Lean concrete subbases Performance requirements under concrete Bases

Lean concrete subbasesLean concrete subbases

Performance requirements under concrete BasesPerformance requirements under concrete Bases

The opinions expressed in this presentation are those of the author and do not necessarily reflect the views ofthe Roads & Traffic Authority NSW (RTA).

Geoff Ayton

lean-mix concrete (LMC)lean-mix concrete (LMC)lean-mix concrete (LMC)lean-mix concrete (LMC)

lean concrete subbase (LCS)lean concrete subbase (LCS)ororlean-mix concrete subbase (LCS)lean-mix concrete subbase (LCS)

lean concrete subbase (LCS)lean concrete subbase (LCS)ororlean-mix concrete subbase (LCS)lean-mix concrete subbase (LCS)

TerminologyTerminologyTerminologyTerminology

- a - a materialmaterial- a - a materialmaterial

- a pavement - a pavement layerlayer- a pavement - a pavement layerlayer

pre -1960s concrete pavements ….pre -1960s concrete pavements ….pre -1960s concrete pavements ….pre -1960s concrete pavements ….

SubgradeSubgrade

1960 - 70s:1960 - 70s: non-erodable non-erodable subbasessubbases1960 - 70s:1960 - 70s: non-erodable non-erodable subbasessubbases



"a broken stone base course"a broken stone base courseof six (6) inches compacted thickness"of six (6) inches compacted thickness"

Warringah Freeway1960s

MDCS ≥ 250 lb/sq in. MDCS ≥ 250 lb/sq in. (1.75 MPa)(1.75 MPa)

"...shall include such added quantity"...shall include such added quantityof gritty cementitious binder as is necessary..."of gritty cementitious binder as is necessary..."

July 1964July 1964De Leuw Cather & CoDe Leuw Cather & Co

July 1964July 1964De Leuw Cather & CoDe Leuw Cather & Co

during the 1960s - 1970s ….during the 1960s - 1970s ….during the 1960s - 1970s ….during the 1960s - 1970s ….

Subbases - Subbases - non-erodablenon-erodable

USA:USA: permeable granular, LCS (econocrete) permeable granular, LCS (econocrete)Europe: bound granular, rolled lean-mix, LCSEurope: bound granular, rolled lean-mix, LCS

RTA: since ~1975: LCS or rolled lean-mix RTA: since ~1975: LCS or rolled lean-mix

SubbaseSubbase

Asphalt subbase (USA)Asphalt subbase (USA)

today’s overseas practices ….today’s overseas practices ….today’s overseas practices ….today’s overseas practices ….

LCSLCS now not so popular overseasnow not so popular overseas

partly due to variable performancepartly due to variable performance we treat it as a structural layer, not merely a we treat it as a structural layer, not merely a

mudmatmudmat(thanks to Ed Haber et al)(thanks to Ed Haber et al)

Roger LarsonRoger LarsonFHWA, 1996FHWA, 1996Roger LarsonRoger LarsonFHWA, 1996FHWA, 1996

USA visitors noticeably impressed by USA visitors noticeably impressed by local LCSlocal LCS

today’s overseas practices ….today’s overseas practices ….today’s overseas practices ….today’s overseas practices ….

LCSLCS now not so popular overseasnow not so popular overseas

partly due to variable performancepartly due to variable performance

Carlos Kraemer (1994): Belgian Motorway Carlos Kraemer (1994): Belgian Motorway failurefailure(~100 km, within 12 months of opening)(~100 km, within 12 months of opening)

David Dash & Carlos KraemerDavid Dash & Carlos Kraemer (Spain, 1994) (Spain, 1994)

David Dash & Carlos KraemerDavid Dash & Carlos Kraemer (Spain, 1994) (Spain, 1994)

"...yours are serious LCS, this was cement "...yours are serious LCS, this was cement bound soil..."bound soil..."

Base (250 Base (250 typ)typ)

Lean concrete subbase Lean concrete subbase (LCS) (150 typ)(LCS) (150 typ)

SMZ (300 SMZ (300 typ)typ)

typical RTA pavement structure ….typical RTA pavement structure ….typical RTA pavement structure ….typical RTA pavement structure ….

Base

Subbase

Select material zone(SMZ)

main structural layer flexural fatigue joint performance durability of surface texture

erosion resistance volumetric stability shear capacity under Base joints water-shedding

etc etc

compressive strengthcompressive strength 5 MPa min by 42D 5 MPa min by 42D

compressive strengthcompressive strength 35 MPa min 35 MPa min

flexural strengthflexural strength 4.5 MPa min 4.5 MPa min

Performance requirementsPerformance requirements Specification requirementsSpecification requirements

Pavement structurePavement structure

Base

Subbase



LCSLCS


adequate strength (> 5 MPa)adequate strength (> 5 MPa) for erosion resistance for erosion resistance

low shrinkagelow shrinkage very fine cracksvery fine cracks



Yass Field Trials - 1994Yass Field Trials - 1994

LCS: typical characteristicsLCS: typical characteristicsLCS: typical characteristicsLCS: typical characteristics

Subbase compressive strength(cores & cylinders)

Yass Field Trials - Yass Field Trials - 19941994

Base

Subbase

7 days7 days

LCS cf Base concrete

Subbase compressive strength(cores & cylinders)

Yass Field Trials - 1994

Subbase

Base

Typical :Typical : 160kg160kg 90 kg90 kg250 kg250 kg

Lab Trial Mix : 6 MPa min Lab Trial Mix : 6 MPa min @ 28D@ 28D

15 MPa max @ 15 MPa max @ 28D28D

RTA specification R82

Beware :Beware : cement < 90 kg/m cement < 90 kg/m33 may may struggle tostruggle to

achieve 5 MPa in colder achieve 5 MPa in colder climate.climate.

SlagSlag

NilNil

RTA specification R82

Shrinkage & AEA contentShrinkage & AEA content

Slump: 20-40 mm for slipformed (± 10)Slump: 20-40 mm for slipformed (± 10)

55-65 mm for fixed-formed (± 15)55-65 mm for fixed-formed (± 15)

Field controls

UCS:UCS: 5 MPa from 100 mm 5 MPa from 100 mm corescores within 42 days; within 42 days;

(cylinders not required)(cylinders not required)

Flexural:Flexural: not specified not specified

Base

Subbase




compressive strengthcompressive strength 15-20 MPa 15-20 MPa @@ 1 -2 yrs 1 -2 yrs


Lean concrete subbase Lean concrete subbase (LCS)(LCS)

* specification requirement* specification requirementnotnot

design requirementdesign requirement* unworkable in a * unworkable in a contract situationcontract situation* hence, minimum * hence, minimum binder levelsbinder levels (90 kg PC, 250 kg (90 kg PC, 250 kg total)total)



LCSLCS

Mooney Mooney Bridge

21Module 1

Transversejoint


LCSLCS

LCS hopefully a water-shedding layerLCS hopefully a water-shedding layer

Photos by Graham FoleyPhotos by Graham Foley

Lean concrete subbaseLean concrete subbaseTweed Heads Bypass (~1986)Tweed Heads Bypass (~1986)

P14P14

P14P14

Fall line

Fall line


Fall lineFall line

P14P14

P14P14

Fall line

Fall line


Base

Subbase




compressive strengthcompressive strength 15-20 MPa 15-20 MPa @@ 1 -2 yrs 1 -2 yrs



* specification requirement* specification requirementnotnot

design requirementdesign requirement


ie a mix of ie a mix of methodsmethods and and end productend product spec spec

Subbase


Pavement Pavement structurestructure



ACAC

Assumed modulusAssumed modulus10,000 MPa10,000 MPa

Under an AC Base :Under an AC Base :

a bound/stabilised granular is a bound/stabilised granular is notnot an equivalent an equivalent alternative !alternative !(nor is a rolled lean concrete likely to be equivalent)(nor is a rolled lean concrete likely to be equivalent)

Base

Subbase


LCS crackingLCS cracking


strength: 15-20 MPastrength: 15-20 MPa (for erosion resistance) (for erosion resistance)

low shrinkagelow shrinkage very fine cracksvery fine cracks


What’s GoodWhat’s Good

Narrow (fine) cracksNarrow (fine) cracks

Strength Strength

7 - 12 MPa @ 42 days7 - 12 MPa @ 42 days

What’s NOTWhat’s NOT

Wide cracksWide cracks

reduced shear capacityreduced shear capacity

increased water ingressincreased water ingress

Strength (in Trial Mix)Strength (in Trial Mix)

< 5MPa< 5MPa

> 15MPa> 15MPa

Cobblestone or block crackingCobblestone or block cracking


3-15 m typ

- R82 criteria- R82 criteria


3-15 m typTransverse

cracks


5.1.15.1.1 Typical Subbase CrackingTypical Subbase Cracking

Lean-mix concrete subbase will Lean-mix concrete subbase will typically form full-depth transverse typically form full-depth transverse cracks continuous for the full width cracks continuous for the full width of the paving run at approximately 3-of the paving run at approximately 3-15 m centres. 15 m centres. In subbase placed in a single In subbase placed in a single pass more than 6 m wide, pass more than 6 m wide, longitudinal full-depth cracks longitudinal full-depth cracks might also typically occur at might also typically occur at spacings of approximately 4 m spacings of approximately 4 m and in continuous lengths and in continuous lengths exceeding 4 m. exceeding 4 m.


12 m



cracks


5.1.15.1.1 Typical Subbase CrackingTypical Subbase Cracking

Lean-mix concrete subbase will typically Lean-mix concrete subbase will typically form full-depth transverse cracks form full-depth transverse cracks continuous for the full width of the continuous for the full width of the paving run at approximately 3-15 m paving run at approximately 3-15 m centres. centres. In subbase placed in a single pass In subbase placed in a single pass more than 6 m wide, longitudinal more than 6 m wide, longitudinal full-depth cracks might also typically full-depth cracks might also typically occur at spacings of approximately 4 occur at spacings of approximately 4 m and in continuous lengths m and in continuous lengths exceeding 4 m. exceeding 4 m. Cracking of this type and extent will not Cracking of this type and extent will not be deemed to be nonconforming unless be deemed to be nonconforming unless subsequent deterioration occurs prior subsequent deterioration occurs prior to its being covered with base. to its being covered with base.



cracks


5.1.25.1.2 Plastic Shrinkage CracksPlastic Shrinkage Cracks

Plastic shrinkage cracks are discrete Plastic shrinkage cracks are discrete cracks of length less than 300 mm and cracks of length less than 300 mm and a depth less than 50% of the slab a depth less than 50% of the slab thickness which do not intersect a thickness which do not intersect a formed edge.formed edge.No remedial action is required if a No remedial action is required if a bond breaker is applied, but the bond breaker is applied, but the Contractor must immediately Contractor must immediately implement Corrective Action. implement Corrective Action.



cracks


5.1.35.1.3 Additional Longitudinal and Transverse Additional Longitudinal and Transverse CracksCracksSubbase cracking other than typical Subbase cracking other than typical cracking as described in Clauses 5.1.1 cracking as described in Clauses 5.1.1 and 5.1.2 is nonconforming if the and 5.1.2 is nonconforming if the cumulative length of cracking in any cumulative length of cracking in any 25m25m22 area of subbase exceeds two area of subbase exceeds two metres.metres.

The Contractor must immediately The Contractor must immediately implement Corrective Action. implement Corrective Action.



cracks


nonconforming LCS crackingnonconforming LCS crackingnonconforming LCS crackingnonconforming LCS cracking



cracks





cracks





cracks





cracks




non-structural layer ?non-structural layer ?



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Lean concrete subbases Performance requirements under concrete Bases