Alternative Testing Strategies for Support of Concrete Pavement Mixture Development Challenges posed in pavement mixture proportioning • Materials concerns Alternative Testing Strategies for Support of Unfamiliar cement sources, blended cements Concrete Pavement Mixture Development Availability and properties of SCMs Multiple admixtures, new products & sources • Sustainability interests & lower clinker content ACI Spring 2014 Convention – Reno, NV Higher cement replacement with SCMs Proportioning of Mixtures for Concrete Pavements session Lower total cementitious content Monday, March 24, 2014 More aggressive admixture use • Impacts that must be accounted for: Tim Cost, P.E., F.ACI Set retardation and lower early strength trends Sr. Technical Service Engineer Greater variability of setting and early strength, Holcim (US) Inc. especially with weather changes 2 Alternative Testing Strategies for Support of Concrete Pavement Mixture Development New challenges for proportioning paving mixtures Testing options for evaluation of materials & proportions • Optimizing early performance is critical for paving Understanding the joint sawing window Concrete batches Avoiding uncontrolled cracking Finish quality and surface durability concerns Lab or plant Paving rate, edge stability Compressive strength cylinders • Dozens of possible Penetrometer time of set combinations – • Challenges: Each materials or Labor and time intensive proportions change Significant equipment & lab has unique effects requirements • How to evaluate, Limited number of batches optimize? possible each day Difficult to simulate job temps 3 4 Alternative Testing Strategies for Support of Concrete Pavement Mixture Development Alternative Testing Strategies for Support of Concrete Pavement Mixture Development 1
Alternative Testing Strategies for Support of Concrete Pavement Mixture Development Testing options for evaluation of materials & proportions Testing options for evaluation of materials & proportions Fluid paste batches Mortar cubes & Vicat & thermal profiles • Modified C109, C191 methods New alternative, paste • Challenges: modeled from concrete mix designs, less aggregates Availability of cement lab & Inexpensive equipment trained technicians Less labor & time required Similar time and labor Dozens of batches possible requirements to concrete each day Limited number of batches Simulating job temps is possible each day relatively simple Not generally possible to include Relative strength & setting w/cm among test variables trends similar to those in Difficult to simulate job temps parallel concrete batches 5 6 Alternative Testing Strategies for Support of Concrete Pavement Mixture Development Alternative Testing Strategies for Support of Concrete Pavement Mixture Development ASTM Standard practice documents under development Equipment used for paste batches and thermal profiles 7 8 Alternative Testing Strategies for Support of Concrete Pavement Mixture Development Alternative Testing Strategies for Support of Concrete Pavement Mixture Development 2
Alternative Testing Strategies for Support of Concrete Pavement Mixture Development Hydration and thermal profile time of set indications Hydration and thermal profile time of set indications The temperature history of the first few hours of hydration The temperature history of the first few hours of hydration (thermal profile) serves as a record of relative C 3 A and C 3 S (thermal profile) serves as a record of relative C 3 A and C 3 S hydration rates and the interaction of CaSO 4 (gypsum). hydration rates and the interaction of CaSO 4 (gypsum). Initial C 3 A Approximate hydration timing of initial set of concrete Dormant period from Main peak interaction rise “M” of CaSO 4 “Main Peak” - with C 3 A C 3 S hydration 0.5 x M “50% fraction” indicator used as a setting time reference 0.2 x M 9 10 Alternative Testing Strategies for Support of Concrete Pavement Mixture Development Alternative Testing Strategies for Support of Concrete Pavement Mixture Development Compressive testing of hardened paste specimens 21% fraction vs. C403 initial set Comparisons for • Essentially via ASTM C39 concrete – time of Neoprene caps set by thermal Sulfur compound methods vs. C403 Machined ends without caps 95% confidence interval limits • Fractions of 21% and 42% have found to be good default values for 42% fraction vs. using thermal testing to C403 final set estimate C403 times (initial and final set) 95% confidence interval limits From: Sandberg and Liberman, “Monitoring and Evaluation of Cement Hydration by Semi-Adiabatic Field Calorimetry,” ACI SP-241-2, American Concrete Institute, 2007. 11 12 Alternative Testing Strategies for Support of Concrete Pavement Mixture Development Alternative Testing Strategies for Support of Concrete Pavement Mixture Development 3
Alternative Testing Strategies for Support of Concrete Pavement Mixture Development Comparison of strength and setting trends, concrete vs. modeled mortar and paste mixtures (example) 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 Six concrete mixtures used for set time comparisons • 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. 13 14 Alternative Testing Strategies for Support of Concrete Pavement Mixture Development Alternative Testing Strategies for Support of Concrete Pavement Mixture Development Laboratory paste testing as a mix development & QC tool Using lab paste mixtures to study concrete setting Set time comparisons: C403 • Evaluation & screening of materials concrete initial set times vs. Cement type & source paste 50% fraction times SCMs & replacement rate Admixtures & dosages • Initial proportioning process Reference paste mixtures modeled from Hydration time, minutes familiar concrete mix designs to establish targets for paste strength & thermal set Thermal profiles with Iterative trials with selected materials to indicated 50% fractions, develop proportions that approximate the lab paste mixtures performance of reference mixtures • Concrete trial batches Paste thermal set trends compared with concrete • Check tests at job temp extremes C403 initial set times 15 16 Alternative Testing Strategies for Support of Concrete Pavement Mixture Development Alternative Testing Strategies for Support of Concrete Pavement Mixture Development 4
Alternative Testing Strategies for Support of Concrete Pavement Mixture Development Example – evaluation / screening of materials Example – evaluation / screening of materials Comparison of WR admixtures in a 30% Class C ash mix Comparison of 7 cements in an aggressive mix design • 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 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 “A/F 1” causes the least retardation, with good early strength influence. 17 18 Alternative Testing Strategies for Support of Concrete Pavement Mixture Development Alternative Testing Strategies for Support of Concrete Pavement Mixture Development Example – mix design development Example – mixture development exercise 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 • 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 Admixture dosages 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 19 20 Alternative Testing Strategies for Support of Concrete Pavement Mixture Development Alternative Testing Strategies for Support of Concrete Pavement Mixture Development 5
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