Challenges in material specification - Concrete Institute · Standards for concrete • AS 1379...

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

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/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%

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.

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

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

Structural &

concrete

Max w/c

0.5 0.5 0.5

Min fly ash 25% 25% 25%

Min cement 190 320 390

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

concrete

Structural &

Mass concrete

Max w/c ratio 0.5 0.5 0.5

Min fly ash 25% 25% 25%

Minimum strength

(28 days)

20 32 40

Maximum strength

(56 days)

28 38 48

Issues – Part 1

Class N20 S32 S40

concrete

Structural &

Mass concrete

Min fly ash 25% 25% 25%

Minimum strength

(28 days)

20 32 40

Maximum strength

(56 days)

28 38 48

Issues – Part 2

Class N20 S32 S40

concrete

Structural &

Mass concrete

Min fly ash 25% 25% 25%

Minimum strength

(28 days)

20 32 40

Maximum strength

(56 days)

28 38 48

Neither the design nor expert panel specified the actual required

performance.

But wait things get worse….

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.

After discussion with client, consultant, contractor and supplier

the following was agreed:

Class N20 S32 S40

concrete

Structural &

Mass concrete

Max w/c ratio 0.85 0.70 0.55

Min fly ash 25% 25% 25%

Average strength (28

20 32 40

Maximum strength

(56 days)

28 38 48

To actually achieve the required performance the following

could have been specified:

Class N20 S32 S40

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

40 MPa at 56

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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