Presentation on theme: "1 Performance Criteria for Tremie Concrete Presenter: Martin Larisch 20 th August 2013, Brisbane."— Presentation transcript:
1 Performance Criteria for Tremie Concrete Presenter: Martin Larisch 20 th August 2013, Brisbane
22 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
33 Introduction - Definitions Tremie 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:
44 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
55 Pouring dry holes Dry pour (layflat tremie or direct discharge): - reduce fall height (segregation) - ensure concrete won’t hit reinforcement cage - control concrete flow
66 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
77 wet Potential damage on piles and diaphragm walls due to use of unsuitable concrete
88 Potential damage on piles and diaphragm walls due to use of unsuitable concrete wet
99 Potential damage on piles and diaphragm walls due to use of unsuitable concrete wet Bleeding channels
10 The Solution… Recommended Practice “Tremie Concrete for Deep Foundations” Kindly supported by: Concrete Institute of Australia PFSF Bauer Foundations Australia Piling Contractors QLD Department of Main Roads CSIRO Hyder Consulting University of Queensland Holcim Australia
11 The Solution… Recommended Practice “Tremie Concrete for Deep Foundations” Dr Karsten Beckhaus, Bauer Foundations Australia Pty Ltd Martin Larisch, Piling Contractors Pty Ltd Peter Ney, Holcim Pty Ltd Dr 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 Australia Lex Vanderstaay, Queensland Dep. of Transport & Main Roads* * contributing the investigation program with 20,000 AUD each
12 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!
13 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 …
14 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
15 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. w o r k a b i l i t y s t a b i l i t y
16 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?
17 How concrete flows during a wet tremie pour (theory): wet concrete must flow and pass obstacles easily
18 How concrete flows during a wet tremie pour (theory):
19 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. w o r k a b i l i t y s t a b i l i t y
20 wet Tremie concrete in Australian standards and specifications: Review of Australian codes, standards and specifications included but was not limited to: AS 3600:Concrete Structures AS 1379:Specification and Supply of Concrete AS 2159:Piling — Design and Installation MRTS 63: Cast-in-Place Piles MRS11.70: Concrete RTA B58:Permanent Cased Piles RTA B59:Cast in Place Piles RTA B80:Concrete Work for Bridges
21 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 Concrete ACI 336:Specification for the Construction of Drilled Piers EN 206-1: Concrete — Part 1: Specification, Performance, Production EN 1536: Execution of Special Geotechnical Work — Bored Piles EN 1538: Execution of Special Geotechnical Work — Diaphragm Walls
22 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
23 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.
24 Characteristic performance of Tremie Concrete: wet
25 Characteristic performance of Tremie Concrete: wet
26 Why is the slump test alone not suitable to determine workability? Samples with similar slump values can have different flow behaviour wet
27 The slump alone is not good enough… wet sufficient slump ?! but can’t pass through 80-mm grid !!
28 wet Backup by investigations on more than 40 trial mixes
29 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
30 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)
31 Laboratory testing (pre-production): wet 5 bar non-permeable soil permeable 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)
32 Testing on site: wet proof of “characteristic” slump and spread should confirm laboratory results good flowability & passing ability of concrete with same composition! No EXTRA EFFORT on site
33 Workability trials cement 390 kg 390 kg390 kg420 kg water168 l179 l191 l181 l w/c slump230 mm220 mm240 mm230 270 mm visuallyexcellentgoodexcellentgood / excellent Slump dia380 mm350 mm500 mm450 570 mm L-Box h(170 mm)*(220 mm)*60 mm40 20 mm *) did not reach the end of L-Box 312 l335 l323 l335 l very stable mix!
34 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!
35 wet Test Method and properties assessed Suggested value for structural element of length l and for optional pouring conditions DryWet, flow distance -< 1.2 m≥ 1.2 m Slump h (mm)≥ 140*≥ 180≥ 220 Slump flow D final (mm) T final (sec) ≤ ≤ 3 L-Box Travel distance from bars (mm) Filling Ratio T end (sec) L-Box Passability (mm) > ≤ 40 (full) ≥ 0.2 ≤ 12 ≤ 40 (full) ≥ 0.4 ≤ 8 ≤ 20 Bauer filtration Filtration loss (l/m³) Filter cake thickness (mm) ≤ 30 ≤ 150 ≤ l ≤ 15 m / ≤ l > 15 m ≤ l ≤ 15 m / ≤ l > 15 m
36 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/m 3 - Carry out pre-production tests (filtration test) - Use experienced concrete supplier who can respond quickly
37 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
38 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
39 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
40 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 $)
41 The Way Forward… YOUR ACTIVE INPUT & INVOLVEMENT IS CRITICAL TO ACHIEVE EXCELLENT ENDPRODUCTS AND TO INCREASE INDUSTRY STANDARDS