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Lean concrete subbases Performance requirements under concrete Bases.

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Presentation on theme: "Lean concrete subbases Performance requirements under concrete Bases."— Presentation transcript:

1 Lean concrete subbases Performance requirements under concrete Bases

2 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

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

4 pre -1960s concrete pavements ….

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

6 "a broken stone base course of six (6) inches compacted thickness" Warringah Freeway 1960s MDCS 250 lb/sq in. (1.75 MPa) "...shall include such added quantity of gritty cementitious binder as is necessary..." July 1964 De Leuw Cather & Co July 1964 De Leuw Cather & Co

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

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

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

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

11 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 compressive strength 5 MPa min by 42D compressive strength 5 MPa min by 42D compressive strength 35 MPa min compressive strength 35 MPa min flexural strength 4.5 MPa min flexural strength 4.5 MPa min Performance requirements Specification requirements Pavement structure

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

13 Yass Field Trials - 1994 LCS: typical characteristics

14 Subbase compressive strength (cores & cylinders) Yass Field Trials - 1994 Base Subbase 7 days LCS cf Base concrete

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

16 Typical :160kg90 kg250 kg Typical :160kg90 kg250 kg Lab Trial Mix : 6 MPa min @ 28D 15 MPa max @ 28D 15 MPa max @ 28D RTA specification R82 Beware : cement < 90 kg/m 3 may struggle to achieve 5 MPa in colder climate. SlagNil

17 RTA specification R82 Shrinkage & AEA content

18 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: 5 MPa from 100 mm cores within 42 days; (cylinders not required) (cylinders not required) Flexural: not specified

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

20 Pavement structure LCS Mooney Mooney Bridge

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

22 Photos by Graham Foley Lean concrete subbase Tweed Heads Bypass (~1986) P14 P14

23 Fall line Photos by Graham Foley Fall line P14

24 P14 Photos by Graham Foley

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

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

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

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

29 LCS cracking 3-15 m typ - R82 criteria

30 LCS cracking 3-15 m typ Transverse cracks - R82 criteria 5.1.1Typical Subbase Cracking Lean-mix concrete subbase will typically form full-depth 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. 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.

31 LCS cracking 12 m

32 LCS cracking 3-15 m typ Transverse cracks - R82 criteria 5.1.1Typical Subbase Cracking Lean-mix concrete subbase will typically form full-depth 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. 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. Cracking of this type and extent will not be deemed to be nonconforming unless subsequent deterioration occurs prior to its being covered with base.

33 LCS cracking 3-15 m typ Transverse cracks - R82 criteria 5.1.2Plastic 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.

34 LCS cracking 3-15 m typ Transverse cracks - R82 criteria 5.1.3Additional 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 in any 25m 2 area of subbase exceeds two metres. The Contractor must immediately implement Corrective Action.

35 LCS cracking 3-15 m typ Transverse cracks - R82 criteria nonconforming LCS cracking

36 LCS cracking 3-15 m typ Transverse cracks - R82 criteria nonconforming LCS cracking

37 LCS cracking 3-15 m typ Transverse cracks - R82 criteria nonconforming LCS cracking

38 LCS cracking 3-15 m typ Transverse cracks - R82 criteria nonconforming LCS cracking

39 LCS cracking 3-15 m typ Transverse cracks - R82 criteria nonconforming LCS cracking

40 LCS cracking

41 non-structural layer ?

42 LCS cracking nonconforming LCS cracking End


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