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Article

Fresh, Hardened, and Microstructural Properties of Ambient Cured One-Part Alkali-Activated Self-Consolidating Concrete

by
Dima Kanaan
1,
Amine el Mahdi Safhi
1,
Ahmed R. Suleiman
2 and
Ahmed M. Soliman
1,*
1
Department of Building, Civil, and Environmental Engineering, Concordia University, Montreal, QC H3G 1M8, Canada
2
Golder/WSP, 100 Scotia Court, Whitby, ON L1N 8Y6, Canada
*
Author to whom correspondence should be addressed.
Sustainability 2023, 15(3), 2451; https://doi.org/10.3390/su15032451
Submission received: 30 December 2022 / Revised: 20 January 2023 / Accepted: 28 January 2023 / Published: 30 January 2023
(This article belongs to the Special Issue Sustainability and Green Construction)
Browse Figures
Versions Notes

Abstract

:
Several studies have investigated the properties of alkali-activated materials (AAM), considering it as a substitute of cementitious concrete. However, the studies on alkali-activated self-consolidating concrete (AASCC) are extremely limited. This paper investigated the properties of AASCCs utilizing ground granulated blast furnace slag (GGBFS) as the main precursor. Single, binary, and ternary AASCCs were produced using fly ash Class-F (FA) and silica fumes (SF) as a replacement for GGBFS. The fresh properties including filing ability, passing ability and stability, as well as the hardened properties including unconfined compressive strength, ultrasonic pulse velocity, electrical resistivity, absorption, and sorptivity of the ambient cured one-part AASCC mixtures with different precursor blends were investigated. In addition, the microstructural properties of 90-day AASCC blends were studied by various microscale analysis methods. This paper demonstrated that the higher fraction of sodium carbonate/silicate activators, ranging from 20% to 25%, contributed to delayed reaction kinetics and satisfactory fresh and mechanical properties in all systems due to their nature. Slag replacement with variable SF or FA class-F ratios, instead, could indeed adjust the particle size distribution of the total binder material and improve the fresh concrete characteristics in binary and ternary systems. Finally, the formation of various reaction products and binding gels, i.e., C-(N)A-S-H, was found to have a significant impact on several transport mechanisms, including capillary sorptivity, permeable pores, and bulk electrical resistivity.

1. Introduction

Self-consolidating concrete (SCC) is a flowable concrete with a low yield stress value that ensures a minimum flow resistance without aggregates’ segregation and excessive bleeding [1]. The design of SCC systems is complicated since it is immediately correlated with the nature of the binder, the liquid-to-powder ratio, as well as used admixtures [2,3]. Furthermore, combining cement with one or more mineral materials is necessary to achieve a high powder content. The most commonly used supplementary cementing materials in concrete manufacturing are granulated blast furnace slag (GBFS), fly ash (FA), metakaolin (MK), and rice husk ash (RHA) [4]. Therefore, SCC necessitates a complete understanding of its different components and their impacts on the fresh, mechanical, and durability attributes [5]. Recently, alkali-activated materials (AAMs) were proposed as an alternative binder for ordinary Portland cement (OPC), meeting sustainability and eco-friendly criteria. A wide range of precursors and activators had been used in AAMs productions. In contrast to OPC systems, AAMs demonstrated higher mechanical properties and resistance to aggressive environments [6,7,8].
Alkali-activated self-consolidating concrete (AASCC) is not widely accepted, which is attributable to the limited data on its rheological and hardened performance. Many questions have been raised about the main factors influencing the performance of AASCC. The entire binder content and type, type of activator including dosage and molar ratio, also type of admixture and dosage, were identified as dominating factors [9,10]. For example, it was revealed that AASCC mixtures satisfying mechanical and workability requirements by EFNARC guideline [11] could produce a high slag content (~900 kg/m3) [12]. Recent studies have revealed that the fluidity rate of fly ash (FA)-based AASCCs decreases as the ratio of ground-granulated blast-furnace slag (GGBFS) substitutes increased [13,14,15,16]. This was attributed to the angular morphology and faster reactivity of GGBFS in a highly alkaline environment. Meanwhile, it was also reported that AASCC mixtures’ workability improved when GGBFS was replaced by 40%, 50%, and 60% FA [16]. Slag and ceramic waste were also used to produce AASCC; however, flowability decreased as slag content increased [13].
Moreover, it was reported that the viscosity of the used activator and pH would have a key role. For instance, the high viscosity of sodium silicate activators was found to reduce bleeding and segregation for AASCC [16]. Moreover, increasing sodium hydroxide (NaOH) content in the activator solution had an adverse influence on AASCC flowability [13]. Moreover, the high alkaline activator was discovered to adversely impact the effectiveness of the superplasticizer (SP) [8,10,17]. A previous study have suggested that the numerous SPs’ influence on the workability and strength of the FA-based mixtures mostly depends on the type of activator and SP [18]. For instance, Naphthalene-based SP was an effective type when using an 8M NaOH solution, whereas modified Polycarboxylate-based SP was the efficient type when a multi-compound activator was used. Moreover, Demie et al. [19] demonstrated that the FA-based AASCC compressive strength and microstructure characteristics had changed as the SP dosages increased up to 7%. In addition, adding low SP dosages resulted in a loose and porous interfacial transition zone (ITZ) and, thus, reduced compressive strength and vice versa.
AASCC combines the benefits of both SCC and sustainable development. Based on previous studies’ results [20,21], the current paper aims to assess the potential production of one-part AASCCs mixtures against the backdrop of indistinguishable OPC concrete characteristics. Additionally, it intends to investigate the effects of nature, concentration, and combination of various materials and dry-powder activators on AASCCs properties cured in ambient conditions. Concrete mixtures were developed by incorporating various dosages of dry-powder activators. The influences of activator dosage and binder composition on the fresh, hardened, and microstructural properties were critically assessed in terms of experimental findings.

2. Experimental Characterization

2.1. Materials Characterization

Ground granulated blast furnace slag (GGBFS) was used as the main precursor to produce single, binary, and ternary AASCC. Class-F Fly ash (FA) and silica fumes (SF) were added with various weight content as a replacement for GGBFS. For all AASCCs, a combination of two dry-powder activators was utilized to activate the source materials, i.e., anhydrous sodium metasilicate (Na2SiO3) and sodium carbonate (Na2CO3). The used Na2SiO3 had a density of 1.09 g/cm3 and a molar ratio of 1.0. The Na2CO3 powder had ≥99.5% purity and a density of 2.53 g/cm3. Natural siliceous sand with a fineness modulus of 2.5, a specific gravity value of 2.68, and water absorption of 1.5% was used. Furthermore, coarse aggregate with a maximum nominal size of 19 mm, a specific gravity value of 2.71, and water absorption of 0.4% was used. Their volumetric contents were set to 60% and 40%, respectively.

2.2. Mixtures Designations

Numerous combination rates of precursor materials were used (i.e., single, binary, and ternary) to manufacture different AASCCs. The total binder content was maintained at a constant of 525 kg/m3, offering a relatively high fine content (paste volume of 381–448 L/m3), complying with the SCC design guidelines [11]. For all mixtures, the dry-powder activator was included at 16%, 20%, and 25% by mass of the precursor material. The rates were chosen based on various trial-and-error assessments until achieving those rates that deliver sufficient alkalinity without efflorescence. The water-to-binder (w/b) ratio was fixed at 0.40 by the mass of the binder. Complete mixtures proportions are shown in Table 1. Before adding water to the mixtures, all solid materials (i.e., aggregates, binders, and activators) were initially mixed. Later, water was added to the mixture followed by mixing for ~3 min until a homogenous mix was achieved. A total of 15 AASCC mixtures were prepared with various contents of precursors (GGBFS, FA, and SF) and activator concentrations (MetaNa2SiO3 and Na2CO3) based on the preliminary results of mortar mixtures.
The single-precursor mixtures with 100% slag are designated as (S) mixtures. Two binary-precursor concrete groups were evaluated: (i) blends with 90% slag and 10% SF, with a assigned code (B1); and (ii) blends with 70% slag and 30% FA with a designated code (B2). Two ternary concrete groups were assessed: (i) mixtures with 60% slag, 33% FA, and 7% SF with a designated code (T1); and (ii) mixtures with 50% slag, 45% FA, and 5% SF, with a designated code (T2). The main variable between the mixtures in the same group is the activator’s content that (i.e., 16, 20, and 25%). The activator was prepared by mixing an equal percentage of the two powder activators (i.e., sodium Metasilicate (Na2SiO3) and sodium carbonate (Na2CO3). Therefore, the mixtures’ identification used is M-xx, where M is the mixture group (S, B, or T), and xx is the MetaNa2SiO3 + Na2CO3 activators %. For example, S-20% represents the mixture with single slag precursor material and 10% MetaNa2SiO3 + 10% Na2CO3 activators.

2.3. Testing Properties

After the mixing procedure, the fresh properties were evaluated, and numerous specimens were casted to study the hardened properties. Each specimen was cast without any vibration. Instantly after casting, samples were covered to prevent the evaporation of water and left intact at room temperature (23 ± 2 °C). Past 24 ± 4-h, the samples were demolded and transported to a curing chamber at 95% relative humidity and controlled temperature (23 ± 2 °C) until the age of testing. Table 2 summarizes the conducted tests on triplicate different samples.
X-ray diffraction (XRD) was conducted employing a Bruker D8 Advance diffractometer (CuKα radiation, 1.5406 Å) with an imaging plate detector to collect data in a range of 10–90° 2θ. In addition, solid-state 29Si MAS nuclear magnetic resonance (NMR) spectra were collected on a Bruker, Avance III HD 400 MHz spectrometer with a high-power 1H decoupling. The spectra were acquired at a spinning speed of 10 kHz and with a delay of 5 s. Representative samples from selected specimens were crushed, ground, and sieved. Powder samples < 75 μm were used in both XRD and 29Si NMR. Scanning electron microscopy (SEM) analysis was conducted on small chunks from selected specimens using a Hitachi S-3400N SEM at 15.0 kV accelerating voltage. This was coupled with energy dispersive X-ray analysis (EDX) utilizing a JEOL 35-cf spectrophotometer for elemental mapping and spot analysis.

3. Results and Discussion

3.1. Fresh Properties

3.1.1. Filing Ability

In terms of unconfined flowability, the S-flow and T500 test results for all AASCC mixtures are reported in Table 3. For all tested mixtures, increasing the activator dosages increased the slump. For AASCC single-precursor mixtures, S-25% was the only mixture that met the EFNARC requirements (i.e., >550 mm). Increasing the activator dosage from 16% to 20% had caused a considerable increase in S-flow from 30 to 510 mm for single-precursor mixtures, but still below the SF1 class [11]. The continuous dissolution of slag particles instigated the silicate and carbonate anions in the medium to be adsorbed on the slag surfaces as Ca2+ cations shield the slag silanol groups. This could lead to strong electric double layer repulsive forces between slag particles and particle separation, resulting in yield stress reduction. These results are in accordance with the literature [27].
A comparable tendency was noticed in binary-precursor concretes while substituting slag with 10% SF. For instance, in the B1 group, adding 16, 20, and 25% activator dosage increased the S-flow values from 443 to 448 and 583 mm, respectively. In the B1 group, replacing slag with 10% SF resulted in higher negative values for zeta potential and elevated pH. Cations such as Ca2+ were released during slag dissolution, where it is more prone to adsorb on slag particles’ silanol groups, resulting in attraction forces. It also caused the rapid formation of C-A-S-H gels and some electrostatic bonding, which led to substantial changes in the fresh properties. Conversely, B2 binary-precursor mixtures with 30% FA replacing slag showed higher S-flow diameter values. For instance, increasing the activator dosage from 16% to 25% led to 19% increase in the achieved flowability (>800 mm). All ternary-precursor mixtures in both groups had the best overall performance following the 550 to 850 mm flow range in EFNARC-guidelines with lower-viscosity levels. The filling capacity of these AASCCs remains high (i.e., >700 mm) beside the low viscosity levels (i.e., T500 < 3.0 s). Moreover, for T1 and T2 mixtures, increasing the activator from 16% to 25% caused ~15% and ~18% increase in the flowability, respectively.
Overall, binary, and ternary mixtures incorporating ≥ 30% FA and using the lowest activator dosage were within the second class (SF2) as per the EFNARC classification. Concrete mixtures in the SF2 class are suitable for various applications with excellent surface finishing and controlled segregation resistance. However, as a conclusion substituting slag with 10% SF at the highest activator dosage in B1 blends decreased the S-flow values and shifted the mixture to the S-flow SF1 class (Figure 1). For highly congested concrete reinforced structures, utilizing a B1 mix is critical. Contrariwise, as the FA ratio increased by up to 50% along with a 20% activator dosage, the blends tended to achieve the S-flow class SF3. This means better surface finishing would be achieved from a set of blends containing less slag, but it would be harder to overcome the segregation, as explained later.

3.1.2. Passing Ability

All AASCC blends prepared with a high dry-powder activator dosage (i.e., 25%) demonstrated better passing ability than those made with lower contents (Table 2). For AASCC single-precursor mixtures, changing the activator dosages from 16% and 20% did not change the L-box test result (≤0.65), while 85% was achieved with 25% activator dosage. Mixtures B1-16% and B1-20% showed a noticeable blocking at an L-box ratio of 0.55. Nevertheless, B1-25% described better performance, with a 36% increase in the measured blocking ratio. The second set of binary mixtures showed a better passing ability value as 30% FA is used. The blocking ratio of the B2 mixtures set ranged from 0.88 to 1.00 as the activator dosage increased, meeting EFNARC guidelines requirements. All ternary-precursor mixtures exhibited similarly blocking ratios > 0.85 (Figure 2), which are greater than the EFNARC guidelines for concrete mixtures vulnerable to blocking around reinforcement bars (i.e., <0.8). Thus, ternary-precursor mixtures showed excellent flowabilities and deficient viscosity levels, suitable for congested reinforcement structures. This is consistent with prior S-flow results (Figure 1), which showed that increasing the activator dosage reduced plastic viscosity and yield stress, improving the rheological properties.

3.1.3. Segregation Resistance (SR)

Table 2 presents the SR test results for all AASCC mixtures. Results were visually examined and ranked by the segregation index (SI%) in Figure 3. Test results of various mixtures showed three zones; resistant, tend to segregate, and severely segregated AASCC mixtures, divided by lines reflecting the suggested values. All concretes exhibited good passing ability with a segregation potential as the activator dosage increases. However, an exception was noticed in single-slag mixtures with 16% and 20% activator dosages and binary B1 (slag-SF) mixtures. For instance, the segregation potential increased marginally by ~5% as the activators’ dosages increased in the single-precursor mixtures. However, all B1 binary-precursor mixtures were found viscous. The SI was ~7% even when the activator dosage increased from 20% to 25%.
Quite the opposite, B2 mixes containing 367.5 kg/m3 of FA replacing slag tended to be segregated SI~15 to 30%. For example, the B2-16% mixture resulted in SI of 15%, which is less than 12% provided by B2-20%. Though, B2-25% reported a higher segregation potential, with ~80% increase in the measured stability ratio compared to B2-16%. Adequate SR is achieved as SI is below 15% as per the EFNARC guidelines. For the two sets of ternary-precursor mixtures, most of the mixtures exhibited a high potential for segregation. The SR increased by ~212% as the activator dosage increased to 25% in T1-AASCC, while it increased by 50% in T2-AASCC mixtures.
Overall, mixtures designed with binary and ternary precursor mixtures and higher activator dosages tend to have higher segregation potentials when S-flow are greater than 700 mm. Thus, there is a clear relationship between SR and activator dosage compared to precursor combination effects. Increasing the activator dosages (carbonate/silicate) had a positive effect on reaction kinetics retardation. The inclusion of sodium metasilicate had raised the magnitude of zeta potential and lowered the yield stress of the AASCC by increasing the double layer repulsive forces, in addition to the carbonate ions effect. It is important to note that such visual observations are insufficient but remain suitable to estimate the AASCC stability visually. This test was coupled with S-flow and l-box tests in the following sections.

3.1.4. Effects of Selected Activator and Dosage

The type and dosage of alkaline activators and their combination fundamentally affect the fresh characteristics of AASCC mixtures. When the activator dosage increased from 16% to 25%, the S-flow diameter and the passing ability increased synchronously for all AASCC mixtures in Figure 4a. This can be ascribed to the retardation in the reaction kinetics as the fraction of sodium carbonate/silicate activators increased [28]. The activator’s efficiency and pH value significantly affect the initial dissolution of source materials and the prolonged condensation reactions [29,30]. Due to their high alkalinity potential, sodium hydroxide and sodium silicate (water glass) are the most often used activators for the alkali activation process [31]; while sodium carbonate (Na2CO3), because of its lower pH potential, produces a lower early-age strength. As a result, the production of early age strength-gaining products would be delayed by the activation with Na2CO3 [32]. This may be because, prior to the production of C-(N)-A-S-H gels, sodium and carbonate ions ( CO 3 2 − ) from the activator quickly reacted with the dissolved calcium ions (Ca2+) from the slag [28]. Thus, delayed initial reactions would affect the mixtures’ workability results.
Meanwhile, the usage of synthetic silica chemicals such as anhydrous sodium metasilicate (Na2SiO3) resulted in better workability and high strength values for slag and FA one-part mixtures, as reported previously [18]. This is attributed to the anhydrous metasilicate particles being not fully dissolved, which significantly reduces the yield stress at early ages, improving workability [33]. Hence, the combination of sodium metasilicate and Na2CO3 is recommended to enhance AASCC workability. The relationship between the S-flow diameter and the SR index derived from the different AASCC mixtures using up to 25% dry-powder activators is shown in Figure 4b. There are straightforward ways to prevent segregation and maintain the homogeneity of OPC-SCC mixtures without the use of chemical admixtures, according to the EFNARC guidelines. For instance, increasing the fine material’s content, decreasing the coarse aggregate content, and lowering the w/b ratio [34]. The addition of activator powder over a constant binder content in AASCC mixtures was expected to influence the plastic viscosity and consequently mixture SR. However, the current study’s values indicated an inversely proportional relationship between the amount of dry-powder activator and the SR percentage, more precisely in binary and ternary-precursor mixtures with FA. The higher the w/b ratio due to FA’s low reactivity and activator dosage, the higher the segregation potential.

3.1.5. Effect of Precursor Combination

The absence of effective chemical additives that improve the flowability of one-part AASCCs necessitates proper precursor materials to ensure that the rheology is stable. In binary and ternary systems, slag substitution with different SF or FA ratios can adjust the particle size distribution of the binder materials. Additionally, the systems’ initial porosity would be modified and decreased, increasing the workability of the fresh concrete. Figure 5 shows the impact of substituting slag with SF and FA in different binary and ternary systems on the S-flow and SR within the first hour from the time of mixing.
According to the EFNARC, AASCC mixes with slag doses of >400 kg/m3 and activator dosages of >20% obtained good results. In contrast, the use of slag-precursor mixtures with an activator dose of at least 16% demonstrated significantly worse workability than binary and ternary precursor blends in AASCCs. In spite of this, the differences in particle size, morphology, and bulk density between binary and ternary precursor blends and slag-based mixtures resulted in a tendency for segregation. Generally speaking, FA with a spherical form has superior workability and lower water content mixes [6].

3.2. Hardened Properties

3.2.1. Compressive Strength Development

The UCS findings of single-precursor AASCC mixtures are shown in Figure 6. At 3 d and 7 d of age, mixture S-25% exhibited the highest UCS values, i.e., 26.5 MPa and 35 MPa, respectively. Increasing the activator dosage from 16% to 25% leads to ~121% increase in the strength value, i.e., since alkali-activated slag mixes’ strength progression is speedy due to the spontaneous reaction at the exceedingly early hydration stage. Increasing the activator dose, the pore solution retains higher Si2+ and Na+ concentrations, accelerating the C-S-H precipitation process [35,36]. A similar trend was obtained at 28-d due to the continued microstructural growth contributing to strength development. In comparison to S-20% (26 MPa) and a 16% activator dosage (22 MPa), respectively, a combination had the maximum 90 d strength when the activator dose was 25%, or approximately 46.3 MPa. The high activator dose causes the system’s high pH, silicate, and carbonate ion concentrations, which in turn causes ongoing interactions with Ca2+ ions from the slag to precipitate C-A-S-H. These findings are consistent with those of a prior research [37], where the primary factor influencing the alkali-activated slag mixes’ mechanical characteristics is the type of anion accompanying the activators after the high pH value. This would lead to the formation of stable hydration products.
Figure 7 shows the UCS values for the binary-precursor mixtures. Like the single-precursor mixtures, the highest strength was achieved at the highest activator dosage regardless of the combination of the binary precursor. For instance, at age 3 d, the B1-16% mixture achieved ~6 MPa, while a sharp increase in strength to 24.4 MPa and 24.7 MPa as the activator dosage increased to 20% and 25%, respectively. After 7 d, B1-25% achieved the highest strength at 36 MPa (i.e., almost double that of B1-16%). At 28 d, both the B1-16% and B1-20% showed about comparable strength values, i.e., ~33 MPa while S-25% exhibited 49.5 MPa. Moreover, the mechanical performance of AASCC binary mixtures was improved by substituting slag with SF. This is in accordance with previous studies that ascribed to SF micro-filling and nucleation effects, leading to a dense matrix [38,39,40,41,42].
For the B2-mixtures set utilizing 30% FA, the increase in strength was proportional with the increase of the activator dosage at different ages. Like the B1-mixtures set, the higher the activator dosage, the higher the UCS, regardless of age. This confirms that the optimum activator dosage for achieving the highest UCS was 25%. Moreover, at this optimum activator dosage, the single-precursor blend of AASCC achieved the highest strength in contrast to B2-25%. This indicated that the variation in chemical composition of slag and FA significantly impacted the alkali-activation mechanisms. In addition, the high reaction level of slag-based mixes attributable to their nature than to the crystalline pozzolanic nature of FA-based mixtures. According to Ismail et al. [43], the first cycle of hydration (slag dissolution) releases Ca2+, which is then absorbed into the N-A-S-H type gel formed by FA activation, resulting in a hybrid C-(N)-A-S-H gel. In the second cycle of the reaction procedure, FA was partially dissolved and participated [44].
The strength development behavior of the two ternary AASCC sets is shown in Figure 8. All ternary AASCC mixtures demonstrated almost similar strength gain of an average of 81%. In addition, a higher activator dosage evidently possesses higher mechanical properties. It was found that the high strength gain of 7 to 28 days instead of 28 to 90 days implies that the reaction rate and intensity are mainly rapid due to the system’s high pH [45]. After 28 d, the strength gained by T1-AASCC mixtures with activator dosage of 16% was 21.9 MPa, 20% (23.5 MPa), and 25% (44.8 MPa), respectively. Similarly, the highest UCS value for T2-AASCC mixtures at 28-d was reported using 25% with 39.3 MPa. The T1-AASCC mixtures incorporating slag with ~60%, ~33% FA, and ~7% SF acquired higher late age strength values than in T2-AASCC mixtures after 90 days of age. For instance, the UCS values of 50.5 MPa and 42.5 MPa, respectively, were achieved by the tested T1-25% and T2-25% specimens.
The lower strength gain in the T2 set than in the T1 set could be related to slag replacement by up to 50% FA and 5% SF, resulting in fewer strength-giving products. It is worth noting that AAM’s mechanical performance depends on the system’s pH value that controls the hydration process. Early production of strength-giving products is driven by rapid reactions at a high pH value > 11.5, which is impossible below pH 9.5 [46]. The higher the activator dosage in a mixture contributed to a higher pH value, which resulted in improved hydration activation capacity and satisfactory mechanical properties [37,47]. Meanwhile, several studies confirmed the slower setting rate of the FA compared with slag [48,49,50,51]. This may be due to the pure slag’s high pH value (11.5) relative to pure FA, which was 8.5 [46]. As FA content increased in the AASCC matrix, lower CaO content and higher SiO2 and Al2O3 concentrations resulted in a slower hydration cycle [16].

3.2.2. Electrical Bulk Resistivity

However, for the electrical resistivity, all single-precursor mixtures exhibited high electrical resistivity values, indicating a remarkably high level of corrosion resistance at ages of 28 d and 90 d (Table 4). The electrical resistivity is significantly decreased as the dosage of activators increases, e.g., S-20% and S-25% achieved resistivity values of 12.5% and 20.3% lower than S-16% at age 28 d. A similar trend was observed after 90 d. Meanwhile, substituting slag with up to 10% SF improved the resistivity of the B1-mixtures.
Incorporating 16, 20, and 25% activator dosage in B1 mixtures resulted in a “very high” resistivity level of 44.61, 43.48, and 28.53 kΩ. cm after 28 d of curing, respectively. The resistivity values continued to increase tremendously with time after 28 d, showing ~43%, ~30%, ~28% increase for mixtures with 16%, 20%, and 25% activator dosage at 90 d. On the other hand, B2-mixtures incorporating 30% FA replacing slag resulted in a “very high” corrosion protection level at age of 28 d and 90 d. When observing each mixture separately, B2-mixtures exhibited a substantial increase in the resistivity values with (60.84, 57.40, 41.75 kΩ. cm) in B2-16%, B2-20%, and B2-25% after 28 days and (73.67, 64.21, 58.48 kΩ. cm) at 90 d of age, respectively. This may be attributed to the densified microstructure of B2-mixtures due to slag replacement and the formation of a significant amount of reaction products [52]. Therefore, this reduces the potential for corrosion due to low pore connectivity and migration of ions. For ternary-precursor mixtures, all mixtures exhibited substantial corrosion resistance at ages 28 and 90 days. For example, mixtures T1-16%, T1-20%, and T1-25% resulted in resistivity values of 13, 21.23, and 26.39 kΩ. cm at 28 d of age, achieving “very high” corrosion protection, respectively. Meanwhile, T2-mixtures of up to 45% FA and 5% SF replacing slag attained “very high” corrosion resistance at all ages, except for the T2-16% at 28-d of age belonging to the “high” category. At 90 d of age, the resistivity values tended to increase tremendously. The increase in resistivity values is 51%, 30.3%, and 46% at 90 d than those at age 28 d.
According to ACI 222R [53], the corrosion properties were analyzed based on the bulk electrical resistivity performance (Figure 9). The electrical resistivity of AASCC mixtures was found to depend on the resistivity of the pore solution. For all AASCC mixtures (i.e., single, binary, and ternary), the higher the activator dosage, the lower the pore solution resistivity was observed. This can be due to the pore solutions’ highly ionic nature and conductivity as the activator dosage increased, contributing to lower resistivity results [54]. Then again, the precursor combination plays an enormous role in the overall electrical resistivity results. For instance, single and binary precursor mixtures resulted in higher corrosion protection levels than ternary-precursor blends, which were highly ionic and conductive. This is in good agreement with the reported literature [54,55].

3.2.3. Ultrasonic Pulse Velocity (UPV)

The findings of the UPV testing of AASCC mixtures using multi-precursor and activator combinations are shown in Table 5. For AASCC single-precursor mixtures, the measured UPV values ranged in 3000–3500 m/s for S-16% and S-20%, meeting medium quality classification. However, the UPV result significantly increased as the activator dosage increased to 25%, indicating the high homogeneity for the S-25% mixture.
UPV is affected by changes in the hardened AASCC matrix due to the activator dosage and the slag replacement ratio. This is better described by considering the results of the two binary-precursor sets and the single-precursor set results. The UPV findings in the B1-AASCC with up to 25% activator dosage were relatively high at 28 d and 90 d. For example, B1 mixtures activated at 16%, 20%, and 25% achieved 3696, 3710, and 4098 m/s at 28-d, respectively, with UPV gain of ~3–4% at 90-d. Replacing slag with 30% FA in B2-mixtures led to a decrease in UPV from 3484 to 3521 to 3883 m/s, respectively, at 28 d as the activator dosage increased 16% to 25% compared with single and B1 mixtures. However, all the measured B2-mixtures displayed UPV readings between 3714 and 4133 m/s after 90 d of age. T1-mixtures showed superior quality classifications at age 28 d and 90 d. In contrast, T2-mixtures followed a decreasing trend as the slag replacement was 50%. At 28 d of age, the UPV values for T2-mixtures were 3446 m/s and 3472 m/s for 16% and 20% activator dosages. The increase in UPV findings was substantial at 90 d compared to 28 d of age, as the quality of AASCC was shifted from medium to good using 16% and 20% activator dosages. T2-AASCC, in contrast, with a 25% activator dosage, reported a UPV value of 3846 m/s after 28 d, with just a 4% increase at 90-d.
Figure 10 presented the relationship between UPV and UCS findings for AASCCs with single, binary, and ternary precursor blends at 28 d and 90 d. The results for all AASCCs showed that, regardless of curing age, the UCS and UPV findings increased gradually with an increase in the activator dosage of up to 25%. This can be due to the higher activator dosage, which accelerates the hydration process of mixtures, leading to the production of major quantities of hydration products, leading to a higher strength [56].
The effect of ageing on the time-dependent microstructural growth of the mixtures has increased the UPV and, accordingly, strength values. The UPV test depends on the mixtures’ density. A precursor material of higher density enables the ultrasonic wave to pass through the matrix very quickly, yet a denser material implies a higher velocity [57]. Hence, the UPV values were affected by the high FA ratio replacing slag due to the higher porosity level. In a previous study, where slag was replaced with up to 70% FA, it was concluded that the higher the FA level in mixtures, the lower the measured density and the corresponding UPV values [58].

3.2.4. Capillary Sorptivity

Under capillary suction, the water sorptivity test is often used to assess the extent of water flow through concrete. The lower water sorptivity index, which reflects the microstructural properties of concrete and curing efficiency, is related to concrete durability. Based on the type of concrete and curing protocol, specimen maturity level may directly impact the test results. Thus, testing before 28 d after casting is not recommended.
Initial Rate of Absorption. Figure 11a shows the initial absorption rates for all AASCC-precursor combinations activated with ~25% activator dosage at ages 28 d and 90 d. In general, the single-precursor S-25% mixture shows the highest initial absorption rate among all precursor combinations. While the early absorption rate decreased as SF and FA replaced slag in binary and ternary mixtures relative to single-precursor mixtures at both ages. For example, binary mixtures B1 and B2 with 25% activator dosage exhibited the lowest initial absorption rate of 0.05 and 0.08 mm/mm1/2 at 28 d, respectively. Ternary mixtures also displayed the second-best performance with 0.09 and 0.015 mm/mm1/2 at ages of 28 d and 90 d, respectively. According to Provis [59], the nature of activators, rather than the chemical composition of precursor materials, plays a major role in developing porosity. In addition, while increasing the activator modulus and decreasing the water content, the rate of water uptake in AAM decreased [60].
Secondary Rate of Absorption. The second absorption rate for all AASCCs at age of 28 d and 90 d is presented in Figure 11b. Except in SF and FA’s binary mixtures, the general trend of using different precursor combinations on the secondary absorption rate values is, indeed, not apparent. However, as mixtures continue to develop with age, their secondary absorption rate decreases. For example, at 28 d, the lowest secondary absorption rate was obtained in binary mixtures B1-25% and B2-25% with 0.015 and 0.037 mm/mm1/2, respectively. This is followed by single-precursor and ternary-precursor mixtures, i.e., S-25% (0.052 mm/mm1/2), T2-25% (0.052 mm/mm1/2) and T1-25% (0.054 mm/mm1/2), respectively.
For all AASCC mixtures, the percentage changes within the secondary absorption rate from 28 to 90 days were calculated. Generally, capillary sorptivity decreased with the degree of maturity and development of the curing age, which is compatible with previous reported findings [60,61]. The single precursor exhibited a 96% reduction compared to all other AASCC mixtures. The ternary-precursor mixtures yielded a reduction level of 88% compared with the single-precursor blend. Binary-precursor blends of FA experienced an almost similar reduction of 82%, while SF replacing slag mixture resulted in a 65% reduction. Capillary pores in AASCC mixtures have been observed to be refined and tortuous, contributing to a comparatively low level of capillary sorptivity. This observation is consistent with prior research, displaying a dense pore structure in mainly AAMs [62,63,64,64].

3.2.5. Permeable Pores Test

Porosity and water absorption are excellent indicators for durability performance. The strong effect of the reaction products and the different binding gels may govern the transport mechanisms. Hence, the following sub-sections present the permeable voids volume results for all AASCC mixtures evaluated for 28 d and 90 d specimens’ age.
Early-Age Test. Permeable pore percentages for all mixtures with different precursor mixtures are shown in Figure 12 after 28 d of age. All AASCC mixtures had an overall average of 23% permeable pores at an early age. When using 100% slag precursor material and 25% activator dosage, the single-precursor mixture experienced 19% permeable pores. Since 10% SF was used to replace slag in binary-precursor blends, the volume of permeable pores was the lowest of the five mixtures at 17%. When ternary- and binary-precursor mixtures with a ≥30% FA than single-precursor blend, the volume of permeable pores showed a tendency to increase. The mixtures B2-25% and T1-25%, for example, exhibited ~21% and ~23% of permeable pores, respectively. The volume of permeable pores in AASCC mixtures with higher slag content, single- and binary-precursor slag/SF mixtures, is lower than in binary- and ternary-precursor mixtures with FA. This can be attributed to the presence of C–A–S–H gel types that dominate the microstructure of slag/FA systems, which is denser than the aluminosilicate gels [43]. The C–A–S–H type of gel has a better pore-filling ability than the aluminosilicate gel due to the presence of more bound water due to Ca2+ in C–A–S–H. The obtained findings are consistent with the previous investigations [65,66]. Permeable pore volume increased when FA replaced slag in AASCC mixtures above 30% due to the gel type’s nature that promotes different pore structure and porosity systems.
Late-Age test. Figure 12 represents the ratio of permeable pores in all the mixtures at a late age, ranging from 13% to 18%. Using the optimal activator dosage of 25%, the volume of voids in single and binary-precursor with SF mixtures decreased at 90 d. In a single-precursor mixture, e.g., the volume of pores was 13.6%. With 472.5 kg/m3 (10%), partial replacement of slag by SF in a binary mixture resulted in ~14% permeable pores volume yet increased to ~17% in B2-25%. The average permeable pores volume increased by up to 17% in both ternary-precursor mixtures when slag was substituted with FA and SF in T1 (315 kg/m3) and T2 (289 kg/m3). With the evolution of curing time up to 90 d, the volume of permeable voids values of AASCC mixtures decreased in samples with higher slag content. These outcomes are reliable comparing to previous findings in several studies [67,68], which found that porosity decreased over time as curing continued due to a greater extent of reaction.

3.3. Microstructural Analysis

The effect of multi-precursor combinations on the structural development of silicate-carbonate-activated AASCC mixtures was investigated in this section. At 90 d of age, the nature and composition of the reaction products produced were determined using XRD, 29Si NMR spectroscopy, and SEM. Figure 13 shows the XRD analyses of AASCC concrete mixtures with single, binary, and ternary-precursor blends.
The predominant crystalline phases present in all AASCCs after 90 d of curing age were quartz (SiO2), and calcium carbonate (CaCO3), i.e., calcite. In calcium-rich systems activated with sodium carbonate, calcite was commonly detected due to a reaction between dissolved carbonate ions present in the pore solution and calcium ions due to slag dissolution [28]. In addition, it contains a series of minority crystalline phases as prehnite, scolecite, paragonite, riversideite, merwinite, sodalite and calcite, magnesian. In addition to nanocrystalline mineral consisting of a calcium magnesium silicate, hydrated calcium aluminum silicate (C-A-S-H), hydrated calcium silicates (C-S-H), and sodium aluminosilicate hydrate (N-A-S-H) gels were found in all AASCC mixtures with various precursor blends. The calcium consumption by carbonate ions, which forms carbonates, has been coupled to the formation of zeolites in sodium carbonate-activated slag binders. This can be related to the pore solution being saturated with silicon and aluminum species, resulting in aluminosilicate zeolite-type products [28].
In a single-precursor mixture, slag was activated with silicate–carbonate activators; the halo was recorded between 25–35° in 2θ. The sharp peaks in the AASCC-slag indicate a higher crystallinity level due to the presence of quartz (SiO2), calcite (CaCO3) and calcite, magnesian (Mg0.03·Ca0.97·CO3). Even though the intensities of merwinite, sodalite (Na8(AlSiO4)6(OH)2·4H2O), scolecite (CaAl2Si3O10·3H2O), prehnite (Ca2Al2Si3O10(OH)2), paragonite (3Al2O3·Na2O6SiO2·2H2O) and riversideite (2CaSiO3·3H2O) are weak. These peaks were identified in all samples regardless of the precursor nature and combination used while using the silicate–carbonate activators as reported by Bernal et al. [28]. The diffraction pattern changed after the replacement of slag in binary- and ternary-precursor blends. In binary-precursor mixtures with 10% SF and 30% FA replacing slag, the diffused broad humps were in the range of 20–40° in 2θ compared to single-precursor mixtures. In the diffractogram of binary mixtures, the same peaks were observed in addition to higher intensities of merwinite, scolecite (CaAl2Si3O10·3H2O), and riversideite (2CaSiO3·3H2O) in slag/SF mixture, yet sodalite in slag/FA mixture. On the other hand, Margarite (CaAl2(Si2Al2)·O10(OH)2) was identified in ternary-precursor mixtures only compared with the single- and binary-precursor blends. When using silicate–carbonate activators under strongly alkaline conditions, the addition of sodium metasilicate induces the formation of sodalite-type zeolites rather than zeolite [69].
In 29Si MAS NMR resonances, the presence of Q0 monomers, Q1 dimers, and Q2 bridging groups can be seen, and their compositions differ depending on the activator composition and curing condition [70]. The 29Si MAS NMR spectra of the AASCC systems containing both high calcium C-A-S-H and low calcium aluminosilicate products C-(N)-A-S-H and activated with silicate–carbonate activators are shown in Figure 14. Together with XRD and SEM, the presence of Q1 to Q3 silicon units defined by 29Si NMR confirms the existence of two distinct types of reaction products in the blended systems. The dissolved Ca2+ and Al3+ groups affect the mixture of C-S-H gel, and its composition gradually changes into C-A-S-H and C-(N)-A-S-H gels, respectively, as the structural shifts of Si are detected [71]. After 90 d of age, high-intensity peaks centered between −80 to −84 ppm were attributed to Q1 and Q2 (1A1) for all mixtures with single, binary, and ternary-precursors blends. Resonance at −97.1 ppm was observed in AASCC single-precursor mixture, corresponding to Q2 site, while −90 ppm for the other AASCC precursor blends consistent with the formation of an Al-replaced C-S-H type (C-(N)-A-S-H) gel structure [43,72]. This is due to the presence of multi-dry-powder activators with high activator dosage, which successfully promote the formation of strength-giving products. In single-precursor and binary-precursor blends with 10% SF and 30% FA mixtures, resonances of −107.6, −105.5, and −107 ppm were detected as the reaction progressed. However, peaks at –100 ppm and −101 ppm were observed for ternary-blends with a higher amount of Al-substituted. These intensities are appointed to Q3 (1A1) and Q3 species in the spectra, which could overlap. This is in line with the authors’ recent structural model and analysis of 29Si MAS NMR findings [6,73], which found a strongly cross-linked and densified C-(N) A-S-H gel type in these systems. Previous analyses of sodium silicate-activated and sodium carbonate-activated slag binders have, indeed, attributed this band to a Q3 (1Al) component [74].
The AASCC hardened segments’ composition was examined and captured using combined SEM/EDX techniques in this study, which also highlighted the evolution of main hydration products affecting the mechanical properties. SEM images of single, binary, and ternary AASCCs activated with 25% dry-powder activator dosage after 90 d of curing are shown in Figure 15a–e. It should be emphasized that large peaks in the EDS analysis for all AASCC mixtures are related to gold because of gold coating. All AASCC mixtures exhibited a homogeneous and highly tortuous structure. Since the major elements of Ca, O, Na, Al, and Si were detected in the gel products by EDS analysis, it is assumed that the gel products in all AASCC blends were C-(N)-A-S-H. The additional quantity of silica and alumina supplied by FA and SF replacements in binary and ternary mixtures profoundly affected the formation of hydration products, leading to the strength’s development. The SEM study was supported by the results of the XRD and 29Si NMR. The densified microstructure and refined pore networks were provided by the presence of prehnite, scolecite, riversideite, and sodalite.

4. Concluding Remarks

In this paper, multi precursor and activator materials were successfully used to develop one-part “just add water” AASCCs. This stage is noteworthy for the adoption of low-carbon binders that are most suitable for in-situ functions. From the present experimental data, the following conclusions can be drawn:
  • The proper selection of precursor materials, proportions, activator type, and dosage plays a decisive role in the effective development of AASCC mixtures in the absence of a distinct methodology.
  • The higher fraction of sodium carbonate/silicate activators in all systems, single, binary, and ternary, contributed to the delayed reaction kinetics due to their nature. The combination of 20% to 25% activator dosage is recommended to achieve satisfactory fresh and mechanical properties.
  • Slag substitution with various SF or FA class-F ratios can correct the particle size distribution of the total binder material and improve the fresh concrete characteristics in binary and ternary systems.
  • For all AASCC mixtures, a 25% activator dosage resulted in the highest UCS and UPV values, particularly in binary-SF and ternary-1 mixtures of more than 50 MPa after 90 days than other combinations.
  • The formation of different reaction products and binding gels, i.e., C-(N)-A-S-H, strongly influences the different transport mechanisms, such as capillary sorptivity, permeable pores, and bulk electrical resistivity.
  • The study of rheological properties as well as durability is highly recommended for these developed AASCC mixtures. A study of external sulfate attack specifically is ongoing.
The combination of carbonate/silicate dry-powder activators is believed to improve the performance of AASCC concrete mixtures. As a result, future research should investigate the effects of using different types of dry-powder activators with various dosages on the fresh, hardened and durability properties of AASCC mixtures.

Author Contributions

Conceptualization, D.K. and A.M.S.; methodology, D.K. and A.M.S.; validation, A.M.S., A.R.S. and A.e.M.S.; formal analysis, D.K.; investigation, D.K.; resources, A.M.S.; data curation, D.K.; writing—original draft preparation, D.K.; writing—review and editing, A.M.S., A.R.S. and A.e.M.S.; visualization, D.K.; supervision, A.M.S.; project administration, A.M.S. and A.R.S.; funding acquisition, A.M.S. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Natural Sciences and Engineering Research Council of Canada, grant number RGPIN-2018-05094.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author, D.K., upon a reasonable request.

Acknowledgments

Authors would like to acknowledge Lafarge Canada for donating the slag and Sika for donating the used admixtures.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Ling, G.; Shui, Z.; Sun, T.; Gao, X.; Wang, Y.; Sun, Y.; Wang, G.; Li, Z. Rheological Behavior and Microstructure Characteristics of SCC Incorporating Metakaolin and Silica Fume. Materials 2018, 11, 2576. [Google Scholar] [CrossRef] [Green Version]
  2. Heikal, M.; Zohdy, K.M.; Abdelkreem, M. Mechanical, Microstructure and Rheological Characteristics of High Performance Self-Compacting Cement Pastes and Concrete Containing Ground Clay Bricks. Constr. Build. Mater. 2013, 38, 101–109. [Google Scholar] [CrossRef]
  3. Hanehara, S.; Yamada, K. Interaction between Cement and Chemical Admixture from the Point of Cement Hydration, Absorption Behaviour of Admixture, and Paste Rheology. Cem. Concr. Res. 1999, 29, 1159–1165. [Google Scholar] [CrossRef]
  4. Moradi, N.; Tavana, M.H.; Habibi, M.R.; Amiri, M.; Moradi, M.J.; Farhangi, V. Predicting the Compressive Strength of Concrete Containing Binary Supplementary Cementitious Material Using Machine Learning Approach. Materials 2022, 15, 5336. [Google Scholar] [CrossRef]
  5. Khayat, K.H.; Ghezal, A.; Hadriche, M.S. Utility of Statistical Models in Proportioning Self-Consolidating Concrete. Mater. Struct. 2000, 33, 338–344. [Google Scholar] [CrossRef]
  6. Bernal, S.A.; Krivenko, P.V.; Provis, J.L.; Puertas, F.; Rickard, W.D.A.; Shi, C.; van Riessen, A. Other Potential Applications for Alkali-Activated Materials. In Alkali Activated Materials: State-of-the-Art Report, RILEM TC 224-AAM; Provis, J.L., van Deventer, J.S.J., Eds.; RILEM State-of-the-Art Reports; Springer: Dordrecht, The Netherlands, 2014; pp. 339–379. ISBN 978-94-007-7672-2. [Google Scholar]
  7. Walkley, B.; San Nicolas, R.; Sani, M.-A.; Rees, G.J.; Hanna, J.V.; van Deventer, J.S.J.; Provis, J.L. Phase Evolution of C-(N)-A-S-H/N-A-S-H Gel Blends Investigated via Alkali-Activation of Synthetic Calcium Aluminosilicate Precursors. Cem. Concr. Res. 2016, 89, 120–135. [Google Scholar] [CrossRef] [Green Version]
  8. Palacios, M.; Puertas, F. Stability of Superplasticizer and Shrinkage-Reducing Admixtures Stability of Superplasticizer and Shrinkage-Reducing Admixtures in High Basic Media. Mater. Construcción 2004, 54, 65–86. [Google Scholar] [CrossRef] [Green Version]
  9. He, X.; Chen, Y.; Wan, Y.; Liu, L.; Xue, Q. Effect of Curing Stress on Compression Behavior of Cement-Treated Dredged Sediment. Int. J. Geomech. 2020, 20, 04020204. [Google Scholar] [CrossRef]
  10. Santana, H.A.; Andrade Neto, J.S.; Amorim Júnior, N.S.; Ribeiro, D.V.; Cilla, M.S.; Dias, C.M.R. Self-Compacting Geopolymer Mixture: Dosing Based on Statistical Mixture Design and Simultaneous Optimization. Constr. Build. Mater. 2020, 249, 118677. [Google Scholar] [CrossRef]
  11. EFNARC. The European Guidelines for Self-Compacting Concrete: Specification, Production and Use; International Bureau for Precast Concrete (BIBM): Brussels, Belgium, 2005. [Google Scholar]
  12. Manjunath, R.; Narasimhan, M.C. An Experimental Investigation on Self-Compacting Alkali Activated Slag Concrete Mixes. J. Build. Eng. 2018, 17, 1–12. [Google Scholar] [CrossRef]
  13. Shafiq, I.; Azreen, M.; Hussin, M.W. Sulphuric Acid Resistant of Self Compacted Geopolymer Concrete Containing Slag and Ceramic Waste. MATEC Web Conf. 2017, 97, 01102. [Google Scholar] [CrossRef] [Green Version]
  14. Ushaa, T.G.; Anuradha, R.; Venkatasubramani, G.S. Performance of Self-Compacting Geopolymer Concrete Containing Different Mineral Admixtures. IJEMS 2015, 22, 473–481. [Google Scholar]
  15. Sashidhar, C.; Jawahar, J.G.; Neelima, C.; Kumar, D.P. Fresh and Strength Properties of Self Compacting Geopolymer Concrete Using Manufactured Sand. Int. J. ChemTech Res. 2015, 7, 183–190. [Google Scholar]
  16. Huseien, G.F.; Shah, K.W. Durability and Life Cycle Evaluation of Self-Compacting Concrete Containing Fly Ash as GBFS Replacement with Alkali Activation. Constr. Build. Mater. 2020, 235, 117458. [Google Scholar] [CrossRef]
  17. Bakharev, T.; Sanjayan, J.G.; Cheng, Y.-B. Effect of Admixtures on Properties of Alkali-Activated Slag Concrete. Cem. Concr. Res. 2000, 30, 1367–1374. [Google Scholar] [CrossRef]
  18. Nematollahi, B.; Sanjayan, J. Effect of Different Superplasticizers and Activator Combinations on Workability and Strength of Fly Ash Based Geopolymer. Mater. Des. 2014, 57, 667–672. [Google Scholar] [CrossRef]
  19. 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]
  20. Kanaan, D.; Soliman, A.M.; Suleiman, A.R. Zero-Cement Concrete Resistance to External Sulfate Attack: A Critical Review and Future Needs. Sustainability 2022, 14, 2078. [Google Scholar] [CrossRef]
  21. Kanaan, D.M.; Soliman, A.M. Fresh and Mechanical Properties of One-Part Alkali-Activated Self-Consolidating Concrete. In Proceedings of the Canadian Society of Civil Engineering Annual Conference 2021; Walbridge, S., Nik-Bakht, M., Ng, K.T.W., Shome, M., Alam, M.S., el Damatty, A., Lovegrove, G., Eds.; Springer Nature: Singapore, 2023; pp. 17–30. [Google Scholar]
  22. ASTM C1611; Test Method for Slump Flow of Self-Consolidating Concrete. ASTM International: West Conshohocken, PA, USA, 2019.
  23. ASTM C39; Test Method for Compressive Strength of Cylindrical Concrete Specimens. ASTM International: West Conshohocken, PA, USA, 2018.
  24. ASTM C1760; Test Method for Bulk Electrical Conductivity of Hardened Concrete. ASTM International: West Conshohocken, PA, USA, 2012.
  25. ASTM C 642, C09; Committee Test Method for Density, Absorption, and Voids in Hardened Concrete. ASTM International: West Conshohocken, PA, USA, 2013.
  26. ASTM C1585; Test Method for Measurement of Rate of Absorption of Water by Hydraulic-Cement Concretes. ASTM International: West Conshohocken, PA, USA, 2020.
  27. Kashani, A.; Provis, J.L.; Qiao, G.G.; van Deventer, J.S.J. The Interrelationship between Surface Chemistry and Rheology in Alkali Activated Slag Paste. Constr. Build. Mater. 2014, 65, 583–591. [Google Scholar] [CrossRef]
  28. Bernal, S.A.; Provis, J.L.; Myers, R.J.; San Nicolas, R.; van Deventer, J.S.J. Role of Carbonates in the Chemical Evolution of Sodium Carbonate-Activated Slag Binders. Mater. Struct. 2015, 48, 517–529. [Google Scholar] [CrossRef]
  29. Lothenbach, B.; Gruskovnjak, A. Hydration of Alkali-Activated Slag: Thermodynamic Modelling. Adv. Cem. Res. 2007, 19, 81–92. [Google Scholar] [CrossRef]
  30. Shi, C.; Day, R. Selectivity of Alkaline Activators for the Activation of Slags. Cem. Concr. Aggreg. 1996, 18, 8. [Google Scholar] [CrossRef]
  31. Yan, Z.; Sun, Z.; Yang, J.; Yang, H.; Ji, Y.; Hu, K. Mechanical Performance and Reaction Mechanism of Copper Slag Activated with Sodium Silicate or Sodium Hydroxide. Constr. Build. Mater. 2021, 266, 120900. [Google Scholar] [CrossRef]
  32. Duran Atiş, C.; Bilim, C.; Çelik, Ö.; Karahan, O. Influence of Activator on the Strength and Drying Shrinkage of Alkali-Activated Slag Mortar. Constr. Build. Mater. 2009, 23, 548–555. [Google Scholar] [CrossRef]
  33. Landrou, G.; Brumaud, C.; Winnefeld, F.; Flatt, R.J.; Habert, G. Lime as an Anti-Plasticizer for Self-Compacting Clay Concrete. Materials 2016, 9, 330. [Google Scholar] [CrossRef] [Green Version]
  34. Okamura, H.; Ouchi, M. Self-Compacting Concrete. ACT 2003, 1, 5–15. [Google Scholar] [CrossRef]
  35. Gebregziabiher, B.S.; Thomas, R.; Peethamparan, S. Very Early-Age Reaction Kinetics and Microstructural Development in Alkali-Activated Slag. Cem. Concr. Compos. 2015, 55, 91–102. [Google Scholar] [CrossRef]
  36. Gruskovnjak, A.; Lothenbach, B.; Holzer, L.; Figi, R.; Winnefeld, F. Hydration of Alkali-Activated Slag: Comparison with Ordinary Portland Cement. Adv. Cem. Res. 2006, 18, 119–128. [Google Scholar] [CrossRef]
  37. Fernández-Jiménez, A.; Puertas, F. Effect of Activator Mix on the Hydration and Strength Behaviour of Alkali-Activated Slag Cements. Adv. Cem. Res. 2003, 15, 129–136. [Google Scholar] [CrossRef]
  38. Kim, T.; Kang, C. The Mechanical Properties of Alkali-Activated Slag-Silica Fume Cement Pastes by Mixing Method. Int. J. Concr. Struct. Mater. 2020, 14, 41. [Google Scholar] [CrossRef]
  39. Alanazi, H.; Hu, J.; Kim, Y.-R. Effect of Slag, Silica Fume, and Metakaolin on Properties and Performance of Alkali-Activated Fly Ash Cured at Ambient Temperature. Constr. Build. Mater. 2019, 197, 747–756. [Google Scholar] [CrossRef]
  40. Cheah, C.B.; Tan, L.E.; Ramli, M. The Engineering Properties and Microstructure of Sodium Carbonate Activated Fly Ash/ Slag Blended Mortars with Silica Fume. Compos. Part B Eng. 2019, 160, 558–572. [Google Scholar] [CrossRef]
  41. Gülşan, M.E.; Alzeebaree, R.; Rasheed, A.A.; Niş, A.; Kurtoğlu, A.E. Development of Fly Ash/Slag Based Self-Compacting Geopolymer Concrete Using Nano-Silica and Steel Fiber. Constr. Build. Mater. 2019, 211, 271–283. [Google Scholar] [CrossRef]
  42. Ramezanianpour, A.A.; Moeini, M.A. Mechanical and Durability Properties of Alkali Activated Slag Coating Mortars Containing Nanosilica and Silica Fume. Constr. Build. Mater. 2018, 163, 611–621. [Google Scholar] [CrossRef]
  43. Ismail, I.; Bernal, S.A.; Provis, J.L.; San Nicolas, R.; Hamdan, S.; van Deventer, J.S.J. Modification of Phase Evolution in Alkali-Activated Blast Furnace Slag by the Incorporation of Fly Ash. Cem. Concr. Compos. 2014, 45, 125–135. [Google Scholar] [CrossRef]
  44. Puertas, F.; Martínez-Ramírez, S.; Alonso, S.; Vázquez, T. Alkali-Activated Fly Ash/Slag Cements: Strength Behaviour and Hydration Products. Cem. Concr. Res. 2000, 30, 1625–1632. [Google Scholar] [CrossRef]
  45. 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] [Green Version]
  46. Song, S.; Jennings, H.M. Pore Solution Chemistry of Alkali-Activated Ground Granulated Blast-Furnace Slag. Cem. Concr. Res. 1999, 29, 159–170. [Google Scholar] [CrossRef]
  47. Song, S.; Sohn, D.; Jennings, H.M.; Mason, T.O. Hydration of Alkali-Activated Ground Granulated Blast Furnace Slag. J. Mater. Sci. 2000, 35, 249–257. [Google Scholar] [CrossRef]
  48. Nath, P.; Sarker, P.K.; Rangan, V.B. Early Age Properties of Low-Calcium Fly Ash Geopolymer Concrete Suitable for Ambient Curing. Procedia Eng. 2015, 125, 601–607. [Google Scholar] [CrossRef] [Green Version]
  49. Kumar, S.; Kumar, R.; Mehrotra, S.P. Influence of Granulated Blast Furnace Slag on the Reaction, Structure and Properties of Fly Ash Based Geopolymer. J. Mater. Sci. 2010, 45, 607–615. [Google Scholar] [CrossRef]
  50. Sugama, T.; Brothers, L.E.; Van de Putte, T.R. Acid-Resistant Cements for Geothermal Wells: Sodium Silicate Activated Slag/Fly Ash Blends. Adv. Cem. Res. 2005, 17, 65–75. [Google Scholar] [CrossRef]
  51. Vijai, K.; Kumutha, R.; Vishnuram, B.G. Effect of Types of Curing on Strength of Geopolymer Concrete. IJPS 2010, 5, 1419–1423. [Google Scholar] [CrossRef]
  52. Li, C.; Sun, H.; Li, L. A Review: The Comparison between Alkali-Activated Slag (Si+Ca) and Metakaolin (Si+Al) Cements. Cem. Concr. Res. 2010, 40, 1341–1349. [Google Scholar] [CrossRef]
  53. ACI. ACI 222R-01 Protection of Metals in Concrete against Corrosion; American Concrete Institute: Indianapolis, IN, USA, 2001. [Google Scholar]
  54. Ma, Q.; Nanukuttan, S.V.; Basheer, P.A.M.; Bai, Y.; Yang, C. Chloride Transport and the Resulting Corrosion of Steel Bars in Alkali Activated Slag Concretes. Mater. Struct. 2016, 49, 3663–3677. [Google Scholar] [CrossRef] [Green Version]
  55. Rodríguez, E.; Bernal, S.; de Gutiérrez, R.M.; Puertas, F. Alternative Concrete Based on Alkali-Activated Slag. Mater. Construcción 2008, 58, 53–67. [Google Scholar] [CrossRef] [Green Version]
  56. Pasupathy, K.; Berndt, M.; Sanjayan, J.; Rajeev, P.; Cheema, D.S. Durability of Low-calcium Fly Ash Based Geopolymer Concrete Culvert in a Saline Environment. Cem. Concr. Res. 2017, 100, 297–310. [Google Scholar] [CrossRef]
  57. Wardhono, A.; Law, D.W.; Molyneaux, T.C.K. Long Term Performance of Alkali Activated Slag Concrete. J. Adv. Concr. Technol. 2015, 13, 187–192. [Google Scholar] [CrossRef] [Green Version]
  58. 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]
  59. Provis, J.L. Alkali-Activated Materials. Cem. Concr. Res. 2018, 114, 40–48. [Google Scholar] [CrossRef]
  60. Glasser, F.P. Mineralogical Aspects of Cement in Radioactive Waste Disposal. Mineral. Mag. 2001, 65, 621–633. [Google Scholar] [CrossRef]
  61. Safhi, A.e.M.; Rivard, P.; Yahia, A.; Henri Khayat, K.; Abriak, N.-E. Durability and Transport Properties of SCC Incorporating Dredged Sediments. Constr. Build. Mater. 2021, 288, 123116. [Google Scholar] [CrossRef]
  62. Bernal, S.; De Gutierrez, R.; Delvasto, S.; Rodriguez, E. Performance of an Alkali-Activated Slag Concrete Reinforced with Steel Fibers. Constr. Build. Mater. 2010, 24, 208–214. [Google Scholar] [CrossRef]
  63. Bernal, S.A.; Mejía de Gutiérrez, R.; Pedraza, A.L.; Provis, J.L.; Rodriguez, E.D.; Delvasto, S. Effect of Binder Content on the Performance of Alkali-Activated Slag Concretes. Cem. Concr. Res. 2011, 41, 1–8. [Google Scholar] [CrossRef]
  64. Adam, A.A.; Molyneaux, T.C.K.; Patnaikuni, I.; Law, D.W. Strength, Sorptivity and Carbonation of Geopolymer Concrete; CRC Press: Boca Raton, FL, USA, 2009; pp. 585–590. ISBN 978-0-429-20652-8. [Google Scholar]
  65. Ismail, I.; Bernal, S.A.; Provis, J.L.; Hamdan, S.; van Deventer, J.S. Microstructural Changes in Alkali Activated Fly Ash/Slag Geopolymers with Sulfate Exposure. Mater. Struct. 2013, 46, 361–373. [Google Scholar] [CrossRef]
  66. Provis, J.L.; Myers, R.J.; White, C.E.; Rose, V.; van Deventer, J.S.J. X-ray Microtomography Shows Pore Structure and Tortuosity in Alkali-Activated Binders. Cem. Concr. Res. 2012, 42, 855–864. [Google Scholar] [CrossRef]
  67. Bernal, S.A.; Rodriguez, E.D.; de Gutierrez, R.M.; Provis, J.L.; Delvasto, S. Activation of Metakaolin/Slag Blends Using Alkaline Solutions Based on Chemically Modified Silica Fume and Rice Husk Ash. Waste Biomass Valorization 2012, 3, 99–108. [Google Scholar] [CrossRef]
  68. Collins, F.G.; Sanjayan, J.G. Capillary Shape: Influence on Water Transport within Unsaturated Alkali Activated Slag Concrete. J. Mater. Civ. Eng. 2010, 22, 260–266. [Google Scholar] [CrossRef]
  69. Chen, S.; Wu, M.; Zhang, S. Mineral Phases and Properties of Alkali-Activated Metakaolin-Slag Hydroceramics for a Disposal of Simulated Highly-Alkaline Wastes. J. Nucl. Mater. 2010, 402, 173–178. [Google Scholar] [CrossRef]
  70. Peng, Z.; Vance, K.; Dakhane, A.; Marzke, R.; Neithalath, N. Microstructural and 29Si MAS NMR Spectroscopic Evaluations of Alkali Cationic Effects on Fly Ash Activation. Cem. Concr. Compos. 2015, 57, 34–43. [Google Scholar] [CrossRef]
  71. García-Lodeiro, I.; Fernández-Jiménez, A.; Palomo, A. Variation in Hybrid Cements over Time. Alkaline Activation of Fly Ash–Portland Cement Blends. Cem. Concr. Res. 2013, 52, 112–122. [Google Scholar] [CrossRef]
  72. Le Saoût, G.; Ben Haha, M.; Winnefeld, F.; Lothenbach, B. Hydration Degree of Alkali-Activated Slags: A 29Si NMR Study. J. Am. Ceram. Soc. 2011, 94, 4541–4547. [Google Scholar] [CrossRef]
  73. Myers, R.J.; Bernal, S.A.; San Nicolas, R.; Provis, J.L. Generalized Structural Description of Calcium–Sodium Aluminosilicate Hydrate Gels: The Cross-Linked Substituted Tobermorite Model. Langmuir 2013, 29, 5294–5306. [Google Scholar] [CrossRef] [PubMed]
  74. Bernal, S.A.; Nicolas, R.S.; van Deventer, J.S.J.; Provis, J.L. Alkali-Activated Slag Cements Produced with a Blended Sodium Carbonate/Sodium Silicate Activator. Adv. Cem. Res. 2016, 28, 262–273. [Google Scholar] [CrossRef]
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Figure 1. Relation between a slump and S-flow rate.
Figure 1. Relation between a slump and S-flow rate.
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Figure 2. Relation between slump and L-Box blocking ratio.
Figure 2. Relation between slump and L-Box blocking ratio.
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Figure 3. Relation between SR and l-box blocking ratio.
Figure 3. Relation between SR and l-box blocking ratio.
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Figure 4. The effect of activator dosage on the relation between (a) S-flow and l-box ratio H2/H1 (b) S-flow and SI%.
Figure 4. The effect of activator dosage on the relation between (a) S-flow and l-box ratio H2/H1 (b) S-flow and SI%.
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Figure 5. The effect of slag content, kg/m2 on the (a) S-flow diameter, mm and (b) SR, %.
Figure 5. The effect of slag content, kg/m2 on the (a) S-flow diameter, mm and (b) SR, %.
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Figure 6. UCS results for the AASCC single-precursor mixtures.
Figure 6. UCS results for the AASCC single-precursor mixtures.
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Figure 7. UCS results for the AASCC binary-precursor mixtures.
Figure 7. UCS results for the AASCC binary-precursor mixtures.
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Figure 8. UCS results for the AASCC ternary-precursor mixtures.
Figure 8. UCS results for the AASCC ternary-precursor mixtures.
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Figure 9. Bulk resistivity results for AASCC mixtures at ages (a) 28 and (b) 90 days.
Figure 9. Bulk resistivity results for AASCC mixtures at ages (a) 28 and (b) 90 days.
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Figure 10. UPV results for all AASCC mixtures at (a) 28 and (b) 90 days of curing age.
Figure 10. UPV results for all AASCC mixtures at (a) 28 and (b) 90 days of curing age.
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Figure 11. Rate of absorption for AASCC mixtures. (a) Initial rate. (b) Secondary rate.
Figure 11. Rate of absorption for AASCC mixtures. (a) Initial rate. (b) Secondary rate.
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Figure 12. Permeable pores results for AASCC mixtures.
Figure 12. Permeable pores results for AASCC mixtures.
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Figure 13. X-ray diffractograms of AASCCs with 25% silicate-carbonate activator dosage.
Figure 13. X-ray diffractograms of AASCCs with 25% silicate-carbonate activator dosage.
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Figure 14. 29Si NMR spectra after 90-d hydration of the mixtures with diverse precursor combinations.
Figure 14. 29Si NMR spectra after 90-d hydration of the mixtures with diverse precursor combinations.
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Figure 15. SEM images of AASCCs using 25% activator dosage. (a) Single, (b) binary-1, (c) binary-2, (d) ternary-1, and (e) ternary-2.
Figure 15. SEM images of AASCCs using 25% activator dosage. (a) Single, (b) binary-1, (c) binary-2, (d) ternary-1, and (e) ternary-2.
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Table
Table 1. Mixture’s proportions of the different AASCC systems.
Table 1. Mixture’s proportions of the different AASCC systems.
ClassMixture I.D.Slag, kg/m3FA, kg/m3SF, kg/m3Sand, kg/m 3CA, kg/m3Paste vol., L/m3
SingleS-1652500661830438
S-2052500654830441
S-2552500646830444
Binary-1B1-16472.5052.5652835440
B1-20472.5052.5652830442
B1-25472.5052.5652825443
Binary-2B2-16367.5157.50641845440
B2-20367.5157.50637845442
B2-25367.5157.50637840443
Ternary-1T1-1631517337629845445
T1-2031517337625845446
T1-2531517337625840448
Ternary-2T2-1628921026629845445
T2-2028921026625845446
T2-2528921026624840448
Table
Table 2. Test methods of the investigated mixtures.
Table 2. Test methods of the investigated mixtures.
PropertiesTest MethodSpecimensTesting Periods
Fresh properties
Filling abilitySlump flow (S-flow)ASTM C1611 [22]-Fresh
T500-Fresh
Passing abilityL-box flowEFNARC [11] -Fresh
StabilitySegregation resistanceEFNARC [11]-Fresh
Visual Stability IndexASTM C1611 [22]-Fresh
Hardened mechanical properties
Unconfined compressive strength (UCS)ASTM C39 [23]100 Ø 200 mm3, 7, 28, and 90 days
Ultrasonic pulse velocityASTM C1760 [24]100 Ø 200 mm28 and 90 days
Electrical resistivity
Absorption ASTM C642 [25]100 Ø 50 mm-
SorptivityASTM C1585 [26]100 Ø 50 mm-
Microstructural properties
X-ray diffraction-Powder < 75 µm90 days
29Si NMR spectra-Powder < 75 µm90 days
Scanning electron microscopy-Small pieces90 days
Table
Table 3. Fresh concrete properties results for AASCC mixtures.
Table 3. Fresh concrete properties results for AASCC mixtures.
Mixture I.D.S-flow, mmS-flow Rate (T500), sL-Box Ratio, H2/H1Segregation Index (%)
S-16%30.00---0.550.00
S-20%510.004.600.652.00
S-25%690.002.020.855.00
B1-16%443.0013.600.552.00
B1-20%448.008.820.557.00
B1-25%583.003.050.757.00
B2-16%698.002.440.8815.00
B2-20%795.001.410.9417.00
B2-25%833.001.131.0027.00
T1-16%718.002.660.888.00
T1-20%768.002.100.9017.00
T1-25%828.001.450.9825.00
T2-16%705.002.630.8520.00
T2-20%798.001.840.9528.00
T2-25%830.001.100.9930.00
Table
Table 4. Electrical resistivity test results for AASCC mixtures.
Table 4. Electrical resistivity test results for AASCC mixtures.
Mixture IDElectrical Resistivity, kΩ. cmCorrosion Protection
28-d90-d
S-16%71.10108.56Very High
S-20%62.2787.50Very High
S-25%56.7076.37Very High
B1-16%44.6163.74Very High
B1-20%43.4856.35Very High
B1-25%28.5336.59Very High
B2-16%60.8473.67Very High
B2-20%57.4064.21Very High
B2-25%41.7558.48Very High
T1-16%13.0025.51High to Very High
T1-20%21.2338.69Very High
T1-25%26.3942.16Very High
T2-16%17.6526.64High to Very High
T2-20%22.6729.54Very High
T2-25%26.3538.37Very High
Table
Table 5. UPV results for AASCC mixtures with up to 25% activator dosage.
Table 5. UPV results for AASCC mixtures with up to 25% activator dosage.
Mixture IDUPV, m/sAASCC Quality
28-d90-d
S-16%32253275Medium
S-20%32943316Medium
S-25%38243944Good
B1-16%36963796Good
B1-20%37103860Good
B1-25%40984262Good
B2-16%34843714Medium to Good
B2-20%35213721Good
B2-25%38834133Good
T1-16%35903659Good
T1-20%36773686Good
T1-25%40164041Good
T2-16%34463582Medium to Good
T2-20%34723594Medium to Good
T2-25%38463981Good
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Kanaan, D.; Safhi, A.e.M.; Suleiman, A.R.; Soliman, A.M. Fresh, Hardened, and Microstructural Properties of Ambient Cured One-Part Alkali-Activated Self-Consolidating Concrete. Sustainability 2023, 15, 2451. https://doi.org/10.3390/su15032451

AMA Style

Kanaan D, Safhi AeM, Suleiman AR, Soliman AM. Fresh, Hardened, and Microstructural Properties of Ambient Cured One-Part Alkali-Activated Self-Consolidating Concrete. Sustainability. 2023; 15(3):2451. https://doi.org/10.3390/su15032451

Chicago/Turabian Style

Kanaan, Dima, Amine el Mahdi Safhi, Ahmed R. Suleiman, and Ahmed M. Soliman. 2023. "Fresh, Hardened, and Microstructural Properties of Ambient Cured One-Part Alkali-Activated Self-Consolidating Concrete" Sustainability 15, no. 3: 2451. https://doi.org/10.3390/su15032451

APA Style

Kanaan, D., Safhi, A. e. M., Suleiman, A. R., & Soliman, A. M. (2023). Fresh, Hardened, and Microstructural Properties of Ambient Cured One-Part Alkali-Activated Self-Consolidating Concrete. Sustainability, 15(3), 2451. https://doi.org/10.3390/su15032451

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