**Jiayuan Kang, Salam Al-Sabah \* and Roger Théo**

School of Civil, Structural & Environmental Engineering, University College Dublin, D04 V1W8 Dublin 04, Ireland; jiayuan.kang@ucdconnect.ie (J.K.); theo.roger@ucdconnect.ie (R.T.)

Received: 8 January 2020; Accepted: 12 March 2020; Published: 13 March 2020

**Abstract:** This study aimed to investigate the effects of single-walled carbon nanotubes (SWCNTs) on strength the properties of cement composites when surfactant (SAA) was applied as the dispersion method. TritonX-100 (TX10) was used as the SAA to pretreat SWCNTs, which has been proved to perform well in dispersing the agglomerates of SWCNTs. In this study, four different concentration of SWCNTs, namely 0.00 wt%, 0.02 wt%, 0.04 wt%, and 0.06 wt% by the mass of cement, were used to prepare cement composite specimens. The compressive strength and flexural strength of specimens were tested and recorded. The results show that the compressive and flexural strengths of cement composites decreased with the increase in the concentration of SWCNTs without the addition of TX10. However, when SWCNT suspensions were pretreated with TX10, the strength variation pattern changed; the compressive and flexural strengths of cement composites increased as a function of the concentration of SWCNTs, although there were reductions compared to non-TX10-treated specimens at all concentrations of SWCNTs. Furthermore, the relationship between the strength of cement composites and bulk density of specimens was considered.

**Keywords:** single wall carbon nanotubes; surfactant; TritonX-100; mass of specimens; compressive strength; flexural Strength; bulk density
