1st Edition

Improving Concrete Quality

By Karthikeyan H Obla Copyright 2015
    214 Pages 39 B/W Illustrations
    by CRC Press

    Improve the Quality of Concrete, Improve the Quality of Construction

    Quality measurement is not prevalent in the concrete industry and quality investment is not seen as potentially generating a positive return. Improving Concrete Quality examines how and why concrete quality should be measured, and includes instruction on developing specifications with the aim of improving concrete quality.

    Reduce Concrete Variability: Reduce Costs and Increase Volume

    The first part of the book considers the tangible and intangible benefits of improved quality. The later chapters explore concrete strength variability in detail. It provides a greater grasp of the variation in concrete, as well as a deeper understanding of how material variability affects concrete performance. The author discusses the components of variability (material, manufacturing, testing) and provides steps to measuring and reducing variability to improve the quality of concrete. The text also contains a chapter on data analysis for quality monitoring and test results.

    Come Away with Practices and Tools That Can Be Applied Immediately:

    • Provides techniques and how specifications can improve concrete quality
    • Offers a clear understanding of the link between the materials (cement, SCM, aggregate, water, air), manufacturing, testing variability, and concrete quality
    • Includes information on analyzing test data to improve quality

    Improving Concrete Quality quantifies the benefits of improved quality, and introduces novel ways of measuring concrete quality. This text is an ideal resource for quality personnel in the concrete industry. It also benefits architects, engineers, contractors, and researchers.

    How Good Is Your Quality?

    Costs Due to Poor Quality

    Why Is It So Important to Lower Standard Deviation?

    Is It Worthwhile Not to Invest in Improved Quality under Certain Circumstances?

    2010 NRMCA Quality Measurement and Bench Marking Survey

    How Can a Concrete Producer Improve Quality?

    Variation in Concrete Strength Due to Cement

    Cement from a Given Source Varies between Shipments

    ASTM C917

    How Should a Ready Mixed Concrete Producer Use ASTM C917?

    Cement Choice

    Better Understand Concrete Variability and Lower It!

    Reduce Low-Strength

    Problems and Optimize Mixture


    Troubleshoot Low-Strength


    How Should a Cement Producer Use ASTM C917?


    Variation in Concrete Strength Due to Water and Air Content


    Mixing Water Content Variation and Its Effect on Compressive

    Strength Variation

    Air Content Variation and Its Effect on Strength Variation

    Combined Effect of Water and Air Content Variation on

    Strength Variation





    Sources of Water

    Washwater in Truck Mixer Drum from Previous Load


    Free Water from Aggregates

    Water Added at Slump Rack

    Water Added at Job Site

    Variations in Mixing-Water


    Effect of Mixing-Water

    Content, Mixing-Water

    Demand on

    Measured Slump

    Plant Tests for Quality Assurance


    Variation in Concrete Strength and Air Content Due to Fly Ash

    Variability of Fly Ash Shipments from Given Source

    Air Entrainment

    Strength Activity

    Fly Ash Testing Required by ASTM C311 and C618

    Suggested Producer Actions

    Air Entrainment

    Strength Activity Index

    Other Tests

    Summary of Suggested Producer Actions

    Variation in Concrete Performance Due to Aggregates

    Variability of Aggregate from Single Source

    Aggregate Properties and Their Effect on Concrete Mixture

    Proportioning and Performance

    Relative Density and Absorption of Aggregate

    Aggregate Moisture Content

    Void Content in Coarse Aggregates

    Void Content of Fine Aggregates

    Aggregate Grading

    Material Finer than 75 μm (No 200)

    Sand Equivalency

    Using Aggregate Test Results

    Table 6.1 Test Results

    Table 6.2 Test Results—Tests Conducted by the Aggregate


    Table 6.2 Test Results—Tests conducted by Concrete Producer

    Basic Statistics

    Basic Statistical Parameters


    Frequency Distributions

    Normal Distribution

    Predictions Using a Normal Distribution

    Types of Variation

    Common Causes and Special Causes

    Step Changes

    Control Charts

    Individual Chart

    Average and Range Charts

    Moving Average and Moving Range Charts

    CUSUM Charts


    Variation in Concrete Performance Due to Batching

    ASTM C94 Scale Accuracy and Accuracy of Plant Batching

    Two Issues with Batching


    Variation of Batch Weights and Its Effects

    Cementitious Weight Variation and Its Effect on Strength


    How Can a Company Improve Batching Accuracy?

    Yield Measurements—A Tool to Improve Batching Accuracy


    Variation in Concrete Performance Due to Manufacturing

    ASTM C94 Requirements for Uniformity of Concrete

    Improving Uniformity of Concrete Produced in Truck Mixer

    Batching Sequence

    Mixing Revolutions

    Mixing Speed

    What Can a Company Do to Improve Uniformity of Concrete Produced in a Truck Mixer?

    Variation in Concrete Performance Due to Temperature

    Effect of Temperature on Setting Time

    Effect of Temperature on Early-Age


    Effect of Temperature on Mixing-Water


    Variation in Concrete Performance Due to Delivery Time


    Variation in Concrete Performance Due to Testing

    A Measure of Testing Variability

    Other Methods of Evaluating Testing

    Other Property Measurements

    Producer Testing

    Rate of Strength Gain

    Cylinder Density

    Laboratory Reports

    ACI Code and Specification Requirements Related to Concrete


    Steps to Improve the Quality of Acceptance Testing



    Testing Programs

    Incentives to Testing Technicians



    Other Strategies


    Internal Concrete Testing

    Why Test at the Plant When We Can Get Job-Site

    Test Data?

    Criteria for Plant Testing

    Selection of Mixture Classes

    Sampling and Types of Testing

    Frequency of Testing

    Data Analysis

    Control Charts


    Air Content





    Compressive Strength

    CUSUM Charts


    Using Job-Site Test Results for Improving Concrete Quality

    Acceptance Test Results

    Data Analysis

    Rejecting Outliers

    Control Charts

    Control Chart Limits

    Monitoring S of Compressive Strength

    CUSUM Charts

    Use of Control and CUSUM Charts to Analyze Project

    Test Data

    Project 1

    Project 2

    Project 3


    Impact of Specifications on Concrete Quality

    Allow Use of Standard Deviations Not Just over Designs

    Move from Prescriptive to Performance-Based


    Minimum Cementitious Content

    Maximum w/cm

    Changes to Mixture Proportions after Submittal


    Producer Qualifications

    Installer and Testing Agency Qualifications




    Concrete Acceptance Testing

    Current information on Material Properties


    Impact of Concrete Quality on Sustainability

    Target a Low Standard Deviation

    Better Job-Site

    Curing and Overall Testing Quality

    Mixture Optimization

    Fewer Returned Concrete and Hardened Concrete Issues

    Plant and Truck Mixer Maintenance

    Temperature Measurements

    Batching Accuracy and Yield Measurements

    Mixture Adjustments


    Elements of a Quality Management System for a Concrete Producer

    Why Should a Company Have a QMS?

    What Are Elements of a QMS and How Does It Improve Quality?

    Quality Objectives and Measurement

    Management Commitment

    Customer Focus

    Personnel Qualifications

    Quality Manager

    Plant Operators

    Field Testing Technicians

    Laboratory Technicians

    Truck Mixer Operators

    Laboratory Testing Capabilities

    Aggregate Tests

    Concrete Tests

    Materials Management and Conformance

    Production Control

    Specification Review, Mixture Development, Optimization

    Receiving Orders and Record Keeping


    Internal Testing at the Plant

    Internal Testing at the Job Site

    Quality Assurance Test Records

    Nonconforming Acceptance Test Results


    Quality Audit

    Returned Concrete and Washwater








    Karthik Obla, Ph.D., P.E., FACI, is vice president, technical services, National Ready Mixed Concrete Association (NRMCA). He has over 20 years of experience in concrete materials technology and has interests in quality control/assurance, mixture optimization, specifications, use of recycled materials, durability, and new technology. He is a Fellow of the American Concrete Institute and a winner of ACI’s Young Professional Achievement Award. He has published over 75 technical articles in journals and has presented in several international conferences. He holds a Ph.D. in civil engineering from University of Michigan, Ann Arbor, and is a licensed professional engineer in the state of Maryland. He served as vice-president and president for the ACI San Antonio Chapter. Prior to joining NRMCA, he was technical manager at Boral Material Technologies.

    "Extremely comprehensive and practical… The chapter on basic statistics is a must read to clear the concepts required to understand how to analyse data for monitoring quality. Apart from the process - be it regarding material or testing, the author has also covered capability building and training which forms a core part of the entire business."
    —Indian Concrete Journal, December 2014

    "Many concrete manufacturers neglect to quantify not only the cost of producing poor quality concrete, but the potential savings in the reduction of cementitious content by focusing on standard deviation and tightening controls, particularly with regards to slump control and moisture contents – this book identifies key areas that manufacturers can focus on to improve and realize these savings."
    ––Charl Marais, Aggregate Industries

    "While there are many books on concrete technology, finding one that focuses strictly on improving concrete quality had been difficult until now. Improving Concrete Quality discusses how to improve performance, reduce time and costs, and lower the environmental footprint of concrete while also resulting in an overall improvement in the quality of concrete construction."
    The Concrete Producer, September 2014