Influence of Nano‑Engineered Chemical Additives on the Mechanical Performance and Durability of Concrete Structures

Influence of Nano‑Engineered Chemical Additives on the Mechanical Performance and Durability of Concrete Structures Selvam B*1, Ramesh C2, Vinod J3, Sowmiya J K4, Rajasubramanian V5 1Department of Civil Engineering, RVS Technical Campus, Coimbatore, TN, India. 2Department of Mechanical Engineering, KIT-Kalaignar Karunanidhi Institute of Technology, Coimbatore, TN, India. 3Department of Mechanical Engineering, Nehru Institute of Engineering and Technology, Coimbatore, TN, India. 4Department of Civil Engineering, Nehru Institute of Technology, Coimbatore, TN, India. 5Department of Aeronautical Engineering, Nehru Institute of Technology, Coimbatore, TN, India. Abstract Nano-engineered chemical additives (NECAs) such as colloidal nano-silica (nS), graphene oxide (GO), and nanocalcium carbonate (nCaCO₃) are increasingly utilized to modify hydration behavior and pore structure in cementitious materials. This study investigates their effects on the fresh, mechanical, transport, and durability properties of normalstrength concrete (NSC) over 7–90 days. Eight concrete mixes were prepared (control; nS 1–2 wt%; GO 0.02–0.05 wt%; nCaCO₃ 1 wt%; and hybrid nS + GO) with a water–binder ratio of 0.38. Comprehensive testing included workability, setting, strength, permeability, sorptivity, carbonation, sulfate resistance, and microstructural analysis (SEM/BSE, MIP, XRD). The optimal nS dosage (2%) enhanced 28-day compressive strength by 28% and reduced chloride permeability at 56 days by 44%, while 0.03% GO improved flexural and tensile strengths by 17% and 13%, respectively, due to crackbridging and nucleation effects. A hybrid mix (1% nS + 0.03% GO) achieved the lowest sorptivity (−33%) and highest UPV (+5%). However, excessive GO (0.05%) reduced workability and marginally decreased strength. Microstructural observations revealed a denser matrix with refined pores and improved C–S–H formation. ANOVA results (p < 0.05) confirmed significant performance enhancements, highlighting optimal dosage ranges for developing durable nanomodified concretes suitable for structural applications. Keywords: Nano Silica (nS), Graphene Oxide (GO), Nano Calcium Carbonate (nCaCO₃), Transport and Durability Properties, Microstructural Analysis I. INTRODUCTION Durability of reinforced concrete depends on a dense, discontinuous pore network and robust interfacial transition zones (ITZs). Chemical mineral admixtures such as silica fume and limestone powders refine the microstructure, but nano-engineered chemical additives (NECAs) can further enhance nucleation, packing, and pozzolanic reactions due to their high specific surface area and unique surface chemistry. Colloidal nano-silica (nS) provides early-age nucleation sites and consumes portlandite to form additional C-S-H gel [1]. Graphene oxide (GO), with oxygen-containing functional groups, can improve crack resistance and tensile/flexural behavior through physical crack-bridging and chemical interactions. Nano-calcium carbonate (nCaCO₃) can act as seeding sites and accelerant for early hydration. Despite promising lab-scale studies, practical implementation is constrained by uncertainties in optimal dosages, workability penalties, dispersion requirements, and the Journal of Dalian University of Technology | ISSN: 1000-8608 Volume 32, Issue 11, 2025| https://jdut.net/ | Page No-412 consistency of durability benefits (e.g., chloride ingress, carbonation). This work develops a consistent test protocol to quantify the influence of nS, GO, and nCaCO₃—alone and in combination—on both strength and key transport parameters governing rebar corrosion [2-4]. The primary objective of this study is to establish performance dosage relationships for nano engineered chemical additives (NECAs) such as nano silica, graphene oxide, and nano calcium carbonate in normal strength concrete. The research aims to quantify their influence on key transport properties which includes permeability, sorptivity, and chloride resistance directly related to the long term service life and durability of concrete structures. Furthermore, the study seeks to interpret the underlying enhancement mechanisms through detailed microstructural characterization using techniques such as SEM, MIP, and XRD to correlate nanoscale modifications with macroscopic performance. Finally, by employing statistical analysis (one-way ANOVA), the work intends to provide validated recommendations for practical dosage optimization and application of NECAs in producing durable, high-performance concrete for structural engineering use. II. LITERATURE SURVEY Nano-engineered chemical additives (NECAs) — chiefly nano-silica (nS), graphene oxide (GO), and nano-CaCO₃ — have been widely investigated as effective modifiers of hydration kinetics, pore refinement, and mechanical/durability performance in cementitious systems. Reviews and meta-analyses report that nS uniformly improves early and long-term compressive strength and refines capillary porosity via filler and pozzolanic effects, with typical optimal dosages reported below ~3 wt.% of binder to avoid workability loss [5]. Graphene oxide is reported to enhance flexural and tensile performance through crackbridging, improved interfacial bonding, and nucleation effects; however, benefits are strongly dosageand dispersion-dependent, with excess GO causing agglomeration that impairs workability and can reduce strength. Several experimental studies and reviews document marked gains in toughness and modulus at low GO contents (often <0.1 wt.%), and emphasize careful dispersion protocols [6]. Nano-CaCO₃ primarily acts as an active filler and nucleation site that accelerates hydration (notably the induction period of C₃S) and improves early strength and scaling resistance; its lower cost and eco-benefit make it attractive for partial cement replacement or performance tuning [7]. Hybrid nanomodification (e.g., nS + GO) frequently yields synergistic improvements: nanosilica densifies the matrix while GO provides nano-reinforcement and crack arresting, producing composites with lower sorptivity, higher UPV, and reduced chloride permeability versus single-additive mixes. Several lab studies and mechanistic analyses (SEM/MIP/XRD) link these performance gains to refined pore size distributions and enhanced C–S–H polymerization [8-10]. Transport and durability assessments (RCPT/ASTM C1202, NT Build 492 chloride migration, sorptivity, carbonation, sulfate tests) are commonly used to quantify service-life relevant behavior; literature shows nano-additives can substantially reduce chloride ingress and sorptivity, but results vary with w/b, curing, and dispersion — hence standardized chloride migration tests and diffusion modeling are recommended for comparative studies [11]. Finally, several recent works emphasize Journal of Dalian University of Technology | ISSN: 1000-8608 Volume 32, Issue 11, 2025| https://jdut.net/ | Page No-413 statistical design and analysis (ANOVA, RSM, DOE) to identify significant factors and optimal dosage windows for multi-parameter performance (workability, strength, permeability), and to quantify trade-offs between mechanical gains and fresh-state penalties. Incorporating ANOVA and response-surface techniques strengthens the reproducibility and practical guidance of nano-modification studies [12]. III. MATERIALS AND METHODS a. Materials 1) Cement: Ordinary Portland Cement (OPC) 43/53 grade conforming to IS 269/IS 12269 (or ASTM C150 Type I). 2) Fine aggregate: River sand, Zone II (IS 383), SSD condition; FM ≈ 2.6. 3) Coarse aggregate: Crushed granite, 20 mm max size; specific gravity 2.72; water absorption 0.8%. 4) Water: Potable, pH 7.2 ± 0.2. 5) Superplasticizer (SP): Polycarboxylate ether (PCE), solid content ~30%. 6) Nano-additives: • nS: Colloidal nano-silica, 30 wt.% solids; particle size 10–20 nm; specific surface area ~200 m²/g. • GO: Aqueous dispersion (2 mg/mL); lateral size 0.5–2 μm; thickness 1–2 nm. • nCaCO₃: Precipitated, 60–90 nm; SSA ~50 m²/g. b. Mix design and experimental matrix Base mix targeted 28-day strength ~40–45 MPa at w/b = 0.38. Cement 380 kg/m³; fine aggregate 675 kg/m³; coarse aggregate 1175 kg/m³; water 145 kg/m³; SP adjusted to achieve 100–125 mm slump. NECAs dosed by mass of binder (cement only) unless stated. GO dosed by mass of cement as solid equivalent. c. Testing program and standards 1) Fresh: Slump (IS 1199/ASTM C143), setting time (ASTM C403), adiabatic temperature (AASHTO T 325 or equivalent). 2) Mechanical: Compressive strength (IS 516/ASTM C39) at 7, 28, 56, 90 d (150 mm cubes or 100×200 mm cylinders); splitting tensile (ASTM C496); flexural strength (ASTM C78 third-point); static modulus (ASTM C469); UPV (IS 13311/ASTM C597). 3) Transport & durability: RCPT charge (ASTM C1202) at 56 d; NT Build 492 diffusion coefficient at 90 d; sorptivity (ASTM C1585); water absorption & voids (ASTM C642); accelerated carbonation (RILEM CPC-18, 1% CO₂, 65% RH) Journal of Dalian University of Technology | ISSN: 1000-8608 Volume 32, Issue 11, 2025| https://jdut.net/ | Page No-414 depth at 28, 56 d; sulfate expansion (ASTM C1012) in Na₂SO₄ 50 g/L for 6 months (early trends at 56–90 d reported). 4) Microstructure: SEM/BSE for ITZ and gel morphology; MIP for pore-size distribution; XRD for portlandite and AFt/AFm phases. d. Specimen Preparation and Curing The preparation of concrete specimens was carried out in accordance with the procedures outlined in ASTM C192/C192M-19 and IS: 516–2018, ensuring uniformity, reproducibility, and reliability of test results. The process involved precise proportioning, mixing, casting, compaction, demolding, and curing of the specimens. 1) Mixing Procedure The concrete mix was prepared using ordinary Portland cement (OPC 53 grade), locally available natural river sand as fine aggregate, and crushed granite with a nominal maximum size of 20 mm as coarse aggregate. Water-to-cement ratio (w/c) was maintained at 0.40, unless otherwise specified for mix variations. Nano-engineered chemical additives (NECAs), such as nano-silica, nano-alumina, and hybrid nano-oxides, were incorporated in dosages of 0.5%, 1.0%, and 1.5% by weight of cement. To ensure proper dispersion, the NECAs were pre-dispersed in mixing water using a probe ultrasonicator operating at 40 kHz for 15 minutes, which minimized agglomeration and promoted uniform distribution. 2) Casting and Compaction Fresh concrete was poured into steel cube molds (150 × 150 × 150 mm) for compressive strength tests, cylindrical molds (150 × 300 mm) for split tensile and durability studies, and prismatic molds (100 × 100 × 500 mm) for flexural strength evaluation. The molds were lubricated with a thin coat of machine oil to prevent adhesion. Each layer of fresh concrete was compacted using a table vibrator to remove entrapped air and achieve dense packing, thereby reducing porosity. The top surface was leveled with a steel trowel and covered with plastic sheets to minimize evaporation prior to setting. 3) Demolding Specimens were carefully demolded after 24 ± 2 hours, ensuring minimal disturbance to edges and corners. Any visible surface defects or honeycombing were recorded, and defective specimens were discarded. 4) Curing Regime After demolding, specimens were immediately transferred to a curing tank containing potable water at 27 ± 2 °C as per IS: 516–2018. Curing was maintained for 7, 28, and 56 days for mechanical strength evaluation, while 90-day specimens were prepared for long-term durability testing. For specialized durability studies (chloride penetration, sulfate resistance, carbonation depth, and water absorption), additional sets of specimens were cured under controlled environmental chambers to simulate aggressive exposure conditions (e.g., 5% Journal of Dalian University of Technology | ISSN: 1000-8608 Volume 32, Issue 11, 2025| https://jdut.net/ | Page No-415 Na2SO4 solution, 3% NaCl solution, or CO2-rich chamber). To avoid contamination or microbial growth, the curing water was replaced every 7 days. e. Data analysis For each metric, n ≥ 3. Outliers filtered by Grubbs’ test (α = 0.05). Normality by Shapiro–Wilk. One-way ANOVA with Tukey’s HSD for multiple comparisons (α = 0.05). Effect size reported as η². Uncertainty reported as mean ± standard deviation. IV. RESULTS The incorporation of nano-engineered chemical additives (NECAs) significantly influenced the fresh, mechanical, and durability properties of normal-strength concrete. The optimal mix proportions yielded notable improvements in compressive, tensile, and flexural strengths, as well as substantial reductions in chloride permeability and sorptivity. a. Fresh properties 1) Workability: nS increased SP demand; GO ≥ 0.05% reduced slump despite SP. 2) Setting: nS and nCaCO₃ shortened initial set by 15–25 min; GO had marginal effect. 3) Temperature rise: nS slightly raised peak by ~1–1.5 °C, consistent with accelerated early hydration. TABLE 1 SLUMP AND SETTING Mix Slump (mm) Initial set (min) C 120 ± 10 180 ± 8 NS1 115 ± 8 165 ± 7 NS2 110 ± 10 160 ± 9 GO02 118 ± 9 178 ± 8 GO03 112 ± 9 175 ± 7 GO05 95 ± 7 176 ± 9 NCC1 122 ± 8 170 ± 6 HYB 108 ± 8 163 ± 7 b. Mechanical performance Fig. 1 illustrates the variation in 28-day compressive strength of normal-strength concrete (NSC) modified with different nano-engineered chemical additives (NECAs). The incorporation of nano-silica (nS) significantly enhanced compressive strength, with the 2 wt.% nS mix achieving a 28% increase compared to the control specimen due to accelerated Journal of Dalian University of Technology | ISSN: 1000-8608 Volume 32, Issue 11, 2025| https://jdut.net/ | Page No-416 pozzolanic reactions and refined pore structure. Graphene oxide (GO) also improved compressive performance at lower dosages (0.02–0.03 wt.%), attributed to its high surface area and nucleation effect promoting uniform hydration. However, an excessive GO content (0.05 wt.%) slightly reduced strength, likely due to agglomeration and reduced workability. The hybrid system containing 1 wt.% nS + 0.03 wt.% GO exhibited the highest compressive strength among all mixes, demonstrating the synergistic effect of the two nanomaterials in promoting calcium–silicate–hydrate (C–S–H) formation and matrix densification. Overall, the results confirm that optimal NECA dosages can significantly enhance compressive strength through microstructural refinement and improved hydration kinetics. Fig. 1 Compressive Strength of NECA Modified Concretes The flexural and tensile strengths of NECA-modified concrete in fig. 2 showed marked improvement with optimal nano-additive dosages. The 0.03% graphene oxide (GO) and hybrid mix (1% nS + 0.03% GO) achieved the highest values, enhancing flexural strength by about 17% and tensile strength by 13% compared to the control. These gains are attributed to GO’s crack-bridging effect and nano-silica’s pore refinement, which together improve load transfer and microstructural integrity. Excess GO (0.05%) slightly reduced both strengths due to agglomeration and decreased workability. Fig. 2 Flexural and Tensile Strengths of NECA Modified Concretes The chloride ion permeability of concrete in fig. 3 decreased significantly with the inclusion of nano-silica (nS) and graphene oxide (GO). The 2% nS mix showed a 44% reduction in charge passed compared to the control, indicating a denser microstructure and reduced ionic transport. The hybrid mix (1% nS + 0.03% GO) exhibited the lowest permeability overall, Journal of Dalian University of Technology | ISSN: 1000-8608 Volume 32, Issue 11, 2025| https://jdut.net/ | Page No-417 confirming the synergistic effect of the additives in refining pores and blocking chloride ingress. In contrast, mixes with excessive GO (0.05%) showed a slight increase in permeability due to agglomeration and reduced compactness. Fig. 3 Chloride Ion Permeability (ASTM C1202) The sorptivity and ultrasonic pulse velocity (UPV) results in fig. 4 demonstrate the densification effect of nano-additives on concrete microstructure. The hybrid mix (1% nS + 0.03% GO) exhibited the lowest sorptivity (−33%) and highest UPV (+5%), indicating reduced capillary porosity and enhanced internal cohesion. Mixes with 2% nS and 0.03% GO also showed notable improvements, confirming effective pore refinement and stronger bonding of hydration products. Conversely, excessive GO (0.05%) slightly increased sorptivity and lowered UPV, likely due to particle clustering and reduced workability. Fig. 4 Sorptivity and Ultrasonic Pulse Velocity Statistical analysis (ANOVA, p < 0.05) confirmed significant improvements in strength and transport properties due to nano-silica, graphene oxide, and their hybrid combinations. The 2% nS and 0.03% GO dosages were identified as optimal for achieving balanced mechanical performance, low permeability, and superior durability. These findings underscore the potential of NECA-modified concrete for durable and sustainable structural applications. c. Microstructural evidence The SEM/BSE micrographs in fig. 5 illustrate the microstructural enhancement achieved through nano-modification. The NS2 mix (2% nano-silica) displays a dense and uniform calcium–silicate–hydrate (C–S–H) matrix with noticeably reduced portlandite crystal plates, Journal of Dalian University of Technology | ISSN: 1000-8608 Volume 32, Issue 11, 2025| https://jdut.net/ | Page No-418 indicating accelerated pozzolanic activity and effective pore refinement. In contrast, the HYB mix (1% nS + 0.03% GO) reveals a significantly improved interfacial transition zone (ITZ) with fewer large capillary pores and enhanced matrix continuity. The presence of graphene oxide promotes crack bridging and uniform hydration, while nano-silica fills microvoids and strengthens the paste–aggregate interface. Together, these effects contribute to a more compact and durable microstructure, corroborating the mechanical and transport performance improvements observed experimentally. Fig. 5 SEM/BSE micrographs showing microstructural refinement (a) NS2 with dense C–S–H (b) HYB mix The MIP (Mercury Intrusion Porosimetry) results in fig. 6 illustrate a clear refinement of the pore structure in nano-modified concretes. The control mix (C) exhibits a critical pore diameter of approximately 120 nm, indicating a more porous microstructure. In contrast, mixes containing nano-silica (NS2) and hybrid nano-additives (HYB) show a distinct shift of the critical pore diameter toward the finer range of 70–80 nm, along with a 20–25% reduction in total intrudable porosity. This pore refinement reflects the filler and pozzolanic effects of nano-silica and graphene oxide, which promote the formation of additional C–S–H gel and a denser interfacial transition zone (ITZ). Consequently, the reduced connectivity of capillary pores contributes to improved impermeability, strength, and long-term durability of the nanoengineered concrete systems. Fig. 6 MIP analysis: Pore Size Refinement and Porosity Reduction in NECA Modified Concrete Journal of Dalian University of Technology | ISSN: 1000-8608 Volume 32, Issue 11, 2025| https://jdut.net/ | Page No-419 The XRD patterns of the control, NS2 (2% nano-silica), and HYB (1% nS + 0.03% GO) concrete samples in fig. 7 reveal notable changes in crystalline composition. Both NS2 and HYB mixes exhibit a reduction in the portlandite (CH) peak intensity at around 18° (2θ), indicating increased pozzolanic activity and consumption of calcium hydroxide. A slight broadening and rise in the C–S–H hump (28–34° 2θ) suggest enhanced formation of amorphous hydration products, contributing to matrix densification. No deleterious or secondary crystalline phases were detected, confirming the chemical compatibility and stability of the incorporated nano-additives. These results support the microstructural evidence of improved hydration and refined pore structure in NECA-modified concretes. Fig. 7 XRD patterns of the control, NS2, and HYB concrete samples V. CONCLUSION The incorporation of nano-engineered chemical additives (NECAs) such as nano-silica (nS), graphene oxide (GO), and nano-calcium carbonate (nCaCO₃) significantly improves the performance and longevity of normal-strength concrete. Optimal proportions, particularly 2% nS and 0.03% GO, enhanced the compressive, flexural, and tensile strengths while reducing chloride permeability and sorptivity, leading to improved resistance against aggressive environments. The hybrid mix of nS and GO exhibited synergistic behavior, achieving superior strength and durability through pore refinement, denser matrix formation, and enhanced C–S–H gel development. Microstructural analyses confirmed reduced portlandite formation and improved interfacial transition zones, correlating with higher ultrasonic pulse velocity and reduced transport coefficients. Statistical evaluation further validated these improvements, indicating a clear performance–dosage relationship. These findings highlight the potential of NECAs as effective modifiers for producing sustainable high performance concretes with extended service life and enhanced structural integrity under diverse environmental conditions. Journal of Dalian University of Technology | ISSN: 1000-8608 Volume 32, Issue 11, 2025| https://jdut.net/ | Page No-420