How Water-Aggregate Interactions Affect Concrete Creep: Multiscale Analysis

Abstract

Customary micromechanics models for the poroelasticity, creep, and strength of concrete restrict the domain affected by the hydration reaction to the cement paste volume, considering the latter as a thermodynamically closed system with respect to the (chemically inert) aggregate. Accordingly, the famous Powers hydration model appears to be a natural choice for the determination of clinker, cement, water, and aggregate volume fractions entering such micromechanical models. The situation changes once internal curing occurs, i.e., once part of the water present is absorbed initially by the aggregate, and then is sucked back to the cement paste during the hydration reaction. This paper develops an extended hydration model for this case, introducing water uptake capacity of the aggregate and paste void-filling extent as additional quantities. Based on constant values for just these two new quantities, and on previously determined creep properties of cement pastes as functions of an effective water:cement mass ratio (i.e., that associated with the cement paste domain rather than with the entire concrete volume), a series of ultrashort-term creep tests on different mortars and concretes can be very satisfactorily predicted by a standard microviscoelastic mathematical model. This further extends the applicability range of micromechanics modeling in cement and concrete research.

Multiscale Thermoelastic Analysis of the Thermal Expansion Coefficient and of Microscopic Thermal Stresses of Mature Concrete

“…Mitigation of this problem is the topic of ongoing research [43,44]. Future pertinent multiscale models shall be based on results obtained from innovative early-age testing of the coefficient of thermal expansion [45,46,47], shrinkage [48,49] and creep [50,51,52] of cementitious materials and on corresponding multiscale early-age models for the thermal expansion [53], shrinkage [54] and creep [55,56,57] of cementitious materials. A 16% variation of the thermal expansion coefficient of concrete is expected to result in an increase of the early-age cracking risk by 15%, see Reference [58].…”

Micro-cantilever testing on the short-term creep behaviour of cement paste at micro-scale

“…On the contrary, the parameter α, which corresponds to the creep compliance at unit time, is found to be largely affected by the compositions of cement paste, degree of hydration and moisture content [6,[17][18][19]. It is also demonstrated by the multiscale studies of cementitious materials that the constituents and microstructures significantly influence the macroscopic viscoelastic behaviour [3,28,31,66,67]. At nanometre scale, Vandamme [2,20] stated that the creep behaviour of the hydrated phases is largely determined by the packing density of C-S-H particles.…”

Viscoelastic Behavior of Polymer-Modified Cement Pastes: Insight from Downscaling Short-Term Macroscopic Creep Tests by Means of Multiscale Modeling

“…Notably, the resulting capillary pressure increased virtually linearly with the hydration degree ξ, in the regime ξ > 30%; see [22]. As for mortars and concretes, the self-desiccation-induced capillary underpressure was shown to result in water migration from the open porosity of the aggregates into the cement paste matrix [22]. A similar mechanism is envisaged to reduce the water content of the polymers.…”

“…Lura et al [62] showed that the internal relative humidity in a cement paste sample with w/c = 0.37 decreased, within the first few days after mixing, from 98% to 92%. Notably, the resulting capillary pressure increased virtually linearly with the hydration degree ξ, in the regime ξ > 30%; see [22]. As for mortars and concretes, the self-desiccation-induced capillary underpressure was shown to result in water migration from the open porosity of the aggregates into the cement paste matrix [22].…”