Autopore 9500

The microstructure of the cement pastes was investigated using field emission scanning electron microscopy (SEM, JSM-7600F, Japan). SEM was carried out on the fractured surface of the cement paste after mechanical testing. Prior to the measurement, samples were soaked in anhydrous ethanol for 48 h and then dried at 60°C in a vacuum oven for 48 hrs. The specimens were mounted on aluminum stubs with conductive carbon tape and sputtered with gold under vacuum at 20 mA for 2 min.
The porosity of cement paste composites was examined as follows. The pore volume and pore size analysis were performed on a mercury intrusion porosimeter (Micromeritics AutoPore 9500, America). The specimens were intruded with mercury and the quantity and pressure required for the intrusion were used to calculate the sizes and amount of pores within the sample according to the Washburn equation:
$\mathrm{r}=-2\frac{rcos\theta }{p}$
where r is the pore radius (μm), γ is the surface tension of mercury (480 mN/m), θ is the contact angle between mercury and probe wall (140° as recommended by the manufacturer of the porosimeter), and P is the applied pressure (MPa) [54 ]. Three repeated measurements were conducted for each test.

Cubic samples with a side length of ≤8 mm were cut from the cured specimens and dried in the oven at 50 °C for one week. The pore structure was measured using mercury intrusion porosimetry (AutoPore 9500, Micromeritics, USA). To observe the fiber–mortar interface, the block samples were firstly cut from the mortar specimens, and also dried at 50 °C for one week. After that, the sample surface was sprayed with gold to increase the conductivity, then the micromorphology of the fiber–mortar interface was obtained using scanning electron microscope (Sigma500, ZEISS, Germany).

Mercury, which is not infiltrated into general solids, can enter the hole by applying external pressure. The larger the external pressure, the smaller the diameter of the hole into which mercury can enter. The volume of the pore is judged by measuring the amount of mercury entering the pore under different external forces. In this paper, mercury pressure experiments were performed on MIP samples in order to evaluate the pore structure of MKPC by the AutoPore 9500 (Micromeritics, Norcross, GA, USA).