Research on irrecoverable creep of the hardened cement paste under different relative humidity

Relative humidity (RH) has an important influence on the creep performance of cement-based materials. In this paper, the creep and creep recovery experiments of hardened cement paste (HCP) were carried on under four humidity balance. The low-field 1H nuclear magnetic resonance (NMR) test was performed on the HCP after the creep recovery test to obtain the internal water distribution characteristics of HCP. The creep properties and volume ratio of different micro phases in HCP were acquired by nanoindentation test, backscattered electron (BSE) test, and thermogravimetric (TG) test. Subsequently, the structure features of C-S-H were acquired by the 29Si NMR test and the nitrogen adsorption-desorption test. The results showed that the raise of RH significantly increased the interlayer water content in HCP. The creep properties of C-S-H reduced significantly with the increase of RH. The volume fraction of low-density (LD) C-S-H elevated with raising RH, while the trend of high-density (HD) C-S-H was opposite to the former. When RH increased, the mean chain length of the gel raised, and the gel pores became more numerous, among which the magnitude of change of LD C-S-H pores was more significant.