טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentZhutovsky Semion
SubjectMechanisms of Internal Curing of High-Performance
Concrete
DepartmentDepartment of Civil and Environmental Engineering
Supervisors Professor Konstantin Kovler
Professor Konstantin Volokh
Full Thesis textFull thesis text - English Version


Abstract

The introduction of new admixtures and cementitious materials allowed the production of a new class of concrete with superior mechanical properties and durability. This new class of concrete was called high-performance concrete (HPC). HPC has its economic benefits, significantly reducing maintenance costs and enhancing service life. Enhanced durability of HPC makes its use very attractive in the environments where ordinary concrete would not suffice. HPC has plenty of merits. However, its use is associated with a variety of problems. Increased tendency to early-age cracking is the principal shortcoming of HPC. The origin of early-age cracking sensitivity of HPC is self-desiccation and autogenous shrinkage. A novel approach to reduce self-desiccation and eliminate autogenous shrinkage has been recently proposed. It suggests incorporating into the mix pre-soaked lightweight aggregate (LWA), which will act as an internal water reservoir preventing reduction of relative humidity and generation of capillary pressure. This method received the name of internal curing (IC). Later, additional materials have been proposed to serve the function of IC agent.

IC reduces autogenous shrinkage of HPC, therewith the higher the content of IC agent, the lower is autogenous shrinkage. However, introduction of porous IC material into HPC is detrimental to superior mechanical and durability properties of HPC. For mix design optimization and further structural design applications, a comprehension of physics of the process of internal curing that could serve as the basis for assessment of autogenous deformations, the risk of cracking and engineering properties of internally cured HPC is required. An understanding of the basic mechanisms would turn the method of IC into a modern technology.

 In the current research, extensive experimental study on the effect of IC on the rate of cement hydration, chemical shrinkage, autogenous deformations, mechanical and durability properties of high-performance cement paste and concrete was conducted. In addition, a comprehensive model that combines chemistry of cement hydration, poromechanics and the microstructural model of cement paste was proposed. The novel approach of combining of chemical, microstructural and mechanical aspects in one model allows taking into account for new mechanisms, such as the chemo-mechanical coupling, osmotic pressure and osmotic flow that were not considered previously. The introduction of new mechanisms offered an explanation for the phenomena of early-age expansion of water-cured cement paste, and the limit of 75% relative humidity for the hydration of cement paste. Furthermore, in the progress of the experimental study, the important recommendations for practical implementation of IC were elaborated.