Performance Engineered Mixtures Program What A Contractor Needs to Know About the New AASHTO Provisional Guidelines and Suite of Tests

Transcription

1 Performance Engineered Mixtures Program What A Contractor Needs to Know About the New AASHTO Provisional Guidelines and Suite of Tests Dr. Peter Taylor, PE (IL) 1

2 What is it? A program to Understand what makes concrete good Specify the critical properties and test for them Prepare the mixtures to meet those specifications 2

3 Step 1 A better specification Require the things that matter Transport properties (everywhere) Aggregate stability (everywhere) Strength (everywhere) Cold weather resistance (cold locations) Shrinkage (dry locations) Workability (everywhere) 3

4 Transport Properties/Permeability (6.6) Section Property Specified Test Specifed Value Mixture Qualification Acceptance Selection Details Special Notes 6.6 Transport Properties Water to Cement Ratio AASHTO T ~ Yes Yes RCPT Value AASHTO T ~ Yes Yes Other criteria could be selected Formation Factor/Resistivity AASHTO xx or AASHTO yy 500 ~ Yes through ρ * Note this is currently based Choose on saturated Only One curing and an adjustment is needed to match with AASHTO Spec Ionic Penetration, F Factor AASHTO xx or AASHTO yy 25 mm at 30 year Yes, F through ρ

5 Aggregate Stability (6.7) Section Property Specified Test 6.7 Aggregate Stability Specifed Value Mixture Qualification Acceptance Selection Details Special Notes D Cracking AASHTO T 161, ASTM C 1646/666 ~ ~ Yes No Alkali Aggregate Reactivity AASHTO PP 65 ~ ~ Yes No

6 Concrete Strength (6.3) Section Property Specified Test Specifed Value 6.3 Concrete Strength Mixture Qualification Acceptance Selection Details Special Notes Flexural Strength AASHTO T MPa 600 psi Yes Yes Compressive Strength AASHTO T MPa 3500 psi Yes Yes Choose either or both

7 Note 1: Choose Either or Note 2: Choose either , , or Hardened Cement Paste Freeze-Thaw Durability (6.5) Section Property Specified Test Specified Value 6.5 Durability of Hydrated Cement Paste for Freeze-Thaw Durability Mixture Qualification Water to Cement Ratio AASHTO T ~ Yes Yes Fresh Air Content AASHTO T 152, T196, TP to 8 % Yes Yes 4% Air; %, Fresh Air Content/SAM AASHTO T 152, T196, TP 118 Yes Yes SAM 0.2 psi Acceptance Selection Details Choose Either or Choose only one Special Notes Time of Critical Saturation "Bucket Test" Specification 30 Years Yes No Note 1 Note Deicing Salt Damage ~ 35% SCM Yes Yes Variation controlled with mixture proportion observation or F Factor and Porosity Measures Are calcium or magnesium chloride used Deicing Salt Damage ~ ~ ~ Yes Yes Calcium Oxychloride Limit Test sent to AASHTO < 0.15g CaOXY/g paste Yes No Choose one Are calcium or magnesium chloride used, needs a use of specified sealers Are calcium or magnesium chloride used

8 Reducing Unwanted Cracking Due to Shrinkage (6.4) Section Property Specified Test Specifed Value 6.4 Reducing Unwanted Cracking Due to Shrinkage Mixture Qualification Acceptance Selection Details Special Notes Volume of Paste 25% Yes No Unrestrained Volume Change ASTM C µε at 28 day Yes No Unrestrained Volume Change ASTM C , 420, 480 µε at 91 days Yes No Restrained Shrinkage AASHTO T 334 crack free at 180 days Yes No Choose only one Restrained Shrinkage AASHTO T??? σ < 60% f'r at 7 days Yes No Probability of Cracking ~ 5, 20, 50% as specified Yes No

9 Workability (6.8) Section Property Specified Test Specifed Value Mixture Qualification Acceptance Selection Details Special Notes 6.8 Workability Box Test ~ <6.25 mm, < 30% Surf. Void Yes No Modified V-Kelly Test ~ mm per root seconds Yes No

10 Step 2 Better test methods (for those critical properties) VKelly Box Resistivity / Formation factor Sorptivity Dual ring SAM 10

11 VKelly Kelly ball test Developed in the 1950s in US Standardized in California DOT test Comparable to slump test 1.1 to 2.0 times the Kelly ball reading Taylor 11

12 VKelly Measure initial slump (initial penetration) Start vibrator for 36 seconds at 8000 vpm Record depth every 6 seconds Repeat Plot on root time Calculate slope = VKelly Index Taylor 12

13 Box Test A test that examines: Response to vibration Filling ability of the grout (avoid internal voids) Ability of the 12 concrete to hold an edge Ley

14 Box Test Add 9.5 of unconsolidated concrete to the box Insert 1 diameter stinger vibrator (8000 vpm) into the center of the box over a three count and then remove over a three count Ley

15 Box Test The edges of the box are then removed and inspected for honey combing and edge slump Ley Ley

16 Super Air Meter Reports air content and SAM number SAM number correlates well with freeze thaw testing Ley

17 Super Air Meter Ley

18 Formation factor A true measurement of how hard it is for ions to move through concrete. If we can get this information then it will be much easier to predict moisture penetration into concrete and the subsequent long term performance. Weiss

19 How do we get it? The resistivity test gives you a single number that is an indication of a lot of different things - Moisture Temperature Geometry Curing conditions Ionic concentration of the pore solution Formation Factor We can fix all of the other variables but the last two. If we can figure out the chemistry of the pore solution then we can back out the formation factor Weiss

20 Ionic Concentration Three approaches 1. Assume a value 2. Calculate a value based on the cement and SCMs 3. Squeeze out the solution and measure it Weiss

21 The Bucket Test Cast concrete and keep sealed for 14 days Measure the cylinder mass after demolding Place three concrete cylinders in lime water Measure their mass at 5 days Measure their mass again every 10 days until they are 60 days old Oven dry cylinder and take mass Vacuum saturate cylinder and take mass Calculate the time to critical degree of saturation. Weiss

22 Invar ring Dual Ring Test Plan View Concrete Strain gauge This ring can measure both expansion and contraction. As the concrete shrinks the ring can measure the strains that occur. We force a temperature gradient in the concrete and make it crack and compare that to 60% of the split tension capacity after 7 days. Weiss

23 Step 2 QC should include Unit weight Calorimetry Maturity Strength development Air void stability Unit Weight (lb/ ft 3 ) Unit Weight Control Chart Sample ID Unit Weight Target Average Upper Control Limit (3s) Lower Control Limit (-3s)

24 Step 3 Better mixtures Understand effects of materials Aggregate gradation SCMs Admixtures Proportioning tools Void ratio approach Sustainability Give contractor control of things they need 24

25 Step 3 Better mixtures 25

26 Does it Work? West Des Moines spec 5% minimum air behind the paver 0.42 w/cm target 35% fly ash Cracking risk MN recommended 400 pcy cement Blankets 26

27 Workability Microwave w/cm VKelly Index in/ s Higher numbers tied to curb slump Box 0.5 (four sites) to 1.5 (one site)

28 Results Air and Durability Air content % in front of paver All cores: >5.8% SAM/spacing factor variable, likely operator training

29 Air and Durability Freeze/thaw resistance (ASTM C666) Durability factor all above 75%

30 Resistance to Chemical Deicers Soak tests 56 day cure Soak in 4% MgCl2 at 40ºF High FA (MQMC) DOT (QMC) 30

31 Permeability Resistivity of Core Samples:

32 Permeability Drop test 28-day WDM results:

33 What next? Understanding and education Validate tests New tests Parallel testing Pilot projects Pooled fund to pay for it 33

34 What do we get? Concrete that delivers what is needed Efficiently w.r.t. Cost Environmental impact Reliably Quality 34