Materiales de Construcción

76 (361) January-March 2026, e399

ISSN-L: 0465-2746, eISSN: 1988-3226

https://doi.org/10.3989/mc.2026.414925

ARTICLE

Impact of ZnO and TiO₂ on C-S-H composition and its correlation with antifungal properties in cement pastes

Impacto de ZnO y TiO₂ en la composición del gel C-S-H y su correlación con las propiedades antifúngicas en pastas de cemento

F. Amor

Laboratory of Applied Materials Chemistry, Center of Materials Science, Faculty of Sciences, Mohammed V University, (Rabat, Morocco), Department of Building Structures, Faculty of Civil Engineering, Czech Technical University in Prague, (Prague, Czech Republic)

Corresponding author: fouad.amor@fsr.um5.ac.ma, https://orcid.org/0000-0001-7517-4652

H. Agourrame

Laboratory of Applied Materials Chemistry, Center of Materials Science, Faculty of Sciences, Mohammed V University, (Rabat, Morocco)

hind.agourrame@gmail.com, https://orcid.org/0000-0002-8794-0702

Z. Racova

Department of Building Structures, Faculty of Civil Engineering, Czech Technical University in Prague, (Prague, Czech Republic)

zuzana.racova@fsv.cvut.cz, https://orcid.org/0000-0003-1245-5769

N. Khachani

Laboratory of Applied Materials Chemistry, Center of Materials Science, Faculty of Sciences, Mohammed V University, (Rabat, Morocco)

n.khachani@um5r.ac.ma, https://orcid.org/0000-0001-5041-0081

P. Hajek

Department of Building Structures, Faculty of Civil Engineering, Czech Technical University in Prague, (Prague, Czech Republic)

petr.hajek@fsv.cvut.cz, https://orcid.org/0000-0003-2389-9306

ABSTRACT

This study presents a self-cleaning cement incorporating zinc oxide and titanium dioxide nanoparticles, used alone or in combination. The objective is to develop high-performance materials suitable for different environments, inhibiting fungal growth while providing self-cleaning properties. In parallel, the impact of these nanoparticles on the mineralogy and structure of C-S-H was examined. Used as partial cement substitutes (0–3% by weight), the pastes were characterized after 28 days of hydration by XRD, XRF, DSC and TG to evaluate reactivity and Ca/Si ratios of the formed C-S-H. Next, a new alternative method for the indirect determination of the Ca/Si ratio of the C-S-H gel in cements is also proposed using three methods. The antimicrobial surfaces were assessed for antifungal activity against Penicillium brevicompactum, Trichoderma reesei and Aspergillus niger on Czapek-Dox agar. Results show that the addition of TiO₂ and ZnO yields fungal-resistant surfaces, promoting hygiene, sustainability and innovation in construction.

Keywords: Nanoparticles; ZnO; TiO₂; Antifungal; Cement hydration; C-S-H; Ca/Si ratio.

RESUMEN

Este estudio presenta un cemento autolimpiante con nanopartículas de óxido de zinc y dióxido de titanio, usadas solas o combinadas. El objetivo es desarrollar materiales de alto rendimiento que inhiban el crecimiento de hongos y aporten propiedades autolimpiantes. Se evaluó además el efecto de estas nanopartículas en la mineralogía y la estructura del gel C-S-H. Empleando estas nanopartículas como sustitutos parciales del cemento (0–3 % en peso), las pastas se caracterizaron tras 28 días de hidratación mediante XRD, XRF, DSC y TG para analizar la reactividad y la relación Ca/Si del gel C-S-H. También se propone un método alternativo para determinar de forma indirecta la relación Ca/Si del gel en cementos a través de tres enfoques. Las superficies antimicrobianas se ensayaron contra Penicillium brevicompactum, Trichoderma reesei y Aspergillus niger en agar Czapek-Dox. Los resultados confirman que la incorporación de TiO₂ y ZnO genera superficies resistentes a hongos, favoreciendo higiene y sostenibilidad en la construcción.

Palabras clave: Nanopartículas; ZnO; TiO₂; Antifúngico; Hidratación del cemento; C-S-H; Relación Ca/Si.

Received: 24-04-2025 / Accepted: 04-03-2026 / Published: 08-06-2026

Citation: Amor F, Agourrame H, Racova Z, Khachani N, Hajek P. 2026. Impact of ZnO and TiO₂ on C-S-H composition and its correlation with antifungal properties in cement pastes. https://doi.org/10.3989/mc.2026.414925

Copyright: ©2026 CSIC. This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) License.

Supplementary information ↓

Contenido

1. INTRODUCTION

2. MATERIALS AND METHODS

2.1. Materials

2.2. Methods

2.3. Anti-fungal activity evaluation

3. RESULTS AND DISCUSSION

3.1. Ca/Si ratios calculated from XRD data

3.2. Thermal analysis and Ca/Si ratios refined using TG data

3.3. Ca/Si ratios from X-Ray fluorescence (XRF) analysis

3.4. Evolution of Ca/Si ratios obtained by different techniques (XRD, TG, XRF)

3.5. Antifungal activity of cement pastes

4. CONCLUSIONS

REFERENCES

1. INTRODUCTION ↑

Cement is a particularly complex system to characterize, both in terms of its chemical composition and crystalline structure, as well as the morphology of the solid phases formed during its hydration. To date, the characterization of cement hydrates, in particular hydrated calcium silicates, remains a challenge despite the numerous research projects carried out in this field (1)1. Qi C, Manzano H, Spagnoli D, Chen Q, Fourie A. 2021. Initial hydration process of calcium silicates in Portland cement: A comprehensive comparison from molecular dynamics simulations. Cem. Concr. Res. 149:106576. https://doi.org/10.1016/j.cemconres.2021.106576. Hydrated calcium silicates (C-S-H) are formed by the hydration of silicates present in clinker and constitute between 60 and 70% of the total volume of the hydrated cement paste. Essential elements of Portland cement, they play a major role in its properties, in particular by ensuring a large part of its mechanical strength (2)2. Tang S, Wang Y, Geng Z, et al. 2021. Structure, fractality, mechanics and durability of calcium silicate hydrates. Fract. Fractional 5(2):47. https://doi.org/10.3390/fractalfract5020047.

The composition of C-S-H is generally described from the CaO/SiO₂ ratio noted Ca/Si and the calcium hydroxide concentration at equilibrium (3)3. Grutzeck M, Benesi A, Fanning B. 1989. Silicon-29 magic angle spinning nuclear magnetic resonance study of calcium silicate hydrates. J. Am. Ceram. Soc. 72(4):665-668. https://doi.org/10.1111/j.1151-2916.1989.tb06192.x. Most of the work carried out on this hydrate suggests the existence of several C-S-H of different stoichiometry, structure or morphology (33. Grutzeck M, Benesi A, Fanning B. 1989. Silicon-29 magic angle spinning nuclear magnetic resonance study of calcium silicate hydrates. J. Am. Ceram. Soc. 72(4):665-668. https://doi.org/10.1111/j.1151-2916.1989.tb06192.x–5)5. Taylor HFW. 1986. Proposed structure for calcium silicate hydrate gel. J. Am. Ceram. Soc. 69(6):464-467. https://doi.org/10.1111/j.1151-2916.1986.tb07446.x. All of these studies agree to demonstrate that the variation of the stoichiometry composition of C-S-H in terms of Ca/Si ratio varies with the concentration of CaO in solution in which it is in equilibrium. Thus, the higher the concentration of CaO, the higher the Ca/Si ratio of C-S-H (6)6. Taylor HFW. 1950. Hydrated calcium silicates. Part I. Compound formation at ordinary temperatures. J. Chem. Soc. 0:3682. https://doi.org/10.1039/jr9500003682. In hydrated calcium silicates, the Ca/Si ratio generally ranges from 0.7 to 2.0, with a mean value of 1.75 for hydrated Portland cement (7)7. Richardson IG. 1999. Nature of C-S-H in hardened cements. Cem. Concr. Res. 29(8):1131-1147. https://doi.org/10.1016/s0008-8846(99)00168-4. H.F.W. Taylor (5)5. Taylor HFW. 1986. Proposed structure for calcium silicate hydrate gel. J. Am. Ceram. Soc. 69(6):464-467. https://doi.org/10.1111/j.1151-2916.1986.tb07446.x identified two types of C-S-H: C-S-H (I), which forms for Ca/Si ratios less than 1.5 and whose structure is close to that of Tobermorite, and C-S-H (II), observed for Ca/Si ratios greater than 1.5, presenting a structure similar to that of Jennite, another natural lamellar mineral. A. Nonat et al. (88. Nonat A. 1994. Interactions between chemical evolution (hydration) and physical evolution (setting) in the case of tricalcium silicate. Mater. Struct. 27(4):187-195. https://doi.org/10.1007/BF02473032,99. Nonat A, Lecoq X. 1998. The structure, stoichiometry and properties of C-S-H prepared by C3S hydration under controlled condition. In: Nuclear Magnetic Resonance Spectroscopy of Cement-Based Materials. p. 197-207. https://doi.org/10.1007/978-3-642-80432-8_14), therefore, suggested a categorization of three types of C-S-H systems: C-S-H (I) for Ca/Si ratios < 1, C-S-H (II) for 1 < Ca/Si < 1.5 and C-S-H (III) for Ca/Si > 1.5. Another study (10)10. Lachowski E, Diamond S. 1983. Investigation of the composition and morphology of individual particles of Portland cement paste: 1. C-S-H gel and calcium hydroxide particles. Cem. Concr. Res. 13(2): 177-185. https://doi.org/10.1016/0008-8846(83)90100-X reported that the Ca/Si ratio of C-S-H in hydrated Portland cement can reach higher values and can reach 3, although the majority of values are between 1.3 and 1.8.

Both calcium and silicon exhibit significant antifungal activity, although based on different mechanisms. Calcium hydroxide, released from materials such as CEM cement, dissociates into Ca²⁺ and OH⁻ ions, leading to an increase in the pH of the medium, which inhibits fungal growth, this effect is enhanced by the diffusion of active components present in the material (11)11. Kangarlou A, Sofiabadi S, Yadegari Z, Asgary S. 2009. Antifungal effect of calcium enriched mixture cement against Candida albicans. Iran Endod. J. 4(3):101-105. https://pubmed.ncbi.nlm.nih.gov/24003330/. Moreover, calcium particularly in the form of nanoparticles, has demonstrated direct antifungal efficacy when used as a deacidification treatment (12)12. Sequeira SO, Laia CAT, Phillips AJL, Cabrita EJ, Macedo MF. 2017. Clotrimazole and calcium hydroxide nanoparticles: A low toxicity antifungal alternative for paper conservation. J. Cult. Herit. 24:45-52. https://doi.org/10.1016/j.culher.2016.12.004. As for silicon, generally used in the form of sodium silicate, it exerts concentration-dependent fungal inhibition, as observed on the genera Penicillium, Fusarium, Alternaria and Trichothecium; this activity is thought to be linked to an increase in pH and physiological effects on fungal spores (1313. Nabil M, Elnouby M, Al-Askar AA, Kowalczewski PŁ, Abdelkhalek A, Behiry SI. 2024. Porous silicon nanostructures: Synthesis, characterization, and their antifungal activity. Open Chem. 22(1). https://doi.org/10.1515/chem-2023-0169, 14)14. Rémus-Borel W, Menzies JG, Bélanger RR. 2005. Silicon induces antifungal compounds in powdery mildew-infected wheat. Physiol. Mol. Plant Pathol. 66(3):108-115. https://doi.org/10.1016/j.pmpp.2005.05.006. Furthermore, silicon can also induce an antifungal response by stimulating the production of defense compounds (15)15. Moreira LFN, Peña-Bengoa F, Niklander SE, da Silveira Bueno CE, de Martin AS, Rocha DGP. 2024. Comparative in vitro analysis of the antifungal activity of different calcium silicate-based endodontic sealers. Braz. J. Oral Sci. 23:e243355. https://doi.org/10.20396/bjos.v23i00.8673355. Furthermore, the recent studies have shown that the addition of nanomaterials such as ZnO and TiO₂ promotes the formation of C–S–H gel, while strengthening the adhesion between aggregates and the cement matrix (16)16. Al-saffar FY, Wong LS, Paul SC. 2023. An elucidative review of the nanomaterial effect on the durability and calcium-silicate-hydrate (C-S-H) gel development of concrete. Gels 9(8):613. https://doi.org/10.3390/gels9080613. Furthermore, the Ca/Si ratio plays an essential role not only in the nucleation and quantity of C–S–H formed, but also in the internal structuring of this gel and its mechanical properties (17)17. Kunther W, Ferreiro S, Skibsted J. 2017. Influence of the Ca/Si ratio on the compressive strength of cementitious calcium–silicate–hydrate binders. J. Mater. Chem. A Mater. 5(33):17401-17412. https://doi.org/10.1039/C7TA06104H.

Microbial attacks, particularly from bacteria and fungi, degrade concrete through biofilm formation, leading to chemical damage, cracking, and reduced mechanical strength (18)18. Mohsen A, Ramadan M, Gharieb M, Yahya A, Soltan AM, Hazem MM. 2022. Rheological behaviour, mechanical performance, and anti-fungal activity of OPC-granite waste composite modified with zinc oxide dust. J. Clean Prod. 341:130877. https://doi.org/10.1016/j.jclepro.2022.130877. Fungi, such as Penicillium chrysogenum and Aspergillus versicolor, are primary contributors to the bio-deterioration of both organic and inorganic materials. They produce organic acids, such as oxalic acid, which react with concrete to form insoluble calcium complexes, causing material degradation. These fungi are commonly found in water-damaged buildings, promoting concrete discoloration and increased porosity (10)10. Lachowski E, Diamond S. 1983. Investigation of the composition and morphology of individual particles of Portland cement paste: 1. C-S-H gel and calcium hydroxide particles. Cem. Concr. Res. 13(2): 177-185. https://doi.org/10.1016/0008-8846(83)90100-X. Microorganisms in corroded concrete often include species such as Thiobacillus and Acidithiobacillus (19)19. Ślosarczyk A, Klapiszewska I, Skowrońska D, Janczarek M, Jesionowski T, Klapiszewski Ł. 2023. A comprehensive review of building materials modified with metal and metal oxide nanoparticles against microbial multiplication and growth. Chem. Eng. J. 466:143276. https://doi.org/10.1016/j.cej.2023.143276. Antimicrobial materials, including metals like Fe, Zn, Mn, Mo, Ni, and Ti, inhibit microbial growth by interacting with microbial cells in the acidic environments created by microorganisms. Zinc oxide (ZnO) is widely used in construction materials for its antimicrobial properties, comparable to commercial biocides (18)18. Mohsen A, Ramadan M, Gharieb M, Yahya A, Soltan AM, Hazem MM. 2022. Rheological behaviour, mechanical performance, and anti-fungal activity of OPC-granite waste composite modified with zinc oxide dust. J. Clean Prod. 341:130877. https://doi.org/10.1016/j.jclepro.2022.130877. Studies have shown that nanoparticles of metals and metal oxides, such as silver, copper, titanium oxide, zinc oxide, and copper oxide, are effective in preventing microbial growth. These nanoparticles enhance the longevity of building materials and enable bioactive coatings for existing structures, including historical buildings. Their antimicrobial efficiency depends on their properties (size, shape, surface area, concentration) and the substrate’s characteristics (porosity, absorbability, pH), as well as environmental factors like humidity, temperature, and material degradation (19)19. Ślosarczyk A, Klapiszewska I, Skowrońska D, Janczarek M, Jesionowski T, Klapiszewski Ł. 2023. A comprehensive review of building materials modified with metal and metal oxide nanoparticles against microbial multiplication and growth. Chem. Eng. J. 466:143276. https://doi.org/10.1016/j.cej.2023.143276. Biofilm formation on concrete leads to discoloration and tarnish, followed by chemical deterioration due to acidic metabolites excreted by bacteria, which lowers the pH, increases porosity, and reduces mechanical properties (19)19. Ślosarczyk A, Klapiszewska I, Skowrońska D, Janczarek M, Jesionowski T, Klapiszewski Ł. 2023. A comprehensive review of building materials modified with metal and metal oxide nanoparticles against microbial multiplication and growth. Chem. Eng. J. 466:143276. https://doi.org/10.1016/j.cej.2023.143276. Recent research indicates that ZnO nanoparticles are particularly effective, acting as semiconductors that degrade pollutants and inhibit microbial activity through the release of Zn²⁺ ions and reactive oxygen species (ROS) generation (20)20. Mohsen A, Abdel-Gawwad HA, Ramadan M. 2020. Performance, radiation shielding, and anti-fungal activity of alkali-activated slag individually modified with zinc oxide and zinc ferrite nanoparticles. Constr. Build. Mater. 257:119584. https://doi.org/10.1016/j.conbuildmat.2020.119584. ZnO is utilized in construction for its photocatalytic properties and ability to inhibit fungal growth, even in low-light conditions, by disrupting microbial membranes and enzymatic functions. Incorporating ZnO into cement has been shown to significantly reduce fungal growth, enhancing the material's durability (2121. Aldosari MA, Darwish SS, Adam MA, Elmarzugi NA, Ahmed SM. 2019. Using ZnO nanoparticles in fungal inhibition and self-protection of exposed marble columns in historic sites. Archaeol. Anthropol. Sci. 11:3407-3422. https://doi.org/10.1007/s12520-018-0762-z. TiO₂, widely used in orthopedic and dental implants, also demonstrates antimicrobial properties, primarily activated by UV light. It prevents microbial adhesion by producing ROS, which disrupt microbial cells . TiO₂-based paints applied to steel and concrete surfaces have effectively inhibited the growth of fungi such as Aspergillus niger and Trichoderma viride . Research indicates that antimicrobial agents in concrete affect its technical properties based on their chemical reactivity and the concrete's constituents . ZnO and TiO₂ enhance the concrete's strength and durability while providing antifungal properties, making them essential in sustainable construction practices . ZnO has been shown to inhibit fungal growth more efficiently than TiO₂, especially under high-nutrient conditions . The literature demonstrates the effectiveness of metal and metal oxide nanoparticles, such as ZnO and TiO₂, in inhibiting microbial growth, with their efficacy dependent on their physicochemical properties and the substrate material's characteristics. Environmental factors influencing microbial activity also play a crucial role in determining the durability and protection of construction materials .

The aim of this work is to evaluate the influence of ZnO and TiO₂ nanoparticles incorporation on the microstructure and composition of cement hydrates (C-S-H), in relation to their self-cleaning and antifungal properties in order to describe the types of C-S-H formed in the hydrates and to optimize the material formulation for sustainable and hygienic construction applications. A particular focus is placed on the correlation between the Ca/Si ratio and antifungal performance, a relationship that remains underexplored in the literature. Moreover, a new alternative method for the indirect determination of the Ca/Si ratio in C-S-H gel is proposed, combining data from X-ray diffraction (XRD), X-ray fluorescence (XRF), and thermogravimetric analysis (TG), offering a more accurate and complementary estimation approach.

2. MATERIALS AND METHODS ↑

2.1. Materials ↑

The chemical and mineralogical composition of the commercial cement CEM I 42.5 R, which was used for the preparation of cement pastes with ZnO and TiO2 nanoparticles during a hydration period of 28 days, is presented in Table 1. The high percentages of CaO oxides and C3S phase, compared to the other components, indicate that this cement is particularly rich in calcium.

Table 1. Chemical and mineral composition of CEM I 42.5 R (% by weight).

Chemical composition [%]

Mineral composition [%]

SiO₂

Al2O3

Fe₂O3

CaO

MgO

SO3

K₂O

TiO₂

P₂O5

C3S

C₂S

C3A

C4AF

18.7

4.5

3.4

65.9

1.3

4.3

0.8

0.3

0.1

66.0

13.8

9.1

7.6

In this work, the used nanomaterials were zinc oxide (ZnO) and titanium dioxide (TiO₂). ZnO was produced by the Czech company Radka and was synthesized by the vaporization of metallic zinc followed by oxidation in air. It has a broader crystallite size of about 60 nm and significantly lower BET surface area of 10-15 m²/g. The company Precheza from Czech Republic provided TiO2 which is made of 99% pure anatase and containing some sulphates (0.7% by weight) implying the use of sulphate process in its production. It has a small crystallite size of 12 nm and high BET surface area of approximately 100 m²/g. Scanning Electron Microscopy (SEM) analysis (Figure 1) revealed that ZnO nanoparticles have a variety of morphologies including nanotubes 200-400 nm in length with hexagonal cross sections (diameter 20-40 nm) and hexagonal nanoprisms with lateral dimensions of 150-450 nm (Figure 1(A)). On the other hand, TiO₂ nanoparticles form agglomerates with uniform spherical shapes and particle sizes between 20-30 nm (Figure 1(B)).


Figure 1. SEM images and EDS Spectra of (A) (67.4k x magnification) ZnO and (B) TiO₂ (178k x magnification).

Analysis of TiO₂ by energy-dispersive spectroscopy (EDS) showed the presence of mainly Ti and O. The notable carbon signal displayed stemmed from contamination of the sample holder used during the analysis.

2.2. Methods ↑

Table 2. Composition of cement paste formulations.

C

CT1

CT2

CT3

CZ0.3

CZ0.6

CZ1

CT1Z0.6

CT2Z0.3

Cement (C) (%)

100

99

98

97

99.66

99.33

99

98.33

97.66

TiO₂ (T) (%)

0

1

2

3

0

0

0

1

2

ZnO (Z) (%)

0

0

0

0

0.34

0.67

1

0.67

0.34

2.3. Anti-fungal activity evaluation ↑

In the context of evaluating antifungal activity, cement samples were carefully immersed in distilled water for 24 hours. After this period, the pH of the water provided an accurate reading of the solution's acidity. The resulting aqueous leachate was then adjusted to a pH range between 6.5 and 7.5, an optimal range to promote fungal growth. This leachate was used to prepare 10% Czapek-Dox Agar, which was evenly distributed into Petri dishes. Once the medium was prepared, it was inoculated with three fungal species known for their pathogenic potential: Penicillium brevicompactum, Trichoderma reesei, and Aspergillus niger. A control was also set up by inoculating a Czapek-Dox medium prepared with distilled water and enriched with nutrients at respective concentrations of 100 and 10%. This control was inoculated with the same fungi to compare the results with the concrete samples. Finally, to ensure stable temperature conditions conducive to fungal growth, all Petri dishes were placed in a biological incubator set to 26°C.

After introducing the liquid medium into the flask, the aforementioned constant concentration of spores became colloidal. A sample disc incorporating antifungal agents was placed in the center of the flask, previously sprayed with the spores using the same procedure. The flask was then sealed and incubated to prevent contamination by other fungi. The detailed and sequential measurement procedure is illustrated in the corresponding figure. To estimate the antifungal inhibition zone, the criteria presented in Figure 2 and Equation [1] consist of calculating the length obtained by subtracting the radius of the sample disc from the distance between the center of the sample and the outer edge of the inhibition zone. This allows quantification of the antifungal effect of the cement mortar containing the active agents. The precise size of the inhibition zone is calculated according to Equation [1]:

I = (I₁ + I₂) / 2 [1]

Where:

With:

Figure 2. Measurement of antifungal zone.

3. RESULTS AND DISCUSSION ↑

3.1. Ca/Si ratios calculated from XRD data ↑

Table 3 presents the phase quantification results by XRD and the corresponding Ca/Si ratios. This part examines the influence of ZnO and TiO₂ nanoparticle additions on the Ca/Si ratio of the C-S-H phases formed after 28 days of hydration, with the aim of establishing a link with the mechanical performances studied in our previous work on concretes of identical formulations (3434. Amor F, Baudys M, Racova Z, Scheinherrová L, Ingrisova L, Hajek P. 2022. Contribution of TiO2 and ZnO nanoparticles to the hydration of Portland cement and photocatalytic properties of high performance concrete. Case Stud. Constr. Mater. 16:e00965. https://doi.org/10.1016/j.cscm.2022.e00965, 35)35. Amor F, Ingrišová L, Rácová Z, Baudys M, Hájek P. 2022. Effect of TiO2 and ZnO powder mixtures on mechanical and photocatalytic performance of high performance concrete. Acta Polytech. CTU Proc. 33:15-19. https://doi.org/10.14311/APP.2022.33.0015. The Ca/Si ratio is an important indicator of the structure and properties of C-S-H and the main contributor to the strength of concrete (36)36. Wang J, Hu Z, Chen Y, et al. 2022. Effect of Ca/Si and Al/Si on micromechanical properties of C(-A)-S-H. Cem. Concr. Res. 157:106811. https://doi.org/10.1016/j.cemconres.2022.106811. The Ca/Si ratio of the reference paste C is 2.67 representing the basic composition of C-S-H in the absence of additions.

Table 3. Phase quantification and Ca/Si ratios (XRD).

C

CT1

CT2

CT3

CZ0.3

CZ0.6

CZ1

CT2Z0.3

CT1Z0.6

Unreacted C₃S (%)

15.33

19.28

15.40

36.80

45.67

51.4

54.4

18.60

23.01

Unreacted C₂S (%)

11.10

13.36

12.90

12.27

13.21

7.67

10.27

9.31

9.54

Portlandite (%)

9.82

6.85

8.24

10.29

2.02

0.53

0.65

3.93

2.33

Ca/Si

2.67

2.77

2.74

2.44

2.83

2.67

2.7

2.80

2.83

The samples containing ZnO showed an increase in the amounts of unreacted C₃S and C₂S and a decrease in portlandite content. As is well established, zinc retards cement hydration by forming, at the early stages, a layer of crystalline calcium zincate (Zn₂Ca(OH)6 . H₂O) or amorphous zinc hydroxide (Zn(OH)2) surrounding the anhydrous grains, which directly hinders the formation of C-S-H (37,37. Arliguie G, Grandet J. 1990. Influence de la composition d’un ciment Portland sur son hydration en présence de zinc. Cem. Concr. Res. 20(4):517-524. https://doi.org/10.1016/0008-8846(90)90096-G 38)38. Yousuf M, Mollah A, Hess TR, Tsai YN, Cocke DL. 1993. An FTIR and XPS investigations of the effects of carbonation on the solidification/stabilization of cement based systems-Portland type V with zinc. Cem. Concr. Res. 23(4):773-784. https://doi.org/10.1016/0008-8846(93)90031-4. The influence on the Ca/Si ratio is nuanced; a slight increase is observed at a low dosage (CZ0.3: 2.83), while at higher dosages (CZ0.6: 2.67 and CZ1: 2.70), the values are similar to, or even slightly higher than, that of the reference. TiO2 also influenced the Ca/Si ratio with a slight increase observed at low dosages (CT1: 2.77 and CT2: 2.74), followed by a more pronounced decrease at 3% (CT3: 2.44). The Ca/Si ratios of the samples CT2Z0.3 (2.80) and CT1Z0.6 (2.83) are between the values observed for the individual additions.

Mechanical strength tests on the corresponding concretes with the same formulation (35)35. Amor F, Ingrišová L, Rácová Z, Baudys M, Hájek P. 2022. Effect of TiO2 and ZnO powder mixtures on mechanical and photocatalytic performance of high performance concrete. Acta Polytech. CTU Proc. 33:15-19. https://doi.org/10.14311/APP.2022.33.0015 revealed contrasting effects of the additions on performance. The addition of ZnO nanoparticles reduced mechanical strength, which can be explained by a slowdown in the hydration of silicates and a lower quantity of C-S-H formed, even though the Ca/Si ratios did not change significantly. In other words, it was primarily the quantity of C-S-H, rather than its composition, that influenced the strength. As for TiO2, an increase in strength was observed at 1%, followed by a decrease at 2% and 3%, suggesting a complex effect on the microstructure. The initial increase might compensate for the slight rise in the Ca/Si ratio, whereas the subsequent decrease could be attributed to other factors, such as the formation of secondary phases (39)39. Chen J, Kou SC, Poon CS. 2012. Hydration and properties of nano-TiO2 blended cement composites. Cem. Concr. Compos. 34(5):642-649. https://doi.org/10.1016/J.CEMCONCOMP.2012.02.009, where the reduction in the Ca/Si ratio at 3% might be a contributing factor. Finally, the combined additions (CT2Z0.3 and CT1Z0.6) showed improved strength compared to individual additions of ZnO and, in the case of CT1Z0.6, compared to CT1, suggesting a synergistic effect on the microstructure (40)40. Du Y, Korjakins A. 2023. Synergic effects of nano additives on mechanical performance and microstructure of lightweight cement mortar. Appl. Sci. 13(8):5130. https://doi.org/10.3390/app13085130, although variations in the Ca/Si ratio remained moderate. A. U. Adebanjo et al. (41)41. Adebanjo AU, Abbas YM, Shafiq N, Khan MI, Farhan SA, Masmoudi R. 2024. Optimizing nano-TiO2 and ZnO integration in silica-based high-performance concrete: Mechanical, durability, and photocatalysis insights for sustainable self-cleaning systems. Constr. Build. Mater. 446:138038. https://doi.org/10.1016/J.CONBUILDMAT.2024.138038 reported that the addition of TiO2 and ZnO nanoparticles to the concrete mixture had a notable influence on the composition and the Ca/Si ratio of the hydration products. This result corroborates the findings of this study.

The obtained values of the Ca/Si ratios of C-S-H and even those after correction for portlandite are generally higher than the commonly accepted range of 1.5 to 2 (42)42. Lothenbach B, Scrivener K, Hooton RD. 2011. Supplementary cementitious materials. Cem. Concr. Res. 41(12):1244-1256. https://doi.org/10.1016/J.CEMCONRES.2010.12.001. This observation can be attributed to several factors. First, the cement used (CEM I 42.5 R) is intrinsically rich in CaO. This basic composition directly influences the stoichiometry of the hydrated phases, in particular that of C-S-H (43)43. Nonat A. 2004. The structure and stoichiometry of C-S-H. Cem. Concr. Res. 34(9):1521-1528. https://doi.org/10.1016/j.cemconres.2004.04.035. The high proportion of C3S (66%) in the clinker may also contribute to this calcium richness. Second, the calculation model used is based on simplifications, even if it is useful to compare estimates between samples. The actual stoichiometry of C-S-H is variable and may deviate from the simplified formula C3S2H8. Furthermore, the calculation does not take into account other potentially present hydrated phases (e.g., hydrated aluminates), which could also influence the CaO balance (31)31. Hoshino S, Yamada K, Hirao H. 2006. XRD/Rietveld analysis of the hydration and strength development of slag and limestone blended cement. J. Adv. Concr. Technol. 4(3):357-367. https://doi.org/10.3151/jact.4.357. Our results are consistent with those of E. Lachowski et al. (10)10. Lachowski E, Diamond S. 1983. Investigation of the composition and morphology of individual particles of Portland cement paste: 1. C-S-H gel and calcium hydroxide particles. Cem. Concr. Res. 13(2): 177-185. https://doi.org/10.1016/0008-8846(83)90100-X, who reported that the Ca/Si ratios observed in C-S-H can reach high values, ranging from 0.9 to just over 3.

3.2. Thermal analysis and Ca/Si ratios refined using TG data ↑

The DTG curves of the hydrated cement pastes after 28 days are shown in Figure 3. These curves allow to identify the main stages of thermal decomposition of the hydrated phases by showing the mass loss rate as a function of temperature. Typically, three main peaks are observed in the DTG curves of hydrated cement pastes: peak between 100 and 200 °C corresponding to the dehydration of C-S-H and ettringite, as well as the evaporation of physically adsorbed water; peak between 400 and
550 °C corresponding to the dehydroxylation of portlandite (Ca(OH)₂); and peak between 600 and
900 °C corresponding to the decarbonation of calcium carbonate (CaCO3) formed by carbonation (44)44. Alarcon-Ruiz L, Platret G, Massieu E, Ehrlacher A. 2005. The use of thermal analysis in assessing the effect of temperature on a cement paste. Cem. Concr. Res. 35(3):609-613. https://doi.org/10.1016/J.CEMCONRES.2004.06.015. The intensity of the peaks between 400 and 550 °C is proportional to the amount of portlandite in the sample. This agrees well with the values in Table 4, where the phase quantifications of portlandite were indicated for both TG and XRD analyses. For example, cement samples CZ0.6, CZ1 and CT1Z0.6 with the lowest amounts of portlandite also show the most reduced peaks in this temperature range on the DTV curves. Conversely, samples C, CT2 and CT3 with the highest amounts of portlandite show the most intense peaks on the DTV curves. The peaks associated with the dehydration of C-S-H and ettringite in samples CZ0.3, CZ0.6 and CZ1 are less intense, indicating a lower amount of hydrated C-S-H phases. This phenomenon is consistent with the results of P. Siler et al. (45)45. Šiler P, Kolářová I, Novotný R, et al. 2018. Application of isothermal and isoperibolic calorimetry to assess the effect of zinc on cement hydration. J. Therm. Anal. Calorim. 133(1):27-40. https://doi.org/10.1007/S10973-017-6815-1, which showed that zinc nanoparticles induce a hydration delay. Cement pastes containing TiO₂ and the reference cement C showed significantly higher intensity peaks, which agrees with the values in Tables 3 and 4, indicating a greater consumption of silicate phases and a significant formation of portlandite in these samples. These observations suggest that the presence of TiO₂ promotes the hydration of silicates. This is consistent with several studies that have shown that titanium oxide can have a beneficial effect on cement reactivity and, consequently, on mechanical strength (3434. Amor F, Baudys M, Racova Z, Scheinherrová L, Ingrisova L, Hajek P. 2022. Contribution of TiO2 and ZnO nanoparticles to the hydration of Portland cement and photocatalytic properties of high performance concrete. Case Stud. Constr. Mater. 16:e00965. https://doi.org/10.1016/j.cscm.2022.e00965,3535. Amor F, Ingrišová L, Rácová Z, Baudys M, Hájek P. 2022. Effect of TiO2 and ZnO powder mixtures on mechanical and photocatalytic performance of high performance concrete. Acta Polytech. CTU Proc. 33:15-19. https://doi.org/10.14311/APP.2022.33.0015,4646. Janczarek M, Klapiszewski Ł, Jędrzejczak P, Klapiszewska I, Ślosarczyk A, Jesionowski T. 2021. Progress of functionalized TiO2-based nanomaterials in the construction industry: A comprehensive review. Chem. Eng. J. 430(3):132062. https://doi.org/10.1016/J.CEJ.2021.132062–5151. Amor F, Diouri A, Ellouzi I, Ouanji F. 2018. Development of Zn-Al-Ti mixed oxides-modified cement phases for surface photocatalytic performance. Case Stud. Constr. Mater. 9:e00209. https://doi.org/10.1016/j.cscm.2018.e00209). Between 600 and
900 °C, zone associated with the decarbonation of CaCO3, the intensity of the peaks for the zinc samples increases, indicating the formation of a greater amount of CaCO3. This may be related to a greater carbonation.

Figure 4 presents the quantified contents of the main hydration products of Portland cement, identified by thermogravimetric analysis (TGA/DTG), expressed on an ignited mass basis after 28 days of hydration. This representation enables a direct comparison of portlandite, C–S–H, and CaCO₃ contents among the different samples. The figure is complemented by a quantitative analysis derived from the corresponding weight losses, providing clearer insights into the hydration process. The results reveal that portlandite content decreases significantly in Zn-doped samples, while TiO₂ additions lead to higher C–S–H formation. These observations are in good agreement with the XRD results shown in Table 3, confirming that Zn strongly inhibits hydration, whereas TiO₂ promotes it.


Figure 3. DTG curves of cement pastes after 28 days.

Figure 4. Quantified amounts (%) of main hydration products in cement pastes after 28 days of curing.

Table 4. Phase quantification and Ca/Si ratios (XRD, TG).

C

CT1

CT2

CT3

CZ0.3

CZ0.6

CZ1

CT2Z0.3

CT1Z0.6

Unreacted C₃S (%)

15.33

19.28

15.40

36.80

45.67

51.40

54.40

18.60

23.01

Unreacted C₂S (%)

11.10

13.36

12.90

12.27

13.21

7.67

10.27

9.31

9.54

Portlandite XRD (%)

9.82

6.85

8.24

10.29

2.02

0.53

0.65

3.93

2.33

Portlandite TG (%)

10.48

9.62

10.44

10.48

2.62

0.94

0.37

5.90

0.51

Ca/Si XRD

2.67

2.77

2.74

2.44

2.83

2.67

2.70

2.80

2.83

Ca/Si TG

2.65

2.68

2.67

2.43

2.78

2.64

2.73

2.74

2.89

Table 4 presents a comparison of the Ca/Si ratios of C-S-H calculated from the XRD data, with those recalculated using the portlandite values derived from the TG analysis. The quantified portlandite content corresponds to the average value obtained from both the step-wise and tangent methods. The aim is to evaluate the impact of using more accurate experimental data of the portlandite phase on the estimation of the Ca/Si ratio. Overall, the Ca/Si ratios calculated from XRD data and those corrected using TG data are very similar, indicating good consistency between the two methods of portlandite quantification. As observed by F. Georget et al. (52)52. Georget F, Bénier C, Wilson W, Scrivener KL. 2022. Chloride sorption by C-S-H quantified by SEM-EDX image analysis. Cem. Concr. Res. 152:106656. https://doi.org/10.1016/J.CEMCONRES.2021.106656, our results also show relative agreement between portlandite measurements obtained by TG and XRD. The differences, although minor, demonstrate the impact of the accuracy of the portlandite calculation on the Ca/Si ratio. The interpretation of the data previously observed in Table 3 regarding the influence of the additions on the Ca/Si ratio remains largely consistent, making it an additional validity. The use of TG data for portlandite correction provides a minor but significant improvement in the estimation of the Ca/Si ratio. Both methods yield consistent results; however, the use of TG data, being more direct, is preferable for greater accuracy.

3.3. Ca/Si ratios from X-Ray fluorescence (XRF) analysis ↑

Figure 5 showed the chemical composition of cement pastes obtained by XRF analysis after 28 days of hydration. The results of this analysis provided a detailed overview of the elemental oxide composition of the cement pastes. A predominance of CaO and SiO₂ was found with variations attributed to the different additions. The incorporation of TiO₂ led to a slight reduction in the CaO content and an increase in SiO₂ oxides, while the addition of ZnO nanoparticles led to a significant increase in the CaO and ZnO contents. When TiO₂ and ZnO nanoparticles were combined, their effects were found to be intermediate. Since XRF analysis provides overall information, these variations reflect the global compositional changes without specifically indicating the stoichiometry of the C-S-H phases.

Table 5 presents the CaO and SiO₂ oxide composition and the corresponding Ca/Si ratios of the C-S-H phases in the cement pastes after 28 days of hydration, as determined by XRF analysis. The addition of ZnO resulted in a significant increase in the Ca/Si ratio compared to the reference cement C whose ratio is 3.51. The higher the ZnO proportion (from 0.3 to 1%), the higher the Ca/Si ratio (3.79, 4.12 and 4.15 respectively). The addition of TiO₂ showed a more complex influence. A slight increase in the Ca/Si ratio was observed for CT1 (3.55) compared to the reference sample C, then a decrease for CT2 (3.32) and a further increase for CT3 (3.44). Samples with combined additions of TiO₂ and ZnO showed Ca/Si ratios intermediate between those observed for the individual additions. CT1Z0.6 (3.8) lies between CT1 (3.55) and CZ0.6 (4.12), while CT2Z0.3 (3.61) lies between CT2 (3.32) and CZ0.3 (3.79). This probably indicates an interaction between the effects of TiO₂ and ZnO on the composition of C-S-H (53)53. Mostafa FEZM, Smarzewski P, El Hafez GMA, et al. 2023. Analyzing the effects of nano-titanium dioxide and nano-zinc oxide nanoparticles on the mechanical and durability properties of self-cleaning concrete. Materials 16(21):6909. https://doi.org/10.3390/MA16216909. As shown by A.U. Adebanjo et al. (41)41. Adebanjo AU, Abbas YM, Shafiq N, Khan MI, Farhan SA, Masmoudi R. 2024. Optimizing nano-TiO2 and ZnO integration in silica-based high-performance concrete: Mechanical, durability, and photocatalysis insights for sustainable self-cleaning systems. Constr. Build. Mater. 446:138038. https://doi.org/10.1016/J.CONBUILDMAT.2024.138038, nanoparticle addition in High Performance Concrete significantly affects morphology and elemental composition, leading to reduced C-S-H and lower Ca/Si ratios, indicating structural and compositional changes. The combined addition appears to attenuate the increase in Ca/Si ratio induced by ZnO alone. The interaction between TiO₂ and ZnO in the combined additions suggests that these two oxides influence hydration in an interdependent manner, modifying the composition of the hydrates formed (54)54. Senff L, Tobaldi DM, Lemes-Rachadel P, Labrincha JA, Hotza D. 2014. The influence of TiO2 and ZnO powder mixtures on photocatalytic activity and rheological behavior of cement pastes. Constr. Build. Mater. 65:191-200. https://doi.org/10.1016/j.conbuildmat.2014.04.121.

Figure 5. XRF analysis of cement paste oxide composition.

Table 5. Quantification of phases and Ca/Si ratios (XRF).

C

CT1

CT2

CT3

CZ0.3

CZ0.6

CZ1

CT1Z0.6

CT2Z0.3

CaO

52.86

52.86

52.74

49.08

57.4

62.27

65.61

61.92

59.74

SiO₂

15.07

14.9

15.89

14.35

15.09

15.12

15.8

16.3

16.57

Ca/Si

3.51

3.55

3.32

3.44

3.79

4.12

4.15

3.8

3.61

3.4. Evolution of Ca/Si ratios obtained by different techniques (XRD, TG, XRF) ↑

Figure 6 presented the comparative graph of the Ca/Si ratios by the three analytical techniques XRD, TG and XRF. The values obtained from the XRF analysis indicate significant deviations from the values obtained by the other two techniques. These deviations highlight the limitations of the direct use of XRF data for the precise calculation of the Ca/Si ratio in C-S-H. XRF gives a global elemental analysis of the sample, providing the proportions of the different oxides present. However, there is no consideration of how these oxides are distributed between the different hydrated phases, in particular portlandite, and C-S-H which have a variable stoichiometry (55)55. Duque-Redondo E, Bonnaud PA, Manzano H. 2022. A comprehensive review of C-S-H empirical and computational models, their applications, and practical aspects. Cem. Concr. Res. 156:106784. https://doi.org/10.1016/J.CEMCONRES.2022.106784. Thus, the direct calculation of the Ca/Si ratio based on XRF data without any correction significantly overestimates the amount of CaO contained in the C-S-H phase, leading to higher values, as observed in the graph. On the other hand, the combined XRD and TG approach allowed a more accurate estimation. XRD data provide indirect information on the amounts of reacted C3S and C2S, allowing to calculate the amounts of CaO and SiO₂ consumed during the formation of C-S-H. In addition, TG data allowed to quantify the portlandite formed, which is crucial to correct the CaO balance and obtain a Ca/Si ratio more characteristic of the C-S-H formula. Thus, the values obtained by this combined approach are considerably lower and closer to the values typically reported in the literature for hydrated C-S-H (77. Richardson IG. 1999. Nature of C-S-H in hardened cements. Cem. Concr. Res. 29(8):1131-1147. https://doi.org/10.1016/s0008-8846(99)00168-4, 3636. Wang J, Hu Z, Chen Y, et al. 2022. Effect of Ca/Si and Al/Si on micromechanical properties of C(-A)-S-H. Cem. Concr. Res. 157:106811. https://doi.org/10.1016/j.cemconres.2022.106811, 4343. Nonat A. 2004. The structure and stoichiometry of C-S-H. Cem. Concr. Res. 34(9):1521-1528. https://doi.org/10.1016/j.cemconres.2004.04.035, 5656. Kirkpatrick RJ, Yarger JL, McMillan PF, Ping Y, Cong X. 1997. Raman spectroscopy of C-S-H, tobermorite, and jennite. Adv. Cem. Based Mater. 5(3-4):93-99. https://doi.org/10.1016/S1065-7355(97)00001-1, 5757. Hong SY, Glasser FP. 1999. Alkali binding in cement pastes: Part I. The C-S-H phase. Cem. Concr. Res. 29(12):1893-1903. https://doi.org/10.1016/S0008-8846(99)00187-8).

To conclude, the Ca/Si ratios found in this work by the three techniques are greater than 2 in all samples. They are in the high range of values reported in the literature for hydrated C-S-H of Portland cement, which can reach 3 (10)10. Lachowski E, Diamond S. 1983. Investigation of the composition and morphology of individual particles of Portland cement paste: 1. C-S-H gel and calcium hydroxide particles. Cem. Concr. Res. 13(2): 177-185. https://doi.org/10.1016/0008-8846(83)90100-X. These values suggest the formation of C-S-H type II according to the classification of H.F.W. Taylor (5)5. Taylor HFW. 1986. Proposed structure for calcium silicate hydrate gel. J. Am. Ceram. Soc. 69(6):464-467. https://doi.org/10.1111/j.1151-2916.1986.tb07446.x, whose structure is similar to that of Jennite, or type III according to Nonat et al. (88. Nonat A. 1994. Interactions between chemical evolution (hydration) and physical evolution (setting) in the case of tricalcium silicate. Mater. Struct. 27(4):187-195. https://doi.org/10.1007/BF02473032, 99. Nonat A, Lecoq X. 1998. The structure, stoichiometry and properties of C-S-H prepared by C3S hydration under controlled condition. In: Nuclear Magnetic Resonance Spectroscopy of Cement-Based Materials. p. 197-207. https://doi.org/10.1007/978-3-642-80432-8_14), characterized by a Ca/Si ratio greater than 1.5. Our results therefore indicate a predominance of C-S-H with a less ordered structure, typical of high Ca/Si ratios.

Figure 6. Ca/Si ratios determined by XRD, TG and XRF.

3.5. Antifungal activity of cement pastes ↑

Figure 7 showed the digital photos of fungal cultures containing the samples. The growth grades based on visual observations of three fungal strains in each case. The test results indicated that the addition of TiO₂ and ZnO in concrete formulations significantly influences the growth of fungi Penicillium brevicompactum, Trichoderma reesei, and Aspergillus niger (Table 6 and Figure 8). Samples containing only cement (C) showed moderate fungal growth, suggesting that cement alone has a limited inhibitory effect. The addition of TiO2 (CT1 to CT3) leads to a progressive decrease in fungal growth, with notable inhibition at higher concentrations (CT3 with 3% TiO₂), which can be attributed to the photocatalytic and antimicrobial properties of TiO2 (58)58. Podporska-Carroll J, Panaitescu E, Quilty B, Wang L, Menon L, Pillai SC. 2015. Antimicrobial properties of highly efficient photocatalytic TiO2 nanotubes. Appl. Catal. B: Environmental. 176-177:70-75. https://doi.org/10.1016/J.APCATB.2015.03.029. This aligns with previous findings where P25 TiO₂, when integrated into cementitious matrices, demonstrated significant antifungal activity against Aspergillus species under UV exposure (59)59. Hegyi A, Grebenişan E, Lăzărescu AV, Stoian V, Szilagyi H. 2021. Influence of TiO2 nanoparticles on the resistance of cementitious composite materials to the action of fungal species. Materials 14(16):4442. https://doi.org/10.3390/MA14164442. Although the TiO₂ material used in our study differs from P25 in terms of phase composition and surface characteristics, the comparable level of inhibition supports the conclusion that the photocatalytic properties of TiO₂ play a major role in controlling fungal proliferation in cement-based systems.

Similarly, samples with ZnO (CZ0.3 to CZ1) exhibit increasing fungal growth reduction as the ZnO percentage increases, reflecting the well-known antifungal properties of this oxide (21)21. Aldosari MA, Darwish SS, Adam MA, Elmarzugi NA, Ahmed SM. 2019. Using ZnO nanoparticles in fungal inhibition and self-protection of exposed marble columns in historic sites. Archaeol. Anthropol. Sci. 11:3407-3422. https://doi.org/10.1007/s12520-018-0762-z. Samples combining TiO₂ and ZnO (CT1Z0.6 and CT2Z0.33) display even more pronounced inhibition, suggesting a synergistic effect between these two additives. The pH of the leachates, generally alkaline and ranging from 10.88 to 11.50, might also play a role in this inhibition by creating a less favourable environment for fungal growth. Overall, these results highlight the enhanced efficacy of formulations containing combinations of TiO₂ and ZnO in limiting fungal growth, offering promising prospects for applications requiring increased biological resistance in concrete materials. Generally, the incorporation of ZnO and TiO₂ in cement system was found to have a significant effect on fungal growth inhibition at all applied strains. The results of the anti-fungal activity test reveal the promising potential of ZnO oxide and TiO2 oxide in controlling fungal growth, particularly on construction materials such as concrete, where fungi can cause significant damage (19)19. Ślosarczyk A, Klapiszewska I, Skowrońska D, Janczarek M, Jesionowski T, Klapiszewski Ł. 2023. A comprehensive review of building materials modified with metal and metal oxide nanoparticles against microbial multiplication and growth. Chem. Eng. J. 466:143276. https://doi.org/10.1016/j.cej.2023.143276. Fungi, being ubiquitous in the environment, require specific conditions such as water availability, pH, and nutrient sources for colonization (60)60. Chaudhuri A, Bhattacharyya S, Chaudhuri P, Sudarshan M, Mukherjee S. 2020. In vitro deterioration study of concrete and marble by Aspergillus tamarii. J. Build. Eng. 32:101774. https://doi.org/10.1016/J.JOBE.2020.101774. ZnO oxide has demonstrated effective antifungal activity, notably against molds like Aspergillus niger and Penicillium brevicompactum (61)61. Reinprecht L, Iždinský J, Vidholdová Z. 2018. Biological resistance and application properties of particleboards containing nano-zinc oxide. Adv. Mater. Sci. Eng. 2018:2680121. https://doi.org/10.1155/2018/2680121. Furthermore, research has shown that incorporating ZnO into cement enhances its antibacterial and antifungal properties (62)62. Singh VP, Sandeep K, Kushwaha HS, Powar S, Vaish R. 2018. Photocatalytic, hydrophobic and antimicrobial characteristics of ZnO nano needle embedded cement composites. Constr. Build. Mater. 158:285-294. https://doi.org/10.1016/J.CONBUILDMAT.2017.10.035. ZnO's antibacterial effectiveness is attributed to its polarized surfaces, caused by zinc (Zn2⁺) or oxygen (O2−) ions, which generate free radicals and reactive oxygen species (ROS), inducing oxidative stress in microbial cells (62)62. Singh VP, Sandeep K, Kushwaha HS, Powar S, Vaish R. 2018. Photocatalytic, hydrophobic and antimicrobial characteristics of ZnO nano needle embedded cement composites. Constr. Build. Mater. 158:285-294. https://doi.org/10.1016/J.CONBUILDMAT.2017.10.035. These free radicals further contribute to its antimicrobial properties (63)63. Lin PY, Huang YH, Chen JS, et al. 2024. Cost-effective microbial induced ZnO synthesis for building material: Antibacterial, photocatalytic and mechanical characteristics. Environ. Technol. Innov. 36:103762. https://doi.org/10.1016/J.ETI.2024.103762. Similarly, A study has demonstrated that Ca(OH)2-ZnO and Ca(OH)2-TiO2 materials exhibit antifungal activity (64)64. Gómez-Ortíz N, De La Rosa-García S, González-Gómez W, et al. 2013. Antifungal coatings based on Ca(OH)2 mixed with ZnO/TiO2 nanomaterials for protection of limestone monuments. ACS Appl. Mater. Interfaces 5(5):1556-1565. https://doi.org/10.1021/am302783h. Another study demonstrated that the incorporation of ZnO in cement composites exhibited antifungal activity, showing almost no growth at a 15% ZnO concentration (62)62. Singh VP, Sandeep K, Kushwaha HS, Powar S, Vaish R. 2018. Photocatalytic, hydrophobic and antimicrobial characteristics of ZnO nano needle embedded cement composites. Constr. Build. Mater. 158:285-294. https://doi.org/10.1016/J.CONBUILDMAT.2017.10.035. On the other hand, TiO₂ oxide has been shown to reduce fungal colonies through its photocatalytic properties, with the incorporation of up to 5% by weight leading to enhanced resistance against microbial growth and confirming its self-cleaning potential in construction materials (65)65. Tuntachon S, Kamwilaisak K, Somdee T, et al. 2019. Resistance to algae and fungi formation of high calcium fly ash geopolymer paste containing TiO2. J. Build. Eng. 25:100817. https://doi.org/10.1016/J.JOBE.2019.100817. Both oxides act similarly, offering a dual approach to preventing the discoloration of biofilms caused by fungi and algae on building façades (66)66. Rosa RH, Silva RS, Nascimento LL, Okura MH, Patrocinio AOT, Rossignolo JA. 2023. Photocatalytic and antimicrobial activity of TiO2 films deposited on fiber-cement surfaces. Catalysts 13(5):861. https://doi.org/10.3390/CATAL13050861. In addition, shifts in pH, such as those caused by fungal infections, can inhibit fungal growth by creating stress on their cells, limiting nutrient acquisition and reducing the availability of essential elements like iron and copper, further supporting the antifungal effects of these oxides (67)67. Fernandes TR, Segorbe D, Prusky D, Di Pietro A. 2017. How alkalinization drives fungal pathogenicity. PLoS Pathog. 13(11):e1006621. https://doi.org/10.1371/JOURNAL.PPAT.1006621. Compared to the results observed previously, this study found that incorporating low percentages of the combination of TiO₂ and ZnO into the samples CT1Z0.6 and CT2Z0.3 resulted in significant antifungal activity. The incorporation of TiO₂ and ZnO at these concentrations demonstrated a notable ability to inhibit fungal growth, demonstrating their potential as effective additives in cement. These findings suggest that even small amounts of these oxides can effectively enhance the antifungal properties of the samples (Table 6). The Influence of the Ca/Si Ratio on the percentage of inhibition, presented in Figure 8, shows that the inhibition zone and the percentage of inhibition generally increase when the Ca/Si ratio is adjusted to values around 2.5–2.9, and that some sample combinations (CT1Z0.6 and CT2Z0.3) provide high antifungal efficacy. This effect can be partly explained by the influence of zinc and titanium ions, which promote C–S–H gel nucleation and growth, thereby enhancing the structure and active surface of the material. The addition of ZnO and TiO₂ can act as heterogeneous nucleation sites, accelerating the formation of C–S–H (16)16. Al-saffar FY, Wong LS, Paul SC. 2023. An elucidative review of the nanomaterial effect on the durability and calcium-silicate-hydrate (C-S-H) gel development of concrete. Gels 9(8):613. https://doi.org/10.3390/gels9080613 and strengthening its interaction with antifungal agents (1111. Kangarlou A, Sofiabadi S, Yadegari Z, Asgary S. 2009. Antifungal effect of calcium enriched mixture cement against Candida albicans. Iran Endod. J. 4(3):101-105. https://pubmed.ncbi.nlm.nih.gov/24003330/, 1515. Moreira LFN, Peña-Bengoa F, Niklander SE, da Silveira Bueno CE, de Martin AS, Rocha DGP. 2024. Comparative in vitro analysis of the antifungal activity of different calcium silicate-based endodontic sealers. Braz. J. Oral Sci. 23:e243355. https://doi.org/10.20396/bjos.v23i00.8673355). These results indicate that optimizing the Ca/Si ratio can significantly improve the antifungal properties of the samples.

Figure 7. Digital photos of different types of fungal cultures affecting Portland cement (C), with and without ZnO and TiO₂.

Table 6. Fungal growth inhibition parameters and corresponding Ca/Si Ratios and pH values for different samples.

Sample

Diameter (mm)

Inhibition zone (mm)

Inhibition (%)

Ca/Si ratio

pH

100% Nutrients (control)

54

0

0.00

–

-

C

49

5

9.26

2.65

10.88

CT1

34

20

37.04

2.68

11.20

CT2

23

31

57.41

2.67

11.21

CT3

22

32

59.26

2.43

11.50

CZ0.3

30

24

44.44

2.78

11.10

CZ0.6

27

27

50.00

2.64

11.14

CZ1

24

30

55.56

2.73

11.45

CT1Z0.6

20

34

62.96

2.74

11.21

CT2Z0.3

21

33

61.11

2.89

11.34

Figure 8. Influence of the Ca/Si Ratio on the percentage of inhibition.

4. CONCLUSIONS ↑

This study shows that TiO₂ and ZnO nanoparticles can tailor the hydration behavior, microstructure, and antifungal activity of cementitious systems. Based on the results:

These findings support optimizing nanoparticle dosage and combinations to develop multifunctional, durable, and hygienic cement-based materials.

Supplementary information ↑

Funding sources

The authors of this article declare that they have no financial, professional or personal conflicts of interest that could have inappropriately influenced this work.

Supplementary material

Not applicable.

Data availability

Not applicable.

Acknowledgements

The authors express their gratitude to ‘’Mobility Faculty of Civil Engineering’’, Projects “Mobility Czech Technical University in Prague’’ Program for the financial support given in order to support this original research.

Authorship contribution statement

Fouad Amor: Conceptualization, Methodology, Research, Formal analysis, Validation, Write-up – original draft.

Hind Agourrame: Write-up – review & editing.

Zuzana Racova: Resources, Visualization.

Nacer Khachani: Write-up – review & editing.

Petr Hajek: Supervision, Fund raising.

Competing interests

The authors declare that they have no known financial conflicts of interest or personal relationships that could have influenced the work reported in this article.

Statement on the use of Artificial Intelligence

Not applicable.

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