An extensive experimental study evaluated the effects of incorporating nano titanium dioxide (NT) into M40 grade concrete, testing dosages of 0.5%, 1%, and 1.5% against a conventional mix labeled 0NT. The research assessed mechanical properties, microstructural characteristics, durability under extreme conditions, and economic feasibility. All mixes maintained a water-to-cement ratio of 0.23, though mortar testing used a higher ratio (0.40–0.45) to ensure workability, in line with IS 4031 standards.
Concrete preparation followed a precise sequence: aggregates were dry-mixed first, followed by cement, then the NT dispersion—prepared using a high-shear mixer at ~2000 rpm for 10 minutes to prevent particle clustering—was gradually introduced. Superplasticizer was added last to achieve a uniform, workable blend. This method ensured consistent nanoparticle distribution within the cement matrix.
Workability, measured via slump tests, decreased with higher NT content: 84 mm at 0.5% NT, 72 mm at 1%, and 64 mm at 1.5%. This reduction is attributed to NT’s large surface area, which increases water demand and accelerates hydration through nucleation effects on C₃S and C₂S phases, leading to faster C-S-H gel formation and reduced flow. To counteract this, additional superplasticizer was used to maintain target consistency.
Compressive strength (CS) results showed significant improvement. After 28 days, the 1.5% NT mix achieved a 28.70% increase in strength compared to the control, while 0.5% and 1% NT yielded gains of 10.54% and 21.98%, respectively. At 180 days, CS values reached 75.25 MPa for 1.5% NT, up from 58.20 MPa in the control. This enhancement is due to NT’s role in refining pore structure and promoting denser matrix formation.
Split tensile strength (STS) also improved, with the 1.5% NT mix showing a 30.30% increase at 28 days. The nanoparticles help bridge microcracks at the nanoscale, enhancing fracture resistance. Flexural strength followed a similar upward trend, confirming improved structural integrity.
Durability assessments included exposure to aggressive chemicals (4% NaCl, HCl, H₂SO₄), freeze-thaw cycles (120 cycles between −28°C and 30°C), fire resistance (up to 600°C), carbonation (2% CO₂, 65% RH), chloride penetration (RCPT), and capillary absorption. NT-modified concrete demonstrated superior resistance across all tests. For instance, no capillary rise was observed in M40 mixes with NT after one month, whereas M25 control samples showed full saturation within three days. Permeability tests under 15 kg/cm² pressure confirmed lower fluid transmission in NT-enhanced specimens.
Microstructural analysis using scanning electron microscopy (SEM) revealed a more compact and cohesive matrix in NT-integrated samples, with fewer voids and better interfacial bonding. Petrographic examination supported these findings, showing refined crystalline structures.
Non-destructive evaluations—rebound hammer and ultrasonic pulse velocity (UPV)—correlated well with compressive strength data, indicating reliable quality assessment methods for field applications. Surface resistivity tests showed higher electrical resistance in NT concrete, suggesting reduced corrosion risk for embedded reinforcement.
Economically, while NT increases material costs, the long-term benefits—extended service life, reduced maintenance, and enhanced performance in harsh environments—justify the investment, particularly in infrastructure projects requiring high durability.
Overall, the integration of nano titanium dioxide into concrete significantly improves mechanical performance and resilience, positioning it as a promising solution for next-generation construction materials.
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Mechanical, microstructure, durability, and economic assessment of nano titanium dioxide integrated concrete
A comprehensive experimental investigation was conducted to assess concrete properties in its fresh and hardened state, incorporating NT. The study focused on M40 grade concrete, incorporating varying NT dosages of 0.5%, 1%, and 1.5%, with results benchmarked against conventional M40 concrete. For clarity in designation, the conventional concrete mix was labeled 0NT, while the NT-modified mixes were designated as 0.5NT, 1NT, and 1.5NT, corresponding to their respective NT content. The mix proportion details for M40 concrete are presented in Table 2.
The concrete was prepared following a controlled mixing sequence to ensure proper dispersion of NT and uniformity of the mix. First, the coarse aggregates and fine aggregates were introduced into a pan mixer and dry-mixed for 2 min. Cement was then added and mixed for another 2 min to obtain a homogeneous dry blend. In parallel, the required dosage of NT was dispersed in the mixing water using a high-shear mechanical disperser operating at ~ 2000 rpm for 10 min, which helped to minimize agglomeration of nanoparticles. The NT dispersed solution was then slowly added to the dry mix while the mixer was running. Finally, the superplasticizer was added, and the mixing continued for an additional 3–4 min until a uniform and workable concrete mix was achieved. This procedure ensured stable dispersion of NT within the cementitious matrix. It is essential to note that, although the water-to-cement ratio for all concrete mixes was maintained at 0.23 (Table 2), a higher water-to-cement ratio of 0.40–0.45 was specifically adopted for mortar cube testing to ensure workability, as per IS 4031.
Testing procedures
Compressive strength of cement mortar
For mortar cube testing, potable tap water was used for the preparation of the matrix as well as for curing. The ratio of the cement to fine aggregate was maintained at 1:3 by weight. A higher water-to-cement ratio of 0.40–0.45 was adopted in mortar mixes to ensure adequate workability for casting 70.06 mm cubes, in line with IS 4031 (Part 6). It should be noted that this differs from the water-to-cement ratio used for concrete mixes, as the mortar tests were intended for preliminary paste–aggregate interaction assessment rather than structural concrete evaluation.
Slump test
The workability of fresh concrete mixtures was assessed via slump testing in accordance with IS 1199–1959 (reaffirmed in 2013)37, measuring consistency and flow characteristics under gravitational settlement. A control mix was designed for a target slump of 100–110 mm, suitable for M40 grade concrete, while NT incorporation was evaluated for its influence on rheological performance. Prior to concrete testing, samples were prepared to examine the binding capacity of the nano-enhanced cementitious matrix—a critical factor governing composite strength. Samples were fabricated using a 1:3 cement-to-fine aggregate ratio per IS 4031-6:1988 and IS 8112:201331,38, cured in potable water, and tested under compressive loading to assess matrix strength development.
Petrographic analysis
To examine the microscopic properties of the prepared cement matrix, the cement mortar cubes were cast and tested under the compression Testing Machine (CTM) and are now studied under a microscope. After testing, the cube pieces are converted into thin microscopic slides, as shown in Fig. 6, to study under a microscope.
To achieve the testing under the microscope, the thick pieces of the cement cubes were first grind to fine particles and stuck on the glass to make a slide. The slide of different proportion of NT added to the cement cubes was prepared, as shown in Fig. 6b, and kept under a microscope for investigation.
Compressive strength test
The CS test for the normal concrete mix and NT-based concrete mix was done according to IS 516–1959 (Reaffirmed in 2021)39. A total of 48 cube specimens (150 mm) were prepared for the CS test, as shown in Fig. 7a–b. For each mix (0NT, 0.5NT, 1NT, and 1.5NT), 12 cubes were cast. These were equally divided for testing at four curing ages (7, 28, 90, and 180 days), i.e., 3 cubes per mix per age. The average of three specimens was reported as the compressive strength at each age. Before testing these concrete specimens, the cube’s surfaces were first dried and then put in the CTM with a loading rate of 0.25 MPa/s (approximately equivalent to 2.5 KN/s) until failure, as shown in Fig. 8a.
Split tensile strength test
The split tensile strength (STS) test of the normal mix concrete and NT-based concrete was done as per IS 5816 − 1999 (Reaffirmed in 2004) to assess its tensile strength40. For STS, 12 cylindrical specimens (100 × 200 mm) were cast as shown in Fig. 7c. Although IS 5816 − 1999 commonly specifies 150 × 300 mm cylinders, the reduced-size specimens were adopted in this study due to ease of handling and to optimize material use. The chosen dimensions comply with ASTM C496 and are widely reported in the literature for indirect tensile strength testing41, as they preserve the standard aspect ratio of 2.0. Therefore, the conversion of applied load to STS remains valid and comparable with standard results For each mix (0NT, 0.5NT, 1NT, and 1.5NT), 3 cylinders were tested at 28 days in the CTM under diametral compression at a loading rate of 1.2–2.4 MPa/min (approximately equivalent to 2 KN/s) until splitting failure occurred as shown in Fig. 8b. The average of three results was reported.
Flexural strength test
A beams of size 100 mm in breadth,100 mm in width, and 500 mm in length were used for evaluation of flexural strength (FS). The test was conducted as per IS 516–1959 (reaffirmed in 2004)39. A total of 12 prismatic beams were cast for FS testing. For each mix, 3 beams were tested at 28 days, and the mean value was reported, as shown in Fig. 7d, and were demoulded after 24 h and placed underwater for curing, as shown in Fig. 7e for 28 days. After 28 days, the rectangular prism beams were taken out from the curing tank, and their facade was wiped with a piece of cloth for testing. Two-point loads were applied on a rectangular prism beam’s top surface to test the rectangular prism beam, as shown in Fig. 8c. The effective span was set to 400 mm, measured centre-to-centre between the support rollers, giving a span-to-depth ratio L/d = 4.0. The two loading noses were positioned at L/3 from each support (i.e., 133.3 mm from the nearest support), creating a constant-moment region over the middle third of the span. The shear span a (support to nearest load point) was therefore a = L/3(133.3 mm), giving a/d = 1.33. Supports and load noses were steel rollers allowing free rotation; bearing strip widths conformed to the standard. The load was applied at a constant rate of 0.06 MPa/s (approximately equivalent to 1.8 KN/min) until failure.
Rebound hammer test (non-destructive testing)
Rebound Hammer (RH) test was performed on normal mix concrete and NT based-concrete according to IS 13,311 Part 2-1992 (reaffirmed in 2004)42. For RH, 12 cube specimens (150 mm) were cast and cured for 28 days. Each mix had 3 cubes, tested on multiple faces, and the average rebound number was compared with compressive strength values. Consequent to curing, the surface was dried with cloth, as discussed in the compressive strength test, and the prepared cubes were then tested with a Schmidt Rebound Hammer, as shown in Fig. 9a.
Ultra-sonic pulse velocity test (non-destructive testing)
Ultra Sonic Pulse Velocity (UPV) test was performed as per IS 13,311 Part 1-1992 (reaffirmed in 2004) on concrete cubes with and without NT43. A Portable Ultrasonic Non-destructive Digital Indicating Tester (PUNDIT Lab) was used. The test employed a pair of 54 kHz longitudinal transducers, which are standard for concrete quality assessment. Petroleum jelly was applied at the transducer surface interface as a coupling medium to ensure effective transmission of ultrasonic pulses. Measurements were taken using the direct transmission method, with the transducers placed on opposite faces of the specimen. The same 12 cubes used for RH were employed for UPV testing (3 cubes per mix at 28 days) as shown in Fig. 9b. The average pulse velocity was reported for each mix.
Microstructure analysis
Scanning electron microscope (SEM) analysis on the NT-based concrete matrix was also carried out to assess the matrix’s behavior at the nano-scale. Small fragments of concrete from compressive strength test cubes (post-failure) were used for SEM and petrographic studies, as shown in Fig. 10a. Thus, no additional specimens were cast exclusively for microstructural analysis. The coated samples were then placed in the SEM machine to get the NT-based concrete matrix’s morphology, as shown in Fig. 10b.
Durability analysis
Durability test: concrete exposure to harmful chemicals
The durability of concrete is a crucial parameter that defines its ability to withstand chemical attacks, particularly from aggressive substances such as sodium chloride (NaCl) present in the surrounding environment. The present investigation focuses on evaluating the influence of nano additives and their composites on the durability performance of concrete when exposed to a chemically aggressive environment. For this purpose, a total of 36 concrete cubes of M40 grade, both with and without NT, were cast and designated properly for identification. The freshly cast specimens were demoulded after 24 h and subsequently submerged in a saline solution containing 4% NaCl, 4% HCl, and 4% H₂SO₄ by weight for different exposure durations of 7, 28, and 90 days to simulate prolonged chemical attack conditions. Specimens were fully submerged in the aggressive solutions throughout the exposure period. The solutions were renewed every 7 days to maintain chemical concentration, and pH was monitored weekly (maintained within ± 0.2). The exposure was conducted at laboratory temperature (27 ± 2 °C). Before compressive strength testing, the specimens were gently rinsed with distilled water and surface-dried to avoid residual chemicals influencing the results. Therefore, the concrete specimens were removed from the solution, surface-dried, and tested using a CTM until complete failure (collapse). The results obtained from this test provide insights into the resistance of concrete against chemical degradation, thereby helping to assess the effectiveness of nano additives in enhancing durability and long-term performance in aggressive environments.
Durability test: concrete exposure to alternate freeze-thaw
The freeze–thaw resistance of NT-modified and control concretes was evaluated in accordance with the guidelines of ASTM C666 44. Concrete cubes (150 mm) were cured for 28 days in water and then subjected to 120 freeze–thaw cycles. Each cycle consisted of 24 h freezing at −28 ± 2 °C, followed by 24 h thawing at 27–30 °C (see Fig. 11). The specimens were fully saturated prior to exposure, and their compressive strength was measured at the end of the exposure period. Three cubes per mix were tested, and the average was reported. In addition to compressive strength, the freeze–thaw durability was evaluated using multiple indices, including mass loss, dynamic modulus change, visual damage index (VDI), and compressive strength loss per cycle. The mass of specimens was recorded before and after 120 cycles, and percentage mass loss was calculated. Relative Dynamic Modulus of Elasticity (RDME) was derived from UPV values before and after cycles using ASTM C666 equation. A visual damage index (0 = intact, 1 = minor surface scaling, 2 = moderate cracking, 3 = severe spalling) was used based on specimen appearance. CS loss per cycle was obtained by dividing the total CS reduction by the number of cycles.
Durability test: accelerated carbonation test
This test was conducted to ascertain the durability of the NT-based concrete. For that, samples were cast with M40 grade (with and without NT) and were cured for a specified 28 days. After curing was completed, the concrete specimens were kept in a carbonation chamber. For the accelerated carbonation test, specimens were exposed to 2% CO2 concentration, 65 ± 5% relative humidity, and 27 ± 2 °C for 30 days. After exposure, specimens were split to obtain fresh cross-sections, and a 1% phenolphthalein alcohol solution was sprayed immediately. The depth of carbonation was measured as the distance from the exposed surface to the colorless zone, using a digital Vernier calliper with 0.01 mm accuracy. For powdered sampling, the outer surface layer was removed in increments of 1 mm thickness using a rotary grinder. The collected powder was tested with phenolphthalein to confirm the depth of carbonation. Each reported value is the average of three measurements per specimen. To induce smooth carbonation of all the concrete specimens at the time of carbonation acceleration, enough space was provided between each concrete specimen to ensure that the specimen’s contact with the air could be smoothly maintained.
Durability test: surface electrical resistivity test
The surface resistivity of concrete was measured according to AASHTO TP 95 using the four-point Wenner probe method45. Cylindrical specimens (100 × 200 mm) were cast and water-cured for 28 days. Prior to testing, the cylinders were saturated in limewater for 24 h to maintain consistent moisture content (see Fig. 12), as resistivity is strongly influenced by pore saturation. Measurements were taken at 23 ± 2 °C by placing the probe on four different quadrants of the specimen surface, and the average of the readings was reported for each mix.
Durability test: rapid chloride penetration test (RCPT)
RCPT test is also an indirect test for measuring concrete permeability. RCPT was conducted according to AASHTO T27746 and ASTM C12024. Cylindrical specimens (100 mm dia. × 200 mm) were cast and water-cured for 28 days. After curing, the cylinders were cut into 50 mm-thick discs. The specimens were vacuum-saturated in limewater for 24 h before testing to ensure full pore saturation. Each disc was then mounted in the test cell, with one side exposed to 3% NaCl solution and the other to 0.3 N NaOH solution. A constant DC potential of 60 V was applied across the specimen for 6 h at a test temperature of 23 ± 2 °C, and the total charge passed (coulombs) was calculated. The cylindrical specimen’s side is coated with epoxy or with electric tape, as shown in Fig. 13a.
It is then installed in the test apparatus, as shown in Fig. 13b. The test cell’s left-hand side (negative terminal) is filled with a 3% NaCl solution, while the right-hand side (positive terminal) contains a 0.3 N NaOH solution. After setting up the system, a voltage of 60 volts is applied for a duration of six hours, with measurements recorded every thirty minutes. Once the six-hour period concludes, the specimen is removed from the cell, and the total number of coulombs passing through the sample is calculated. The resulting data are then compared against the specifications outlined in AASHTO T277-83 and ASTM C120246,47.
Durability test: concrete exposure to oven drying at 300 °C
To evaluate the NT based concrete matrix under the influence of thermal stresses due to oven drying of the concrete cubes at 300 °C (see Fig. 14a). For the test, the cubical sample of 150 mm size is casted, demoulded after 24 h and curing of the concrete cubes was conducted for 28 days. Concrete cubes after 28 days of curing were taken out from the curing tank and were left for some hours in the environment so that the surfaces of the cubes were dried. As soon as the cubes’ surfaces were dried, the concrete specimens were kept inside the Oven for 24 h at 300 °C, as shown in Fig. 14a.
After 24 h of oven drying at 300 °C, the oven power was disconnected, and the gate of the Oven was opened to cool down the concrete specimens. As soon as the concrete specimens were cool down to normal after some time, the concrete specimens were then placed under CTM to get the CS.
Durability test: concrete exposure to fire at 200 °C, 400 °C, and 600 °C
To analyse the concrete performance against the fire, 36 nos. of M40 grade concrete cubes of 100 mm were cast. The reason for casting 100 mm small concrete cubes instead of 150 mm concrete cubes was the muffle furnace’s small mouth size. The cubes were removed from the moulds after 24 h and placed in a water tank for curing over a period of 28 days. After the curing period, the cubes were taken out of the tank and air-dried for 24 h. Once the surfaces had dried, the cubes were then oven-dried at 100 °C for an additional 24 h to eliminate any remaining moisture from the concrete.
After oven drying for 24 h, the cubes were finally kept in the muffle furnace, as shown in Fig. 14b, for about 6 h to assess the concrete’s resistance against fire at high temperatures. i.e., 200 °C, 400 °C, and 600 °C. After heating at different temperatures for 6 h, the cubes were then allowed to cool down at room temperature. As soon as the cubes’ surface was cooled down, the cubes were subjected to CTM to assess the CS of the concrete matrix.
Durability test: capillary porosity test
The capillary porosity test was also conducted on NT based concrete matrixes to assess the pores and voids present in the concrete’s internal structure. The concrete cubes of M40 grade were cast with M40 grade (with and without NT), demoulded, and cured for 28 days. Cured concrete specimens after 28 days were taken out and were air-dried for 24 h. After the surface becomes dry, the cubes were then placed in the oven for oven drying at 100 °C for another 24 h to wipe out the moisture from the concrete cubes. After oven drying for 24 h, the cubes were finally kept in the water reservoir again so that the half surface of the cube submerged in water and the remaining half portion free in the environment, as shown in Fig. 15a. This test was conducted for about one month, and no capillary movements of water through pores were observed within the concrete for the normal mix as well as the concrete mixed with NT. The half portion of the concrete cube, free in the environment, remains dry even after a month, as shown in Fig. 15b. On the other hand, in the same manner mentioned above, the concrete cube of M25 grade was submerged (see Fig. 15c) to draw a comparison between the two mixes. The capillary action through pores was evident in the M25 grade concrete as water moves up to the cube’s top surface, making the whole concrete cube wet, as shown in Fig. 15d within three days.
Durability test: permeability test
The concrete cubes of M40 grade were cast with M40 grade (with and without NT, demoulded, and cured for 28 days. The test was conducted for more than a month at a pressure head of 15 kg/cm2 as per IS: 3085 − 1965 (reaffirmed in 2002) code48, as shown in Fig. 16a–b. Flow through the specimen was measured volumetrically over a 24 h interval. The coefficient of permeability, k, was calculated from Darcy’s law using Eq. 1. The permeability apparatus used has a detection limit of 1 × 10− 12 m/s.
$$ :k= : frac{Q*L}{A*t*H}$$
(1)
where Q is the total volume of flow (m3), L is the specimen thickness (m), A is the cross-sectional area (m2), t is the measurement time (s), and H is the applied hydraulic head (m).
Compressive strength of cement mortar
The compressive strength of the cement paste cubes of normal mix, using different dosages of NT, cured for 28 days, is given in Table 3. The compressive strength of the cement mortar increases by 2.73%, 7.54%, and 10.38% after incorporating 0.5%, 1%, and 1.5% NT, respectively, in comparison with the control the cement mortar. This enhancement in the strength property of cement mortar is due to the filling of cracks at the nano scale after the incorporation of NT and the formation of an extra layer of hydrate gels.
Workability
The workability of the fresh concrete mix incorporating NT was evaluated through the slump test, with the results presented in Table 4. The recorded slump values for mixes containing 0.5 wt%, 1 wt%, and 1.5 wt% NT were 84 mm, 72 mm, and 64 mm, respectively. The observed reduction in workability can be attributed to the high surface area of NT particles19, which increases water demand within the mix due to enhanced particle interactions and a higher degree of cementitious material hydration.
Zhang et al.8 observed a 2.8–20.8% decrease in workability with the incorporation of 1–5 wt% NT, demonstrating a consistent decline in slump values with increasing NT content. Although setting time measurements were not directly performed, the reduction in slump retention suggests an accelerated hydration process and reduced flowability with higher NT content. Previous studies have reported similar trends, attributing this to the nucleation effect of NT, which enhances the early hydration of cementitious phases19. To address the increased water demand and reduced slump retention, adjustments to the water-to-cement ratio or the use of superplasticizers are recommended when incorporating NT into concrete mixtures.
In the present study, the reduction in workability was effectively managed by incorporating an additional dosage of superplasticizer to maintain the desired consistency. The results of the slump test are further illustrated in Fig. 17. The reduction of workability on the addition of NT can be accounted for by hydration reactions and particle interactions with the cementitious system. The following are the chief mechanisms involved:
Increased hydration rates
NT acts as a nucleation site, accelerating the tricalcium silicate (C₃S) and dicalcium silicate (C₂S) hydration reaction of the cement. The rapid growth of the calcium silicate hydrate (C-S-H) gel is the result, trapping free water and reducing workability (Eqs. 2–3):
$$ :2{ text{C}}_{{ text{3}}} { text{S}} + 6{ text{H}}_{2} { text{O}} to :3{ text{C}} – { text{S}} – { text{H}} + 3{ text{Ca}} left( {{ text{OH}}} right)_{2}$$
(2)
$$ :2{ text{C}}_{2} { text{S}} + 4{ text{H}}_{2} { text{O}} to :3{ text{C}} – { text{S}} – { text{H}} + { text{Ca}} left( {{ text{OH}}} right)_{2}$$
(3)
Increased water demand
Due to its high surface area, NT can absorb water molecules, hence reducing the free water for workability (Eq. 4):
$$ :2{ text{C}}_{2} { text{S}} + 4{ text{H}}_{2} { text{O}} to :3{ text{C}} – { text{S}} – { text{H}} + { text{Ca}} left( {{ text{OH}}} right)_{2}$$
(4)
Agglomeration effect
The strong van der Waals forces among the NT particles result in particle agglomeration, increasing the viscosity of the blend and also reducing workability. When NT is added to a cementitious system, it interacts with Ca²⁺ ions from cement hydration, forming secondary hydration products that further contribute to agglomeration (Eq. 5):
$${ text{TiO}}_{2} + { text{H}}_{2} { text{O}} to { text{TiO}}_{2} cdot { text{H}}_{2} { text{O}}$$
(5)
Compressive strength (CS)
Each CS value in Table 5 represents the mean of three specimens, reported as mean ± standard deviation (SD) (n = 3). The inclusion of NT reduced data variability compared to the control, indicating more uniform matrix densification. The improvements, particularly at 1.5% NT, were statistically consistent across all curing ages. As shown in Table 5, the incorporation of NT in the concrete mix resulted in a significant rise in CS compared to the 0NT. Among the three dosages of NT tested, the highest increase in CS was observed at a 1.5% NT dosage, with an impressive 28.70% enhancement in strength after 28 days of curing. These results corroborate the findings of Jenima et al. 19, who also reported similar improvements in strength with NT incorporation. At the 0.5% NT dosage, the CS increase was 10.54%, while at 1% NT, the enhancement was 21.98%, both compared to the conventional mix (0NT) cured for 28 days.
This pattern of strength improvement was consistent across all curing durations. Specifically, the maximum CS values at 180 days of curing were 58.20 MPa, 64.50 MPa, 71.00 MPa, and 75.25 MPa for the 0%, 0.5%, 1.0%, and 1.5% NT mixes, respectively. The rise in strength over time can be attributed to the role of nanoparticles in enhancing the bonding between the matrix ingredients, which in turn improves the impermeability and overall strength of the concrete. These results indicate that the addition of NT significantly enhances the strength properties of M40 grade concrete, transforming it into a higher strength concrete capable of performing better under various load conditions. The comparison of the CS at varying percentage of NT is visually presented in Fig. 18.
The significant increase in the percentage of gain in strength is also observed by other researchers after the incorporation of 1.5% NT in concrete due to the participation of NT in pozzolanic reaction, which is helpful in accelerating the phenomena of development of C-S-H gel19,26,49. In another study conducted by Mousavi, et al.50. The optimal NT percentage was found to be between 1% and 2%. The CS of NT based concrete is decreased after the incorporation of an excess amount of NT due to the non-uniform dispersion of NT particles in the matrix51.
Split tensile strength (STS)
As presented in Table 6, the results are reported as mean ± SD, n = 3 for each mix. The STS exhibited a clear positive correlation with the increasing dosage of NT. The maximum rise in STS was observed in the mix containing 1.5% NT, which showed an impressive 30.30% improvement in tensile strength at 28 days compared to the 0NT. Concrete mixes with 0.5% NT and 1.0% NT also exhibited increases in STS of 6.81% and 16.28%, respectively. The observed gain in tensile strength can be attributed to the role of nanoparticles, which enhance the fracture resistance of the concrete matrix.
The nanoparticles improve the overall structural integrity by effectively controlling microcracks within the matrix at the nano-scale, leading to enhanced tensile properties (see Fig. 19). This finding aligns with the