Per Freiesleben Hansen

Water-entrained cement-based materials

The invention relates to a method for reducing autogenous shrinkage in a material based on a hydraulic mineral binder, e.g. cement, by preparing a mixture comprising the binder, water and a water-entraining agent selected from the group consisting of hydrogels and microencapsulated water, casting the mixture in a desired configuration, and allowing the mixture to cure. The method is in particular directed to high performance cement-based materials with a low water/cement ratio and optionally comprising ultrafine particles such as silica fume. The water-entraining agent is in particular a hydrogel. Also disclosed are dry compositions comprising fine particles such as cement, ultrafine particles such as silica fume, optionally a dispersing agent such as a concrete superplasticizer, and a water-entraining agent such as a hydrogel.

Water-entrained cement-based materials: II. Experimental observations

Abstract This paper concerns a new concept for the prevention of self-desiccation in hardening cement-based materials. The concept is based on using fine, superabsorbent polymer (hydrogel, SAP) particles as a concrete admixture. This permits a controlled formation of water-filled macropore inclusions—water entrainment—in the fresh concrete. Consequently, the pore structure is actively designed to control self-desiccation. In the paper, experimental observations in relation to this technique are described and discussed. The observations show that self-desiccation can be controlled by water entrainment. The paper forms the second part of a series. In the first part, the theoretical background was presented [Cem. Concr. Res. 31(4) (2001) 647].

Autogenous deformation and RH-change in perspective

Abstract Autogenous deformation and change of the relative humidity (RH-change) have been described and registered for a century. However, it is only within the last decade that these phenomena have received appreciable attention. The reason for this is that autogenous deformation and autogenous RH-change are phenomena of special importance within high-strength (high-performance) concrete technology, and a significant utilisation of these concretes did not take place until the early 1980s. In the present paper an historical overview of autogenous deformation and RH-change is given. In addition, due to the present status of this research field both terminology and measuring techniques are described in detail. Finally, some expectations for future research in this field are given.

Influence of temperature on autogenous deformation and relative humidity change in hardening cement paste

This paper deals with autogenous deformation and autogenous relative humidity change (RH change) in hardening cement paste. Theoretical considerations and experimental data are presented, which elucidate the influence of temperature on these properties. This is an important subject in the control of early age cracking of concrete. It is demonstrated that the traditional maturity concept generally is not applicable to autogenous deformation and autogenous RH change.

Chloride ingress in cement paste and mortar

In this paper chloride ingress in cement paste and mortar is followed by electron probe microanalysis. The influence of several paste and exposure parameters on chloride ingress are examined (e.g., water-cement ratio, silica fume addition, exposure time, and temperature). The measurements are modelled on Ficks law modified by a term for chloride binding. Inclusion of chloride binding significantly improves the profile shape of the modelled ingress profiles. The presence of fine aggregate and formation of interfacial transition zones at paste-aggregate boundaries does not significantly affect diffusion rates.

Clinker mineral hydration at reduced relative humidities

Abstract Vapour phase hydration of pure cement clinker minerals at reduced relative humidities is described. This is relevant to modern high performance concrete that may self-desiccate during hydration and is also relevant to the quality of the cement during storage. Both theoretical considerations and experimental data are presented showing that C 3 A can hydrate at lower humidities than either C 3 S or C 2 S. It is suggested that the initiation of hydration during exposure to water vapour is nucleation controlled. When C 3 A hydrates at low humidity, the characteristic hydration product is C 3 AH 6 , hydrogarnet.

The Science of Construction Materials

Systems of matter.- Thermodynamic concepts.- First law.- Second law.- Calculations of equilibrium.- Electrochemistry.- Mathematical appendix.- Tables.- Solutions to check-up questions and exercises.