Properties of fresh and hardened concrete

https://ciks.cbt.nist.gov/bentz/Earlyagereview.pdf

A review of early-age properties of cement-based materials

Autogenous shrinkage of high performance concrete: A review

Alkali activation of fly ash. Part III: Effect of curing conditions on reaction and its graphical description

The coefficient of thermal dilation (CTD) of hardened cement paste and concrete is a function of the state of internal moisture in the pore system. It has been theorized that changes in the pore fluid pressure induced by temperature change causes additional dilation when the material is partially saturated. Drying shrinkage stresses in early-age concrete also evolve from changes in the pore fluid pressure. The Kelvin-Laplace equation relates changes in the pore fluid pressure to the measured internal relative humidity (RH). This research investigated the role of pore pressure changes on the CTD through internal RH measurements. A maximum change in humidity (ΔRH) due to temperature change (ΔT) was measured when the initial humidity was at an intermediate value. Likewise, the maximum CTD was also measured at an intermediate initial RH. Based on these findings, the additional thermal strain caused by changes in pore fluid pressure was modelled using internal RH measurements as a primary parameter.

Thermal dilation and internal relative humidity of hardened cement paste

A moisture gradient develops as concrete dries, inducing a drying shrinkage stress gradient that can lead to early-age cracking in restrained concrete. A new internal relative humidity measurement system was used to quantify the moisture gradient in early-age concrete exposed to drying. A simple model was developed to estimate the stress gradient associated with drying in both free and fully restrained concrete specimens. The model predicts that the stresses in the surface layer of restrained concrete exceed the tensile strength of the material prior to complete specimen failure. Comparison of the model and experimental results indicate that the fully restrained specimens with the most severe drying stress gradients failed at the earliest ages.

Internal relative humidity and drying stress gradients in concrete

Alkali silica reaction and its effect on concrete and mortar have been studied for many years. Several tests and procedures have been formulated to evaluate this reaction, particularly in terms of ...

Effect of alkali silica reaction on the mechanical properties of aging mortar bars: Experiments and numerical modeling:

Unreinforced portland-cement concrete exhibits a nonlinear relationship between applied stress and observed strain, even though the strains are at magnitudes that warrant the infinitesimal strain approximation (i.e., the norm of the displacement gradient is appropriately small). Previous efforts to model this nonlinear response of concrete express a dependence of stress on the deformation gradient (via the infinitesimal strain). However, models derived from the class of Cauchy elastic bodies do not allow a nonlinear relationship between the stress and linearized strain. Nonlinear constitutive relations that are implicit relations between the stress and a proper measure of strain, or nonlinear expressions of an appropriate measure of strain as a function of stress, lead to a logical linearization procedure wherein the linearized strain can be a nonlinear function of the stress. Using such a constitutive model, the authors accurately characterize both axial strain and circumferential strain in concr...

Model of Infinitesimal Nonlinear Elastic Response of Concrete Subjected to Uniaxial Compression

Relative Humidity in Concrete

Passive restrained concrete ring experiments provide enough information to extract useful aging viscoelastic constitutive properties when combined with free drying shrinkage and mass loss experiments. In this paper, analytical techniques are described for deriving a closed-form solution to extract the viscoelastic Young’s modulus from solidifying concrete in a restrained concrete ring test. Using limit theorems, approximate closed-form solutions are derived for the non-uniform internal relative humidity ( RH ), free drying shrinkage, and tangential stress gradients. An example problem demonstrates the utility of the derived solutions and illustrates the effect that viscoelastic relaxation and solidification have on the tangential stress profile in the restrained, drying concrete ring. Both viscoelastic and solidification effects have a significant impact on the predicted stress profile.

Matthew D. D'Ambrosia

Papers

Internal relative humidity and drying stress gradients in concrete

Effect of alkali silica reaction on the mechanical properties of aging mortar bars: Experiments and numerical modeling:

Model of Infinitesimal Nonlinear Elastic Response of Concrete Subjected to Uniaxial Compression

Relative Humidity in Concrete

Viscoelastic properties and drying stress extracted from concrete ring tests