Draft PEM Specification The What s and How s. Peter Taylor and Tom Van Dam

Transcription

1 Draft PEM Specification The What s and How s Peter Taylor and Tom Van Dam 1

2 What Do We Want? Adequate strength Low risk of restrained shrinkage cracking Durable F-T Deicers Aggregate Impermeable Workable 2

3 What Do We Want? Batch to batch consistency Workability Durability Strength The question is not so much what we want, but how do we know we are getting it? During construction As basis for payment

4 But I have been doing it this way for 30 years

5 How Do We Get What We Want? Prescriptive approach Provide a recipe that should achieve the goal Performance approach Set the goal and verify that it is met

6 Property Prescriptive approach Performance approach Adequate Cementitious type and Flexural and compressive Strength content, w/cm strength Cracking Risk Paste content, SRA Unrestrained shrinkage Restrained shrinkage F-T Durability Total air, air-void system, w/cm, SAM F-T testing (ASTM C666 and C672) Resistance to Chemical Deicers SCM type and content, w/cm Low temperature differential scanning calorimetry (LT-DSC) Durable Aggregate Impermeable Workable Pre-qualify source (PP65, IA Pore index, ASTM C666) SCM type and content, w/cm Job mixture (PP65, IA Pore index, ASTM C666) Resistivity testing Formation factor Box test, Vkelly applied during mixture design and during construction

7 Prescriptive Approach Adequate Strength Flexural strength (ASTM C78) at 28 days Compressive strength (ASTM C39) at 28 days What is adequate? Can it be too high? Is consistency more important than strength?

8 Prescriptive Approach Reduced Cracking Risk Minimize paste volume Enough to fill voids and then a bit more Typically 23 to 27 percent Test using unrestrained shrinkage (ASTM C157) Maximum ultimate shrinkage of 450 με How is this assessed?

9 Prescriptive Approach Reduced Cracking Risk Combined aggregate gradation Use of Tarantula Curve will minimize paste volume while reducing risk of poor workability

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11 Prescriptive Approach Paste Freeze-Thaw Durability Specify air content based on exposure and paste volume Typically between 5 and 8 percent Use Super Air Meter (SAM) 0.2 Minimum Minimize loss of air through paver Less than 3 percent

12 SAM

13 Prescriptive Approach Resistance to Chemical Deicers Specify air content for severe environment Maximum w/cm 0.40 to 0.42 Use SCMs Class F fly ash (maximum 25 percent) Class C fly ash (maximum 35 percent) Slag cement (maximum 50 percent) Interground limestone Maximum 15 percent Maximum total binder replacement 50 percent

14 Increase saturation Salts

15 Typical Symptoms Shadowing Thin flakes

16 Chemical Deicer Attack Magnesium and calcium chloride Calcium oxychloride formation Causes paste to expand / separate from aggregate

17 Prescriptive Approach - Impermeability Maximum w/cm of 0.40 to 0.42 Use SCMs Class F fly ash (maximum 25 percent) Class C fly ash (maximum 35 percent) Slag cement (maximum 50 percent) Interground limestone Maximum 15 percent Maximum total binder replacement 50 percent

18 Prescriptive Approach Durable Aggregate F-T durability Pre-qualification using ASTM C666, Iowa pore index ASR resistance Prescriptive measures as provided in AASHTO PP 65 Based on mortar bar testing (ASTM C1260), level of risk, and level of required prevention Mitigation strategies often involve SCMs

19 Prescriptive Approach - Workability Slump 1 inch minimum w/o WRA Box Test Edge slump less than 0.25 inch Less than 30 percent surface voids Vkelly 0.8 inch/ s, minimum

20 Box Test Surface Voids

21 Vkelly Results

22 Performance Approach - Strength Similar to prescriptive approach Flexural and compressive strength

23 Performance Approach Reduced Cracking Risk Restrained shrinkage ring testing (ASTM C1581) Crack-free at 14 days Applied during mixture design phase How is this monitored during construction phase?

24 ASTM C1581

25 Performance Approach Paste Freeze-Thaw Durability Same as prescriptive for total air content and SAM Conduct ASTM C666 on proposed job mixture? RDM 80 percent, minimum Conduct ASTM C457? Spacing factor inch, maximum

26 Air-Void System Analysis

27 Performance Approach Resistance to Chemical Deicers Low-temperature differential scanning calorimetry (LT-DSC) No peak at 50 C Peak is indicative of calcium oxychloride formation Still under development

28 Performance Approach - Impermeability Electrical resistivity AASHTO TP kω-cm at 28 days Formation factor Under development Allows for normalization of various test methods Different electrical loading Different specimen geometry

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30 Performance Approach Durable Aggregate F-T durability Test proposed aggregates using ASTM C666, Iowa pore index or hydraulic fracture during production? ASR resistance Performance measures as provided in AASHTO PP 65 Must have concrete prism test results

31 Performance Approach - Workability Same as prescriptive approach Slump 1 inch minimum w/o WRA Box Test Edge slump less than 0.25 inch Less than 30 percent surface voids Vkelly 0.8 inch/ s, minimum

32 Other Test Methods Calorimetry tells us about the chemistry of the system (Uniformity) Hydration Profile Sample "5P" Sample "5C" Sample "5F" Sample "5S" 9.00 J/gh :00:00 6:00:00 12:00:00 18:00:00 24:00:00 Time of Hydration (hrs)

33 Other Test Methods Unit weight something is wrong

34 Other Test Methods Ultrasonic Pulse Velocity (UPV) Setting and therefore sawing time

35 Other Test Methods Ultrasonic Pulse Velocity (UPV) Setting and therefore sawing time Saw time, minutes IA Early Entry Saw Conventional Saw y = x R² = y = x R² = LATE MN Early UPV Initial Set, minutes

36 Other Test Methods Maturity strength development up to 24 hours

37 Other Test Methods Embedded Sensors Slowik Movement Temperature Moisture Chemicals Ceylan

38 Discussion