lean concrete subbases performance requirements under concrete bases
TRANSCRIPT
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
pre -1960s concrete pavements ….pre -1960s concrete pavements ….pre -1960s concrete pavements ….pre -1960s concrete pavements ….
pre -1960s concrete pavements ….pre -1960s concrete pavements ….pre -1960s concrete pavements ….pre -1960s concrete pavements ….
"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
Select material zone(SMZ)
Pavement structurePavement structure
LCSLCS
erosion resistance volumetric stability shear capacity under Base joints water-shedding
adequate strength (> 5 MPa)adequate strength (> 5 MPa) for erosion resistance for erosion resistance
low shrinkagelow shrinkage very fine cracksvery fine cracks
compressive strengthcompressive strength 5 MPa min by 42D 5 MPa min by 42D
Performance requirementsPerformance requirements Specification requirementsSpecification requirements
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
Select material zone(SMZ)
compressive strengthcompressive strength 5 MPa min by 42D 5 MPa min by 42D
Performance requirementsPerformance requirements Specification requirementsSpecification requirements
compressive strengthcompressive strength 15-20 MPa 15-20 MPa @@ 1 -2 yrs 1 -2 yrs
Pavement structurePavement structure
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)
erosion resistance volumetric stability shear capacity under Base joints water-shedding
Pavement structurePavement structure
LCSLCS
Mooney Mooney Bridge
21Module 1
Transversejoint
Pavement structurePavement structure
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
Photos by Graham FoleyPhotos by Graham Foley
Fall lineFall line
P14P14
P14P14
Fall line
Fall line
Photos by Graham FoleyPhotos by Graham Foley
Base
Subbase
Select material zone(SMZ)
compressive strengthcompressive strength 5 MPa min by 42D 5 MPa min by 42D
Performance requirementsPerformance requirements Specification requirementsSpecification requirements
compressive strengthcompressive strength 15-20 MPa 15-20 MPa @@ 1 -2 yrs 1 -2 yrs
Pavement structurePavement structure
Lean concrete subbase Lean concrete subbase (LCS)(LCS)
* specification requirement* specification requirementnotnot
design requirementdesign requirement
erosion resistance volumetric stability shear capacity under Base joints water-shedding
ie a mix of ie a mix of methodsmethods and and end productend product spec spec
Subbase
Performance requirementsPerformance requirements Specification requirementsSpecification requirements
Pavement Pavement structurestructure
Lean concrete subbase Lean concrete subbase (LCS)(LCS)
erosion resistance volumetric stability shear capacity under Base joints water-shedding
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
Select material zone(SMZ)
LCS crackingLCS cracking
erosion resistance volumetric stability shear capacity under Base joints water-shedding
strength: 15-20 MPastrength: 15-20 MPa (for erosion resistance) (for erosion resistance)
low shrinkagelow shrinkage very fine cracksvery fine cracks
LCS crackingLCS cracking
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
LCS crackingLCS cracking
3-15 m typ
- R82 criteria- R82 criteria
LCS crackingLCS cracking
3-15 m typTransverse
cracks
- R82 criteria- R82 criteria
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.
LCS crackingLCS cracking
12 m
LCS crackingLCS cracking
3-15 m typTransverse
cracks
- R82 criteria- R82 criteria
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.
LCS crackingLCS cracking
3-15 m typTransverse
cracks
- R82 criteria- R82 criteria
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.
LCS crackingLCS cracking
3-15 m typTransverse
cracks
- R82 criteria- R82 criteria
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.
LCS crackingLCS cracking
3-15 m typTransverse
cracks
- R82 criteria- R82 criteria
nonconforming LCS crackingnonconforming LCS crackingnonconforming LCS crackingnonconforming LCS cracking
LCS crackingLCS cracking
3-15 m typTransverse
cracks
- R82 criteria- R82 criteria
nonconforming LCS crackingnonconforming LCS crackingnonconforming LCS crackingnonconforming LCS cracking
LCS crackingLCS cracking
3-15 m typTransverse
cracks
- R82 criteria- R82 criteria
nonconforming LCS crackingnonconforming LCS crackingnonconforming LCS crackingnonconforming LCS cracking
LCS crackingLCS cracking
3-15 m typTransverse
cracks
- R82 criteria- R82 criteria
nonconforming LCS crackingnonconforming LCS crackingnonconforming LCS crackingnonconforming LCS cracking
LCS crackingLCS cracking
3-15 m typTransverse
cracks
- R82 criteria- R82 criteria
nonconforming LCS crackingnonconforming LCS crackingnonconforming LCS crackingnonconforming LCS cracking
LCS crackingLCS cracking
non-structural layer ?non-structural layer ?
LCS crackingLCS cracking
nonconforming LCS crackingnonconforming LCS crackingnonconforming LCS crackingnonconforming LCS cracking
EndEnd