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Paving operations

Forming time & retempering under RMS R83 & R82

Geoff AytonSupervising Pavement Engineer (Rigid)Engineering Technology Services BranchRoads & Maritime Services24 February 2014

the issue

how old will this concrete be when it goes under the paver ?how old is "too old" ?

the issue

AS 1379

!?

ie. retempering is acceptable up to 90 mins

forming time

R83 Ed2 Rev8

Systematic consideration of: • mix characteristics & admixtures• weather conditions• your paving equipment etc

Mark Elliott - ex Abigroup (circa 1992)Mark Elliott - ex Abigroup (circa 1992)

Systematic consideration of: • mix characteristics & admixtures• weather conditions• your paving equipment etc

Charging

Mixing

"Batching""Batching""Batching"

Slump adjustment

10 mins max10 mins max "Completion of Batching""Completion of Batching""Completion of Batching"

Haul

Retemper& remix

SlumpSpread, compact& form

Finish, texture & cureFinish, texture & cure

Contractor to nominate& monitor under Cl 4.2.2 Contractor to Contractor to nominatenominate&& monitor undermonitor under Cl 4.2.2 Cl 4.2.2

"Forming Time""Forming Time""Forming Time"

(maybe)

Charging

Mixing

"Batching""Batching""Batching"

Slump adjustment

10 mins max10 mins max "Completion of Batching""Completion of Batching""Completion of Batching"

Haul

Retemper& remix



"Forming Time""Forming Time""Forming Time"Contractor to nominate& monitor under Cl 4.2.2 Contractor to Contractor to nominatenominate&& monitor undermonitor under Cl 4.2.2 Cl 4.2.2

R83 Ed2 Rev8

forming time

forming time

Cl A4.2(c):The Contractor’s production and transport must .... :

(c) result in workability, at the time of incorporation,which is compatible with the capacity of the pavingequipment to achieve the specified compaction andsurface finish requiring only nominal manualfinishing.”

CRCP Overlay(North of Holbrook)

~2 hours old, but still OK~2 hours old, but still OK

forming time

• mix characteristics (set retardation etc)• season & weather conditions• slipforming vs hand-forming• paver mass• vibrator intensity

Relevant factors:

CRCP Overlay(North of Holbrook)

~2 hours old, but still OK~2 hours old, but still OK

R83 Ed2 Rev8

forming time

.... but no mention of maximum forming time

R83

z

.... but where is the procedure ?

(from a Paving Management Plan on a recent project)

.... but no mention of maximum forming time

.... again no mention of maximum forming time

but a fixed forming time is nonconforming under R83 !!

xxxxx ....

2 paragraphs later ....

from another project < 2 years ago ...

R83

• all determined long before they even began paving ....• not consistent with the intent ....

Project Quality Plan

R83

AS 1379Alternatively ...

Retempering under RMS R83 & R82

- prompted by an RMS Senior Project Manager- apologies to Grey Card holders

R83 industry review

Lack of understanding:w/c basicsR83 intent

Charging

Mixing

"Batching""Batching"

Slump adjustment

10 mins max "Completion of Batching""Completion of Batching"

Slump adjustment

Haul

Retemper& remix



40 mins max40 mins max

(maybe)(maybe)

(for the purpose of"age of batch")

(for the purpose of"age of batch")

Time 0Time 0

50 mins max

w/c ratio

Mix 1

Is slump a reasonable indicator of w/c ?

(for a given temperature etc)

0.3 0.4 0.5 0.6

Slump(mm)

6060

100100

8080

4040

Mix 3

Mix 2

for a specific mix: Yes(all other factors being equal)

Slump(mm)

Time (mins)

6060

100100

8080

4040

00 2020 4040 6060 8080 100100 120120

Mix A

Mix B

Mix C

90

Mix variations

(for example)

Slump(mm)

Time (mins)

6060

100100

8080

4040

00 2020 4040 6060 8080 100100 12012090

Mix variations

autumn

wintersummer

- season / temperature

(for example)

Mix B

Slump(mm)

Time (mins)

6060

100100

8080

4040

00 2020 4040 6060 8080 100100 12012090

Mix variations

autumn

wintersummer

- season / temperature

(for example)

Mix B

butfor a specific mixunder uniform conditions ....slump is a useful indicator of

* age and/or* w/c ratio

Cement hydration with time

crystalline "velcro" growthCement grains ~~ Velcro tennis balls

(Human hair ~100 um)??


crystalline "velcro" growthCement grains ~~ Velcro tennis balls

??

Higher w/c ratio :greater spacing between velcro ballslower velcro densityslower strength gainlower ultimate strength


Source: CCAA

~~

Time

SlumpSlump

40 mins

nonconformingretempering

slumpadjustment

60mm60mm

Dormant period Dormant period

0

" Completion of batching”" Completion of batching”

absorption and/or

evaporation

absorptionand/or

evaporation+ hydration+ hydration

10 mins

Conditions !Conditions !

normal temperature conditions (both air~ & concrete~)normal temperature conditions (both air~ & concrete~)

Ordinary Portland cement (OPC, ie not HES cement)Ordinary Portland cement (OPC, ie not HES cement)

no accelerators (such as CaClno accelerators (such as CaCl22))

no highno high--range water reducers (at this stage)range water reducers (at this stage)


water/cement ratio

• Aggregates @ SSD (saturated surface dry)

The trial mixThe trial mix

water/cement ratio (w/c):

60 mmslump

(say)

400400 kg PCkg PC= 0.5= 0.5200200 kg kg HH22OOegeg

• the absorbed water doesn’t count in the w/c ratioso SSD is the assumed default condition for all aggregates

Quick quizz: is the absorbed water counted ?

The trial mixThe trial mix 400400 kg PCkg PC= 0.5= 0.5200200 kg kg HH22OOegeg

water/cement ratio

• Aggregates @ SSD (saturated surface dry)

• the absorbed water doesn’t count in the w/c ratioso SSD is the assumed default condition for all aggregates

Time

Slump

40 mins

nonconformingretempering

slumpadjustment

60mm60mm

Dormant period Dormant period

0

absorption and/or

evaporation

absorptionand/or

evaporation+ hydration

Water/cement & Slump

under RMS specs R82, R83, R84under RMS specs R82, R83, R84and AS 1379and AS 1379

Time

Slump

Slump adjustment & retempering

0

N N ±± 15 mm15 mm

“Completion of batching”“Completion of batching”

N mmN mm 60 60 ±± 15 mm15 mm

N = nominated slumpN = nominated slump

7575

4545

60mm60mmconformance windowconformance window

40 mins

(under RMS specs R82, R83, R84)(under RMS specs R82, R83, R84)

Slump

60mm60mm

0

workability limitworkability limit

"Forming"FormingTime"Time"

((R83 Cl 4.2.2)R83 Cl 4.2.2)

7575

4545



80 mins (say)

(1) Quality of concrete(as supplied)

(2) Quality of construction

40 mins

30


Slump

60mm60mm

0

workability limitworkability limit

"Forming"FormingTime"Time"

((R83 Cl 4.2.2)R83 Cl 4.2.2)

7575

4545



80 mins (say)

(1) Quality of concrete(as supplied)

(2) Quality of construction

40 mins

R83 industry review

10 mins


Slump

60mm60mm

0 "Forming"FormingTime"Time"

((R83 Cl 4.2.2)R83 Cl 4.2.2)

7575

4545



40 mins10 mins

absorption absorption (?)(?)

hydration hydration (?)(?)

??

Time

Slump

0


7575

4545

60mm60mm

20

4040

Case study 1Case study 1

5555

identical mix, inclidentical mix, incl

same same added wateradded water

wet aggregateswet aggregates

ovenoven--dry aggregatesdry aggregates

except :except :

??

40 mins

7575

4545

Slump

60mm60mm

0

Case study 2Case study 2aa

8585

conformingconforming


Time

acceptable ?acceptable ?

suggests a mixing problemsuggests a mixing problem

40 mins

(as long as the load has been agitated or re-mixed)

7575

4545

Slump

60mm60mm

0

Case study 3


Time

??

20

4040

??

OK to retemper (on conditions)must re-check slumpsuggests a mixing problem(Wodonga Place, Albury. 1990s)

OK to retemper (on conditions)must re-check slumpsuggests a mixing problem(Wodonga Place, Albury. 1990s)

(after partial(after partialdischarge)discharge)

Becomes unworkable afterpartial discharge.

40

What if you were controlling by w/c ratio ?


100

150

Supe

rplas

ticise

r

40

100

Are these "similar" mixes ?

If you don't test initial slump (pre-HRWR*), how will you know what you've got ?

* HRWR:High range water reducer(superplasticiser)

End product vs method

(with a questionable response)

Beware the unconscious ignorant !!Beware the unconscious ignorant !!

End product vs method

"... a young contractor's interpretation of R83 was basically that Clause 5 (End Product Criteria) is all that 'really matters' and that if these requirements are met, any other non conformances don't justify NCRs."

My response:What about all the missing "End product criteria" for properties like:• mixing uniformity in the pavement (?)• uniform compaction throughout a Lot (?)• w/c ratio in the finished pavement (?)

Following a project audit:


Slump

60mm60mm

0

7575

4545



40 mins

absorption absorption (?)(?)

hydration hydration (?)(?)

??

80 mins

End product assessment ?

My conclusions:

control of batching & supply

control of slump & retempering

control of Forming Time

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