Next Article in Journal
Transforming Urban Façade Condition Assessments with Semantic Data Visualizations and 3D Spatial Layouts from BIMs
Previous Article in Journal
Carbon Emission Assessment During the Recycling Phase of Building Meltable Materials from Construction and Demolition Waste: A Case Study in China
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Buildings
Volume 15
Issue 3
10.3390/buildings15030457
buildings-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Impact of Curing Temperature and Steel Slag Aggregates on High-Strength Self-Compacting Alkali-Activated Concrete

by
Lucas B. R. Araújo
1,2,3,
Daniel L. L. Targino
1,4,
Lucas F. A. L. Babadopulos
1,
Antonin Fabbri
2,*,
Antonio Eduardo. B. Cabral
1,
Rime Chehade
3 and
Heloina N. Costa
1
1
Departamento de Engenharia Estrutural e Construção Civil, Universidade Federal do Ceará, Fortaleza 60455-760, Brazil
2
Univ. of Lyon, ENTPE, Ecole Centrale de Lyon, CNRS, LTDS, UMR5513, 69518 Vaulx-en-Velin, France
3
BUILDERS Ecole d’ingénieurs, Unité de Recherche “Builders Lab”, ComUE NU, Campus Lyon, 69120 Vaulx-en-Velin, France
4
Université Gustave Eiffel, MAST-MIT, Campus Nantes, All. des Ponts et Chaussées, 44340 Bouguenais, France
*
Author to whom correspondence should be addressed.
Buildings 2025, 15(3), 457; https://doi.org/10.3390/buildings15030457
Submission received: 25 December 2024 / Revised: 24 January 2025 / Accepted: 26 January 2025 / Published: 1 February 2025
(This article belongs to the Section Building Materials, and Repair & Renovation)
Browse Figures
Versions Notes

Abstract

:
There is a growing demand for sustainable solutions in civil engineering concerning the carbon footprint of cementitious composites. Alkali-Activated Binders (AAB) are materials with great potential to replace ordinary Portland cement (OPC), with similar strength levels and lower environmental impact. Despite their improved environmental performance, their durability remains a gap in the literature, influenced by aspects of mechanical behavior, physical properties, and microstructure. This paper aims to assess the impact of steel slag aggregates and curing temperature of a proposed AAB based concrete formulation by characterizing fresh state, mechanical behavior, and microstructure. The proposed AAB is composed of fly ash (FA) and basic oxygen furnace (BOF) steel slag (SS) as precursors, sodium silicate and sodium hydroxide solution as activators, in total replacement of OPC, using baosteel slag short flow (BSSF) SS as aggregate in comparison with natural aggregate. The concrete formulation was designed to achieve a high-performance concrete (HPC) and a self-compacting concrete (SCC) behavior. Mechanical characterization encompassed hardened (compressive strength and Young’s modulus), fresh state (J-ring, slump flow, and T50), and durability tests (scanning electronic microscopy, water penetration under pressure, and chloride ion penetration). The compressive strength (64.1 ± 3.6 MPa) achieves the requirements of HPC, while the fresh state results fulfill the SCC requirements as well, with a spread diameter from 550 mm to 650 mm (SF-1 class). However, the flow time ranges from 3.5 s to 13.8 s. There was evidence of high chloride penetrability, affected by the lower electrical resistance inherent to the material. Otherwise, there was a low water penetration under pressure (3.5 cm), which indicates a well-consolidated microstructure with low connected porosity. Therefore, the durability assessment demonstrated a divergence in the results. These results indicate that the current durability tests of cementitious materials are not feasible for AAB, requiring adapted procedures for AAB composite characterization.

1. Introduction

The global demand for more sustainable solutions continues to rise. In the field of civil engineering, ordinary Portland cement (OPC) significantly contributes to the carbon footprint of structural applications, accounting for 5% to 7% of worldwide greenhouse gas emissions (GHGe) [1,2,3]. On average, its production releases between 0.73 and 0.99 tons of CO2 per ton of OPC [2,3]. Alternative materials, known as supplementary cementitious materials (SCMs), have been highlighted for their ability to meet structural requirements while reducing environmental impact [1,4].
Alkali-activated binders (AABs), also known as geopolymers, are discussed in the literature as potential substitutes for OPC due to their lower greenhouse gas emissions (GHGe). Unlike OPC, AABs do not require calcination or direct extraction of raw natural materials, as they are mainly produced from industrial by-products. When used in concrete, AABs can reduce the binder’s carbon footprint by up to 75% [5] while maintaining similar strength, workability, and durability [1,6,7] as normal strength concretes (NSC), high-strength concretes (HSC), and self-compacting concretes (SSC) that use OPC as a binder. However, the development of AABs for concrete applications with suitable fresh-state properties and mechanical behavior remains an area that requires further attention [1,8,9,10]. While high-strength concrete (HSC) can already be produced using AABs [9], it has been observed to exhibit higher viscosity compared to OPC pastes [8], which does not meet fluidity and workability requirements. In addition, it is crucial to develop materials with adequate strength and durability. Microstructural aspects play a significant role in these outcomes [4,11,12]. Understanding the chemical composition of precursors and the curing process is essential to assess their effects on durability [4,7,13,14].
For the AAB formulation, powder materials are used as a source of aluminosilicates, named precursors, and alkaline solutions are used to activate them (aluminosilicates dissolution and reaction). The main products highlighted in the literature are gels of C-A-S-H (CaO-Al2O3-SiO2-H2O) and N-A-S-H (Na2O-Al2O3-SiO2-H2O), with their proportions influenced by the calcium content of the precursors [4,15].
The most common materials that have been established for AAB production are fly ash (FA), ground granulated blast-furnace slag (GGBFS), and metakaolin [15]. However, other materials also show potential for further exploration. Steel slag (SS) has various applications in construction, particularly as an aggregate [16] in concrete and as an SCM for cement production. Given its chemical composition, SS also holds potential for use in AABs [17]. Its use as a binary mixture of precursors with FA may produce high-performance binders, with intermediate calcium contents. Indeed, this mixture results in the coexistence of C-A-S-H and N-A-S-H gels, which are characteristic of high and low calcium systems, respectively [4,15]. This combination tends to enable superior chemical resistance of N-A-S-H and the low porosity of C-A-S-H [4,15].
Despite this, the utilization of SS as both a precursor and an aggregate remains relatively low compared to its potential [18,19,20,21,22]. For example, in 2020, global crude steel production reached 1.95 billion tons [23], generating 130 to 200 kg of SS per ton of steel [24]. Only 36% of this total was properly managed, highlighting the need for sustainable solutions to ensure proper disposal [17,25]. To overcome that issue, one way may be to fill the research gaps related to workability, mechanical performance, and durability of AAB using SS/FA mixtures as precursors. For that purpose, the rheological and curing process optimization may be a promising solution. For the latter, high temperatures are known to accelerate the setting and hardening of alkali-activated binders, influenced by factors like solution alkalinity and water/binder ratio, which affect phase formation during alkali-activation [4,15]. Strength gains, particularly at early ages, have been observed under thermal curing at 60–70 °C for 24 h, especially in low-calcium binders [26].
In addition, in steel slag (SS) production, two primary methods are commonly described: the basic oxygen furnace (BOF-SS) and the electric arc (EAC) furnace process [17]. The BOF-SS system accounts for 74.5% of global production [23,27]. BOF-SS is more reactive due to its slow cooling at ambient temperature [17], which enhances its potential as a precursor. When thermal treatments such as a water-cooling process at the reactor exit are applied, Baosteel slag short flow (BSSF-SS) is produced. This material has an amorphous structure and lower calcium content, mitigating the BOF-SS expansibility issue [27], and making it a suitable aggregate called BSSF. However, due to the lack of knowledge on the impact of the use of this kind of aggregate on the concrete behavior, its use remains quite low.
In this context, this paper explores the utilization of steel slag aggregates in high-strength, self-compacting alkali-activated concrete, examining both its fresh and hardened states. Additionally, the study analyzes the impact of curing conditions on mechanical properties, microstructure, and durability parameters for both types of formulations—those containing conventional aggregates and those incorporating steel slag aggregates.

2. Materials and Methods

2.1. AAB Concrete Formulations

The AAB pastes were produced by a binary combination of FA from mineral coal combustion and SS from the basic oxygen furnace (BOF) process. The specific gravity of the precursors was 2.34 for FA and 3.13 for SS. The specific surface area of the precursors was 4790 cm2/g (FA) and 3360 cm2/g (BOF-SS). The particle size distribution (PSD) of the precursors was obtained with a Shimadzu SALD-2300, and the results are presented in Figure 1a. The FA PSD had an average diameter of 5.6 µm and a maximum diameter of 106.9 µm, while the BOF-SS had an average of 35.4 µm and a maximum diameter of 141.0 µm.
Figure 1b compares the diffraction patterns of BOF-SS and FA. The FA exhibited crystalline phases such as quartz (SiO2), magnetite (Fe3O4), mullite (Al(Al1.272Si0.728O4.864)), brushite (CaPO3(OH)2·H2O), and monetite (CaPO3(OH)) [21,28]. The FA hump at 2θ between 20° and 35° suggests the presence of reactive (amorphous) silica. BOF-SS showed peaks of gypsum (CaSO4), calcium hydroxide (Ca(OH)2), berlinite (AlPO4), and katoite (Ca3Al2O6(H2O)6), indicating a more complex composition [21,29] and without the presence of amorphous material. Additionally, XRF analysis revealed high FeO and CaO contents in BOF-SS.
SS also was used as aggregate, in fine and coarse granulometries. The SS used as aggregates were obtained by the Baosteel short slag flow (BSSF) process, a different method, mainly concerning cooling procedure using water [27,30]. The oxide composition of these materials was performed by X-ray Fluorescence (XRF) with a Rigaku ZSX Mini II, which is presented in Table 1.
FA was classified as class F [31], with pozzolanic activity. Both precursors presented high quantities of Al2O3, SiO2, Cao, and Fe2O3, mainly contributed by the alkali-activated products [9,15]. The BOF-SS precursor presented a high calcium content (53.14% of CaO). The BSSF-SS aggregate presented an oxide composition similar to the BOF-SS precursor with lower calcium, aluminum, and silicon content. This variation is possibly due to the cooling process of the aggregate with water (due to the partial lixiviation of calcium content), decreasing the expansibility, favoring its use as aggregates [27,30].
A blend of 53.1% of sodium hydroxide (NaOH) and 46.9% of sodium silicate (Na2SiO3), by mass, was used as activators. Sodium hydroxide was used as a solution, with a concentration of 10 mol/L, composed of 31.3% NaOH and 68.7% H2O in mass ratios [32,33]. The alkaline sodium silicate solution was composed of 14.98% Na2O, 31.83% SiO2, and 53.19% H2O, by mass. These solutions presented a specific gravity of 1.31 and 1.58, respectively. The activator to precursor ratio was 0.5, in mass.
The aggregates used to produce the AAB concretes were composed of natural aggregates and BSSF-SS aggregates. Their specifications are presented in Table 2. The conventional fine aggregate used was natural sand with a specific gravity of 2.57 and a fineness modulus of 2.66. The BSSF-SS fine aggregate had a dry specific gravity of 3.58 and a fineness modulus of 2.58. The conventional coarse aggregates were composed of two granulometries of granitic rocks from the same origin. The PSD of the aggregates used were 4.75–12.5 mm and 9.5–25 mm (Figure 2a). These aggregates had a dry specific gravity of 2.62 and 2.63, open porosity of 1.5% and 1.6%, and bulk densities of 1406 kg/m3 and 1487 kg/m3, respectively. Those aggregates were named “coarse aggregates 1” and “coarse aggregates 2”, respectively. The BSSF-SS coarse aggregate had a PSD range of 9.5–25 mm (Figure 2a), with a dry specific gravity of 3.60, open porosity of 6.0%, and bulk density of 1835 kg/m3.
This paste was selected based on a high compressive strength paste of 65 MPa under thermal (65 °C during 24 h in a laboratory oven) and 50 MPa under ambient curing (25–30 °C), room temperature [26]. Also, there was high fluidity in the fresh state. This AAB paste was produced using FA and BOF-SS in a mass ratio of 75% FA to 25% BOF-SS. The activators consisted of a blend of 53.1% sodium hydroxide (10 mol/L) and 46.9% sodium silicate (14.98% Na2O, 31.83% SiO2, and 53.19% H2O) by mass. This composition corresponds to an alkali content (N/B, i.e., Na2O to binder precursors by mass) of 10% and a silica modulus (S/N, i.e., SiO2 to Na2O activator by mass) of 0.75.
For the production of alkali-activated concretes, the combinations of coarse and fine aggregates composed of 100% natural or 100% BSSF-SS aggregates were used. The aggregate void content was determined based on packing analysis [32,34], as shown in Figure 2b.
The lower voids content was obtained for a proportion of 40% of gravel 4.75–12.5 mm and 60% of gravel 9.5–25 mm, with a void content of 41.37%. Figure 2b presents the packing curve of the coarse aggregate, based on the aforementioned proportion (40% of 4.75–12.5 mm and 60% of 9.5–25 mm) and natural sand. The ratio of 35% to 65% fine aggregate to coarse aggregate, with a 32.0% voids content was adopted for the conventional aggregates. These proportions were similar to Rafeet et al. (2017) [32]. The same procedure was applied for the BSSF-SS aggregates in Figure 2b, obtaining a ratio of 60% to 40% BSSF-SS coarse aggregate to fine aggregate, with 32.9% of void contents.
A fixed paste content (P%, i.e., paste/concrete, represented as a volume ratio) was adopted to produce AAB concrete with self-compacting concrete (SCC) properties. The SCC requirement was met with a paste content of 38.6%, with an additional 20% to account for the voids content (32%) addressed previously. This paste content is similar to values of Bondar et al. (2019) [34] ranging from 24% to 45%. The compositions of the AAB concrete mixes are presented in Table 3.
The visual aspect of the AAB concrete is presented in Figure 3. In Figure 3a, the formulation with conventional aggregates is presented, while Figure 3b does the same for the concrete with BSSF-SS aggregate.

2.2. Fresh State Characterization

The AAB concretes were characterized in the fresh state using slump flow tests, T50 (time to reach a spread of 50 cm) [35] and J-ring [36] were classified according to the European Federation of National Associations Representing for Concrete (EFNARC) [37]. The specimens were cast into cylindrical plastic 10 cm diameter and 20 cm height molds. The AAB concrete specimens were submitted either to thermal curing, at 65 °C for 24 h in an aerated oven, and ambient curing, with average temperatures between 25 and 30 °C [26]. These two conditions were chosen to evaluate the production of concrete under field conditions at room temperature, as well as its maximum strength, obtained through thermal curing [4,9,38].

2.3. Mechanical Evaluation

The tests performed in the hardened state were performed to characterize the mechanical and durability performance of the AAB concretes. The AAB concretes were tested for compressive strength [39], with a universal testing machine with a load capacity of 1000 kN. The test was performed with an incremental loading rate of 0.45 (±0.15) MPa/s. These tests were performed for ages of 7, 14, and 28 days. The target strength was 60 MPa, based on the HSC criteria [40]. All the tests of the hardened state were performed in triplicate.
Three tests were performed to assess the Young’s modulus. At first, there was the static Young’s modulus [41], the most widely used, based on longitudinal strain measurements. After, non-destructive tests were employed, based on wave propagation: (i) the resonance impact test [42], using Equation (1) for modulus calculation; (ii) and the ultrasonic test [43] with Equation (2). To differentiate the non-destructive tests, they will be called resonant Young’s modulus and ultrasonic Young’s modulus.
E d , r = D M ( n ’ ) 2 ,
where E d , r : dynamic Young’s modulus (resonant Young’s modulus), measured by impact resonance (GPa); D: equal to 5093 × (L/d2), L is specimen length (m) and d is specimen diameter (m); M: specimen mass (kg); n’: longitudinal resonance frequency (Hz). The impact resonance test was performed using the equipment developed by BEZERRA et al. (2022) [44].
E d , u , p = C p 2 ρ ( 1 + μ ) ( 1 − 2 μ ) ( 1 − μ ) ,
where E d , u , p : dynamic Young’s modulus (ultrasonic Young’s modulus), measured from the velocity of ultrasonic P-waves (GPa); Cp: velocity of propagation of the ultrasonic P-waves (mm/μs); ρ : density (kg/m3); μ: Poisson’s ratio (dimensionless), adopted as 0.2 based on recommendations of ASTM C597 [43] and based on AAB concretes literature [45]. However, this assumption will be discussed hereafter.
The ultrasonic Young’s modulus can also be calculated according to Equation (3) [46]. Both P-waves and S-waves are body waves, but differ in the propagation direction, longitudinal for P-waves (frequency of 54 kHz) and transversal for S-waves (frequency of 40 kHz) [45].
E d , u , s = 2   C s 2 1 − μ ρ ,
where E d , u , s : dynamic Young’s modulus (ultrasonic Young’s modulus), measured from the velocity of ultrasonic S-waves (GPa); C s : velocity of propagation of the ultrasonic S-waves (mm/μs); ρ : density (kg/m3); μ : Poisson’s ratio (dimensionless).
The presented values of resonant Young’s modulus were obtained through the longitudinal resonant frequency (n’, cf. Equation (1)) of AAB concretes. For the resonant Young’s modulus calculations, the measured average resonance frequencies were 8924 Hz and 9537 Hz for AAB concrete with conventional aggregates under ambient and thermal curing, respectively, and 8485 Hz and 8981 Hz for AAB concrete with BSSF-SS aggregates under ambient and thermal curing, respectively. For the ultrasonic Young’s modulus calculations, the measured average ultrasonic P wave speed (Cp, cf. Equation (2)) were 4135 m/s and 4011 m/s for AAB concrete with conventional aggregates under ambient and thermal curing, respectively, and 4854 m/s and 4718 m/s for AAB concrete with BSSF-SS aggregates under ambient and thermal curing, respectively. Following the recommendations of the study by Bezerra (2023) [47], the hypothesis for determining the time of flight of the “S” wave was adopted as the instant at which the waves begin to show greater amplitude.
The ultrasonic Young’s modulus results, calculated using a Poisson’s ratio of 0.2, exhibited higher values compared to other methodologies, presenting values up to 2 times higher. This observation suggests the hypothesis that Poisson’s ratio of AAB concretes differs from 0.2. The results obtained from the dynamic impact resonance methodology, based on Equation (1), demonstrated high accuracy in determining Young’s modulus values without requiring the use of Poisson’s ratio. Assuming that the material exhibits purely linear elastic behavior, characterized by the absence of viscous effects, it is possible to infer the Poisson’s ratio of the material through retroanalysis, based on the Equations (1)–(3), as recommended by [43]. To test this hypothesis, P-wave (compression wave) and S-wave (shear wave) measurements were performed on AAB concrete specimens with conventional aggregates subjected to thermal curing, in order to estimate Poisson’s ratio. Only this configuration was tested because this hypothesis was proposed after the experimental stage of the research was completed, and there was not enough material to produce the four configurations analyzed.
The compressive strength values obtained were used as the basis for estimating the Young’s modulus of the analyzed concretes. The calculation was performed using specific equations like Equation (4), developed exclusively for alkali-activated concretes by Thomas and Peethamparan (2015) [48,49]. This approach was adopted to evaluate and compare the accuracy of equations specifically developed for alkali-activated concretes with those traditionally used for Portland cement-based concretes (such as Equation (5)) in determining the Young’s modulus [48,49].
E c = 2900   f c 3 / 5
E c = 4700   f c 1 / 2
where E c : Estimated Young’s modulus, based on concretes compressive strength (GPa); fc: concrete compressive strength (MPa).

2.4. Durability Assessment

Chloride percolation into concrete is associated with the corrosive processes of the steel reinforcement concretes, being prejudicial to the concrete’s durability [50]. To directly evaluate the electrochemical penetration of chlorides, short tests were performed according to ASTM C1202 [51]. It is also possible to estimate the durability of concrete by measuring its electrical resistivity, which indicates how easily ions can be transported through the material’s structure under the influence of an electric field [52]. The AAB concretes also had their bulk electrical resistivity measured with the Resipod equipment from Proceq SA, according to ASTM C1876 [52]. The present paper proposed a comparison between these methods. Meanwhile, the measured electrical resistivity values were used to estimate the chloride ion penetrability values and to compare them with the measured values in the chloride ion penetrability test. To perform this comparison, Ohm’s 1st and 2nd laws were utilized, the concrete was represented as an isotropic material and the power loss between the electrode and the electrolytes was considered negligible [12,53]. The chloride ion penetrability was calculated based on the first- and second-Ohm’s laws, along with the bulk resistivity test values and the dimensions of the tested specimen (5 cm in height and 10 cm in diameter). The calculation also considered the test parameters specified in ASTM C1202 [52], including a test voltage of 60 V and a total duration of 6 h. These results were compared with the chloride percolation values obtained in accordance with ASTM C1202 [52].
Therefore, it is important to evaluate the pore structure of the material [7,13,54]. To indirectly identify how connected those porous structures are, the test of water penetration under pressure was performed according to EN 12390 [55]. To evaluate the magnitude of open porosity, nitrogen pycnometry, and ASTM C642 [56] tests were performed.
The microstructure of the interfacing zone (ITZ) between the alkali-activated binder and the aggregates represents the concrete area of higher fragility structure [57,58]. Thus, the binder and the interface between the alkali-activated binder were characterized with the scanning electron microscopy (SEM) to characterize the ITZ, the formed gels and the magnitude of the ITZ gaps. The evaluation of the binder’s microstructure was also performed. Complementary XRD tests were carried out using a Rigaku ZSX Mini II to assess the oxide composition of the AAB powder samples. For XRD analysis, a PANalytical X’Pert PRO was employed, performing scans from 3° to 100° (2θ) with a step size of 0.013°.
To complement the characterization of the AAB concretes, the determination of water absorption, void content, and density were performed [56]. The durability evaluation was focused on the thermal curing AAB concretes, as they presented higher mechanical performance.

3. Results and Discussions

3.1. Fresh State Evaluation

The results of self-compacting concrete properties on fresh state are summarized in Table 4 in terms of flow time (T50 test) and passing ability (J-rig test). The initial setting time of the AAB paste was 13.4 h. Consequently, the loss of workability due to hardening reactions was not considered in this study.
The flow time presented by the concretes was higher than two seconds, classifying both concrete (AABs) as VS2 [37]. This overall behavior of both formulations is associated with the higher viscosity presented by the binders investigated [8]. The substitution of conventional aggregates by BSSF-SS resulted in a flow time decrease (13.8 to 3.5), which can be associated with a smoother aspect of BSSF-SS aggregates, which favors the flow or the absence of an intermediate-sized aggregate for concretes with BSSF-SS aggregates, which results in lower binder demand and flow.
The AAB concrete with conventional aggregate was classified as class 1 (SF1), slump diameter between 550 mm and 650 mm, with a slump flow of 575 mm. AAB concrete with BSSF-SS aggregate achieved a spread class 2 (SF2), slump diameter between 660 mm and 750 mm, with a slump flow value of 737 mm [37]. These values are similar to those observed in OPC-SCC. Due to the great diversity of materials used in OPC-based concretes, the slump flow can range from 555 mm to 880 mm, while the T50 flow time may vary between 0.91 s and 3.80 s [59,60]. The AAB concretes showed low blocking by the J-ring method, with a passing ability between 25 mm and 50 mm [36]. No evidence of segregation or exudation (cf. Table 4) was observed during the tests. The utilization of BSSF-SS aggregates improved the fresh state properties of the AABs concretes [60].
Few researchs works evaluated the self-compacting of AAB concretes. Mohammedameen (2022) [61], Saini and Vattipalli (2020) [6] and Huseien, Sam and Alyousef (2021) [59] evaluated the self-compacting properties of AAB concretes based on FA and ground granulated blast-furnace slag (GGBSF) activated with sodium hydroxide and sodium silicate. The authors obtained similar values for T50 (2.6–5.5 s) and slump flow (630–721 mm) in this research. Besides, the results of passing ability (5–10 mm), evaluated by the J-ring method suggested that the referred authors managed to obtain a concrete with better passing ability than those investigated in this research. However, aside from the research mentioned, the current concrete formulations did not use any additional water and/or superplasticizer additives, which may favor workability but may have a negative effect on the mechanical performance [10].

3.2. Dry Density Characterization

AAB concretes with BSSF-SS aggregates obtained a higher apparent density compared to conventional aggregates, with 2842 kg/m3 and 2306 kg/m3 respectively [56]. This behavior is aligned with the literature, as BSSF-SS aggregates have a higher specific gravity up to 40% higher than conventional aggregates. Also, the AAB concrete with BSSF-SS aggregates presented an apparent density value higher than 2600 kg/m3, achieving the classification as a heavy concrete [62], expanding its application especially for radiation shielding. Moreover, Palankar, Shankar, and Mithun (2017) [18], obtained densities results of 2528 kg/m3 for natural coarse aggregates and 2730 kg/m3 for BOF-SS aggregates, which are similar to the results of the current study.

3.3. Mechanical Evaluation Results

3.3.1. Compressive Strength

The compressive strengths of AAB concretes at 7, 14, and 28 days are presented in Figure 4. The comparison in this study was conducted based on the volumetric replacement of conventional aggregates with BSSF-SS aggregates to evaluate the effects of this substitution on the performance of the concrete. The three ages tested enabled monitoring the development of compressive strength over time, up to 28 days, which is the standard timeframe in engineering applications for measuring the characteristic compressive strength ( f c k ).The thermal curing to high initial strength (7 days), followed by minor increases over time, reaching values of 64.1 ± 3.6 MPa (28 days), for the AAB concrete with conventional aggregate, and 49.6 ± 1.2 MPa (28 days), for the AAB concrete with BSSF-SS aggregates. The AAB concrete with conventional aggregate under thermal curing showed similar strength values to the binder, while the same concrete under ambient curing showed a reduction in its strength by 10 MPa, when compared to the binder under the same cure condition. This may be associated with a positive effect of thermal curing on the interface between the binder and aggregates, discussed in Section 3.4.4.
A decrease in compressive strength of AAB concretes occurred with the exchange of conventional aggregates for SS aggregates, from 64.1 MPa to 49.6 MPa under thermal curing (−22%) and from 40.3 MPa to 35.1 MPa under ambient curing (−13%), both at 28 days. Although the change in aggregates improved the passing ability (+26%) and reduced the flow time properties (−75%), its effect on strength was negative. This is attributed to the partial consumption of alkalis by the reactions between the paste and the BSSF-SS aggregates [20], resulting from the alkaline activation reactions between them and promoting a superficial alkaline activation on the aggregate, which may have affected the development of binder strength and, consequently, the concrete. An alternative explanation for the strength decrease may relate to differences in the granular skeleton. AAB concretes with conventional aggregates includes intermediate size particles (Figure 2a), improving the packing curve (Figure 2b).Decreases in strength resulting from the exchange of aggregates were also observed in the literature [10].
The conventional aggregates’ of AAB concretes achieves the highest compressive strength when compared to other self-compacting. Which reports values from 47 MPa [6,59] to 54.4 MPa [61]. BSSF-SS aggregates concretes achieved similar compressive strength to those presented in the literature related to SS aggregates. Palankar, Shankar, and Mithun (2017) [18] obtained 54.4 MPa and 51.2 MPa in concretes with pastes based on FA and for GGBFS and natural aggregates, respectively. Also, Palankar, Shankar, and Mithun (2015) [63] obtained 55.9 MPa and 49.8 MPa respectively, for paste of FA and GGBFS.

3.3.2. Young’s Modulus Evaluation

The Young’s modulus results are shown in Figure 5. The values range from 20.2 GPa to 31.1 GPa. In the literature, HPC tends to achieve high Young’s modulus (50–60 GPa in average) [64]. Although the current formulations presented high compressive strengths, Young’s modulus results are expected to be below average of Portland cement HPC. This is a usual outcome for AAB concretes, which can often present about half the values of Young’s modulus of Portland cement concretes of the same order of compressive strength [65].
Young’s modulus is affected by the products’ ratio (gels’ proportions) during alkali activation. AABs produced with rich calcium precursors present higher modulus when compared to low calcium content, aligned with the literature, with results between 12 GPa and 47 GPa [49,66]. N-A-S-H gels present lower Young’s modulus than C-S-H gels and other calcium-based gels [49,66]. Thus, the use of binary mixtures of precursors with different calcium contents presented intermediate values of Young’s modulus.
Moreover, the thermal curing increased the modulus results for both aggregates. For the conventional aggregates concretes, there was an improved result from 20.2 GPa to 26.2 MPa (+30%), while for BSSF-SS aggregates, it was from 26.5 GPa to 31.1 GPa (+17%), for static modulus test. This is aligned with the literature, as thermal curing induces higher compressive strength at 28 days, which is also reflected in a higher modulus as well [67].
The use of BSSF-SS aggregates led to an increase in the modulus, oppositely the compressive strength behavior. This is associated with the insertion of stiffer aggregates such as SS, which have a compressive strength of up to 300 MPa [68,69]. Palankar, Shankar, and Mithun (2017) [18], reported small decreases in Young’s modulus values upon the exchange of conventional aggregates for SS aggregates. These results were different from the present research.
Table 5 presents the estimated Young’s modulus values derived from the compressive strength data using Equations (4) and (5). Neither the equations developed for AAB concretes nor those for Portland cement-based concretes demonstrated satisfactory accuracy in estimating the modulus values for AAB concretes produced with conventional aggregates. However, for AAB concretes produced with BSSF-SS aggregates, both methodologies yielded results closely aligned with the measured values. This highlights a significant research gap, underscoring the need to adapt existing methodologies to account for the specific characteristics of the alkali-activated materials employed.

3.3.3. Poisson’s Ratio

The average values of flight time for the S-waves were 91.1 µs while the average values of flight time for P-waves were 46.1 µs. Based on these results, the value found for Poisson’s ratio was 0.325 higher than the mentioned assumption employed for ultrasonic Young’s modulus calculation presented in Figure 5. Therefore, the utilization of Poisson’s ratio, equal to 0.2 is incorrect, and this factor should always be determined to obtain accurate values of the ultrasonic Young’s modulus. With the new Poisson’s ratio, the value of the ultrasonic Young’s modulus for the specimen analyzed changed from 35.4 GPa to 25.5 GPa, presented in Figure 5. To evaluate the accuracy of the Poisson’s ratio obtained, an inverse calculation was performed in order to find the Poisson’s ratio values required to achieve the measured resonant modulus results. Table 6 presents the results of this analysis. As observed, there is a variability of Poisson’s ratio values between 0.27 and 0.41, which confirms that the value adopted by ASTM C597 [43] for Portland cement materials is not appropriate for AAB concretes. The observed difference in Poisson’s ratio values compared to OPC concretes is attributed to the microstructural characteristics of AAB pastes, which, as previously discussed, result in mechanical changes, including variations in compressive strength and Young’s modulus [49,66].

3.4. Durability Assessment Results

3.4.1. Electrical Resistivity

The bulk electrical resistivity of the investigated AAB concretes are presented in Figure 6. The results found were 1.91 kΩ.cm and 0.97 kΩ.cm for the conventional aggregate concrete and BSSF-SS respectively, both under thermal curing. Based on Figure 6, those finding classify the concrete as of very high probability of corrosion [70] of the steel bars. Concerning the curing, there was no significant impact on the observed resistivity.
The electrical resistivities were similar to Noushini and Castel (2016) [54] with values up to 1.19 KΩ.cm, for mixtures of FA, Kaolite and GGBFS with sodium hydroxide and sodium silicate, submitted to thermal curing of 60 °C for 24 h. The low resistivity values are associated with high content presence of free metallic ions in the precursors or/and the high alkalinity in the pore solution due to the activators employed, such as Na+ [52,54,71]. The presence of very high iron contents in SS combined with a higher open porosity of the aggregates may justify the lower resistivity of AAB concretes with SS compared to AAB concretes with conventional aggregates, due to a higher conducting network and tunneling conduction [72].

3.4.2. Rapid Chloride Ions Penetration Test

Figure 7 presents a comparison between the measured chlorine ion penetration results, and the estimated values, based on the material’s electrical resistivity, calculated According to Section 3.4.1, AAB concretes with conventional aggregate and BSSF-SS aggregate showed chloride ion penetrability results of 8978 C and 17,332 C, respectively. The observed values classify the concrete as high chloride ion penetrability [51], a poor indication of durability, as illustrated in Figure 7. After the test completion, the superficial aspect of the AAB concretes specimens with BSSF-SS aggregates demonstrated electrochemical corrosion. The high results of chloride ion penetrability were associated with the low electrical resistivity of the material and the porosity present in binders produced with low calcium precursors such as FA [4,54], aligned with the superficial aspect visualized by Lee et al. (2019) [7].I In their studies involving AAB concrete based on FA and GGBFS, they detected that the resistance to chloride ion penetration increases with time. Concretes that presented values of chloride ion penetration close to 4000 C at 28 days decayed to values below 1000 C at 270 days.
The results obtained based on the Ohm’s laws, bulk resistivity, and dimensions of the tested specimen were 10,684 C and 20,987 C for conventional and BSSF-SS aggregate, respectively, under thermal curing, presented in Figure 7. The estimated chloride penetrability values based on electrical resistivity and ohm’s law were similar to those obtained using the rapid chloride ion penetrability test [12]. This indicates that the electrical properties of the material are a relevant parameter in the chloride ion penetrability test of ASTM C1202. The applicability of this accelerated test for measuring chloride ion penetrability in AAB concrete is questionable, considering its chemical composition. Further investigation is required into this characteristic of AAB, including the evaluation of chloride ion penetrability using alternative methodologies, such as visual analysis with the silver nitrate colorimetric method [73] or direct measurement of chloride content within the concrete through chemical analysis. Therefore, whether chloride ion penetrability should be assessed differently than for OPC, or adapted, especially when SS-aggregates are used.

3.4.3. Water Penetration Under Pressure

The results of the water penetration under pressure test are presented in Figure 8. The AAB concretes thermal cured with conventional aggregates showed an average penetration height of 3.5 cm and AABs concretes with BSSF-SS aggregates showed an average penetration of 17.3 cm, for 20-cm height specimens. This difference between the water penetration values can be attributed to the large porosity of BSSF-SS coarse aggregates (6%), 4 times higher than conventional coarse aggregates (1.6%). The AAB concretes with BSSF-SS aggregate also presented higher porosity values (11.9%) than those presented by AAB concrete with conventional aggregates (9.4%). The interaction between the binder and BSSF-SS aggregate could be created by an interconnected structure, as discussed in Section 3.4.4 The AAB concretes, ambient cured, with conventional aggregates showed an average penetration height of 8.5 cm and AABs concretes with BSSF-SS aggregates showed a total penetration.
The AAB concrete with conventional aggregates presented low values of water penetration under pressure. This concrete can be considered impermeable, since it presented penetration values of less than 5 cm [74]. The literature on this type of test in alkali-activated binders is still incipient. Atabey et al. (2020) [75] studied the penetration of water under pressure in alkali-activated mortars based on only FA and found penetration values between 9 mm and 150 mm. This reference serves as an example for alkali-activated concretes, as it uses different materials and proportions than in this study.

3.4.4. Microstructural Analysis

The AAB paste, after thermal curing, presented an open porosity of 33.9%, while under ambient curing presented open porosity of 26.6%. The higher porosity (27% higher) exhibited by thermal curing may be associated with the faster water exit during the curing process, the presence of thermal microcracks and the production of stronger and more compact alkali activation gels [11,76,77]. These results are between 20% and 45% recurrent in the literature of AAB and OPC [11,50]. Hardened binder pastes with low calcium content such as FA show higher porosity because N-A-S-H gels, common in this type of precursor are less dense than C-A-S-H gels [4,54]. The AAB utilized to produce the concrete was composed of 75% of FA to 25% of BOF-SS, by mass, which resulted in the intermediate porosity values.
AAB concrete with conventional aggregate presented an open porosity of 9.4%, while AAB concrete with BSSF-SS aggregates presented values of 11.9%, both under thermal cure at 28 days. The values found were lower than those presented by the AAB concretes of Noushini and Castel (2016) [54] with porosity between 13.7% to 15.4%, for binary mixtures of FA, Kaolite, and GGBFS, with natural aggregates. The AAB concretes evaluated by those authors showed lower porosity values than the OPC reference concretes, however, the AAB concretes showed lower electrical resistivity, indicative of conflicting durability results.
Figure 9 compares the diffraction patterns of alkali-activated binders (AABs) with and without thermal curing. The comparison between the precursors’ diffraction patterns (Figure 1b) and those of the produced binders (Figure 9) highlights the mineralogical transformations induced by alkali activation [21]. The AAB pastes displayed peaks associated with quartz (SiO2), calcium oxide (CaO), calcium iron silicate, and calcium iron oxide phases. Thermal curing enhanced the intensity of crystalline peaks, particularly secondary phases related to calcium and iron oxides, while reducing the amorphous hump at 2θ between 20° and 35°. This occurs because thermal curing promotes and accelerates structural reorganization, increasing the intensity and sharpness of crystalline peaks [4,9,78].
Figure 10 presents this research’s AAB microstructure under ambient and thermal curing after 28 days of contact between precursors and activators. The paste presented some voids associated with “free” water or water released during the condensation step of the gels, which is totally or partially removed during the curing process [76,77]. AAB cured at 65 °C presented a few cracks of thermal origin that may facilitate the penetration of products harmful to the durability of concrete [11,26].
AABs composed of precursors with low calcium content (such as FA comparatively to SS) present a more porous structure, with a sugary-looking granular aspect, and worse performance regarding chloride penetration [11,21,26]. Meanwhile, precursors from binary mixtures or with higher calcium content present a more homogeneous and compact appearance, performing better regarding durability comparisons [26,79]. The microstructure of the binder applied to the concrete presented a predominantly homogeneous aspect, but with spots of “sugary” aspect. Moreover, the paste presented voids and cracks of thermal origin. This behavior addresses the low durability parameters presented, as discussed in Section 3.4.
The microstructure of AAB pastes can exhibit distinct characteristics depending on the calcium content and the reaction products formed. Zones with higher calcium content tend to experience shrinkage and the formation of microcracks over time, whereas those with lower calcium content become progressively less permeable [30]. An increase in curing temperature densifies the fly ash-based matrix but induces microcracks in slag-based matrices due to drying shrinkage [67]. This behavior is associated with gel pores smaller than 10 nm [80], which are more pronounced in C-S-H hydrates than in N-A-S-H hydrates under elevated temperatures [26]. Conversely, pores in the range of 10 to 104 nm play a more significant role in reducing chloride penetration coefficients [80].
Figure 11 presents micrographs of the interfacial transition zones (ITZs) between the conventional aggregates and the AAB for the material after 28 days of contact between precursors and activators. This zone is composed of dense and uniform alkali-activation products highly bound to the aggregate surface [81,82].
The AAB concretes present a reduced ITZ (up to 4 μm) [57] compared to other concretes, such as those based on Portland cement (from 15 μm to 50 μm) [79], is associated with the high strength of AABs concretes [57]. The AAB concrete with conventional aggregates under thermal cure, in Figure 11c,d, presented a smaller ITZ and more homogeneous gels, attributed to the thermal curing process. This explains the similar compressive strength values presented by the binder (64.4 MPa) and the AAB concrete with conventional aggregate (64.1 MPa), both under thermal curing. This was only possible due to the proper interaction between the aggregates interface and the paste, and the formation of a transition zone composed of high-strength gels. In other words, there seems not to exist a zone of fragility in the ITZ, since the strength of the binder was inherited directly by the concrete.
It was not possible to identify the zones between the AAB paste and the BSSF-SS aggregate, since the material presented a very uniform appearance. The use of SS aggregates optimizes the interfacial zone between the aggregate and the binder [10,13] and ITZ delimitations could not be visually detected in the micrographics. This may be associated with the reaction between the binder and SS aggregates, which has similar chemical composition [15]. This interfacial interaction occurs due to the formation of hydrated ion agglomerates from the interaction of water accumulated on the surface of the steel aggregate and the migration of metallic ions Ca2+ and Na+ to this region, forming a stabilized region [15].
It is observed that the durability indications found in this research were conflicting. The durability measurements based on electrical parameters presented indications of low durability, but the material presented regular porosity and low water penetration under pressure. Since the chloride ingress into concrete can occur by capillarity, permeability, diffusion, and migration through an electric field [71], the lower porosity observed is not favorable to the ingress of harmful substances such as chlorides, but the lower resistivity can facilitate their electrochemical ingress. Also, the calculated electrical currents allowed demonstrate that the measured electrical current in chloride penetration tests are not necessarily due to chloride penetration, but to the materials’ low electrical resistivity. Therefore, further analysis should be carried out before classifying the material as low durability concrete. A comprehensive understanding of AAB concrete’s durability requires more in-depth analyses. Key areas of investigation include the relationship between pore structure formation and chloride ion penetration rates, water permeability under pressure, comparative evaluations of methodologies for measuring chloride penetration, and a detailed characterization of the pore solution. This area is a research gap for future studies.

4. Conclusions

In this research, self-compacting concrete parameters, mechanical performance, and durability of alkali-activated concretes were evaluated. The alkali-activated binder is composed of a precursor that is a blend of steel slag and fly ash activated with sodium hydroxide and sodium silicate. The alkali-activated concrete is a mix of this binder and conventional or steel slag aggregates. Furthermore, two curing processes were evaluated: thermal curing (65 °C) and ambient curing. In the fresh state, slump flow, T50, and J-ring tests were performed. The mechanical performance of the material was evaluated with compressive strength and Young’s modulus based on static [43], ultrasonic [45], and resonant [44] methodologies. The durability behavior was evaluated with chloride ions penetrability tests, electrical resistivity, water penetration under pressure and characterization of the pore structure, and microstructure. The main conclusions obtained from the results were:
  • All concretes formulations presented a high passing ability, however, with elevated flow time in comparison with the OPC concretes, higher than the OPC average;
  • The thermal curing process increases up to 60% the compressive strength and up to 30% the Young’s modulus at 28 days. Thermal curing resulted in an initial compressive strength of 80% of the 28-day strength;
  • The AAB concrete Young’s modulus values were lower than OPC concretes, however with a similar strength;
  • Static and Dynamic methodologies show satisfactory accuracy for Young’s modulus estimation. However, to estimate the Young’s modulus from ultrasonic compression waves, the assumed fixed value of 0.2 for the Poisson’s ratio proved to be unsatisfactory;
  • The use of BSSF-SS aggregates decreases the compressive strength, and increased the Young’s modulus and flow time of AABs concretes;
  • The approaches used to evaluate the durability of OPC concretes resulted in conflicting durability results when applied to AAB concretes, especially when associated with electrical measurements. This should be further investigated, and it seems reasonable to suppose that methods of durability investigation should be adapted for geopolymer concretes;
  • AAB concretes presented a reduced transition zone gap compared to Portland cement concretes. Moreover, the thermal curing process is beneficial for the transition zone properties and for the production of AAB concretes with high strength.
This research contributed to the characterization of AAB concretes based on SS and FA, with natural and SS aggregates. The results provided information regarding self-compacting concrete parameters, compressive strength, Young’s modulus, chloride penetrability, pore structure, and interfacial transition zone. In addition, it has contributed to the necessary knowledge for the future utilization of industrial waste to produce technically feasible materials. Furthermore, it has contributed to the knowledge development for the future application of industrial by-products in the production of technically viable materials. It also provides a basis for advancing the understanding of durability and optimizing the selection of by-products to meet the specific performance requirements of engineering projects.

Author Contributions

Conceptualization, L.B.R.A., D.L.L.T. and L.F.A.L.B.; methodology, L.B.R.A., D.L.L.T. and H.N.C.; validation, L.F.A.L.B., R.C. and A.F.; formal analysis, H.N.C.; investigation L.B.R.A., D.L.L.T. and L.F.A.L.B.; resources, L.F.A.L.B., D.L.L.T., A.E.B.C. and H.N.C.; data curation, L.B.R.A., D.L.L.T. and L.F.A.L.B.; writing—original draft preparation, L.B.R.A. and D.L.L.T.; writing—review and editing, all authors; visualization, all authors; supervision, L.F.A.L.B., R.C., A.E.B.C. and A.F.; project administration, L.F.A.L.B. and A.E.B.C.; funding acquisition, L.F.A.L.B., A.F. and A.E.B.C. All authors have read and agreed to the published version of the manuscript.

Funding

This research has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie COFUND grant agreement No. 101034248. This research was supported by the following institutions: Coordination for the Improvement of Higher Education Personnel (CAPES) and the National Council for Scientific and Technological Development (CNPq), project numbers: 312817/2020-7; 409236/2022-5; 308888/2020-0.

Data Availability Statement

The data referenced in this study are accessible upon formal request to the corresponding author.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Singh, N.B.; Middendorf, B. Geopolymers as an Alternative to Portland Cement: An Overview. Constr. Build. Mater. 2020, 237, 117455. [Google Scholar] [CrossRef]
  2. Benhelal, E.; Zahedi, G.; Shamsaei, E.; Bahadori, A. Global Strategies and Potentials to Curb CO2 Emissions in Cement Industry. J. Clean. Prod. 2013, 51, 142–161. [Google Scholar] [CrossRef]
  3. Hasanbeigi, A.; Price, L.; Lin, E. Emerging Energy-Efficiency and CO2 Emission-Reduction Technologies for Cement and Concrete Production: A Technical Review. Renew. Sustain. Energy Rev. 2012, 16, 6220–6238. [Google Scholar] [CrossRef]
  4. Provis, J.L.; Van Deventer, J.S.J. (Eds.) Alkali Activated Materials: State-of-the-Art Report, RILEM TC 224-AAM; RILEM State-of-the-Art Reports; Springer: Dordrecht, The Netherlands, 2014; Volume 13, ISBN 978-94-007-7671-5. [Google Scholar]
  5. Yang, K.-H.; Song, J.-K.; Song, K.-I. Assessment of CO2 Reduction of Alkali-Activated Concrete. J. Clean. Prod. 2013, 39, 265–272. [Google Scholar] [CrossRef]
  6. Saini, G.; Vattipalli, U. Assessing Properties of Alkali Activated GGBS Based Self-Compacting Geopolymer Concrete Using Nano-Silica. Case Stud. Constr. Mater. 2020, 12, e00352. [Google Scholar] [CrossRef]
  7. Lee, W.-H.; Wang, J.-H.; Ding, Y.-C.; Cheng, T.-W. A Study on the Characteristics and Microstructures of GGBS/FA Based Geopolymer Paste and Concrete. Constr. Build. Mater. 2019, 211, 807–813. [Google Scholar] [CrossRef]
  8. Alonso, M.M.; Gismera, S.; Blanco, M.T.; Lanzón, M.; Puertas, F. Alkali-Activated Mortars: Workability and Rheological Behaviour. Constr. Build. Mater. 2017, 145, 576–587. [Google Scholar] [CrossRef]
  9. Xie, T.; Visintin, P.; Zhao, X.; Gravina, R. Mix Design and Mechanical Properties of Geopolymer and Alkali Activated Concrete: Review of the State-of-the-Art and the Development of a New Unified Approach. Constr. Build. Mater. 2020, 256, 119380. [Google Scholar] [CrossRef]
  10. Pradhan, P.; Panda, S.; Kumar Parhi, S.; Kumar Panigrahi, S. Factors Affecting Production and Properties of Self-Compacting Geopolymer Concrete—A Review. Constr. Build. Mater. 2022, 344, 128174. [Google Scholar] [CrossRef]
  11. Zhang, Z.; Wang, H. 9—Analysing the Relation between Pore Structure and Permeability of Alkali-Activated Concrete Binders. In Handbook of Alkali-Activated Cements, Mortars and Concretes; Pacheco-Torgal, F., Labrincha, J.A., Leonelli, C., Palomo, A., Chindaprasirt, P., Eds.; Woodhead Publishing: Oxford, UK, 2015; pp. 235–264. ISBN 978-1-78242-276-1. [Google Scholar]
  12. Tibbetts, C.M.; Paris, J.M.; Ferraro, C.C.; Riding, K.A.; Townsend, T.G. Relating Water Permeability to Electrical Resistivity and Chloride Penetrability of Concrete Containing Different Supplementary Cementitious Materials. Cem. Concr. Compos. 2020, 107, 103491. [Google Scholar] [CrossRef]
  13. Aldawsari, S.; Kampmann, R.; Harnisch, J.; Rohde, C. Setting Time, Microstructure, and Durability Properties of Low Calcium Fly Ash/Slag Geopolymer: A Review. Materials 2022, 15, 876. [Google Scholar] [CrossRef] [PubMed]
  14. Thomas, R.J.; Peethamparan, S. Stepwise Regression Modeling for Compressive Strength of Alkali-Activated Concrete. Constr. Build. Mater. 2017, 141, 315–324. [Google Scholar] [CrossRef]
  15. Provis, J.L.; van Deventer, J.S.J. 16—Geopolymers and Other Alkali-Activated Materials. In Lea’s Chemistry of Cement and Concrete, 5th ed.; Hewlett, P.C., Liska, M., Eds.; Butterworth-Heinemann: Oxford, UK, 2019; pp. 779–805. ISBN 978-0-08-100773-0. [Google Scholar]
  16. dos Santos, W.W.; Coelho, L.M.; Monteiro, S.N.; Marques, M.E.S.; Guimarães, A.C.R. Evaluation of Steel Slag as a Sustainable Alternative Aggregate for Railway Ballast: A Shakedown Theory-Based Approach. Buildings 2024, 14, 3546. [Google Scholar] [CrossRef]
  17. Nunes, V.A.; Borges, P.H.R. Recent Advances in the Reuse of Steel Slags and Future Perspectives as Binder and Aggregate for Alkali-Activated Materials. Constr. Build. Mater. 2021, 281, 122605. [Google Scholar] [CrossRef]
  18. Palankar, N.; Ravi Shankar, A.U.; Mithun, B.M. Investigations on Alkali-Activated Slag/Fly Ash Concrete with Steel Slag Coarse Aggregate for Pavement Structures. Int. J. Pavement Eng. 2017, 18, 500–512. [Google Scholar] [CrossRef]
  19. Guo, X.; Pan, X. Mechanical Properties and Mechanisms of Fiber Reinforced Fly Ash–Steel Slag Based Geopolymer Mortar. Constr. Build. Mater. 2018, 179, 633–641. [Google Scholar] [CrossRef]
  20. Cristelo, N.; Coelho, J.; Miranda, T.; Palomo, Á.; Fernández-Jiménez, A. Alkali Activated Composites—An Innovative Concept Using Iron and Steel Slag as Both Precursor and Aggregate. Cem. Concr. Compos. 2019, 103, 11–21. [Google Scholar] [CrossRef]
  21. Zhu, X.; Li, W.; Du, Z.; Zhou, S.; Zhang, Y.; Li, F. Recycling and Utilization Assessment of Steel Slag in Metakaolin Based Geopolymer from Steel Slag By-Product to Green Geopolymer. Constr. Build. Mater. 2021, 305, 124654. [Google Scholar] [CrossRef]
  22. Tian, Z.; Zhang, Z.; Liu, H.; Zheng, W.; Tang, X.; Gui, Z. Interfacial Characteristics and Mechanical Behaviors of Geopolymer Binder with Steel Slag Aggregate: Insights from Molecular Dynamics. J. Clean. Prod. 2022, 362, 132385. [Google Scholar] [CrossRef]
  23. Crude Steel Production and 2021 Global Crude Steel Production Totals. December 2021. Available online: https://worldsteel.org/ (accessed on 1 February 2024).
  24. Yu, J.; Wang, K. Study on Characteristics of Steel Slag for CO2 Capture. Energy Fuels 2011, 25, 5483–5492. [Google Scholar] [CrossRef]
  25. Naidu, T.S.; Sheridan, C.M.; van Dyk, L.D. Basic Oxygen Furnace Slag: Review of Current and Potential Uses. Miner. Eng. 2020, 149, 106234. [Google Scholar] [CrossRef]
  26. Soutsos, M.; Boyle, A.P.; Vinai, R.; Hadjierakleous, A.; Barnett, S.J. Factors Influencing the Compressive Strength of Fly Ash Based Geopolymers. Constr. Build. Mater. 2016, 110, 355–368. [Google Scholar] [CrossRef]
  27. Campos, S.A.; Rafael, M.F.C.; Cabral, A.E.B. Evaluation of Steel Slag of Companhia Siderúrgica Do Pecém Replacing Fine Aggregate on Mortars. Procedia Struct. Integr. 2018, 11, 145–152. [Google Scholar] [CrossRef]
  28. Rashad, A.M.; Khafaga, S.A.; Gharieb, M. Valorization of Fly Ash as an Additive for Electric Arc Furnace Slag Geopolymer Cement. Constr. Build. Mater. 2021, 294, 123570. [Google Scholar] [CrossRef]
  29. Hwang, C.-L.; Huynh, T.-P. Effect of Alkali-Activator and Rice Husk Ash Content on Strength Development of Fly Ash and Residual Rice Husk Ash-Based Geopolymers. Constr. Build. Mater. 2015, 101, 1–9. [Google Scholar] [CrossRef]
  30. Amancio, F.A. Estudo de Propriedades no Estado Fresco de Argamassas de Revestimento Com Escória de Aciaria BSSF. Master’s Thesis, Universidade Federal do Ceará, Fortaleza, Ceará, Brazil, 2019. [Google Scholar]
  31. ASTM C618; Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use as a Mineral Admixture in Concrete. American Society for Testing and Materials: West Conshohocken, PA, USA, 2019. [CrossRef]
  32. Rafeet, A.; Vinai, R.; Soutsos, M.; Sha, W. Guidelines for Mix Proportioning of Fly Ash/GGBS Based Alkali Activated Concretes. Constr. Build. Mater. 2017, 147, 130–142. [Google Scholar] [CrossRef]
  33. Nagaraj, V.K.; Babu, D.L.V. Assessing the Performance of Molarity and Alkaline Activator Ratio on Engineering Properties of Self-Compacting Alkaline Activated Concrete at Ambient Temperature. J. Build. Eng. 2018, 20, 137–155. [Google Scholar] [CrossRef]
  34. Bondar, D.; Nanukuttan, S.; Provis, J.L.; Soutsos, M. Efficient Mix Design of Alkali Activated Slag Concretes Based on Packing Fraction of Ingredients and Paste Thickness. J. Clean. Prod. 2019, 218, 438–449. [Google Scholar] [CrossRef]
  35. ASTM C1611; Standard Test Method for Slump Flow of Self-Consolidating Concrete. American Society for Testing and Materials: West Conshohocken, PA, USA, 2010. [CrossRef]
  36. ASTM C1621; Standard Test Method for Passing Ability of Self-Consolidating Concrete by J-Ring. American Society for Testing and Materials: West Conshohocken, PA, USA, 2014. [CrossRef]
  37. European Federation of National Associations Representing for Concrete (EFNARC). European Guidelines for Self-Compacting Concrete: Specification, Production and Use, EFNARC—Publication Index|NBS; European Project Group: Brussels, Belgium, 2005; p. 68. [Google Scholar]
  38. Talha Junaid, M.; Kayali, O.; Khennane, A.; Black, J. A Mix Design Procedure for Low Calcium Alkali Activated Fly Ash-Based Concretes. Constr. Build. Mater. 2015, 79, 301–310. [Google Scholar] [CrossRef]
  39. ASTM C39; Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens. American Society for Testing and Materials: West Conshohocken, PA, USA, 2021. [CrossRef]
  40. Gjørv, O.E. 7—High-Strength Concrete. In Developments in the Formulation and Reinforcement of Concrete, 2nd ed.; Mindess, S., Ed.; Woodhead Publishing Series in Civil and Structural Engineering; Woodhead Publishing: Cambridge, UK, 2008; pp. 153–170. ISBN 978-0-08-102616-8. [Google Scholar]
  41. ASTM C469; Standard Test Method for Flexural Strength of Hydraulic-Cement Mortars. American Society for Testing and Materials: West Conshohocken, PA, USA, 2022. [CrossRef]
  42. ASTM C215; Standard Test Method for Fundamental Transverse, Longitudinal, and Torsional Resonant Frequencies of Concrete Specimens. American Society for Testing and Materials: West Conshohocken, PA, USA, 2019. [CrossRef]
  43. ASTM C597; Standard Test Method for Pulse Velocity Through Concrete. American Society for Testing and Materials: West Conshohocken, PA, USA, 2016. [CrossRef]
  44. Bezerra, A.K.L.; Monteiro, N.d.C.; Amaral, C.C.d.; Coelho, A.A.d.P.; Silveira, J.A.N.d.; Babadopulos, L.F. de A.L.; Soares, J.B. Desenvolvimento de ensaio de ressonância por impacto para determinação de rigidez de diferentes materiais. Transportes 2022, 30, 2757. [Google Scholar] [CrossRef]
  45. Nguyen, K.T.; Ahn, N.; Le, T.A.; Lee, K. Theoretical and Experimental Study on Mechanical Properties and Flexural Strength of Fly Ash-Geopolymer Concrete. Constr. Build. Mater. 2016, 106, 65–77. [Google Scholar] [CrossRef]
  46. Mandel, J. Cours de Mécanique Des Milieux Continus. Tome 2: Mécanique Des Solides; Gauthier-Villars: Paris, France, 1966. [Google Scholar]
  47. Bezerra, A.K.L. Development of a Non-Destructive Test for Viscoelastic Characterization of Asphalt Mixtures. Master’s Thesis, Universidade Federal do Ceará: Fortaleza, Ceará, Brazil, 2023. [Google Scholar]
  48. Thomas, R.J.; Peethamparan, S. Alkali-Activated Concrete: Engineering Properties and Stress–Strain Behavior. Constr. Build. Mater. 2015, 93, 49–56. [Google Scholar] [CrossRef]
  49. Ding, Y.; Dai, J.-G.; Shi, C.-J. Mechanical Properties of Alkali-Activated Concrete: A State-of-the-Art Review. Constr. Build. Mater. 2016, 127, 68–79. [Google Scholar] [CrossRef]
  50. Mehta, P.K.; Monteiro, P.J.M. Concrete: Microstructure, Properties, and Materials, 4th ed.; McGraw-Hill Education: New York, NY, USA, 2014; ISBN 978-0-07-179787-0. [Google Scholar]
  51. ASTM C1202; Standard Test Method for Electrical Indication of Concrete’s Ability to Resist Chloride Ion Penetration. American Society for Testing and Materials: West Conshohocken, PA, USA, 2019. [CrossRef]
  52. ASTM C1876; Standard Test Method for Bulk Electrical Resistivity or Bulk Conductivity of Concrete. American Society for Testing and Materials: West Conshohocken, PA, USA, 2019. [CrossRef]
  53. Filho, J.H.; Medeiros, M.H.F.; Pereira, E.; Helene, P.; Isaia, G.C. High-Volume Fly Ash Concrete with and without Hydrated Lime: Chloride Diffusion Coefficient from Accelerated Test. J. Mater. Civ. Eng. 2013, 25, 411–418. [Google Scholar] [CrossRef]
  54. Noushini, A.; Castel, A. The Effect of Heat-Curing on Transport Properties of Low-Calcium Fly Ash-Based Geopolymer Concrete. Constr. Build. Mater. 2016, 112, 464–477. [Google Scholar] [CrossRef]
  55. EN 12390-8; Testing Hardened Concrete—Part 8: Depth of Penetration of Water Under Pressure. European Standard: Pilsen, Czech Republic, 2020.
  56. ASTM C642; Standard Test Method for Density, Absorption, and Voids in Hardened Concrete. American Society for Testing and Materials: West Conshohocken, PA, USA, 2021. [CrossRef]
  57. Demie, S.; Nuruddin, M.F.; Shafiq, N. Effects of Micro-Structure Characteristics of Interfacial Transition Zone on the Compressive Strength of Self-Compacting Geopolymer Concrete. Constr. Build. Mater. 2013, 41, 91–98. [Google Scholar] [CrossRef]
  58. Kai, M.-F.; Dai, J.-G. Understanding Geopolymer Binder-Aggregate Interfacial Characteristics at Molecular Level. Cem. Concr. Res. 2021, 149, 106582. [Google Scholar] [CrossRef]
  59. Huseien, G.F.; Sam, A.R.M.; Alyousef, R. Texture, Morphology and Strength Performance of Self-Compacting Alkali-Activated Concrete: Role of Fly Ash as GBFS Replacement. Constr. Build. Mater. 2021, 270, 121368. [Google Scholar] [CrossRef]
  60. Gupta, N.; Siddique, R.; Belarbi, R. Sustainable and Greener Self-Compacting Concrete Incorporating Industrial By-Products: A Review. J. Clean. Prod. 2021, 284, 124803. [Google Scholar] [CrossRef]
  61. Mohammedameen, A. Performance of Alkali-Activated Self-Compacting Concrete with Incorporation of Nanosilica and Metakaolin. Sustainability 2022, 14, 6572. [Google Scholar] [CrossRef]
  62. EN 206:2013+A2:2021; Concrete—Specification, Performance, Production and Conformity. European Standard: Pilsen, Czech Republic, 2021.
  63. Palankar, N.; Ravi Shankar, A.U.; Mithun, B.M. Studies on Eco-Friendly Concrete Incorporating Industrial Waste as Aggregates. Int. J. Sustain. Built Environ. 2015, 4, 378–390. [Google Scholar] [CrossRef]
  64. Bahmani, H.; Mostofinejad, D. Microstructure of Ultra-High-Performance Concrete (UHPC)—A Review Study. J. Build. Eng. 2022, 50, 104118. [Google Scholar] [CrossRef]
  65. Fernandez-Jimenez, A.M.; Palomo, A.; Lopez-Hombrados, C. Engineering Properties of Alkali-Activated Fly Ash Concrete. Mater. J. 2006, 103, 106–112. [Google Scholar] [CrossRef]
  66. Němeček, J.; Šmilauer, V.; Kopecký, L. Nanoindentation Characteristics of Alkali-Activated Aluminosilicate Materials. Cem. Concr. Compos. 2011, 33, 163–170. [Google Scholar] [CrossRef]
  67. Aliabdo, A.A.; Abd Elmoaty, A.E.M.; Salem, H.A. Effect of Cement Addition, Solution Resting Time and Curing Characteristics on Fly Ash Based Geopolymer Concrete Performance. Constr. Build. Mater. 2016, 123, 581–593. [Google Scholar] [CrossRef]
  68. Beushausen, H.; Dittmer, T. The Influence of Aggregate Type on the Strength and Elastic Modulus of High Strength Concrete. Constr. Build. Mater. 2015, 74, 132–139. [Google Scholar] [CrossRef]
  69. Wang, G.C. 2—Ferrous Metal Production and Ferrous Slags. In The Utilization of Slag in Civil Infrastructure Construction; Wang, G.C., Ed.; Woodhead Publishing: Cambridge, United Kingdom, 2016; pp. 9–33. ISBN 978-0-08-100994-9. [Google Scholar]
  70. AASHTO PP 84—Standard Practice for Developing Performance Engineered Concrete Pavement Mixtures|GlobalSpec. Available online: https://standards.globalspec.com/std/14221373/AASHTO%20PP%2084 (accessed on 11 December 2023).
  71. Mazer, W.; Lima, M.G.; Medeiros-Junior, R.A.; Wickzick, L.F.S. Chloride Ingress into Concrete under Different Conditions of Temperature and Marine Zones. Mag. Concr. Res. 2021, 73, 1180–1188. [Google Scholar] [CrossRef]
  72. Ahmed, S.M.; Kamal, I. Electrical Resistivity and Compressive Strength of Cement Mortar Based on Green Magnetite Nanoparticles and Wastes from Steel Industry. Case Stud. Constr. Mater. 2022, 17, e01712. [Google Scholar] [CrossRef]
  73. Pontes, C.V.; Réus, G.C.; Araújo, E.C.; Medeiros, M.H.F. Silver Nitrate Colorimetric Method to Detect Chloride Penetration in Carbonated Concrete: How to Prevent False Positives. J. Build. Eng. 2021, 34, 101860. [Google Scholar] [CrossRef]
  74. Neville, A.; Brooks, J. Concrete Technology: Update, 2nd ed.; London, Longman Group UK Limited: London, UK, 1997; ISBN 0-582-98859-4. [Google Scholar]
  75. Atabey, İ.İ.; Karahan, O.; Bilim, C.; Atiş, C.D. The Influence of Activator Type and Quantity on the Transport Properties of Class F Fly Ash Geopolymer. Constr. Build. Mater. 2020, 264, 120268. [Google Scholar] [CrossRef]
  76. Lloyd, R.R.; Provis, J.L.; Smeaton, K.J.; van Deventer, J.S.J. Spatial Distribution of Pores in Fly Ash-Based Inorganic Polymer Gels Visualised by Wood’s Metal Intrusion. Microporous Mesoporous Mater. 2009, 126, 32–39. [Google Scholar] [CrossRef]
  77. Wang, Y.-S.; Alrefaei, Y.; Dai, J.-G. Silico-Aluminophosphate and Alkali-Aluminosilicate Geopolymers: A Comparative Review. Front. Mater. 2019, 6, 106. [Google Scholar] [CrossRef]
  78. Fernández-Jiménez, A.; Palomo, A.; Criado, M. Microstructure Development of Alkali-Activated Fly Ash Cement: A Descriptive Model. Cem. Concr. Res. 2005, 35, 1204–1209. [Google Scholar] [CrossRef]
  79. Nath, P.; Sarker, P.K. Effect of GGBFS on Setting, Workability and Early Strength Properties of Fly Ash Geopolymer Concrete Cured in Ambient Condition. Constr. Build. Mater. 2014, 66, 163–171. [Google Scholar] [CrossRef]
  80. Hu, X.; Shi, C.; Shi, Z.; Zhang, L. Compressive Strength, Pore Structure and Chloride Transport Properties of Alkali-Activated Slag/Fly Ash Mortars. Cem. Concr. Compos. 2019, 104, 103392. [Google Scholar] [CrossRef]
  81. Luo, Z.; Li, W.; Wang, K.; Castel, A.; Shah, S.P. Comparison on the Properties of ITZs in Fly Ash-Based Geopolymer and Portland Cement Concretes with Equivalent Flowability. Cem. Concr. Res. 2021, 143, 106392. [Google Scholar] [CrossRef]
  82. Fan, J.; Zhu, H.; Shi, J.; Li, Z.; Yang, S. Influence of Slag Content on the Bond Strength, Chloride Penetration Resistance, and Interface Phase Evolution of Concrete Repaired with Alkali Activated Slag/Fly Ash. Constr. Build. Mater. 2020, 263, 120639. [Google Scholar] [CrossRef]
Buildings 15 00457 g001
Figure 1. Precursors characterization: (a) Particle size distribution (PSD); (b) Precursors diffraction patterns.
Figure 1. Precursors characterization: (a) Particle size distribution (PSD); (b) Precursors diffraction patterns.
Buildings 15 00457 g001
Buildings 15 00457 g002
Figure 2. Aggregates characterization and dosage: (a) Particle size distribution (PSD); (b) Aggregate packaging by void content analysis.
Figure 2. Aggregates characterization and dosage: (a) Particle size distribution (PSD); (b) Aggregate packaging by void content analysis.
Buildings 15 00457 g002
Buildings 15 00457 g003
Figure 3. Aspect of sections of the produced AAB concretes: (a) Ground specimen with conventional granitic aggregate; (b) Ground specimen with BSSF-SS aggregate.
Figure 3. Aspect of sections of the produced AAB concretes: (a) Ground specimen with conventional granitic aggregate; (b) Ground specimen with BSSF-SS aggregate.
Buildings 15 00457 g003
Buildings 15 00457 g004
Figure 4. Compressive strength of AAB concretes with conventional and BSSF-SS aggregates, at 7, 14, and 28 days.
Figure 4. Compressive strength of AAB concretes with conventional and BSSF-SS aggregates, at 7, 14, and 28 days.
Buildings 15 00457 g004
Buildings 15 00457 g005
Figure 5. Comparison between the methods for determining Young’s modulus for AABs concretes, at 28 days.
Figure 5. Comparison between the methods for determining Young’s modulus for AABs concretes, at 28 days.
Buildings 15 00457 g005
Buildings 15 00457 g006
Figure 6. Bulk electrical resistivity of AAB concretes, at 28 days.
Figure 6. Bulk electrical resistivity of AAB concretes, at 28 days.
Buildings 15 00457 g006
Buildings 15 00457 g007
Figure 7. Rapid chloride ion penetration test of AAB concretes, under thermal cure, at 28 days.
Figure 7. Rapid chloride ion penetration test of AAB concretes, under thermal cure, at 28 days.
Buildings 15 00457 g007
Buildings 15 00457 g008
Figure 8. Water penetration under pressure of AABs concretes under thermal cure, at 28 days (a) Conventional Aggregate, (b) BSSF Steel Slag Aggregate.
Figure 8. Water penetration under pressure of AABs concretes under thermal cure, at 28 days (a) Conventional Aggregate, (b) BSSF Steel Slag Aggregate.
Buildings 15 00457 g008
Buildings 15 00457 g009
Figure 9. Diffraction patterns of the AAB pastes with ambient and thermal curing.
Figure 9. Diffraction patterns of the AAB pastes with ambient and thermal curing.
Buildings 15 00457 g009
Buildings 15 00457 g010
Figure 10. SEM images of AAB paste, at 28 days: (a) Ambient cure (b): Thermal cure.
Figure 10. SEM images of AAB paste, at 28 days: (a) Ambient cure (b): Thermal cure.
Buildings 15 00457 g010
Buildings 15 00457 g011
Figure 11. Microstructure of the interface zone of AAB concretes with conventional aggregates, at 28 days: (a,b) Ambient cure; (c,d) Thermal cure.
Figure 11. Microstructure of the interface zone of AAB concretes with conventional aggregates, at 28 days: (a,b) Ambient cure; (c,d) Thermal cure.
Buildings 15 00457 g011
Table 1. Chemical composition of precursors by XRF.
Table 1. Chemical composition of precursors by XRF.
MaterialAl2O3SiO2P2O5SO3ClK2OCaOTiO2MnOFe2O3
BOF Steel slag precursor (%m.)1.945.640.840.830.040.1453.14-2.9734.40
BSSF Steel slag aggregate (%m.)0.704.780.96-0.010.0540.460.424.1350.14
Fly ash (%m.)11.1442.170.531.080.063.9710.252.740.2726.98
Table 2. Aggregates physical properties.
Table 2. Aggregates physical properties.
ParametersCoarse AggregateFine Aggregate
Granitic (Conv.)BSSF-SSQuart Sand (Conv.)BSSF-SS
PSD (mm)4.75–12.59.5–259.5–25--
Bulk density (kg/m3)140614871835--
Open porosity (%)1.51.66.0--
Specific gravity (-)2.622.633.602.573.58
Fineness mod. (-)---2.662.58
Table 3. Mix parameters of AAB concretes.
Table 3. Mix parameters of AAB concretes.
MaterialsAAB Concrete—Conv. Aggr.AAB Concrete—BSSF-SS Aggr.
(kg/m3)% vol.(kg/m3)% vol.
Fly ash 382.116.3382.116.3
BOF Steel slag prec. 127.44.1127.44.1
NaOH (solution) 135.910.4135.910.4
Na2SiO3 (solution)120.17.6120.17.6
Conv. fine aggr.561.621.8--
BSSF Steel slag fine aggr. --889.324.8
Conv. coarse aggr. 1 417.216,0--
Conv. coarse aggr. 2625.823.8--
BSSF Steel slag coarse aggr. --1333.936.8
Table 4. Results of T50, Slump Flow, and J-Ring for fresh state AAB concretes.
Table 4. Results of T50, Slump Flow, and J-Ring for fresh state AAB concretes.
Fresh State Tests AAB Concr. Conv. Aggr. AAB Concr. BSSF-SS Aggr. Classification Based:
EFNARK and ASTM C1621 		Slump Flow and J-Ring Aspect
T50 (s)13.83.5T50 ≤ 2 s → VS1T50 ≥ 2 s → VS2Buildings 15 00457 i001
Slump Flow (cm)57.573.755–65 → SF-166–75 → SF-2
J-ring (mm)27340–25 → No block25–50 → Min. block
Table 5. Estimated Young’s modulus based on compressive strength of AABs concretes, at 28 days.
Table 5. Estimated Young’s modulus based on compressive strength of AABs concretes, at 28 days.
Concrete TypeYoung’s Modulus
Static ModulusEstimated (Equation (4))Estimated (Equation (5))
Conv. Aggr.—Ambient cure20.226.629.8
Conv. Aggr.—Thrermal cure26.235.237.6
BSSF-SS Aggr.—Ambient cure26.524.527.8
BSSF-SS Aggr.—Thermal cure31.130.233.1
Table 6. Poisson’s ratio value for equivalence between ultrasonic and the Young’s modulus.
Table 6. Poisson’s ratio value for equivalence between ultrasonic and the Young’s modulus.
Poisson’s Ratio Based on Young’s Modulus TypeAAB Concrete—Conv. Aggr.AAB Concrete—BSSF-SS Aggr.
Ambient CureThermal CureAmbient CureThermal Cure
Resonant modulus0.3510.2700.4070.379
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Araújo, L.B.R.; Targino, D.L.L.; Babadopulos, L.F.A.L.; Fabbri, A.; Cabral, A.E.B.; Chehade, R.; Costa, H.N. Impact of Curing Temperature and Steel Slag Aggregates on High-Strength Self-Compacting Alkali-Activated Concrete. Buildings 2025, 15, 457. https://doi.org/10.3390/buildings15030457

AMA Style

Araújo LBR, Targino DLL, Babadopulos LFAL, Fabbri A, Cabral AEB, Chehade R, Costa HN. Impact of Curing Temperature and Steel Slag Aggregates on High-Strength Self-Compacting Alkali-Activated Concrete. Buildings. 2025; 15(3):457. https://doi.org/10.3390/buildings15030457

Chicago/Turabian Style

Araújo, Lucas B. R., Daniel L. L. Targino, Lucas F. A. L. Babadopulos, Antonin Fabbri, Antonio Eduardo. B. Cabral, Rime Chehade, and Heloina N. Costa. 2025. "Impact of Curing Temperature and Steel Slag Aggregates on High-Strength Self-Compacting Alkali-Activated Concrete" Buildings 15, no. 3: 457. https://doi.org/10.3390/buildings15030457

APA Style

Araújo, L. B. R., Targino, D. L. L., Babadopulos, L. F. A. L., Fabbri, A., Cabral, A. E. B., Chehade, R., & Costa, H. N. (2025). Impact of Curing Temperature and Steel Slag Aggregates on High-Strength Self-Compacting Alkali-Activated Concrete. Buildings, 15(3), 457. https://doi.org/10.3390/buildings15030457

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop