Knowledge of microstructure of concrete for the design of durable reinforced concrete structures

Author(s): Folker H. Wittmann, Tiejun Zhao
Paper category: conference
Book title: Microstructural-related Durability of Cementitious Composites
Editor(s): Guang Ye, K. van Breugel, Wei Sun and Changwen Miao
Print ISBN: 978-2-35158-129-2
e-ISBN: 978-2-35158-123-0
Publisher: RILEM Publications SARL
Publication year: 2012
Pages: 1 - 12
Total Pages: 12
Language: English

Abstract: In this contribution the formation of the microstructure of cement-based materials is briefly described. It is shown that clusters of calcium silicate hydrates are growing into the initially water filled space between the individual cement grains. These clusters have an intrinsic nano-porosity of about 26 %. The space between the clusters forms the micro-pores. In concrete there exists also a certain percentage of compaction pores. The micro-porosity decreases with decreasing water-cement ratio and the pore size distribution is shifted to lower radii. In hardened cement paste with a given water-cement ratio the micro-porosity and the mean pore size decrease as hydration goes on. First the influence of the evolution of the microstructure on mechanical properties is outlined. Durability and service life of concrete structures depend primarily on transport mechanisms. The influence of the time-dependent development of the microstructure on capillary absorption and diffusion is explained on the basis of experimental results. Finally the interaction of mechanical load with the microstructure is discussed. It is shown that both tensile and compressive load change porosity of the microstructure. As a consequence transport processes are modified. Durability is reduced by the application of tensile stress. Durability is also reduced if the compressive stress is higher than a critical value. These synergetic effects of combined loads have to be taken into consideration if service life is to be designed in a realistic way.

Online publication: 2012-07-05
Publication Type: full_text
Public price (Euros): 0.00