[PPT] - Alternative Testing Strategies for Support of Concrete Pavement PowerPoint Presentation

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Alternative Testing Strategies for Support of Concrete Pavement Mixture Development

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Alternative Testing Strategies for Support of Concrete Pavement Mixture Development

ACI Spring 2014 Convention – Reno, NV

Proportioning of Mixtures for Concrete Pavements session Monday, March 24, 2014

Tim Cost, P.E., F.ACI

Sr. Technical Service Engineer

Holcim (US) Inc.

Alternative Testing Strategies for Support of Concrete Pavement Mixture Development

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Challenges posed in pavement mixture proportioning

Materials concerns

 Unfamiliar cement sources, blended cements  Availability and properties of SCMs  Multiple admixtures, new products & sources

Sustainability interests & lower clinker content

 Higher cement replacement with SCMs  Lower total cementitious content  More aggressive admixture use

Impacts that must be accounted for:

 Set retardation and lower early strength trends  Greater variability of setting and early strength,

especially with weather changes

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New challenges for proportioning paving mixtures

Optimizing early performance is critical for paving

 Understanding the joint sawing window  Avoiding uncontrolled cracking  Finish quality and surface durability concerns  Paving rate, edge stability

Dozens of possible

combinations –

 Each materials or

proportions change has unique effects

How to evaluate,
ptimize?

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Testing options for evaluation of materials & proportions

Concrete batches

 Lab or plant  Compressive strength cylinders  Penetrometer time of set

Challenges:

 Labor and time intensive  Significant equipment & lab

requirements

 Limited number of batches

possible each day

 Difficult to simulate job temps

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Testing options for evaluation of materials & proportions

Mortar cubes & Vicat

Modified C109, C191 methods
Challenges:

 Availability of cement lab &

trained technicians

 Similar time and labor

requirements to concrete

 Limited number of batches

possible each day

 Not generally possible to include

w/cm among test variables

 Difficult to simulate job temps

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Testing options for evaluation of materials & proportions

Fluid paste batches & thermal profiles

 New alternative, paste

modeled from concrete mix designs, less aggregates

 Inexpensive equipment  Less labor & time required  Dozens of batches possible

each day

 Simulating job temps is

relatively simple

 Relative strength & setting

trends similar to those in parallel concrete batches

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Equipment used for paste batches and thermal profiles

Alternative Testing Strategies for Support of Concrete Pavement Mixture Development

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ASTM Standard practice documents under development

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Hydration and thermal profile time of set indications The temperature history of the first few hours of hydration (thermal profile) serves as a record of relative C3A and C3S hydration rates and the interaction of CaSO4 (gypsum).

Initial C3A hydration Dormant period from interaction

f CaSO4

with C3A “Main Peak” - C3S hydration

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Hydration and thermal profile time of set indications The temperature history of the first few hours of hydration (thermal profile) serves as a record of relative C3A and C3S hydration rates and the interaction of CaSO4 (gypsum).

Approximate timing of initial set of concrete “50% fraction” indicator used as a setting time reference

Main peak rise “M” 0.5 x M 0.2 x M

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Comparisons for concrete – time of set by thermal methods vs. C403

Fractions of 21% and

42% have found to be good default values for using thermal testing to estimate C403 times (initial and final set)

42% fraction vs. C403 final set 21% fraction vs. C403 initial set

From: Sandberg and Liberman, “Monitoring and Evaluation of Cement Hydration by Semi-Adiabatic Field Calorimetry,” ACI SP-241-2, American Concrete Institute, 2007.

95% confidence interval limits 95% confidence interval limits

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Compressive testing of hardened paste specimens

Essentially via ASTM C39

 Neoprene caps  Sulfur compound  Machined ends without caps

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Comparison of strength and setting trends, concrete

vs. modeled mortar and paste mixtures (example)
All mixtures using identical

dosages of 3 admixtures, comparing trends of:

 Type I/II OPC vs. Type IL PLC

cements (from the same plant)

 Control mix without SCMs vs.

a mix with 40% Class C ash replacement of cement “Thermal set” values are 50% fraction times derived from thermal profile data using a spreadsheet.

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Six concrete mixtures used for set time comparisons

Using lab paste mixtures to study concrete setting

Paste proportions identical to concrete mix designs, without aggregates
Example uses 50% fraction thermal set indications of paste

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Thermal profiles with indicated 50% fractions, lab paste mixtures

Set time comparisons: C403 concrete initial set times vs. paste 50% fraction times

Hydration time, minutes

Paste thermal set trends compared with concrete C403 initial set times

Using lab paste mixtures to study concrete setting

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Laboratory paste testing as a mix development & QC tool

Evaluation & screening of materials

 Cement type & source  SCMs & replacement rate  Admixtures & dosages

Initial proportioning process

 Reference paste mixtures modeled from

familiar concrete mix designs to establish targets for paste strength & thermal set

 Iterative trials with selected materials to

develop proportions that approximate the performance of reference mixtures

Concrete trial batches
Check tests at job temp extremes

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Comparison of WR admixtures in a 30% Class C ash mix

5 different WR admixtures (2 Type A/D, 2 Type A/F, 1 MR)
Dosages selected for approx. 6% water reduction
A single Type II cement sample, w/cm = 0.40
Paste mixtures @ 70°F mix and cure temps

“A/F 1” causes the least retardation, with good early strength influence. Example – evaluation / screening of materials

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Comparison of 7 cements in an aggressive mix design

Otherwise identical paste mixtures comparing 7 cements, with 25% Class C fly ash, upper-limit dose of Type A/D WR, and 35ºC (95ºF) mix and cure temps Example – evaluation / screening of materials

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Example – mixture development exercise

Challenge / objective: develop a concrete mixture for a

paving project with unfamiliar materials that achieves at least 50% replacement of cement, with acceptable setting and early strength for constructability

Job temps expected to range from 70ºF to 95ºF during

construction

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Performance of traditional low-SCM mixtures

“Reference” mixtures to establish performance targets for mix development
15% C ash, 15% F ash, 30% slag cement with mild WR dosages
For these examples, criteria to be based on these mixtures (green bands), 50%

fraction thermal set indications and 1-day strengths in bar charts

mL/kg mL/100kg L/100kg fl oz/cwt 2.0 195 0.20 3 2.6 260 0.26 4 3.3 325 0.33 5 6.5 650 0.65 10 9.1 910 0.91 14 11.7 1170 1.17 18 13.0 1300 1.30 20 19.5 1950 1.95 30 26.0 2600 2.60 40

Admixture dosages

Example – mix design development

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Effects of increasing SCM replacement rate to 50%

Same temps & admix dosages, with the addition of an F ash mix w/ A/F WR
Set time with F ash and A/D WR driven by admix
Good set performance with slag and F ash + A/F
C ash set time goes quite long (indication of potential issues)
All 1-day strengths now unacceptable

mL/kg mL/100kg L/100kg fl oz/cwt 2.0 195 0.20 3 2.6 260 0.26 4 3.3 325 0.33 5 6.5 650 0.65 10 9.1 910 0.91 14 11.7 1170 1.17 18 13.0 1300 1.30 20 19.5 1950 1.95 30 26.0 2600 2.60 40

Admixture dosages

Example – mix design development

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Effects of lower w/cm using HRWR dosages

Lower w/cm needed to restore early strengths, A/F WR dose increased
All 1-day strengths now marginally acceptable, slag mix healthiest
60% replacement mix with slag added, still acceptable strength
All set times now unacceptable, need help from accelerators (esp. C ash)

mL/kg mL/100kg L/100kg fl oz/cwt 2.0 195 0.20 3 2.6 260 0.26 4 3.3 325 0.33 5 6.5 650 0.65 10 9.1 910 0.91 14 11.7 1170 1.17 18 13.0 1300 1.30 20 19.5 1950 1.95 30 26.0 2600 2.60 40

Admixture dosages

Example – mix design development

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Compensating for delayed set with accelerating admix

All mixtures repeated with varying &

incremental dosages of non-chloride accelerator (NCA)

Moderate dosages restore

acceptable set for F ash and slag

NCA less effective with C ash and

seems to create sulfate balance issues (incompatibility) at higher dosages (in pursuit of restored set)

1-day strengths benefit from NCA

mL/kg mL/100kg L/100kg fl oz/cwt 2.0 195 0.20 3 2.6 260 0.26 4 3.3 325 0.33 5 6.5 650 0.65 10 9.1 910 0.91 14 11.7 1170 1.17 18 13.0 1300 1.30 20 19.5 1950 1.95 30 26.0 2600 2.60 40

Admixture dosages

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Sulfate balance evaluation of the C ash mix

An affected mixture using NCA repeated with incremental CaSO4 additions
Profile shapes and 1-day strengths improve with additions, but not set time
Confirms sulfate balance issues

 C ash not considered a candidate for 50% replacement mix design  Lower replacement mix could be developed mL/kg mL/100kg L/100kg fl oz/cwt 2.0 195 0.20 3 2.6 260 0.26 4 3.3 325 0.33 5 6.5 650 0.65 10 9.1 910 0.91 14 11.7 1170 1.17 18 13.0 1300 1.30 20 19.5 1950 1.95 30 26.0 2600 2.60 40 Admixture dosages

Example – mix design development

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Verification of proportions at extreme field temps

F ash and slag mixtures with same A/F dose & max NCA dose repeated at

highest envisioned concrete field temps: 36ºC (96ºF) mix and cure temps

No sulfate balance issues indicated; NCA dosages could be reduced
OK to proceed to trial concrete mixtures

mL/kg mL/100kg L/100kg fl oz/cwt 2.0 195 0.20 3 2.6 260 0.26 4 3.3 325 0.33 5 6.5 650 0.65 10 9.1 910 0.91 14 11.7 1170 1.17 18 13.0 1300 1.30 20 19.5 1950 1.95 30 26.0 2600 2.60 40

Admixture dosages

Example – mix design development

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Summary / conclusions for this set of materials:

F ash or slag cement sources OK for 50% replacement

with these materials (possibly higher for slag)

C ash source should not be used at 50% with these

materials, lower replacement mix could be developed

W/cm at 0.32 should produce acceptable early strengths
Mild NCA dosage should restore acceptable set
Proportions (F ash & slag) OK for sulfate balance to 36ºC

(96ºF) in the field

Next step – trial concrete mixtures, refinements of

proportions

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Weather (temp) influences on incompatibility potential

4 paste mixtures compared at 70°F and 93°F mix/cure temps:

100% OPC, no WR, w’c = 0.45
25% C ash, no WR w/cm = 0.45
25% C ash, 4 oz/cwt WR, w/cm = 0.40
25% C ash, 6 oz/cwt WR, w/cm = 0.40

Type A/D recommended dosage range: 3-6 oz/cwt Note that with these materials and proportions, higher temps alone drive incompatible behavior in the mixtures with WRA.

Example – temperature effects

Questions?

Tim Cost, P.E., F.ACI Holcim (US) Inc. tim.cost@holcim.com