Accelerated corrosion test simulation

Abstract

A series of accelerated corrosion tests were done by SGS INTRON (commenced by Combinatie Aanpak Maastunnel, constructor of the Maastunnel project) to investigate for a proper repair material for the deteriorated concrete floor in the Maastunnel at Rotterdam. Five types of fiber reinforced mixtures with different tensile behavior ranging from SHCC (strain-hardening cementitious composite) to ON06 (similar tensile behavior as normal concrete) were designed. Different cracking behavior was observed due to the different tensile behavior in the repair mortar. It is of utmost importance to investigate if the cracking behavior can be simulated by numerical modeling and if in the future, the parametric analysis might be performed without large experimental series.

Two types of numerical models are implemented in this master thesis, namely the lattice model and the continuum model. The lattice model can simulate the crack pattern of different materials in the accelerated corrosion test. The continuum model cannot show the behavior of decreasing number of cracks with decreasing fracture energy in the strain-softening materials due to the bifurcation problem brought by its incremental solution method. However, the lattice model shows the trend to underestimate the crack width of the strain-softening material. The continuum model has better performance in predicting the crack width. Also, the lattice model can predict the influence of the repair mortar-substrate bond strength on the crack pattern. Meanwhile, the continuum model always shows a complete failure in the repair mortar-substrate interface.
The boundary conditions at the bottom edge are observed to influence the direction of the bottom cracks. The edges of the specimen are kept free in the experiment. However, the repaired area is constrained by the surrounding concrete in reality. This indicates that the laboratory test may not represent the cracking behavior of the concrete floor in the tunnel accurately. SHCC is observed to be more sensitive to the repair mortar-substrate bond strength than material with lower stain capacity. Extra caution on the bond quality is advised while applying SHCC in a concrete repair system.

From the material point of view, with increasing fracture energy and strain capacity, more but thinner cracks can be performed in the accelerated corrosion test. SHCC material can perform the distributed crack pattern with a maximum crack width of 0.1mm which is ten times smaller than normal concrete. This behavior of SHCC is very suitable for being applied to a concrete repair system. The distributed cracks with smaller crack width can effectively limit the possibility of further corrosion. Besides SHCC, some strain-softening (under direct tension) materials can also show the deflection-hardening behavior in the bending test and produce the distributed crack pattern. SHCC and fiber reinforced concrete with deflection-hardening behavior in the bending test are suggested to be used in the concrete repair system.