AS 3600:2018 (Existing Structure Provisions)
AS 3600 Existing Structure Provisions — Assessment, Strengthening and Repair of Concrete Components
AS 3600:2018 contains a focused set of provisions addressing concrete components in existing structures, drawing on the assessment-and-repair methodology referenced from sector documents such as AS 5100.5 and from international assessment-level frameworks. These provisions cover the engineering treatment of existing concrete elements where assessment, modification, strengthening or repair is required, providing guidance on the application of AS 3600 capacity equations to measured material properties and as-built geometry rather than design-intent values. Section 17 addresses durability assessment of existing concrete (corrosion-induced section loss, chloride-induced corrosion initiation, carbonation-induced corrosion, alkali-aggregate reaction, sulphate attack), residual-capacity calculation under AS 3600 partial-factor framework, strengthening-system design (bonded reinforcement, CFRP wraps and laminates, externally bonded steel plates, post-installed reinforcement, supplementary post-tensioning), and integration of strengthening-system capacity with the residual-substrate capacity. The section is a relatively recent addition to AS 3600 (introduced in the 2018 edition; not present in AS 3600:2009 or earlier) and reflects the engineering profession's increasing focus on existing-asset assessment as a distinct discipline from new-design. Section 17 is referenced from AS 5100.5 Section 14 (bridge concrete assessment) and from sector-specific guidance documents on concrete remediation. The provisions remain limited compared with international assessment-level frameworks (ASCE 41, Eurocode 8 Part 3), but represent the most authoritative codified Australian source for existing-concrete-asset assessment methodology.
AS 3600 Section 17 is the most-cited section of AS 3600 in TRSC's existing-asset practice, despite its relative brevity compared with the design sections. The section provides explicit codified support for the methodology TRSC has applied since well before the 2018 edition — measured-property capacity calculation, residual-life assessment based on measured durability indicators, and engineering-judgement-based deviation from default design provisions. Three application points matter for TRSC practice. First, Section 17 explicitly supports the use of measured material properties in capacity calculation, replacing the design-intent values that AS 3600 capacity equations would otherwise assume. For existing concrete, this means using measured compressive strength (from extracted-core testing per AS 1012.14) rather than the as-supplied AS 1379 specification, measured cover depth (from GPR or Ferroscan survey) rather than design-intent cover, measured reinforcement section (accounting for any documented section loss from corrosion or physical damage), and measured concrete density (where decision-controlling, from extracted-core gravimetric testing). The Marina Mirage marine-deck capacity assessment used this methodology under Section 17 — measured concrete strength of 41 MPa (against design-intent 32 MPa, reflecting decades of ongoing hydration), measured cover of 38 mm (against design-intent 50 mm, reflecting placement tolerance), and measured reinforcement section (full nominal section retained in protected zones, with localised section loss documented in exposed-edge zones). The resulting capacity assessment under Section 17 demonstrated adequacy with explicit engineering basis, where a default-property assessment would have triggered conservative remediation. Second, Section 17 durability-assessment provisions are the codified support for residual-life calculation. The section accepts measured chloride profile, measured carbonation depth, and measured corrosion rate as inputs to residual-life modelling, with the resulting calculation supporting continuing-life Form 15 certification. AS 3600 design provisions assume 50-year design life with deemed-to-satisfy cover and exposure-class compliance; Section 17 supports calculations against alternative residual-life targets calibrated to actual asset use and maintenance program. The 12 Creek Street facade investigation used Section 17 durability provisions applied to chloride-profile and carbonation-depth measurements to derive a 30-year residual life with specified ongoing maintenance, supporting a coating-only intervention rather than the full facade replacement that conservative desktop assessment would have recommended. Third, Section 17 strengthening-system provisions integrate strengthening capacity with residual-substrate capacity, ensuring that the design pathway is technically defensible. The section covers bonded reinforcement (Sika Sikadur 32-N bonding agent applications), CFRP wrap and laminate systems, externally bonded steel plates, post-installed reinforcement (using AS 5216-compliant anchorage), and supplementary post-tensioning. For each system, Section 17 prescribes the substrate-condition requirements, the integration methodology with the existing reinforcement, and the partial-factor treatment in the combined capacity calculation. TRSC's strengthening designs cite Section 17 explicitly as the engineering-basis reference, with the calculation pathway documented in the Form 15 file.
Form 15 RPEQ certifications for existing-concrete-element structural adequacy and remediation completion reference AS 3600:2018 Section 17 as the codified Australian Standard support for measured-property capacity calculation, residual-life assessment, and strengthening-system design integration. The Form 15 file retains the Section 17 calculation pathway (measured-property inputs, capacity equations applied, comparison against AS 1170.0 controlling action), the durability-assessment derivation (chloride profile, carbonation depth, corrosion rate, residual-life calculation), and the strengthening-system integration where applicable (substrate-condition assessment, system specification per Section 17 provisions, partial-factor treatment in combined capacity). For continuing-life recertifications and high-stakes adaptive-reuse projects, Section 17 provides the codified Australian Standard reference that supports the engineering basis for the certification — replacing the engineering-judgement-only basis that pre-2018 assessments necessarily relied upon.