Alkali-activated Slag Concrete Research Articles

Compressive Strength Prediction of Alkali‐Activated Slag Concretes by Using Artificial Neural Network (ANN) and Alternating Conditional Expectation (ACE)

Compressive strength of alkali‐activated slag (AAS) concrete is influenced by multi‐factors in a nonlinear way. Both artificial neural network (ANN) and alternating conditional expectation (ACE) models of 3‐day (3 d) and 28‐day (28 d) compressive strength of AAS were established in this study by using the data reported in related literature, where alkali concentration of activator (Na2O%), modulus of activator (Ms), water/binder ratio (W/B), surface area of slag (SA), and basicity index of slag (Kb) were taken as input parameters. The models were employed later to predict 3 d and 28 d compressive strength of AAS concretes, respectively, and the results were validated by experimental work. The results show that both the ANN and the ACE models had adequate accuracy, no matter 3 d or 28 d compressive strength was considered. Compared to the 3 d compressive strength, due to data scattering that increased with the increase of data size, both the models did not yield a higher accuracy in the case of 28 d strength. However, also due to the increase in data size, both the models were more feasible to implement 28 d strength prediction as a result of sufficient learning and training during modeling. In addition, based on ACE analysis, the weight‐influencing compressive strength of AAS decreased in a sequence of Na2O% > Ms > W/B > Kb > SA. If data size was sufficiently large, it was more suitable to establish an ANN model for compressive strength prediction of AAS concretes. Otherwise, ACE could be considered as an alternative to yield an acceptable result.

Effect of fiber content and stress–strength ratio on the creep of basalt fiber–reinforced alkali‐activated slag concrete

AbstractAlkali‐activated materials are increasingly being used in practical applications as potential alternatives to Portland cement. If alkali‐activated slag (AAS) is to be applied to prestressed engineering and large‐size structures, it is necessary to study the creep performance of AAS. Existing studies have found that the creep of AAS concrete is larger than that of ordinary Portland cement (OPC) concrete, and adding fiber is an effective way to overcome this defect. In this study, we investigated the creep of basalt fiber–reinforced AAS (FRAAS) concrete for fiber contents ranging from 0% to 0.9% (by volume) at a stress–strength ratio of 0–0.6. After analyzing the experimental results, it was found that the basalt FRAAS concrete had no obvious linear creep range. It was observed that with an increase in the fiber content, the inhibition effect of fiber on creep became stronger initially and then weaker. The inhibitory effect of fiber on creep was strengthened by the increase in the stress–strength ratio. The creep coefficient showed no obvious change when the fiber content was in the range of 0%–0.9%. Based on the existing OPC concrete creep models, a method for predicting the creep of basalt FRAAS concrete was proposed.

Durability and microstructure study of alkali-activated slag concrete with quartz sand subjected to different exposure conditions

PurposeOne of the sources for the increase in the carbon footprint on the earth is the manufacturing of cement, which causes a severer environmental impact. Abundant research is going on to diminish CO2 content in the atmosphere by appropriate utilization of waste by-products of industries. Alkali-activated slag concrete (AASC) is an innovative green new concrete made by complete replacement of cement various supplementary cementitious raw materials. Concrete is a versatile material used in different fields of structures, so it is very important to study the durability in different exposures along with the strength. The purpose of this paper is to study the performance of AASC by incorporating quartz sand as fine aggregate under different exposure conditions.Design/methodology/approachThe materials for this innovative AASC are selected based on preliminary studies and literature surveys. Based on numerous trials a better performance mix proportion of AASC with quartz sand is developed with 1:2:4 mix proportion, 0.8 alkali Binder ratio, 19 M of NaOH and 50% concentration of Na2SiO3. Subsequently, AASC cubes are prepared and exposed for 3, 7, 14, 28, 56, 90, 112, 180, 252 and 365 days in ambient, acid, alkaline, sulfate, chloride and seawater and tested for compressive strength. In addition, to study the microstructural characteristics, scanning electron microscope (SEM), energy dispersive X-ray analysis and X-ray diffraction analysis was also performed.FindingsLong-term performance of AASC developed with quartz sand is very good in the ambient, alkaline environment of 5% NaOH and seawater with the highest compressive strength values of 51.8, 50.83 and 64.46, respectively. A decrease in compressive strengths was observed after the age of 14, 56 and 112 days for acid, chloride and sulfate exposure conditions, respectively. SEM image shows a denser microstructure of AASC matrix for ambient, alkaline of 5% NaOH and seawater.Research limitations/implicationsThe proposed AASC is prepared with a mix proportion of 1:2:4, so the other proportions of AASC need to verify. In general plain, AASC is not used in practice except in few applications, in this work the effect of reinforced AASC is not checked. The real environmental exposure in fields may not create for AASC, as it was tested in different exposure conditions in the laboratory.Practical implicationsThe developed AASC is recommended in practical applications where early strength is required, where the climate is hot, where water is scarce for curing, offshore and onshore constructions exposed to the marine environment and alkaline environment industries like breweries, distilleries and sewage treatment plants. As AASC is recommended for ambient air and in other exposures, its implementation as a construction material will reduce the carbon footprint.Originality/valueThe developed AASC mix proportion 1:2:4 is an economical mix, because of low binder content, but it exhibits a higher early age compressive strength value of 45.6 MPa at the age of 3 days. The compressive strength increases linearly with age from 3 to 365 days when exposed to seawater and ambient air. The performance of AASC is very good in the ambient, alkaline environment and seawater compared to other exposure conditions.

Stress-Strain Relationship of Steel Fiber Reinforced Alkali Activated Slag Concrete under Static Compression

Stress-strain curve can accurately reflect the mechanical behavior of materials, and it is very important for structural design and nonlinear numerical analysis. Some cube and prism specimens were made to investigate the physical and mechanical properties of steel fiber reinforced alkali activated slag concrete (AASC); test results show that the strength, Young’s Elastic Modulus, and Poisson’s ratio all increase with the increase of steel fiber content. The steel fiber reinforced AASC shows an excellent postcracking behavior. Damage evolution parameter (D) was used to describe the formation and propagation of cracks, and continuum damage evolution model of steel fiber reinforced AASC was established by Weibull and Cauchy distribution. The establishing model can well describe the geometric characteristics of the key points of the concrete materials stress-strain curve. Finally, the accuracy of the model was verified by comparing the test stress-strain relationship curve of steel fiber reinforced AASC.

Alkali-activated slag cellular concrete with expanded polystyrene (EPS) – physical, mechanical, and mineralogical properties

With better deformation capacity and less resistance than conventional concrete, cellular concrete with expanded polystyrene (EPS) is a more suitable alternative for obtaining concrete with a low specific mass. Since the late 1980s, alkali-activated slag concrete (AASC) without Portland cement has been gaining attention. However, no comprehensive study has been conducted to analyze blast furnace slag as a binder in the mixture of cellular concrete with EPS; further, the effects of the variation in water/binder ratios (w/b) on the characteristics of the foam have not been sufficiently studied. Tests using X-ray diffraction, thermogravimetry, ultrasound, resistance to axial compression, and absorption demonstrate the behavior of cellular concrete with an apparent density below 800 kg/m³ and mechanical resistance of 3 MPa. This work introduces an innovative application of the AASC for producing cellular concrete using EPS, as the foam with this type of binder seems more common.

Effect of fibre dosage and stress-strength ratio on creep of polypropylene fibre-reinforced alkali-activated slag concrete

Effect of fibre dosage and stress-strength ratio on creep of polypropylene fibre-reinforced alkali-activated slag concrete

Mix Design Effects on the Durability of Alkali-Activated Slag Concrete in a Hydrochloric Acid Environment

Because of its high strength, energy reduction, and low environmental impact, researchers have encouraged considering alkali-activated slag concrete (AASC) as a potential alternative to conventional concrete. In this study, the impact of mix design parameters on the durability of AASC, made with ground granulated blast furnace slag and activated with different alkaline solutions (NaOH, KOH, and Na2SiO3) immersed up to six months in a hydrochloric acid bath with pH = 3, has been investigated. A total of 13 mix designs were made in a way that, in addition to the type of alkaline solution, considered three other parameters, namely the molarity of alkaline solutions, the weight ratio of alkaline solutions to slag, and the weight ratio of alkaline solutions to sodium silicate. Visual inspections displayed that the AASC samples almost remained intact after exposure to an HCl acid solution with pH = 3 for up to 6 months, while the OPC sample experienced deleterious deterioration. The results clearly show that AASC outperformed OPC concrete when it comes to durability in an HCl acid solution. The strength reduction and weight loss of AASC compared with OPC concrete were approximately one-tenth and one-fifth, respectively. The AASC samples containing potassium hydroxide showed a higher strength reduction and weight loss in the HCl acid solution than the samples made with sodium hydroxide.

Investigation on Electrical Resistance of Chloride Penetration of Alkali Activated Slag Concrete

Alternating-current method for measuring chloride penetration resistance of concrete, test method for coulomb electric flux and rapid chloride migration coefficient (RCM) were applied to evaluate the resistance of chloride penetration in alkali-activated slag concrete in this paper. At the same time, the applicability of the above three electrical parameters test methods to the alkali slag concrete was discussed. The results show that NaOH activated slag concrete behaves higher resistance to chloride penetration than water glass activated slag concrete. Blend of fly ash increases the porosity of alkali-activated slag concrete and weakens the resistance of chloride penetration. Correlation coefficient between chloride migration coefficient and AC electrical resistivity is 0.99. There are good correlations among the evaluation results of three electrical parameters test methods, and all of them behave sound applicability to alkali-activated slag concrete.

Influence of seawater on alkali-activated slag concrete

This study examines the use of natural seawater as mixing water for alkali-activated slag concrete and reports the characteristics of alkali-activated slag concrete with exposure to seawater. Preliminary experiments were conducted on pastes in order to measure pH and select optimum activator content under the experimental conditions. Wet-sieved pastes from fresh concrete were used to evaluate the mineralogical and microstructural characteristics of reaction products. Compressive strengths and chloride contents were measured with the hardened concrete samples. The activators used in alkali-activated slag concrete were sodium hydroxide (5% weight of slag) and liquid sodium silicate (5% weight of slag). The alkali-activated slag samples showed the carbonation of calcium silicate hydrate (C–S–H), which resulted in the reduction in strength with time. The seawater-mixed alkali-activated slag samples produced additional reaction products, C4AH13, and chloride-bearing hydrocalumite, and they improved the strength. The seawater-mixed alkali-activated slag samples exposed in seawater exhibited improved mechanical performance compared to other samples. C–S–H carbonation did not occur, refinement of the pore structure was confirmed, and the compressive strength increased after exposure to seawater. The release of partial chloride ions, which were bound in solid phases, occurred; however, such slight leaching did not affect the strength of the samples. The investigation within the experimental conditions of this study showed a positive result regarding the use of seawater as mixing water in alkali-activated slag concrete.

Experimental investigation of mix design for high-strength alkali-activated slag concrete

Alkali-activated slag concrete is attracting increasing attention because of its potential as an alternative to Portland cement concrete, and it has been studied in several countries. The development of high-strength alkali-activated Portland-cement-free concrete, made with ground granulated blast furnace slag and sodium silicate solution as the binder, is proposed. The Institute for Technological Research/Polytechnic School of the University of São Paulo (IPT/EPUSP) mix design method, which has never been used before for production of this type of concrete, is employed. Tests of compressive strength and dynamic modulus of elasticity were carried out at 1, 3, 7, and 28 days. In addition, static modulus of elasticity and splitting tensile strength tests were performed at 28 days. The results showed that high-strength alkali-activated slag concrete (HSAASC) developed high initial and final compressive strengths. The compressive strengths of the concretes ranged from 41 to 58 MPa and from 86 to 105 MPa at 1 and 28 days, respectively. The IPT/EPUSP mix design method proved to be a suitable methodology that can be followed for the efficient production of HSAASC.

Understanding the rheological properties of alkali-activated slag pastes from the cohesion and friction interactions

The workability and pumping performance of alkali-activated slag (AAS) concrete are affected by its rheological properties, which are related to the interactions between slag particles in the pastes. The rheological properties of AAS paste with different equivalent sodium oxide (Na2Oeq) dosage activated by sodium hydroxide (NaOH) and sodium silicate (waterglass) with different SiO2/Na2O molar ratios were investigated in this study. The rheological mechanism was studied from the cohesion and friction interactions by calculations from parameters such as the Zeta potential of particles in the pastes, surface energy, hydrogen bond, and friction coefficient of the alkaline activators. The results indicated that the yield stress of AAS pastes was lower than that of the paste made with slag and water, whereas the plastic viscosity was higher. The yield stress of AAS pastes was mainly determined by the friction interactions between particles. The plastic viscosity was mainly affected by attractive interactions, including van de Waals interactions and Lewis acid-base interactions. The electrostatic repulsion interactions were felt at a very short distance because the AAS pastes were systems with the high ionic strength, which means that the electric double layer were severely compressed, therefore, the attractive interactions were predominant. Taken together, these results suggest that the improvement of plastic viscosity of AAS pastes should be achieved by changing the attractive interactions.

Efficiency of bacteria based self-healing method in alkali-activated slag (AAS) mortars

Alkali-activated slag (AAS) is a promising alternative to ordinary Portland cement (OPC) as a sole binder for concrete structures and offers advantages such as superior acid resistance and higher strength development. However, AAS basically suffers from a high rate of drying shrinkage causing more cracks in AAS concrete compared to the OPC concrete. The Microbially Induced Calcium Carbonate precipitation (MICP) is a self-healing technology whose effects on AAS mortars is not thoroughly investigated. Therefore, it would be highly desirable to impart the self-healing process into AAS concrete. In the present paper, the effect of using Bacillus pasteurii with three different cell concentrations of 103, 105, and 107 cells/ml as a microbial self-healing agent on the strength parameters and microstructures of AAS mortars was investigated. In order to investigate the strength parameters of specimens, the bacteria were directly added to the mix water of the mortars. Then, the compressive and flexural strength tests were performed at the ages of 7 and 28 days. In addition, scanning electron microscopy (SEM), X-ray spectroscopy (EDS) and X-ray diffraction (XRD) were conducted to analyse the microstructures of the AAS mortars specimens. The obtained results indicated that Bacillus pasteurii produced calcium carbonate precipitation and probably remained viable to decompose urea in highly alkaline environment of AAS mortars. In addition, the activity of bacteria not only healed the cracks but also increased the strength of the AAS mortars up to 24.67%.

The performance of fiber GGBS based alkali-activated concrete

The fast construction and renovation of roads and bridges and the infrastructures in Egypt and developing countries cause concrete and cement production on a large scale. This huge market demand for precast units and concrete production harms the environment and global warming. Thus, the Ordinary Portland Cement (OPC) should reduce by developing new materials such as geopolymer concrete or alkali-activated concrete. This study investigated alkali-activated slag concrete (AAC) performance reinforced with structural polypropylene and steel fibers cured at ambient room temperature. The structural polypropylene and steel fibers were incorporated into the alkali-activated mix by 1.5% and 5% of the total binder weight, respectively. A wide range of engineering properties was assessed, including compressive strength, split tensile strength and stress-strain behavior, density, water absorption, and porosity. Microstructural analysis of the AAC samples was evaluated through scanning electron microscopic (SEM). The results showed that compressive strength at 1-day curing developed about 85% of the compressive strength for ACC at 28-days, which was considered as early high strength. A 10% enhancement of the AAC specimens' average compressive strength was reported after 7 and 28 days while fiber addition. The split tensile strength significantly increased by 19.28 and 26.80% by incorporating structural polypropylene and steel fibers, respectively. Comparison between the ACI 318 and ECP 203 provisions was handled along with those experimental results obtained elastic and rupture modulus. The ACI 318 provisions provided a more conservative prediction to the experimental results than the ECP 203 provision, which overestimated the experimental values by an average value of 1.1. The electron microscopy images confirmed the improvement in the engineering properties by showing a proper and coherent bond between the mortar matrix and the added fibers.

Alkali-activated concrete mixes with ground granulated blast furnace slag and paper sludge ash in seawater environments

Predicted sea level rise due to global warming will necessitate the construction of coastal defenses to protect the populations in the vicinity of the coasts. Large quantities of concrete will be required with consecutive increases in greenhouse emissions, hence an increasing need for alternative to Ordinary Portland Cement (OPC) cements. Feasible potential alternatives could be found in alkali-activated cements, which also include industrial by-products or waste materials. This paper presents a laboratory study of concrete mixes based on the alkali-activation of an industrial by-product, ground granulated blast furnace slag (GGBFS) and includes an industrial waste, paper slugde ash (PSA) in the alkali-activator mixes. The use of seawater as mixing and curing water was also examined. The compressive strength and a number of durability-related properties of alkali-activated mixes in marine environment were investigated and compared to OPC systems. The incorporation of paper sludge ash led to high early strengths, a decrease in the effective porosity of alkali-activated slag concretes and generally a reduced water absorption, and enhanced the performance against chloride ion attack in mixes with freshwater, as well as the resistance of the cements in sulphate attack especially when mixed with seawater. The addition of seawater in the mixes increased the resistance to sulphate attack and the compressive strength in alkali-activated systems, as opposed to OPC concretes in which mixing and curing in seawater had deleterious effects. The study gives promise for the suitability of the tested alkali-activated concrete mixes in seawater environments.

A review on alkali-activated slag concrete

Alkali-activated concrete (AAC) has attracted considerable attention since its first use as an alternative material to the well-known traditional Portland cement concrete (PCC) due to their superior properties and environmental impact. In this paper, a comprehensive review on the present knowledge about the AAC in terms of historical background, environmental impact, constituent materials and characteristics of alkali-activated slag concrete (AASC) is presented. The following topics are reviewed in details for AASC: historical background, environmental impact, constituent materials, reactions mechanism, hydration products, compressive strength, stress–strain behavior, elasticity modulus, Poisson’s ratio, tensile strength, bond characteristics with reinforcing steel bars and behavior under elevated temperature. Most studies have demonstrated the superior mechanical properties of AASC and their applicability in the construction engineering field. Moreover, AASC exhibits bond performance and elevated temperature resistance better than PCC. However, the review reveals that more studies and investigations related to mix design including mix proportions, mixing procedures and curing regime, with which the AASC could demonstrate the best engineering properties, are required.

Effect of recycled fine aggregates on alkali-activated slag concrete properties

Normally, recycled fine aggregate (RFA) is an unwanted by-product of construction demolished waste crushing, with high contaminant content. The presence of RFA is highly restricted in ordinary Portland cement (OPC) concrete production because of the poor durability and mechanical performance. This paper presents a study of the effect of RFA on the mechanical and durability of alkali activated slag concrete (AASC). Results indicated that RFA can be used as fine aggregate in AASC with superior early age compressive strength compared to river sand in AASC. It is caused by the presence of non-hydrated cement paste attached to the RFA with alkali activate property, which is equivalent to increase the quantity of alkali activator, and accelerate the hydration of ground granulated blast furnace slag (GGBFS) especially in the early age. In later age, the mechanical properties of AASC incorporating RFA are slightly lower than conventional AASC due to the larger porosity in the concrete.

Mechanical properties of fly ash and blast furnace slag based alkali activated concrete using high silica modulus activator

The alternative to cement is grabbing attention of inventors due to the numerous advantages with their usage. Fly Ash (FA) and Blast furnace slag (BFS) are abundantly available in bi product form. There is heavy problem in disposal and land availability for industries. So many studies are going on to reduce these problems by usage as cementitious materials in concrete adding advantages towards green concrete. It is developed that Alkali activated flyash concrete has high strength, high acid resistance and heat resistance where as Alkali activated slag concrete has rapid setting time, high strength, impermeable and improved fire resistance. In this study FA and BFS are activated with high silica modulus activator with different activator/binder ratios and binder contents. The alkali activated FA-BFS concrete is verified for workability, compressive strength, split tensile strength, and flexural strength.

Effect of Bauxite Residue Content as A Replacement of Slag on the Strength, Shrinkage, and Abrasion of Alkali-Activated Slag Concrete

Effect of Bauxite Residue Content as A Replacement of Slag on the Strength, Shrinkage, and Abrasion of Alkali-Activated Slag Concrete

The Effect of Mixture Proportion on the Performance of Alkali-Activated Slag Concrete in the Sulfuric Acid Attack

The Effect of Mixture Proportion on the Performance of Alkali-Activated Slag Concrete in the Sulfuric Acid Attack

Seasonal effect on compressive strength of ambient cured, nominal mix proportioned alkali-activated slag concrete

Strength of the concrete is a very important factor for the safe design of concrete and safe construction. Nowadays high strength concrete has an important role in the construction of different structures. It is difficult to enhance the strength of the concrete and enhancing strength requires a lot of changes in the mix design. The present study is to develop Geopolymer concrete to increase the compressive strength of low nominal mix proportions using alkali actuators like NaOH and Na2SiO3 solutions. Geopolymer concrete is one of the best alternative concrete for conventional and other cement concretes for many reasons. The Geopolymer concrete is prepared with ground granulated blast furnace slag (GGBS) and silica fume (SF) as a binder. NaOH and Na2SiO3 solutions are adopted as alkali activators. Quartz sand is used as fine aggregate along with normally used coarse aggregate. Cubes are prepared with different combinations of ingredients and after 28 days of ambient curing conditions, the cubes are tested for compressive strength. And this study is conducted in summer, monsoon and winter seasons to study the effect of seasons on ambient curing of the Geopolymer concrete.