFS) were prepared by curing them under high‐temperature accelerated curing (HTAC) for 7 days. The characterization tests suggest that CaO, SiO2, MgO, and Al2O3 are the main compounds of raw LFS used in this study. The mineralogical phases present in the raw slag are calcio‐olivine, akermanite, α‐quartz, merwinite, magnetite (Fe3O4), and calcium‐aluminium oxide. Both raw and sieved LFS‐blended mortars yield good consistency up to 25% cement replacement in mortars. The compressive strength of NTC mortar suggests that 5% and 10% replacement of cement with raw and sieved LFS yields higher strength than the control mortar. Seven days strengths of raw and sieved LFS blended mortars obtained for HTAC are closely comparable to that of 28 days under NTC. This study recommends that LFS could be a sustainable supplementary material to use as a partial replacement of cement in mortar, preferably up to a level of 15% for standard works.

Study on Oxidation Behavior of Industrial Basic Oxygen Furnace Slag and Recovery of Magnetic Iron‐Containing Phase

The BOF slag contains a lot of iron‐containing species and its efficient recovery is a difficult problem in metallurgy. Herein, the oxidation behavior of industrial BOF slag under air atmosphere is investigated to explore the optimal oxidation conditions for transforming nonmagnetic FeO into magnetic MgFe2O4, including oxidation temperature, oxidation time, and airflow rate. The raw slag and oxidized slags are analyzed using chemical analysis, X‐ray diffraction (XRD) analysis, scanning electron microscope (SEM)‐energy dispersive spectroscopy (EDS) analysis, and Factsage thermodynamic simulation. The results show that the formation of MgFe2O4 phase is closely related to the oxidation temperature, oxidation time, and airflow rate. With the increase in temperature, the conversion rate of MgFe2O4 increases, and reaches the maximum at 1050 °C. However, the conversion rate of MgFe2O4 decreases and part of β‐C2S is converted to α‐C2S above 1050 °C. When the oxidation time and airflow rate increase, the conversion rate of MgFe2O4 increases and reaches the maximum value at 100 min and 1.25 L min−1, respectively. Correspondingly, the grade increased from 16.3% of the raw slag to 27.86% of the magnetic slag, an increase of 11.5%. This is a more convenient and effective method, which can not only bring economic benefits for relevant enterprises but also reduce environmental pollution.

Analysis of the Possibility of Using Slags from the Thermal Treatment of Municipal Waste as Potential Component of Cement-Case Study.

In Europe there are nearly 500 incinerators. There are over 2000 of them in the world. It is estimated that the combustion of 1 ton (Mg) of waste produces about 250–300 kg of slag. Due to the large amounts of this waste, the construction industry’s demand for raw materials and the reduction of CO2 emissions, research was undertaken to use slags as a cement component. The problem was complex because slags generated in the thermal treatment of municipal waste have different chemical compositions and physical properties and contain variable amounts of impurities. The choice of chemical analyses of slag was dictated by the potential influence on the properties of cement mortars. The total moisture of raw slag (4–10%), the bulk density (600–1267 kg/m3) and the specific surface after grinding (over 3000 cm2/g) were determined. The pH (11.9) and the content of sulphates (3.5% by weight), chlorides (0.3% by weight) and selected heavy metals (Cd, Cu, Fe, Mn, Zn, Pb) were measured in the aqueous extract. The obtained results of the washing test were compared with the values resulting from the currently binding legal regulations. In the next step, cement mortars with 30% addition of tested slags were designed and made. The article presents the results of compressive strength tests, which were compared with the results of samples without the addition of slag. The addition of slag to the cement mortar decreased S_MSWI 1 by 64% and S_MSWI 2 by 31%. The high loss of strength and the swelling of the S_MSWI 1 test led to the activation of the NaOH slag. In the endurance test, an increase from 16 to 32 MPa was recorded. Preliminary studies show that the addition of slag in the cement mortar allows obtaining the strength at the level of 30–32 MPa.

Separation of heavy metals from hazardous lead slag by carbothermic reduction and thermal volatilization: Effect of phase transformation on Sn, Pb, Zn removal

In this study, the carbothermic reduction and volatilization were applied to recover valuable metals from lead slag. The removal and volatilization mechanisms, especially the migration and distribution behavior of heavy metals, were investigated. The results showed that the removal ratio of Sn was lower than those of Pb and Zn. Increasing the temperature was beneficial to the removal of Zn, but unfavorable for the removal of Sn and Pb. SEM/EDS analysis of the reduced pellets and the flue dust showed that ZnFe2O4 and ZnS in the raw slag were reduced to Zn for volatilization and then reoxidized and formed ZnO(s) in the flue. At lower temperatures, SnO2 and FeOx·PbO·SiO2 in the raw slag was reduced to the volatile SnO and PbO. However, SnO and PbO were further reduced to nonvolatile metallic Sn and Pb at higher temperatures. Fe-Sn and Fe-Pb alloys easily formed when metallic Sn and Pb coexisted with metallic Fe, leading to lower removal ratios. For the metallization of Fe, the iron grains grew up gradually and easily formed joined crystals at higher temperatures, which inhibited the volatilization of Sn and Pb.

Recovery of Valuable Metals from Nickel Smelting Slag Based on Reduction and Sulfurization Modification

Nickel smelting slag contains valuable metals including nickel and copper. Failure to recycle these metals wastes resources, and disposal of nickel slag in stockpiles results in environmental pollution. Nickel slag recycling is important, and metals can be recovered from slag by flotation. However, considering the complex forms in which valuable metals occur in nickel slag, high yields are difficult to achieve by direct flotation. In this study, nickel slag was modified by reduction and sulfurization to render it more amenable to metal recovery through flotation. The mechanism was assessed based on thermodynamics and elements’ phase distributions. Thermodynamic analyses indicated the feasibility of nickel slag modification by reduction–sulfurization smelting. The results of chemical phase analysis show that the forms in which valuable metals occur in nickel slag can be modified by reduction–sulfurization, and the proportion of metals existing in sulfide and free metal states in nickel slag can be increased. Compared with the direct flotation of raw slag, the recovery of nickel and copper from top-blowing slag increased by 23.03% and 14.63%, respectively. The recoveries of nickel and copper from settling slag increased by 49.68% and 43.65%, respectively.

Influence of Hydrothermal Pretreatment Temperature on the Hydration Properties and Direct Carbonation Efficiency of Al-Rich Ladle Furnace Refining Slag

The influence of hydrothermal pretreatment temperature on the hydration products and carbonation efficiency of Al-rich LF slag was investigated. The results showed that the carbonation efficiency was strongly dependent on the morphology of hydration products and the hydration extent of the raw slag. Hydrothermal pretreatment at 20 °C or 80 °C favored the formation of flake-shaped products with a higher specific surface area and therefore resulted in a higher CO2 uptake of 20 °C and 80 °C-pretreated slags (13.66 wt% and 10.82 wt%, respectively). However, hydrothermal pretreatment at 40 °C, 60 °C or 100 °C led to the rhombohedral-shaped calcite layer surrounding the unreacted core of the raw slag and the formation of fewer flake-shaped products, resulting in a lower CO2 uptake of 40 °C, 60 °C and 100 °C-pretreated slags (9.21 wt%, 9.83 wt%, and 6.84 wt%, respectively).

The use of blast furnace slag as a supplementary cementitious material

Waste material recycling in mortar production not only provides a promising resource for producing high-quality mortar, but it also aids in properly addressing the waste disposal issue. This study investigates the potential of utilizing blast furnace slag wastes as a supplementary cementitious material in blended cement-based mortars.The experimental program includes investigation of compressive strength of cement-based mortar composites contained different types and percentages of slag wastes. The mortar specimens were prepared and cured following related international standards. After curing, the compressive strengths of the tested specimens were assessed and compared with control specimens. The influence of the chemical composition of the investigated slag types on the resulted strength of the blended cement mortar was also discussed. Results of this study revealed that the chemical compositions of the raw slag wastes have significant effects on the pozzolanic activity of the produced slag. Slag samples contained higher percentages of calcium oxides present the most promising results regarding the production of supplementary cementitious material.

X-ray Diffraction-Based Quantification of Amorphous Phase in Alkali-Activated Blast Furnace Slag

Abstract The X-ray diffraction (XRD) signature of the glassy phase in blast furnace slag undergoing alkaline dissolution is evaluated. The intensity signature of the glassy phase present in slag can consistently be decomposed into three underlying pseudo-Voigt (PV) peaks. It is shown that the fundamental underlying characteristics of the XRD signature of the undissolved glassy phase of slag in terms of the underlying PV peaks do not change after dissolution in an alkaline solution. The stability of the calcium ions depends on the [OH−] concentration in the solution. An intensity-based procedure is developed for quantifying the unreacted glassy phase content in alkali-activated slag. The XRD profile information of the glassy phase in raw slag is suitable for fitting the intensity profile of the dissolved glassy phase. The mass percentage of the unreacted glassy phase of slag within alkali-activated slag is validated with selective acid dissolution. A procedure for determining the degree of reaction in alkali-activated slag is established. The procedure developed here could be used to determine the activity of slag in an alkaline environment.

Investigation of Alkali-Silica Reactivity in Sustainable Ultrahigh Performance Concrete

Considering its superior engineering properties, ultrahigh performance concrete (UHPC) has emerged as a strong contender to replace normal strength concrete (NSC) in diverse construction applications. While the mechanical properties of UHPC have been thoroughly explored, there is still dearth of studies that quantify the durability of UHPC, especially for sustainable mixtures made with local materials. Therefore, this research aims at investigating the alkali-silica reactivity (ASR) potential in sustainable UHPC in comparison with that of NSC. Sustainable UHPC mixtures were prepared using waste untreated coal ash (CA), raw slag (RS), and locally produced steel fibers. UHPC and benchmark NSC specimens were cast for assessing the compressive strength, flexural strength, and ASR expansion. Specimens were exposed to two curing regimes: accelerated ASR conditions (as per ASTM C1260) and normal water curing. UHPC specimens incorporating RS achieved higher compressive and flexural strengths in comparison with that of identical UHPC specimens made with CA. ASR expansion of control NSC specimens exceeded the ASTM C1260 limits (&gt;0.20% at 28 days). Conversely, experimental results demonstrate that UHPC specimens incurred much less ASR expansion, well below the ASTM C1260 limits. Moreover, UHPC specimens incorporating steel fibers exhibited lower expansion compared to that of companion UHPC specimens without fibers. It was also observed that the mechanical properties of NSC specimens suffered more drastic degradation under accelerated ASR exposure compared to UHPC specimens. Interestingly, UHPC specimens exposed to accelerated ASR conditions attained higher mechanical properties compared to that of reference identical specimens cured in normal water. Therefore, it can be concluded that ASR exposure had insignificant effect on sustainable UHPC incorporating CA and RS, especially for specimens incorporating fibers. Results indicate that UHPC is a robust competitor to NSC for the construction of mega-scale projects where exposure to ASR conducive conditions prevails.