# Effect of Electrospun Nanofiber Additive on Selected Mechanical Properties of Hardened Cement Paste
## 1 Introduction  
Electrospinning has been viewed as a strong technique in nanomaterials science due to its simplicity and flexibility [1, 2]. The basic principle of this technique is the electrostatic interaction between two electrodes [3]. Electrospun nanofibers have many promising properties, such as their high strength, rough surface, high specific surface area, good functional abilities, and so forth. Therefore, the feasibility of the industrial use of electrospun nanofibers has been clarified through numerous works. According to a literature review, various types of composite fiber membranes show a good ability for use in wastewater treatment, with applications in oil/water mixture separation [4, 5], oil filtration [6], and heavy metal ion adsorption [7]. In the biomedical industry, nanofibers also have impressive applications as treatments of skin carcinoma [8], tissue regeneration [9], and wound healing [10]. In addition, the tremendous application of electrospun nanofibers has been recognized in other industries such as the textile industry [11, 12, 13], the battery industry [14, 15, 16], and so forth. However, it seems that fewer works have focused on the application of electrospun nanofibers to increase the mechanical properties of construction materials, especially of cementitious materials. From the literature review, it is worth mentioning that the application of nanosized short fibers to enhance the mechanical properties of cement has been conducted and has gained a considerable amount of attention in the research community. For instance, [PERSON] and [PERSON] [17] reported an increase inthe mechanical characteristics of Portland cement paste that included silicon carbide nanow whiskers (SiC NWS): 25% in compressive strength and 75% in flexural strength when using a silicon carbide nanowhisher proportion of 0.25-1.5 wt %. They observed the bridging phenomenon of SiC NWS across the pores and cracks inside the cement paste, showing good linkage between them. [PERSON] and [PERSON] [18] showed an increase in compressive strength of cement when using 0.2 wt % of carbon nanofibers (CNFs) in the paste. They found the crack bridging effect of CNFs in the microscale structure, as well as an increase in the high-density calcium-silicate-hydrate (CSH) gel. [PERSON] et al. [19] pointed out an enhancement of up to 19% in compressive strength and up to 25% flexural strength when introducing carbon nanotubes into cementitious materials. They found that CSH layers wrap tightly around the fibers in the microstructure of the paste, indicating good bonding between cement hydration products and the nanosized fibers. [PERSON] et al. [20] reported an increase of 45% in tensile strength and 46% in flexural strength when adding 0.1% of carbon nanotubes (CNTs) into the pastes. From the micrographs, they found that CNT filaments were embedded and well-adhered to cement paste. However, increasing the mechanical strength of cement by blending with electrospun nanofibers has not been widely studied. Therefore, this present work aimed to evaluate the feasibility of using electrospun nanofibers to enhance the mechanical properties of Portland cement paste, as well as the enhancing mechanism of electrospun nanofibers in the cement matrix. Four types of electrospun nanofibers were utilized for combination with Portland cement powder in this study: nylon 66 nanofibers (N66 NFs), tetraethyl orthosilicate/polyvinylpyrrolidone nanofibers (TEOS/PVP NFs), hybrid nanofibers containing carbon nanotubes and nylon 66 (CNTs-N66 NFs), and hybrid nanofibers containing carbon nanotubes and TEOS/PVP (CNTs-TEOS/PVP NFs). The combination process was conducted by means of an improved collector, details of which were published in previous works [21; 22; 23]. The observations from the compressive strength test and the tensile strength test showed the effectiveness of the electrospun nanofibers on the mechanical properties of the hardened cement pastes.