High-volume Slag Research Articles

Evaluating the sustainability of microwave pre-cured high-volume slag concrete: Mechanical properties, environmental impact and cost-benefit analysis

Microwave pre-curing, a novel method, offers numerous advantages including energy and time efficiency. The mechanical performance and durability of high-volume slag concrete (HVSC) subjected to microwave curing were experimentally investigated in this study. Additionally, the environmental impact and cost-effectiveness of microwave-cured HVSC were studied, and the ecological efficiency and cost efficiency were analyzed in conjunction with compressive strength and durability. Experimental results indicate that microwave curing significantly enhances the early-stage hydration reaction rate of concrete, increasing the yield of hydration products, especially AFm. Consequently, the early-stage porosity decreases, and the early compressive strength and electrical resistivity of the mortar increase significantly. Furthermore, microwave curing significantly improves the early-stage ecological efficiency and cost efficiency of HVSC. Although the ecological efficiency and cost efficiency of later-stage strength decrease slightly, the durability ecological efficiency and cost efficiency have increased by 12.41–24.6 % and 13.79–26.89 %, respectively, compared to the control group. Time-saving analysis indicates that microwave curing can significantly reduce the curing time for samples by quickly enhancing the early mechanical properties of the materials. Specifically, microwave curing can shorten the curing time by 2.09 days when the compressive strength requirement reaches 20 MPa, and by 2.62 days when the requirement is 30 MPa.

Utilization of air granulated basic oxygen furnace slag as a binder in belite calcium sulfoaluminate cement: A sustainable alternative

Basic oxygen furnace (BOF) slag negatively impacts ordinary Portland cement performance when replacement levels exceed 5%. This necessitates the exploration of alternative applications for the slag. Simultaneously, a high-volume slag utilization is desired to benefit slag recycling as supplementary cementitious materials. Therefore, this study aims to optimize the air granulated BOF slag substitution potential in belite calcium sulfoaluminate cement by investigating the hydration products in standard mortar. The reactivity of the novel binder is correlated with workability, and mechanical performance by thermal, mineralogical, and microstructure analysis. Consequently, the 10–30% replacement delays the final setting time by inhibiting the ettringite formation leading to a decrease in mechanical performance till 28 days. At later ages (28–180 days), the 30–50% substitution exhibited the synergy in mechanical performance, which is attributed to the hydrogarnet, calcium silicate hydrate, and strätlingite formation. Moreover, all the mortar samples exhibited heavy metals’ leaching and drying shrinkage below the permissible limit.

Effect of nano-SiO2 on rheology and early hydration of cement containing high volume slag

Using nano-SiO2 particles is a viable approach for enhancing early performance of blended cement containing high volume slag. The present research aims to investigate the rheology and early hydration of cement incorporating high volume slag and nano-SiO2. The initial and time-varying rheology of blended cement have been evaluated by testing static/dynamic yield stress, plastic viscosity as well as apparent viscosity. Besides, early hydration of blended cement has also been studied through measuring the setting time and heat of hydration. Results show that nano-SiO2 significantly increases the initial and time-varying rheological value of blended cement, the enhancement effect becomes more obvious with the increased dosage of nano-SiO2. In addition, nano-SiO2 can shorten the setting time of blended cement, which is beneficial to rapid construction of concrete with high volume slag. Further, nano-SiO2 shortens induction period, promote C3S hydration, accelerate the transformation from ettringite (AFt) to monosulfate (AFm). Ultimately, nanosilica decreases the content of C3S+C2S in hardened cement paste, resulting in more hydration products. This paper will provide scientific support for revealing the rheology and early hydration of blended cement with high volume slag and nano-SiO2.

On the chemo-mechanical evolution process of high-volume slag cement paste

This study investigated the evolution process of high-volume slag cement (HVSC) paste from a chemo-mechanical standpoint. HVSC specimens with a 70 w.t. % slag replacement rate were studied at various ages. Evolution of phase assemblage, microstructure development, and micromechanical properties were analyzed using TGA/XRD/MIP/SEM-EDS and nano-/micro-indentation techniques. A two-scale micromechanical model was built to predict the effective elastic modulus based on the nanoindentation results. Key findings include: 1) Between 7 and 28 days, the formation of calcium silicate hydrate (C-S-H) gel phase improves the effective elastic modulus by filling capillary pores; 2) From 28 to 90 days, the phase assemblage and microstructure remain stable, with a transition from low-density to high-density C-S-H; 3) Between 90 days and 2 years, slag rims produced by slag grains result in increased elastic modulus; 4) The two-scale micromechanical model, combined with nanoindentation data, accurately predicts the effective modulus of HVSC composites, although the unhydrated slag grains-hydrated cement matrix interface may cause an overestimation at an early age. With longer curing time, this interface disappears owing to the continuous hydration of large slag particles and therefore a good match is found between the modelling and experimental results.

Hydration of blended cement with high-volume slag and nano-silica

Utilization of nano-silica is an effective method to improve the early properties of blended cement containing high-volume slag. In current work, the hydration of blended cement with high-volume slag (40 wt%, 60 wt% and 80 wt%) and nano-silica has been investigated by testing setting time, heat of hydration, compressive strength, hydration products and pore structure. The results illustrate that nano-silica can improve the hydration of slag and cement (including tricalcium silicate (C3S) hydration and transition from ettringite to monosulfate) before 3 d. The increased slag content affects the promotion of nano-silica on cement hydration. Besides, nano-silica inhibits the hydration of cement after 3 d. Furthermore, nano-silica can improve the content of chemically bound water and reduce Ca(OH)2 content. Combined use of appropriate content slag and nano-silica can better optimize the pore structure of hardened pastes, including pore size and cumulative porosity. Ultimately, nano-silica enhances the compressive strength of hardened paste, but the improvement effect of nano-silica gradually weakens with the increase of slag content and the extension of curing time. This paper can provide a theoretical basis for nano-silica modified cement with high-volume slag, and help to improve the early performance of cement with high-volume slag.

Pore structure evolution and sulfate attack of high-volume slag blended mortars under standard curing and steam curing

Partial replacement of cement with high-volume slag reduces the amount of cement in concrete and thereby lessens the environmental pressure caused by cement production. This paper investigates the pore structure evolution and sulfate attack of high-volume slag blended mortars under standard curing and steam curing, discusses the effects of slag content and pore structure on sulfate attack, and evaluates the methods for determining the sulfate resistance performance. The pore structure results show that the hydration of cement and/or slag reduces the porosity and most probable pore diameter (MPPD) and refines the pore structure of mortars. Steam curing primarily affects the pore size distribution but not the porosity for the mortars within 3 d. Increasing slag replacement increases the porosity for standard-cured and steam-cured mortars at the age of 28 d; however, it significantly reduces the air voids that are detrimental to sulfate resistance. Sulfate attack results show that the combination of the flexural strength test with the sulfate-ion content can evaluate the sulfate resistance well. The sulfate resistance improves with increasing slag content, and 70% of slag improves the sulfate resistance significantly for both standard-cured and steam-cured mortars. In addition, the MPPD, gel pores, and mesopores do not seem to determine the sulfate resistance. Reducing the volume fractions of large capillary pores, especially air voids, can improve sulfate resistance.

Application and development of reverse osmosis brine in building materials: high-volume slag cement

Due to the increasing depletion and pollution of drinking water, there has been an increase in the construction of desalination plants. However, reverse-osmosis brine (ROB) generated during seawater desalination and processing is released into the ocean, which affects the marine ecosystem and contributes to desertification. In this study, the author investigated the use of ROB as mix water in fabricating building materials, which would simultaneously reduce carbon dioxide emissions and ROB discharge in water bodies. Samples fabricated using ROB showed higher strength than those fabricated using tap water (TW)—ROB reduced the initial setting time and promoted the formation of dense hydration reaction products. Furthermore, ROB samples showed improved early-age strength, which solves the problem of poor early-age strength reported for high-volume slag cement (HVSC). These results show that the use of ROB in HVSC provides an ecofriendly building material and protects the marine ecosystem.

Chloride-Induced Corrosion Resistance of High-Volume Slag and High-Volume Slag–Fly Ash Blended Concretes Containing Nanomaterials

Chloride-Induced Corrosion Resistance of High-Volume Slag and High-Volume Slag–Fly Ash Blended Concretes Containing Nanomaterials

Hydration and Microstructure of High-Volume Ground Granulated Blast Furnace Slag Concrete Incorporating Metakaolin

In order to relieve the carbon emission of concrete industry, the application of high-volume ground granulated blast furnace slag (HVGGBFS) concrete is one of low cost and effective methods, but its properties develop slowly which needs to be solved. The impact of metakaolin (MK) on the microstructure and hydration evolution of HVGGBFS concrete has been investigated through the compressive strengths, non-evaporable water, morphology and nanoindentation. The results show that the non-evaporable water evolution of HVGGBFS concrete with MK has a similar trend with the compressive strength evolution. The use of 10% MK increases the compressive strengths of HVGGBFS concrete, and from the beginning of 28 days, its strengths are higher than those of the control concrete without GGBFS and MK. The use of 10% MK replacing cement reduces pores and unhydrated particles of HVGGBFS concrete, and however, increases high density calcium-silicate-hydrate (HD C–S–H) and ultra-high density C–S–H (UHD C–S–H), which may be attributed to C–S–H generated by the pozzolanic reaction of MK largely being HD C–S–H and UHD C–S–H.

Enhancement of the properties of silicate activated ultrafine-slag based geopolymer mortar using retarder

Application of high-volume slag based geopolymer mortar is often confined to usage in controlled environments due to its limited flexibility in controlling the setting time. The main aim of the study is to regulate the fast setting of Ultrafine blast furnace slag (UBFS)-based geopolymer mortar (GM) by utilizing mineral admixture. UBFS, partially replaced by Flyash (FA), are investigated by both sodium hydroxide (SH), and a combined solution of sodium hydroxide and sodium silicate (SHSS) of different alkali content and the fresh properties are modified by incorporating Borate, a Type B retarder. The microstructure of the GM is studied by conducting X-ray diffraction (XRD) and Field emission scanning electron microscope (FESEM) tests. Test results indicate that GM containing a high volume of UBFS exhibits prompt setting with a significant mechanical strength when activated by SHSS solution. High molar concentration (M) of SH within 12 M largely enhances the strength of GM, and a good correlation between flexural strength and compressive strength is obtained for SS/SH of 1.5. Application of Borate successfully controls the setting, which also assists in retaining the fluidity of GM. The optimal retarder dose of 4% produces a densely packed microstructure, resulting in improved mechanical properties. The test results show that an ideal GM mix has a strong potential to achieve an acceptable fresh property with improved mechanical strength.

Effect of chlorine bypass system dust on fresh state properties and strength development of high-volume blast-furnace slag mortar

In this study, chlorine bypass system (CBS) dust is proposed as a new alkali activator and the feasibility of applying CBS dust for high-volume blast-furnace slag (HVBFS) mortar is confirmed. CBS is a dust-collecting system for the cement-manufacturing process that collects dust with chloride and alkali. In general, most of the collected CBS dust in South Korea is wasted. As an effort to reduce waste and incidental costs during the cement-manufacturing process, in this study, cement powder was replaced by CBS dust as an alkali activator for blast-furnace slag. From the experiment of HVBFS mortar activated with various CBS dust proportions, favourable results were observed in terms of fluidity and air content when the CBS dust replacement exceeded 5%. Additionally, regarding strength development, CBS dust was successful as an alkali activator for the latent hydraulic reaction of blast-furnace slag. Therefore, when CBS dust was used as a 5% replacement, its efficiency as an alkali activator in which a large amount of blast-furnace (HVBFS) slag was substituted under the research conditions in this study was confirmed in terms of fluidity and strength development performance.

Thermal conductivity and shrinkage properties of slag-based cement concretes

The thermal conductivity, specific heat, and total drying shrinkage test of slag blended OPC cement is conducted by using a Hotdisk-2500S thermal conductivity, and non-contact shrinkage deformation measurement apparatus based on ISO 22007-2 and GB/T50082-2009 test standards, respectively. The influence of replacement rates of slag cement (0, 30, 50, and 70%) and high-temperature exposure (21, 200, 400, 600, and 800 °C) on the thermal properties of concrete is analysed. The results show that for all three concretes, the thermal conductivity initially decreases with increasing temperature up to 400 °C, then after it remains almost constant between 400 and 600 °C, and gradually begins to decrease again up to 800 °C. Furthermore, thermal diffusivity of concrete group G-70, shows 21.4, 21.6, and 37.6% increment in 21, 200, and 600 °C temperature exposure respectively compared to concrete group G-0. Though, as the exposure temperature keeps rise to 800 °C, its value starts to decrease. Furthermore, the results indicated that high volume slag cement content in the concrete mix lessen the drying shrinkage of the concrete at later age. Test data is used as a function of temperature and slag replacement to establish high temperature relations for thermal properties. The proposed thermal property relationships can be used as input data for validation in computer programs and to evaluate the response of OPC and slag blended Portland cement concrete structures subjected to fire.

RETRACTED: Influence of nano-CaCO3 addition on the compressive strength and microstructure of high volume slag and high volume slag-fly ash blended pastes

This article has been retracted: please see Elsevier Policy on Article Withdrawal ( https://www.elsevier.com/about/our-business/policies/article-withdrawal ). The article duplicates significant parts of a paper that had already appeared in Sustainable Materials and Technologies, Volume 20, July 2019, e00111, https://doi.org/10.1016/j.susmat.2019.e00111 . One of the conditions of submission of a paper for publication is that authors declare explicitly that the paper has not been previously published and is not under consideration for publication elsewhere. Re-use of any data should be appropriately cited. As such this article represents a misuse of the scientific publishing system. The scientific community takes a very strong view on this matter and apologies are offered to readers of the journal that this was not detected during the submission process.

Properties of high-volume slag cement mortar incorporating circulating fluidized bed combustion fly ash and bottom ash

This study investigates the incorporation of circulating fluidized bed combustion (CFBC) fly ash as an activator and CFBC bottom ash as fine aggregate in high-volume slag cement mortar. A series of investigations were carried out to analyze the influence of CFBC ash products on the properties of mortar. For comparison, control specimens of ordinary Portland cement and high-volume slag cement were considered. The results obtained from X-ray diffraction and thermogravimetric analyses revealed that the addition of CFBC fly ash activated the hydration of the slag and improved the initial strength of the mortar. Additionally, a pore size distribution test showed that the introduction of CFBC fly ash resulted in decrease of the critical pore diameter and the porosity of the high-volume slag mixes up to 28 days of curing. Similarly, it was found that the compressive strength of high-volume slag mortar manufactured with CFBC fly ash and CFBC bottom ash was improved. Furthermore, the enhanced hydration of high-volume slag mortar due to CFBC ash products resulted in decreased water absorption and fewer total voids. However, inferior resistance to chemical attack was also observed.

Compressive strength development and durability properties of high volume slag and slag-fly ash blended concretes containing nano-CaCO3

This paper presents the effect of nano-CaCO3 (NC) on the compressive strengths and durability properties of high volume slag (HVS) and high volume slag-fly ash (HVS-FA) blended concretes. The study examined the improvement in early and later age compressive strengths and durability properties such as sorptivity, volume of permeable voids, rapid chloride penetration and drying shrinkage of HVS concrete containing 69% blast furnace slag (BFS) and HVS-FA concrete containing combined BFS and fly ash (FA) content of 69% due to the addition of 1% NC. Results show that the addition of 1% NC improved the compressive strengths of HVS and HVS-FA concretes significantly by 43% and 28%, respectively at 3 days compared to the control HVS and HVS-FA concretes without NC and exceeded the compressive strengths of control OPC concrete at later ages. It is also found that 1% NC inclusion reduced the water sorptivity of HVS and HVS-FA concretes reasonably after 28 days of curing and reduction is greater after 90 days of curing exhibited comparable water sorptivity to OPC concrete. Significant improvement is also observed in reducing the volume of permeable voids and controlling the drying shrinkage strain at early age as well as later ages of both HVS and HVS-FA concretes due to 1% NC inclusion. Outstanding resistance against chloride ion penetration is also observed in HVS and HVS-FA concretes due to addition of 1% NC to the very low level of chloride ion penetration according to ASTM standard. SEM and EDS analysis revealed a denser microstructure of paste and interfacial transition zone (ITZ) around aggregates.

Nano- and micro-scale characterisation of interfacial transition zone (ITZ) of high volume slag and slag-fly ash blended concretes containing nano SiO2 and nano CaCO3

There is a strong demand of higher volume replacement of ordinary Portland cement (OPC) in concrete and cementitious composites by supplementary cementitious materials such as blast furnace slag (BFS) and fly ash (FA) to reduce their carbon footprint. This paper presents the effect of addition of nano calcium carbonate (NC) and nano silica (NS) on improving the interfacial transition zone (ITZ) of high volume slag (HVS) and high volume slag-fly ash (HVS-FA) blended concretes. Nanoindentation, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) techniques were used to characterise the nano- and microstructure of the ITZ area between aggregates and matrix. Results show that the addition of NC and NS improved the modulus and hardness of hydration products in the ITZ area of matrix of HVS and HVS-FA concretes. The thickness of ITZ is also reduced in those concretes due to addition of NS and NC. SEM and EDS analysis also confirm the above observation where dense microstructure with less voids and micro cracks and higher peaks of Ca, Si and Al were observed. The observed improvement of 28 days compressive strengths of the HVS and HVS-FA concretes due to addition of NC and NS also correlated well with the improvement of microstructures of ITZ area.

Influence of nano silica on compressive strength, durability, and microstructure of high‐volume slag and high‐volume slag–fly ash blended concretes

AbstractThis study investigated the influence of nano silica (NS) addition on the early‐ and later‐age compressive strengths and durability properties such as sorptivity, drying shrinkage, volume of permeable voids, and rapid chloride permeability, along with microstructural changes, of high‐volume slag (HVS) and high‐volume slag–fly ash (HVS‐FA) blended concrete. The results showed that the addition of NS improved the early‐age (3 days) compressive strength of HVS and HVS‐FA concretes significantly by 34 and 45%, respectively. In addition, the HVS concrete containing 78% blast furnace slag (BFS) gained considerable compressive strengths at later age due to the addition of 2% NS than the control HVS concrete with 80% BFS and showed comparable compressive strengths to ordinary Portland cement (OPC) concrete. On the other hand, the compressive strengths of HVS‐FA concrete containing 67% BFS‐FA blend and 3% NS surpassed OPC concrete at 28 days and exhibited superior strengths at later ages than the OPC concrete. Significant reduction in sorptivity of both HVS and HVS‐FA concretes is observed at 28 and 91 days, respectively, due to the addition of NS. Similar substantial reduction of drying shrinkage, chloride ion permeability, and volume of permeable voids are also witnessed in both HVS and HVS‐FA concretes due to the inclusion of NS than their respective control concretes without NS, and these exhibited better performance than control OPC concrete on most occasions. A denser and compacted interfacial transition zone (ITZ) is also found in the HVS and HVS‐FA concretes due to the addition of a small amount of NS.

Effect of gypsum on the properties of composite binder containing high-volume slag and iron tailing powder

• Composite binder with high-volume slag and ITP shows low early compressive strength. • The addition of gypsum compensates for the poor early properties of composite binder. • The addition of gypsum negatively affects later-age properties of composite binder. • Adding gypsum increases Ca/Si ratio and S/Si ratio but doesn’t affect Al/Si ratio. • High-volume slag and ITP can be used to produce high performance green concrete. The effect of gypsum on the properties of composite binder containing high-volume slag and iron tailing powder was studied by measuring compressive strength, hydration heat, bound water content, hydration products, pore structure and morphology. The addition of gypsum increases early-age compressive strength and bound water content, but the opposite trend is observed at later ages. A higher quantity of gypsum leads to a higher third exothermic peak and a higher total hydration heat. Although incorporating gypsum promotes early hydration of cement and slag, it limits their further hydration at later ages. Adding gypsum forms a large amount of ettringite and densifies early-age pore structure, but it coarsens later-age pore structure. The addition of gypsum increases Ca/Si and S/Si ratios of C-S-H, but it doesn’t affect Al/Si ratio. The addition of gypsum compensates for the poor early-age properties of composite binder containing high-volume slag and iron tailing powder, and the later-age properties are acceptable.

Damage evolution of cement mortar with high volume slag exposed to sulfate attack

Sulfate attack is one of the important reasons for the premature failure of cement-based materials. In this paper, the deterioration law of mortar by sulfate attack was investigated through expansion, mass change, relative dynamic elastic modulus (Erd) and the distribution of sulfate ion content. Moreover, the pore size distribution, corrosion products and three-dimensional crack distribution were performed by Mercury intrusion porosimetry (MIP), X-ray diffraction (XRD) and X-ray computed tomography (X-ray CT), respectively. In addition, the degradation process of mortar with slag immersed in sulfate solution was investigated. The results showed that combined the mass change and Erd can more accurately evaluate the damage of mortar by sulfate attack. The increase of water-to-cement ratio significantly aggravates the mortar deterioration. Adding slag can significantly improve the pore size distribution and improve the sulfate resistance of mortar. The deterioration process of mortar with slag by sulfate attack is different from that of mortar without slag. The degradation process of the mortar with slag is that the surface layer peels off first, and then the sulfate ion continues to invade the interior of the sample to form a new expansion area.

Nondestructive assessment of the compressive strength of concrete with high volume slag

Experimental research was performed to clarify the influence of slag content, type and particle size of coarse aggregate on the rebound value and compressive strength of concrete with high volume slag. Furthermore, a model of rebound strength curve for concrete with high volume slag was established. In addition, the porosity and pore structure of sample surface were analyzed by X-ray computed tomography (X-ray CT) and mercury intrusion porosimetry (MIP), respectively. The results demonstrate that the largest rebound value of the concrete is obtained when the content of slag is 40%. Furthermore, the particle size and type of coarse aggregate have an effect on the rebound value of concrete. When the coarse aggregate is basalt and the particle size is between 10–20 mm, the rebound value is the largest. In addition, when the carbonation depth is large, the rebound strength of concrete with high volume slag is larger than that of the national unified strength curve. The establishment of rebound strength curve of concrete with high volume slag is helpful to improve the accuracy of compressive strength test of slag concrete.