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Quality Control Testing
Mississippi Concrete IndustriesAssociation
Robert Varner, P.E.
Topics For Discussion
Some Basis for Specifications Plastic Concrete Properties and Field
Test Curing & Handling Cylinders ASTM C94 Overview
Specification RequirementsCompressive Strength f’c
General-use concrete:3000 to 5000 psi
High-Strength: 6000to 20,000+ psi
Known relationshipswith other concreteproperties
Specification RequirementsFlexural Strength (MR)
Typical values: 450to 750 psi @ 28days
650 to 750 psicommon forpavements
Normal weightconcreteapproximation: MR= (7.5 to 10) (f’c)0.5
Specification RequirementsMix Proportions
Maximum Water Cement Ratio– Table 9-1, 9-2 Pg 150– Make sure w/c correlates with strength
Minimum Cement– Table 9-7 Pg 156
Specification RequirementsFreshly Mixed Properties
Air Content– Table 8-6 Pg 146
Slump– Table 9-3 Pg 155
Temperature– Maximum Pg 229– Minimum Temperature Table 14-1 Pg 243
Specification RequirementsMaterials Material Requirements
– Cement - ASTM C 150– Fly Ash - ASTM C 618– GGBFS - ASTM C 989– Aggregate - ASTM C 33
Note 2 – Allows the use of state agencygrading requirements.
Specification RequirementsMDOT VS ASTM Fine Agg.Sieve ASTM C33
Percent PassingMDOT
Percent Passing½ inch Na 1003/8 inch 100 97 – 100No. 4 95 – 100 92 – 100No. 8 80 – 100 75 – 100No. 16 50 – 85 45 – 100No. 30 25 – 60 25 – 70No. 50 10 – 30 3 – 35No. 100 2 - 10 0 – 10
Testing Freshly MixedConcrete
Sampling - ASTM C172 Slump - ASTM C143 Temperature - ASTM C1064 Density - ASTM C138 Air Content - ASTM C231/C173 Strength Specimens - ASTM C31
Sampling - ASTM C 172
1 ft3
Composite sample Middle of truck Protect sample
Slump - ASTM C143
Consistency: Theability of freshlymixed concrete toflow as measured inthe slump test.(expressed ininches of slump)
Temperature ASTM C1064• Affects concrete behavior• May be important in trouble-shooting problems• May be a specification issue
Density - ASTM C138 Density (Unit
Weight)– Weight of concrete
divided by a knownvolume.
– Conventional concretehas a unit weight inthe range of 137 to150 pcf Lightweight: 15 pcf Heavyweight: 375 pcf
– Measured primarily tocompute yield
Yield
Yield is the volume of concrete produced in abatch (typically expressed in yd 3)
yield = Batch weights (Cement,FA,CA,H2O)Unit Weight
Air ContentASTM C 173 - ASTM C231 Measures entrained (tiny) and entrapped
(larger) air voids, expressed as a percentageof the total volume of concrete
Entrained: generally 0.0004” to 0.04” Ø Entrapped: 0.04” Ø and up Somewhat a function of aggregate
characteristics– Non-air-entrained concrete w/ 1” coarse
aggregate has about 1-1/2% entrapped air
Volumetric MethodASTM C173
Pressure Method ASTM C231
Strength Specimens
Cylinders– 6 X 12– 4 X 8
Beams– 6 X 6 X 20
Curing Specimens– Standard curing– Field curing
Making & CuringConcrete Test Specimens
ASTM C31 Field
ASTM C192 Lab
Compressive Strength ofCylindrical Specimens
ASTM C39
ASTM C 78Flexural Strength -Third Point Loading
Making & Curing ConcreteTest SpecimensASTM C31 FieldASTM C192 Lab
Standard Curing
Curing procedures required by ASTMC 31 for strength specimens that aremade for:– Acceptance testing
– Checking adequacy of mix proportions– Quality control
Includes 2 curing stages:– Initial curing– Final curing
Initial Curing
Temperature– < 6000 psi – 60 to
80 ° F– ≥ 6000 psi – 68 to
78 ° F Moisture
– Prevent moistureloss
Time– Up to 48 hours
Transportation ofCylinders To Laboratory
Wait 8 hours after final set Protect with suitable cushioning material Protect from freezing Prevent moisture loss Transportation time not to exceed 4 hours
Final Curing
Temperature– 73° ± 3° F
Moisture– Free moisture on
surface at all times
Time– Within 30 minutes
after removing themolds until testing
Field CuringTemperature and moisture conditions as closeas possible to those of the in-place concretefor curing specimens that are made for:
– Strength verification prior to putting the structureor pavement into service
– Comparison with test results of standard curedspecimens or various in-place test methods
– Adequacy of curing and protection of concrete inthe structure
– Strength check for form or shoring removal
ASTM C 94 Overview
The Standard Specification forReady-Mixed Concrete
ASTM C 94: StandardSpecification For Ready-MixedConcrete By reference in project specifications
controls the following:– Materials– Mix-Design Procedures– Batching, Mixing, and Delivery Procedures– Acceptance Criteria– Acceptable Tolerances– Required Quality Control Testing
Sect. 4: Basis of Purchase
Sect. 4.2: Unit Weight C 138– Average of at least 3 measurements– Sample taken from midpoint of 3 different
trucks using C 172
Sect. 5: OrderingInformation
• Sect. 5.1: In the absence of applicablegeneral specifications, the purchaser shallspecify the following: Coarse Aggregate Size Slump Air Content Unit Weight - structural lightweightMix Design Options: A,B,C
Sect. 7.1.1: Slump Tolerances IfSpecified AS Maximum
To Be Used Only If One Addition Of Water IsPermitted
Plus Tolerance:Minus Tolerance:
Specified Slump:If 3 in. If more thanOr less 3 in.
0 01 1/2” 2 1/2”
Sect. 7.1.2: Slump TolerancesIf Not Specified AS Maximum
Tolerances For Normal Slumps
For Specified Slump of:
2 in. and lessMore than 2 through 4 in.More than 4 in.
Tolerance
± 1/2 in.± 1 in.
± 1 1/2 in.
Slump
Sect. 7.2– Producer responsible for slump to be in
tolerance range for a period of 30 min. startingeither on the arrival at the job site or after theinitial slump adjustment permitted in 12.7,whichever is later. Exemptions:
– First and Last 1/4 yd3
Sect. 12.7– Allows for one time addition of water.
Air
Sect. 8– Table 1 - Recommended Total Air
Content– Sect. 7.2: Tolerance of ± 1.5
Discharge of Concrete
Sect. 12.7– Completed within 1 ½ hours– Or before drum has revolved 300
revolutions– Whichever comes first
Sect. 12.8: Minimum ConcreteTemperature As Placed
Section Size, in.
<1212-3636-72>72
Temperature, min F
55504540
Concrete temperature shall not exceed 90F whenusing heated materials.
Required Quality ControlTesting Sect. 17.2 Technician Certification Sect. 17.4 Required Test
– Slump, Air Content, Density, Temperature,Strength
Sect. 17.5 Required Frequency– Strength
one per day per class of concrete or every150 yd3
– Slump, Air Content, Density, Temperature witheach strength test and as necessary for controlchecks .
Strength Criteria ForConcrete Acceptance
Sect. 18.1: Cylinders Made and Cured AccordingTo ASTM C 31
Sect. 18.2: One Test = Two Cylinder Breaks– Can a cylinder be discarded?
Sect. 18.4: Two Requirements For Strength– Average of any three consecutive test f’c
and f’c ≤ 5000 - No test more than 500psi below f ‘c f’c > 5000 – No test less than 0.90 f’c
Required Average CompressiveStrength With Standard DeviationTable X1.1
f’c ≤ 5000 psi– f ‘cr = f ‘c +1.34s– f ‘cr = f ‘c +2.33s-500(psi)
f’c >5000 psi– f’cr = f’c + 1.34s– f’cr = 0.90f’c + 2.33s
– s = Standard Deviation
Required Average CompressiveStrength Without Standard DeviationTable X1.2
Specified Compressive
Strength, f’c (psi)
Less Than 3000
3000 to 5000
Over 5000
Required AverageCompressive Strengthf’c (psi)
f ’c + 1000
f ’c + 1200
1.10f ’c + 700
QC / QA Concepts
Quality Control / Quality Assurance Responsibility to Contractor Performance Based
– Statistical Controlled– Data Comparisons– Pay Reductions
Questions?Mississippi Concrete IndustriesAssociationPhone: (601) 957-5274email:[email protected]: mississippiconcrete.com