Mateusz Wyrzykowski

Influence of superabsorbent polymers on hydration of cement pastes with low water-to-binder ratio

Internal curing with superabsorbent polymers (SAP) is a method for promoting hydration of cement and limiting self-desiccation, shrinkage and cracking in high-performance, and ultra high-performance concrete with low water-to-binder ratio. SAP are introduced in the dry state during mixing and form water-filled inclusions by absorbing pore solution. The absorbed solution is later released to the cement paste during hydration of the cement. In this paper, cement pastes with low water-to-binder ratios incorporating superplasticizer and different dosages of SAP and corresponding additional water were prepared. Reference cement pastes without SAP but with the same amount of water and superplasticizer were also mixed. Isothermal calorimetry was used to measure hydration heat flow. Water entrainment by means of SAP increased the degree of hydration at later hydration times in a manner similar to increasing the water-to-binder ratio. Addition of SAP also delayed the main calorimetric hydration peak compared to the reference pastes, however, in a less prominent manner than the increase in water-to-cement ratio.

Modeling of Water Migration during Internal Curing with Superabsorbent Polymers

The mobility of water in hardening cement paste is an important aspect in view of the effectiveness of internal curing. A mechanistic-type numerical model of cementitious materials is applied for the analysis of water migration kinetics from internal curing agents [superabsorbent polymers (SAP)] into hydrating cement pastes with a low water-to-cement ratio. It is shown that the release of curing water at early age (i.e., during approximately the first day of hydration) allows for a uniform and practically instantaneous distribution of water within the whole volume of cured paste, even if the distances for water migration are as high as 2–3 mm. The evolution of permeability, as a result of the hydration process, is shown to have a major impact on the mobility of water in the cement paste. The depercolation of capillary porosity may substantially inhibit the water transport. The analysis shows that a part of the water first received by the paste in the proximity of the SAP can be later redistributed to a large volume of hardening paste, even after the permeability has become very low.

Nonlinear elastic response of thermally damaged consolidated granular media

The mechanical properties of consolidated granular media are strongly affected by large temperature changes which induce the development and localization of stresses, leading in turn to damage, e.g., cracking. In this work, we study the evolution of linear and nonlinear elasticity parameters when increasing the temperature of the thermal loading process. We prove the existence of a link between linear and nonlinear elasticity properties. We show that the change of the nonlinear elasticity parameters with the increase in the thermal loading is larger at the lower temperatures than the corresponding change for the linear parameters, suggesting that nonlinear elasticity can be exploited for early thermal damage detection and characterization in consolidated granular media. We finally show the influence of grain size upon the thermal damage evolution with the loading temperature and how this evolution is mirrored by the nonlinear elasticity parameters.

Modeling Hygro-thermal Performance and Strains of Cementitious Building Materials Maturing in Variable Conditions

A novel model of hygro-thermal performance of cement-based building materials during their maturing, considering evolution of their strength properties and deformations (shrinkage and creep strains), described in terms of effective stress is briefly presented. Creep is described by means of the modified microprestress — solidification theory by Bazant et al., with some modifications to take into account the effects of temperature and relative humidity on the cement hydration. Shrinkage strains are modeled by using effective stresses in the form introduced by Gray and Schrefler, giving a good agreement with experimental data also for low values of relative humidity. Results of three numerical examples based on the real experimental tests are solved to validate the model. They demonstrate its possibilities to analyze both autogenous deformations in maturing cementitious materials, and creep and shrinkage phenomena, in building elements of different age, sealed or drying at various conditions.

Kinetics of Water Migration in Cement-Based Systems Containing Superabsobent Polymers

Superabsorbent polymers (SAP) absorb pore solution during mixing of concrete and release it when cement paste self-desiccates or is exposed to drying. Knowledge of the kinetics of water migration in and out of the SAP is essential for understanding and optimizing internal curing of concrete. This chapter discusses absorption of pore solutions in SAP and desorption of the SAP, both in model systems and in cement paste or concrete. When experimental results about SAP are missing in the literature, results obtained with other internal curing agents are presented and the applicability to SAP is discussed. A final section is dedicated to modeling of internal curing of concrete by SAP and especially to modeling of water migration to and from the SAP.

Numerical benchmark campaign of COST Action TU1404 – microstructural modelling

This paper presents the results of the numerical benchmark campaign on modelling of hydration and microstructure development of cementitious materials. This numerical benchmark was performed in the scope of COST Action TU1404 “Towards the next generation of standards for service life of cement-based materials and structures”. Seven modelling groups took part in the campaign applying different models for prediction of mechanical properties (elastic moduli or compressive strength) in cement pastes and mortars. The simulations were based on published experimental data. The experimental data (both input and results used for validation) were open to the participants. The purpose of the benchmark campaign was to identify the needs of different models in terms of input experimental data, verify predictive potential of the models and finally to provide reference cases for new models in the future. The results of the benchmark show that a relatively high scatter in the predictions can arise between different models, in particular at early ages (e.g. elastic Young’s modulus predicted at 1 d in the range 6-20 GPa), while it reduces at later age, providing relatively good agreement with experimental data. Even though the input data was based on a single experimental dataset, the large differences between the results of the different models were found to be caused by distinct assumed properties for the individual phases at the microstructural level, mainly because of the scatter in the nanoindentation-derived properties of the C-S-H phase.