Zhanqi Guo

MODERN ROUTES TO EXPLORE CONCRETE’S COMPLEX PORE SPACE

This paper concentrates on discrete element computer-simulation of concrete. It is argued on the basis of stochastic heterogeneity theory that modern concurrent-algorithm-based systems should be employed for the assessment of pore characteristics underlying durability performance of cementitious materials. The SPACE system was developed at Delft University of Technology for producing realistic schematizations of realcrete for a wide range of other particle packing problems, involving aggregate and fresh cement, and for the purpose of exploring characteristics in the hardened state of concrete, including of the pore network structure because of obvious durability problems. Since structure-sensitive properties are involved, schematization of reality should explicitly deal with the configuration of the cement particles in the fresh state. The paper concentrates on the stereological and mathematical morphology operations executed to acquire information on particle size, global porosity, and on distribution of porosity and of the connected pore fraction as a result of the near neighbourhood of aggregate grains. Goal is to provide information obtained along different exploration routes of concretes pore space for setting up a pore network modelling approach. This type of methodological papers is scarce in concrete technology, if not missing at all. Technical publications that report on obtained results in our investigations are systematically referred to.

Numerical assessment of concrete's self-healing potential for promoting durability

Transport of harmful substances through pore space of concrete can give rise to the deterioration of concrete structure or to the corrosion of steel reinforcement. Internal and external influences will additionally lead to the formation of myriads of tiny cracks in the virgin state. These cracks can have detrimental impact on concrete durability. Cement particle nuclei left unhydrated in concrete after complete maturation can provide under favourable conditions self-healing capability to microcracked concrete. Basically, the self-healing capability can be expected depending on the amount of unhydrated cement, however, also on the number and spacing of the nuclei of unhydrated particles. Therefore, the concurrent algorithm-based computer simulation system with the acronym SPACE has been employed. The impact of principal design parameters of concrete (cement fineness, water to cement ratio) on maximum healable microcrack opening is emphasised in this paper.

Modern perspectives on aggregate in concrete

The jammed aggregate is the prime, load-bearing phase in compressed concrete. The Interfacial Transition Zones (ITZs) around all aggregate grains constitute a second phase in the form of an interconnected spatial structure of shells. ITZs delineate gradients in structure descriptors of which the configuration-sensitivity governs the ITZ’s extent. Concurrent algorithm-based discrete element computer simulations of concrete can offer unbiased information on configuration-sensitive parameter gradients. Such systems (SPACE and HADES) are used for studying gradient structures, such as relevant for transport-based durability issues. This paper touches upon the various aspects of a sound methodological approach to studying properties linked to the aggregate in concrete.