Improving Concrete Quality: 1st Edition (Hardback) book cover

Improving Concrete Quality

1st Edition

By Karthikeyan H Obla

CRC Press

214 pages | 39 B/W Illus.

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pub: 2014-06-25
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Description

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.

Reviews

"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

Table of Contents

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

Proportions

Troubleshoot Low-Strength

Problems

How Should a Cement Producer Use ASTM C917?

Summary

Variation in Concrete Strength Due to Water and Air Content

Variation

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

Discussion

Summary

Mixing-Water

Control

Sources of Water

Washwater in Truck Mixer Drum from Previous Load

Batchwater

Free Water from Aggregates

Water Added at Slump Rack

Water Added at Job Site

Variations in Mixing-Water

Demand

Effect of Mixing-Water

Content, Mixing-Water

Demand on

Measured Slump

Plant Tests for Quality Assurance

Summary

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

Producer

Table 6.2 Test Results—Tests conducted by Concrete Producer

Basic Statistics

Basic Statistical Parameters

Variability

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

Example

Variation in Concrete Performance Due to Batching

ASTM C94 Scale Accuracy and Accuracy of Plant Batching

Two Issues with Batching

Over-Batching

Variation of Batch Weights and Its Effects

Cementitious Weight Variation and Its Effect on Strength

Variation

How Can a Company Improve Batching Accuracy?

Yield Measurements—A Tool to Improve Batching Accuracy

Summary

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

Strength

Effect of Temperature on Mixing-Water

Demand

Variation in Concrete Performance Due to Delivery Time

Summary

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

Testing

Steps to Improve the Quality of Acceptance Testing

Education

Round-Robin

Testing Programs

Incentives to Testing Technicians

Preconstruction

Conferences

Other Strategies

Summary

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

Slump

Air Content

Density

Air-Free

Density

Temperature

Compressive Strength

CUSUM Charts

Summary

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

Summary

Impact of Specifications on Concrete Quality

Allow Use of Standard Deviations Not Just over Designs

Move from Prescriptive to Performance-Based

Specifications

Minimum Cementitious Content

Maximum w/cm

Changes to Mixture Proportions after Submittal

Qualifications

Producer Qualifications

Installer and Testing Agency Qualifications

Bonus-Penalty

Provisions

Job-Site

Concrete Acceptance Testing

Current information on Material Properties

Summary

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

Summary

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

Testing

Internal Testing at the Plant

Internal Testing at the Job Site

Quality Assurance Test Records

Nonconforming Acceptance Test Results

Identification/Traceability

Quality Audit

Returned Concrete and Washwater

Summary

Bibliography

References

Terminology

Appendices

Index

About the Author

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.

Subject Categories

BISAC Subject Codes/Headings:
TEC005000
TECHNOLOGY & ENGINEERING / Construction / General
TEC063000
TECHNOLOGY & ENGINEERING / Structural