These days, nanotechnology has already influenced many fields of science and technology, including civil engineering. Cementitious composites incorporating various nanomaterials have emerged as novel materials with improved microstructure, mechanical properties and durability. Over the past decades, graphene oxide has appeared as one of the most promising nanomaterials for civil engineering applications. However, the effect of graphene oxide addition on the properties of cementitious composites has not yet been fully investigated. The paper presents the studies on the mechanical properties of cement mortar reinforced with the 0.03 wt.% of graphene oxide (dosage by weight of cement). Graphene oxide proved to accelerate the cement hydration, in particular at the early stages of mortar hardening, hence improving the mortar performance during mechanical tests. The significant enhancement of the flexural, cubic and cylindrical compressive strength has been reported, thus showing the great nanotechnology potential for concrete structures.

Over the past decade, nanotechnology has attracted considerable attention in many areas of science and technology, including civil engineering and concrete structures. Since 1974, when the term “nanotechnology” was first created by Norio Taniguchi, the definition of “nanotechnology” has evolved over the years [

Due to the extraordinary mechanical properties of graphene and the high effectiveness of the graphene-matrix bonding, graphene has emerged as one of the most promising nanomaterials to be applied in concrete structures. Graphene, defined as a single, planar, 2-dimensional, honeycomb-shaped carbon layer, has been isolated from graphite intercalation compounds for the very first time in 2004 [

Graphene oxide (GO) – the best-known graphene derivative – has one major advantage, if compared to graphene, i.e. GO exhibits high dispersibility in water due to the oxygen functional groups attached on its sheets [_{3}H functional groups attached to the GO nanosheets being the nucleation sites and C_{3}S, C_{2}S, C_{3}A compounds existing in cement, as a result of which the additional growth points for cement hydrates are created and micropores can be significantly filled. Additionally, according to Wang et al. [^{2+} ions present in cement and -COOH groups from GO sheets. This reaction leads to more compact, denser, reinforced 3D structure composed of GO nanosheets and cement hydrates. Interestingly, Gholampour et al. [

The present paper introduces the study on the mechanical properties of the cement mortar reinforced with graphene oxide. The water-to-cement ratio of mortar is 0.5 with the graphene oxide loading of 0.03 wt.% (dosage by weight of cement). The effect of GO on the flexural, cubic and cylindrical compressive strength as well as Young’s modulus has been investigated and benchmarked with the performance of plain cement mortar. The preliminary results of this study have been presented in [

Cement, sand, distilled water and graphene oxide have been used to fabricate cement mortar. Portland cement CEM I 32.5R was employed in this study to manufacture both reference mortar (labelled as R) and mortar with the addition of 0.03 wt.% of GO (GO dosage by weight of cement, mortar labelled as GO0.03). The chemical and physical properties of cement are listed in Tab.

Chemical and physical properties of cement

Average values | |
---|---|

Loss on ignition [%] | 2.99 |

Insoluble residue [%] | 0.81 |

SO_{3} content [%] |
3.20 |

Cl^{-} content [%] |
0.063 |

Na_{2}O content [%] |
0.75 |

Start of setting time [min] | 217 |

Compressive strength after 2 days [MPa] | 26.5 |

Compressive strength after 28 days [MPa] | 51.4 |

Stability of volume [mm] | 0.80 |

Specific surface area [cm^{2}/g] |
3416 |

Results of the sand sieve analysis

Composition of fabricated cement mortars

Sample | Components | ||||
---|---|---|---|---|---|

Cement [g] | Water for GO dispersion [g] | Remaining water [g] | Sand [g] | Graphene oxide [g] | |

R | 3400 | 0 | 1700 | 10200 | 0 |

GO0.03 | 3400 | 222 | 1478 | 10200 | 1.02 |

To provide the uniform dispersion of graphene oxide within cement matrix, graphene oxide was first ultrasonicated with a certain amount of water for ca. 15 min using a compact ultrasonic homogenizer (UP50H Hielsher, 30 kHz, 50 W). The dispersion with the concentration of 4.6 mg/ml was thus obtained. Cement mortars were then fabricated according to PN-EN 196-1 [

At the age of 28 days rectangular samples 40×40×160 mm were subjected to bending to obtain the flexural strength of tested hardened mortars and then the remaining halves were compressed to obtain the cubic compressive strength. The loading rates for bending and compression were 0.05 kN/s and 2.4 kN/s, respectively. The compressive strength of cylindrical samples with the height of 80 mm was measured at the age of 7, 14 and 28 days to investigate the variability of the compressive strength in time. Five specimens were tested at each hardening age with a loading rate of 0.5 kN/s. In addition, the compressive strength tests were also performed on the cylindrical specimens with the height of 120 mm at the age of 28 days. To obtain the compression stress-strain curves and to calculate the values of Young’s modulus and Poisson’s ratio, two pairs of linear strain gauges were used for each sample to measure axial and transverse strain. The gauge factor of strain gauges was of 2.13.

The results of the flexural and cubic compressive strength tests conducted on rectangular samples are shown in Tab.

The variability of the cylindrical compressive strength of plain cement mortar and mortar reinforced with GO are presented in Fig.

Results of the flexural and cubic compressive strength tests at the age of 28 days [

Sample | Parameters | |||||
---|---|---|---|---|---|---|

Flexural strength | Compressive strength | |||||

Force [kN] | Strength [MPa] | Average strength [MPa] (increase) | Force [kN] | Strength [MPa] | Average strength [MPa] (increase) | |

1.78 | 4.17 | 64.55 | 40.34 | |||

60.94 | 38.08 | |||||

1.75 | 4.10 | 62.10 | 38.81 | |||

64.91 | 40.57 | |||||

1.59 | 3.73 | 65.71 | 41.06 | |||

64.84 | 40.52 | |||||

1.74 | 4.07 | 80.81 | 50.50 | |||

79.94 | 49.96 | |||||

2.23 | 5.22 | 69.80 | 43.65 | |||

79.92 | 49.94 | |||||

1.82 | 4.26 | 80.21 | 50.13 | |||

79.69 | 49.80 |

Interestingly, further comparison of reference mortar and mortar with GO has revealed that these two types of mortar differ also visibly in the forms of damage of compressed cylindrical samples. In particular, the unique influence of GO addition was highly visible in samples cured for 7 days. The complete damage of reference mortar occurred rapidly in these specimens, while cracking and loosing of cement-GO mortar occurred only on sides of the samples showing the typical cone shape of damage. After 14 and 28 days of mortar hardening, the cone shape of damage is clearly noticeable in both cement mortar samples (Fig.

Results of compression tests conducted on 60×80 mm cylindrical specimens. a) The variability of compressive strength in time [

The studies on the variability of cylindrical compressive strength in time were followed by tests in the uniaxial stress state using cylindrical samples with the height twice their width, that was 60×120 mm. In this case, the average compressive strength at the age of 28 days is improved by 28% (Tab.

Results of compression tests conducted on 60 x 120 mm cylindrical specimens.

a) Stress-strain curves and b) variability of Young’s modulus values under increasing load [

Results of the uniaxial cylindrical compressive strength and Young’s modulus tests at the age of 28 days [

Sample | Parameters | ||||
---|---|---|---|---|---|

Force [kN] | Strength [MPa] | Average strength [MPa] (increase) | Young’s modulus [GPa] | Average Young’s modulus value [GPa] (increase) | |

88.65 | 31.25 | 30.61 | |||

95.69 | 33.84 | 28.74 | |||

87.20 | 30.74 | 27.16 | |||

101.12 | 35.76 | 32.75 | |||

81.74 | 28.91 | 31.24 | |||

118.08 | 41.78 | 31.52 | |||

113.10 | 40.02 | 30.63 | |||

115.02 | 40.70 | 30.43 | |||

120.45 | 42.62 | 33.23 | |||

115.30 | 40.78 | 33.69 |

Cement mortar with the incorporation of 0.03 wt.% of graphene oxide has been fabricated to investigate the mechanical properties of produced nanocomposite. The addition of GO proved to enhance both the flexural and compressive strength of cement mortar. The increase up to 13%, 23% and 28% has been reported for the flexural, cubic compressive and uniaxial cylindrical compressive strength, respectively. The investigation of the variability of compressive strength in time has revealed that GO accelerates the cement hydration, in particular the early age hydration. Noteworthy, the significant improvement of mechanical properties has been achieved with simultaneous low material consumption. Such findings indicate the great potential of reinforcing cementitious composites with GO and represent a step forward towards practical applications of nanomaterials in civil engineering.

The author acknowledges financial support from the Silesian University of Technology with statutory founds of Department of Structural Engineering (grant agreement BKM-504/RB6/2017). Author would like to thank the researchers from Institut de Science et d’Ingénierie Supramoléculaires of University of Strasbourg (Strasbourg, France), Faculty of Chemistry and Centre for Advanced Technologies of Adam Mickiewicz University (Poznań, Poland) for providing graphene oxide, which has been used in this studies.