Abstract
Geopolymer concrete (GPC) is a rising eco-conscious substitute for traditional cement-based concrete, bringing the construction industry closer to sustainability. Self-compacting geopolymer concrete (SCGC) enhances the concrete flowability and fills the congested reinforced areas without vibrators in concrete structures such as bridges, tunnels and canals. This study aims to analyze the impact of silicon dioxide nanoparticles (NS) on the rheological and mechanical properties of SCGC to optimize the dosage of NS in SCGC. For this purpose, NS (0–6%) blended in partially distributed binders of fly ash and ground granulated blast furnace slag (50:50) with 0.5 alkaline binder ratio, 2% superplasticizers (9 kg m−3) (MasterGlenium SKY 8233) and 12% extra water (54 kg m−3). Sodium silicate solution and sodium hydroxide ratio of 2.5 was used for this study. It is observed that SCGC with 3% NS replacement complied with the guidelines of EFNARC. According to the T50cm slump flow test, V-funnel test, and L-box test results meet the guidelines of up to 4% NS replacement, and 3% NS addition offers excellent mechanical properties in SCGC. This study concluded that the replacement of 3% of NS improved the fresh and hardened properties of SCGC, which can apply to construction.
1 Introduction
Worldwide, concrete is highly utilized and irreplaceable for innumerable significant materials for infrastructure developments that remain pivotal to addressing the growing population demand and economic development [1, 2]. Cement is an essential resource for concrete production, but cement manufacturing produces CO2 that greatly contributes to global warming [3–5]. Globally, cement requirement is estimated to rise by 2050, reaching 6 billion tons [6, 7]. In addition, the CO2 emissions of this sector account for 5–7% of global manmade CO2 contributions [8]. Therefore, cement-free alternatives for concrete are necessary to reduce global CO2 [9].
Joseph Davidovits, a French materials scientist, developed the geopolymer concrete (GPC) in the late 1970s, which employed byproducts to produce cement-free substitute resources for concrete production [10, 11]. The resource materials comprise aluminium (Al), silicon (Si), sodium or potassium-based hydroxide and silicate solutions [12, 13]. Furthermore, GPC can be formulated using various materials and a combination of fly ash (FA), ground granulated blast furnace slag (GGBS), and nano-silica (NS) [14]. FA is a byproduct generated from coal combustion in power plants [15]. It is rich in amorphous aluminosilicate materials mixed with an alkaline activator solution and undergoes geopolymerization, forming a strong, durable binding matrix like cement in traditional concrete [16]. GGBS is a byproduct of iron and steel industry and is another common supplementary material that contains a high level of amorphous silicate and aluminate materials, which contribute to the geopolymerization process [17, 18]. GGBS can enhance the performance of GPC by improving workability, reducing heat of hydration, and increasing long-term strength [19]. One major drawback of the GPC is high viscosity, which affects its workability [20, 21]. Self-compacting GPC (SCGC) was established to resolve these problems by settling its weight without any external compaction [22].
Although SCGC with FA and GGBS addresses environmental concerns, provides improved performance characteristics, and provides economic advantages, it is still difficult to achieve the enhanced reactivity for densification of the geopolymer matrix that facilitates faster and more complete geopolymerization to contribute to the early development of SCGC strength [23, 24]. NS offers superior benefits to the geopolymer matrix because a very small particle size and high surface area can help to increase reactivity when mixed with alkaline activators [25, 26]. Also, NS can improve mechanical properties, including compressive, flexural strength and densification of the geopolymer matrix, resulting in a more compact structure [27]. Furthermore, NS reduces the permeability of GPC because the fine particles fill the voids within the matrix [28]. The addition of very fine particles of NS influences the rheological properties that enhance the workability and flowability, more suitable for SCGC [29]. The characteristics of SCGC are flowability, filling, and passing ability without segregation or bleeding [30]. These characteristics can be achieved by the varieties of superplasticizer (SP) types included in the Polycarboxylate Ether (PC), Sulphonated Naphthalene Formaldehyde (SNF), Naphtha (NP, Lignosulphonates (LS) and Mother Liquor (ML) [20]. Among that, the generation PC-based MasterGelenium SKY 8233 provide superior benefits for the SCGC [31].
This study explores the effects of silicon dioxide nanoparticle-based SCGC on rheological and mechanical properties at the molarity of NaOH from 14 M. In this investigation, FA and GGBS were blended equally at 50% and varying the NS from 0 to 6% and then tests were conducted such as slump flow, T50cm Slump flow, V-funnel and L-box to assess the rheological properties of SCGC. Compressive strength (CS), split tensile strength (STS) and flexural strength (FS) of SCGC were examined at 7 and 28 days under ambient curing.
2 Materials and methods
2.1 Fly ash, GGBS and Nano silica
In the present experimental work, FA (class F) was procured at Thoothukudi coal-fired power station in Tamil Nadu and used. The collected FA was grey coloured fine powder. The FA has a specific gravity of 2.1 [32]. The iron and steel industry generates enormous volumes of GGBS, making it an attractive material for sustainable construction practices. It was procured from the JSW plant at Madurai and the specific gravity of GGBS was 2.9 [33]. NS can be used as an additive in SCGC to enhance its properties and performance. NS was procured at Astra Chemicals, Chennai, India. The relative gravity of NS is 2.4 [34].
A scanning electron microscope of ZEISS-EVO 18, Japan equipped with EDX (EDAX -APEX) was used to analyse the morphology of the FA, GGBS, and NS. The scanning electron micrographs (SEM) showed that the FA particles are spherical and have a smooth surface, as shown in Fig. 1 (A&B) [35].
Scanning electron micrograph of FA(A&B), GGBS(C&D), NS(E&F)
Citation: International Review of Applied Sciences and Engineering 15, 3; 10.1556/1848.2024.00794
These SEM images prove the original FA morphological structure. GGBS has irregular shapes and rough surfaces, as shown in Fig. 1 (C&D) [36]. SEM image of NS is shown in Fig. 1 (E&F) [37]. Therefore, GGBS, FA, and NS can be mixed to form a cementitious binder to provide better workability of SCGC. The elemental analysis was carried out on FA, GGBS and NS using X-ray diffraction as shown in Figs 2–4.
Energy-dispersive X-ray (EDX) of FA
Citation: International Review of Applied Sciences and Engineering 15, 3; 10.1556/1848.2024.00794
Energy-dispersive X-ray (EDX) of GGBS
Citation: International Review of Applied Sciences and Engineering 15, 3; 10.1556/1848.2024.00794
Energy-dispersive X-ray (EDX) of NS
Citation: International Review of Applied Sciences and Engineering 15, 3; 10.1556/1848.2024.00794
The elemental composition of FA from the EDAX spectrum is shown in Fig. 2, silica (22.3%) and aluminium (15.3%) are the major components. Iron (3.7%), magnesium (1.2%), potassium (1.2 %) are the minor components present in the FA. The elemental composition of GGBS is shown in Fig. 3, calcium (22.5%) and silica (12%) are the major components. Aluminium (7.4%) and magnesium (4.3%) are the minor components present in the GGBS. The elemental composition of NS is shown in Fig. 4, silica is the only element present in NS. The qualitative and quantitative analysis of material composition is carried out using XRF spectroscopy (XRF) Bruker S8 Tiger (Germany) and their chemical composition of FA, GGBS, and NS is indicated in Table 1.
Chemical composition of FA, GGBS, and NS
| S. No | Chemical composition | FA | GGBS | NS |
| 1 | SiO2 | 63.16 | 35.14 | 99.88 |
| 2 | Al2O3 | 29.69 | 16.81 | 0.03 |
| 3 | K2O | 1.85 | 0.41 | – |
| 4 | TiO2 | 1.60 | 0.85 | – |
| 5 | CaO | 1.41 | 37.37 | 0.03 |
| 6 | MgO | 0.99 | 7.24 | – |
| 7 | P2O5 | 0.97 | – | – |
| 8 | Fe2O3 | 0.35 | 0.07 | – |
| 9 | Na2O | 0.21 | 0.24 | – |
| 10 | SO3 | 0.16 | 1.65 | 0.04 |
| 11 | PbO | 0.02 | – | – |
| 12 | BaO | – | 0.10 | – |
| 13 | MnO | – | 0.07 | – |
| 14 | Cl | – | 0.03 | 0.03 |
XRF result showed that the FA contains the concentrations of SiO2 and Al2O3 as 63.16% and 29.69% and the remaining elemental compositions are presented in minor concentrations. XRF result showed that the GGBS contains the major concentrations of CaO, SiO2, and Al2O3, MgO as 37.37, 35.14, 16.81, and 7.24% remaining elemental compositions are presented in minor concentrations. XRF result showed that the NS contains the major concentration of SiO2 at 99.88%. Elemental compositions FA, GGBS and NS also confirmed the aluminosilicate characters, which is suitable for the feedstock of SCGC according to ASTM C618 and IS: 12089-1987 [38, 39].
2.2 NaOH and Na2SiO3
The alkaline solution is a crucial component in geopolymerization, as it serves as the activator for the reaction between aluminosilicate materials to form the geopolymer structure. The alkaline solution typically consists of sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) with 1:2.5 ratio is considered in this study. These solutions were mixed 24 h before casting and stirred well with the specific gravity of 1.47 and 1.6 respectively.
2.3 Aggregates
This study used coarse aggregate (CA) of 12.5 mm, and the fineness modulus was 7.16. The specific gravity of CA was found to be 2.83. Manufactured sand (M-sand), obtained as a byproduct from the crushing process in quarries, is used as fine aggregate with a specific gravity of 2.73 and a fineness modulus of 2.65.
2.4 Superplasticizers
The new generation polycarboxylic ether-based superplasticizer is used to enhance the workability and flow ability using MasterGlenium Sky 8233 supplied by Astra Chemicals, Chennai. Its relative density is roughly 1.08.
2.5 Mix proportion
The mix design of the SCGC mixes was carried out as per the EFNARC guidelines for the SCC [40]. Table 2 shows the mix proportion of SCGC. The constant binder content of 450 kg m−3 with partially distributed GGBS and FA. The mix designations are NS-0% to NS-6% with different percentages of SCGC mixes prepared with different NS dosages from 0 to 6% NS with 1% intervals. The Na2SiO3 to NaOH proportion was used at 2.5 with a 14 M of NaOH. The alkali/binder ratio (a/b) was kept constant at 0.5. The water content (54 kg m−3) and SP (9 kg m−3) were used in this study to acquire optimum fresh properties.
Mix proportion of FA, GGBS, and NS-based SCGC
| Mix ID | FA (kg m−3) | GGBS (kg m−3) | NS (kg m−3) | Fine aggregate (kg m−3) | Coarse aggregate (kg m−3) | Na2SiO3 + NaOH (kg m−3) | Molarity | SP (kg m−3) | Extra water (kg m−3) |
| NS-0% | 225 | 225 | 0 | 961.08 | 786.33 | 225 | 14 | 9 | 54 |
| NS-1% | 225 | 225 | 4.5 | 961.08 | 786.33 | 225 | 14 | 9 | 54 |
| NS-2% | 225 | 225 | 9 | 961.08 | 786.33 | 225 | 14 | 9 | 54 |
| NS-3% | 225 | 225 | 13.5 | 961.08 | 786.33 | 225 | 14 | 9 | 54 |
| NS-4% | 225 | 225 | 18 | 961.08 | 786.33 | 225 | 14 | 9 | 54 |
| NS-5% | 225 | 225 | 22.5 | 961.08 | 786.33 | 225 | 14 | 9 | 54 |
| NS-6% | 225 | 225 | 27 | 961.08 | 786.33 | 225 | 14 | 9 | 54 |
2.6 Blending, casting, process, and curing
The aggregates were dry-mixed for 3 min, and then fine powder materials like FA, GGBS, and NS were added to the mixer. The mixer includes an alkaline activator solution, MasterGlenium Sky 8233, and water are mixed for about five minutes till it reaches homogeneity. The rheological properties of fresh concrete were assessed and then it was poured into specimens without compaction. The mechanical behaviors were analyzed after an ambient curing period of 7 days and 28 days.
3 Experimental programs
3.1 Rheological properties
The rheological properties of the SCGC blend mixed with FA, GGBS, and NS were investigated from slump flow, T50cm slump flow, L-box, and V-funnel experiments. A slump flow test was performed to determine the filling capacity of freshly poured concrete. The filling capacity of the mix was determined by measuring the time required for the mix to reach a diameter of 50 cm, using the T50cm slump flow test. Concrete resistance to withstand the reinforcement was determined, using the L-box test. The vertical section (H1) and the horizontal components (H2) lead to the concrete flow heights considered in the L-box test. The consistency and filling capacity of the concrete was performed using V-funnel test. Figure 5 displays the test on properties of fresh SCGC carried out as per the recommendations of EFNARC 2002 [40].
Tests on the flow ability of SCGC
Citation: International Review of Applied Sciences and Engineering 15, 3; 10.1556/1848.2024.00794
3.2 Mechanical properties
The SCGC specimens based on FA, GGBS, and NS were analyzed versus hardened properties such as CS, STS, and FS after curing for 7 and 28 days at room temperature. Cube specimens of SCGC with dimensions 100 × 100 × 100 mm were cast for CS.
The cylinder specimens (100 × 200 mm) were used to analyze the STS, and prismatic specimens (100 × 100 × 500 mm) were used for FS. The cube-shaped specimens were then tested in a CTM as per IS: 516-1959 after 7 and 28 days for CS [41]. A STS test was performed after 7 and 28 days as per IS: 5816 -1999 [42]. The prism was tested in a UTM at 400 kN after 7 and 28 days as per IS 516-1959 to determine the FS shown in Fig. 6 [41].
Tests for the mechanical properties of SCGC
Citation: International Review of Applied Sciences and Engineering 15, 3; 10.1556/1848.2024.00794
4 Results and discussion
4.1 SCGC rheological properties
Rheological properties of SCGCs are evaluated by slump flow, T50cm slump flow, V-funnel test, and L-box test, which assess its workability, flowability, and ability to fill intricate forms. Table 3 shows the rheological properties of FA, GGBS, NS NS-based SCGC mixes.
Rheological properties of FA, GGBS, NS based SCGC mixes
| Mix ID | Slump flow (mm) | T50cm slump flow (S) | V-funnel (S) | L-box |
| NS-0% | 790 | 2.4 | 7.2 | 0.91 |
| NS-1% | 740 | 2.7 | 7.9 | 0.88 |
| NS-2% | 710 | 3.1 | 8.6 | 0.87 |
| NS-3% | 680 | 3.4 | 9.3 | 0.85 |
| NS-4% | 640 | 4.2 | 10.7 | 0.81 |
| NS-5% | 610 | 5.6 | 12.5 | 0.79 |
| NS-6% | 580 | 6.3 | 12.9 | 0.77 |
4.1.1 Slump flow test
The flowability of SCGC was studied with a slump flow test and the findings are shown in Table 3 and Fig. 7. It shows that every mix ranges within guidelines (650–800 mm) except for Mix ID NS-5 and NS-6% [40]. A maximum value of 790 mm is arrived at NS-0%. It was observed that the NS proportion increased, and the flow of SCGC mixes decreased.
Slump flow test result
Citation: International Review of Applied Sciences and Engineering 15, 3; 10.1556/1848.2024.00794
4.1.2 T50cm flow time
The time taken to concrete spread at 50 cm diameter is analyzed by slump T50cm test. The findings were tabulated in Table 3 and Fig. 8. It is observed, except for Mix ID NS-5% and NS-6% and five SCGC mixes attained under guidelines (2–5 s) [40].
T50cm flow test result
Citation: International Review of Applied Sciences and Engineering 15, 3; 10.1556/1848.2024.00794
It varies between 2.4 and 6.3 and, the lowest of 2.4 s is attained for NS-0%. It is observed that the NS increment was increased at the T50cm time.
4.1.3 V-funnel flow time
The flow time from the V-funnel test is analyzed to assess the passing ability of SCGC.
The observed findings are shown in Fig. 9 and Table 3. Flowability time ranges between 7.2 and 12.9 s. All five SCGCs met the allowable flow time except for Mix NS-5 and NS-6%. A minimum of 7.2 s time is observed in the NS-0 % mix. It is observed that NS increases, fluidity of SCGC reduces due to a negative impact on flowability, increased water demand, and changes in rheological properties.
V-funnel test result
Citation: International Review of Applied Sciences and Engineering 15, 3; 10.1556/1848.2024.00794
4.1.4 L-box test
The passing ability of SCC is obtained by the L-box test. The blocking ratio (H2/H1) of SCGCs is displayed in Table 3 and Fig. 10. The allowable range for SCGC is 0.8–1.0 as per EFNARC [40]. The observation shows that, although the H2/H1 ratio decreases, there is an increase in NS content. It can be seen that, except for Mix NS-5 and NS-6%, the remaining SCGCs are in the allowable range of below 0.8 to 1.0 compared to all other mixes on SCGC.
L-box test result
Citation: International Review of Applied Sciences and Engineering 15, 3; 10.1556/1848.2024.00794
4.2 Hardened SCGC properties
The CS, STS, and FS are essential for assessing the mechanical properties, load-bearing capacity, and durability of SCGC. The mechanical properties of FA, GGBS, and NS-based SCGC are indicated in Table 4.
Mechanical properties of FA, GGBS, NS-based SCGC
| Mix ID | CS (MPa) | STS (MPa) | FS (MPa) | |||
| 7 days | 28 days | 7 days | 28 days | 7 days | 28 days | |
| NS-0% | 29 | 38 | 3.45 | 4.56 | 3.91 | 5.05 |
| NS-1% | 32 | 44 | 3.68 | 5.06 | 4.32 | 5.94 |
| NS-2% | 36 | 48.5 | 4.14 | 5.58 | 5.13 | 6.54 |
| NS-3% | 42 | 56.2 | 4.83 | 6.74 | 5.80 | 7.58 |
| NS-4% | 35 | 49.2 | 4.02 | 5.65 | 4.72 | 6.64 |
| NS-5% | 31.5 | 42 | 3.62 | 4.83 | 4.45 | 5.67 |
| NS-6% | 27 | 33.5 | 3.1 | 3.85 | 3.64 | 4.56 |
4.2.1 Compressive strength
The CS for NS proportions after 7 and 28 days were indicated in Table 4 and Fig. 11. A maximum of 42 and 56.2 MPa was noted for NS-3% at 7 and 28 days. The increase in the percentage of CS found for NS-3% was recorded as 32.38% more than NS-0%. The finer and nano-sized grains filled in SCGC as the binder's paste and enhanced the strength. In addition, the NS particles increase the hydration process of curing due to the NS surface area. The 7 days compressive strength for NS-1–5% developed strength gain of 9.37, 19.44, 30.95, 17.14 and 7.93% compared to the NS-0% control specimen. The 28 days compressive strength for NS-1–5% developed strength gain of 13.63, 21.64, 32.38, 22.76 and 9.52% respectively, compared to the NS-0% control specimen. The 7- and 28-day compressive strength for NS-6% decreased by 6.89 and 11.84% respectively, compared to the NS-0% control specimen. Overall, NS tends to improve the CS of the mechanical concrete at NS-3% then decreased by 24.25%.
Compressive strength test result
Citation: International Review of Applied Sciences and Engineering 15, 3; 10.1556/1848.2024.00794
4.2.2 Split tensile strength
The STS findings for SCGCs with various NS proportions were analyzed after seven and twenty-eight days which is indicated in Table 4 and Fig. 12. STS is observed at NS-3% after 7 and 28 days with maximum STS of 4.83 and 6.74 MPa. At 7 days under ambient curing, the STS was enhanced as 6.25, 16.66, 28.57, 14.17 and 4.69% for NS-1, 2, 3, 4 and 5% respectively compared to the control specimen NS-0%.
Split tensile strength test result
Citation: International Review of Applied Sciences and Engineering 15, 3; 10.1556/1848.2024.00794
Also, STSs were observed as 9.88, 18.27, 32.34, 19.29 and 5.59% for NS-1–5% at 28 days of ambient curing. The 7 and 28-day strength for NS-6% decreased the strength of STS by 10.14% and 15.57% respectively compared to the NS-0% control specimen. Overall, NS tends to improve the STS of the mechanical concrete at NS-3% mix, afterwards it decreased by 26.97%.
4.2.3 Flexural strength
The FS findings of SCGCs-based NS proportions were tabulated in Table 4. From Fig. 13, maximum flexural strength was noted for NS-3% at seven and 28 day as 5.80 and 7.58 MPa respectively. The optimum flexural strength (FS) was obtained at NS-3% and recorded as 32.33%.
Flexural strength test result
Citation: International Review of Applied Sciences and Engineering 15, 3; 10.1556/1848.2024.00794
The 7 days FS for NS-1–5% developed strength gain of 6.25, 21.05, 30.17, 14.19 and 8.98% compared to NS-0% control specimen. The 28 days FS for NS-1–5% developed strength gain of 14.98, 22.78, 33.37, 23.94 and 10.93% respectively compared to the NS-0% control specimen. The 7- and 28-days FS for NS-6% decreases the strength of compressive strength by 6.90 and 9.70% respectively compared to the control specimen NS-0%. Overall, NS enhanced the FS of SCGCs with increments up to NS-3% mix due to the proper aggregate paste matrix interaction on SCGC.
5 Conclusion
The effect of NS addition on the rheological and mechanical properties of SCGC was examined and the following conclusions may be drawn based on the findings of the study.
It was observed that the addition of NS gradually decreases the slump flow of SCGC. It is one of the workability indicators of concrete, and it is a sign that the concrete's ability to flow and fill formwork is reducing as slump flow decreases. The decrease in slump flow was observed, but it was noted that the SCGC with 3% NS replacement still complied with the guidelines of EFNARC. According to the T50cm slump flow test, the V funnel test, and the L box test results meet the guidelines for up to 4% NS replacement in SCGC. These tests assess the passing ability, flowability, and segregation resistance of SCGC. The fact that they meet the guidelines indicates that concrete can flow well and pass through tight spaces, even with the addition of NS. This study suggests that, according to EFNARC standards, the workability of concrete is within acceptable limits. Hence, up to 3% of the NS addition is suitable for SCGC.
It is highlighted that a 3% NS addition in SCGC enhanced the mechanical properties in terms of CS, STS, and FS. This is a positive aspect as the concrete not only meets the fresh property requirements but also exhibits strength characteristics that are desirable for structural applications. Hence, the study suggests that there is an optimal percentage of NS (3%) that provides a good balance between workability and mechanical properties in SCGC. This is an important finding for practical applications, as it allows for the enhancement of both fresh and hardened properties without compromising one for the other.
Overall, 3% of NS dosage has improved the fresh and hardened properties of SCGC. Additionally, NS dosage above 3% negatively impacts fresh properties, indicating unsuitability for SCGC. Hence, the study concluded that NS addition of up to 3 % in SCGC can support various construction projects such as bridges, tunnels, and high-rise buildings where both workability and strength are important factors. Also, further research for the future can be suggested and the investigation of microstructural behaviors such SEM, EDAX, FTIR, and XRD of NS-based hardened concrete for different proportions and synthesized NS from silica-rich industrial byproducts such as rice husk ash, FA can replace the commercial NS to enhance rheological and mechanical properties of SCGC. Furthermore, another future study possibility is shrinkage assessment in SCGC with material behaviors and mitigation strategies to adopt NS as a sustainable and durable construction material.
Author contribution
Mr. Vigneshkumar A*: Investigation, methodology framing, experimental setup, writing – original draft.
Dr. C. Freeda Christy: Supervision, methodology suggestions, writing – reviewing, and editing.
Dr. M. Muthukannan: Supervision and reviewing.
Dr. U. Johnson Alengaram: Methodology suggestions and reviewing.
Mr. M. Maheswaran: Methodology framing, experimental setup and editing.
Mr. Nittin Johnson Jeyaraj: Writing and editing.
Acknowledgement
The author Vigneshkumar A is grateful to the International Research Centre (IRC), Kalasalingam Academy of Research and Education (KARE) for providing University Research Fellowship (URF) and instrumental research facilities.
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