Research on the influence mechanism of adding nanocrystalline cellulose on the compressive strength and drying shrinkage performance of hardened cement paste under different pressure environments

The compressive strength and dry shrinkage performance of cement based composite material under 0.63 atm low-pressure (LP) environment and standard atmospheric pressure (SP) environment are compared. The nanocrystalline cellulose (NCC) dosage is 0 wt%, 0.3 wt% and 0.6 wt%, and the relative curing humidity is 34%RH. The results showed that the mechanism of NCC enhancing hardened cement paste is the same under the two pressure environments, but the effect is significantly different. Under the LP environment, adding 0.3 wt% NCC increases the 28d compressive strength from 31.8 MPa to 41.4 MPa and reduced the 28d drying shrinkage by 605μm/m relative to the LP control without NCC (L-0N). Notably, the compressive strength of hardened paste under LP environment at this dosage is similar to that of hardened paste with 0 wt% NCC under SP environment. In addition, compared with the SP environment, the effect of NCC on enhancing the compressive strength and resisting dry shrinkage is more significant under LP environment. The improvement is associated with the modification of calcium-related chemical environments and microstructural characteristics of hardened cement paste by NCC addition. Meanwhile, NCC increase the van der Waals force between globules of C–S–H gel, enhanced the stiffness of the observed-scale silicate chains, significantly enhancing the micro Young's modulus, mechanical properties and deformation resistance of the hardened paste.