Challenges in material specification - Concrete Institute...Case Study –Concrete requirements To...
Transcript of Challenges in material specification - Concrete Institute...Case Study –Concrete requirements To...
Greg van Rooyen | Technical Director - Material Technology
Challenges in material specification
Introduction
Challenges in material specification CIA 2018
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
Challenges in material specification CIA 2018
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
Challenges in material specification CIA 2018
Standards for concrete
• Lets take a closer look as AS 1379
• Density range 2100 to 2800 kg/m3
• Chloride content below 0.8 kg/m3
• 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%
Challenges in material specification CIA 2018
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
Challenges in material specification CIA 2018
Standards for concrete structures AS3600
Challenges in material specification CIA 2018
Standards for concrete AS5100.5
Challenges in material specification CIA 2018
Types of specifications
• Drawings
• Reference to standards
• Supplementary Specifications
• Reference to Client / Authority standards
• Comprehensive Specifications
• Stand alone documents with limited
external references
Challenges in material specification CIA 2018
Types of specifications
Understanding local constraints
Challenges in material specification CIA 2018
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.
Challenges in material specification CIA 2018
SCM’s are a critical material with regard
durability
Queensland is fortunate in availability of
SCM’s
Not everything is available everywhere
The specifier should work with the
supplier – Early engagement to
establish availability and options.
This does require the specification to be
broad.
Material availability – SCM’s
High performance precast boats
70 MPa GP + FA + SF
Low heat, late age infill
40 MPa GP + FA
Challenges in material specification CIA 2018
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
Challenges in material specification CIA 2018
Development of the specification
Client requirements (SWTC)
Design requirements
Durability requirements
Review panel requirements
Final Specification
Challenges in material specification CIA 2018
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
Structural &
Mass
concrete
Max w/c
ratio
0.5 0.5 0.5
Min fly ash 25% 25% 25%
Min cement 190 320 390
Challenges in material specification CIA 2018
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)
20 32 40
Maximum strength
(56 days)
28 38 48
Challenges in material specification CIA 2018
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)
20 32 40
Maximum strength
(56 days)
28 38 48
Challenges in material specification CIA 2018
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)
20 32 40
Maximum strength
(56 days)
28 38 48
Challenges in material specification CIA 2018
Case Study – Concrete requirements
Neither the design nor expert panel specified the actual required
performance.
But wait things get worse….
Challenges in material specification CIA 2018
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/m3 cementitious – 45 to 50 MPa
S40 – 0.45 w/c 390 kg/m3 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.
Challenges in material specification CIA 2018
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)
20 32 40
Maximum strength
(56 days)
28 38 48
Challenges in material specification CIA 2018
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
- 80 80
Characteristic
strength
- 32 MPa at 28
days
40 MPa at 56
days
Durability, sustainability and performance
Challenges in material specification CIA 2018
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
Challenges in material specification CIA 2018
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
Challenges in material specification CIA 2018
Standard testing
Data availability
Data never (hardly ever) available but:
Challenges in material specification CIA 2018
Standard testing
Challenges in material specification CIA 2018
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
Challenges in material specification CIA 2018
Heat of hydration and temperature control
Challenges in material specification CIA 2018
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
Challenges in material specification CIA 2018
Concrete placement time
Discussion
Challenges in material specification CIA 2018
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