Synergic influence of fly ash and graphene oxide-carbon nanotubes hybrid on mechanical, microstructural and porosity properties of cement mortars

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The current study investigates the better reinforcing tendency of superplasticizer stabilized carbon nanomaterials hybrid, i.e. FCNT@GO in comparison to the individual carbon nanomaterials, i.e. either graphene oxide (GO) or functionalized carbon nanotubes (FCNTs) on the fly ash blended cement mortars (FCMs). The compressive strength for 0.08% FCNT-FCMs and 0.08% GO-FCMs (by weight percent of cement-FA blend) was improved by 24.9% and 39.8%, in comparison to Control (FA) sample, respectively, at 90 days of curing. However, for FCNT@GO hybrid incorporated mortars, a superior improvement of 52.1% was found at the dosage of 0.16%. On the contrary, the maximum split tensile strength improvement was 64.3% for 0.08% FCNT@GO-FCMs whereas, 0.08% GO-FCMs and 0.16% FCNT-FCMs showed an enhancement of 48.9% and 39.7%, respectively. These results were also compared to the Control (cement) samples. The compressive and tensile strength values for 0.16% FCNT@GO-FCMs (39.7 MPa and 5.2 MPa) were shown to be comparable or even better than the values obtained for Control (cement) mortars (37.6 MPa and 4.1 MPa). The better production of hydration products leading to the densification of the cement-FA matrix in FCNT@GO-FCMs is attributed to the synergic effect of fly ash and carbon nanomaterials in the mortar sample as examined by FE-SEM and XRD studies. Mercury Intrusion Porosimetry (MIP) showed porosity decline by 34.7%, 51.4%, and 57.8% for FCNT-FCMs, GO-FCMs and FCNT@GO-FCMs in comparison to Control (FA), respectively.