77
International RILEM Conference on Materials, Systems and Structures in Civil Engineering
Conference segment on Service Life of Cement-Based Materials and Structures
22-24 August 2016, Technical University of Denmark, Lyngby, Denmark
the cast-in-place piers and bearing platforms, using both stainless bars in first reinforcement
layer and surface silane impregnation, have quite high reliability index, >5.0; the
prefabricated piers adopt epoxy-coated bars in first reinforcement layer and surface saline
impregnation, achieving =2.32 at 120 years.
Figure 2: Failure probability of concrete elements in HZM project through Monte-Carlo
simulation for bridge elements in splashing and tidal zones.
The bridge elements in immerged zone also have satisfactory durability safety margin: the
cast-in-place platforms use stainless bars and surface silane
impregnation and the failure
probability is very low; the prefabricated platforms use epoxy-coated steel bars instead thus
have a reliability index =2.81 at 120 years; the bored hole piles achieve =2.42 at 120 years
without special protection. For prefabricated tunnel segments, the reliability index is
evaluated respectively as =2.81 (interior) and =2.13 (exterior) at 120 years.
5. Preliminary maintenance planning
A preventive maintenance strategy is adopted, intervening in the deterioration of concrete
elements in early stage. The basic maintenance planning considers mainly two aspects: the
durability performance level of elements denoted by failure probability pf or reliability index
SL
at 120 years, and the structural importance of elements. The maintenance techniques
consist in performing the surface chloride extraction by electrochemical method and applying
silane impregnation on the surface of elements periodically. The maintenance period is
recommended to be 20-40 years: the intervention period 20 years is recommended for the
elements without stainless steel bars and the period of 40 years is attributed to the elements
using stainless bars due to their much lower failure probability (<10
-6
). For tunnel segments, a
cathodic protection system has been installed to protect the steel bars against the unexpected
durability failure. The activation time is preliminarily set as 100 years, corresponding to the
failure probability p
f
=1%. It should be noted that this basic maintenance scheme is to interact
78
International RILEM Conference on Materials, Systems and Structures in Civil Engineering
Conference segment on Service Life of Cement-Based Materials and Structures
22-24 August 2016, Technical University of Denmark, Lyngby, Denmark
with the durability inspection/ monitoring data and the real-time durability assessment during
the service life.
6. Summary
This paper introduces the HZM sea link project in construction, covering the durability design,
quality control, durability assessment in construction and the maintenance planning of
concrete structures in the project. The durability design establishes firstly a general
philosophy and divides the requirements onto material and structural levels, and then employs
model-based methods to determine the quantitative design parameters for durability. On the
basis of the quantitative requirements, the quality control is performed with concrete
compressive strength and chloride diffusivity as control parameters. The on-site data were
collected for the chloride diffusivity and concrete cover thickness. Using these data, the
statistical properties for variables in chloride ingress model are updated, and a comprehensive
durability assessment is given through a full probabilistic method. The assessment shows that
the durability safety margin is satisfactory, with
SL
>2.0 at 120 years. A preventive
maintenance planning is recommended for the RC elements.
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