Influences of curing period on mechanical properties of reactive powder concrete incorporating nanoparticles

The influences of curing period on mechanical properties of nanoparticles modified reactive powder concrete (RPC) were investigated in this paper. Nano-SiO2 (NS), nano-ZrO2 (NZ) and nano-TiO2 (NT) with concentration of 1 wt% and 3 wt% were separately introduced into RPC, and then the flexural strength and compressive strength of RPC samples were measured after 28 d, 90 d and 360 d of curing. The experimental results show that the flexural strength and compressive strength of RPC doped with nanoparticles tend to increase as the curing period increases, and the increase of strength at late curing stage (from 90 d to 360 d) is generally greater than that at early curing stage (from 28 d to 90 d). The flexural/compressive strength of 3 wt% NZ/NS modified RPC cured for 360 d maximally increased by 51.41%/50.22% compared with that cured for 28 d. Furthermore, thermogravimetric analysis, x-ray diffraction analysis and scanning electron microscopy observation were used to investigate the mechanism of how curing period affects the mechanical properties. It maybe attributed to the fact that with the increasing curing period, cement continues to hydrate, the orientation and the size of calcium hydroxide (CH) decrease, and the incorporation of nanoparticles makes the microstructure of cement denser. Besides, the reaction between mineral admixtures and CH is slow at the early stage and relatively fast at the later stage, resulting in a great increase in the late strength.