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Performance Criteria for Tremie Concrete

Presenter: Martin Larisch

20th August 2013, Brisbane

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Introduction

- Drilling is perceived to be the main scope of piling companies

(focus on big drilling rigs, state of the art drill tools, hard rock)

- Concrete placement is often perceived as the non critical activity

- In the past the slump was the almighty workability factor

- Did we (engineers) get involved into concrete mix design review?

- How did we determine if a mix is suitable or not?

- Did we review placement techniques CRITICALLY in the past

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Introduction - DefinitionsTremie pipe:Steel pipe surmounted by a hopper or chute for concreting both under dry or wet conditions. For application in wet conditions a tremie pipe may comprise several joined lengths but must have watertight joints.

Schematics of a tremie pour:

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Why should we use a tremie pipe?

Wet tremie:

- Ensure concrete is not placed through water (segregation)

- Ensure we don’t have inclusions

- Ensure concrete won’t hit cage (risk of segregation)- Control concrete placement (embedment of tremie, suitable

separator, no vibrator for SCC, etc.)

WE SHOULD NEVER REPLACE A TREMIE PIPE WITH

A CONCRETE BOOM PUMP SECTION!

NEVER POUR A BORED PILE USING ADDITIONAL

PRESSURE

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Pouring dry holes

Dry pour (layflat tremie or direct discharge):- reduce fall height (segregation)- ensure concrete won’t hit reinforcement cage- control concrete flow

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Why is pouring piles different to pouring structural concrete?

- Commonly up to 50 m deep

- Maybe deeper than 100m

- Subject to high pressure (at pile base)

- Concrete must displace fluid

- Concrete must be self-leveling

- Concrete must flow around cages

- Concrete must achieve bond with reo

Pouring piles & D-walls is a blind process

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wet

Potential damage on piles and diaphragm walls due to use of

unsuitable concrete

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Potential damage on piles and diaphragm walls due to use of

unsuitable concrete

wet

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Potential damage on piles and diaphragm walls due to use of

unsuitable concrete

wet

Bleeding channels

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The Solution…

Recommended Practice “Tremie

Concrete for Deep Foundations”

Kindly supported by:Concrete Institute of AustraliaPFSFBauer Foundations AustraliaPiling ContractorsQLD Department of Main RoadsCSIROHyder Consulting University of QueenslandHolcim Australia

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The Solution…

Recommended Practice “Tremie Concrete for Deep Foundations”

Dr Karsten Beckhaus, Bauer Foundations Australia Pty LtdMartin Larisch, Piling Contractors Pty LtdPeter Ney, Holcim Pty LtdDr Habib Alehossein, CSIRO

Sherard Northey, Concrete Institute of Australia Professor Peter Dux, University of Queensland Stephen Buttling, Piling and Foundation Specialists Federation*Gary Lucas, Cement Concrete and Aggregates AustraliaLex Vanderstaay, Queensland Dep. of Transport & Main Roads*

* contributing the investigation program with 20,000 AUD each

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Purpose of the Recommended Practice:

- Provide guidance for those involved in the preparation of specs for the use of

tremie concrete for bored piles and diaphragm walls

- Cover special requirements for the mix design or properties of tremie concrete

with respect to its specific field of application

- Special attention should be given to the fact that the workability required has to be

achieved and maintained under considerable hydraulic pressure and for the total

time span until the last working step

- Provide recommendations on properties, constituents and proportioning, as well

as on testing of concrete; based on international and Australian experience

- Give advice on the usual range of application and to show principal measures to

achieve proper workability does not offer full prescriptive information!

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Areas of applications of the Recommended Practice:

This Recommended Practice

- refers to TC for bored piles, diaphragm walls and cut-off walls, min d = 400 mm

- applies to concrete for casting under both dry and wet conditions

- includes descriptions of suitable workability test methods

- refers to the Recommended Practice for Super-Workable Concrete

- generally applies to low, normal and high strength concrete on site or ready-mixed

But this Recommended Practice

- does not refer to the intended service life / not to specific durability needs etc.

- may not cover requirements as stated within particular project specification

(which may require additional measures or deviations from this guide)

- does not cover health and safety requirements …

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What makes a good mix - Risk of potential issues

1. Unsuitable Concrete at its plastic stage (prior to and during placement)

- e.g. insufficient flow-ability insufficient workability

- Insufficient fill-ability

- Insufficient water retention insufficient stability

- Insufficient retardation

2. Unsuitable placement techniques integrity issue of pile / D-wall

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Flowability The ease of flow of fresh concrete when unconfined by formwork or any other obstacles such as reinforcement.

Passing ability (blocking resistance)The ability of fresh tremie concrete to flow through tight openings such as spaces between steel reinforcing bars without segregation and blocking.

Water retention ability (filtration resistance)The ability of fresh tremie concrete to retain its water despite being subject to pressure caused by supporting fluid or fresh concrete above.

Slump retention ability (flow maintenance)The ability of fresh tremie concrete to maintain its flow characteristic, measured by slump test, over a certain period of time, possibly controlled by appropriate admixtures.

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Background:

Unsuitable Concrete at its plastic stage,

may have insufficient rheological properties, characterised by ...

Viscosity In general viscosity describes a fluid's

internal resistance to flow and may be

thought of as a measure of fluid friction;

here simplistically the flow resistance of

fresh tremie concrete once flow has started.wet

Velocity Profile inside a “pipe” or similar!

What about the shearing zone inside the pile?

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How concrete flows

during a wet tremie

pour (theory):

wet

concrete must flow and pass obstacles easily

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How concrete flows during a wet tremie pour (theory):

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Flowability The ease of flow of fresh concrete when unconfined by formwork or any other obstacles such as reinforcement.

Passing ability (blocking resistance)The ability of fresh tremie concrete to flow through tight openings such as spaces between steel reinforcing bars without segregation and blocking.

Water retention ability (filtration resistance)The ability of fresh tremie concrete to retain its water despite being subject to pressure caused by supporting fluid or fresh concrete above.

Slump retention ability (flow maintenance)The ability of fresh tremie concrete to maintain its flow characteristic, measured by slump test, over a certain period of time, possibly controlled by appropriate admixtures.

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Tremie concrete in Australian standards and specifications:

Review of Australian codes, standards and specifications included but was not limited to:

AS 3600: Concrete StructuresAS 1379: Specification and Supply of ConcreteAS 2159: Piling — Design and Installation

MRTS 63: Cast-in-Place PilesMRS11.70: Concrete

RTA B58: Permanent Cased PilesRTA B59: Cast in Place PilesRTA B80: Concrete Work for Bridges

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wet

Tremie concrete international standards and specifications:

Review of international codes, standards and specifications included but was not limited to:

ACI 301: Specifications for Structural ConcreteACI 336: Specification for the Construction of Drilled Piers EN 206-1: Concrete — Part 1: Specification, Performance, ProductionEN 1536: Execution of Special Geotechnical Work — Bored PilesEN 1538: Execution of Special Geotechnical Work — Diaphragm Walls

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Summary of review:

Summary of the detailed review of standards, codes and specifications and of investigations in terms of addressing fresh concrete criteria on Tremie Concrete:

- Only solitary specific recommendations for tremie concrete are given:- slump / slump tolerance- materials, proportioning and testing- production and control

- Modern concrete’s rheology can’t be described by slump only , but can be well described by special tests (e.g. as for super-workable concrete)

wet

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Characteristic performance of Tremie Concrete:

wet

“Normal” Concrete compacting by vibrating after placing

Tremie Concrete (self) compacting, only by help of hydraulic head

Super-Workable Concrete self-compacting

Independent of the required hardened concrete properties, by looking at viscosity of concrete, and on viscosity of the paste, there are some important differences in the mixture composition as well.

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Characteristic performance of Tremie Concrete:

wet

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Characteristic performance of Tremie Concrete:

wet

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Why is the slump test alone not suitable to determine workability?

Samples with similar slump values can have different flow behaviour

wet

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The slump alone is not good enough…

wet sufficient slump ?!

but

can’t pass through 80-mm grid !!

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wet

Backup by investigations on more than 40 trial mixes

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Laboratory testing (pre-production):

wet

distinctive slump: for correlation on site (only!)

Required workability

to be confirmed by

L-Box and/or slump flow test

f i l m !

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Laboratory testing (pre-production):

wet

Required stability

to be confirmed by Visual Stability Index (VSI) test in one procedure with slump flow test

VSI “Class 0”:- no indication of segregation or separation- very good aggregate distribution- no bleeding

(Class 1: starting to exhibit a mortar halo)

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Laboratory testing (pre-production):

wet

5 bar

non-permeable soilpermeable soil

++ < 15 l/m³ water loss + < 30 l/m³ water loss (plus requirements to filter cake)

Filtration loss (l/m³)Filter cake thickness (mm) Proof of sufficient stability

(high hydraulic head pressure)

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Testing on site:

wet

proof of “characteristic” slump and spread

should confirm laboratory resultsgood flowability & passing abilityof concrete with same composition!

No EXTRA EFFORT on site

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Workability trialscement 390 kg 390 kg 390 kg 420 kgwater 168 l 179 l 191 l 181 lw/c 0.43 0.46 0.49 0.43

slump 230 mm 220 mm 240 mm 230 270 mm

visually excellent good excellent good / excellent

Slump dia 380 mm 350 mm 500 mm 450 570 mm

L-Box Dh (170 mm)* (220 mm)* 60 mm 40 20 mm *) did not reach the end of L-Box

312 l 335 l323 l 335 l very

stable mix!

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Recommended concrete testing for future projects

Pre-production tests (spend $1-2k in advance to get a suitable mix)

- L-Box (time and ratio)

- Slump flow (time and diameter)

- Slump (height)

- VSI (visual)

- Filtration press (bleed water & filter cake thickness)

Site tests (correlate to pre-production test)

- Slump flow (time, diameter and VSI)

- Slump (height)

NO EXTRA EFFORT ON SITE!

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wet

Test Methodand properties assessed

Suggested value for structural element of length land for optional pouring conditions

Dry Wet, flow distance

- < 1.2 m ≥ 1.2 m

Slumph (mm) ≥ 140* ≥ 180 ≥ 220

Slump flowDfinal (mm)Tfinal (sec)

--

400 - 600≤ 5

450 - 650≤ 3

L-BoxTravel distance from bars (mm)Filling RatioTend (sec)L-Box Passability (mm)

> 200

--

≤ 40

(full)

≥ 0.2≤ 12≤ 40

(full)

≥ 0.4≤ 8

≤ 20

Bauer filtrationFiltration loss (l/m³)Filter cake thickness (mm)

≤ 30≤ 150

≤ 30 @ l ≤ 15 m / ≤ 15 @ l > 15 m≤ 150 @ l ≤ 15 m / ≤ 100 @ l > 15 m

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Potential Issues

Bleeding channels

- Free water can’t be retained by fines in the concrete mix and escapes

How to avoid it:

- Limit free water to max 180l/m3

- Carry out pre-production tests (filtration test)

- Use experienced concrete supplier who can respond quickly

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Potential Issues

Insufficient concrete cover

- Mostly insufficient workability or placement technique

How to avoid it:

- Ensure concrete spacers are in place

- Ensure sufficient concrete flowability (spread, slump, L-Box)

- Review & discuss methodology prior to implementing new procedures

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Potential Issues

Inclusions

- Insufficient flowability, placement techniques or cleaning of pile base

How to avoid it:

- Ensure pile base is free of drill sludge

- Ensure sufficient concrete flowability (L-box & slump flow)

- Ensure tremie pipe remains 3m inside the concrete throughout pour

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Potential Issues

Others:

- Anchor ducts

- Concrete supply by others (specification)

- Tremie pipe lifted out of concrete during pour

- Pouring under pressure (concrete pump)

- Leaving too much tremie inside concrete

- Understand behaviour of drilling fluid

- Insufficient separator

- Fully cased piles (bleeding)

- Inexperienced concrete supplier

- Lack of resources / commitment of supplier

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Concrete for CFA piles

Similar requirements as for tremie concrete, in addition consider:

- Carry out pre-production tests whenever possible

- Use max aggregate of 10mm to ensure sound cage installation

- Focus on stability of the mix (filtration press)- Focus on L-Box and slump flow (low viscosity)- Increase workability to 4 hours (project specific)

- Avoid cage vibrator whenever possible, rather use excavator and push cage into concrete carefully under steady pressure

- Ideally, cages should be plunged into concrete under gravity

- Use experienced and capable concrete supplier (value for $)

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The Way Forward…

YOUR ACTIVE INPUT & INVOLVEMENT IS CRITICALTO ACHIEVE EXCELLENT ENDPRODUCTS AND TO INCREASE INDUSTRY STANDARDS

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THANK YOU

FOR YOUR

ATTENTION