Non-Destructive In Situ Strength Assessment of Concrete: Practical Application of the RILEM TC 249-ISC Recommendations (RILEM State-of-the-Art Reports, 32)

The book presents the work of the RILEM Technical Committee 249-ISC. Addressing the effective application of new recommendations for non-destructive in situ strength assessment of concrete, it provides information about the different steps of the investigation and processing of test results, until the delivery of strength estimates, and includes tables giving the minimum required number of cores in a variety of situations as well as several examples of how the recommendations can be used in practice. The book explores a topic which is of major importance, i.e. the assessment of concrete compressive strength in existing structures. This property (both mean and standard deviation) is a key input in many cases, such as the reinforcement of structures, the safety checking, the extension of service life. As the new RILEM recommendations imply a deep revision (and improvement) of field practice, the book is intended for managers of structures, structural engineers and specialists of NDT that have to answer these issues. More widely, it will benefit engineers and students who are interested in NDT and in the safety analysis of structures. RILEM Members Preface RILEM Publications RILEM Proceedings (PRO) RILEM Reports (REP) Contents Contributors Part ITheory 1 In-Situ Strength Assessment of Concrete: Detailed Guidelines 1.1 Scope 1.2 Preliminary Considerations 1.2.1 Context and Objective of the Investigation 1.2.2 Details of the Structure to Investigate 1.2.3 Constraints of the Investigation 1.2.4 Investigation as Part of a Wider Evaluation Program 1.3 Planning of the Investigation 1.3.1 Methods 1.3.2 Preliminary Recommendations Before Performing the Tests 1.3.3 Methodology for Determining the Locations and Number of NDT Locations 1.4 Cores 1.4.1 Location of Cores 1.4.2 Number of Cores 1.4.3 Dimensions 1.4.4 Extraction, Conservation and Preparation of Cores 1.4.5 Core Testing (Mechanical Testing, NDT) 1.5 Identification of the Conversion Model 1.5.1 Main Steps and Principles 1.5.2 NDT Test Result Precision 1.5.3 Data Processing: The Case of Outliers 1.5.4 Types of Conversion Models 1.5.5 Model Identification Approach 1.5.6 Using the Conversion Model and Quantifying Its Error 1.6 Overall Assessment Methodology and Recommended Number of Cores 1.6.1 Organization of the Evaluation Approach 1.6.2 Recommended Number of Cores References 2 How to Identify the Recommended Number of Cores? 2.1 Introduction 2.2 Theoretical Principles—Strength Assessment Precision and Risk Curves 2.2.1 Considering Risk in Non-destructive Concrete Strength Assessment 2.2.2 Risk of a Wrong Estimation 2.2.3 Most Influencing Factors 2.2.4 Risk Curves 2.2.5 Multi-objective Risk Curves and Recommended Number of Cores 2.3 How Risk Curves Are Built 2.3.1 The Principles of Synthetic Simulations 2.3.2 Application Domain and Assumptions 2.3.3 Illustration of Risk Curves in a Specific Case and Illustration of the Influencing Factors 2.3.4 From Risk Curves to Recommended Number of Cores 2.4 Modeling Risk Curves and Deriving the Required Number of Cores 2.4.1 Modelling Risk Curves 2.4.2 Identification and Validation of Risk Models 2.4.3 Analysis of the Risk Models and of Their Influencing Factors 2.4.4 Identification of the Required Number of Cores 2.5 Recommendations Regarding the Prescribed Minimum Number of Cores 2.5.1 Preliminary Statements 2.5.2 Illustrating the Effect of EQL and TRP 2.5.3 Influence of How the Targets Are Expressed 2.5.4 How Are the Tables Giving the Minimum Number of Cores Organized and How Can They Be Used? 2.6 Tables Providing the Recommended Minimum Number of Cores References 3 Evaluation of Concrete Strength by Combined NDT Techniques: Practice, Possibilities and Recommendations 3.1 Introduction 3.2 How Variations of the Concrete Properties Influence the NDT Measurements 3.3 How to Combine NDT Measurements 3.3.1 Multiple Regression Methods 3.3.2 Artificial Neural Networks 3.3.3 Data Fusion 3.4 Applying the RILEM TC 249-ISC Recommendations and Combining Several NDT 3.5 Conclusion References 4 Identification of Test Regions and Choice of Conversion Models 4.1 Introduction 4.2 Identification of TR 4.2.1 TR Identification in a Continuous Structure 4.2.2 TR Identification in a Real Case Study Building 4.2.3 Conclusions 4.3 Choice of Conversion Models 4.3.1 Description of the Process 4.3.2 Example of Application on Three Case Studies 4.3.3 Conclusions References 5 Identification and Processing of Outliers 5.1 Context and Principles 5.2 Outlier Identification 5.2.1 General Considerations and Methods 5.2.2 Identification of Candidate Outliers for Univariate Data Sets (Situation A) 5.2.3 Identification of Candidate Outliers for Bivariate Data Sets (Situation B) 5.3 Dealing with Outliers 5.3.1 General Considerations 5.3.2 Outlier Accommodation Techniques for Univariate Data Sets (Situation A) 5.3.3 Outlier Accommodation Techniques for Bivariate Data Sets (Situation B) References Part IIApplications 6 How Investigators Can Assess Concrete Strength with On-site Non-destructive Tests and Lessons to Draw from a Benchmark 6.1 Introduction 6.1.1 Original Idea of Benchmark and Methodology 6.1.2 Synthetic Simulations for Assessing Strategies 6.2 Presentation of the Benchmark: Case Study and Rules to Be Applied 6.2.1 Case Study 6.2.2 Resources and Cost 6.2.3 Resources Available 6.2.4 Cores and Conservation 6.2.5 What is Expected from Each Benchmark Participant 6.3 Generation of Synthetic Data 6.3.1 How Simulation Works 6.3.2 Analysis of Synthetic Data 6.3.3 How to Model the Assessment Methodology 6.4 Feedback from the Benchmark Contributions—Defining Strategies 6.4.1 Participants 6.4.2 Analysis and Modelling of the Investigation Strategies 6.4.3 Short Note About Precision and Representativeness of Test Results 6.5 Feedback from the Benchmark Contributions—Deriving Strength Estimates 6.5.1 Approaches Using a Prior Model Without Calibration 6.5.2 Approaches Developing a Specific Model 6.5.3 Composite Approach 6.6 Comparison of Results and Discussion 6.6.1 Assessment of Strength Properties at the Various KL 6.6.2 Important Issues Identified Thanks to the Benchmark 6.7 Conclusions and Contribution of the Benchmark to the Preparation of RILEM TC 249-ISC Recommendations References 7 How Investigators Can Answer More Complex Questions About Assess Concrete Strength and Lessons to Draw from a Benchmark 7.1 Introduction 7.2 Presentation of the Benchmark: Case Study and Rules to Be Applied 7.2.1 Case Study 7.2.2 The Investigation Strategy 7.2.3 What Can Be Measured 7.2.4 Available Resources for the Investigation 7.2.5 What Is Looked for? 7.3 Generation of Synthetic Data 7.3.1 How the Simulation Process Works 7.3.2 Simulation of Material Properties 7.3.3 Simulation of NDT Properties 7.3.4 Simulation of Test Results 7.3.5 What Was Simulated—What Are the Right Answers? 7.4 Analysis of Investigation Methodologies 7.4.1 Comparison of Methodologies at the Three Knowledge Levels 7.4.2 Resource Distribution Between DT/NDT and Between Tanks 7.4.3 Resource Distribution Between Different Types of NDT Methods 7.4.4 What Would Be an “Average Investigation Program”? 7.5 Description of Data Processing Methodologies 7.5.1 Description of the Assessment Methodology for All Contributions 7.5.2 Synthesis About the Definition of Core Location 7.5.3 Synthesis About the Data that Can Be Used for Correlation with Cores 7.5.4 Synthesis About the Identification of Conversion Models 7.6 Analysis of Assessments Provided by the Contributors 7.6.1 Specific Problem Due to Carbonation Effect on Rebound Test Results 7.6.2 Answer to Question 1: The Four Tanks Have Similar Properties? 7.6.3 Answer to Question 2: Provide Average and Standard Deviation of Strength 7.6.4 Answer to Question 3: Can You Identify Defective Areas in Tank A 7.6.5 Summary of Contributor Performances Regarding All Objectives 7.7 Synthesis of What Can Be Derived for RILEM Guidelines 7.7.1 Example of a Successful Investigation with a Limited Amount of Resource (KL2) 7.7.2 Lessons Regarding the RILEM Recommendations Appendix 7.1: Number of Tests of Each Type for KL1 and KL2 Investigations Appendix 7.2: Recommendations Regarding the Conversion Model Identification and Validation Appendix 7.3: Repeatability of Test Results (or Test Result Precision, TRP) References 8 Illustration of the Proposed Methodology Based on Synthetic Data 8.1 Description of the Case Study 8.1.1 The Synthetic Structure 8.1.2 The Synthetic Investigation Program 8.2 Organization of the Chapter and Content 8.3 Developing the Investigation and Assessment 8.3.1 Task 1. Defining EQL 8.3.2 Task 2. Performing NDT Measurements 8.3.3 Task 3. Assessing the Test Results Precision (TRP) 8.3.4 Task 4. Identifying Test Regions 8.3.5 Task 5. Defining the Number of Cores 8.3.6 Task 6. Defining the Location of Cores 8.3.7 Task 7. Choosing a Conversion Model 8.3.8 Task 8. Identifying and Calibrating the Conversion Model 8.3.9 Task 9. Estimating Concrete Strength and the Uncertainty on Strength Estimates References 9 Illustration of the Proposed Methodology Based on a Real Case-Study 9.1 Description of the Case Study—Original Methodology 9.2 Critical Analysis of the Expert Methodology and of Its Results—What Could Be Improved 9.2.1 Interesting Ideas Developed in the Original Study 9.2.2 What Would Have Deserved Further Attention 9.3 Concrete Properties Assessment of the Same Structure Following the RILEM TC 249-ISC Recommendations 9.3.1 T1. Defining EQL 9.3.2 T2. Carrying Out NDT Measurements 9.3.3 T3. Assessing Test Result Precision 9.3.4 T4. Identifying Test Regions 9.3.5 T5. Defining the Number of Cores 9.3.6 T6. Defining the Location of Cores 9.3.7 T7. Choice of a Conversion Model 9.3.8 T8. Model Identification and Calibration 9.3.9 T9. Strength Estimation and Estimation of Strength Assessment Uncertainty (Model Prediction Error) 9.4 Comparison Between the Original Approach and the RILEM Approach 9.5 Conclusions Appendix References Part IIIAppendix 10 Statistics 10.1 List of Definitions 10.1.1 Repeatability, Reproducibility and Variability 10.1.2 Precision, Accuracy and Uncertainty 10.2 Test Result Precision (TRP) as a Function of the Number of Measurements 10.3 Minimum Distance Between Test Locations 11 Model Identification and Calibration 11.1 Introduction 11.2 Assessment of Model Error 11.2.1 Context 11.2.2 Definitions. r2 Versus RMSE: How to Quantify the Model Uncertainty? 11.2.3 Example. Comparison Between Different Investigation Strategies 11.3 Model Identification and Trade-Off Between Model Parameters: Explanations and Consequences 11.4 Identification of Conversion Model Parameters: Influence of the Model Shape and Advantage of the Bi-objective Method 11.4.1 Possible Mathematical Expressions of the Conversion Model—Common Practice 11.4.2 Possible Mathematical Expressions of the Conversion Model—Bi-objective Method 11.4.3 Comparison of the Performance of Different Possible Univariate Conversion Models Identified Using Linear Regression 11.4.4 Comparison of the Performance Between the Identification of Parameters Using Linear Regression and Using the Bi-objective Method References 12 For Those Who Want to Go Further 12.1 Objectives—The Advantage of Repeating the Simulation 12.2 Assessment of the TRP Level 12.3 Simulation Results: Estimation of Mean Strength and Strength Standard Deviation 12.4 Uncertainty and Its Effects: Trade-Off Between Model Parameters and Model Error 12.5 NDT Based Concrete Strength Assessment: Effect of the TRP Level 12.6 NDT-Based Concrete Strength Assessment: Effect of the EQL Requirement, from EQL1 to EQL3 12.7 NDT Based Concrete Strength Assessment: The Advantage of Conditional Coring 12.8 NDT Based Concrete Strength Assessment: The Advantage of the Bi-objective Method for Assessing Concrete Variability 12.9 NDT Based Concrete Strength Assessment: Interest of Combining Two NDTs (“SonReb” Approach) Index