Challenges in material specification Greg van Rooyen Technical Director - Material Technology
Introduction
Introduction 1. Shortfalls in the standards Why specify 2. Understanding local constraints 3. Supply chain issues 4. Types of specifications 5. Durability and sustainability 6. Common issues 7. Discussion
Australian Standards
Standards for concrete AS 1379 Specification and supply of concrete AS 1012 Methods of testing concrete AS 1141 Methods for sampling and testing aggregates AS 1289 Methods of testing soils for engineering purposes AS 3550 Methods for the analysis of water AS 1478.1 Admixtures for concrete AS 2758.1 Concrete aggregates AS 3582.1 SCM s Fly ash AS 3582.2 SCM s Slag AS 3582.3 SCM s Amorphous silica AS 3972 Portland and blended cements
Standards for concrete Lets take a closer look as AS 1379 Density range 2100 to 2800 kg/m 3 Chloride content below 0.8 kg/m 3 Sulfate content below 50 g/kg of cement Drying shrinkage below 1000 microstrain Minimum 7 day strength Cement and aggregate comply to relevant standards Standard N-grades N20, N25, N32, N40, N50 Slump 20 to 120 mm in 10 mm increments Maximum nominal aggregate 10, 14 or 20 mm Air content up to 5.0%
Standards for concrete structures AS 2159 Piling AS 3600 Concrete structures AS 5100.5 Bridge design Concrete AS 3735 Concrete structures retaining liquids AS 4997 Guidelines for the design of maritime structures AS 2876 Concrete kerbs and channels (gutters) manually or machine placed
Standards for concrete structures AS3600
Standards for concrete AS5100.5
Types of specifications Drawings Reference to standards Supplementary Specifications Reference to Client / Authority standards Comprehensive Specifications Stand alone documents with limited external references
Types of specifications
Understanding local constraints
Material availability A common problem facing specifiers is knowing what local materials are available. Consider airport pavement Traditionally this required: Basalt aggregate, then Basaltic aggregate + performance requirements, then Performance requirements only.
Material availability SCM s SCM s are a critical material with regard durability Queensland is fortunate in availability of SCM s Not everything is available everywhere High performance precast boats 70 MPa GP + FA + SF The specifier should work with the supplier Early engagement to establish availability and options. This does require the specification to be broad. Low heat, late age infill 40 MPa GP + FA
What performance is achievable Generally avoid issues by specifying N-grades or as per relevant standard. As noted this is not always possible or desirable. Contractual problems Unclear specification Creating partnership Dealing with non-conformance
Supply chain issues a consultants view
Development of the specification Client requirements (SWTC) Design requirements Durability requirements Review panel requirements Final Specification
Case Study Concrete requirements A project required remediation of several concrete elements (near Brisbane) The structural design identified three concrete mixes for various elements The mix requirements table from the Specification looked like this: Class N20 S32 S40 Use Mass infill General concrete Max w/c ratio Structural & Mass concrete 0.5 0.5 0.5 Min fly ash 25% 25% 25% Min cement 190 320 390
Case Study Concrete requirements After review by the review panel and client concerns with high in-situ strength (as experienced on another project and heat of hydration were raised). The requirements were amended as follows: Class N20 S32 S40 Use Mass infill General concrete Structural & Mass concrete Max w/c ratio 0.5 0.5 0.5 Min fly ash 25% 25% 25% Min cement 190 320 390 Minimum strength (28 days) Maximum strength (56 days) 20 32 40 28 38 48
Case Study Concrete requirements Issues Part 1 Class N20 S32 S40 Use Mass infill General concrete Structural & Mass concrete Max w/c ratio 0.5 0.5 0.5 Min fly ash 25% 25% 25% Min cement 190 320 390 Minimum strength (28 days) Maximum strength (56 days) 20 32 40 28 38 48
Case Study Concrete requirements Issues Part 2 Class N20 S32 S40 Use Mass infill General concrete Structural & Mass concrete Max w/c ratio 0.5 0.5 0.5 Min fly ash 25% 25% 25% Min cement 190 320 390 Minimum strength (28 days) Maximum strength (56 days) 20 32 40 28 38 48
Case Study Concrete requirements Neither the design nor expert panel specified the actual required performance. But wait things get worse.
Case Study Concrete requirements Concrete supplier mix performance: N20 220 kg cementitious 30% fly ash 24 to 28 MPa S32 0.55 w/c 320 kg/m 3 cementitious 45 to 50 MPa S40 0.45 w/c 390 kg/m 3 cementitious 55 to 60 MPa In short the current mix performance exceeds all of the nominated criteria. However the client cannot ignore expert panel advise therefore designer has to relax requirements.
Case Study Concrete requirements After discussion with client, consultant, contractor and supplier the following was agreed: Class N20 S32 S40 Use Mass infill General concrete Structural & Mass concrete Max w/c ratio 0.85 0.70 0.55 Min fly ash 25% 25% 25% Min cement 190 320 390 Average strength (28 days) Maximum strength (56 days) 20 32 40 28 38 48
Case Study Concrete requirements To actually achieve the required performance the following could have been specified: Class N20 S32 S40 Use Mass infill General concrete Structural & Mass concrete Max w/c ratio - 0.60 0.50 Min fly ash - 25% 25% Min / Max cement - 320 / 380 380 / 420 Maximum in-situ peak temperature Characteristic strength - 80 80-32 MPa at 28 days 40 MPa at 56 days
Durability, sustainability and performance
Durability Specifying performance criteria Chloride testing Special testing Mix design deemed to comply criteria Cement Admixture Rebar Surface Electrochem PC Plasticisers Carbon Steel Rebar Extended Curing Chloride Monitoring Micro-silica Self-compacting agents Non-reinforced Design Controlled Permeability Formwork Corrosion Monitoring FA / SFA Water-proofers Stainless Steel Rebar Penetrating Sealers Provision for Future CP GGBFS Corrosion Inhibitors GRP reinforcement Surface Coatings Cathodic Prevention
Sustainability Current requirements focus on CO2 or embodied energy reduction. Most easily achieved through use of SCM s Great deal of research into alkali activated / geopolymer concrete. This has not translated into standards yet. Development ongoing.
Common areas of concern
Standard testing Data availability Data never (hardly ever) available but:
Standard testing
Heat of hydration and temperature control Common issue is dealing with temperature control Requirements not allowed for becomes contractual cost issue How do we get the right technical soluton
Heat of hydration and temperature control
Water addition to concrete AS1379 Specification and supply of concrete Need to consider the conditions Large number of variables involved, simplest solution is to not permit water additions
Concrete placement time
Discussion
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