Influence of Shrinkage-Reducing Admixtures on Early-Age Properties of Cement Pastes

Abstract

Because most shrinkage-reducing admixtures (SRAs) significantly reduce the surface tension of a cement paste pore solution, they will naturally influence all physical properties and processes that are dependent in some way on surface tension. Such properties include internal relative humidity, capillary stresses, and freezing point depression, all via the Kelvin equation and its variants (Kelvin-Laplace, Gibbs-Thomson). Processes that will thus be strongly influenced by the presence of SRAs include drying, autogenous stress and strain development, and freezing. In this paper, experimental measurements of these processes in cement pastes and mortars with and without SRA additions will be presented in light of the Kelvin equation. The experimental measurements that are applied to early-age specimens include X-ray absorption measurements to quantify drying profiles, bulk mass loss measurements, measurements of internal relative humidity, assessments of autogenous deformation under sealed curing conditions, and low temperature calorimetry scans to quantify freezable water content. The results indicate that SRAs can provide benefits in several new applications beyond their conventional usage to reduce drying shrinkage.

Prediction of self-desiccation in low water-to-cement ratio pastes based on pore structure evolution

“…Different angles can be applied, e.g. Bentz [39] measured a contact angle of 28°for distilled water on hydrated cement paste surfaces. Fig.…”

“…The opinion of the authors is that at this moment there is insufficient information available for a quantitative model based on the disjoining pressure approach. In this paper, the approach based on capillary pressure has been followed, which is according to a number of authors [2,5,[15][16][17][18]37,39,44] the dominant mechanism of both autogenous shrinkage and drying shrinkage in the high RH range. The results demonstrate that this is perfectly adequate to predict the RH evolution with good accuracy.…”

Effects of Shrinkage Reducing Agent and Expansive Admixture on the Volume Deformation of Ultrahigh Performance Concrete

“…The results indicated that the compressive strength of UHPC decreased with the increase of dosage of shrinkage reducing agent. Some published studies also drew the same conclusion that the addition of shrinkage reducing agent decreased the compressive strength of mortar sample [16][17][18]. For the samples without mixing with shrinkage reducing agent, 7-day and 28-day compressive strength reached 114.7 MPa and 133.1 MPa.…”

Study on early autogenous shrinkage and crack resistance of fly ash high-strength lightweight aggregate concrete

“…As shown in Figures 3-5, with the addition of fly ash, early autogenous shrinkage of LWAC is significantly restrained (Bentz, 2006;Henkensiefken et al, 2009 It was concluded, therefore, that fly ash, as a filling powder material, does not take part in hydration at an early age, which means that the content of cement decreases and the effective waterÀcement ratio increases because fly ash has replaced cement equivalently. This leads to the relative augmentation of free water, which effectively decreases the autogenous shrinkage caused by the self-desiccation of the internal capillary microstructure.…”