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Article

Evaluating the Influence of Hydrophobic Nano-Silica on Cement Mixtures for Corrosion-Resistant Concrete in Green Building and Sustainable Urban Development

by
Mohammadfarid Alvansazyazdi
1,2,3,*,
Fabricio Alvarez-Rea
2,
Jhon Pinto-Montoya
2,
Majid Khorami
4,*,
Pablo M. Bonilla-Valladares
5,
Alexis Debut
6 and
Mahdi Feizbahr
7
1
Institute of Science and Concrete Technology (ICITECH), Universitat Politècnica de València, 46022 Valencia, Spain
2
Carrera de Ingeniería Civil, Universidad Central Del Ecuador, Av. Universitaria, Quito 170521, Ecuador
3
Facultad Ingenieria, Industria y Construccion, Carrera Ingenieria Civil, Universidad Laica Eloy Alfaro de Manabi, Manta 130212, Ecuador
4
Facultad de Arquitectura y Urbanismo, Universidad UTE, Calle Rumipamba S/N y Bourgeois, Quito 170147, Ecuador
5
Facultad de Ciencias Químicas, Universidad Central del Ecuador, Francisco Viteri s/n y Gilberto Gato Sobral, Quito 170521, Ecuador
6
Departamento de Ciencias de la Vida y la Agricultura, Centro de Nanociencia y Nanotecnología, Universidad de las Fuerzas Armadas ESPE, Sangolquí 171103, Ecuador
7
School of Civil Engineering, Engineering Campus, University Sains Malaysia, Nibong Tebal 14300, Penang, Malaysia
*
Authors to whom correspondence should be addressed.
Sustainability 2023, 15(21), 15311; https://doi.org/10.3390/su152115311
Submission received: 2 August 2023 / Revised: 29 September 2023 / Accepted: 3 October 2023 / Published: 26 October 2023
(This article belongs to the Special Issue Green Building and Sustainable Urban Development)
Browse Figures
Review Reports Versions Notes

Abstract

:
The use of hydrophobic nano-silica particles in concrete for improved corrosion resistance and durability has been explored in recent years, and its potential impact on sustainable urban development and green building practices has been studied. The impact of substituting hydrophobic nano-silica particles for 2% of the cement weight in high-strength concrete mixes was investigated in this research. The study focuses on evaluating the physical-mechanical properties, including compressive strength, tensile strength, modulus of elasticity, and Poisson’s ratio. Additionally, the influence of these mixes on corrosion resistance is examined. The concrete designs feature a high strength of 42 MPa, and the hydrophilic nano-silica particles undergo functionalization processes to obtain hydrophobic properties. Contact angle measurements and water absorption tests confirm the hydrophobicity of the material. Physical, electrochemical, and electrical tests were conducted to determine the corrosion resistance contribution of the nano-silica particles when substituted at 2% of the cement weight. The research findings reveal that concrete containing nano-silica particles demonstrates improved physical-mechanical properties compared to other mixes. Incorporating nano-silica enhances concrete by accelerating hydration, increasing early-age strength, and providing hydrophobicity, resulting in improved physical-mechanical properties over other mixes. However, it was observed that the addition of hydrophobic and non-hydrophobic nano-silica tends to reduce corrosion resistance compared to concrete without these particles, despite exhibiting greater compactness. This suggests a direct influence of nano-silica on the corrosion phenomenon.

1. Introduction

Concrete is the most widely used construction material in the world due to the benefits it offers compared to other materials in civil engineering works. To provide better characteristics, additional materials are being researched for use in mixtures to incorporate improved proposals over conventional ones [1,2,3,4].
The development of green architecture and sustainable urban development depends on the creation of corrosion-resistant concrete. In recent years, researchers have investigated the possibility of enhancing the mechanical characteristics and corrosion resistance of cured concrete by adding hydrophobic nano-silica particles to cement mixes [5,6,7,8]. This article explores how hydrophobic nano-silica affects the performance of concrete with a particular emphasis on how it might reduce corrosion and increase structural durability.
Nano-silica, which is made up of tiny silicon dioxide particles, has special qualities that can greatly enhance the mechanical properties of concrete [9]. By reacting with cement during the hydration process, nano-silica enhances the mechanical strength of the resulting concrete [10]. However, nano-silica particles are functionalized to have a high level of hydrophobicity to maximize their efficacy by achieving the desired hydrophobic properties for enhanced performance, even though these properties can potentially hinder dispersion in the matrix due to agglomeration tendencies caused by reduced affinity to polar components [11]. Because of its hydrophobic properties, hardened concrete responds to corrosion better and does not degrade as quickly as other types of concrete [12].
By repelling water and preventing the penetration of chloride and carbonate ions, hydrophobic nano-silica provides a key advantage in mitigating the ingress of harmful elements into the concrete microstructure [13]. These ions, known for decreasing the pH of concrete, compromise the protective barrier between steel reinforcement and concrete, initiating the corrosion process [14]. While permitting substantial absorption, nano-silica’s hydrophobicity does not obstruct the passage of chloride or carbonate ions. Instead, it acts as an extra layer of defense that prevents water from diffusing through the microstructure of the concrete [15]. Furthermore, the presence of nano-silica in concrete contributes to improved durability by reducing transport properties against erosion, abrasion resistance, carbonation, and chloride ion attack [16,17,18]. With its nano-pozzolanic content, nano-silica aggregates in the small pores of the cement paste, saturating them and strengthening the overall concrete matrix [19]. Although the inclusion of nano-silica polydimethylsiloxane (PDMSO) does not directly contribute to the hydration process, it is important to note that nano-silica increases early-age strength because of its capacity to speed up cement hydration [20], As a result, less cement and water interact, which retards the development of strength. However, concrete mixes incorporating nano-silica PDMSO nonetheless adhere to design specifications and offer sufficient strength [21,22,23,24].
In conclusion, the incorporation of hydrophobic nano-silica in cement mixtures offers a promising avenue for developing corrosion-resistant concrete. By improving mechanical properties, reducing water absorption, and enhancing durability, nano-silica provides a valuable solution to counteract the corrosion phenomenon and ensure the longevity of structures [25,26]. This article delves into the evaluation of hydrophobic nano-silica’s influence on cement mixtures, shedding light on its potential for sustainable urban development and green building practices.
Previous studies have shown that the addition of nano-silica particles to concrete mixes causes changes in the microstructure of the concrete. Being a pozzolanic material, it accelerates the hydration process of the mixes, decreasing voids, and thus reducing water permeability and absorption.
Similarly, the nano-silica particles are functionalized to have a high degree of hydrophobicity, which reduces water absorption in hardened concrete, resulting in a better response to the corrosion phenomenon, preventing its deterioration and providing greater durability to the structures.
The novelty of this research lies in the exploration of hydrophobic nano-silica particles’ impact on concrete’s corrosion resistance and durability, revealing their potential influence on structural integrity and addressing the complex interplay between material properties, corrosion behavior, and mechanical strength in concrete mixes. Furthermore, the functionalization of nano-silica particles to create hydrophobic properties represents an innovative approach to mitigate water-induced degradation while offering insights into the intricate relationship between material composition, microstructure, and resistance to corrosion in concrete structures.

2. Theoretical Framework

According to the American Concrete Institute [27], concrete is classified as high strength when it can withstand a compressive force of 6000 pounds per square inch (psi) or 42 megapascals (MPa) after 28 days of curing. These types of concrete usually incorporate appropriate materials to improve their mechanical properties, especially compressive strength. To achieve these improvements, additives, whether chemical or mineral, are added, and the concrete is designed to achieve the desired strength.
The materials used in high-strength concrete are carefully chosen to meet specific standards. Fresh concrete properties such as workability, consistency, and cohesion are crucial for proper placement. Hardened concrete properties like compressive strength and modulus of elasticity are essential for its intended use. Nano-silica, a nanoscale silicon dioxide, improves concrete’s mechanical properties through reactions during hydration.
Nano-silica’s hydrophobic version is used to enhance concrete’s durability. It can replace a portion of cement in the mix to improve the aggregate–matrix bond. Nano-silica’s interactions with cement at a nanoscale level enhance concrete’s properties, including durability, abrasion resistance, and carbonation resistance. It acts as a pozzolanic material, improving hydration, bonding, and mechanical properties [28,29].
Corrosion in concrete structures is a significant concern due to exposure to various environmental factors. Corrosion leads to structural deterioration and loss of mechanical strength. It affects both the concrete matrix and reinforcement steel. Corrosion results in the reduction of the steel’s cross-sectional area, leading to a loss of strength and functionality in the structure. Various zones, including corrosion, passivation, and non-corrosion zones, can be identified based on the state of the steel.
Evaluation of corrosion involves multiple tests, such as water absorption capacity, porosity, chloride penetration, open circuit potential, and electrochemical impedance spectroscopy. The study highlights the importance of understanding and managing corrosion to maintain the structural integrity and durability of concrete structures [30].

3. Experimental Plan

In the research conducted by Fallah-Valukolaee et al. (2022) [31], the optimal variation is demonstrated where the results for the mechanical properties of concrete were highest, thus giving the substitution of 2% of the weight of cement with nano-silica as a base result for the development of the research.

3.1. Functionalization of Nano-Silica Particles

To obtain hydrophobic nano-silica particles, they were subjected to chemical processes through trial and error, allowing thorough tests to verify their hydrophobicity by measuring the contact angle. The procedure described in the research by Mora, González, etc. [12] was used to functionalize the nano-silica particles. However, due to the difficulty of obtaining reagents, N-Dodecyltriethoxysilane was replaced with Polydimethylsiloxane, resulting in low hydrophobicity after the aforementioned process, and thus was not used. A bromination was carried out on polydimethylsiloxane and nano-silica to change their molecular structure, as bromine tends to repel water particles. To verify if there was a change, AFM and infrared tests were carried out as demonstrated in the research by José (2021) [32]. Through expert opinions, it was recommended to directly use polydimethylsiloxane, abbreviated as PDMSO, and the nano-silica particles were mixed in a 1:6 ratio, meaning for every gram of silica, six grams of PDMSO was added, resulting in a hydrophobic mixture.

Measurement of Contact Angle

The contact angle allows us to determine whether the surface on which the drop sits is hydrophilic or hydrophobic. With the help of a microscope and the ImageJ program (Java 8), the contact angle of the different nano-silica particles with varying densities of PDMSO can be observed (Figure 1).
The best result was obtained using PDMSO of 12,500 mPas grade. As it is a hydrophobic material within the mixture, it is difficult to prepare the concrete. Therefore, it is mixed with cement in different proportions, with the 1:2 ratio being the most suitable for subsequent final mixing.

3.2. Concrete Mix Design: ACI 211.4r-08 Method for High-Strength Concrete

The natural disasters that have occurred throughout our country’s history give us an idea of how basic the construction processes of certain buildings are, resulting in failures or collapses due to low- to medium-intensity earthquakes. Therefore, this research was carried out to understand the behavior of concrete when using nanoparticles in resistance to mechanical properties and corrosion in reinforcement bars.
To obtain sufficient data and make a comparison of the advantages and disadvantages of incorporating these materials into concrete, three types of mixtures were made: a standard mixture without the incorporation of nano-silica, a mixture with the incorporation of nano-silica replacing 2% of the weight of cement, and a mixture with the incorporation of PDMSO nano-silica replacing 2% of the weight of cement. The following dosage was used to prepare high-strength concrete with 42 Mpa (Table 1):
For the tests, a total of 20 specimens were used for each of the aforementioned mix types, with dimensions of 20 cm in height and 10 cm in diameter, and two of them containing a 14 mm diameter rod in the center with a length of 30 cm and a height of 15 cm above the surface of the specimen.
This was carried out to obtain variability of results and to ensure acceptability and confidence in the reader.
For the results of mechanical properties, a curing process of 7 and 28 days was used according to the type of test to be performed.
For the corrosion results, a time of 56 days was used, including 28 days of curing and 28 days under normal and severe or accelerated corrosion conditions, depending on the type of test. Within the corrosion tests, the specimens were cut at a height of 5 cm, resulting in 4 parts for each specimen.

3.3. Mixing Process

3.3.1. Standard Mix

Once the properties of the materials have been obtained and the quantity of concrete to be produced has been determined, taking into account losses during its execution, the final mix can be carried out.
Turn on the mixing machine and deposit the following materials in it as follows:
  • Place the previously weighed stone aggregates and allow the mixing to run for 30 s.
  • Add the cement and let it mix for about 1 min.
  • Increase the water and add the pre-mixed additive.
  • Allow the mixture to run for 5 min.

3.3.2. Mix with 2% Nano-Silica Replacing the Weight of Cement

The procedure is similar to item 3.3.1, with the difference that nano-silica particles are added. Due to their specific surface area, they require a high water consumption in addition to their low water/cement ratio, as it is a high-strength concrete. The materials are added in a specific order, as follows:
Place the coarse and fine aggregate in the machine. Allow it to mix for 30 s.
Add the cement and wait for it to mix for 1 min.
Divide the amount of water into 3 parts:
Mix the first third with the quantity of nano-silica previously mixed using a nanoparticle mixer, and add this mixture to the concrete mixer. Mix for 1 min.
In the second third, add the corresponding additive and place it in the mixture. Wait for 1 min.
Add the last third of water to the concrete mixer and wait for 1 min. Allow the mixture to become uniform for 5 min.

3.3.3. Mix with 2% Nano-Silica PDMSO Replacing the Weight of Cement

  • The procedure is similar to item 3.3.1, with the difference that PDMSO nano-silica particles are added and, due to their hydrophobicity, materials are added in a specific order as follows:
  • Place coarse and fine aggregate in the machine. Wait for it to mix for 30 s.
  • Increase the cement. 2.1. Separate the necessary amount of cement according to the grams of hydrophobic nano-silica required in a 1:2 ratio; one part PDMSO nano-silica and two parts cement. 2.2. Thoroughly mix the cement with the PDMSO nano-silica particles. 2.3. Add the previous mixture with the remaining cement to the concrete mixer and wait for 1 min.
  • Divide the amount of water into 3 parts: a. The first third will be mixed with the normal amount of nano-silica previously. Add this mixture to the concrete mixer. Wait for 1 min. b. Add the corresponding additive to the second third and place it in the mixture. Wait for 1 min. c. Add the last third of water to the concrete mixer and wait for 1 min.
  • Wait for the mixture to be uniform for 5 min.
  • 3.1 Curing process
  • Since a characteristic of high-strength concrete is a low water/cement ratio, the curing process must consist of direct contact with water so that the cement particles are constantly hydrated. Therefore, for both the pattern mix and the mix with 2% nano-silica replacing the weight of cement, the cylinders were placed in a humidity chamber completely submerged in water. For the mix made with 2% PDMSO nano-silica replacing the weight of cement, plastic covers were implemented to seal it tightly and prevent water loss since, having hydrophobic particles, it ensures constant contact with water.

4. Results

4.1. Fresh Concrete Results

The obtained slump values are similar because they are intended for high-strength concrete mixes, and the substitution of nano-silica and nano-silica PDMSO particles is also present. Due to the use of plasticizer admixture, workability has been improved, resulting in a plastic and workable consistency with good cohesion. This allows for a uniform mixture with good flowability, and its placement on site would require vibration due to its slump (Table 2).

4.2. Hardened Concrete Results

4.2.1. Compressive Strength

The results obtained in the tests for both 7 and 28 days are presented below.
The normal nano-silica increases compressive strength due to its distribution throughout the mixture and its nanometric size occupying spaces left by the cement and aggregates union, generating a denser concrete. The concrete incorporating hydrophobic nano-silica achieved the design strength at 7 and 28 days, exceeding 75% and 100%, respectively, as required by regulations (Table 3).

4.2.2. Tensile Strength

The tensile strength of the concrete for the different mixtures was tested using the Brazilian method, which subjects the specimens to axial forces until they break (Table 4). The following are the results at 28 days.
The strength of this mechanical property of concrete exceeded the criterion of having around 10 to 12% of compressive strength, so these mixes comply with what is stipulated in research.

4.2.3. Modulus of Elasticity and Poisson’s Ratio

According to the results, the mixture that substitutes 2% of the weight of cement with nano-silica has the highest modulus of elasticity of the three mixtures with an increase of 8.90% compared to the standard mixture, while the mixture that substitutes 2% of the weight of cement with nano-silica PDMSO has a decrease of 7.55% compared to the standard mixture (Table 5).
In addition, the mixtures that substitute 2% of the weight of cement with nano-silica and nano-silica PDMSO decreased their Poisson’s ratio by 8.44% compared to the standard mixture.

4.3. Concrete Corrosion Resistance Tests

4.3.1. Accelerated Corrosion

To carry out these tests, we used the research of Terán Guillén et al. (2022) [32], which provides a detailed explanation of the calculation of mass loss and the instruments to be used.
Accelerated corrosion was obtained through the application of a constant current density (350 μA/(cm2)), to theoretically estimate the mass loss that will occur over time.
The specimens subjected to these conditions were exposed for approximately 6.3 days at a current density of (350 μA/(cm2)), applied through a galvanostat. The detailed calculation is presented in the research by José, C. R. J. (2021) [33], estimating a 2% mass loss.
Table 6 presents the results of the accelerated corrosion test.
The specimens under normal corrosion conditions, i.e., 56 days outdoors, did not undergo significant changes. It was demonstrated that the mass loss is not significant for the first two mixtures: a standard concrete and the substitution of 2% nano-silica. However, for the mixture with 2% nano-silica PDMSO, there is already a value that is not representative, but it does indicate a faster increase in the corrosion of the reinforcement bars. In any of the mixtures under normal environmental conditions, the corrosion rate is extremely slow.
On the other hand, when the specimens are subjected to accelerated corrosion, 22 days in a 5% sodium chloride solution and through an electrochemical process in a period of 6.3 days after the normal curing process, there is a significant variation in the mass loss. For the standard mixture, there is a 2% loss, observing a layer of oxide throughout the exposed area, meeting the selected percentage in the calculation. However, for the concrete with the incorporation of 2% nano-silica, there is a percentage of 2.87%, somewhat exceeding the selected value in the calculation. Nano-silica has very low resistance to electrical passage, so it acts as a protective barrier together with the aggregates and cement. This demonstrates that the materials do influence the resistance that concrete offers to electrical passage.
The mixture with 2% nano-silica PDMSO demonstrates more pronounced corrosion, with a layer of oxide in the exposed area resulting in a 3.91% loss of mass in the bar, a representative value that demonstrates a loss in diameter and could decrease the anchorage of the bar to the concrete.

4.3.2. Open Circuit Potential

The ASTM 876-91 standard provides criteria for qualifying concrete and its likelihood of corrosion. Values below 0.2 V indicate a probability of less than 10%, while values between 0.2 V and 0.35 V indicate uncertainty and values above 0.35 V indicate a 90% probability of corrosion (Table 7).
The concrete with the incorporation of 2% PDMSO nano-silica has the lowest probability of corrosion because the hydrophobic material repels water to a certain extent.
In the specimens exposed to normal conditions, both for the standard concrete and the concrete with the incorporation of 2% nano-silica under normal conditions and with the application of accelerated corrosion, values were obtained that exceed the limit to be considered probable in 90% of cases of corrosion occurrence in these types of mixtures after a period of 56 days.

4.3.3. Water Absorption Rate

According to the ASTM C-1585 standard, the procedure for this test was carried out, and the necessary parameters for evaluating the absorption and determining each mixture were elaborated. The average results for the tested specimens are presented below (Table 8).
It was determined that the initial absorption rate in the concrete samples, compared to the standard mix, increases by 93.37% in the mix that replaces 2% of the cement weight with NS, while it decreases by 76.66% in the mix that replaces 2% of the cement weight with NS PDMSO.
As for the secondary absorption rate, both mixes decrease compared to the standard mix, with the mix that replaces 2% of the cement weight with NS decreasing by 19.09%, while the mix that replaces 2% of the cement weight with NS PDMSO decreases by 25.45%.

4.3.4. Porosity or Void Volume

Using the ASTM C-642 standard as a guide, the necessary parameters for evaluating the results of the void volume were determined. The following are the average results for the test (Table 9).
The variation in the void volume of the study mixtures was determined. For the mixture that replaces 2% of the weight of cement with NS, the void volume needs to be increased by 10.85%, while for the mixture that replaces 2% of the weight of cement with NS PDMSO, there is a decrease in the void volume by 22.78% compared to the standard sample.
The mixture with the least void volume is the one that replaces 2% of the weight of cement with NS PDMSO, due to the hydrophobic particles that act in the cement paste, which is reflected in the microstructure of the concrete making it less porous and with less capacity to absorb water.
While the mixture that replaces 2% of the weight of cement with NS has the highest void volume, because the nano-silica particles are not functionalized and are hydrophilic, they will tend to absorb more water in the pores of the concrete microstructure compared to the standard mixture.

4.3.5. Chloride Ion Penetration

According to the ASTM C-1202 standard, we can classify concrete according to ranges of charge passing through it. Values less than 100 Coulombs indicate an ineligible chloride ion penetrability, between 100 and 1000 Coulombs correspond to very low penetrability, 1000 to 2000 Coulombs correspond to low penetrability, 2000 to 4000 Coulombs indicate moderate penetrability, and greater than 4000 indicate high-chloride ion penetrability (Table 10).
According to the average results, the standard concrete has a penetrability classified as very low, meaning that the aggregates and cement paste do not allow the passage of ions even though they are hydrophilic materials. For concrete with 2% nano-silica replacing the cement, there is low penetrability, increasing the passage of chloride ions because nano-silica, besides occupying smaller spaces, has greater absorption capacity, allowing the passage of a higher number of ions. Finally, the mixture incorporating PDMSO nano-silica has moderate penetrability, meaning that the amount of chloride ions is higher, resulting in low resistance due to the material used.

4.3.6. Electrochemical Impedance Spectroscopy

This test allows us to determine and verify the behavior of concrete during the corrosion process. The study conducted by Volpi León [34] was used to configure the Autolab Galvanostat with the required parameters.
In Figure 2 and Figure 3, we can observe the behavior of the concrete with the different mixtures when subjected to normal environmental conditions and accelerated corrosion. Although the standard concrete maintains its resistance of approximately 450 Ω after the aforementioned processes, it continues to exhibit resistance to ion penetration, allowing the corrosion process to be extremely slow while maintaining the protective layer between the reinforcement and concrete.
The concrete with 2% nano-silica and nano-silica PDMSO shows extremely low resistances of 125 Ω and 280 Ω under normal conditions, and resistances of 50 Ω and 45 Ω, respectively, under accelerated corrosion conditions, which are very low values considering that only 2% was replaced. Therefore, this concrete allows the corrosion process in the reinforcement due to the ingress of chlorides or carbonates, ions that degrade the protective layer between the reinforcement and concrete. Furthermore, it was observed that for these mixtures, the figures have elongated tails, which the galvanostat represents as vibrations caused by chemical reactions, indicating that corrosion is in full process. Using a microscope and Image computer software, the hydrophobicity of the different concretes was examined. The concrete with 2% NS PDMSO demonstrated a contact angle of 31.63°, confirming its hydrophobicity as the water droplet did not absorb and disappeared due to evaporation after several hours. For the concrete with 2% NS, the contact angle was 124.8°, a value exceeding 90° and thus considered a possible hydrophobic surface. The standard concrete had a contact angle of 146.8°, with the water droplet absorbing in milliseconds, indicating its hydrophilic behavior.

4.3.7. Contact Angle in Concrete

Below, Figure 4 illustrates the results of water contact in three different concrete samples, highlighting the impact of different additives on the material’s performance.

5. Conclusions

  • The incorporation of nano-silica and nano-silica PDMSO to the concrete mix causes a loss of workability; therefore, the use of a superplasticizer additive was necessary to obtain a homogeneous mixture and improve the fresh-state properties of the concrete.
  • Functionalizing the nano-silica particles and giving them hydrophobicity generates additional protection against water diffusion through the microstructure of the concrete compared to other mixtures.
  • Concerning mechanical properties, nano-silica contributes to increasing the early-age strength due to its ability to accelerate the cement hydration process. However, nano-silica PDMSO does not participate in the hydration process, and as a result, water reacts with less cement, generating lower strengths but still meeting the estimated design.
  • Nano-silica has a high absorption property, so it does not present a barrier to the passage of chloride or carbonate ions, which are harmful elements that decrease the pH of the concrete, degenerating the steel-concrete protective barrier, and initiating the corrosion process.
  • When comparing results among the mixtures, the standard concrete exhibits the most stable mechanical and chemical properties, with mechanical strengths higher than the design and maintains its resistance to the electrochemical process, resulting in a very low corrosion rate. In contrast, the concrete with 2% nano-silica achieves very high mechanical strengths that may help preserve its durability but may accelerate the corrosion process under unfavorable conditions. The mixture with 2% nano-silica PDMSO achieves the design mechanical strengths and has good behavior under the electrochemical process, so the use of these mixtures depends on the purpose and conditions to which they will be subjected.

Author Contributions

Methodology, M.K.; Validation, M.K., P.M.B.-V. and A.D.; Formal analysis, M.K.; Investigation, M.A.; Writing—original draft, M.A., F.A.-R. and J.P.-M.; Writing—review & editing, M.F.; Supervision, M.A. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Informed Consent Statement

Not applicable.

Acknowledgments

We are grateful to Alexis Debut from the Center of Nanoscience and Nanotechnology, Universidad de las Fuerzas Armadas ESPE and the staff members at the laboratory for their support.

Conflicts of Interest

The authors hereby state that they have no known financial interest or personal relationship that may have influenced the work reported in this paper.

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Figure 1. Measurement of the contact angle.
Figure 1. Measurement of the contact angle.
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Figure 2. Nyquist diagram (natural corrosion).
Figure 2. Nyquist diagram (natural corrosion).
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Figure 3. Nyquist diagram (accelerated corrosion).
Figure 3. Nyquist diagram (accelerated corrosion).
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Figure 4. Results of water contact in concrete. (a) Concrete with 2% NS PDMSO replacing cement by weight; (b) Concrete with 2% NS (nano-silica) replacing the weight of cement; (c) Standard concrete.
Figure 4. Results of water contact in concrete. (a) Concrete with 2% NS PDMSO replacing cement by weight; (b) Concrete with 2% NS (nano-silica) replacing the weight of cement; (c) Standard concrete.
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Table 1. Weight dosage per m3 of concrete.
Table 1. Weight dosage per m3 of concrete.
WaterCementA. FineA. Coarse
0.391.000.841.26
Table 2. Results for the properties in fresh concrete.
Table 2. Results for the properties in fresh concrete.
PropertyStandard2% NS in Replacement of Cement Weight2% NS PDMSO in Replacement of Cement Weight
Settlement8 cm5 cm6.5 cm
WorkabilityWorkableWorkableWorkable
ConsistencyPlasticPlasticPlastic
CohesionGoodGoodGood
FluidityGoodGoodGood
SegregationLowLowLow
UniformityHighMediumHigh
ExudationMediumLowLow
Table 3. Compression results at 7 and 28 days.
Table 3. Compression results at 7 and 28 days.
AgeCompression Mixtures (MPa)
DaysStandard2% of NS Cement Weight Replacement2% NS PDMSO in Replacement of Cement Weight
737,32538,21637,178
2849,15352,58542,226
Table 4. Tensile strength results.
Table 4. Tensile strength results.
AGETensile Mixtures (MPa)
DaysStandard2% NS in Replacement of Cement Weight2% NS PDMSO in Replacement of Cement Weight
284.486.464.25
Table 5. Results for modulus of elasticity and Poisson’s ratio.
Table 5. Results for modulus of elasticity and Poisson’s ratio.
MixElastic Modulus (MPa)Poisson’s Ratio
Standard concrete28,149.920.225
Concrete with 2% NS replacing the weight of cement30,655.420.206
Concrete with 2% NS PDMSO replacing the weight of cement26,025.690.206
Table 6. Accelerated corrosion results.
Table 6. Accelerated corrosion results.
MixNo CorrosionCorrosion (Accelerated)
% Corroded Mass% Corroded Mass
Standard concrete0.172.03
Concrete with 2% NS replacing the weight of cement0.282.87
Concrete with 2% NS PDMSO replacing the weight of cement0.483.91
Table 7. Open circuit potential results.
Table 7. Open circuit potential results.
MixNo CorrosionCorrosion
VoltageVoltage
Standard concrete0.3590.398
Concrete with 2% NS (nano-silica) replacing the weight of cement0.4130.614
Concrete with 2% NS PDMSO (polydimethylsiloxane-modified nano-silica) replacing the weight of cement.0.2490.473
Table 8. Absorption rate results.
Table 8. Absorption rate results.
MixAbsorption Rate
InitialSecondary
1 × 10−3 (mm/s1/2)
Concrete standard mix4.071.1
Concrete mix with 2% NS replacing the weight of cement7.870.89
Concrete mix with 2% NS PDMSO replacing the weight of cement0.950.82
Table 9. Void volume results.
Table 9. Void volume results.
MixApparent DensityAbsorptionVoid Volume
(g/cm3)(%)(%)
Standard concrete2.415.2611.24
Concrete with 2% NS replacing the weight of cement2.385.9812.46
Concrete with 2% NS PDMSO replacing the weight of cement2.264.28.68
Table 10. Results for resistance to chloride ion penetration.
Table 10. Results for resistance to chloride ion penetration.
MixCharge Adjustment (Coulombs)Resistance to Chloride Ion Penetration
Standard concrete953.87Very low
Concrete with 2% NS replacing the weight of cement1652.97Low
Concrete with 2% NS PDMSO replacing the weight of cement3724.18moderate
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Alvansazyazdi, M.; Alvarez-Rea, F.; Pinto-Montoya, J.; Khorami, M.; Bonilla-Valladares, P.M.; Debut, A.; Feizbahr, M. Evaluating the Influence of Hydrophobic Nano-Silica on Cement Mixtures for Corrosion-Resistant Concrete in Green Building and Sustainable Urban Development. Sustainability 2023, 15, 15311. https://doi.org/10.3390/su152115311

AMA Style

Alvansazyazdi M, Alvarez-Rea F, Pinto-Montoya J, Khorami M, Bonilla-Valladares PM, Debut A, Feizbahr M. Evaluating the Influence of Hydrophobic Nano-Silica on Cement Mixtures for Corrosion-Resistant Concrete in Green Building and Sustainable Urban Development. Sustainability. 2023; 15(21):15311. https://doi.org/10.3390/su152115311

Chicago/Turabian Style

Alvansazyazdi, Mohammadfarid, Fabricio Alvarez-Rea, Jhon Pinto-Montoya, Majid Khorami, Pablo M. Bonilla-Valladares, Alexis Debut, and Mahdi Feizbahr. 2023. "Evaluating the Influence of Hydrophobic Nano-Silica on Cement Mixtures for Corrosion-Resistant Concrete in Green Building and Sustainable Urban Development" Sustainability 15, no. 21: 15311. https://doi.org/10.3390/su152115311

APA Style

Alvansazyazdi, M., Alvarez-Rea, F., Pinto-Montoya, J., Khorami, M., Bonilla-Valladares, P. M., Debut, A., & Feizbahr, M. (2023). Evaluating the Influence of Hydrophobic Nano-Silica on Cement Mixtures for Corrosion-Resistant Concrete in Green Building and Sustainable Urban Development. Sustainability, 15(21), 15311. https://doi.org/10.3390/su152115311

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