Lean concrete subbases Performance requirements under concrete Bases

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

Terminology lean concrete subbase (LCS) - a pavement layer or lean-mix concrete subbase (LCS) lean-mix concrete (LMC) - a material

pre -1960 s concrete pavements ….

pre -1960 s concrete pavements …. 1960 - 70 s: non-erodable Subgrade subbases

pre -1960 s concrete pavements …. Warringah Freeway 1960 s "a broken stone base course of six (6) inches compacted thickness" July 1964 De Leuw Cather & Co MDCS ≥ 250 lb/sq in. (1. 75 MPa) ". . . shall include such added quantity of gritty cementitious binder as is necessary. . . "

during the 1960 s - 1970 s …. Subbases - non-erodable USA: permeable granular, LCS (econocrete) Europe: bound granular, rolled lean-mix, LCS RTA: since ~1975: LCS or rolled lean-mix

today’s overseas practices …. Asphaltsubbase(USA) LCS Roger Larson FHWA, 1996 now not so popular overseas partly due to variable performance USA visitors noticeably impressed by local LCS we treat it as a structural layer, not merely a mudmat (thanks to Ed Haber et al)

today’s overseas practices …. LCS David Dash & Carlos Kraemer (Spain, 1994) now not so popular overseas partly due to variable performance Carlos Kraemer (1994): Belgian Motorway failure (~100 km, within 12 months of opening) ". . . yours are serious LCS, this was cement bound soil. . . "

typical RTA pavement structure …. Base (250 typ) Lean concretesubbase(LCS) (150 typ) SMZ (300 typ)

Pavement structure Performance requirements main structural layer flexural fatigue joint performance durability of surface texture erosion resistance volumetric stability shear capacity under Base joints water-shedding etc Specification requirements compressive strength 35 MPa min Base flexural strength 4. 5 MPa min Subbase compressive strength 5 MPa min by 42 D Select material zone (SMZ)

Pavement structure LCS Performance requirements Specification requirements Base erosion resistance volumetric stability shear capacity under Base joints water-shedding adequate strength (> 5 MPa) for erosion resistance very fine cracks low shrinkage Subbase Select material zone (SMZ) compressive strength 5 MPa min by 42 D

Yass Field Trials - 1994 LCS: typical characteristics

Base 7 days e as b ub S LCS cf Base concrete Subbase compressive strength (cores & cylinders) Yass Field Trials - 1994

Base Subbase compressive strength (cores & cylinders) Yass Field Trials - 1994

RTA specification R 82 Slag Typical : 160 kg 90 kg 250 kg Nil Lab Trial Mix : 6 MPa min @ 28 D 15 MPa max @ 28 D Beware : cement < 90 kg/m 3 may struggle to achieve 5 MPa in colder climate.

RTA specification R 82 Shrinkage & AEA content

Field controls UCS: 5 MPa from 100 mm cores within 42 days; (cylinders not required) Flexural: not specified Slump: 20 -40 mm for slipformed (± 10) 55 -65 mm for fixed-formed (± 15)

Pavement structure Lean concrete subbase (LCS) Performance requirements Specification requirements Base erosion resistance volumetric stability shear capacity under Base joints water-shedding compressivestrength 15 -20 MPa@ 1 -2 yrs * unworkable in a contract situation * hence, minimum binder levels (90 kg PC, 250 kg total) Subbase Select material zone (SMZ) compressivestrength 5 MPamin by 42 D * specification requirement not design requirement

Pavement structure LCS Mooney. Bridge

Pavement structure LCS Transverse joint LCS hopefully a water-shedding layer Module 1 21

P 14 Lean concretesubbase Photos by Graham Foley Tweed Heads Bypass (~1986)

Fal l lin e Fall line P 14 Photos by Graham Foley

Fal l lin e P 14 Photos by Graham Foley

Pavement structure Lean concrete subbase (LCS) Performance requirements Specification requirements Base erosion resistance volumetric stability shear capacity under Base joints water-shedding compressivestrength 15 -20 MPa@ 1 -2 yrs Subbase Select material zone (SMZ) compressivestrength 5 MPamin by 42 D * specification requirement not design requirement ie a mix of methods and end product spec

Pavement structure Under an AC Base : Lean concrete subbase (LCS) Performance requirements Specification requirements AC erosion resistance volumetric stability shear capacity under Base joints water-shedding Subbase Assumed modulus 10, 000 MPa a bound/stabilised granular is not an equivalent alternative ! (nor is a rolled lean concrete likely to be equivalent)

LCS cracking Base erosion resistance volumetric stability shear capacity under Base joints Subbase water-shedding Select material zone (SMZ) strength: 15 -20 MPa (for erosion resistance) very fine cracks low shrinkage

LCS cracking What’s Good í Narrow (fine) cracks í Strength · 7 - 12 MPa @ 42 days What’s NOT Wide cracks · reduced shear capacity · increased water ingress Strength (in Trial Mix) · < 5 MPa · > 15 MPa Cobblestone or block cracking

LCS cracking - R 82 criteria 3 -15 m typ

LCS cracking 5. 1. 1 - R 82 criteria Typical Subbase Cracking Lean-mix concrete subbase will typically form fulldepth transverse cracks continuous for the full width of the paving run at approximately 3 -15 m centres. In subbase placed in a single pass more than 6 m wide, longitudinal full-depth cracks might also typically occur at spacings of approximately 4 m and in continuous lengths exceeding 4 m. 3 -15 m typ Transverse cracks

LCS cracking 12 m

LCS cracking 5. 1. 1 - R 82 criteria Typical Subbase Cracking Lean-mix concrete subbase will typically form fulldepth transverse cracks continuous for the full width of the paving run at approximately 3 -15 m centres. In subbase placed in a single pass more than 6 m wide, longitudinal full-depth cracks might also typically occur at spacings of approximately 4 m and in continuous lengths exceeding 4 m. 3 -15 m typ Cracking of this type and extent will not be deemed to be nonconforming unless subsequent deterioration occurs prior to its being covered with base. Transverse cracks

LCS cracking 5. 1. 2 - R 82 criteria Plastic Shrinkage Cracks Plastic shrinkage cracks are discrete cracks of length less than 300 mm and a depth less than 50% of the slab thickness which do not intersect a formed edge. No remedial action is required if a bond breaker is applied, but the Contractor must immediately implement Corrective Action. 3 -15 m typ Transverse cracks

LCS cracking 5. 1. 3 - R 82 criteria Additional Longitudinal and Transverse Cracks Subbase cracking other than typical cracking as described in Clauses 5. 1. 1 and 5. 1. 2 is nonconforming if the cumulative length of cracking 2 area of subbase exceeds two metres. in any 25 m The Contractor must immediately implement Corrective Action. 3 -15 m typ Transverse cracks

LCS cracking - R 82 criteria 3 -15 m typ nonconforming LCS cracking Transverse cracks

LCS cracking

non-structural layer ?

LCS cracking nonconforming LCS cracking End