PSI - Issue 67

Available online at www.sciencedirect.com Structural Integrity Procedia 00 (2024) 000–000 Available online at www.sciencedirect.com ScienceDirect Structural Integrity Procedia 00 (2024) 000–000 Available online at www.sciencedirect.com ScienceDirect

www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia

ScienceDirect

Procedia Structural Integrity 67 (2025) 61–79

International Symposium on Nanotechnology in Construction Materials NICOM8 A Comparative Study of the Impact of Nano-TiO 2 and Nano-silica on the Durability of Concretes Cured at Different Temperatures Dan Huang a* , Mirian Velay-Lizancos b , and Jan Olek b International Symposium on Nanotechnology in Construction Materials NICOM8 A Comparative Study of the Impact of Nano-TiO 2 and Nano-silica on the Durability of Concretes Cured at Different Temperatures Dan Huang a* , Mirian Velay-Lizancos b , and Jan Olek b a Department of Physics and Engineering Science, Coastal Carolina University, Conway, SC 29528, USA b Lyles School of Civil and Construction Engineering, Purdue University, West Lafayette, IN 47907, USA a Department of Physics and Engineering Science, Coastal Carolina University, Conway, SC 29528, USA b Lyles School of Civil and Construction Engineering, Purdue University, West Lafayette, IN 47907, USA Abstract A comparative study was conducted to evaluate the impact of diffident types of nanoparticles, specifically nano-TiO 2 and two types of proprietary nano-silica, on the mechanical and durability properties of concretes cured at varying temperatures. The study involved the assessment of compressive and flexural strengths of concretes with and without the incorporation of nanoparticles. Resistivity measurements were also performed to assess the influence of nanoparticles on pore connectivity. Additionally, the total pore volume of concretes with and without the addition of nanoparticles was also measured and water absorption tests were conducted to explore the impact of nanoparticles on concrete permeability. The study further evaluated the damage incurred by concretes exposed to freeze-thaw cycles and deicers, comparing materials with and without nanoparticles. The findings indicated that all types of nanoparticles enhanced concrete’s mechanical properties and durability. Specifically, they significantly reduced total porosity, pore connectivity, and water permeability, with these improvements being more pronounced effect in concretes cured at low temperatures. In terms of increasing the scaling resistance, the optimal dosage of nano-TiO 2 was determined to be 0.5%. However, both the 0.5% and 1.0% dosages contributed to improved mechanical strength of concrete. Finally, a synergistic effect was observed when both types of nano-silica were combined, leading to improvements in the overall performance of the concrete. © 2024 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of NICOM8 Chairpersons Abstract A comparative study was conducted to evaluate the impact of diffident types of nanoparticles, specifically nano-TiO 2 and two types of proprietary nano-silica, on the mechanical and durability properties of concretes cured at varying temperatures. The study involved the assessment of compressive and flexural strengths of concretes with and without the incorporation of nanoparticles. Resistivity measurements were also performed to assess the influence of nanoparticles on pore connectivity. Additionally, the total pore volume of concretes with and without the addition of nanoparticles was also measured and water absorption tests were conducted to explore the impact of nanoparticles on concrete permeability. The study further evaluated the damage incurred by concretes exposed to freeze-thaw cycles and deicers, comparing materials with and without nanoparticles. The findings indicated that all types of nanoparticles enhanced concrete’s mechanical properties and durability. Specifically, they significantly reduced total porosity, pore connectivity, and water permeability, with these improvements being more pronounced effect in concretes cured at low temperatures. In terms of increasing the scaling resistance, the optimal dosage of nano-TiO 2 was determined to be 0.5%. However, both the 0.5% and 1.0% dosages contributed to improved mechanical strength of concrete. Finally, a synergistic effect was observed when both types of nano-silica were combined, leading to improvements in the overall performance of the concrete. © 2024 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of NICOM8 Chairpersons © 2024 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of NICOM8 Chairpersons Keywords: Concrete; Nano-TiO 2 ; Nano-silica; Strength; Porosity; Formation factor; Water absorption; Scaling resistance. Keywords: Concrete; Nano-TiO 2 ; Nano-silica; Strength; Porosity; Formation factor; Water absorption; Scaling resistance.

* Corresponding author. Tel.: +1-843-349-6489. E-mail address: dhuang@coastal.edu * Corresponding author. Tel.: +1-843-349-6489. E-mail address: dhuang@coastal.edu

2452-3216 © 2024 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of NICOM8 Chairpersons 2452-3216 © 2024 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of NICOM8 Chairpersons

2452-3216 © 2024 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of NICOM8 Chairpersons 10.1016/j.prostr.2025.06.009

Dan Huang et al. / Procedia Structural Integrity 67 (2025) 61–79 Huang, D., Velay-Lizancos, M., Olek, J./ Structural Integrity Procedia 00 (2024) 000–000

62 2

1. Introduction In a region with a cold climate, transportation infrastructure constructed from concrete (including pavement, bridges, sidewalks, etc.) may suffer adverse effects due to freeze-thaw cycles (Harnik et al., 1980; Mehta & Monteiro, 2001; J. J. Valenza & Scherer, 2005). Especially in the late fall and winter season, such low temperature during the placement of concrete in the field leads to a challenging curing environment for concrete. Concrete placed at low temperature is typically more sensitive to failure (Husem & Gozutok, 2005; Kim et al., 1998). Furthermore, freeze-thaw cycles, coupled with the presence of deicing chemicals, can lead to damage such as surface scaling (John J. Valenza & Scherer, 2007a, 2007b). This type of damage is often observed on flat surfaces such as pavements and bridge decks, manifesting as the gradual removal of small flakes or chips of the material. (John J. Valenza & Scherer, 2007a). Besides being aesthetically unpleasing, neglected damage of this nature can degrade ride quality and expose the underlying layers of concrete, microstructure, thereby increasing the risk of future deterioration from freeze-thaw cycles by facilitating the penetration of chloride ions and moisture (Verbeck & Klieger, 1957; Wu et al., 2014). It has been reported previously that numerous instances of scaling damage in real-world scenarios have been linked to factors such as poor mix design, subpar finishing, and inadequate curing (Afrani & Rogers, 1994; Amini et al., 2019; Panesar & Chidiac, 2007). However, there remains room for enhancing the inherent durability of concrete through the application of nanoparticles. The utilization of nanoparticles has garnered significant interest from both industry and research communities because of their unique physical and chemical attributes, such as extremely small particle size and high specific surface area (Z. Li et al., 2018; Ren et al., 2018; Shekari & Razzaghi, 2011). It was reported that adding a relatively small amount of nano-TiO 2 in concrete mixtures accelerates the hydration process (Chen et al., 2012; D Huang et al., n.d.; Jayapalan et al., 2009), enhances the mechanical properties(D Huang et al., n.d.; Dan Huang et al., n.d.; Jalal et al., 2013), and improves the durability of concrete (Dan Huang et al., n.d., 2023; Ma et al., 2015; Zhang & Li, 2011), especially when curing temperature is low (Francioso et al., 2019; D Huang et al., n.d.). Such an improvement in the properties of cementitious composites is mainly due to the nucleation effect of nano-TiO 2 , which provides more nucleation sites and facilitates the hydration process of cementitious materials (Chen et al., 2012; Z. Li et al., 2018). Moreover, the incorporation of nanoparticles into cementitious composites induces a pore-filling effect, resulting in an improved particle packing density (Z. Li et al., 2018). Such an improved particle packing density, therefore, leads to an enhanced compressive strength of concrete (Abd Elrahman & Hillemeier, 2014; L. G. Li et al., 2017; Sun et al., 2018). Furthermore, numerous studies have investigated how nano-silica impacts the properties of concrete (Ji, 2005; Madani et al., 2012; Said et al., 2012; Senff et al., 2009; Singh et al., 2013). As an example, Singh et al. (Singh et al., 2013) reported that the incorporation of nano-silica in cementitious materials enhances their strength and durability through the refinement of pore structure and acceleration of hydration processes. In addition to its nucleation and pore-filling effects, nano-silica exhibits pozzolanic reactivity owing to its chemical composition. This reactivity generates additional C-S-H, thereby facilitating the strength development of the cementitious composites (Singh et al., 2013). The improvement in the mechanical and durability performance in concrete resulted from the incorporation of nanoparticles has a great potential in reducing the expensive maintenance cost caused by the deterioration of freeze-thaw and deicers (Ali & Kharofa, 2021; Ferreira et al., 2023; Haleema Saleem, 2021). Nonetheless, nanomaterials are not as economical or abundantly available as other supplementary cementitious materials (e.g., fly ash, slag, etc.). More research should undertake to develop more economical synthesis methods and manufacturing technology on producing nanomaterials (Haleema Saleem, 2021) and assess the impact of nanomaterials from a life cycle perspective (Papanikolaou et al., 2019). Despite the considerable number of publications on the utilization of nano-TiO 2 and nano-silica to modify the properties of cementitious composites, there is a shortage of studies that compare the effects of using these nanomaterials on the durability of concrete cured at various temperatures. To partially fill this gap, the current paper presents the results of a series of experiments which were conducted to compare the impact of different nanoparticles (i.e., nano-TiO 2 and nano-silica) on the properties of concretes and how different curing temperatures impact the influence of nanoparticles on the performance of concrete. These properties include compressive and flexural strength, total pore volume, pore connectivity, water absorption, and scaling resistance. Two different curing

Dan Huang et al. / Procedia Structural Integrity 67 (2025) 61–79 Huang, D., Velay-Lizancos, M., Olek, J./ Structural Integrity Procedia 00 (2024) 000–000

63

3

temperatures: (a) room temperature (23°C) and (b) low temperature (4°C), were selected to simulate the different environmental conditions in the field. 2. Sample Preparations 2.1. Materials ASTM C150M-20 (ASTM C150-20, 2018) Type I ordinary portland cement (purchased from Buzzi Unicem USA) was used in this study. The chemical composition of this cement is provided in Table 1. The particle size distribution of this cement was obtained using the PSA 1090 series, Anton Paar, Austria, and is presented in Fig. 1.

Table 1. The chemical composition of Type I portland cement used in this study. Oxide/Phase, wt. % Type I OPC Silicon dioxide/SiO 2 19.55 Aluminum oxide/Al 2 O 3 5.22 Iron oxide/Fe 2 O 3 2.74 Calcium oxide/CaO 62.91 Magnesium oxide/MagO 2.94 Sulfur oxide/SO 3 3.22 Sodium oxide/Na 2 O 0.69 Loss of ignition, % 2.25

Fig. 1. Particle size distribution of Type I portland cement used in the study.

Crushed limestone was used as coarse aggregate, and natural siliceous sand was used as fine aggregate. The gradation curves of both aggregates are shown in Fig. 2, and their physical properties are presented in Table 2. The gradations of both of these aggregates met the requirements of section 900 of the Indiana Department of Transportation (INDOT) standard specifications for, respectively, #23 fine and #8 coarse aggregates (Division of Construction Management, 2020). All concrete mixtures were air-entrained using the MasterAir AE200 air entraining agent. High-range water-reducing admixture (HRWR, MasterGlenium 7700) was used during mixing to

Dan Huang et al. / Procedia Structural Integrity 67 (2025) 61–79 Huang, D., Velay-Lizancos, M., Olek, J./ Structural Integrity Procedia 00 (2024) 000–000

64 4

ensure an adequate level of workability and aid with the dispersion of nano-TiO 2 (Z. Li et al., 2018). A constant amount of HRWR was used in all mixtures.

Fig. 2. The gradation curves of coarse and fine aggregates. (Note: CA=coarse aggregate; FA=fine aggregate.)

Table 2. The physical properties of coarse and fine aggregates. Aggregates Maximum Particle Size, mm

Specific gravity (SSD)

Fineness Moduli

Absorption, %

Coarse aggregate Fine aggregate

25

3.34 2.87

2.61 2.74

2.28 1.97

9.5

Note: SSD = Saturated surface dry condition

Nano-TiO 2 admixture used in this study was obtained from the US Research Nanomaterials, Inc. Based on the information provided by the seller, the average particle size of the nano-TiO 2 particles was 18 nm and the material mostly contained anatase phase. Additionally, the purity level of the nano-TiO 2 particles was 99.9%, their specific surface area was 200 – 240 m 2 /g, and the density of the material was 0.24 g/cm 3 . Nano-silica used in this study was manufactured by Specification Products (brand name Element Five-E5). Two types of nano-silica were studied: E5 LFA and E5-IC. Both of these materials are proprietary products. Fig. 3(a) and (b) present the transmission electron microscopy (TEM) graphs for E5-LFA and E5-IC, respectively. As shown in Fig. 3, the nano-silica particles appear to have a size in the range of 5 to 20 nm.

Dan Huang et al. / Procedia Structural Integrity 67 (2025) 61–79 Huang, D., Velay-Lizancos, M., Olek, J./ Structural Integrity Procedia 00 (2024) 000–000

65

5

Fig. 3. TEM graphs for (a) E5-LFA nano-silica and (b) E5-IC nano-silica.

2.2. Mixing procedures To compare the effect of different nanoparticles (i.e., nano-TiO 2 and nano-silica) on the strength and durability of concretes, a series of OPC concretes (i.e., concretes solely utilizing ordinary portland cement as the cementitious binder) were prepared in the laboratory. The mixture proportions of these concretes are presented in Table 3. There are two types of OPC reference concretes (OPC1 concrete had a w/c = 0.44, and OPC2 had a w/c = 0.45). For OPC1, three levels of addition of nano-TiO 2 addition were used (0%, 0.5% and 1 % by weight of cement). The OPC2 concretes contained different combinations of E5 nano-silica (E5-LFA and EE-IC, E5-LFA, E5-IC) as shown in Table 3. For all the concrete studies, consistent amounts of HRWR (5.3 oz/cwt cement or 331 ml/100 kg cement) and air entrainer (1.5 oz/cwt cement or 94 ml/100 kg cement) were added into the concrete. All materials needed for mixing were preconditioned at room temperature and accurately measured before mixing. Batch weights of the aggregates and water were adjusted as needed to account for the moisture content and absorption of both coarse and fine aggregates. Mixing commenced by introducing both coarse and fine aggregates into the mixer along with a portion of the batch water. Subsequently, these components underwent brief mixing, after which cementitious materials and the remaining portion of the batch water were added into the mixer. When incorporating nano-TiO 2 , the material was introduced into the remaining batch water, with a high-range water reducer (HRWR) already dissolved in it, and manually mixed for a few minutes. Subsequently, this suspension was added to the mixer for the final mixing stage. Air-entraining admixture (AEA) was introduced towards the conclusion of the mixing process. To prepare concrete incorporating nano-silica, the mixing protocol prescribed by the supplier was followed. Initially, 50% to 70% of the water was placed into the mixer before introducing the fine and coarse aggregates. The mixer was then started, and cement, air-entraining admixture (AEA), and high-range water reducer (HRWR) were added sequentially, followed by at least 2-5 minutes of mixing. Subsequently, the nano-silica was blended with the remaining mixing water and carefully added to the mixer using a syringe. The mixing process concluded with an additional 5-6 minutes of mixing. Following the completion of mixing, fresh concrete underwent testing for slump and air content. Subsequently, concrete samples were cast into molds to prepare various specimens required for future tests, followed by a 24-hour storage period in the laboratory, maintained at a temperature of 23°C and relative humidity of 50%. Afterward, the concrete samples were demolded and subjected to curing in saturated lime water at two distinct temperatures: room temperature (23°C) and low temperature (4°C), for the specified durations. The low curing temperature was selected to simulate the temperature conditions in the late fall season in the state of Indiana in the U.S. (where the study was

Dan Huang et al. / Procedia Structural Integrity 67 (2025) 61–79 Huang, D., Velay-Lizancos, M., Olek, J./ Structural Integrity Procedia 00 (2024) 000–000

66 6

conducted). After the corresponding curing period was finished, concrete samples were subjected to various testing and measurement procedures described in the following section.

Table 3. The mixture proportions of plain and nanomodified OPC concretes.

Content (lb/yd 3 )/(kg/m 3 )

Nano-silica, (oz/cwt* cem.) /ml/100kg cem.

Mix No.

Coarse aggregate

Nano-TiO 2 , % wt. of cem.

Water

Cement

Fine aggregate

OPC1-0nT w/c=0.44 OPC1-0.5nT w/c=0.44 OPC1-1nT w/c=0.44 OPC2-0nS w/c=0.45

248/147

564/335

1350/801

1700/1009

0

/

248/147

564/335

1350/801

1700/1009

0.5

/

248/147

564/335

1350/801

1700/1009

1

/

254/151

564/335

1345/798

1700/1009

/

0

12 (8 LFA + 4 IC)/750 (500 LFA+ 250 IC)

OPC2-12nS w/c=0.45

254/151

564/335

1345/798

1700/1009

/

OPC2-8nS w/c=0.45 OPC2-4nS w/c=0.45

8 LFA/500 LFA

254/151

564/335

1345/798

1700/1009

/

254/151

564/335

1345/798

1700/1009

/

4 IC/250 IC

*oz/cwt= oz/100 lb of cement

3. Testing methods 3.1. Compressive strength

Concrete cylinders were cast to evaluate the effect of both nano-TiO 2 and nano-silica on the 28-day compressive strength of OPC concrete. For each concrete type listed in Table 3, six 4 in. by 8 in. (100 mm x 200 mm) cylinders were fabricated, with three of them subjected to lime-saturated water with a curing temperature of 23°C, while the remaining three were cured at a low temperature of 4°C. The compressive strength of the concrete was determined in accordance with ASTM C39-20 (ASTM C39/C39M-20, 2003) after a curing period of 28 days. 3.2. Flexural strength To explore the effects of various nanoparticles on the flexural strength of concrete, 12 prism concrete samples (measuring 3 in. x 4 in. x 16 in. (76 mm x 100 mm x 406 mm)) were prepared for each concrete type. Consistent with the curing protocol outlined earlier, the concrete prisms were split into two groups, each group subjected to distinct curing temperatures (standard 23°C and low 4°C). Following this, the flexural strength of the concrete was evaluated according to ASTM C78-18 (C78-18, 2010) test method after both 7 and 28 days of curing.

Dan Huang et al. / Procedia Structural Integrity 67 (2025) 61–79 Huang, D., Velay-Lizancos, M., Olek, J./ Structural Integrity Procedia 00 (2024) 000–000

67

7

3.3. Total permeable porosity and formation factor The total pore volume of concrete was determined following the procedure outlined in AASHTO TP135 ( AASHTO TP 135 - Standard Method of Test for Determining the Total Pore Volume in Hardened Concrete Using Vacuum Saturation , n.d.). This method involves determining the oven-dry mass ( A ), vacuum saturated mass ( B ), and apparent mass ( C ) of concrete disc samples (measuring 4 in. (100 mm) in diameter and 2 in. (50 mm) in height). The total volume of the permeable pores can then be computed using the following equation 1: ,% � � � � � � � � 100 (1) The assessment of concrete resistivity was conducted in accordance with AASHTO TP119-19 ( AASHTO TP 119 15(2019) | Techstreet Enterprise , n.d.), employing the uniaxial resistance test. This test utilized 4 in. x 8 in. (100 mm x 200 mm) concrete cylinders. The apparatus for uniaxial resistivity measurement comprised stainless-steel plate electrodes, electrical cables, a resistivity meter, and sponges saturated with lime. These sponges were positioned between the electrodes and the end surfaces of the concrete cylinders during testing. The resistance displayed by the resistivity meter during the test ( R measured ) is the actual bulk resistance (i.e., the resistance of the system composed of the concrete cylinder plus two sponges). To obtain the actual value of the concrete resistivity ( R cylinder ), the resistances of both the top and the bottom sponges ( R top sponge , R bottom sponge , respectively) need to be determined and subtracted from the bulk resistance ( R measured ) following the following formula given in Equation 2: �������� � �������� � ��� ������ � ������ ������ (2) The resistivity of the cylinder can be calculated using Equation 3: � �������� � � � (3) where is the resistivity of the cylinder, R cylinder is the resistance of the cylinder, A is the cross-sectional area of the cylinder, and L is the length of the cylinder. The formation factor was calculated following AASHTO PP84-19 ( AASHTO PP 84 - Standard Practice for Developing Performance Engineered Concrete Pavement Mixtures , n.d.) using Equation 4: ��� � � � � (4) where, ��� is the formation factor that can be determined by dividing the resistivity determined by AASHTO TP119-19 ( AASHTO TP 119-15(2019) | Techstreet Enterprise , n.d.) by a pore solution resistivity � (0.127 Ωꞏ m). The resistivity of pore solution was estimated according to AASHTO PP84-19 ( AASHTO PP 84 - Standard Practice for Developing Performance Engineered Concrete Pavement Mixtures , n.d.), by combining information on mixture proportions, chemistry of the cementitious materials and degree of hydration. The formation factor is an important indicator on the connectivity of pores in the concrete, and related the concrete durability (Qiao et al., 2019; Weiss et al., 2016). Concrete with a higher value of formation factor typically has less pore connectivity, less ingression of harmful chemicals, and thus better durability performance. As a side note, it should be pointed out that while AASHTO PP84-19 ( AASHTO PP 84 - Standard Practice for Developing Performance Engineered Concrete Pavement Mixtures , n.d.) stipulated a test age of 91 days, in this study, to ensure consistency across all testing procedures, the resistivity of cylinders was determined at 28 days. 3.4. Water absorption The assessment of total water absorption and the absorption rate in concrete was conducted as per requirements of the ASTM C1585-20 (ASTM C1585, 2013), which involves testing of two concrete discs (measuring 4 in. (100 mm) in diameter and 2 in. (50 mm) in height). Prior to conducting the absorption test, the specimens need to be pre-

Dan Huang et al. / Procedia Structural Integrity 67 (2025) 61–79 Huang, D., Velay-Lizancos, M., Olek, J./ Structural Integrity Procedia 00 (2024) 000–000

68 8

conditioned. The first phase of the preconditioning procedure involves placing specimens in a 50°C/80% relative humidity (RH) oven for 3 days. Subsequently, the specimens undergo a 15-day long “equilibration period”, during which they are placed in a sealed container kept at 23°C and 50% RH. After the sample conditioning procedure was completed, the side surface of each specimen was sealed with electrical tape, and the end of the specimen that was not intended to be exposed to water was sealed with a loosely attached plastic sheet. The other end of the specimen is exposed to room temperature water, and the increase in the mass of the specimen ( � ) was recorded at predetermined time intervals specified by ASTM C1585-20 (ASTM C1585, 2013). The recorded changes in the mass of the specimen � were then used to calculate the absorption values using equation 5: � � � ����� (5) where is the absorption, � is the change in the mass of concrete samples (in grams) at time t, is the cross section area of the sample exposed to the water (mm 2 ), and is the density of the water (g/mm 3 ). Following this, the absorption values (I) were plotted against the square root of time. The initial rate of water absorption was determined from the slope of the line that best fitted all data points gathered between 1 minute and 6 hours of testing. Similarly, the secondary rate of water absorption was derived from the slope of the line that best fitted the data points collected from 1 day to 7 days of testing. Considering the significant influence of initial water content on the water absorption of concrete samples, as reported in previous studies (Hall & Hall, 1989; Nokken & Hooton, 2002; Zhutovsky & Douglas Hooton, 2019), this research implemented a modified sample conditioning procedure to enhance the linearity of the initial water absorption rate results. This modified procedure, guided by recommendations outlined in (Zhutovsky & Douglas Hooton, 2019) and affected only the first phase of the previously described specimens conditioning process. Specifically, it involved replacing drying of specimens at 50°C for 3 days with drying at 60°C oven until constant mass was achieved (defined as when the difference between two consecutive mass measurements was less than 0.2%). 3.5. Scaling resistance test Concrete slabs (3 in. x 8 in. x 11in. (76 mm x 203 mm x 279 mm)) were fabricated to be tested for scaling resistance according to ASTM C672-03 (ASTM C672/C672M-12, 2012). The sample conditioning involved a 14 day curing period in saturated lime water, followed by an additional 14-day air drying. Prior to the initiation of exposure to deicers, small dikes were installed around the perimeter of the top surface of the slabs. These dikes served to contain the deicing solution to which the concrete specimens would be subjected throughout the scaling test. The scaling resistance test was performed in the programmable environmental chamber, which lowered the temperature of the specimens to -18±3°C within one hour and maintained it with a full load of specimens for 16 hours. At the end of the freezing cycle, the chamber was programmed to start increasing the temperature to 23±3°C (within a period of about one hour) and maintaining it for an additional 6 hours. Thus, the length of one testing cycle was 24 hrs. Qualitative and qualitative assessments were conducted every 5 cycles throughout the entire 50-cycle testing duration. These assessments involved thorough flushing of the surface of the slab, followed by visual examination and collection (with subsequent weighing) of any spalled flakes of concrete. In accordance with the criterion established by the Ontario Ministry of Transportation (MTO) (Transportation, 2022), the cumulative mass loss should not exceed 0.8 kg/m 2 after 50 freeze-thaw cycles for the concrete to be considered scaling resistant.

Dan Huang et al. / Procedia Structural Integrity 67 (2025) 61–79 Huang, D., Velay-Lizancos, M., Olek, J./ Structural Integrity Procedia 00 (2024) 000–000

69

9

4. Results and discussions 4.1. The effect of nano-TiO 2 and nano-silica on the 28-day compressive strength of OPC concretes Fig. 4 illustrates the impact of incorporating nano-TiO 2 and nano-silica on the 28-day compressive strength of OPC concretes subjected to varying curing temperatures. Upon comparing the compressive strength of the reference concrete (without the addition of either type of nanoparticles), it is evident that the concrete with a lower water-to cement ratio (OPC1, w/c=0.44, depicted in Fig. 4(a)) achieved a comparable 28-day compressive strength to that of the concrete with a higher water-to-cement ratio (OPC2, w/c=0.45) displayed in Fig. 4(b)) when cured at room temperature. However, there is a significant difference in the compressive strength between reference concrete with different w/c values when cured at low temperature (4688 psi for OPC1 vs 4168 psi for OPC2, though results from OPC2 concrete presents a higher standard deviation). This discrepancy can be attributed to the inherent porosity of concrete with higher water-to-cement ratios, coupled with the deceleration of the hydration process at lower curing temperatures. Consequently, the concrete with greater porosity exhibits a delayed strength development compared to its counterpart cured at room temperature. Hence, a disparity in the 28-day compressive strength (fc') of reference OPC concrete with different water-to-cement ratios is observed under low curing temperatures.

Fig. 4. The 28-day compressive strength of OPC concretes (OPC1, w/c=0.44, and OPC2, w/c=0.45) with and without the addition of (a) nano TiO 2 and (b) nano-silica cured at different temperatures. (adapted from (Dan Huang, 2022)) Analysis of Fig. 4 (a) and (b) suggests that the incorporation of both nano-TiO 2 and nano-silica leads to improved 28-day compressive strength in OPC concretes, irrespective of curing temperature. Notably, when examining the relative increases in 28-day compressive strength (fc’) at low curing temperatures compared to reference OPC concrete, denoted as xx% at the top of the bars in both Fig. (a) and (b), nano-silica appears to be more effective compared to nano-TiO 2 (~16.9% vs. 11.6%). This can be attributed to the fact that in addition to its "nucleation effect," nano-silica undergoes a reaction with calcium hydroxide (CH), resulting in the formation of additional calcium-silicate-hydrate (C-S-H). This additional C-S-H contributes significantly to the enhancement of concrete strength. Furthermore, it is notable that the increase in compressive strength attributed to nanoparticle addition is more pronounced when the concrete is cured at low temperatures. Moreover, when comparing different categories of nano-silica nanoparticles, it appears that the combination of both LFA and IC (OPC2-12nS) is more effective with respect to enhancing concrete’s compressive strength compared to using either one of them alone (OPC2-8nS or OPC2-4nS). Considering both types of nano-silica nanoparticles yield beneficial effects, it is reasonable to assume that the simultaneous addition of both types will yield synergistic effects (El-Sadany et al., 2023; Liu et al., 2021; Uthaman et al., 2018). For nano-TiO 2 nanoparticles, while 1% of nano-TiO 2 outperformed 0.5% in improving the compressive strength of concrete cured at room temperature, 0.5% of nano-TiO 2 appears more effective in concrete cured at low temperature.

Dan Huang et al. / Procedia Structural Integrity 67 (2025) 61–79 Huang, D., Velay-Lizancos, M., Olek, J./ Structural Integrity Procedia 00 (2024) 000–000

70

10

4.2. The effect of nano-TiO 2 and nano-silica on the flexural strength of OPC concretes The flexural strength (both 7-day and 28-day) of OPC concrete with and without the addition of nanoparticles (nano-TiO 2 and a combination of E5-LFA and E5-IC nano-silica) cured at different temperatures are presented in Fig. 5. After 7-day of curing, the flexural strength of both OPC concretes was improved by the addition of nanoparticles, regardless of the type of nanoparticles and curing temperature. In addition, the relative enhancement of flexural strength (shown as xx% in Fig. 5(a)) due to the addition of nano-silica was slightly higher than that of nano-TiO 2 . At a later age (28 days), as shown in Fig. 5(b), the increase in flexural strength due to the addition of nanoparticles was less significant compared to that observed at early age (7 days). This can be explained by the fact that at a later age (28 days), most of the hydrating phases have reacted, and thus the addition of nanoparticles is not as effective as early age (7 days). Moreover, the effect of different types of nanoparticles (i.e., nano-TiO 2 and nano silica) on the flexural strength becomes comparable.

Fig. 5. The variation of the flexural strength of concretes with and without the addition of nano-TiO 2 or nano-silica (with both LFA and IC nano-silica) cured at both room and low temperatures at (a) 7 days and (b) 28 days. (adapted from (Dan Huang, 2022))

In addition, an attempt was made to establish the correlation between the measured and estimated values of the 28-day flexural strength. The estimated values of the flexural strength were obtained from the expression (see equation 6) suggested in reference ( ACI CODE-318-19: Building Code Requirements for Structural Concrete and Commentary , n.d.) (modified equation to reflect the value obtained from this study). � 12 � , (6) where is the flexural strength of concrete, and is the compressive strength of concrete. As shown in Fig. 6, the correlations between the actual and estimated values of the 28-day flexural strength of OPC concretes exhibit a strong alignment, irrespective of the type of nanoparticles and curing temperatures applied. The actual 28-day flexural strength falls within the ±10% error margin from the estimated flexural strength. This high level of correlation underscores the reasonableness of the predictive equation selected for this study.

Dan Huang et al. / Procedia Structural Integrity 67 (2025) 61–79 Huang, D., Velay-Lizancos, M., Olek, J./ Structural Integrity Procedia 00 (2024) 000–000

71

11

Fig. 6. Comparison between the actual and estimated 28-day flexural strength for OPC concretes with and without nanoparticles cured at (a) 23°C and (b) 4°C. (adapted from (Dan Huang, 2022))

4.3. The effect of the addition of nano-TiO 2 and nano-silica on the total pore volume and formation factor of OPC concretes To investigate the effect of different types of nanoparticles on the characteristics of porosity of OPC concretes, the total pore volume and formation factor of concretes were measured. Fig. 7 compares the relationship between the values of total porosity (pore volume) and formation factor for 28-day-old OPC concretes with and without nanoparticles cured at two different temperatures. When comparing the reference OPC concretes (those without nanoparticle additions), it is observed that concretes cured at low temperatures exhibit a higher total porosity volume and a lower formation factor, indicating increased pore connectivity. This is as expected as low curing temperature delays the hydration process, thus the microstructure is more porous compared to samples cured at standard temperature. Furthermore, in addition to the above observations, it is noted that the reference OPC concrete with a lower water-to-cement ratio (OPC1-0nT) demonstrates a reduced total porosity and a higher formation factor when cured at low temperatures, as opposed to the OPC2-0nS reference concrete. However, contrary to the expected trend, the formation factor of the OPC1-0nT concrete cured at 23°C is lower than the formation factor of the reference concrete with higher w/c ratio OPC2-0nS cured at the same temperature. This unexpected result is likely an outlier.

Fig. 7. Comparison of relationships between total porosity and formation factor values for 28-day-old OPC concretes with and without nano TiO 2 (red labels) and nano-silica (black labels) cured at the temperature of (a) 23°C and (b) 4°C. (adapted from (Dan Huang, 2022))

72 12

Dan Huang et al. / Procedia Structural Integrity 67 (2025) 61–79 Huang, D., Velay-Lizancos, M., Olek, J./ Structural Integrity Procedia 00 (2024) 000–000

The addition of nano-silica not only reduced the total volume of porosity but also increased the formation factor, while nano-TiO 2 addition reduced the porosity, though its impact on the formation factor is not significant. These observations suggest that both types of nanoparticles decrease the overall quantity of permeable pores by accelerating the hydration process. Additionally, nano-silica appears to be particularly effective in reducing pore connectivity. Furthermore, as depicted in Fig. 7(b), the simultaneous addition of both types of nano-silica led to a more substantial increase in the formation factor compared to adding only one type. Once more, this underscores the synergistic impact of employing both varieties of nano-silica to enhance concrete quality. Moreover, the decrease in total pore volume of concrete resulting from the addition of nano-silica is more pronounced when cured at low temperatures as opposed to room temperature. 4.4. The effect of the addition of nano-TiO 2 and nano-silica on the water absorption of OPC concretes The effects of nanoparticles (both nano-TiO 2 and nano-silica) on the water absorption of OPC concrete cured at the temperature of 23°C are presented in Fig. 8. It was found that both the initial and secondary absorptions of concrete were reduced due to the addition of nanoparticles, regardless of the type of nanoparticles.

Fig. 8. The water absorption test results for OPC concrete with and without the addition of (a) nano-TiO 2 and (b) nano-silica cured for 28 days at the temperature of 23°C (adapted from (Dan Huang, 2022)).

Fig. 9 presents the water absorption data for the same type of samples but cured at 4°C. While these graphs also show the reduction in the water absorption values upon the addition of nanoparticles, in the case of OPC concrete with nano-silica (Fig. 9(b)), the absorption curves exhibit greater differentiation compared to those associated with concrete containing nano-TiO 2 (Fig. 9(a)). This might be related to the fact that the low curing temperature significantly slows down the hydration process. This slowed pace of hydration may provide more opportunities for different types of nano-silica to exert their effects, thereby impacting water absorption to varying degrees.

Fig. 9. The water absorption test results for OPC concrete with and without the addition of (a) nano-TiO 2 and (b) nano-silica cured for 28 days at the temperature of 4°C. (adapted from (Dan Huang, 2022))

73 13

Dan Huang et al. / Procedia Structural Integrity 67 (2025) 61–79 Huang, D., Velay-Lizancos, M., Olek, J./ Structural Integrity Procedia 00 (2024) 000–000

The quantitative data for initial and secondary absorption values of the OPC concretes with and without the addition of nanoparticles cured at different temperatures are shown in Fig. 10. When comparing the reference concretes (OPC1 vs OPC2), the OPC1 concrete exhibits a lower initial and secondary absorption. This is expected as OPC1 concrete (with lower w/cm) intrinsically contains a lower amount of capillary porosity compared to OPC2. Another observation is that both the initial and secondary absorptions of concrete cured at a low temperature (4°C) are slightly higher than that of concrete cured at room temperature (23°C). This, again, underscores the influence of curing temperature on the properties and microstructure of concretes.

OPC1-0nT

OPC1-0.5nT

OPC2-0nS OPC2-12nS OPC2-8nS OPC2-4nS

3

3

(a) Initial absorption, mm 3 /mm 2 0 1 2 23°C

(b) Initial absorption, mm 3 /mm 2 0 1 2 23°C

4°C

4°C

Curing Temperature

Curing Temperature

OPC1-0nT

OPC1-0.5nT

OPC2-0nS OPC2-12nS OPC2-8nS OPC2-4nS

0 1 2 3 4 5 6

0 1 2 3 4 5 6

(c)

(d)

mm 3 /mm 2

mm 3 /mm 2

Secondary absorption,

Secondary absorption,

23°C

4°C

23°C

4°C

Curing Temperature

Curing Temperature

Fig. 10. The initial and secondary absorption values of OPC concrete with and without the addition of nano-TiO 2 (a, c) and (b) nano-silica (b, d) cured at different temperatures. (adapted from (Dan Huang, 2022))

As shown in Fig. 10, the addition of nanoparticles reduced both the initial and secondary absorptions, irrespectively of the type of nanoparticles used and the curing temperature. This implies that both types of nanoparticles likely reduced the capillary porosity. Moreover, such porosity reduction effect is more pronounced in specimens containing nano-silica, compared to nano-TiO 2 , especially at low curing temperature. Table 4 provides a summary of both the initial and secondary rates of absorption, as well as the R 2 values for the lines fitted to absorption data shown in Fig. 8 and Fig. 9 for various concrete samples. These parameters are essential components of the report generated from the water absorption test, as stipulated by ASTM C1585-20 [34].

Dan Huang et al. / Procedia Structural Integrity 67 (2025) 61–79 Huang, D., Velay-Lizancos, M., Olek, J./ Structural Integrity Procedia 00 (2024) 000–000

74

14

Table 4. The initial and secondary rate of absorptions data for concretes with and without nano-additives cured at different temperatures. (adapted from (Dan Huang, 2022)) Curing Temperature Sample Rate of initial absorption, ×10 -4 R 2 Rate of secondary absorption, ×10 -4 R 2

OPC1-0nT OPC1-0.5nT OPC2-0nS OPC2-12nS OPC2-8nS OPC2-4nS OPC1-0nT OPC1-0.5nT OPC2-0nS OPC2-12nS OPC2-8nS OPC2-4nS

102

0.9974 0.9970 0.9976 0.9905 0.9941 0.9944 0.9974 0.9966 0.9948 0.9958 0.9946 0.9934

31 25 41 39 36 36 33 27 44 47 39 32

0.9801 0.9809 0.9802 0.9882 0.9839 0.9811 0.9813 0.9763 0.9818 0.9861 0.9844 0.9828

85

106

23 °C

93 98 90

103

94

128 105

4 °C

88 92

From Table 4, it is evident that irrespective of the curing temperature, OPC reference concretes featuring a lower w/cm ratio (OPC1) exhibited a reduced rate of both initial and secondary absorption. Furthermore, when comparing differences in the rate of initial absorptions at different curing temperatures, OPC1 reference concrete demonstrates a lower difference compared to OPC2 reference concrete (102×10 -4 vs 103×10 -4 , and 106×10 -4 vs 128×10 -4 , respectively). This is, again, an indication that concretes with higher w/cm values are more sensitive to low curing temperatures. The addition of nanoparticles (both nano-TiO 2 and nano-silica) reduced both the initial and secondary rates of absorption, more significantly when cured at low temperature. Another prevailing observation is that the R 2 of the initial absorption tends to be higher than that of the secondary absorption. This is related to the fact that the initial degree of saturation of the sample is the lowest during the period of testing, and the suction force due to the capillary porosity is the highest. Consequently, water absorption tends to exhibit more linear behavior during the initial stage compared to the second phase of the test. To better illustrate the comparison between the two types of reference OPC concretes, Fig. 11 displays only the absorption curves for both. OPC1 reference concrete exhibits lower initial and secondary absorptions as well as rates of absorption, validating the effectiveness of the modified sample conditioning method in providing suitable sample conditions for the water absorption test. Moreover, the distinction between these reference OPC concretes becomes more pronounced at lower curing temperatures, indicating that the influence of w/cm values on water absorption is particularly notable under such conditions.

Fig. 11. The results of the water absorption test for the 28-day reference OPC concretes cured at (a) 23°C and (b) at 4°C. (adapted from (Dan Huang, 2022))

Dan Huang et al. / Procedia Structural Integrity 67 (2025) 61–79 Huang, D., Velay-Lizancos, M., Olek, J./ Structural Integrity Procedia 00 (2024) 000–000

75

15

4.5. The effect of nano-TiO 2 and nano-silica on the scaling resistance of OPC concretes The effect of nano-TiO 2 and nano-silica on the scaling resistance of concretes (assessed by the cumulative mass loss during the scaling test) cured at two different temperatures is shown in Fig. 12. As previously mentioned, the Ontario Ministry of Transportation (MTO) established a criterion that states the cumulative mass loss due to scaling should be no higher than 0.8 kg/m 2 after 50 freeze-thaw cycles for the concrete to be considered scaling resistant. In this study, all concrete samples, irrespective of curing temperatures, types, or dosages of nanoparticles, demonstrated excellent scaling resistance, as illustrated by the fact that after 50 freeze-thaw cycles, the observed mass losses were much lower than 0.8 kg/m 2 . This outcome was anticipated, given that scaling is typically not a major concern for OPC concrete, especially if the concrete is air-entrained. Nonetheless, the addition of nanoparticles (both nano-TiO 2 and nano-silica) reduced the mass loss of concrete, regardless of the curing temperature. However, the data for OPC1-0nT reference concrete cured at 23°C appears to be an outlier, as the observed mass loss exceeded that of OPC2-0nS reference concrete cured at the same temperature. This is difficult to explain considering that a lower w/cm ratio typically indicates higher scaling resistance compared to concrete with a slightly higher w/cm ratio. This discrepancy suggests a possible experimental error, particularly since the mass loss value obtained from specimens cured at 23°C should theoretically be lower than those cured at 4°C.

OPC1-1nT OPC1-0.5nT OPC1-1nT

OPC2-0nS OPC2-12nS OPC2-8nS OPC2-4nS

(a) Cumulative mass loss, kg/m 2 0.00 0.05 0.10 0.15 0.20 0.25 0.30

(b) Cumulative weight loss, kg/m 2 0.00 0.05 0.10 0.15 0.20 0.25 0.30 23°C

4°C

23°C

4°C

Curing Temperature

Curing Temperature

Fig. 12. Cumulative mass losses due to the scaling for OPC1 and OPC2 concretes with and without (a) nano-TiO 2 and (b) nano-silica cured at different temperatures (adapted from (Dan Huang, 2022)).

As shown in Fig. 12(a) and (b), the scaling resistance appears to depend on both the dosage and type of nanoparticles. As an example, the addition of 0.5 wt.% of nano-TiO 2 to concrete cured at 23°C reduced the cumulative mass loss and enhanced the scaling resistance of the concrete. This is due to the fact that the microstructure of concrete was densified, and the permeability of concrete was reduced due to the addition of nano TiO 2 prior to the exposure of FT cycles. However, concrete cured at the same temperature but containing 1.0 wt.% of nano-TiO 2 had lower scaling resistance (as indicated by higher mass loss). This might be related to the fact that a higher dosage of nano-TiO 2 can limit the space available for the growth of various hydration products (Jalal et al., 2013; Nazari & Riahi, 2010; Zhang & Li, 2011), thus making it less effective with respect to enhancing the strength and densifying the microstructure of concrete. When samples were cured at a lower temperature before the scaling test, it was observed that incorporating a higher dosage (1.0 wt.%) of nanoparticles proved more effective than using a lower dosage (0.5 wt.%). This can be attributed to the reduced formation of hydration products in concrete cured at lower temperatures. Consequently, such concrete required a higher nanoparticle dosage to achieve the desired beneficial effects on scaling resistance. On the other hand, when nano-silica was introduced, it appeared that the E5-LFA variant exhibited less effectiveness compared to the E5-IC nano-silica. Despite previous evidence demonstrating a synergistic effect of combining both LFA and IC nano-silica in enhancing compressive strength and diminishing pore connectivity in concrete, such a phenomenon did not translate to improved scaling resistance in OPC concrete. There are many

Dan Huang et al. / Procedia Structural Integrity 67 (2025) 61–79 Huang, D., Velay-Lizancos, M., Olek, J./ Structural Integrity Procedia 00 (2024) 000–000

76

16

factors affecting the scaling resistance of concrete. Such discrepancies between the influence of nano-silica on the mechanical properties and scaling resistance might be related to the impact of nano-silica on the chemical composition of cementitious matrix. The nature of this impact is unknown, as the chemical composition of the paste matrix plays an important role in affecting the scaling resistance of the concrete (Dan Huang et al., 2023; John J. Valenza & Scherer, 2007b). Additionally, because the nano-silica product was proprietary, its precise chemical composition was not available. 4.6. Performance index of nanoparticles on the performance of OPC concretes Table 5 presents an overview of the impact of both nanoparticles studied (i.e., nano-TiO 2 and nano-silica) on the performance of concrete, including compressive strength, flexural strength, total volume of porosity, pore connectivity, water absorption, and scaling resistance. Quantitative comparisons are presented with respect to the reference concrete (i.e., without any usage of nanoparticles) except for the results from the scaling resistance test. Though both types of nanoparticles enhanced the scaling resistance of concrete (~56% by nano-TiO 2 and ~25% by nano-silica/with type IC), a quantitative analysis may undermine the fact that reference concrete already has a fairly good scaling resistance (with a cumulative mass loss much less than 0.8 kg/m 3 ).

Table 5. Performance index of the nanoparticles (nano-TiO 2 and nano-silica) on the properties of concrete. Properties Nano-TiO 2 Nano-silica Cured at 23°C Cured at 4°C Cured at 23°C Cured at 4°C Compressive strength at 28 days ↑ 15.3% ↑ 11.5% ↑ 14.5% ↑ 16.9% Flexural strength at 7 days ↑ 35% ↑ 42% ↑ 33% ↑ 40% Flexural strength at 28 days ↑ 6.3% ↑ 6.5% ↑ 7.8% ↑ 7.5% Total volume of porosity ↓ 7.3% ↓ 5.8% ↓ 6.5% ↓ 8.3% Pore connectivity - - ↓ 6.2% ↓ 7.9% Water absorption ↓ 17.5% ↓ 14.5% ↓ 13.2% ↓ 27.3% Scaling resistance Improved Improved Improved Improved

5. Conclusions This paper presents a study focused on comparing the effects of different types of nanoparticles (i.e., nano-TiO 2 and nano-silica) on the strength, porosity, water absorption, and scaling resistance of OPC concretes cured at different temperatures. It was found that the addition of both types of nanoparticles is beneficial in enhancing the mechanical properties and durability of concrete, as manifested by improvement in the values of the compressive and flexural strengths, reduction in the porosity and water absorption, and improvement of the scaling resistance, irrespective of the curing temperature. However, it should be noted that these effects were more pronounced in concretes cured at lower temperature. The following detailed conclusions can be drawn from this study: i) The extent of property enhancement varied depending on the type of nanoparticles employed. Specifically, the increase in compressive strength appeared slightly more pronounced with the addition of nano-silica compared to nano-TiO 2 . Conversely, no significant differences were observed in the case of flexural strengths regardless of the type of nanoparticles used. Furthermore, there appears to be a synergistic effect when both types of nano silica were used in the concrete in enhancing the compressive strength of concrete. ii) The impact of nano-silica addition was also notably more significant in increasing the formation factor values compared to nano-TiO 2 , regardless of level of dosages. This suggests that incorporating nano-silica into concrete is more effective in reducing pore connectivity. iii) Both types of nanoparticles were approved to decrease the total amount of porosity in concrete. Similarly, both nanoparticles were also found to be effective in reducing the overall permeability of concrete, as both the values of the initial and secondary absorptions, as well as the rates of initial and secondary absorptions of concrete were reduced. iv) Furthermore, the scaling resistance of OPC concretes was improved by adding either type of nanoparticles (i.e.,