Alkali-activated Slag Cement Research Articles

The formation of CaCO3-based binder by carbonating high-dosage Ca(OH)2 + slag + NaHCO3 (HCHSN) cement paste

Normally, carbonation can cause the decalcification of C-(A)-S-H gel of alkali-activated cement and the degradation of mechanical properties. While, we propose another possibility to form CaCO3-based binder by carbonating the alkali-activated slag cement of high-dosage Ca(OH)2 (30 %) + slag (70 %) + NaHCO3 (5.11 % by weight of Ca(OH)2 and slag) (HCHSN) in this study. The results supported that the compressive strength and volume stability of HCHSN cement paste can be improved by the carbonation curing and the carbonated HCHSN cement paste could reach a maximum compressive strength of 32.4 MPa. According to the micro-analysis of XRD, TGA, FTIR, 1H NMR, BSE and SEM, the carbonated HCHSN cement paste was developed into a CaCO3-based binder with a CaCO3 content approaching 60 % (based on the mass of the samples heated to 800℃). NaHCO3 played a key role in the formation of the CaCO3-based binder, which not only accelerated the carbonation rate, but also promoted the carbonation of slag. The eco-efficiency assessment showed that compared to the production of 12.5 kg CO2 /MPa/t from carbonated ordinary Portland cement, the carbonated HCHSN cement paste only produced 3.5 kg CO2 /MPa/t, making it a very green CaCO3-based cementitious materials.

A Review on Research Progress of Corrosion Resistance of Alkali-Activated Slag Cement Concrete.

China is the largest producer and user of Ordinary Silicate Cement (OPC), and rapid infrastructure development requires more sustainable building materials for concrete structures. Portland cement emits large amounts of CO2 in production. Given proposals for "carbon peaking and carbon neutralization", it is extremely important to study alternative low-carbon cementitious materials to reduce emissions. Alkali-activated slag (AAS) cement, a new green cementitious material, has high application potential. The chemical corrosion resistance of AAS concrete is important for ensuring durability and prolonging service life. This paper reviews the hydration mechanism of AAS concrete and discusses the composition of hydration products on this basis, examines the corrosion mechanism of AAS concrete in acid, sulfate, and seawater environments, and reviews the impact of its performance due to the corrosion of AAS concrete in different solutions. Further in-depth understanding of its impact on the performance of concrete can provide an important theoretical basis for its use in different environments and provides an important theoretical basis for the application of AAS concrete, so that we can have a certain understanding of the durability of AAS concrete.

РОЛЬ САСО3 У ФОРМУВАННІ МІЦНІСНИХ І ДЕКОРАТИВНИХ ВЛАСТИВОСТЕЙ ПОРОШКОВОГО ЛУЖНО-АКТИВОВАНОГО ШЛАКОПОРТЛАНДЦЕМЕНТНОГО БЕТОНУ

The article discusses approaches to the formation of compositions of alkali-activated decorative Portland slag cements containing Portland cement type CEM1 5...45% with high performance and decorative properties. The optimization of the compositions of decorative alkali-activated Portland slag cements was carried out using statistical methods for designing experiments. Finely dispersed TiO2 and CaCO3 additives with a whiteness of 90% were used as bleaching components. The alkaline component is sodium metasilicate in the form of a non-hygroscopic powder. The research carried out made it possible to obtain decorative Portland slag cements with a whiteness of 45...77%, which allows them to be used to produce colored cements with a wide range of colors from white to black. It has been established that alkali-active decorative Portland slag cements have an activity of 37...59 MPa at the age of 28 days. All compositions have good hardening dynamics and, based on the strength at the age of 2 days  22...36.6 MPa, they can be classified as fast-hardening. Based on them, it is possible to produce dry construction mixtures. All mortar compositions based on alkali-active decorative Portland slag cements demonstrate fairly high frost resistance  F200. This allows them to be used for the manufacture of products and solutions both for indoor use and when exposed to atmospheric influences without loss of design characteristics and decorative appeal. The inherent shrinkage strains of decorative alkali-activated Portland slag cements are 0.51...0.61 mm/m, which eliminates cracking and premature destruction of products. The use of the CaCO3 additive is especially effective for controlling the shrinkage deformations. Thus, the CaCO3 additive performs the functions of not only a decorative component, but also a structure-forming component. Concrete and mortar mixtures can be used to produce decorative products using the traditional method, extrusion, 3D printing on construction printers, etc. And not too long setting times and a rapid increase in strength make it possible to produce products without thermal treatment or with minimal consumption of thermal energy.

Correction: Comparison of thermogravimetry response of alkali-activated slag and Portland cement pastes after stopping their hydration using solvent exchange method

Correction: Comparison of thermogravimetry response of alkali-activated slag and Portland cement pastes after stopping their hydration using solvent exchange method

The Influence of FA Content on the Mechanical and Hydration Properties of Alkali-Activated Ground Granulated Blast Furnace Slag Cement

This study primarily investigates the effect of fly ash (FA) content on the mechanical properties and hydration performance of alkali-activated ground granulated blast furnace slag cement (AAGC) and compares the related properties with ordinary Portland cement (OPC). Additionally, we examined the hydration products; performed thermal analysis, MIP, and SEM; and determined chemically bound water and pH values of AAGC. The compressive strength of AAGC showed a retrogression phenomenon from 3 to 28 days, with the 14-day and 28-day compressive strengths of AAGC being higher than those of OPC. The AAGC with 20% FA content exhibited the highest 28-day compressive strength (75 MPa). The hydration heat release rate curve of OPC and AAGC was divided into the initial induction period, induction period, acceleration period, deceleration period, and steady period. As FA content increased, the 28-day pore volume of AAGC increased, while pH values and chemically bound water decreased. SEM images of AAGC with low FA content showed more microcracks.

Life Cycle Analysis Comparison of Stabilizing Materials for Expansive Soils

Expansive soils present significant challenges to infrastructure stability, necessitating the use of stabilizing materials. This study conducts a comprehensive life cycle analysis (LCA) research design to evaluate the environmental sustainability of various stabilizing materials for expansive soil. The study uses a quantitative analysis assessing materials, including cement, limestone, natural pozzolana, iron ore tailings, and geopolymers (especially alkali-activated slag cement). The method involves a comprehensive LCA, considering phases from raw material extraction through production, use, and disposal. The analysis reveals distinct differences in environmental impact. Cement and lime, common stabilizers, show a high carbon footprint. Natural pozzolana and iron ore tailings exhibit potential as supplementary cementitious materials with reduced environmental impact. Geopolymers, particularly alkali-activated slag cement, offer promising alternatives with lower carbon emissions. This research contributes insights into sustainable geotechnical practices, guiding material selection aligned with environmental goals for effective expansive soil stabilization.

Effects of different activators on autogenous shrinkage of alkali-activated slag cement

Despite the exceptional early strength of sodium silicate or sodium hydroxide-activated slags, much emphasis has always been drawn to the volume instability brought on by their autogenous shrinkage. In this study, a ternary composite activation system was developed by introducing sodium sulfate (Na2SO4), and the effect of Na2SO4-Na2O·1.5SiO2-NaOH ternary composite activators system on the autogenous shrinkage, setting time, and mechanical properties of alkali-activated slag (AAS) was investigated. The effect mechanism of different activator compositions on the autogenous shrinkage of AAS was discussed through the internal relative humidity (IRH), surface tension of pore solution, and microstructure analysis. According to experimental results, the surface tension of pore solution can be reduced and IRH increased by increasing Na2SO4 content in AAS. Additionally, the formation of crystals (anhydrite, ettringite, and thenardite) with specific expansion properties can effectively mitigate autogenous shrinkage in AAS with Na2SO4. The proportions of Na2O·1.5SiO2 and NaOH determine the extent to which Na2SO4 impact the autogenous shrinkage of AAS. An optimal composite activator composition for AAS was determined using a model analysis: When the content of Na2O·1.5SiO2 ranged from 5 % to 17 %, Na2SO4 content ranged from 40 % to 55 %, and NaOH content ranged from 33 % to 56 %, the AAS mortar exhibited a compressive strength exceeding 42.5 MPa at 28 days. Furthermore, the autogenous shrinkage strain of AAS paste remained below 1500 microstrain within 7 days, with an initial setting time surpassing 45 min and a final setting time under 390 min.

Comparison of thermogravimetry response of alkali-activated slag and Portland cement pastes after stopping their hydration using solvent exchange method

AbstractThe critical step for any subsequent instrumental analysis of cementitious binders is to stop their hydration reactions, i.e., to remove free water. One of the most available techniques is a solvent exchange method. However, the solvents are known to be strongly bound in ordinary Portland cement (OPC) paste and alter the results of thermogravimetric analysis (TGA) and sensitive hydrates, while their effect on TGA response of alkali-activated slag (AAS) has not been comprehensively investigated. Therefore, the objective of this paper is to track the effects of fundamental aspects of the solvent exchange on the TGA response of AAS with different sodium activators (hydroxide, carbonate, waterglass) and to support these results by X-ray diffraction and effluent gas analysis. All solvents used (acetone, diethyl ether, isopropyl alcohol, ethanol, and methanol) affected the TGA response of all tested pastes, and their effect was enhanced by prolonged immersion time. All solvents induced an additional mass loss at around 800 °C and, especially for OPC paste, increased in situ carbonation, even in an inert atmosphere. Methanol and ethanol had a detrimental effect on ettringite and decreased the basal distance of the C–(A)–S–H gel, while they only marginally affected gaylussite. For AAS, hydration stoppage by washing out the alkali-rich pore solution with water was also investigated and can usually be recommended (except for its detrimental effect on gaylussite), as it is more efficient than organic solvents, which lack solubility for activators. Methanol and ethanol are the most suitable alternatives, particularly for NaOH.

Design and evaluation of alkali-activated slag-calcined coal gangue cement and the shrinkage control by calcium carbonate whisker

The rapid solidification and significant shrinkage of alkali-activated slag cement are key issues that restrict its practical engineering application. This paper explores the composition design of alkali-activated cements (AAC) with slow coagulation and shrinkage reduction. This paper adjusts the proportion of slag (SG) and calcined coal gangue powder (CCGP), regulates the content of Na2O·2.4SiO2-NaOH-Na2CO3 ternary activator components, and uses calcium carbonate whiskers (CW) instead of SG to prepare AAC with slow coagulation and shrinkage reduction. When the activator is composed of (66 %) Na2O·2.4 SiO2-(2 %) NaOH-(32 %) Na2CO3 mixed composition, the CO32- and Ca2+ in the system react preferentially to produce CaCO3. The decrease of Ca2+ concentration delays the formation of C-(A)-S-H, resulting in the initial and final setting time of AAC reaching 334 min and 346 min, respectively. When the CW substitution rate is 3 %, the 28d compressive strength of AAC reaches 102.2 MPa. The 49d drying shrinkage of the AAC is 7020μm/m and the 49d autogenous shrinkage is 2387μm/m. This is attributed to the combined effect of enhancement mechanisms such as whisker bridging, crack deflection, whisker pullout, whisker–matrix coalition pullout and whisker breakage. This study establishes the relationship between the composition and performance of high performance AAC, which is significance for the resource utilization of coal gangue and the practical engineering application of AAC.

Analysis of strength characteristics and microstructure of alkali-activated slag cement fluidized solidified soil

In order to solve such as difficulties in backfilling narrow foundation trenches in engineering, it was proposed to use alkali-activated slag cement (AASC) instead of traditional Portland cement to solidify silt and form AASC fluidized solidified soil. The effect of the content of AASC and the curing period on fluidized solidified soil has been studied by unconfined compression strength test, SEM and EDS. Moreover, the root cause for the improvement of the strength by the microstructure was explored. The results showed that: The fluidity increased first and then decreased with the increase of the content of AASC; 40% was the optimal content; in the same curing period, the unconfined compression strength increased with the increase of the content; 40% was the optimal content; the soil with different contents could reach the most of the 28d strength on Day 7; AASC generated a lot of low-Ca/Si C-S-H gel that consolidated soil particles into a denser structure. These results provide a theoretical basis for the application of AASC in fluidized solidified soil engineering.

Investigating the promising effect of thermally-treated talc powder on the performance of alkali-activated slag cement

Investigating the promising effect of thermally-treated talc powder on the performance of alkali-activated slag cement

Projection-Pursuit Regression-Based Optimization of Frost Resistance and Mechanical Performance in Alkali-Activated Slag Cement Pavements

In recent years, applying slag micro-powder as a substitute for cement in preparing alkali-activated slag cement stabilized sand (AASCSS) mixtures has become increasingly widespread. In the severe cold regions of Xinjiang, multi-objective optimization of the mechanical and frost resistance properties of AASCSS is particularly crucial. This paper adopts slag micro-powder to replace Portland cement, together with lime and desulfurization gypsum as activators, to explore the effects of activator type and dosage on the mechanical and frost-resistance properties of AASCSS. A prediction model for the mechanical and frost-resistance properties of AASCSS based on projection-pursuit regression (PPR) was proposed and established. Using the developed PPR model, contour plots of the comprehensive performance were calculated, simplifying the multi-objective problem into two single-objective problems focusing on mechanical and frost resistance properties for analysis. This method avoids subjective weighting and hypothesis-based modeling. By analyzing the contour plots of comprehensive performance, the optimal performance indices for mechanical and frost–thaw properties and the corresponding types and dosages of activators can be directly determined. When the required 7-day unconfined compressive strength in road engineering is 5.6 MPa, the optimal value of the freeze–thaw performance index (BDR) is 94.08%. At this point, the corresponding lime content is 2.1%, and the desulfurization gypsum content is 3.3%. The research results provide a reference for applying slag to road-based materials.

Influence of Waste Coral Powder on the Properties of Alkali-Activated Slag Cement Prepared with Seawater

Influence of Waste Coral Powder on the Properties of Alkali-Activated Slag Cement Prepared with Seawater

Hydration Characteristics of Slag-Ca(OH)2-Al2O3 Binder in a 60 °C Curing Environment with Brine as Mixing Water

Recently, research results on PC-based or alkali-activated slag cement (AASC) using seawater as mixing water have been reported. Unlike seawater, reverse osmosis brine (brine) is waste discharged into the ocean from seawater desalination plants. There is a need to develop new and effective methods of disposing or utilizing brine to reduce marine pollution, protect marine ecosystems, and increase marine plant construction. However, research on cement or concrete using brine as a mixing water is very limited. Brine has almost the same composition as seawater, and the ion concentration is 2–4 times higher. Therefore, it is believed that new methods of using brine can be investigated and developed based on existing research and experimental results on seawater. The effects of brine and aluminum oxide (AO) on activated slag with calcium hydroxide (CH) were investigated for hydration and mechanical properties. 5% and 10% of CH were used, and samples using fresh water (FC) were prepared at the same time for comparison with brine. The slag sample without CH has a low initial (1 and 3d) strength of about 10 MPa for both FC and brine, but increases rapidly from 7d. Incorporation of CH was effective in improving the mechanical performance of FC and brine samples. In addition, the brine sample exhibited higher strength than the FC sample because it formed fewer C3AH6 phases that cause volume instability than the FC sample and affected the hydration promotion of slag particles. And more calcite phases were observed in the brine samples than in the FC samples. Through this study, the possibility of using brine as a building material was confirmed. In addition, the effect of chloride ion adsorption of slag mixed with AO and CH on the physical properties and mechanical performance of the hydration reaction was confirmed.

Experimental Study and Numerical Modeling of the Solidification Capacity of Chloride Ions in Alkali-Activated Slag Cement Exposed to Sodium Chloride

Experimental Study and Numerical Modeling of the Solidification Capacity of Chloride Ions in Alkali-Activated Slag Cement Exposed to Sodium Chloride

How does carbonation of alkali-activated slag and Portland cement systems impact steel corrosion differently?

Carbonation of cementitious materials, associated with neutralization of pore solution, is one of the prevalent reasons for inducing corrosion of steel in concrete. Compared with ordinary Portland cement (OPC) concrete, the poorer carbonation resistance of alkali-activated slag (AAS) concrete leads to serious durability concerns of a higher risk of steel corrosion. This work investigates the corrosion behaviors of steel embedded in intact and carbonated AAS and OPC mortars exposed to various relative humidity conditions, with the aim of fostering a better understanding of how carbonation impacts steel corrosion differently in these two cementitious systems. The results show that uncarbonated AAS mortars have better protective ability against corrosion than OPC counterparts; however, poorer performance after complete carbonation. It is mainly attributed to the combined effect of severe deterioration and coarsening of pore structure and increased ratio of chloride ion concentration to hydroxide ion concentration ([Cl−]/[OH−]) in pore solution, resulted from the consumption of hydroxide ions and release of bound chloride after carbonation. Besides, the different shifts of R-C (material resistivity versus corrosion rate) relationship lines in AAS and OPC mortars after carbonation are observed, which is ascribed to the different compositional and microstructural evolutions induced by carbonation in these two cementitious systems.

Corrosion of ribbed carbon steels in ecological mortars and its influence on their rotative fatigue behavior

Ribbed carbon steel rebars were embedded in mortars manufactured with three different eco-friendly binders (alkali-activated slag, and slag and fly ash-based hybrid cements) and with a commercial cement (CEM IV). This research evaluates the corrosion of reinforcements, fully assessed by natural diffusion, and its impact on the fatigue performance of the bars. Results obtained after 17-month corrosion testing on reinforced innovative mortars reveal that different pit morphologies and locations appear on the bars depending on the mortar composition, with the extent of the attack being related to the pH and the free-chloride content in each mortar. Rotative fatigue tests of the corroded bars have proven that the reduction of the fatigue life is dependent on the global extent of the corrosive attack, when the shape and distribution of the pits correspond to those generated exclusively by chloride diffusion in mortars. Bars corroded in alkali-activated slag and CEM IV mortars shown the best fatigue performances.

An eco-friendly and low-cost superhydrophobic alkali-activated Portland slag cement mortar

Alkali-activated slag cement (AASC) has shown immense potential for application as a low-carbon and eco-friendly cementitious material. It’s crucial to modify the AASC with superhydrophobic property to obtain excellent durability performance. In this paper, low-cost and non-toxic stearic acid (SA) is selected as a hydrophobic agent to impart integral hydrophobic property to the alkali-activated Portland slag cement mortar (AAPSCM). The SA-modified AAPSCM (M-AAPSCM) shows superhydrophobicity with a contact angle of 150.6° and a sliding angle of 9.5°, even when hammered to reveal its broken inner structure. The characterization analysis indicates that stearic acid not only successfully grafts onto the mortar surface but also forms calcium stearate, which successfully reduces the surface energy of the material. Combined with the porous rough structure constructed by medium sand and ethanol volatilization, the originally hydrophilic material achieves hydrophobic modification under the dual synergistic effect. The M-AAPSCM reached a compressive strength of 20.8 MPa after 28 days of curing, satisfying the requirements for hydraulic engineering applications. And the M-AAPSCM not only exhibits an excellent self-cleaning ability against contaminants like sand particles and chalk powder, but also demonstrates remarkable mechanical robustness, even after being subjected to blade scratching or mechanical fracture. Concurrently, the initial and final setting times of M-AAPSCM were determined to be 32 minutes and 41 minutes respectively, demonstrating its rapid-setting characteristic. Additionally, following the hydrophobic modification, AAPSCM effectively overcomes its inherent issues of severe autogenous shrinkage and poor carbonation resistance. Furthermore, when compared with the ordinary AAPSCM (O-AAPSCM), the durability of the M-AAPSCM against dry-wet cycles, icing, and freeze-thaw cycles is significantly enhanced.

Leaching kinetics and reactivity regulation of red mud in an NaOH solution

Red mud is an alkaline silico-aluminous solid waste with application potential in alkali-activated slag cement, determined by the leaching activity of Si, Al, and Ca ions in an alkaline solution. This study investigated the reactivity and leaching kinetics of silica and alumina in red mud in an NaOH solution. The leaching kinetics of Si and Al ions were investigated through inductively coupled plasma emission spectroscopy, X-ray diffraction, scanning electron microscopy, and Fourier transform infrared absorption spectroscopy. Leached Si and Al primarily contributed to N-(C)-A-S-H formation. Diffusion across the product layer governed the leaching process of red mud in the NaOH solution. The activation energies for Si and Al leaching were 16.368 and 23.037 kJ/mol, respectively. Adding slag powder activated the chemical bonds between Si-O and Al-O, increasing the leaching activity of the red mud. This study clarified the interrelationships between the physicochemical properties, leaching behaviour, and reactivity of red mud.

Investigation into the alkali-activation of lithium slag: A sustainable alternative to conventional cement with optimized mechanical properties

Utilizing lithium slag as a precursor for alkali-activated cementitious materials offers a sustainable alternative to conventional cement, addressing both environmental pollution and land-use challenges posed by lithium slag waste. Additionally, this practice reduces energy consumption and CO2 emissions associated with cement production. This study presents a novel methodology involving high-temperature calcination and mechanical grinding to enhance the reactivity of lithium slag. Analytical techniques, such as X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR), were employed to elucidate the mechanisms behind lithium slag's increased reactivity. Subsequently, these activated materials were used to formulate alkali-activated lithium slag cement composites (ALC). Various factors, including the calcination temperature, water-to-cement ratio, NaOH concentration, and lithium slag content, were investigated for their effects on the fluidity and mechanical properties of the mortar. Analytical techniques including XRD, scanning electron microscopy (SEM)/energy dispersive spectroscopy (EDS), FTIR, and thermogravimetric analysis (TGA)/derivative thermogravimetry (DTG), were used to explore the hydration mechanisms. Results indicate that the optimal calcination temperature for lithium slag was 700 °C, while the optimal NaOH concentration was 1 mol/L. ALC exhibited robust mechanical properties, with compressive, flexural, and fluidity measures reaching 37.66 MPa, 10.13 MPa, and 200 mm, respectively. Predominant hydration products were found to be N-A-S-H and C-A-S-H. The production cost of 1 ton of ALC is $49.8, which is roughly 70% of the cost of producing 1 ton of OPC. Additionally, the total CO2 emissions and energy consumption of producing ALC amount to 60.56% and 64.95% respectively, compared to the total CO2 emissions and energy consumption of producing 1 ton of OPC.