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Guide to Troubleshooting Concrete Mixture Issues as Influenced by Constitutive Materia Is, Jobsite Conditions, or Testing Practices Reported by ACI Committee 211

� American Concrete Institute � a c I • Always advancing �

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American Concrete Institute Always advancing

First Printing June 2015

ISBN: 978-1-942727-26-2

Guide to Troubleshooting Concrete Mixture Issues as Influenced by Constitutive Materials, Jobsite Conditions, or Testing Practices

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ACI 211.8R-15

Guide to Troubleshooting Concrete Mixture Issues as Influenced by Constitutive Materials, Jobsite

Conditions, or Testing Practices

Reported by ACI Committee 211

Gary F. Knight, Chair

Timothy S. Folks', Vice Chair

William L. Barringer .

G. Terry Harris Sr'

Katie J. Barto jay Richard D. Hill

Muhammed P. A. Basheer David L. Hollingsworth

David A. Berg Said Iravani

James C. Blankenship' Tarif M. Jaber

Casimir J. Bognacki Robert S. Jenkins

Michael J. Boyle Joe Kelley

Ramon L. Carrasquillo Frank A. Kozeliski

Bryan R. Castles Dannawan Ludirdja

Teck L. Chua Allyn C. Luke'

James E. Cook Kevin A. MacDonald

John F. Cook' Gary R. Mass

David A. Crocker Warren E. McPherson Jr

D. Gene Daniel Jon I. Mullarky

Kirk K. Deadrick Karthik H. Obla

Donald E. Dixon H. Celik Ozyildirim

Darrell F. Elliot James S. Pierce

David W. Fowler Steven A. Ragan

This guide describes adjustments that can be made to existing

proportions for normal-density concrete with and without chemical

admixtures, pozzolans, and slag. These adjustments are based on

the performance of the concrete mixture as used in construction.

The adjustments consider evaluation for placeability, consistency,

strength, and durability. The procedures used in making these

adjustments can be found in ACI 211.1. Adjustments to concrete

mixture proportions or sources may require resubmittal to the

design professional as detailed in A CJ 30 I. This guide also provides

ACI Committee Reports, Guides, and Commentaries are intended for guidance in planning, designing, executing, and inspecting construction. This document is intended for the use of individuals who are competent to evaluate the significance and limitations of its content and recommendations and who will accept responsibility for the application of the material it contains. The American Concrete Institute disclaims any and all responsibility for the stated principles. The Institute shall not be liable for any loss or damage arising therefrom.

Reference to this document shall not be made in contract documents. If items found in this document are desired by the Architect/Engineer to be a part of the contract documents, they shall be restated in mandatory language for incorporation by the Architect/Engineer.

Ed T. McGuire, Secretary

Royce J. Rhoads Dimitri Feys

John P. Ries Plinio Estuardo Herrera

G. Michael Robinson Gene Hightower

James M. Shilstone Jr Berndt Kanduth

Ava Shypula Kenneth G. Kazanis

Woodward L. Vogt' Tyler Ley

Michael A. W hisonantzl Guy Lortie 'Members who contributed to this Blaine B. Nye

document. Bryan L. Petty IChair of subcommittee. Nicholas J. Popoff

Subcommittee Members Domenick Thomas Ruttura Yasar Yahia Abualrous Lawrence L. Sutter

David Anstine Paul D. Tennis Dale P. Bentz James R. Van Acker Zane Bussler HermanW. Wentz

Laurence M. Clodic Patrick J. Harrison Cesar A. Constantino Consulting Member

Kenneth W. Day James N. Lingscheit

information regarding jobsite conditions and testing practices that

should be evaluated before adjustments are made to the mixture.

Keywords: admixtures; aggregates; cementitious materials; durability; fine

aggregates; fly ash; metakaolin; mixture proportioning; pozzolans; quality;

silica fume; slag; slag cement; slump tests; water-cementitious material

ratio.

CONTENTS

CHAPTER 1-INTRODUCTION AND SCOPE, p. 2

1.1-Introduction, p. 2 1.2-Scope, p. 2

ACI 211.8R-15 was adopted and published June 2015.

Copyright © 2015, American Concrete Institute.

All rights reserved including rights of reproduction and use in any form or by any

means, including the making of copies by any photo process, or by electronic or

mechanical device, printed, written, or oral, or recording for sound or visual reproduc

tion or for use in any knowledge or retrieval system or device, unless permission in

writing is obtained from the copyright proprietors.

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2 TROUBLESHOOTING CONCRETE ISSUES AS INFLUENCED BY MATERIALS, CONDITIONS, OR PRACTICES (ACI 211.8R-15)

CHAPTER 2 -DEFINITIONS, p. 2

CHAPTER 3-REASONS FOR ADJUSTING

MIXTURE PROPORTIONS, p. 2

CHAPTER 4-REFERENCES, p. 9

Authored documents, p. 9

CHAPTER 1-INTRODUCTION AND SCOPE

1.1-lntroduction This document provides guidance for evaluating the

performance of concrete mixture proportions and making adjustments during the construction process as well as identifying construction or testing issues that can be wrongfully attributed to mixture proportioning. Adjustments to the mixture proportions or materials in the production process may be needed to accommodate variations in materials, changes in climatic conditions, consistency or yield of the mixture, and deficiencies in the fresh or hardened concrete properties.

1.2 -Scope

ACI 211.1 provides methods for selecting proportions for concrete mixtures. Concrete may require adjustments to the mixture proportions throughout the course of the project due to the normal variation of the materials used in production, and the various conditions under which it will be delivered, placed, consolidated, and finished. The concrete properties required in the hardened state may also require adjustments to the mixture proportions. It is important to note that no document can replace experience with the materials at hand when deciding what adjustments need to be made for a concrete mixture.

CHAPTER 2 -DEFINITIONS

ACI provides a comprehensive list of definitions through an online resource "ACI Concrete Terminology" at http:// www. concrete. org/store/productdetail. aspx?ItemiD=CT 13.

CHAPTER 3-REASONS FOR ADJUSTING MIXTURE PROPORTIONS

There are numerous reasons for adjusting the mixture proportions. The following are two examples showing the need to adjust mixtures to alleviate an existing problem on a jobsite and also to correct the yield as a result of the change.

3.1 Example No. 1-A mixture design is being used in the field and the water required to produce a 5 in. (130 mm) slump is 10 lb/yd3 (6 kg/m3) more than the design water. To correct the water content, it will be added into the design. The original mixture proportions are as follows:

a) Cement: 550 lb/yd3 (326 kg/m3) b) No. 57 coarse aggregate: 1850 lb/yd3 (1 098 kg/m3) c) Fine aggregate: 1083 lb/yd3 (643 kg/m3) d) Water: 268 lb/yd3 (159 kg/m3) e) Air content: 5 percent The following is the information used in the original

mixture design:

a) Maximum water-cementitious material ratio (w/cm)

required: 0.49 b) Coarse aggregate factor: 0. 7 c) Specific gravity of cement: 3.15 d) Specific gravity of coarse aggregate: 2.48 e) Unit weight of coarse aggregate: 97.9 lb/ft3 (1568.2 kg/

m3) f) Specific gravity of fine aggregate: 2.63 The adjustment for the water demand will be based on the

w!cm.

The water will increase from 268 to 278 lb/yd3 (159 to 165 kg/m3). To keep the w!cm the same, the cement will increase to 568 lb/yd3 (337 kg/m3). The coarse aggregate will remain the same and the fine aggregate will be adjusted so the mixture will continue to yield 27 ft3/yd3 (1 m3/m3).

The adjusted mixture proportions will be as follows: a) Cement: 568 lb/yd3 (337 kg/m3) b) No. 57 coarse aggregate: 1850 lb/yd3 (1 098 kg/m3) c) Fine aggregate: 1042 lb/yd3 (618 kg/m3) d) Water: 278 lb/yd3 ( 165 kg/m3) e) Air content: 5 percent 3.2 Example No. 2-A mixture proportioned for a design

strength of 4000 psi (28 MPa) at 28 days is only achieving an average of 2700 psi (19 MPa) at 7 days. Based on historical data of the relationship of 7 to 28-day strengths, the 28-day strength is predicted to be approximately 3800 psi (26 MPa). The mixture proportion will be adjusted to increase the strength by a targeted 500 psi (3.4 MPa). The original mixture proportions are as follows:

a) Cement: 550 lb/yd3 (326 kg/m3) b) No. 67 coarse aggregate: 1920 lb/yd3 (1139 kg/m3) c) Fine aggregate: 1187 lb/yd3 (704 kg/m3) d) Water: 275 lb/yd3 (163 kg/m3) e) Air content: 4 percent f) Water reducer: 17.0 oz./yd3 (658 mL!m3) The following is the information used in the original

mixture proportions: a) w/cm required: 0.52 maximum b) Coarse aggregate factor: 0. 72 c) Specific gravity of cement: 3.15 d) Specific gravity of coarse aggregate: 2.68 e) Unit weight of coarse aggregate: 100.2 lb/ft3 (1605.1

kg/m3) f) Specific gravity of fine aggregate: 2.63 This concrete mixture, with an expected 28-day compres

sive strength of 3800 psi (26 MPa) and having 550 lb/yd3 (326 kg/m3) of cement produces a cement efficiency at 28 days of 6.9 psi/lb (0.080 MPa/kg/m3) (3800 psi/550 lb/yd3 = 6.9 psi/lb/yd3 [26 MPa/326 kg/m3]). To adjust the mixture to yield an additional 500 psi (3.4 MPa) would take an additional 72 lb/yd3 (43 kg/m3) of cement (500 psi/6.9 psi/lb/yd3 = 72 lb/yd3 [3.4 MPa/0.080 MPa/kg/m3 = 43 kg/m3]).

The new mixture will be as follows: a) Cement: 622 lb/yd3 (370 kg/m3) b) No. 67 coarse aggregate: 1920 lb/yd3 ( 1139 kg/m3) c) Fine aggregate: 1126 lb/yd3 (668 kg/m3) d) Water: 275 lb/yd3 (163 kg/m3) e) Air content: 4 percent

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TROUBLESHOOTING CONCRETE ISSUES AS INFLUENCED BY MATERIALS, CONDITIONS, OR PRACTICES (ACI 211.8R-15) 3

f) Water reducer: 19.25 oz/yd3 (745 mL/m3) The weight of fine aggregate was reduced to compensate

for the additional cement. Adding the additional cement lowers the w/cm to 0.44. The water reducer dose increased, as its use was based on the amount of cement in the mixture.

These two examples demonstrate the consequence of one change in a concrete mixture to the final mixture proportions.

3.3 Evaluation and adjustment of concrete mixtures-The evaluation of concrete mixture proportions during the course of a project will usually consist of observing changes in the properties of the concrete and addressing problems as they arise.

Tables 3 .3a through 3 .3c indicate possible causes of typical production and application issues involving concrete. The tables do not attempt to address every possible situation that

Table 3.3a-Fresh property issues Area of

Issue occurrence Possible cause

I. Air content: Mixture A. Improper amount of admixture high/low

B. Admixture interaction

C. Insufficient slump

may occur; only the most common causes are covered. The situations in the table are also assumed to be single issues. Many times in practice, there are several issues occurring simultaneously. In most cases, issues with concrete arise in the initial construction phase. Issues such as low chemical resistance, however, may take some time to become evident and will likely not be observed during the initial construction phase. In some cases, building design, construction practice, and mixture design adjustments are all discussed. In these cases, there are numerous field changes outside of mixture design adjustment that can correct a situation in the field. Often, correcting the field issue will alleviate the problem. If correcting the field issue does not solve the problem, then changes to mixture proportions should be considered.

Possible adjustments

a) Increase or decrease amount. b) Ensure proper functioning of admixture dispenser. a) Change dosage or type. b) Follow manufacturers' recommendations. c) Change admixture dosage sequence. Adjust slump; refer to Issue 2, Slump: high/low.

D. High-carbon fly ash. An increase in the loss on ignition a) Change fly ash or admixture dosage/type.

Testing

(LOI) generally indicates an increase in carbon content. Carbon has a tendency to absorb air-entraining admixture. The high surface area of fly ash may also decrease air content at a fixed dose. E. Concrete temperature a) Correct temperature; refer to Issue 4, Temperature: high/low.

b) Adjust dosage for temperatures of admixtures (set-accelerating and retarding, air-entraining, etc.)

F. Cement or other cementitious materials. Slag cement a) Change source of cementitious material. fineness may change the air content of the mixture. b) Change air entrainment type. Silica fume has a very high surface area. The high surface c) Change air-entraining agent dosage. area may decrease the air content of the mixture. Metakaolin, like silica fume, has a high surface area and may decrease the air content of the mixture. An increase in soluble alkalis in the cement may increase air content. G. Varied air contents due to improper mixing Clean mixer, use different charging sequence, or correct

mixing time/speed. H. Decrease in air content due to increased fines a) Adjust air entraining dosage.

b) Decrease the amount of material on the No. 200 (75 11m) steve.

I. Varied air contents of a concrete mixture due to aggregate Adjust aggregate grading and adjust air-entraining agent grading or blending dose accordingly. J. Unintentionally entrained air from fibers a) Use alternate secondary reinforcement.

b) Adjust air-entraining agent dosage. Faulty air meter/test a) Rerun ASTM C231/C231M test.

b) Verify accuracy of air meter. c) Run ASTM C l38 /C l 38M unit weight test to confirm the air meter results.

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Table 3.3a (cont.)-Fresh property issues Area of

Issue occurrence Possible cause Possible adjustments

2. Slump: Mixture A. Improper amount of water a) Adjust water content. high/low b) All sources of water must be confirmed, including

ensuring that no water is present in drum before batching, as well as any other nonmeasured water sources after batching. c) Some admixtures may include enough water to affect slump at higher dosage rates. d) Check aggregate moistures.

B. Aggregate gradation. A change in the coarse or fine a) Adjust grading. aggregate gradation or aggregate blending may cause a b) Change source of aggregate. change in slump because of increased or decreased water c) Monitor and adjust aggregate gradations when possible. demand. d) Use of water reducer or high-range water reducer to help Gap-graded coarse aggregates may increase water demand to increase slump without adding water to the mixture. maintain slump. e) Increase of cement content will need to occur if water is If the fine aggregate gradation becomes finer or the particles added to maintain maximum w/cm and slump. more angular, the water demand will increase. f) Adjust the fine-to-coarse aggregate ratio to reduce some

water demand. C. Fly ash. Spherical particles typically make concrete A reduction in water content may be required to reduce mixtures more workable than those with angular particles, slump. An increase in air-entraining agent dose may be this will increase the slump. required to maintain air content and slump. D. Slag cement may alter the water demand to achieve Adjust water content as needed to adjust slump. An increase slump. in air-entraining agent dose may be required to maintain air

content and slump. E. Silica fume in the mixture will decrease the slump. Use appropriate dosage of high-range water-reducing Generally, I gal. of water is required for each 10 lb of silica admixture. fume added to maintain slump. F. High temperatures may increase slump loss over time; a) Reduce concrete temperature. cold temperatures may slow loss b) Adjust admixture dosage. G. Improper amount of admixture or admixture-dispensing Check batching operations, calibrations, adjust amount.

I problems Check admixture-dispensing system. Testing Sampling and testing issue Resample and rerun test. Check result with different testing

equipment or verify procedure. 3. Density: Mixture A. Batching error Check scales and batch weights. Check the charging of high/low materials into the load.

B. Aggregate relative density (specific gravity) change Check density and adjust mass if needed C. Air content deviation Adjust air content; refer to Issue I, Air content: high/low D. Water content deviation Check water demand.

Testing Testing issue Rerun test and check equipment. 4. Mixture Aggregate, cement, cementitious material, and water Adjust temperature by using adequate cooling or heating Temperature: temperature techniques. high/low Testing Improper test Check procedure and calibrate thermometer. 5. Yield: high/ Mixture A. Changes in material relative density will affect the yield Check the relative density of the materials and adjust the low of the concrete mixture. If the relative density increases, the quantity of the coarse or fine aggregate to compensate for the

mixture will under-yield; if the relative density decreases, the volume difference. mixture will over-yield. B. Batching errors, either in the production or mixture entry a) Correct scale issues. Correct batch weight input. Ensure tssues that proper moisture determinations and adjustments are

performed. b) Ensure that all equipment is operating properly and that the charging sequence is correct.

C. Adjusting mixtures for other reasons may alter the overall When adjusting a concrete mixture, ensure that the final I yield of the mixture. yield is still correct.

Testing Incorrect determination of yield ASTM C l 38/Cl38M is the accepted method to determine fresh density, which is used to determine yield as specified in ASTM C94/C94M.

6. Segregation Mixture A. Improper amount of water a) Confirm that all sources of water are measured, including ensuring that no water is present in drum before batching, as well as any other nonmeasured water sources. b) Ad i ust water content.

B. Excessive high-range water-reducing admixture Reduce high-range water-reducing admixture dosage. Jobsite A. Excessive drop a) Reduce free drop to less than 6 ft.

b) Adjust pump configuration, pressure, or both. B. Over-vibration Use short bursts of vibration in compliance with ACI 309R.

7. Rapid set Jobsite and High concrete or ambient placement or curing temperatures a) Cool water, aggregates, or both. mixture b) Increase retarder dosage.

c) Decrease cement content.

8. Slow set Jobsite and Low concrete or ambient placement or curing temperatures a) Heat water, aggregates, or both. mixture b) Adjust admixture dosage.



Table 3.3b-Finishing issues

Area of

Issue occurrence Possible causes Possible adjustments

I. Sticky Mixture A. Fine aggregate gradation is too fine. Excess fines in one a) The addition of an aggregate or changing proportions or mixtures or more of the aggregates. Contamination of one or more of source of aggregates to improve overall gradation. (refer to ACI the aggregates. b) If contamination is occurring in the material storage, 302.1R) separate and ensure that no material flows into another.

c) Ensure there are no holes or leaks between batch storage bins.

B. High air content Reduce air content of the mixture. Refer to Table 3.3a, Issue I, Air content: high/low.

C. High concrete temperatures a) Reduce component materials' temperature. b) Do not exceed maximum placement time. Refer to Table 3.3a, Issue 4, Temperature: high/low.

D. Increasing the amount of cementitious materials can a) The use of high-range water reducers can decrease the increase stickiness. Using very fine cementitious materials stickiness of the mixture. Placing the concrete at a higher such as silica fume or metakaolin will increase stickiness. slump may also help to reduce the stickiness.

b) The reduction of fine aggregate in a concrete mixture with high cementitious content may reduce stickiness. c) Reducing the cementitious content will help reduce the stickiness.

E. Proportioning Reduce mortar volume by increasing coarse aggregate factor or a decrease in sand, cementitious material, water, plastic air content, or all of the aforementioned.

2. Bleed rate Mixture A. Gap-graded aggregates can increase the rate and amount Change the source or proportions of aggregate to improve too fast/too of bleed water from a concrete mixture. the overall gradation. slow B. Low air content normally causes increased rate and Increase air-entraining agent dose as long as final air content (refer to ACI amount of bleed water removed from a concrete mixture. is within specification. 302. 1 R) C. Lack of fines normally causes an increased rate and a) Change the source or proportions of aggregate to improve

amount of bleeding removed from a concrete mixture. the overall gradation b) Increase fines in the fine aggregate. c) Increase the cementitious material content. d) Use admixtures such as high-range water reducers to reduce the overall water content of the mixture.

D. High air content can slow the amount and rate of Reduce air-entraining agent dose as long as the final air bleeding. content is within specification.

E. High volume of fines can slow the amount and rate of Change the source or proportions of aggregate to improve bleeding. the overall gradation.

Table 3.3c-Hardened properties issues

Area of


I. Surface Mixture A. Sticky mixtures (refer to Table 3.3b, Issue 1, Sticky a) Reduce the amount of mortar by reducing fines in the air voids mixtures) mixture by reducing the fine aggregate volume, blending (bugholes) with or changing to a coarser sand, reducing cement or

supplemental cementitious materials where allowed and feasible to meet requirements. b) Reducing concrete temperatures may reduce stickiness (refer to Table 3.3a, Issue 4, Temperature: high/low. c) Reducing entrained air within specified limits may reduce stickiness (refer to Table 3.3a, Issue 1, Air content: high/ low).

B. Segregation of the mixture a) Ensure proper admixture dosage and water content of the mixture. Ensure proper cohesiveness of the mixture. b) Check mixture grading, especially below No. 50 (300 Jlm) sieve, including cementitious materials, and adjust if necessary.

Jobsite C. Consolidation a) Improper consolidation can cause air and water to collect at the surface of the form. Adjust the consolidation of the concrete to eliminate localized migration of air and water. b) Use fonn vibrators to supplement immersion vibrators where practical.

D. Form release agent The use of too much or the wrong type of form release can trap air and water at the form surface, causing voids.



Table 3.3c (cont.)-Hardened properties issues Area of


2. Poor Mixture A. Low air content Refer to Table 3 .3a, Item I, Air content: high/low.

resistance to B. Inadequate air void system a) Check water and fine material content. freezing and b) Check the quality of the air-void system following the thawing (refer procedures of ASTM C457/C457M. to ACI 20 1.2R) c) Consider using another air-entraining admixture that may

produce smaller bubbles, a better air void distribution, or

both.

C. Use of nondurable aggregates Aggregates to be used should conform to the durability

requirements specified.

3. Chemical Mixture A. High permeability a) Reduce water, use a cementitious material that reduces

resistance permeability, or both.

(refer to ACI b) Increase cementitious materials, improve homogeneity of

201.2) mixing, and check workability of concrete proportions.

B. Cracking Use low-heat cement or consider using supplementary

cementitious materials to reduce temperature differential of

concrete proportions.

Jobsite Cracking a) Avoid and protect from rapid surface drying.

b) Cure properly and completely.

4. Abrasion Mixture A. Nonresistant aggregates Change to more resistant materials. Additional mineral fines

resistance from quality rock can improve the abrasion resistance.

(refer to ACI B. Segregation or settlement of aggregates a) Check specific gravities and gradations of aggregates, 201.2R) water content, and admixture dosage.

b) Do not over-vibrate the concrete.

C. Excessive bleed water a) Reduce water, increase cement. Consider using pozzolans.

b) Increase fines in fine aggregate.

Jobsite Premature finishing Be sure the surface is not finished until the bleed water

evaporates.

5.Aikali- Mixture Material selection a) Check reactivity maps (Mielenz 1978) and lists (ACI

aggregate alkali silica 20 1.2R, Table 5.1 ).

reactivity reactivity b) Reactive materials should be avoided if at all possible.

(refer c) Many aggregates should be considered to be reactive

to ACI unless proven otherwise.

201.2R, d) If reactivity of the aggregates is in doubt, it should be

ACI checked.

221.1R, e) If reactive aggregates must be used, reduce the alkali

and ACI content of the cementitious materials.

212.3R) f) Use cement with lower alkali content.

g) Use pozzolans and or other cementitious materials to

reduce the alkali content and potential for alkali-aggregate

reactivity.

h) Consider using admixtures containing soluble salts of

lithium and barium (ACI 212.3R).




Issue occurrence

6. Plastic Jobsite

shrinkage

cracking

7. Drying Jobsite

shrinkage

cracks

(refer to ACI

224R)

8. Crazing and Jobsite

map cracking

9. Settlement Jobsite

cracking

10. Thennal Mixture

cracking

Jobsite

I I. Surface Mixture

problems

blistering/

delaminating

Jobsite

12. Mixture

Discoloration

Jobsite

Possible causes Possible adjustments

Plastic shrinkage cracks occur due to the top surface of the a) Ensure that the upper portion of the concrete does not dry

concrete drying while the underlying concrete is still in its or set prior to the entire volume of the slab by using wind

plastic state. This typically happens on low-humidity, high- shields, water sprays, or other methods.

wind days. Most corrective measures, such as water sprays b) Increase bleeding.

and wind screens, are in construction practices and not in c) Reapply finishing float or trowel to close surface.

mixture design adjustments. d) Ensure proper air content as well as type and dosage of

other admixtures.

e) Consider adding fiber reinforcement.

f) Spray evaporative retarding solution on the surface. Apply

curing compound as early as possible and then reapply later

to ensure coverage.

Drying shrinkage cracks occur due to the moisture loss of the a) Apply proper curing as soon as possible.

concrete over time. As the moisture leaves the concrete, the b) Wet cure for 7 days or as long as possible.

concrete shrinks and, if it is restrained, it will crack. Most c) Use properly spaced and designed joints.

corrective actions are in design or construction practices and d) Properly using shrinkage-reducing admixtures or

not in mixture design adjustments. shrinkage-compensating cements can lessen shrinkage.

e) Use a properly proportioned mixture with the largest

coarse aggregate size and volume available.

f) Reduce the overall water content using admixtures.

g) Use aggregates, which induce less shrinkage.

Crazing occurs due to higher-than-normal w/cm at the a) Do not work bleed water into the surface of the concrete.

surface of the concrete. Most corrective actions are in the b) Do not sprinkle portland cement on the surface of

finishing process and not in mixture design adjustments. bleeding concrete to dry the surface.

Settlement cracking occurs along rigid elements, typically a) Reduce slump.

horizontal reinforcement, when the concrete is in its plastic b) Reduce bleeding.

state. c) Consider late vibration to close settlement cracks.

d) Consider low-slump concrete.

Thermal cracks occur when concrete cools and contracts a) Use mass concrete practices as stated in ACI 207.1 R.

and the concrete is restrained. Restraint can be caused by b) Reduce content of cementitious materials when strength

external forces such as friction between a slab-on-ground, or allows.

by internal forces such as differential between the concrete c) Use cement with low heat properties.

and ambient temperatures on the exterior of the concrete. d) Use pozzolans with low heat properties.

e) Precool concrete to reduce peak temperature.

A thermal concrete plan needs to be developed for the Incorporate a heat-dissipation system, such as tubes

particular project (refer to ACI 207.1R). circulating cooling fluid, through the interior of the concrete.

Insulate exposed surfaces and allow gradual cooling.

Postpone removal of formwork while interior concrete

temperature remains elevated.

Blistering and surface delaminating typically occur due a) Reduce air content to the minimum possible if applying a

to finishing practices; however, some concrete mixture hard steel trowel surface.

proportioning can affect the possibility of blistering or b) Reduce bleed water (refer to Table 3.3b, Item 2, Bleed

delaminating taking place. rate too fast/too slow).

c) If using fibers, ensure that unintentional air has not been

entrained.

Blistering and surface delaminating typically occur due to a) Lengthen period of time prior to first finishing procedure.

finishing practices. b) Do not work bleed water into the surface of concrete.

Variations in mixture proportioning a) Ensure homogeneity of mixing and as constant a w/cm as

possible.

b) Avoid using calcium chloride admixtures.

c) Use the same source and type of cementitious materials.

Discoloration typically occurs due to finishing practices a) Avoid premature or excessive finishing operations.

rather than mixture design issues. b) Uniformly cure with the same curing medium.

c) Change forms, release agents, or both, to reduce the

effects/reaction with the form face.





13. Mixture Low degree of workability; aggregate size and shape; mortar a) Reduce coarse aggregate size.

Honeycombing content or paste content. b) Use more rounded aggregate.

(refer to ACI c) Avoid lower slump sticky mixtures; refer to Table 3.3b,

302.1R) Issue I, Sticky mixtures.

d) Check water-reducing admixture dosage.

e) Insufficient paste content can compromise compaction/

consolidation and result in honeycombing.

Jobsite A. Contamination by a foreign substance in the field or a) Make sure that the mixer and placing equipment have

materials left in the mixer been properly cleaned.

B. Improper consolidation b) Improve consolidation methods.

c) Increase vibration techniques to improve consolidation.

14. Dusting Jobsite Improper finishing and curing techniques a) Avoid finishing operation while bleed water is on the

surface or before concrete has stopped bleeding to prevent

working bleed water into the surface

b) Provide sufficient curing to avoid dehydration of surface

moisture

c) Avoid excessive exposure to carbon dioxide from heaters

causing carbonation

IS. Scaling Mixture Improper proportioning a) Use adequate entrained air to protect against freezing-and-

thawing damage as specified in ACI 30 I.

b) Mixtures should maintain w/cm below 0.45

c) A lternate cementitious contents should not exceed the

limits in ACI 301.

Jobsite Excess finishing Avoid excessive finishing properties; avoid finishing water

into the surface of concrete

16. Curling Jobsite Curing a) Protect concrete surface to prevent differential shrinkage

through the concrete section caused most commonly by

drying the top surface relative to the bottom.

b) Protect concrete surface to prevent differential thermal

stress through the concrete section caused, most commonly,

by cooling of the surface relative to the mass.

c) Avoid over-finishing that may produce a dense, cement-

rich surface relative to the mass.

17. Mixture A. Changes in cementitious or other raw material production a) New trial batches may be needed to confirm the impact on

Low-strength the strength and workability of the mixture.

concrete b) A temporary increase in cementitious materials may be

required to maintain satisfactory results.

B. Seasonal changes a) Verify proper field sampling and curing conditions.

b) Hotter weather can reduce later-age concrete strength.

If possible, use higher volumes of alternate cementitious

materials.

c) Significant changes in air or concrete temperatures can

affect admixture characteristics, requiring adjustment to

maintain perfonnance.

Jobsite A ddition of water beyond that originally specified a) Do not add water beyond the amount originally specified.

b) If workability of the mixture needs to be higher, refer to

Table 3.3a, Issue 2, Slump: high/low.

c) Check the moisture content and absorption of the

aggregates.

Testing Improper sampling, molding, curing, and testing procedures a) Ensure that all tests comply with the referenced

specifications for the job, such as ASTM C 172/C 172M, C31/

C3IM, C39/C39M, CI43/CI43M, C231/C231M, and C78/

C78M.

b) Ensure that all technicians are certified by ACI or an

equivalent agency for the tests they are performing.





18. Slow Mixture A. Fly ash or slag used as a replacement for part of the Follow curing procedures outlined in ACI 308R. Additional

strength gain cement may result in lower early-age compressive strength, curing/insulation or artificial heat may be required at lower

extended time of set, or both. This may be more apparent in temperatures. An accelerating admixture can also be added

cooler temperatures. Refer to ACI 233R and ACI 232.1R. to the mixture to increase early-age strength and reduce the

time of set. It may also be necessary to reduce the amount of

fly ash or slag in the mixture.

B. Mixtures proportioned for use in warmer weather may Adjust the admixture dosages to reflect changes in weather

have increased dosages of chemical admixtures that could conditions.

slow strength development

C. An increase in the amount of material passing the No. 200 Change the aggregate source or wash the aggregate to

(75 f.Lm) sieve may cause a reduction in the aggregate-to- remove the excess of No. 200 (75 f.Lm) materials.

paste bond. This could affect the strength gain, especially in

high-strength concrete.

Jobsite A. Addition of excessive water Do not exceed the design w/cm.

B. Improper curing of concrete Ensure proper curing and add wind breaks, shade, foggers,

or all of the aforementioned, to increase humidity near the

surface.

Testing Improper fabricating or curing of compressive strength Follow the procedures of testing and curing cylinders in

cylinders

CHAPTER 4-REFERENCES

Committee documents are listed first by document number and year of publication followed by authored documents listed alphabetically.

American Concrete Institute

ACI 201.2R-08�Guide to Durable Concrete ACI 207.1R-05(11)�Guide to Mass Concrete ACI 211.1-91(09)�Standard Practice for Selecting

Proportions for Normal, Heavyweight, and Mass Concrete ACI 212.3R-10�Report on Chemical Admixtures for

Concrete ACI 221.1R-98(08)�Report on Alkali-Aggregate

Reactivity ACI 224R-01(08)�Control of Cracking in Concrete

Structures ACI 232.1R-12�Report on Use of Raw or Processed

Natural Pozzolans in Concrete ACI 233R-03(11)�Slag Cement in Concrete and Mortar ACI 301-1 O�Specifications for Structural Concrete ACI 302.1R-04�Guide for Concrete Floor and Slab

Construction ACI 308R-01(08)�Guide to Curing Concrete ACI 309R-05�Guide for Consolidation of Concrete

ASTM International

ASTM C31/C31M-12�Standard Practice for Making and Curing Concrete Test Specimens in the Field

ASTM C31/C31M.

ASTM C39/C39M-14�Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens

ASTM C78/C78M-10�Standard Test Method for Flexural Strength of Concrete (Using Simple Beam with ThirdPoint Loading)

ASTM C94/C94M-14�Standard Specification for Ready-Mixed Concrete

ASTM C138/C138M-14�Standard Test Method for Density (Unit Weight), Yield, and Air Content (Gravimetric) of Concrete

ASTM C143/C143M-12�Standard Test Method for Slump of Hydraulic-Cement Concrete

ASTM C 1 72/C 172M -14�Standard Practice for Sampling Freshly Mixed Concrete

ASTM C231/C231M-14�Standard Test Method for Air Content of Freshly Mixed Concrete by the Pressure Method

ASTM C457/C457M-12�Standard Test Method for Microscopial Determination of Parameters of the Air-Void System in Hardened Concrete

Authored documents

Mielenz, R. C., 1978, "Petrographic Examination, " Significance of Tests and Properties of Concrete-Making Materials, STP-169D, ASTM International, West Conshohocken, PA.



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