Issue 36

P. Jinchang et alii, Frattura ed Integrità Strutturale, 36 (2016) 130-138; DOI: 10.3221/IGF-ESIS.36.13 136 Nanoindentation Test Results and Analysis XRD quantitative analysis results suggested that, UHPCC hardened cement paste contained hydrated gel phase, Ca(OH) 2 phase, CaCO 3 phase and unhydrated cement particles. C-S-H gel phase of ordinary concrete is mainly composed of high and low density hydrated calcium silicate gel (LD C-S-H and HD C-S-H) whose elasticity modulus are 14 ~ 24 GPa and 24 ~ 35 GPa. Results of previous researches [13, 14] demonstrated that, UHPCC contains a large amount of higher- density C-S-H gel (UHD C-S-H) which has stronger mechanical performance and an elastic modulus of 35 ~ 50 GPa that is close to Ca(OH) 2 phase. We made nanoindentation test on single-doped and double-doped test specimens which were processed by standard maintenance for 90 days. As Ca(OH) 2 phase accounted for a small proportion in the material, it was ignored during analysis. Distribution of mechanical performance parameters of single-doped and double-doped test specimens maintained for 90 days is shown in Fig. 6. We can find that, test specimens contain a large amount of unhydrated cement particles and UHD C-S-H phase; HD C-S-H phase is surrounded by hydration product UHD C-S-H; LD C-S-H phase has disappeared; a distinct interfacial transition zone could not be seen. (1) NSC0 (2) NSC3 Figure 6 : Distribution of elasticity modulus on the surface of single-doped and double-doped test specimen. After making a statistical analysis on the data, distribution of probability of elasticity modulus of measured points on test specimen was obtained (Fig. 7). It can be seen from the figure that, peak value of elasticity modulus of the test specimens was between 30 and 70 GPa; a large amount of UHD-C-S-H phase and a small amount of unhydrated cement particle phase existed in the test specimens; as to hydration products of double-doped test specimens, UHD C-S-H phase accounted for a larger proportion, HD C-S-H phase was in a small amount and LD C-S-H was not found. Thus we conclude that, hydration products of UHPCC are significantly different with ordinary concrete; UHD C-S-H phase is the major hydration product; and the above difference is more obvious in double-doped material. Because of generation of a large amount of high-strength and high-elasticity hydration products, interface of composite material is fully strengthened and structure tends to be tighter. (1) NSC0 (2) NSC3 Figure 7 : Distribution of probability of elasticity modulus of single-doped and double-doped test specimen