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TECHNICAL PAPER

Figure 18: Microstructure of HSSCC and HSSSCCFRA50
hydration products, which leads to a larger strength. The as well as nuclear containment structures, which require
EDS (Energy Dispersive X-ray Spectroscopy) spectrum, which significantly longer service life than is generally the case for
indicated the atomic distribution of the hydration of the cement infrastructure projects. Service life is influenced by numerous
or in the aggregate, was used to further explain the matrix factors including quality of material, structural design,
microstructure. The presence of the C-S-H gel in every possible construction practice, and exposure condition such as chloride
combination is demonstrated by the concentration of calcium, ingress and carbonation. These factors have been considered
silicate, and alumina in the matrix. The Ca/Si ratio was used to in the durability design which considers that the concrete cover
describe the reaction product. The control concrete’s Ca/Si ratio can protect the concrete against aggressive agents which cause
was determined to be 2.68. The mixture with RA used in place of steel corrosion, as the principal causes of concrete degradation.
fine particles had a Ca/Si ratio of 1.53. The Ca/Si ratio was shown Although prescriptive specifications are being superseded by
to decrease as RFA concentration increased, which is related to performance based approaches in durability design, they now
a decrease in compressive strength. The matrix composites also allow for more innovative materials and methods that result from
exhibited more porosity than the control mix. measurable performance criteria.
Service life design is the integration of serviceability and
6.3 Service life
durability limit states which are the thresholds of acceptable
Service life in reinforced concrete structures is the estimated performance. Structural stability and safety are dealt with by the
length of time at which the structure will satisfactorily serve ultimate limit state (ULS), functionality and material degradation
its intended purpose after it is placed into service. Service life with time by serviceability limit state (SLS) and durability limit
design has a broad scope including deterioration prediction, state (DLS). For example, Codes like the fib Model Codes, ISO
performance assessment, reliability against structural demands 13823, EN 206-1, outline design principles and provide guidance
under environmental exposures, especially in public facilities on the practice of durability modeling and partial factor design.

Figure 19: EDS depicting the distribution of elements in HSSCC and HSSCCFRA50

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