Alkali-activated Slag Concrete Research Articles

Optimal Quantity Investigation of Metakaolin and Silica Fume in Production of Durable Acid Resistance Alkali Activated Slag Concrete

The urgent requirement to reduce greenhouse gas emissions during Portland cement production and to enhance the durability of concrete in destructive environments are essential reasons to seek other alternative materials like alkaline activated binders. In this study, the feasibility of producing durable alkali-activated slag-based concrete under deteriorative environmental conditions was studied using 0, 10, 20, 30, and 40% of metakaolin (MK) and 0, 5, and 10% of silica fume (SF) instead of ground granulated blast furnace slag (GGBFS) and optimizing contents through the response surface method (RSM).To evaluate the performance of studied alkali-activated slag-based concrete in an aggressive environment, the permeability and the reduction in compressive strength of alkali-activated slag-based concrete under sulfuric acid attack have been investigated. In addition, the mass change of specimens after exposure was measured. The results indicate that replacing 40% of the slag with metakaolin and 10% with silica fume in alkali-activated concrete has reduced 9% and 34.9% of the compressive strength at 28 days, respectively. Also, increasing MK replacement up to 40% increased the water absorption to 27.8%, but 10% SF replacement reduced it to 17.7%. In addition, the alkali-activated slag-based concrete mass changes after 90 days of acid exposure were 2.3%, while the replacement of slag by 40% of MK and 10% of SF reduced this value to 1.14%. However, it improved the durability performance of alkali-activated concrete against sulfuric acid attacks.

Effect of hybrid polypropylene fibers on mechanical and shrinkage behavior of alkali-activated slag concrete

The growing global demand for cement in construction led to an increase in environmental concerns from the carbon dioxide gas release associated with its production. To foster the acceptance of other alternatives, such as alkali-activated slag (AAS) systems, mitigation of their main drawbacks, notably high shrinkage, is imperative. This study explores the influence of macro and micro polypropylene (PP) fiber hybridization in AAS concrete. Seven mixes with different fiber volume fractions (VF) of macro and hybrid fibers, in addition to a control mix, were investigated. Three macro-PP fiber mixes had fiber VFs of 0.3 %, 0.6 %, and 0.9 %. The other three hybrid PP fiber mixes were like macro fiber mixes with the addition of 0.1 % microfibers. The influence of PP fiber hybridization was explored concerning flowability, static elastic modulus, compressive, splitting tensile, and 3-point flexural strength and compared to control and macro-PP fiber mixes. Additionally, Shrinkage was measured for control and optimum fiber mixes. The results showed that the hybridization of PP fibers led to reductions in shrinkage up to 15 % compared to the control mix, while macro-PP fibers reached a maximum reduction of 6 %. Furthermore, the study evaluates the applicability of various literature and current code guidelines for predicting elastic modulus and tensile strength with the experimental results. ACI 318 could provide relatively accurate predictions in terms of splitting tensile and flexural strengths. Apart from that, with some exceptions, other codes and proposed equations in the literature were inadequate in providing satisfactory predictions.

Effect of CaO/SiO2 and Al2O3/SiO2 on the chloride permeability of one-part alkali-activated nickel slag concrete

To study the effect of CaO/SiO2 and Al2O3/SiO2 ratios on the chloride permeability of one-part alkali-activated nickel slag (AANS) concrete, the chloride ion electromigration coefficient and the distribution of total chlorine concentration at different permeability depths of the one-part AANS concrete were investigated. The ratio of CaO/SiO2 and Al2O3/SiO2 of cement were designed in the range of 0.85–1.3 and 0.3–0.75, respectively. The reaction product and pore structure of paste were analyzed. The Results showed that the total chloride ion concentration in concrete first decreased and then increased with CaO/SiO2 and Al2O3/SiO2 ratios increasing. The chloride permeability of the concrete with CaO/SiO2 of 1.0 and Al2O3/SiO2 of 0.45 was the lowest, as the hydration degree of the concrete was the highest, which effectively optimized the pore structure. The chloride ion migration coefficient of concrete decreased with porosity, and an exponential relationship was observed between the chloride ion migration coefficient with porosity.

The influence of additive MgO and its content on the carbonation resistance of alkali-activated slag concrete with different activators

The influence of additive MgO and its content on both the compressive strength and carbonation depth of alkali-activated slag concrete (AASC) was investigated under an accelerated carbonation environment. Furthermore, the modification mechanism of MgO on the carbonation resistance of AASC was explored by multiple analytical techniques. Results showed that the incorporation of MgO effectively enhanced the post-carbonation compressive strength and diminished the carbonation depth of concrete. As the MgO content increased, there was a gradual reduction in carbonation depth. The incorporation of MgO promotes the hydration of slag, altering the Al environment, and promoting the formation of C-S-H and Mg-Al hydrotalcite phases. Moreover, the addition of MgO resulted in the emergence of magnesium carbonate and calcium magnesium carbonate in the carbonation products, which filled the pores and prevented the further diffusion of CO2 into the interior. In addition, the improvement effects are more pronounced in the water glass system compared to the NaOH system.

In-situ shrinkage measurement of alkali-activated materials using focused ion beam combined with environmental scanning electron microscopy

Drying shrinkage of alkali-activated slag (AAS) has gained significant attention since the volumetric instability of this material can generate premature cracking and degrade the long-term durability of concrete structures. The unique shrinkage behavior of AAS originates mainly from the particular characteristics of its main hydrated products. However, few studies have even at-tempted to investigate the shrinkage behavior of hydrated products in AAS materials. This paper presented a new method of investigating drying shrinkage behavior of AAS using focused ion beam (FIB) combined with environmental scanning electron microscopy (ESEM). This innovative experimental method allowed the in-situ measurement of phase-specific shrinkage. The results showed FIB/ESEM technique can be successfully implemented to cementitious material to prepare phase-specific samples. Furthermore, object-oriented finite element method (OOF2) has been utilized to compute the shrinkage behavior of AAS concrete using a proposed multi-scale scheme. The computations can be made at multi-scales which highlight the effect of hydration products on shrinkage behaviors. OOF2 calculation at the micro-length scale predicted an increase in the shrinkage due to the well-dispersed hydration products inside the matrix. At larger scale, the decrease in the overall shrinkage is related to the extremely low shrinkage value by aggregates. The findings reveal OOF2 offers the capability to accurately measure local stress and strain distribution within heterogeneous materials, a feature notably absent in conventional numerical homogenization approaches. The importance of this benefit is highlighted particularly in the context of free-restrained shrinkage prediction, as conventional homogenization methods fail to account for stress.

Experimental Studies on Self-Compacting Alkali Activated Slag Concrete Mixes Incorporating Reclaimed Asphalt Pavement as Fine Aggregate

Here performance evaluation of Self Compacting Alkali Activated Slag Concrete incorporating Reclaimed Asphalt Pavement as fine aggregate was carried out. Investigation on mechanical properties by replacing the fine aggregate by Reclaimed Asphalt Pavement in different proportions were also evaluated. Development of Self Compacting Alkali Activated Concrete mixes (SCAAC) was made with GGBFS and Lime are used binders, with binder content varying between 550 to 650 kg/m3 of fresh concrete and lime content varying from 10% to 20% of binder content. The net W/B ratio of the mixes was kept around 0.57. The fine aggregate was replaced by Reclaimed Asphalt Pavement with percentage replacement from 50 to 100% of Crushed Stone Sand. The alkaline solutions had Na2O dosage percentages in the range 5-6% with a constant activator modulus maintained at 1. By using Minitab Statistical Software nine mixes were produced with 4 factors and 3 levels. In this study the TOPSIS (Technique for Order of Preference by Similarity to Ideal Solution) optimization technique was carried out to know the effectiveness. Results showed the slump flow greater than 650 mm, with their L–Box, U-box and V-Funnel values ranging between 0.85,20mm and10s respectively, results showed enhanced mechanical properties as compared to control OPCC mix.

Performance of Alkali-Activated Slag Concrete Masonry Blocks Subjected to Accelerated Carbonation Curing

This study investigates the effect of accelerated carbonation curing on the carbon sequestration potential, performance, and microstructure of alkali-activated slag mixes representing concrete masonry blocks (CMBs). The carbonation curing process parameters varied, including initial curing duration, carbonation curing duration, and carbonation pressure. Research findings showed that a maximum CO2 uptake of 12.8%, by binder mass, was attained upon exposing concrete to 4 h initial curing and 20 h carbonation curing at a pressure of 5 bars. The compressive strength and water absorption capacity improved with longer initial and carbonation curing durations and higher pressure. Upon subjecting to salt attack, the mass and strength of 28-day concrete samples increased, owing to the formation of Friedel’s salt and Halite. All mixes could be used as non-load-bearing CMB, with a 1-day strength greater than 4.1 MPa. Based on the global warming potential index, the carbon footprint of carbonation-cured, alkali-activated slag concrete masonry units was up to 46% lower than non-carbonation-cured counterparts. Research findings offer valuable information on the production of carbonation-cured, cement-free concrete masonry blocks to replenish natural resources, recycle industrial waste, and mitigate CO2 emissions.

Parametric Sensitivity Analysis of High-Strength Self-compacting Alkali-Activated Slag Concrete for Enhanced Microstructural and Mechanical Performance

Parametric Sensitivity Analysis of High-Strength Self-compacting Alkali-Activated Slag Concrete for Enhanced Microstructural and Mechanical Performance

Experimental Studies on Bagasse Ash-Based Self-Compacting Alkali Activated Slag Concrete

In the present study, an attempt was made to develop Self Compacting Alkali Activated Slag Concrete mixes incorporating Bagasse Ash as binder content. This study investigates the physical and mechanical properties of Bagasse Ash based Self Compacting Alkali Activated Slag Concrete (BSAASC) with varying proportions of Bagasse Ash. Lime and GGBS (Ground Granulated Blast Furnace Slag) are used along with Bagasse Ash as binder materials in the BSAASC. The total binder content was restricted to 600kg/m3 containing Bagasse Ash at 10%, 20% and 30% of total binder content. The solution-to-binder ratio was 0.6. the dosage of Na2O was varied by 5%, 6% and 7%. The molarity of the alkaline solution is 1M. By using Minitab Statistical Software nine mixes were produced with 3 factors and 3 levels. The analysis was done by Desirability Function Approach (DFA) to check the effectiveness of the considered factors. The workability tests for properties of concrete samples are carried out according to EFNARC guidelines. Microstructural studies such as SEM, EDX and XRD analysis were also carried out, showing denser morphologies indicating effective activation of slag by the alkaline solution.

Durability of alkali-activated slag concrete incorporating silica fume and rice husk ash

To improve the mechanical properties and durability of alkali-activated slag concrete (AASC), as well as to reduce carbon emissions and exploitation of natural resources. This paper attempts to introduce rice husk ash (RHA) and silica fume (SF) into the AASC system. The effects of RHA and SF on the physical properties (water absorption and density), mechanical properties (flexural strength and compressive strength), and durability properties (dry shrinkage, resistance to sulfuric acid attack and carbonation) of AASC are examined. The optimization mechanisms are also explored from the points of pore structure and microstructure analysis. The experimental results suggest that RHA and SF can substantially reduce water absorption and improve the mechanical and durability properties of AASC. Remarkably, adding 10 wt% RHA into concrete can reduce the water absorption by 42%, increase the strength by 9.7–20%, the resistance to sulfuric acid attack by 26.91%, and the resistance to carbonization by 54.4%. Unfavorably, its dry shrinkage increases by 3.2–33%. Microstructural investigations demonstrate that the addition of RHA and SF to the AASC system provides an additional source of silica, which could have a filler effect, pore refinement, and pozzolanic nature. Moreover, RHA has more silica content than SF, and the particle size of RHA is finer and the reaction is more adequate, so the effect is more remarkable. The findings of the study suggest that RHA and SF demonstrate promising prospects in improving the durability and sustainability of AASC.

Influence of bagasse ash powder and marble powder on strength and microstructure characteristics of alkali activated slag concrete cured at room temperature for rigid pavement application

In this research, an attempt is made to partially replace ground granulated blast furnace Slag (GGBS) with a binder rich in SiO2 and CaO in alkali activated slag concrete (AASC) to increase workability and setting time. GGBS is replaced with bagasse ash powder (BAP) in 5%, 10%, and 15% of the binary mix, and subsequently with marble powder (MP) in 5% and 10% of the binary mix. After establishing the best mix for both binder replacements, a ternary mix with 5% BAP and 10% MP is created. The fine aggregates used in the comparison are 100 % river sand and slag sand. 10 M sodium hydroxide and the alkaline to binder ratio is 0.4, were used. Mechanical properties such as compressive strength, split tensile strength, and flexural strength are performed cured at 1, 3, 7, and 28 days samples. To further understand the intrinsic mechanism of strength development, microstructure, morphology and mineralogy on AASC are investigated. Based on the findings, it can be inferred that AASC mixes have a higher strength than OPC mixes. The mechanical strengths of the AASC binary mix with 10% MP and 5% BAP are higher. The microstructural analysis reveals the mixes developed with BAP and 100 % GGBS, had a denser microstructure than the normal mixes. The mechanical properties obtained for most of the AASC mixes are significantly higher than the IRC SP:62-2014 recommendations for rigid pavements for low volume roads.

Effect of Activator Concentrations on the Postfire Impact Behavior of Alkali-Activated Slag Concrete

Changing concrete ingredients significantly affects its performance due to changing the type of hydration products formed. The stability of these hydration products will dominate concrete impact behavior before and after exposure to fire. Limited research had explored the role of activators, as the main ingredient of alkali-activated slag concrete (AASC), on impact performance. Hence, this study highlights the effects of activator characteristics on the impact behavior of AASC at an ambient condition (23°C) and after exposure to elevated temperatures (200°C, 400°C, and 600°C). Conventional ordinary portland cement (OPC) concrete was also tested for general performance comparison. Besides the drop weight impact test, compressive and indirect splitting tensile strength, shrinkage, ultrasonic pulse velocity and water absorption tests were conducted to evaluate AASC performance. In addition, thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM) were used to confirm and analyze findings. Results confirmed the better impact performance of AASC compared to OPC concrete. Activator concentrations showed contrary effects on AASC performance at ambient and elevated temperatures. High activation levels improved strength and impact capacity at ambient temperature, showing lower internal defects and higher hydration product formation. Conversely, lowering the activation level at elevated temperatures was preferable and resulted in a higher residual strength and impact absorption capacity. This was ascribed to the high unreacted slag particle crystallization to akermanite at higher temperatures, leading to strength gain, fewer hydration products to decompose, and high microstructure ductility that accommodated the thermal incompatibility. Hence, designing AASC while focusing only on maximizing strength can be misleading based on the targeted performance and exposure conditions.

Realistic Evaluation of Reinforcement Bond Strength in Alkali-Activated Slag Concrete Exposed to Elevated Temperature

Alkali-activated concrete (AAC) has attained great popularity since finding it as an alternative to Portland cement concrete due to its superior characteristics in terms of mechanical properties and durability, and its low negative environmental impact. This research investigated both experimentally and analytically the bond behavior between alkali-activated slag concrete (AASC) and steel rebars considering some important parameters (rebar diameter and development length-to-diameter ratio) before and after exposure to elevated temperature using beam-end bond testing technique. The obtained experimental results were compared with those obtained from applying the CEB-FIP model and the well-known available equations in the literature. A modified model was proposed for predicting the bond behavior of AASC. Results have showed that the CEB-FIP model provides more conservative values for bond strength compared to the experimentally obtained results which increases the safety level when estimating the bond strength for design purposes. The proposed modified model achieved a higher correlation with the experimental results than the CEB-FIP model at ambient temperature.

State-of-the-Art Report: The Self-Healing Capability of Alkali-Activated Slag (AAS) Concrete.

Alkali-activated slag (AAS) has emerged as a potentially sustainable alternative to ordinary Portland cement (OPC) in various applications since OPC production contributed about 12% of global CO2 emissions in 2020. AAS offers great ecological advantages over OPC at some levels such as the utilization of industrial by-products and overcoming the issue of disposal, low energy consumption, and low greenhouse gas emission. Apart from these environmental benefits, the novel binder has shown enhanced resistance to high temperatures and chemical attacks. However, many studies have mentioned the risk of its considerably higher drying shrinkage and early-age cracking compared to OPC concrete. Despite the abundant research on the self-healing mechanism of OPC, limited work has been devoted to studying the self-healing behavior of AAS. Self-healing AAS is a revolutionary product that provides the solution for these drawbacks. This study is a critical review of the self-healing ability of AAS and its effect on the mechanical properties of AAS mortars. Several self-healing approaches, applications, and challenges of each mechanism are taken into account and compared regarding their impacts.

Impact Behaviour of Steel-Fibre-Reinforced Alkali-Activated Slag Concrete Exposed to Elevated Temperatures.

Concrete protective structures are mainly meant to withstand impact loads. However, fire events weaken concrete and reduce its impact resistance. This study investigated the impact behaviour of steel-fibre-reinforced alkali-activated slag (AAS) concrete before and after exposure to elevated temperatures (i.e., 200 °C, 400 °C, and 600 °C). Hydration products' stability under elevated temperatures, their effects on the fibre-matrix bond, and, consequently, AAS's static and dynamic responses were investigated. The results reveal that adopting the performance-based design concept to achieve a balance between AAS mixtures' performance under ambient and elevated temperatures is a crucial designing aspect. Advancing hydration products' formation will increase the fibre-matrix bond at ambient temperature while negatively affecting it at elevated temperatures. High amounts of formed and, eventually, decomposed hydration products at elevated temperatures reduced the residual strength due to lowering the fibre-matrix bond and developing internal micro-cracks. Steel fibre's role in reinforcing the hydrostatic core formed during impact loads and delaying crack initiation was emphasized. These findings highlight the need to integrate material and structure design to achieve optimum performance and that low-grade materials can be desired based on the targeted performance. A set of empirical equations for the correlation between steel fibre content in the AAS mixture and corresponding impact performance before and after fire exposure was provided and verified.

Experimental study on basic and drying creep for an alkali‐activated slag concrete and comparison with existing creep models

AbstractSlag is a by‐product of the steel industry that can be activated using alkali solutions to form concrete. This study presents new experimental results of basic and drying creep behavior of alkali‐activated slag (AAS) concrete. Different parameters affecting creep such as loading age, sample size and creep stress‐strength ratio were varied for experimental studies. The results show that the basic creep of AAS concrete is higher than that of ordinary Portland cement (OPC) concrete. The drying creep of AAS is lower than for OPC and this could be explained by a higher internal drying during the activation of slag. The experimental results were used to check the applicability of two existing engineering models, the fib MC 2010 and the B4s model, for AAS concrete. It was found that both models could be extended to predict the basic creep of AAS concrete. For drying creep, the B4s could better capture the creep behavior. For the fib MC 2010, a new formulation for drying creep would be required.

Thermal-Related Stress-Strain Behavior of Alkali Activated Slag Concretes under Compression.

In this paper, the thermal-related stress-strain behavior of alkali-activated slag (AAS) concretes, with different alkali concentrations and moduli, was studied under compression. After exposure to high temperatures (200 °C, 400 °C, 600 °C, 800 °C, and 1000 °C), a compression test was carried out on the specimens. The stress-strain relationship, axial compressive strength, and elastic modulus were expressed using both a displacement extensometer and the digital image correlation (DIC) technique. It was mainly determined that: (1) With the increase in temperature, the stress-strain curves of the AAS concretes tended to be flattened, indicating reductions in both axial compressive strength and elastic modulus. After 1000 °C, only 2.5-3.7% axial compressive strength and 1.4-3.9% elastic modulus remained, respectively. (2) The DIC technique was used for thermal strain measurements of the AAS concrete. Compared to the traditional extensometer, DIC yielded a small error of 4.5% and 7.2% for axial compressive strength and elastic modulus measurements, respectively. The strain cloud chart obtained from DIC was helpful for monitoring the damage process of the specimens. The findings of this paper refined scientific systems of AAS concrete under thermal action, and also provided a newly non-contact approach for thermal strain measurements of AAS concrete under compression.

Multi-scale experimental investigation and analytical micro-mechanical modeling to determine Young’s modulus of alkali-activated slag concrete

In this study, multi-scale experiments and analytical micro-mechanics based modeling are conducted to evaluate Young’s modulus of alkali-activated slag (AAS) concrete. The evolution of volume fractions of phases is obtained using a thermodynamic model coupled with a kinetic model. Nano-indentation measurements indicate the existence of a soft and a hard matrix made of reaction products, independently of the mix tested. The homogenization model for Young’s modulus is validated against results on paste and concrete with more than 95 % accuracy. Sensitivity analysis reveals Young’s modulus of aggregates and of the soft matrix as the main influencing parameters.

Post-fire impact behaviour of rubberized alkali-activated slag concrete

Rubberized concrete is eco-friendly concrete with improved impact resistance. However, impact loads may also be combined with fire due to blasting, explosions, and earthquake. Hence, this study investigates the post-fire impact behaviour for rubberized alkali-activated slag (AAS) concrete. Static and dynamic properties of AAS mixtures, incorporating 5%, 10%, and 15% crumb rubber, were evaluated under ambient and after exposure to elevated temperatures (200, 400, and 600 °C). Results reveal that AAS properties' degradations were similar to ordinary Portland cement (OPC) at ambient temperature. At elevated temperatures, the differences in hydration products’ nature between AAS and OPC alternated the performance. The formed low Ca/Si ratio calcium silicate hydrated in the AAS exhibited higher stability at elevated temperatures. AAS with 10% rubber content showed an optimum impact performance. Above 400 °C, degradation of the binder microstructure and voids due to rubber particle decomposition adversely affected the impact performance of AAS. The addition of 0.5% steel tire wire showed a high potential sustainable solution to maintain adequate performance.

An experimental study on the development of self-compacting alkali-activated slag concrete mixes under ambient curing

This study was carried out to develop alkali-activated blast furnace slag concrete having self-compacting properties under ambient curing. Ground Granulated Blast Furnace Slag was used as the binder, and the blended sodium silicate liquid and sodium hydroxide pellets were added to activate the GGBFS. Fine aggregate and coarse aggregate were replaced by unprocessed blast furnace slag and electric arc furnace slag. There were a huge number of parameters, such as binder content, water-binder ratio (w/b), Na2O% and activator modulus (Ms), that influence the fresh and hardened properties of self-compacting alkali-activated Slag concrete. Taguchi’s Design of Experiments (DOE) method was used to minimize the possible number of mixes to perform experiments. Taguchi’s DOE method uses a specific design based on the orthogonal arrays to understand the entire parametric space with a less number of possible experiments. Therefore, based on Taguchi’s DOE method, detailed experiments were carried out corresponding to only nine mixes known as calibration mixes. Mix-7 shows higher compressive strength (at 28 days), modulus of elasticity, split tensile and flexural strength are 46.2 M of 46.2 MPa, 30.27 GPa, 4.43 MPa and 5.31 MPa, respectively. The results of this study show that the 28 days mechanical strength of SCAASC mixes is most controlled by Na2O% followed by binder content (GGBFS), Ms value and w/b ratio.