The search for new supplementary cementitious materials (SCMs) to reduce CO2 emissions has become increasingly vital in cement and concrete research. Non-ferrous metallurgical slag (NFMS), often ...overlooked due to their low pozzolanic and hydraulic reactivity, present a promising alternative, particularly given their enhanced reactivity in the presence of alkalis. This study explores the hydration behaviour of NFMS under varying concentrations of CaO, Ca(OH)2, and NaOH, with a focus on dissolution kinetics and phase evolution. 1 M and 6 M NaOH solutions were selected to examine the effect of calcium additives on NFMS hydration, representing scenarios without (1 M NaOH) and with (6 M NaOH) alkali activation reactions. In 6 M NaOH, the addition of CaO/Ca(OH)2 had a minimal impact on dissolution rates but significantly influenced phase assemblage, with CaO promoting strätlingite formation and 10 % Ca(OH)2/CaO leading to katoite. At higher replacement levels (20 % CaO/Ca(OH)2), phase formation was hindered, although microstructure densification persisted, accompanied by reduced strength. In 1 M NaOH, low concentrations of CaO/Ca(OH)2 enhanced Al and Si dissolution but had limited impact on phase assemblage. Higher CaO content favoured katoite formation, while Ca(OH)2 exhibited traces of hydrocalumite. Both additives improved microstructure, but CaO addition, associated with katoite formation, predominantly enhanced strength. The findings confirm that NFMS has significant potential as a cement replacement in hybrid systems utilizing high ratios of slag, Portland cement, and alkalis. By promoting the formation of Ca-Al phases, NFMS improves microstructure and strength, making it a viable and environmentally friendly alternative in construction materials.
The effect of phosphogypsum (PG) on the hydration and retardation mechanism of phosphogypsum-based excess-sulfate slag cement (PESC) was mainly investigated. Based on the natural characteristics of ...PG, such as low pH value and the presence of soluble phosphorus impurities, the content of PG passing the 4.75 mm standard sieve was used as a variable to study the retardation mechanism of PG on PESC. It can be inferred from the heat flow and cumulative heat flow that the induction period is significantly prolonged with the content of PG, which is also reflected in the increase of the setting time of PESC. In the early period of hydration, as the content of PG increases, the soluble phosphorus concentration increases, and the pH value decreases. The changes in soluble phosphorus concentration and pH value affect the microstructure and amount of hydrates. Combined with experimental results, it has been demonstrated that the delay in the hydration of PESC by PG content is mainly due to: the excessive dissolution of Ca2+ and SO42- promotes the recrystallization of dihydrate gypsum; the dissolution of soluble phosphorus reduces the pH value in the pore solution and forms precipitates of calcium phosphate and hydroxyapatite; in the initial reaction period, a large amount of ettringite and C-S-H gel precipitate to form a protective film; the decrease in pH value leads to a decrease in carbonization resistance, and CO2 in the air is more likely to attack the PESC paste, react with alkaline substances in PESC, or degrade hydrated C-S-H and ettringite. The above factors all lead to a decrease in exchangeable ions during the hydration, thereby prolonging the setting of PESC.
•Using phosphogypsum-based excess-sulfate cement (PESC) for the preparation of super retarding materials.•PESC can achieve initial setting for 86 hours and final setting for 134 hours without additional retarders, and its 28d-compressive strength is 24.9 MPa.•The retardation mechanisms of phosphogypsum in PESC has been explored.•The microstructure and amount development of hydrates in PESC were analyzed.
•More than 140 published articles are reviewed.•LF and SCMs are compared on a same spectrum as cement replacement.•LF is similar to SCMs on reducing global warming potential of cement-based ...materials.•Hydration, mechanical properties, permeability and durability are evaluated.
Using supplementary cementing materials (SCMs) as cement replacing materials is common practice in the construction industry to achieve more durable concrete and less CO2 emissions associated with producing concrete materials. The use of finely ground limestone filler (LF) as a cement replacing material is also becoming a widely considered option, partly because of the limited availability of SCMs in some geographic regions. This study provides a comprehensive review based on published literature on the properties of cement-based materials (paste, mortar and concrete) containing limestone filler compared to the properties and performance of cement-based materials containing SCMs (fly ash, slag cement, silica fume or metakaolin). The properties that are examined include early age hydration, mechanical properties, permeability, durability and environmental impacts. At replacement levels up to 10%, concrete or mortar containing LF exhibits similar properties to that of control mix without any cement replacing material. The cementitious and pozzolanic properties of SCMs permit higher cement replacement levels (>10%) which can achieve equivalent or superior properties and durability performance than conventional Portland cement concrete. Based on the available literature, concrete containing LF can exhibit a similar effect as SCMs on reducing global warming potential of the cement-based materials.
Water quenched blast furnace slag is an excellent hydrated material. However, dry granulation is a new treatment method for molten blast furnace slag that has numerous advantages compared to water ...quenching. This study investigated the size distribution of slag particles obtained from the dry granulation of molten slag. In addition, the effect of using the slag obtained from dry granulation in slag cement blends was analyzed. All the results showed that there was a wide size distribution range of blast furnace slag particles in ligament formation. The mean diameter of the solid particles decreased as the rotating speed increased. Meanwhile, the glass content in slag particles decreased for a fixed diameter of the metal collecting tray. The strength of slag cement concrete was low at a low rotating speed. In contrast, obtaining slag particles at a high rotating speed was beneficial for producing a compact structure in the slag cement blend.
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•The mean diameter of solid particles decreased with an increase in rotating speed.•It is easy to form compact structure in slag cement at high rotating speed.•The strength of slag cement was determined by slag powder size distribution.
Exploring low-cost and high-performance phosphorus (P) adsorbents is key to controlling P contamination in water. This study evaluated the P adsorption performance of three types of cement: Ordinary ...Portland cement (OPC), Portland slag cement (PSC), and Portland pozzolana cement (PPC). Furthermore, SEM-EDS, XRD, XPS, and FTIR were employed to reveal the adsorption mechanism. The results showed that the pseudo-second-order model exhibited higher regression coefficients than the pseudo-first-order model, indicating that chemisorption dominated the adsorption process. The Langmuir equation fitted the P adsorption data well, with maximum P adsorption capacities of 245.8, 226.1, and 210.0 mg g
−1
for OPC, PSC, and PPC at 25 °C, respectively. P adsorption capacities decreased gradually with increasing initial pH and reached their maximum values at pH 3. The anions of F
−
, CO
3
2−
, and SO
4
2−
negatively affected P adsorption due to the competitive adsorption with Ca
2+
. The results of XPS, XRD, and FTIR confirmed that Ca-P precipitates (
i.e.
, hydroxyapatite) were the main removal mechanism. A real domestic sewage experiment showed that 0.6 g L
−1
OPC effectively reduced the P concentration from 2.4 to below 0.2 mg L
−1
, with a dosage cost of 0.034 $ per ton. This study indicated that cement, as a low-cost and efficient P adsorbent, has great potential for application in removing P from acidic and neutral wastewater.
This study reveals the potential of cement as a cost-effective and high-capacity adsorbent for removing phosphorus from acidic and neutral wastewaters.
Current demand for waste recycling, phosphogypsum-based excess-sulphate slag cement (PESSC) as a sustainable cement prepared by solid wastes, urges enhancing its performance development based on ...microstructure optimisation. For the purpose of improving the performance and durability of PESSC used in normal or corrosive environments, it is deemed an efficient technique to produce iron-doped compounds with high thermodynamic stability. This paper presents a systematic study of the effect of iron modification on PESSC binders by introducing 0%–2% polyferric sulphate (PFS) from a multiscale viewpoint. XPS, 29Si and 27Al NMR, and TEM were used to characterise the nanostructure of solid particles firstly at Level I. Then, the chemical composition and phase assemblage of PESSC binders were revealed at Level II in terms of ICC, ICP, DTG-DSC, FTIR, BSE-EDS and XRD. Finally, setting time and strength development were determined at Level III. Results indicated that the soluble FeOH4− supplied by the hydrolysis of PFS promotes the generation of iron-doped ettringite with a greater length-to-diameter ratio and thermodynamic stability. Seeding effect of iron doping also promotes the production of spherical and retiform gels with a slight influence on the chemical components and polymerisation. Despite the fact that iron doping weakens the early strength of PESSC mortars, it promotes the persistent hydration rate by retarding precipitation and encapsulation of hydrates on the surface of the slag, showing excellent strength in the later stages. In view of microstructure evolution and performance development during each stage, PFS supplementation within 1.0% is considered a feasible modification of PESSC relying on the formation control of iron-doped hydrates.
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•An eco-friendly phosphogypsum-based excess-sulphate slag cement (PESSC) was developed.•Soluble ferric salt introduced by polyferric sulphate was used to modify PESSC.•Multiscale study has been conducted to investigate the effect mechanism.•Feasibility of the modified PESSC as a sustainable alternative to cement was confirmed.
•The use of MRA improved the plastic shrinkage and flexural strength of concretes.•The use of seawater improved the mechanical properties, reduced setting time and increased drying shrinkage.•The ...cement type was more influential than the use of seawater on concretes’ properties.•The use of seawater and cement with blast-furnace slag improved the performances of the RAC.
Recycled aggregates of mixed composition (MRA) may exhibit great variability in their properties, which in turn reduces their applicability. This study intends to extend the use of MRA in a broadened scope of applications by producing recycled aggregate concretes (RAC), which were mixed using two different types of cement, ordinary Portland cement and cement incorporating blast-furnace slag, and two types of water, fresh and seawater. The testing programme included analyses of the properties of concrete in its fresh (setting time and plastic shrinkage) and hardened state (physical, mechanical and drying shrinkage). The results showed that all of the physical and several of the mechanical properties as well as drying shrinkage were negatively influenced by the use of MRA. In contrast, however, the plastic shrinkage and flexural strength were improved. The use of seawater improved the mechanical properties, reduced setting time and increased drying shrinkage, however, it was found that the cement type was more influential on most of the properties. The use of seawater and cement with blast-furnace slag improved the performances of the RAC.
Portland cement tends to exhibit negative environmental impacts; thus, it is required to find measures that will improve its green credentials. In this study, we report a blended Portland slag cement ...as an alternative environmentally-friendly building material in order to reduce the total carbon footprint resulted from the production of the ordinary Portland cement (OPC), which may resolve the environmental issues associated with carbon dioxide emissions. The ordinary Portland cement type I enhanced by basic oxygen steelmaking slag (BOF) is produced and casted into cubic and beam-like samples for the compressive and three-point bending tests, and the compressive and flexural strengths are experimentally measured. Numerical simulations are conducted to compare with the experimental result and satisfactory agreements are obtained. X-ray diffraction (XRD) investigations and porosity tests are then carried out using the semi-adiabatic calorimetry, which indicates that 5% BOF is the optimal ratio to accelerate the hydration process while increasing the amount of hydration products, especially at the early curing age of 3 days. Scanning electron microscope (SEM) images further indicate that BOF can be used to prevent the development of microcracks while mitigating their propagation within cement mortar. Our study indicates that the compressive strength of OPC can be critically increased by BOF at the relatively low concentrations of 5%. The blended slag cement reported in this paper provides advanced understanding on the green building material that uses byproduct wastes for the mechanical and electrical performance.
This paper reviews the potential use of silico-manganese slag (SiMnS) as binder and aggregate in Portland cement and geopolymer concrete. SiMnS is a byproduct of alloy steel production. Depending on ...the process of solidification, the slag is available in crystalline hard stone type and granulated glassy form. The latter one is more reactive due to the presence of amorphous phases. Therefore, granulated slag has been mostly used as supplementary cementitious material, either blending with clinker or as a precursor for alkali activated binder. Whereas the former is less reactive, and has been mostly used as aggregate, which can enhance the properties of the concrete. The reactive component such as CaO and SiO2 improve the binding capability of the cement gel. The leaching of toxic and heavy metals from the SiMnS reacted binder matrix is not reported. This paper also highlights the future potential of this slag by a process called slag engineering to modify its chemistry similar to granulated blast furnace slag (GBFS), to be utilized more effectively.
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This paper presents research on the impact of fly ash addition on selected physical and mechanical parameters of concrete made with slag cement. Experimental tests were carried out to measure the ...migration of chloride ions in concrete, the tightness of concrete exposed to water under pressure, and the compressive strength and tensile strength of concrete during splitting. Six series of concrete mixes made with CEM IIIA 42.5 and 32.5 cement were tested. The base concrete mix was modified by adding fly ash as a partial cement substitute in the amounts of 25% and 33%. A comparative analysis of the obtained results indicates a significant improvement in tightness, especially in concrete based on CEM IIIA 32.5 cement and resistance to chloride ion penetration for the concretes containing fly ash additive. In the concretes containing fly ash additive, a slower rate of initial strength increase and high strength over a long period of maturation are shown. In accordance with the presented research results, it is suggested that changes to the European standardization system be considered, to allow the use of fly ash additive in concrete made with CEM IIIA 42.5 or 32.5 cement classes. Such a solution is not currently acceptable in standards in some European Countries.
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