Estimating In Situ Strength Of Concrete Pavements

1. Report No.FHWA/TX-04/0-1700-14. Title and SubtitleTechnical Report Documentation Page2. Government Accession No.3. Recipient’s Catalog No.ESTIMATING IN SITU STRENGTH OF CONCRETEPAVEMENTS UNDER VARIOUS FIELD CONDITIONS7. Author(s)5. Report DateJune 2001 Rev. August 20036. Performing Organization CodeShantala V. Ramaiah, B. Frank McCullough, Terry Dossey8. Performing Organization Report No.0-1700-110. Work Unit No. (TRAIS)9. Performing Organization Name and AddressCenter for Transportation ResearchThe University of Texas at Austin11. Contract or Grant No.3208 Red River, Suite 2000-1700Austin, TX 78705-265012. Sponsoring Agency Name and Address13. Type of Report and Period CoveredTexas Department of TransportationResearch ReportResearch and Technology Implementation Office(9/1/99—8/31/04)P.O. Box 508014. Sponsoring Agency CodeAustin, TX 78763-508015. Supplementary NotesProject conducted in cooperation with the Texas Department of Transportation and the U.S. Department ofTransportation, Federal Highway Administration.16. AbstractDuring the past few years, the transportation industry has expressed the desire to create performancebased specifications. One of the key developments required to characterize and improve the performance of(PCC) pavements is a better understanding of its in situ properties. Of great importance is the accurateestimation of in situ concrete strength. There are currently many methods used to estimate in situ strength,each providing unique benefits. However, many of these techniques can introduce variables that affectaccurate estimation. Thus, a reevaluation of current procedures is required to appropriately reflect soundengineering principles and to produce a quality product. This project addresses many factors, which arise inpractice, but whose effects on strength need to be determined, quantified, or reevaluated. These include theeffects of core diameter, cylinder curing regime, pavement curing history, presence of reinforcement in acore, vertical location of core, aggregate type, and surface evaporation on both compressive and tensilestrength.This project is different from previous research in that in situ strength is determined directly from tensilestrength test. If pavement strength is to be determined, it is suggested that indirect tensile tests should beconducted rather than estimating tensile strength from compressive or flexural tests, because of the fact thatpavements fail in tension.17. Key Wordsin situ strength, concrete pavements, tensilestrength, compressive tests, flexural tests18. Distribution StatementNo restrictions. This document is available to the publicthrough the National Technical Information Service,Springfield, Virginia 22161.19. Security Classif. (of report) 20. Security Classif. (of this page)21. No. of pages22. PriceUnclassifiedUnclassified186Form DOT F 1700.7 (8-72)Reproduction of completed page authorized

Estimating In Situ Strength of Concrete PavementsUnder Various Field ConditionsShantala V. RamaiahB. Frank McCulloughTerry DosseyResearch Report 0-1700-1Research Project 0-1700Improving Portland Cement Concrete Pavement PerformanceConducted for theTexas Department of Transportationin cooperation with theU.S. Department of TransportationFederal Highway Administrationby theCenter for Transportation ResearchBureau of Engineering ResearchThe University of Texas at AustinJune 2001Revised August 2003

Implementation StatementThe observations and recommendations developed in this report provide excellentadditions to the existing improvement program for (PCC) pavements. An implementation planreflecting this new information is provided in Chapter 9 in terms of specific recommendationsfor continued improvement of high performance concrete (HPCP) pavement concerningdevelopments in specifications, testing, construction, monitoring, design, and conditionevaluation. The objective of this program is to increase pavement life and quality leading topavements that serve for 25 to 40 year on high-volume facilities with minimal maintenance.The reader is referred to Chapter 9 for specific recommendations in five basic areasdiscussed in the following sections.AbstractDuring the past few years, the transportation industry has expressed the desire to createperformance-based specifications. One of the key developments required to characterize andimprove the performance of (PCC) pavements is a better understanding of its in situ properties.Of great importance is the accurate estimation of in situ concrete strength. There are currentlymany methods used to estimate in situ strength, each providing unique benefits. However, manyof these techniques can introduce variables one that affect accurate estimation. Thus, areevaluation of current procedures is required to appropriately reflect sound engineeringprinciples and to produce a quality product. This project addresses many factors which arise inpractice but whose effects on strength need to be determined, quantified, or reevaluated. Theseinclude the effects of core diameter, cylinder curing regime, pavement curing history, presenceof reinforcement in a core, vertical location of core, aggregate type, and surface evaporation onboth compressive and tensile strength.This project is different from previous research in that in situ strength is determineddirectly from tensile strength tests. If pavement strength is to be determined, it is suggested thatindirect tensile tests should be conducted rather than estimating tensile strength fromcompressive or flexural tests, because of the fact that pavements fail in tension.

DisclaimersThe contents of this report reflect the views of the authors, who are responsible for thefacts and the accuracy of the data presented herein. The contents do not necessarily reflect theofficial views or policies of the Federal Highway Administration or the Texas Department ofTransportation (TxDOT). This report does not constitute a standard, specification, or regulation.There was no invention or discovery conceived or first actually reduced to practice in thecourse of or under this contract, including any art, method, process, machine, manufacture,design or composition of matter, or any new and useful improvement thereof, or any variety ofplant, which is or may be patentable under the patent laws of the United States of America or anyforeign country.NOT INTENDED FOR CONSTRUCTION, BIDDING, OR PERMIT PURPOSESB. Frank McCulloughP.E. License: Texas No. 19914Research SupervisorAcknowledgmentsThe authors would like to thank the many engineers, TxDOT staff, and the El PasoDistrict for their input, supply of equipment, testing technicians, mobilization, and execution ofthe project in the El Paso area. Appreciation is also expressed to Jobe Materials whose input,services, construction material contribution, and labor were invaluable to the success of thisproject. Additionally, appreciation is expressed to the research teams of the University of Texasat El Paso, the University of Texas at Houston, and the Texas Transportation Institute fromTexas A&M University for equipment and time contributions involving nondestructive testing(seismic), microwave sensors, and dew point sensors, respectively. Finally, the authors wouldlike to thank CTR employees Tracy Pilson and Dave Merritt, Nancy Kurio, Jerrie England, andJohn Miller for their assistance in this project.Research performed in cooperation with the Texas Department of Transportation and theU.S. Department of Transportation, Federal Highway Administration.

Table of Contents1. INTRODUCTION .11.1 Background.11.1.1 PCCP Developments.11.1.2 Review/Critique of Current Practices .31.1.3 Defining Study Needs .51.1.4 Partnering.61.2 Objectives .61.2.1 Small Slab I Objectives.61.2.2 Small Slab II Objectives .71.3 Scope.71.3.1 Scope of Small Slab I.81.3.2 Scope of Small Slab II .91.4 Report Organization.92. STUDY APPROACH .112.1 Small Slab I Study Approach.112.2 Small Slab II Study Approach .112.3 Data Analysis.133. LITERATURE REVIEW .153.1 Factors Affecting Measurement of Concrete Strength .153.1.1 General Effects of Decreasing Core Diameter.153.1.2 Effects of Reinforcement .213.1.3 Strength Relationships .213.1.4 Maturity.233.1.5 Nondestructive Testing .243.2 Factors Affecting Concrete Strength .253.2.1 Curing Method Effects.253.2.2 Effects of Vertical Location.283.3 Summary of Literature Review.294. EXPERIMENTAL DESIGN .314.1 Background.314.2 Small Slab I Testing Program.314.2.1 Layout .314.2.2 Specimen Details .354.3 Small Slab II Testing Program.374.3.1 Equipment Details.404.3.2 Specimen Details .435. SMALL SLAB I DESTRUCTIVE TEST RESULTS AND ANALYSES .475.1 Core Diameter.475.1.1 Compressive Strength .475.1.2 Tensile Strength .485.2 Cylinder Curing Method.50vii

5.35.45.55.6Strength Relationships .52Reinforcement.57Pavement Surface Treatment .60Vertical Location of Sample in Slab.625.6.1 Original Analysis .635.6.2 Effects of Time Exposed, Evaporation Rate, and Water Loss.645.7 Aggregate Type.675.8 Age.675.9 Summary.676. SMALL SLAB I NONDESTRUCTIVE RESULTS AND ANALYSES .696.1 Nondestructive Determination of Seismic Modulus.696.1.1 Cylinder Curing Method Using Resonant Frequency.696.1.2 Reinforcement.716.1.3 Tining and Elimination of Curing Compound .726.1.4 Vertical Position.746.2 Seismic Test Comparison: Resonant Frequency Versus Portable SeismicPavement Analyzer.756.3 Seismic Modulus versus Mechanical Modulus .776.4 Use of Seismic Modulus for Strength Prediction .797. EXPERIMENTAL TEST RESULTS OF SMALL SLAB STUDY II .877.1 Temperature .877.1.1 Small Slab II Temperature History .877.1.2 Preparatory i-Button Lab Experiments .917.2 Tensile Strength Results .937.3 Aquameter.997.3.1 Small Slab Study II Results .997.3.2 Lab Tests to Determine Aquameter Sensitivity .1017.4 Humidity and Dew Point Sensors.1027.4.1 Preparatory Humidity Sensor Tests .1027.4.2 Small Slab II Humidity Sensor Results .1047.5 Moisture Sensor Comparisons .1058. DISCUSSION .1098.1 Core Diameter.1098.2 Cylinder Curing Method.1098.3 Strength Relationships .1098.4 Reinforcement in Specimens .1108.5 Effects of Curing Regime and/or Surface Finish.1118.5.1 SSII Temperature and Evaporation Effects .1118.5.2 Strength and Tensile Strength Vertical Profile .1118.6 Aggregate Type.1128.7 Age.1138.8 SSI Nondestructive Tests.1138.9 Aquameter.1148.10 Humidity Sensor .1148.11 Moisture Sensor Comparisons .116viii

9. IMPLEMENTATION .1179.1 Effectiveness of Curing Compound and Monomolecular Film.117Specific Recommendations:.1189.2 Testing Techniques for Measuring Concrete Temperature .118Specific Recommendations.1199.3 Estimation of Evaporation .119Specific Recommendations:.1199.4 Opening to Traffic / In Situ Strength Estimation.119Specific Recommendations:.1209.5 Confirmation of NDT Strength Estimations.120Specific Recommendations:.1209.6 Forensics: Coring Strength Tests.1209.7 Aggregate Type.121Specific Recommendations:.12110. CONCLUSIONS .12310.1 Small Slab Study I .12310.1.1 Factors Affecting Mechanical Tests: Core Size and Reinforcement .12310.1.2 Factors Affecting Strength: Curing, Vertical Location, and AggregateType .

strength test. If pavement strength is to be determined, it is suggested that indirect tensile tests should be conducted rather than estimating tensile strength from compressive or flexural tests, because of the fact that pavements fail in tension. 17. Key Words in situ strength, concrete pavements, tensile strength, compressive tests, flexural .