Durability performance of nano-silica modified fly ash concrete under accelerated CO₂ carbonation conditions

ABSTRACT

Greenhouse gases, namely carbon dioxide emissions, cause variations in global temperature and relative humidity (RH), which some projections show that there will be a reduction in RH in certain areas as CO₂ level increases. These fluctuations in CO₂, temperature and RH significantly impact on carbonation depth in current systems. However, models for forecasting carbonation depth as a function of time in concrete components are limited to the extent of implementing important factors associated with the effects of climate change. Various concrete mixes containing 10 to 30% fly ash (FA), 3% nano silica particles (NSP) with a constant water to cement (w/c) ratio of 0.34 were used to test the durability and mechanical characteristics of nano fly ash concrete (NFC). After exposing these specimens for up to 28 days, the depth of carbonation (2% (vol.) CO₂, 20°C, 65% RH) were investigated. Carbonation results show that NSP incorporated concrete mixes reduce carbonation depth by approximately 73% when compared to the control specimens.

Keywords:
Nano silica particles; Fly ash; Carbonation; Mechanical properties; Durability.

1. INTRODUCTION

Concrete production is a major contributor leading to global carbon footprint, predominantly due to CO₂ emissions during the production of cement, that fosters climatic change and elevates the danger of CO₂ penetration, resulting in durability effect in concrete structures. The ingress of CO₂ within concrete may result in carbonation, lowering long term performance of materials and structural behavior. Overcoming such constraints is essential for sustainable construction [¹]. Therefore, greenhouse gases, especially CO₂, are the main cause of climate change, which is an extreme environmental risk [²]. It is widely recognized that greenhouse gases, particularly carbon dioxide resulting from human activities, acts as the primary contributor for global warming. While these gases certainly govern radiative forcing, they also cause several high-level changes to the climate system. Simultaneously, increased atmospheric CO₂ concentrations and temperature plays a significant effect on the lifespan of structural concrete, especially in relation to chloride penetration and carbonation [³, ⁴]. The global production of concrete has quadrupled, and this has led to the degradation of ecosystems, depletion of resources, and social conflicts, while the CO₂ emissions from concrete production have tripled from 1990 to 2020 [⁵]. The increased CO₂ levels and temperatures will lead to a higher porosity of concrete, which will have different impacts on Portland cement-based systems [⁶]. Global climate change may also affect the carbonation depth of concrete structures, leading to their performance and rates of cracking in urban areas [⁷]. Accelerated carbonation can reduce the carbon footprint of the concrete industry, but it does not a reliable method for enhancing mechanical characteristics [⁸]. The depth of carbonation of concrete tends to decrease when the percentage of emission of CO₂ decreases (2–20%) and conversely, increase significantly when it increases (50–100%), majorly leads to a densification in the surface layer [⁹]. CO₂ emissions, temperature and relative humidity play important roles in affecting the carbonation depth and compressive strength of concrete structure. Linear correlations between carbonation depth, compressive strength and temperature were established [¹⁰].

The reduction of CO₂ emissions is feasible through CO₂ mineralization in concrete, which increases strength and is a cost-effective way to minimize carbon footprint in concrete structures [¹¹, ¹²]. A quadruple low carbon concrete, incorporating cementitious substitutes, primarily reduces carbon dioxide emissions, while contributing enhanced mechanical properties and microstructures, leading as an effective replacement to normal concrete in environmental conditions [¹³]. The limestone calcined clay cement (LC3) incorporated with fly ash, silica fumes, acai stone ash and sugarcane bagasse ash leads to reductions in CO₂ emissions and also ensures optimal performance as it modifies concrete materials [¹⁴].

Fly ash incorporation with concrete facilitates sustainability through minimizing the usage of cement and CO₂ emissions, whereas the increasing characteristics of concrete and its performance [¹⁵]. Optimum mix designs of high-volume fly ash concrete minimize CO₂ emissions and allow the evaluation of carbonation resistance, climate change effects, and CO₂ absorption based on strength. Within permissible limits, it improves the strength development process by pozzolanic reactions [¹⁶]. It reduces the carbon footprint as fly ash is used for geopolymer concrete, thus increasing its utilization in the concrete industry as an alternative replacement for Portland cement [¹⁷]. Addition of fly ash to concrete improves its mechanical as well as durability properties and can be predicted using an artificial neural network (ANN) model [¹⁸].

Fly ash, Nano silica particles and recycled plastic may substantially lower carbon footprint and enhance durability in sustainable concrete structures [¹⁹]. Addition of nano silica could be a potential partial replacement of cement, enabling improved strength and durability whereas decreasing workability and CO₂ emissions in concrete infrastructures [²⁰]. Nano silica greatly improves the mechanical, durability and microstructural characteristics of cementitious materials, thus ensuring sustainability by reducing greenhouse gas emissions [²¹]. Optimization of particle size distribution and proportions of colloidal nano silica in cement mortar improves the compressive strength, microstructure and reduces environmental effects [²²]. The use of 3% nano silica particles as a partial replacement for cement in high strength concrete mixtures improves the mechanical properties while reducing CO₂ emissions [²³]. Inclusion of nano silica in geopolymer concrete optimizes strength performance, durability and environmental advantages by elevating compressive and tensile strengths while reducing permeability and water absorption [²⁴]. High performance concrete provides better durability and lower CO₂ emissions with the addition of nano silica and silica fume, and also it helps in resolving debris clearance and redeeming natural materials [²⁵].

Adding nano-silica to fly ash based geopolymer concrete enhances strength and durability properties, providing an environmentally friendly replacement for portland cement [²⁶]. The addition of nano silica in fly ash modified geopolymer concrete increases the residual strength of the concrete and can be used as a feasible substitute for ordinary portland cement concrete [²⁷]. Nano-modified fly ash concrete minimizes the depth of carbonation and enhances the ability to withstand against sulphate attack, improving its lifespan over control specimens [²⁸]. The addition of optimal proportions of nano-silica improves the mechanical properties and reduces the water absorption capacity of fly ash and coal gangue based geopolymer concrete, but high amount of nano-silica inhibits sulphate attack resistance [²⁹]. Utilizing 5% nano-silica and 15% coal fly ash incorporated in blended cements substantially strengthen the microstructure and enhance mechanical properties, leading to sustainable concrete [³⁰]. Adding 1% nano silica and 10% metakaolin to fly ash modified cement helps in improving the mechanical and durability properties of concrete, while decreasing the emission of CO₂ [³¹]. Utilizing nano-silica in high volume fly ash lime modified concrete improves compressive strength and reduce carbon emissions, and contributes a 10% decrease in cost when compared with the ordinary portland cement [³²]. Incorporating ceramic waste powder in the concrete acts as a micro filler and it is reducing voids and improve the particle packing [³³].

Although the prevalence of studies examining the effects of nano-silica modified cementitious materials is rising, little research exists on the durability behavior of fly ash concrete with nanosilica in an accelerated carbonation state resulting from climate change scenarios. Furthermore, the combination of fly ash replacement and nanosilica particles on carbonation resistance and long-term durability has not been sufficiently studied. Consequently, this current study will evaluate the mechanical and durability properties of fly ash concrete modified with nano-silica particles under controlled CO₂ exposure conditions. The general purpose of the study is to determine an optimal mix that enhances strength development and improves the resistance of carbonation and aggressive environments, and also contributes to sustainable low-carbon concrete materials development.

2. EXPERIMENTAL PROGRAM

2.1. Materials and methods

For the course of this study, OPC 53 Grade has been used. Fly ash having fineness modulus of 425 m²/kg and specific gravity of 2.3 has been employed, and it is based on ASTM C618 and IS 3812 standards. As previously reported, the powder form of NSP having a surface area 116 m²/g. Table 1 summarizes the chemical properties of FA and NSP. The coarse aggregate in the overall mix has a maximum size of 12.5 mm, fineness modulus of 7.52, and a specific gravity of 2.59. Natural river sand with a fineness modulus of 2.69 and a specific gravity of 2.6 is used. The M40 concrete mix design was carried out as per IS 10262:2019 guidelines for high strength concrete with a target strength of 40 MPa at 28 days. The guidelines provide procedures for determining the proportions of cement, fine aggregate, coarse aggregate and water based on the properties of materials, workability, exposure and strength. The final mix ratio was 1: 1.44: 2.56 (Cement: FA: CA). The concrete mix was prepared with a constant water-to-cement (w/c) ratio of 0.34. Initial dry materials including cement, fly ash, fine aggregate, coarse aggregate and nano silica particles were mixed thoroughly in a laboratory mixer in order to have a homogenous distribution of materials. Dry mix was then gradually mixed with water until a uniform blend of concrete was obtained. The fresh concrete was then poured into moulds for cubes, cylinders and prisms used for the compressive, split tensile and flexural strengths of concrete. All specimens were consolidated using a table vibrator to expel trapped air. The samples were removed from their moulds after 24 hours and subsequently cured in potable water at room temperature for their required testing ages of 7, 28 and 90 days in accordance with IS 516:1959. Mechanical characteristics were investigated by conducting following tests i.e., compressive, flexural and split tensile tests by standard methods carried out on cubes, cylinders and prisms. Tests of durability properties were established by measuring the carbonation depth, weight and strength losses upon exposures to acid, and testing for rapid chloride penetration for permeability assessment. The carbonation depth was evaluated by putting samples in a carbonation chamber at 2% (vol.) CO₂, 20^o C, and 65% RH. A phenolphthalein solution was used to determine the depth of carbonation. Because of the high alkalinity, the non-carbonated area of exposed samples is purple red in colour, while the carbonated area is colorless. Samples were exposed after 7, 28 and 90 days, depth averaged from the split face taken after phenolphthalein spray. The depth of carbonation DCO₂ is determined as the average of the depth of colourless area.

Table 1
Chemical properties of fa and NSP.

MINERALS (%)	CEMENT	FA	NSP
Density (g/cc)	3.14	2.2	1.4
Calcium oxide	62.28	1.5	-
Silicon dioxide	18.4	56.63	99.5
Aluminium oxide	3.8	25.58	-
Ferric oxide	3.98	7.99	-
Magnesium oxide	2.98	2.11	-

From Figure 1, by examining SEM images the analysis of particle size offers details on the mean particle size and the range of particle sizes present in the sample. It can determine if the NSP are monodisperse (of uniform size) or polydisperse (of varied size). Furthermore, SEM pictures can provide information about the shape and morphology of NSP. According to the production technique and circumstances, NSP can be spherical, rod-like, or irregular in shape. Figure 1 shows that the average particle size is 30 nm.

Figure 1
SEM image of NSP.

Figure 2
Variation of compressive strength of fly ash concrete incorporating nano silica (NSP) at curing ages of 7, 28 and 90 days.

3. RESULTS AND DISCUSSION

3.1. Mechanical properties

3.1.1. Compressive strength

Compressive strength test was carried out on 150 × 150 × 150 mm cube specimens prepared as per the IS 516:1959 and cured in water was determined after 7, 28 and 90 days. Figure 2 shows how the strength varies in all mix combinations. Addition of 3% nano-silica significantly enhanced compressive strength in all the fly ash replacement levels (10%, 20% and 30%), but the strongest effects were recorded at 20% FA mix. At 28 days, the 20% FA mix produced 43.6 MPa that rise to 52.7 MPa when NSP (20%FA + 3%NSP) was added and this corresponded to a 20.9 percent increment.

3.1.2. Flexural strength

Flexural strength of the specimens was evaluated on prism samples of sizes 100 m × 100 m × 500 m at three-point loading of the sample within the requirements of IS 516: 1959 at 7, 28 and 90 days. The mean values of each mix were demonstrated as the average of three specimens. Figure 3 highlights the flexural strength results at 28 days. Flexural strength of the mix that was prepared using 20% fly ash attained 4.6 MPa at 28 days, and increases to 5.3 MPa with 3% NSP (FA 20% + NSP 3%). This increment is a reflection of the recorded growth in strength which could be attributed to refinement of the interfacial transition zone (ITZ).

Figure 3
Flexural strength of fly ash concrete mixes incorporating nano silica at different curing ages.

According to ZHANG et al. [³⁵], the incorporation of nano-SiO2 enhances the mechanical properties of concrete composites with fly ash. Blends with high fly ash content had worse performance, the mix 30% FA + 3% NSP recorded 4.5 MPa, which was reduced compared to 20% FA and 3% NSP. The reduction is explained that cement is diluted and this reduces the development of calcium hydroxide which strengthens the ITZ. This outlines 20% FA + 3% NSP as the optimal proportion for flexural strength in sustainable concrete structures.

3.1.3. Splitting tensile strength

Splitting tensile strength was calculated based on IS 5816:1999 of cylindrical specimens (diameter 150 mm, height 300 mm) at ages of 7, 28, and 90 days. Figure 4 shows the mean values of the three replicates. The recorded values of splitting tensile strength with various mix combinations of FA and NSP are highlighted in Figure 4.

Figure 4
Splitting tensile strength of fly ash-based concrete mixes with nano silica particles at 7, 28 and 90 days.

At 28 days, the concrete with 20% fly ash showed a split tensile strength of 3.7 MPa. The addition of 3% nano-silica (20% FA + 3% NSP) increased the value to 4.1 MPa which is an increment of 10.8%. Enhancement of tensile properties is due to the densification of the interfacial transition zone (ITZ). This densification is obtained by nanoscale void filling and formation of C-S-H gel from nano-silica of high surface area reacting with calcium hydroxide, increasing resistance to micro-cracking. However, NS reduces the workability, which can be overcome by adding fly ash which is supported by FENG et al. [³⁶]. The specimens with 30% fly ash mixed with 3% nano-silica (30% FA + 3% NSP) reached 3.6 MPa, which is 12.2% lower than 20% FA + 3% NSP mix, limited by reduced availability of calcium hydroxide that reduces pozzolanic strengthening in the ITZ. This interaction recommends such optimized mixes achieves enhanced tensile properties, improved durability when exposed to environmental load conditions.

The significant enhancement observed in the concrete mixes containing 20% fly ash and 3% nano silica is a result of both pozzolanic activity produced by the fly ash and nucleation induced by the presence of nano silica particles. The presence of nano silica particles accelerates the generation of secondary C–S–H gel and refines the pore structure, thereby creating a denser microstructure and stronger interfacial transition zone. In contrast, when the fly ash content was increased to 30%, the reduced early-age strength can be attributed to the dilution of the cement as well as the slower development of pozzolanic reactions. As such, the improved mechanical performance of the 20% fly ash with 3% nano silica mixture can be attributed to the optimal balance between cement hydration and pozzolanic reaction. The flexural and splitting tensile strength values show similar trends, and hence justifies the beneficial effect of nano silica in optimizing the microstructure of fly ash concrete.

3.2. Durability properties

Durability tests included a 60-day immersion in 5% aqueous solutions of sulphuric and hydrochloric acids to determine respective weight and strength losses, exposure to magnesium sulphate solution to determine sulphate attack, and the use of the rapid chloride permeability test to measure chloride diffusivity.

3.2.1. Weight loss (%) due to acid exposure

The effect of acid attack on weight loss was assessed on samples placed in the 5% HCl and H₂SO₄ solution up to a maximum of 60 days (Figure 5). The mix of 20% FA + 3% NSP had a superior resistance, with 4.7 and 5.8 percent losses in HCl and H₂SO₄ respectively, which was 63 and 54 percent lower than the control. Such high performance may be explained by the well-developed pore structure that nano-silica particles seals capillary pores, which reduces acid penetration, and the pozzolanic reaction of fly ash with Ca(OH)₂ converts the leachable Ca(OH)₂, consequently lowering the formation of soluble salts. The relative loss in H₂SO₄ is relatively larger, owing to the expansion of gypsum (CaSO₄·2H₂O), which results in physical damage.

Figure 5
Loss in weight (%) due to acid exposure.

3.2.2. Strength loss (%) due to acid exposure

The strength loss of the specimens at the end of 60 days was immersed in 5 percent of HCl and H₂SO₄ solution is shown in Figure 6. The strength losses in the 20% FA + 3% NSP mixture were relatively low with 9.4 percent and 11.1 percent losses reported in HCl and H₂SO₄, when compared to the control mixture which had losses of 22.4 and 19.7, respectively. The ratio of NSP is maximized to limit the amount of the excess, which can impair the workability, whereas pore refinement is emphasized to prevent the occurrence of microcracks [³⁶]. The noted strength losses which are estimated to be two times the subsequent mass losses show that the damage on the surface has a disproportionate impact on the mass-bearing capacity of the specimens. Addition of nano-silica ensures the integrity of interfacial transition zone (ITZ) and hence allowing the bonds between aggregates and cement paste to be preserved as the surface continues to degrade.

Figure 6
Loss in strength (%) due to acid exposure.

3.3. Rapid chloride penetration test

Penetrability of the chloride ions was measured according to ASTM C1202 is shown in Table 2. The optimum mix of 20% FA + 3% NSP had recorded 850 Coulombs, which was an improvement of 18.7% over 20% FA mixture and reducing 68.5% for the control. These changes can be explained that the pozzolanic densification of fly ash leads to the pore refinement and their connectivity, and the nano-silica covers pore throats, hence enhancing the ionic diffusion pathways.

Table 2
RCPT results.

CONCRETE SAMPLE	CHARGE PASSED (COULOMBS)	CHLORIDE PERMEABILITY
Control mix	2700	Moderate
20% FA	1045	Low
20% FA + 3% NSP	850	Low

3.4. Sulphate attack

The presence of sulphate ions leads to the development of gypsum and ettringite crystals in the interfacial transition zone that may cause loss of cohesion, cracking, and spalling. The effect on building materials by sulphate ions was determined through testing established by monitoring the concentrations of sulphate ions after 28 and 90 days. Specimens containing FA 10, FA 10 NSP 3, FA 20, FA 20 + NSP 3, FA 30 and FA 30 + NSP 3 were treated to a magnesium sulphate solution. Figure 7 show that FA 20 with NSP 3 shows 49% reduction in sulphate ion penetration when compared to FA 20 however FA 10 + NSP 3 confirms only 31% reduction in sulphate ion penetration when compared to FA 10. The results indicated that FA 30 with NSP 3 shows 39% reduction in sulphate ion penetration when compared to FA 30. The outcomes reveal that NSP outperforms SF owing to its smaller particle dimensions and reaction time that increase its microscopic properties and minimize porosity. The comparison of sulphate ion concentrations readily indicates the three-percentage dosage of NSP is superior to other substitutions.

Figure 7
Sulphate ion concentration of samples.

3.5. Validation of depth of carbonation

The carbonation depth was evaluated by placing samples in a carbonation chamber at two percent CO₂, 20 degrees Celsius, and 65 percent relative humidity. The specimens, after exposure, were removed from the chamber, and on the split surfaces, the indicator called phenolphthalein was sprayed to determine the carbonation depth of the sample. The depth of carbonation of the colourless area was identified as shown in Figure 8, immediately the indicator was applied while the average value of the carbonation depth is presented in the results section.

Figure 8
Specimen tested after exposure.

The outcomes of the model are validated through a comparison of them to the existing results from experiments from this study as well as other studies in the literature. As shown in Figure 9, expected values correlate with experimental data (the R² values for most of these charts exceeds 0.93), implying the degree of carbonation can be identified with the present model. Because the results showed less than a 20% variation in R² for each response, it is apparent that the forecasts made by the models were correct.

Figure 9
Relationship between predicted and observed carbonation depth.

Each mix (FA 10, FA 20+NSP 3) were exposed, the findings presented in Figure 8 reveal that FA 20 with NSP 3 had the smallest depth. Predictive analyses were done using linear regression modeling using experimental data created using OriginPro and had a high level of concordance with the observed results.

For Novel Contributions and Limitations, we have added a dedicated section that explicitly addresses: Systematic investigation of combined FA (10–30%) and NSP (3%) effects on carbonation resistance under climate change-relevant CO₂ exposure conditions (2% vol. CO₂, 20°C, 65% RH), which specifically addresses the gap in understanding durability under projected climate scenarios. Identification of the optimal 20% FA + 3% NSP mixture that balances mechanical performance, durability, and sustainability objectives. Comprehensive durability assessment including carbonation, acid attack, sulphate resistance, and chloride penetration in a single study framework. For Limitations, the study is limited to specific FA replacement levels (10%, 20%, 30%) and a fixed NSP dosage (3%), which were selected based on preliminary optimization but may not represent the absolute optimum for all conditions. Testing was conducted under controlled laboratory conditions (constant temperature and RH) which may not fully replicate the complex and variable field exposure conditions with fluctuating temperature, humidity cycles, and wetting-drying cycles. The study used specific sources of FA and NSP; results may vary with different sources having different chemical compositions and physical properties.

4. CONCLUSION

This study evaluated the mechanical and durability behavior of fly ash concrete altered with nano silica particles under the accelerated carbonation environment. On the basis of experimental investigation, the following conclusions can be made:

1. High CO₂ concentration is attributed to global warming and subsequent rise in temperatures, both of which have the potential of affecting relative humidity and accelerating the process of carbonation in concrete.

2. Incorporation of nano-silica (NSP) in concrete improves particle packing and accelerates the generation of secondary C-S-H gel.

3. The modification of hydration products by nano-silica particles (NSP) in cementitious systems improves the mechanical properties of fly ash concrete and also reduces the ingress of deleterious agents, hence improving the durability qualities.

4. The combination of 20% FA and 3% NSP showed the optimal mechanical performance at 28 days, with compressive strength of 52.7 Mpa (an increase of 20.9%), and flexural strength of 5.3 Mpa (an increase of 15.2%) and split tensile strength of 4.1 Mpa (an increase of 10.8%) compared to the 20% FA mix. This enhancement occurs as nano-silica improved the pore structure and accelerated the formation of C-S-H.

5. Durability tests show that nano-silica is efficient to refine the pore structure and consequently lead to decreased chloride permeability, reduced acid induced weight and strength losses and enhanced sulphate attack resistance.

6. Carbonation resistance was significantly enhanced in nano-silica modified mixtures, with the optimal mix exhibits a reduction of about 73% of carbonation depth relative to conventional concrete. This emphasizes the superior performance of NSP in retaining alkalinity and act as lowered aggressive diffusion agent during increased CO₂ emissions and humidity conditions.

7. The results indicate that the combination of fly ash with nano-silica produces durable as well as environmentally friendly concrete mixes, which is suitable for harsh environmental conditions.

8. As a result, environmental mitigation strategies must be implemented, keeping the aforementioned forecasts in mind to minimise potential costly maintenance and repair expenses.

4.1. Limitations

1. Although the current study provides valuable information on durability performance of nano-silica modified fly ash concrete, there are a number of weaknesses which must be recognized.

2. The present study investigated fly ash replacing 10–30% of cement with a fixed amount of nano silica at 3%, but it should be understood that different mixes may produce varying results in terms of strength and durability.

3. In addition, all the experiments were performed in a controlled environment, which may not be exactly same in real time situations when climate changes are taken into consideration.

5. DATA AVAILABILITY

The dataset supporting the results of this study is not publically available because this is the Ph.D Research work.

6. BIBLIOGRAPHY

• ^[1] GOLEWSKI, G.L., “Green concrete based on quaternary binders with significant reduced of CO₂ emissions”, Energies, v. 14, n. 15, pp. 4558, 2021. doi: https://doi.org/10.3390/en14154558.
  » https://doi.org/10.3390/en14154558
• ^[2] AL-AMEERI, A.S., RAFIQ, M.I., TSIOULOU, O., et al, “Impact of climate change on the carbonation in concrete due to carbon dioxide ingress: experimental investigation and modelling”, Journal of Building Engineering, v. 44, pp. 102594, 2021. doi: https://doi.org/10.1016/j.jobe.2021.102594.
  » https://doi.org/10.1016/j.jobe.2021.102594
• ^[3] MALYSZ, G.N., BOSSE, R.M., DE MIRANDA SALEME GIDRÃO, G., et al, “Service-life prediction of recycled coarse aggregate concrete under natural carbonation: a time-dependent reliability analysis”, Construction & Building Materials, v. 387, pp. 131632, 2023. doi: https://doi.org/10.1016/j.conbuildmat.2023.131632.
  » https://doi.org/10.1016/j.conbuildmat.2023.131632
• ^[4] OJEDOKUN, O.O., MANGAT, P.S., “Chemical composition and physico-mechanical properties of carbonated alkali activated concrete and mortar”, Journal of Building Engineering, v. 71, pp. 106480, 2023. doi: https://doi.org/10.1016/j.jobe.2023.106480.
  » https://doi.org/10.1016/j.jobe.2023.106480
• ^[5] WATARI, T., CAO, Z., SERRENHO, A., et al, “Growing role of concrete in sand and climate crises”, iScience, v. 26, n. 5, pp. 106782, 2023. doi: https://doi.org/10.1016/j.isci.2023.106782. PubMed PMID: 37250298.
  » https://doi.org/10.1016/j.isci.2023.106782
• ^[6] BRETTI, G., CESERI, M., “Climate change effects on carbonation process: a scenario-based study”, Heritage, v. 6, n. 1, pp. 236–257, 2023. doi: https://doi.org/10.3390/heritage6010012.
  » https://doi.org/10.3390/heritage6010012
• ^[7] TALUKDAR, S., BANTHIA, N., “Carbonation in concrete infrastructure in the context of global climate change: development of a service lifespan model”, Construction & Building Materials, v. 40, pp. 775-782, 2013. doi: https://doi.org/10.1016/j.conbuildmat.2012.11.026.
  » https://doi.org/10.1016/j.conbuildmat.2012.11.026
• ^[8] LI, L., WU, M., “An overview of utilizing CO₂ for accelerated carbonation treatment in the concrete industry”, Journal of CO2 Utilization, v. 60, pp. 102000, 2022. doi: https://doi.org/10.1016/j.jcou.2022.102000.
  » https://doi.org/10.1016/j.jcou.2022.102000
• ^[9] CUI, H., TANG, W., WEI, L., et al, “Experimental study on effects of CO2 concentrations on concrete carbonation and diffusion mechanisms”, Construction & Building Materials, v. 93, pp. 522–527, 2015. doi: https://doi.org/10.1016/j.conbuildmat.2015.06.007.
  » https://doi.org/10.1016/j.conbuildmat.2015.06.007
• ^[10] CHEN, Y., LIU, P., YU, Z., “Effects of environmental factors on concrete carbonation depth and compressive strength”, Materials (Basel), v. 11, n. 11, pp. 2167, 2018. doi: https://doi.org/10.3390/ma11112167. PubMed PMID: 30400164.
  » https://doi.org/10.3390/ma11112167
• ^[11] VAN TONDER, P., LOW, M., “The effect of CO2 loading on the properties of normal concrete vs fly ash concrete”, Journal of Engineering, Design and Technology, v. 19, n. 6, pp. 1472–1487, 2021. doi: https://doi.org/10.1108/JEDT-08-2020-0315.
  » https://doi.org/10.1108/JEDT-08-2020-0315
• ^[12] WANG, X., “Impact of climate change on the optimization of mixture design of Low-CO₂ concrete containing fly ash and slag”, Sustainability, v. 11, n. 12, pp. 3394, 2019. doi: https://doi.org/10.3390/SU11123394.
  » https://doi.org/10.3390/SU11123394
• ^[13] GOLEWSKI, G., “Green concrete based on quaternary binders with significant reduced of CO₂ emissions”, Energies, v. 14, n. 15, pp. 4558, 2021. doi: https://doi.org/10.3390/en14154558.
  » https://doi.org/10.3390/en14154558
• ^[14] BALESTRA, C., GARCEZ, L., DA SILVA, L., et al, “Contribution to low-carbon cement studies: effects of silica fume, fly ash, sugarcane bagasse ash and acai stone ash incorporation in quaternary blended limestone-calcined clay cement concretes”, Environmental Development, v. 45, pp. 100792, 2023. doi: https://doi.org/10.1016/j.envdev.2022.100792.
  » https://doi.org/10.1016/j.envdev.2022.100792
• ^[15] KRITHIKA, J., KUMAR, G., “Influence of fly ash on concrete – A systematic review”, Materials Today: Proceedings, v. 33, pp. 906–911, 2020. doi: https://doi.org/10.1016/j.matpr.2020.06.425.
  » https://doi.org/10.1016/j.matpr.2020.06.425
• ^[16] WANG, X., “Simulation for optimal mixture design of low-CO2 high-volume fly ash concrete considering climate change and CO2 uptake”, Cement and Concrete Composites, v. 104, pp. 103408, 2019. doi: https://doi.org/10.1016/j.cemconcomp.2019.103408.
  » https://doi.org/10.1016/j.cemconcomp.2019.103408
• ^[17] MEESALA, C., VERMA, N., KUMAR, S., “Critical review on fly‐ash based geopolymer concrete”, Structural Concrete, v. 21, n. 3, pp. 1013–1028, 2019. doi: https://doi.org/10.1002/suco.201900326.
  » https://doi.org/10.1002/suco.201900326
• ^[18] ROSHANI, M., KARGAR, S., FARHANGI, V., et al, “Predicting the effect of fly ash on concrete’s mechanical properties by ANN”, Sustainability, v. 13, n. 3, pp. 1469, 2021. doi: https://doi.org/10.3390/SU13031469.
  » https://doi.org/10.3390/SU13031469
• ^[19] COTTO-RAMOS, A., DÁVILA, S., TORRES-GARCÍA, W., et al, “Experimental design of concrete mixtures using recycled plastic, fly ash, and silica nanoparticles”, Construction & Building Materials, v. 254, pp. 119207, 2020. doi: https://doi.org/10.1016/j.conbuildmat.2020.119207.
  » https://doi.org/10.1016/j.conbuildmat.2020.119207
• ^[20] PRIYA, K., VANITHA, S., “Effect of nano silica on the properties of concrete and mortar – A state of art”, International Review of Applied Sciences and Engineering, v. 13, n. 1, pp. 70–79, 2021. doi: https://doi.org/10.1556/1848.2021.00309.
  » https://doi.org/10.1556/1848.2021.00309
• ^[21] TABISH, M., ZAHEER, M., BAQI, A., “Effect of nano-silica on mechanical, microstructural and durability properties of cement-based materials: a review”, Journal of Building Engineering, v. 65, pp. 105676, 2022. doi: https://doi.org/10.1016/j.jobe.2022.105676.
  » https://doi.org/10.1016/j.jobe.2022.105676
• ^[22] KHAN, K., JOHARI, M.A.M., AMIN, M.N., et al, “Evaluation of the mechanical properties, microstructure, and environmental impact of mortar incorporating metakaolin, micro and nano-silica”, Case Studies in Construction Materials, v. 20, pp. e02699, 2024. doi: https://doi.org/10.1016/j.cscm.2023.e02699.
  » https://doi.org/10.1016/j.cscm.2023.e02699
• ^[23] CHEKRAVARTY, D.S.V.S.M.R.K., MALLIKA, A., SRAVANA, P., et al, “Effect of using nano silica on mechanical properties of normal strength concrete”, Materials Today: Proceedings, v. 51, n. Pt 8, pp. 2573–2578, 2022. doi: https://doi.org/10.1016/j.matpr.2021.12.409.
  » https://doi.org/10.1016/j.matpr.2021.12.409
• ^[24] MANSOURGHANAEI, M., BIKLARYAN, M., MARDOOKHPOUR, A., “Experimental study of the effects of adding silica nanoparticles on the durability of geopolymer concrete”, Australian Journal of Civil Engineering, v. 22, n. 1, pp. 81–93, 2022. doi: https://doi.org/10.1080/14488353.2022.2120247.
  » https://doi.org/10.1080/14488353.2022.2120247
• ^[25] NANDA, A., BANSAL, P., KUMAR, M., “Effect of nano silica and silica fume on durability properties of high-performance concrete”, International Journal of Civil Engineering and Technology (IJCIET), v. 9, n. 2, pp. 115–129, 2018.
• ^[26] VYAS, S., MOHAMMAD, S., PAL, S., et al, “Strength and durability performance of fly ash based geopolymer concrete using nano silica”, International Journal of Engineering Science and Technology, v. 4, n. 2, pp. 1–12, 2020. doi: https://doi.org/10.29121/ijoest.v4.i2.2020.73.
  » https://doi.org/10.29121/ijoest.v4.i2.2020.73
• ^[27] ÇEVIK, A., ALZEEBAREE, R., HUMUR, G., et al, “Effect of nano-silica on the chemical durability and mechanical performance of fly ash based geopolymer concrete”, Ceramics International, v. 44, n. 11, pp. 12253-12264, 2018. doi: https://doi.org/10.1016/J.CERAMINT.2018.04.009.
  » https://doi.org/10.1016/J.CERAMINT.2018.04.009
• ^[28] SINGH, L., ALI, D., TYAGI, I., et al, “Durability studies of nano-engineered fly ash concrete”, Construction & Building Materials, v. 194, pp. 205–215, 2019. doi: https://doi.org/10.1016/J.CONBUILDMAT.2018.11.022.
  » https://doi.org/10.1016/J.CONBUILDMAT.2018.11.022
• ^[29] XU, Z., LONG, H., LIU, Q., et al, “Mechanical properties and durability of geopolymer concrete based on fly ash and coal gangue under different dosage and particle size of nano silica”, Construction & Building Materials, v. 387, pp. 131622, 2023. doi: https://doi.org/10.1016/j.conbuildmat.2023.131622.
  » https://doi.org/10.1016/j.conbuildmat.2023.131622
• ^[30] GOLEWSKI, G.L., “Combined Effect of Coal Fly Ash (CFA) and Nanosilica (nS) on the strength parameters and microstructural properties of eco-friendly concrete”, Energies, v. 16, n. 1, pp. 452, 2022. doi: https://doi.org/10.3390/en16010452.
  » https://doi.org/10.3390/en16010452
• ^[31] KUMAR, R., SHAFIQ, N., KUMAR, A., et al, “Investigating embodied carbon, mechanical properties, and durability of high-performance concrete using ternary and quaternary blends of metakaolin, nano-silica, and fly ash”, Environmental Science and Pollution Research International, v. 28, n. 35, pp. 49074–49088, 2021. doi: https://doi.org/10.1007/s11356-021-13918-2. PubMed PMID: 33928510.
  » https://doi.org/10.1007/s11356-021-13918-2
• ^[32] GUNASEKARA, C., SANDANAYAKE, M., ZHOU, Z., et al, “Effect of nano-silica addition into high volume fly ash–hydrated lime blended concrete”, Construction & Building Materials, v. 253, pp. 119205, 2020. doi: https://doi.org/10.1016/j.conbuildmat.2020.119205.
  » https://doi.org/10.1016/j.conbuildmat.2020.119205
• ^[33] SHANMUGAM, K., SUBRAMANIAM, A., SHANAVAS, S., et al, “Influence of ceramic waste powder (CWP) in strength and durability performance of kenaf fiber reinforced concrete”, Matéria (Rio de Janeiro), v. 30, pp. e20240774, 2025. doi: https://doi.org/10.1590/1517-7076-rmat-2024-0774.
  » https://doi.org/10.1590/1517-7076-rmat-2024-0774
• ^[34] SRIVASTAVA, S., ROY, S., “Study of effect of fly ash and nano silica on strength of concrete mix and it’s microstructure analysis”, International Research Journal of Engineering and Technology (IRJET), v. 8, n. 7, pp. 1813–1819, 2021.
• ^[35] ZHANG, P., ZHAO, Y.-N., LI, Q.-F., et al, “Mechanical properties of fly ash concrete composite reinforced with nano-SiO2 and steel fibre”, Current Science, v. 106, n. 11, pp. 1529–1537, 2014. doi: http://www.jstor.org/stable/24102457
  » http://www.jstor.org/stable/24102457
• ^[36] FENG, W., TANG, Y., ZHANG, Y., et al, “Partially fly ash and nano-silica incorporated recycled coarse aggregate based concrete: constitutive model and enhancement mechanism”, Journal of Materials Research and Technology, v. 17, pp. 192–210, 2022. doi: doi: https://doi.org/10.1016/j.jmrt.2021.12.135.
  » https://doi.org/10.1016/j.jmrt.2021.12.135

Publication Dates

• Publication in this collection
  05 June 2026
• Date of issue
  2026

History

• Received
  01 Jan 2026
• Accepted
  12 Mar 2026