Swelling, shrinkage and creep: a mechanical approach to cement hydration

Abstract

Recent advances in physical understanding of creep and shrinkage of cement paste suggest a novel approach to setting and hardening processes. In high-strength concrete, due to a low water-cement ratio, self-desiccation occurs immediately after setting, and capillary pressure produces compaction of the assembly of hydrating cement grains. For higher watercement ratio, water possibly can withstand cavitation, but then the volumetric balance of hydration requires that water move through the solid skeleton. According to Darcy's law, water only can be displaced by a gradient of hydraulic pressure, as long as the water pressure remains lower than its cavitation threshold. This water pressure only can be equilibrated by a compaction of the solid matrix, with compressive contacts particularly between the C-S-H layers. In both cases, with or without liquid-gas menisci, hydration acts like a distributed pumping of water, the liquid phase is under tension, and the solid skeleton is compressed. The high affinity of C-S-H for water and the viscoplastic behavior of the cement gel can explain the evolution of the contact between two hydrating cement grains and the formation of a continuous and cohesive bridge. Swelling and shrinkage then can be analyzed as two co-existing mechanisms, whose balance is controlled by the permeability of the solid matrix. RF~SUMF~ Les progrks accomplis r~cemment clans la comprehension des m~canismes de retrait et de fluage des matdriaux h base de ciment apportent un nouvel

A Coupled Nanoindentation/SEM‐EDS Study on Low Water/Cement Ratio Portland Cement Paste: Evidence for C–S–H/Ca(OH)2 Nanocomposites

“…2 This fine porous structure, akin to that of a colloidal gel, creates a high interfacial surface area between solid and liquid phases, which subsequently gives rise to the characteristic poro-viscoelastic response of concrete to mechanical loading and drying, [3][4][5] as well as to the generation of crystallization pressure from the growth of ice or salts in small pores. [6][7][8] These mechanisms are critical in determining the long-term performance of concrete structures.…”

Long Term Deformation of Beams and Columns of High Performance Concrete

“…The hydration process begins by the reaction of C3S, C2S, and C3A. Every chemical reaction accompanies changes of volume, temperature, and bonding forces (Acker, 2004). Alite (pure C3S) constitutes about 50-80% of Portland cement, and its hydration makes a major contribution towards the evolution of properties (Kumar et al, 2012).…”

Drying, Shrinkage, and Cracking of Cementitious Materials

“…If w/c ≥ 0.6, then there is plenty of water to allow hydration without creation of significant capillary suction. In that case, the paste will expand slightly (Acker 2004) owing to crystallization pressure (Scherer 1999), probably driven primarily by growth of calcium hydroxide (Baroghel-Bouny et al 2006). In high-performance concretes made with a low amount of water, autogenous shrinkage can cause significant damage, so water-saturated aggregate or polymers may be incorporated to reduce the capillary suction by gradually releasing additional moisture (Bentz and Weiss 2011).…”