Slag Mortars Research Articles

Effect of magnetized water on alkali-activated slag mortars incorporating raw and calcined marble powder

This study investigates the impact of magnetized water (MW) on the fresh and hardened properties of alkali-activated slag (AAS) mortars incorporating raw marble powder (RMP) and calcined marble powder (CMP). In the initial stage of the study, control specimens were manufactured to ascertain the optimal parameters for molarity, curing temperature, and curing time. The optimal parameters were determined based on the highest strength results: a molarity of 10, curing time of 24 hours, and curing temperature of 110 ℃. In the second stage of the study, while maintaining these optimal parameters, RMP and CMP were substituted in place of blast furnace slag (BFS) at rates of 10%, 20%, 30%, and 40%. In this study stage, tap water (TW) and MW were employed as the mixing water. A mini-slump test was conducted to assess the fresh state properties of the prepared AAS mortars. Subsequently, ultrasonic pulse velocity (Upv), flexural strength (ff), and compressive strength (fc) tests were carried out to evaluate the hardened state properties of the specimens. Finally, scanning electron microscopy (SEM) analysis was performed to examine microstructural properties. According to the results, the ff and fc values of the mortars produced with CMP substitution using TW showed an increase of up to 20.6% compared to the mortars based on RMP and produced withTW. Additionally, utilizing MW as the mixing water enhanced the workability of AAS mortars. Consequently, incorporating CMP and MW in AAS mortars further improved fresh and hardened state properties compared to RMP and TW.

Optimizing pore structure of perforated cenospheres for effective internal curing of alkali-activated slag mortars

Based on the controllability of the pore structure of perforated cenospheres (PCs), this study utilized PCs with different etching concentrations for the internal curing of alkali-activated slag (AAS), aiming to achieve the optimal etching parameters for efficient internal curing. Three etching concentrations (0.3 M, 0.7 M, 1.0 M) were set to investigate the effects of water-filled PCs on the performance of internal curing of AAS mortars. The results indicated that the water released from the PCs delayed the hydration of AAS and maintained high internal relative humidity. The chemical shrinkage of AAS could be reduced. Water-filled PCs internal curing promoted the generation of hydration products around the PCs and increased their packing density, leading to a reduction in mesopores and a 12.7—27.7% increase in elastic modulus at 28 d. With the optimal etching concentration of 0.7 M, water-filled PCs significantly mitigate the autogenous shrinkage by 75.8% while enhancing the compressive strength of AAS mortars.

Malzemelerin Isıtılarak Kullanılması ile Alkali-Aktive Cürufların Erken-dönem Dayanım Gelişimlerinin İyileştirilmesi

Alkali-activated cements have gained attention as sustainable alternatives to Portland cement-based concretes. This study aims to enhance the early strength development of alkali-activated slag (AAS) mortars by preheating the alkali activator, ground granulated blast furnace slag, and aggregates to temperatures reaching up to 65°C before their utilization. Preheating at 50°C enhances both early and ultimate strength of AAS, compared to specimens that were not subjected to preheating. Similarly, preheating at 65°C results in a substantial increase in early strength but leads to some strength reduction after three days. SEM and FTIR analyses reveal that preheating at 50°C improves the interfacial transition zone between paste and aggregate, reduces microcracks, and promotes alkali activation. Furthermore, FTIR analysis confirms the occurrence of hydration reactions in AAS upon contact with water.

Accelerated aging resistance, abrasion resistance and other properties of alkali-activated slag mortars containing limestone powder

The Earth's crust is widely recognized for its abundance of limestone (LS). Limestone powder (LSP) has a wide range of potential properties that make it suitable for various applications and fields. It has found extensive usage in Portland cement-based materials. Recently, the incorporation of LSP into geopolymers is becoming more of a concern than before and has become a hot topic. In this article, high range of LSP (2.5–50 wt%) was introduced into alkali-activated slag (AAS) mortars activated with NaOH and sodium silicate solution as a substitution of slag. For the first time, the effect of LSP on the accelerated aging resistance and abrasion resistance of AAS mortars was examined. In addition, the typical traditional routine properties such as flowability, setting time, mechanical strength, water absorption, and total porosity were studied. Sophisticated equipment was utilized to observe the changes in crystalline phases, hydration products, and microstructures of selected samples. The results showed higher flowability and longer setting time with including LSP. As the amount of LSP increased as the flowability and setting time increased. The introduction of 2.5–25% LSP positively affected the mechanical strength, aging resistance, abrasion resistance and transport properties. In contrast, the introduction of 35% did not show an essential change, whilst the introduction of 50% LSP negatively affected the mentioned properties.

Optimization of Mechanical Properties and Embodied Energy of Polyvinyl Alcohol Fiber-Reinforced High-Strength Alkali-Activated Slag Mortars: Comparative Study

Optimization of Mechanical Properties and Embodied Energy of Polyvinyl Alcohol Fiber-Reinforced High-Strength Alkali-Activated Slag Mortars: Comparative Study

Thermal insulation and durability of alkali-activated lightweight slag mortar modified with silica fume and fly ash

Green building indices prioritize energy efficiency, which in turn promotes sustainable development. One of the most energy-consuming sectors globally is the building sector. Developing green insulating materials based on byproducts has environmental benefits and profits in reducing energy consumption in the building sector and other sectors. This study aimed to develop thermal insulating materials based on byproducts for binders and expanded perlite (EP) for fine aggregate cured at room temperature. Alkali-activated lightweight slag mortars with/without foaming agent were prepared. To increase the efficiency of the thermal insulation, the slag was partially replaced with a fixed ratio of silica fume (SF) (15%) and different ratios of fly ash (FA) (15%, 40% and 65%). After room temperature curing, the bulk density, mechanical strength, accelerated aging resistance, water absorption, total porosity and thermal conductivity were measured. The selected samples were examined using sophisticated tools. The results showed that the selected byproducts can be efficiently employed as insulation materials, of which the obtained results of thermal conductivity, bulk density, total porosity, water absorption, compressive strength and flexural strength were in the range of 0.172–0.082 W/mK, 1191.6–450 kg/m3, 33.2–48.7%, 28–45.1%, 12.48–1.5 MPa and 3.43–0.46 MPa, respectively. All the studied specimens exhibited strength reduction after accelerating aging, but the reduction rate was mitigated by increasing the FA content. Increasing FA content has a benefit in increasing the efficiency of thermal insulation.

Relationship of electrical resistivity and corrosion rate in alkali-activated mortars with varying alkalinity and nitrite inhibitor

The quantitative relationship between electrical resistivity and corrosion rate of steel (noted as R-C relationships) is empirical but informative in indicating corrosion risk of reinforced concrete in complex environments. However, it remains unclear how the R-C relationship line is affected by the chemistry and microstructure of cementitious binders. In this work, the corrosion behaviors of steel embedded in alkali-activated slag (AAS) mortars with varying alkali dosages were investigated to uncover the role of hydroxide ion concentration (pH) of pore solution in R-C relationship lines. Additionally, the effectiveness of sodium nitrite as a corrosion inhibitor in AAS was evaluated under high pH and chloride-rich conditions, as well as its effect on the R-C relationships. The results show that the intercept of R-C relationship lines increases with the decrease of alkali dosage in activators, which is mainly attributed to the pH drop in cementitious materials. Moreover, the slope of R-C relationship lines is a parameter related to pore structure and has a linear correlation with the average pore diameter measured by mercury intrusion porosimetry. Additionally, the efficacy of sodium nitrite as a corrosion inhibitor in AAS is insignificant, likely due to its detrimental effect on pore structure and enhanced water absorption.

Interactions between alkali-activated and cement-based mortars and biofilm and their influence on microbial induced mortar deterioration

Alkali-activated fly ash (AAF) and alkali-activated slag (AAS) mortars were exposed to the sewage environment with acidophilic sulfur oxidizing bacteria and high concentration H2S to study their interaction. It was found that when they suffered the biogenic sulfuric acid attack, both the AAF and calcium aluminate cement (CAC) mortars had a strong inhibition effect on the growth and activity of microorganisms. There are more aluminum ions dissolved from AAF mortar into sewage, and its structure was characterized by the increase in 100-1000 nm pores. Still, a hard high silicon skeleton was formed to keep the apparent intact. However, CAC mortar had a higher killing rate for the bacteria in the attached biofilm. For AAS mortar, the formation of excessive gypsum increased the macropores content and was more conducive to the growth of biofilm, thereby accelerating the penetration of corrosive medium and the deterioration of mortar.

Monitoring early age elastic and viscoelastic properties of alkali-activated slag mortar by means of repeated minute-long loadings

This study investigates the development of elastic and creep properties of sodium hydroxide-activated blast furnace slag mortar, utilizing three different molarities of the activator solution and two solution-to-binder ratio and a reference OPC-based mixture, since the earliest age. The experimental phase involves a series of hourly-repeated 5-min long creep tests on the aging material. This approach enables continuous monitoring, facilitating the characterization of early-age elastic stiffness and creep properties. Linear regression is employed to calculate the tangent unloading (elastic) modulus and Poisson's ratio. To model short-term creep behaviour, a power-law creep function is utilized. The integration of these findings with calorimetry-derived evolutions of cumulative heat release establishes linear correlation between (compressive) strength and heat release, along with a power function relationship between unloading (elastic) modulus and heat release. An optimal alkali dosage (Na2O content) appears to be vital for long-term strength development. Additionally, the creep parameters, namely amplitude (A) and kinetic (K), demonstrate a gradual decrease, although they maintain values higher than those of the corresponding OPC mixture, as the heat release progresses.

Preparing hydrophobic alkali-activated slag mortar with lotus-leaf-like microstructure by adding polydimethylsiloxane (PDMS)

In this study, polydimethylsiloxane (PDMS) was applied for overall hydrophobic modification of alkali-activated slag (AAS) mortars aiming to reduce its high water sorptivity. The effects of the amount and viscosity of PDMS on the water absorption characteristics and mechanical properties of AAS mortars were investigated. Meanwhile, MIP, the surface contact angle of AAS mortars and SEM-EDS, Inverse gas chromatography (IGC), FT-IR, XRD of hardened AAS pastes were performed for analyzing the modification mechanisms. The results indicated that the water sorptivity of PDMS-modified AAS mortar decreased by 90 %, and the contact angle of the inner surface increased from 14° to 128° when the dosage of PDMS reached 8 % (by weight of binder). The main modification mechanisms of PDMS in AAS system can be summarized as: Firstly, the formation of hydrophobic coatings on the surface due to the cross-linking reaction between C-S-H gel and PDMS reduces the surface energy and the hydrophilicity of hardened AAS pastes, achieving chemical modification; Secondly, the hierarchical structures formed by micro papillary increases the surface roughness, thus enhancing the hydrophobic effect further through physical modification. Moreover, the coarsening of capillary pores also reduces the capillary force during water absorption process. Meanwhile, the addition of PMDS maintains comparable strength development of AAS mortars, which is beneficial for the practical application.

Effect of Modified Cow Dung Fibers on Strength and Autogenous Shrinkage of Alkali-Activated Slag Mortar.

Alkali-activated slag (AAS) presents a promising alternative to ordinary Portland cement due to its cost effectiveness, environmental friendliness, and satisfactory durability characteristics. In this paper, cow dung waste was recycled as a renewable natural cellulose fiber, modified with alkali, and then added to AAS mortar. The physico-chemical characteristics of raw and modified cow dung fibers were determined through Fourier transform infrared (FTIR), X-ray diffraction (XRD), and Scanning electron microscope (SEM). Investigations were conducted on the dispersion of cow dung fibers in the AAS matrix, as well as the flowability, strength, and autogenous shrinkage of AAS mortar with varying cow dung fiber contents. The results indicated that modified fiber has higher crystallinity and surface roughness. The ultrasonic method showed superior effectiveness compared to pre-mixing and after-mixing methods. Compared with raw cow dung fibers, modified fibers led to an increase of 11.3% and 36.3% of the 28 d flexural strength and compressive strength of the AAS mortar, respectively. The modified cow dung fibers had a more significant inhibition on autogenous shrinkage, and the addition of 2 wt% cow dung fibers reduced the 7 d autogenous shrinkage of the AAS paste by 52.8% due to the "internal curing effect." This study provides an alternative value-added recycling option for cow dung fibers as a potential environmentally friendly and sustainable reinforcing raw material for cementitious materials, which can be used to develop low autogenous shrinkage green composites.

Impact of magnesia and titania nanoparticles on characteristics of alkali-activated slag mortars exposed to sulfuric acid solution and elevated temperatures

Nanotechnology is being employed as potential solution to alleviate limitations of alkali-activated slag mortars (AASMs). The current study investigated the impact of prepared magnesia (NMg) and titania nanoparticles (NT) at various dosages (0, 1, 3 and 5 wt%) on mechanical and durability characteristics of AASMs. Specimens were either fully immersed in an aqueous solution of sulfuric acid (1 wt% concentration) or subjected to elevated temperatures (250, 500 and 750℃). Microstructural development and densification were analyzed by XRD, FTIR, and SEM with EDX technique to determine the primary improvement mechanism imparted as a result of employing nanoparticles to AASMs systems. Optimum performance prior to and after exposures was achieved for specimens containing 3% NMg and 1% NT in terms of compressive strength, water absorption for unexposed specimens, and weight loss and compressive strength retention for specimens exposed to sulfuric acid solution and elevated temperature. Nanoparticles produced more densified mixtures imparted by their ability to accelerate geopolymerization processes, filling effect and formation of voluminous compounds that further block available spaces in the microstructure.

Alkali-silica reaction of high-magnesium nickel slag fine aggregate in alkali-activated ground granulated blast-furnace slag mortar

The construction industry is presently encountering a significant challenge regarding the shortage supply of natural sands. The use of metallurgical slags as fine aggregates in building materials presents a solution that not only mitigates the over-exploitation of natural sands, but also provides a sustainable and valuable approach for managing industrial solid wastes instead of traditional landfill disposal. This study investigated the alkali-silica reaction (ASR) of air-cooled and water-quenched high-magnesium nickel slag (HMNS) fine aggregates in alkali-activated ground granulated blast-furnace slag (AAS) mortars. The mortars exhibited satisfactory volume stability and structural integrity throughout the 120 days of accelerated mortar bar test. The lab-simulated dissolution test revealed the formation of a thin precipitate layer of sodium silicate hydrate on the surface of HMNS fine aggregates, which contained a significant amount of Mg with Mg/Si ratios ranging from 0.16 to 0.18. The divalent Mg cations were released from the HMNS fine aggregates and served as the pseudo network former to crosslink the ASR gel instead of Ca. This reduced the moisture adsorption capacity and mitigated the expansion of ASR gel.

Fluidity, mechanical properties, shrinkage of alkali-activated slag/stainless steel slag mortars with composite activators

In order to efficiently utilize steel slag and reduce carbon emissions, the performance of alkali-activated slag/stainless steel slag mortar (ASM) prepared with a composite activator is investigated. In this work, CaO, Na2CO3 and water glass (WG) are used as composite activators, where the alkali equivalents of CaO and Na2CO3 are maintained at 4% and the alkali equivalents of WG (i.e. WG content) as variables were 0, 0.5%, 1.0%, 1.5% and 2.0% respectively. The properties of ASM, including mechanical properties, autogenous and drying shrinkage, are investigated. Results show that the mechanical properties of ASM decrease and then increase as the WG content increases, with the worst mechanical properties of ASM occurring when the WG content is 0.5%. The autogenous shrinkage of ASM decreases as the WG content increases from 0 to 0.5% followed by an increase as the WG content increases further to 2.0%. Autogenous shrinkage depends on chemical shrinkage, small pore (<50 nm) volume, MCL and capillary pressure. When the WG content is increased from 0 to 0.5%, the hydration reaction is inhibited by the reaction of the WG and CaO which reduces the pH of activator solution and gel amount, leading to a reduction in chemical shrinkage, small pore volume, MCL and capillary pressure. However, the high WG content accelerates the hydration reaction when the WG content is greater than 0.5%, which increases the autogenous shrinkage. The drying shrinkage of ASM decreases and subsequently increases as the WG content increases. The higher drying shrinkage is associated with weight loss due to the excellent connectivity of the pores.The pore structure also affects the drying shrinkage, which can be justified on the basis of capillary pressure.

Assessment of lithium slag as a supplementary cementitious material: Pozzolanic activity and microstructure development

In this study, lithium slag was utilised as a supplementary cementitious material (SCM) to develop pozzolanic activity and reduce CO2 emissions related to cement production, with a focus on comprehensive chemical tests and microstructural assessments. Lithium slag was primarily characterised through laser particle size analyser, X-ray fluorescence, X-ray diffraction, scanning transmission electron microscopy coupled with energy dispersive X-ray spectroscopy, and thermogravimetry. These tests indicate that lithium slag holds 31.6% amorphous phase with rich aluminosilicate minerals, making it an excellent candidate as pozzolan. The unsaturated lime and electrical conductivity pozzolanic activity precursor tests evaluated the potentiality of using lithium slag as a low carbon pozzolan. The optimum percentage of lithium slag as a supplementary cementitious material was determined from Frattini, strength activity index, and R3 tests by replacing 0–60% cement. Results show that 40% lithium slag mortar could achieve 93% strength activity index in 28 days. The microstructure development of lithium slag was assessed and ettringite, monocarboaluminate, and intermixed calcium aluminosilicate hydrates were formed at 56 days.

Chloride-induced corrosion propagation of alkali-activated slag mortar with pulverized fuel ash and metakaolin replacements

Alkali-activated materials have great potential in reducing CO2 emissions in cement production industry. This study aims to investigate the corrosion propagation performance of alkali-activated slag mortars with various pulverized fuel ash (PFA) and metakaolin (MK) replacements subject to chloride-induced corrosion. The corrosion propagation performances including corrosion potential, corrosion rate and mortar electrical resistivity under wetting and drying cycles in seawater are studied. Scanning electron microscope (SEM), mercury intrusion porosimetry (MIP) and pH value measurement were conducted to analyze the effects of PFA and MK replacements on the relationship between reaction degree, pore structure, pH value and corrosion propagation performances. The results show that the MK replacement can enhance the corrosion propagation resistance of slag-based alkali-activated mortars under high activator concentration while the PFA replacement reduces the resistance to metallic corrosion of alkali-activated mortars. Mechanisms controlling the corrosion propagation are discussed.

Effect of water‐reducing admixtures water content on rheology, workability, and mechanical properties of fly ash‐based geopolymer and slag‐based alkali‐activated mixtures

AbstractAdmixtures used in concrete have been produced for conventional concrete and the behavior of these additives in geopolymer/alkali‐activated systems is still complicated. In this study, the effects of different types of water‐reducing admixtures on the fresh and mechanical properties of Class F fly ash‐based geopolymer mortars and alkali‐activated slag mortars were investigated. For this purpose, flow diameter, rheological examination, compressive and flexural strength tests were carried out. The data obtained showed that the admixtures used in the study did not have a positive effect on the fresh properties of geopolymer/alkali‐activated mortars, and the improvements in the flow properties were due to the extra water contributed by the admixture. The flow diameters of the mixtures containing the same amount of water with the mixture containing plasticizer were generally higher than those of the mixtures prepared with the admixture up to 10.3% in the fly ash‐based mortars and 15.4% in the slag‐based mortars. Addition of plasticizers reduced the compressive strength of fly ash‐based geopolymer and slag‐based alkali‐activated mortars up to 31.7% and 29.7%, respectively.

Performance of Self-Healed Alkali-Activated Slag Mortar at Elevated Temperature

Performance of Self-Healed Alkali-Activated Slag Mortar at Elevated Temperature

Durability performance of waste glass powder and calcium oxide added sodium carbonate-activated slag mortar

Cement manufacturing consumes large quantities of natural resources, emits considerable amounts of greenhouse gases, and brings harm to the environment. Alkali-activated cementation materials are promising candidates to replace ordinary Portland cement. However, Na2CO3-activated slag mortars suffer from long setting times, low early strengths, and poor durability. In this study, CaO and recycled waste glass were added to Na2CO3-activated slag mortars to overcome these issues. Accordingly, in this experiment, the effects of the CaO and glass powder (GP) contents on the setting time, fluidity, compressive strength, drying shrinkage, chloride ion electric flux, sulfate erosion, and fire resistance of Na2CO3-activated slag mortar were investigated. X-ray diffraction and nuclear magnetic resonance were used to characterize the reaction products and pore structure. It was found that the initial setting time and final setting time of slag mortar activated by sodium carbonate are more than 3 days. The setting time and fluidity of mortar decrease with the increase of calcium oxide. When 4% calcium oxide was added, the initial and final setting time was reduced to 95 min and 160 min, and the fluidity was reduced to 170. However, after GP replaced part of the slag, the setting time and mobility increased. The effect of CaO content on compressive strength and drying shrinkage of sodium carbonate activated slag mortar is similar (increasing first and then decreasing). The main reason may be that when CaO content is less than 6%, the calcite generated in the reaction fills the pores, which makes the number of pores in smaller pores (less than 50 nm) increase and the structure becomes more dense. GP is good for reducing drying shrinkage, but not good for early compressive strength. CaO is beneficial to improve the chloride ion erosion resistance of sodium carbonate activated slag mortar, which is related to the porosity and the adsorption of hydrotalc. The addition of GP has no effect on the improvement of chloride ion erosion resistance of CaO and sodium carbonate composite activated slag mortar, but the chloride ion electric flux is lower than 1200 C at 28 d. CaO and GP are beneficial to improve the resistance of alkali-excited slag mortar to sulfate attack. The effect of CaO on the resistance to sulfate attack is mainly related to the porosity and the content of hydrotalcite. The effect of GP on the resistance to sulfate attack is mainly related to the silicon and aluminum separated by GP. CaO and GP are beneficial to improve the fire resistance of alkali-excited slag mortar. The increase of fire resistance is related to decomposition temperature and content of reaction products. The combination of CaO and Na2CO3 to activate the slag and the addition of GP were significantly better than the use of only Na2CO3 to activate the slag.

Effects of Mud Content on the Setting Time and Mechanical Properties of Alkali-Activated Slag Mortar.

High mud content in the sand has a negative impact on cement mortar but there is little research on Alkali-activated slag (AAS) mortar. In order to explore the impacts of mud content in the sand on the performance of AAS mortar, this paper used sand that contains silt, clay, and a mixture of silt and clay; tested the setting time of AAS with different mud contents of 0%, 2%, 4%, 6%, 8%, and 10%; and measured the unconfined compressive strength and beam flexural strength of 3 d, 7 d, and 28 d AAS mortar specimens. The microstructure of AAS mortar with different kinds of mud was observed by scanning electron microscope (SEM), the elemental composition of the hydration product was tested by energy dispersive spectroscopy (EDS), and the AAS interaction mechanism with different kinds of mud was analyzed. The main conclusions are: the higher the mud content in the sand, the shorter the initial setting time and the longer the final setting time of AAS, mainly because the mud in the sand affects the hydration process; mud content above 4% causes a rapid decrease in the compressive and flexural strengths of AAS mortar, mainly because the mud affects the hydration process and hinders the bonding of the hydration product with the sand. When there is no mud in the sand, the main hydration product of AAS is dense calcium-alumina-silicate-hydrate (C-A-S-H) gel. When the sand contains silt, the hydration product of AAS is loose C-A-S-H gel. When the sand contains clay, the hydration products of AAS contain C-A-S-H gel and a small amount of sodium-aluminum-silicate-hydrate (N-A-S-H), and needle-like crystals. Loose gel and crystals have a negative effect on the AAS mortar strength.