Issue 41

X. Wu et alii, Frattura ed Integrità Strutturale, 41 (2017) 388-395; DOI: 10.3221/IGF-ESIS.41.50 389 carbon atoms. Single-wall carbon nano-tubes which was expensive is generally applied in the fields of field emission panel display and sensors. Multiple-wall carbon nano-tubes which is low in cost and has achieved scale production and extensive application is usually applied in the study of reinforced composite materials. Base materials such as polymer base, metal base and ceramic base are frequently studied, while few studies concern cement-based composite materials [5-9]. In 2003, Campillo I. et al. [10] from Spain reported the reinforcement of cement-based composite materials using carbon nano-tubes for the earliest and found single-wall carbon nano-tubes and multiple-wall carbon nano-tubes could improve the compressive strength of cement paste for 6% and 30% respectively in 14 days and that effective control of the structure of multiple-wall carbon nano-tubes in cement base could significantly enhance its strength. In 2008, Kowald T. et al. [11] from Suegen in Germany investigated the effects of unprocessed and oxidized multiple-wall carbon nano-tubes on cement hydration products taking pure C 3 S as the simplified model system as well as the effects of multiple-wall carbon nano-tubes on the micro-mechanical properties of cement hydration products using nanoindentation technology. The unprocessed multiple-wall carbon nano-tubes increased the number of low-density C-S-H in composite materials and oxidized multiple- wall carbon nano-tubes increased the high-density C-S-H. They also pointed out that multiple-wall carbon nano-tubes could enhance the performance of ultra high performance concrete as the regulation phase of cement hydration product. Since 2008, studies on carbon nano-tubes cement-based composite materials has began around the world. Luo J.L. et al. [12] analyzed the correlation between the electrical resistivity of carbon nano-tubes cement-based composite materials and the mixing amount of carbon nano-tubes and further analyzed its voltage-sensitive property. Morsy M.S. et al. [13] found adding multi-walled carbon nano-tubes whose mass was 0.02% that of cement could enhance its compressive strength. For material researchers, it is urgent to study on the application of carbon nano-tubes in cement-based materials.The breakthrough of production and application of carbon nano-tubes are bound to motivate the development of nanotechnology and the emergence of related high-tech industries, which may induce a new scientific reformation and bring huge benefits to the whole society. In this study, carbon nano-tubes were evenly scattered in water solution by ultrasonic method using cetyl trimethyl ammonium bromide (CTAB), and then the solution was added into cement paste to investigate mechanical and endurance performance of the carbon nano-tubes cement-based composite materials. T EST PROFILE Raw materials for test arbon nano-tubes which was prepared by chemical vapor deposition and purchased from a nanometer material enterprise in Shandong, China was used; its physical parameters are shown in Tab. 1, and the structure diagram is shown in Fig. 1. P·O 42.5 ordinary Portland cement produced by Qingdao, Shandong, China was used, and its physical properties and mineral composition are shown in Tab. 2. CTAB, white chemical powder, was used. The water reducing agent used was polycarboxylate superplasticizer (solid content: 20%; water-reducing rate: 30%; Jiangsu Bote New Material Co., Ltd., China). Purity/% External diameter/nm Length/μ m Specific surface area/(m 2 /g) Ash content/% Electric conductivity/(s/cm) -COOH content/% >95 10-20 10-30 40-300 <1.5 100-1000 2.00 Table 1 : The basic physical parameters of carbon nano-tubes. Specific surface area/(m 2 /Kg) Setting time/min Stability Rupture strength/MPa Compressive strength/MPa Mineral composition/% Initia l set Final set 3d 28d 3d 28d C 3 S C 2 S C 3 A C 4 AF SO 3 330 191 247 Qualified 5.2 8.1 31.2 65.2 48.12 24.03 9.88 11.02 2.24 Table 2 : The physical properties and mineral composition of the cement. C