The deformation of CSH gels and its link with dynamic length change of cement pastes upon drying and resaturation

Drying shrinkage of cement pastes (CPs) facilitating superficial cracking deserves primary concern when evaluating durability performance. To clarify shrinkage mechanism, the changes of mass, length and pore-scale water allocation of two mature CPs were monitored non-destructively through low-field NMR relaxometry. Experimental results indicated that, heat treatment under hot water slightly coarsens the pore structure of CPs through modifying

packing, and reduces shrinkage remarkably through stiffening

clusters. Upon drying at 43% RH, the interlayer pores are still saturated and compacted with reduced volume. At 80% RH, although the interlayer and gel pores are both saturated, they lose water gradually at reducing rates. Drying shrinkages of CPs are caused by compaction of interlayer and gel pores, whose contributions to shrinkage are at the ratio of 1:3 roughly. Most of

compaction is compensated by the coarsening of pore structure, and only 2–6 percent shows up as observable shrinkage.