Issue 36

P. Jinchang et alii, Frattura ed Integrità Strutturale, 36 (2016) 130-138; DOI: 10.3221/IGF-ESIS.36.13 137 C ONCLUSIONS ano materials with outstanding performance have been applied in many fields. Li H et al. [15] once researched the influence of nano-SiO 2 and nano-Fe 2 O 3 on mechanical performance and microstructure of cement mortar and found nano-SiO 2 and nano-Fe 2 O 3 could improve compressive strength of cement mortar for 20% over. Ltifi M et al. [16] found that, cement mortar tended to have poorer flowability and faster hydration after nano-SiO 2 was added. They thought compressive and bending strength of cement mortar strengthen if nano-SiO 2 was added. That is because nano-SiO 2 as an activator promotes hydration of cement and moreover nanoparticles dispersing in a high degree could improve microstructure of mortar. It is seldom applied in UHPC field and moreover few studies focus on influence of nanomaterials on performance of UHPC, though ordinary cementing material in combination with nanomaterials has been reported frequently. Based on the current research achievements of UHPC [17, 18], this paper discussed over the enhancement effect of nanomaterials on performance of UHPC in aspects of tightness and chemical reaction. We made systematic test and analysis on doped UHPCC and concluded that: 1) UHPCC with excellent performance can be prepared through adopting reasonable mix proportion of raw materials and adding nanomaterials; mechanical performance of material can be significantly improved if nano-SiO 2 and nano-CaCO 3 are added, and the optimal mixing proportion is 3% ~ 5%. 2) adding nano-SiO 2 can accelerate hydration progress of cement; as to double-doped UHPCC, hydration acceleration period of cement starts earlier and exothermic peak appears earlier; mutual action of nano-SiO 2 and nano-CaCO 3 further accelerates hydration progress. 3) hydration of cement can be promoted by nano-SiO 2 due to its high reaction activity; C-S-H gel generates when nano- CaCO 3 reacts with Ca(OH) 2 which is the hydration product of cement; benefitting from the supplement effect of nano- CaCO 3 added, UHPCC becomes tighter and microscopic defects dramatically reduces. 4) UHPCC added with both nano-SiO 2 and nano-CaCO 3 is found with significantly lowered porosity, a large amount of UHD C-S-H gel with higher performance, fully strengthened interface region, tighter microstructure and excellent mechanical performance. R EFERENCES [1] Wang, C., Yang, C.H., Liu, F., Wan C.J., Pu, X.C., Preparation of ultra-high performance concrete with common technology and materials, Cement and Concrete Composites, 34(4) (2012) 538-544. [2] Kang, S.T., Kim, J.K., The relation between fiber orientation and tensile behavior in an ultra high performance fiber reinforced cementitious composites (UHPFRCC), Cement and Concrete Research, 41(10) (2011) 1001-1014. [3] Rong, Z.D., Sun, W., Xiao, H.J., Wang, W., Effect of silica fume and fly ash on hydration and microstructure evolution of cement based composites at low water-binder ratios, Construction and Building Materials, 51 (2014) 446- 450. [4] Wang, J.X., Wang, L.J., Advances in the applied research of nano-material in concrete, Concrete, (11) (2004) 18-21. [5] Yao, W., Wu, K.R., Research situation and development trend of intelligent concrete, New Building Materials, (10) (2000) 22-25. [6] Ye, Q., Research and development for nano-composite cement structure material, New Building Materials, (11) (2001) 4-6. [7] Ye, Q., Zhang, Z.N., Kong, D.Y., Chen, R.S., Ma, C.C., Comparison of properties of high strength concrete with nano-SiO 2 and silica fume added, Journal of Building Materials, 6(4) (2003) 381-385. [8] Bigley, C., Greenwood, P., Using silica to control bleed and segregation in self-compacting concrete, Concrete, 37(2) (2003) 43-45. [9] Chen, R.S., Ye, Q., Research on the comparison of properties of hardened cement paste between nano-SiO 2 and silica fume added, Concrete, (1) (2002) 7-10. [10] Wang, D.Z., Meng, Y.F., Mechanical properties of concrete mixed with SiO 2 and CaCO 3 nanoparticles, Ningxia Engineering Technology, 10(4) (2011) 330-333. [11] Rong, Z.D., Yu, H.X., Lin, F.B., Microstructure mechanism analysis of cementitious composites at low water-cement ratio, Journal of Wuhan University Technology, 35(4) (2014) 6-10. N