• No results found

109-05-Aci Materials Journal Sept.-oct. 2012 Complete

N/A
N/A
Protected

Academic year: 2021

Share "109-05-Aci Materials Journal Sept.-oct. 2012 Complete"

Copied!
90
0
0

Loading.... (view fulltext now)

Full text

(1)

ACI

MATERIALS

JOURNAL

VOL. 109, NO. 5

SEPTEMBER-OCTOBER 2012

499 Creep Testing of Epoxy-Bonded Reinforcing Bar Couplers/G. Brungraber 503 Effect of Na2SiO3/NaOH Ratios and NaOH Molarities on Compressive Strength

of Fly-Ash-Based Geopolymer/A. M. Mustafa Al Bakri, H. Kamarudin, M. Bnhussain, A. R. Rafiza, and Y. Zarina

509 Effect of Using Mortar Interface and Overlays on Masonry Behavior by Using Taguchi Method/M. Farouk Ghazy

517 Experimental Study on Dynamic Axial Tensile Mechanical Properties of Concrete and Its Components/S. Wu, Y. Wang, D. Shen, and J. Zhou 529 Potential Recycling of Bottom and Fly Ashes in Acoustic Mortars and

Concretes/C. Leiva, L. F. Vilches, C. Arenas, S. Delgado, and C. Fernández-Pereira

537 Early-Age Creep of Mass Concrete: Effects of Chemical and Mineral

Admixtures/S. Botassi dos Santos, L. C. Pinto da Silva Filho, and J. L. Calmon 545 Proposed Flexural Test Method and Associated Inverse Analysis for

Ultra-High-Performance Fiber-Reinforced Concrete/F. Baby, B. Graybeal, P. Marchand, and F. Toutlemonde

557 A First-Cut Field Method to Evaluate Limestone Aggregate Durability/ J. R. Emry, R. H. Goldstein, and E. K. Franseen

565 Investigation of Properties of Engineered Cementitious Composites Incorporating High Volumes of Fly Ash and Metakaolin/E. Özbay, O. Karahan, M. Lachemi, K. M. A. Hossain, and C. Duran Ati¸s

573 Fatigue Analysis of Plain and Fiber-Reinforced Self-Consolidating Concrete/ S. Goel, S. P. Singh, and P. Singh

(2)

Discussion is welcomed for all materials published in this issue and will appear in the July-August 2013 issue if received by April 1, 2013. Discussion of material received after specified dates will be considered individually for publication or private response.

ACI Standards published in ACI Journals for public comment have discussion due dates printed with the Standard.

Annual index published online at www.concrete.org/pubs/journals/mjhome.asp.

ACI Materials Journal

Copyright © 2012 American Concrete Institute. Printed in the United States of America.

The ACI Materials Journal (ISSN 0889-325x) is published bimonthly by the American Concrete Institute. Publication office: 38800 Country Club Drive, Farmington Hills, MI 48331. Periodicals postage paid at Farmington, MI, and at addi-tional mailing offices. Subscription rates: $161 per year (U.S. and possessions), $170 (elsewhere), payable in advance. POSTMASTER: Send address changes to: ACI Materials Journal, P. O. Box 9094, Farmington Hills, MI 48333-9094. Canadian GST: R 1226213149.

Direct correspondence to P. O. Box 9094, Farmington Hills, MI 48333-9094. Telephone: (248) 848-3700. Facsimile (FAX): (248) 848-3701. Web site: http://www.concrete.org.

CONTENTS

Board of Direction President James K. Wight Vice Presidents Anne M. Ellis William E. Rushing Jr. Directors Neal S. Anderson Khaled Awad Roger J. Becker Jeffrey W. Coleman Robert J. Frosch James R. Harris Cecil L. Jones Steven H. Kosmatka David A. Lange Denis Mitchell Jack P. Moehle David H. Sanders

Past President Board Members

Kenneth C. Hover Florian G. Barth Luis E. García

Executive Vice President

Ron Burg

Technical Activities Committee

David A. Lange, Chair Daniel W. Falconer, Secretary Sergio M. Alcocer JoAnn P. Browning Chiara F. Ferraris Catherine E. French Trey Hamilton Ronald Janowiak Kevin A. MacDonald Antonio Nanni Jan Olek Michael Sprinkel Pericles C. Stivaros Eldon G. Tipping Staff

Executive Vice President

Ron Burg Engineering Managing Director Daniel W. Falconer Managing Editor Khaled Nahlawi Staff Engineers Matthew R. Senecal Gregory Zeisler Publishing Services Manager Barry M. Bergin Editors Carl R. Bischof Karen Czedik Kelli R. Slayden Denise E. Wolber Publishing Assistant Ashley Poirier

ACI M

AterIAls

J

ournAl

s

epteMber

-o

Ctober

2012, V. 109, n

o

. 5

ajournaloftheamericanconcreteinstitute aninternationaltechnicalsociety

499 Creep Testing of Epoxy-Bonded Reinforcing Bar Couplers by

Griffin Brungraber

503 Effect of Na2SiO3/NaOH Ratios and NaOH Molarities on Compressive

Strength of Fly-Ash-Based Geopolymer by A. M. Mustafa Al Bakri, H. Kamarudin, M. Bnhussain, A. R. Rafiza, and Y. Zarina

509 Effect of Using Mortar Interface and Overlays on Masonry Behavior

by Using Taguchi Method by Mariam Farouk Ghazy

517 Experimental Study on Dynamic Axial Tensile Mechanical Properties

of Concrete and Its Components by Shengxing Wu, Yao Wang, Dejian Shen, and Jikai Zhou

529 Potential Recycling of Bottom and Fly Ashes in Acoustic Mortars

and Concretes by Carlos Leiva, Luis F. Vilches, Celia Arenas, Silvia Delgado, and Constantino Fernández-Pereira

537 Early-Age Creep of Mass Concrete: Effects of Chemical and Mineral

Admixtures by Sergio Botassi dos Santos, Luiz Carlos Pinto da Silva

Filho, and João Luiz Calmon

545 Proposed Flexural Test Method and Associated Inverse Analysis for

Ultra-High-Performance Fiber-Reinforced Concrete by Florent Baby, Benjamin Graybeal, Pierre Marchand, and Fran¸cois Toutlemonde

557 A First-Cut Field Method to Evaluate Limestone Aggregate Durability

by Julienne Ruth Emry, Robert H. Goldstein, and Evan K. Franseen

565 Investigation of Properties of Engineered Cementitious Composites

Incorporating High Volumes of Fly Ash and Metakaolin by E. Özbay, O. Karahan, M. Lachemi, K. M. A. Hossain, and C. Duran Ati¸s

573 Fatigue Analysis of Plain and Fiber-Reinforced Self-Consolidating

Concrete by S. Goel, S. P. Singh, and P. Singh

(3)

Permission is granted by the American Concrete Institute for libraries and other users registered with the Copyright Clearance Center (CCC) to photocopy any article contained herein for a fee of $3.00 per copy of the article. Payments should be sent directly to the Copyright Clearance Center, 21 Congress Street, Salem, MA 01970. ISSN 0889-3241/98 $3.00. Copying done for other than personal or internal reference use without the express written permission of the American Concrete Institute is prohibited. Requests for special permission or bulk copying should be addressed to the Managing Editor, ACI Materials Journal, American Concrete Institute.

The Institute is not responsible for statements or opinions expressed in its publications. Institute publications are not able to, nor intend to, supplant individual training, responsibility, or judgment of the user, or the supplier, of the information presented.

Papers appearing in the ACI Materials Journal are reviewed according to the Institute’s Publication Policy by individuals expert in the subject area of the papers.

MEETINGS

Contributions to ACI Materials Journal

The ACI Materials Journal is an open forum on concrete technology and papers related to this field are always welcome. All material submitted for possible publi-cation must meet the requirements of the “American Concrete Institute Publi-cation Policy” and “Author Guidelines and Submission Procedures.” Prospective authors should request a copy of the Policy and Guidelines from ACI or visit ACI’s Web site at www.concrete.org prior to

submitting contributions.

Papers reporting research must include a statement indicating the significance of the research.

The Institute reserves the right to return, without review, contributions not meeting the requirements of the Publication Policy.

All materials conforming to the Policy requirements will be reviewed for editorial quality and technical content, and every effort will be made to put all acceptable papers into the information channel. However, potentially good papers may be returned to authors when it is not possible to publish them in a reasonable time.

Discussion

All technical material appearing in the

ACI Materials Journal may be discussed.

If the deadline indicated on the contents page is observed, discussion can appear in the designated issue. Discussion should be complete and ready for publication, including finished, reproducible illustra-tions. Discussion must be confined to the scope of the paper and meet the ACI Publi-cation Policy.

Follow the style of the current issue. Be brief—1800 words of double spaced, typewritten copy, including illustrations and tables, is maximum. Count illustrations and tables as 300 words each and submit them on individual sheets. As an approximation, 1 page of text is about 300 words. Submit one original typescript on 8-1/2 x 11 plain white paper, use 1 in. margins, and include two good quality copies of the entire discussion. References should be complete. Do not repeat references cited in original paper; cite them by original number. Closures responding to a single discussion should not exceed 1800-word equivalents in length, and to multiple discussions, approximately one half of the combined lengths of all discussions. Closures are published together with the discussions.

Discuss the paper, not some new or outside work on the same subject. Use references wherever possible instead of repeating available information.

Discussion offered for publication should offer some benefit to the general reader. Discussion which does not meet this requirement will be returned or referred to the author for private reply.

Send manuscripts to:

http://mc.manuscriptcentral.com/aci Send discussions to:

Journals.Manuscripts@concrete.org

2012 SEPTEMBER

19-21—4th International Conference on Accelerated Pavement Testing, Davis, CA, www.ucprc.ucdavis.edu/APT2012

19-21—18th IABSE Congress,s Seoul, South Korea, www.iabse.org/Seoul2012 19-21—8th RILEM International Symposium on Fibre Reinforced Concrete, Guimarães, Portugal, www.befib2012.civil.uminho.pt 20-23—ASCC Annual Conference, Chicago, IL, www.ascconline.org

21-23—4th International Conference on Problematic Soils, Wuhan, China, www.cipremier.com/page.php?487 24-28—15th World Conference on Earthquake Engineering, Lisbon, Portugal, www.15wcee.org

SEPTEMBER/OCTOBER

29-2—PCI Annual Convention & Exhibition and National Bridge Conference, Nashville, TN, www.pci.org

OCTOBER

2-4—Tilt-Up Concrete Association Annual Convention, Amelia Island, FL, www.tilt-up.org

3-6—NCPA 47th Annual Convention, New Orleans, LA, www.precast.org/ convention

11-14—International Concrete Polishing & Staining Conference, Duluth, GA, www.icpsc365.com/icpsc2011

22-23—Building Envelope Technology Symposium, Phoenix, AZ,

www.rci-online.org/symposium.html 28-31—Tenth International Conference on Superplasticizers and Other Chemical Admixtures in Concrete, Prague,

Czech Republic, www.intconference.org

OCTOBER/NOVEMBER

31-2—Twelfth International Conference on Recent Advances in Concrete Technology and Sustainability Issues, Prague, Czech Republic,

www.intconference.org

NOVEMBER

3-8—International Pool | Spa | Patio Expo, New Orleans, LA,

www.poolspapatio.com

4-7—First International Conference for PhD Students in Civil Engineering, Cluj-Napoca, Romania,

http://sens-group.ro/ce2012

11-14—Bridges Middle East, Doha, Qatar, www.bridgesme.com

14-16—Greenbuild 2012, San Francisco, CA, www.greenbuildexpo.org

UPCOMING ACI CONVENTIONS

The following is a list of scheduled ACI conventions: 2012—October 21-25, Sheraton Centre, Toronto, ON, Canada

2013—April 14-18, Hilton & Minneapolis Convention Center, Minneapolis, MN 2013—October 20-24, Hyatt Regency & Phoenix Convention Center, Phoenix, AZ 2014—March 23-27, Grand Sierra Resort, Reno, NV

For additional information, contact: Event Services, ACI

38800 Country Club Drive Farmington Hills, MI 48331 Telephone: (248) 848-3795 e-mail: conventions@concrete.org

(4)

Title no. 109-M47

ACI MATERIALS JOURNAL

TECHNICAL PAPER

ACI Materials Journal, V. 109, No. 5, September-October 2012.

MS No. M-2010-154.R1 received May 25, 2011, and reviewed under Institute publication policies. Copyright © 2012, American Concrete Institute. All rights reserved, including the making of copies unless permission is obtained from the copyright proprietors. Pertinent discussion including author’s closure, if any, will be published in the July-August 2013 ACI Materials Journal if the discussion is received by April 1, 2013.

Creep Testing of Epoxy-Bonded Reinforcing Bar Couplers

by Griffin Brungraber

test exists for reinforcing bar couplers; however, a creep test for adhesive concrete anchors is applicable due to their phenomenological similarity to epoxy-bonded reinforcing bar couplers.

Materials

System C is a two-component structural adhesive. It is a solvent-free, nonshrink, nonsag anchoring compound. The mixing ratio of the system is 1:1, resin:hardener. The resin and hardener are dispensed from a dual-cartridge system and simultaneously mixed in a static mixing nozzle. The system meets ASTM C881/C881M-02; Types I, II, IV, and V; Grade 3; Classes A, B, and C.1

The first component of System C is composed primarily of a bisphenol A-epichlorohydrin diepoxy resin and neopentyl glycol diglycidyl ether mixture; together these compounds act as the epoxy resin. The second component is composed primarily of n-aminoethyl piperazine and a nonylphenol mixture; together these compounds act as an amine adduct.

System F is a two-component, 100% solids, structural epoxy. When mixed, the resin and hardener combine into a smooth, nonabrasive paste adhesive. The mixing ratio of the system is 1:1, resin:hardener. The resin and hardener are dispensed from a dual-cartridge system and simultane-ously mixed in a static mixing nozzle. The system meets ASTM C881/C881M; Types I, II, IV, and V; Grade 3; Classes A, B, and C, except gel times.1 The gel time for the

system varies from 10 to 30 minutes at temperatures from 4 to 32°C (39.2 to 89.6°F), respectively.

The first component of System F is composed primarily of bisphenol A-epichlorohydrin diepoxy resin; the component also contains small portions of methyl toluenesulfonate. The second component is composed primarily of piperazinyl-ethylamine and nonylphenol; the component also contains a proprietary mixture of fillers.

Specimens

Number 5 (No. 16 metric) epoxy-bonded reinforcing bar couplers were assembled with two different epoxy systems. Two specimens were assembled with each epoxy system for a total of four test specimens. Specimen assembly, curing, and testing were performed at a temperature of 23°C (73°F) and a relative humidity of 50%. The test setup is shown sche-matically in Fig. 1 and in a photograph in Fig. 2.

Experimental rationale

Creep of adhesive concrete anchors is typically evalu-ated using ASTM E1512-01(2007)2; therefore, the creep test

A 40-day creep test was performed on epoxy-bonded reinforcing bar coupler specimens to assess their resistance to sustained tensile load. The reinforcing bar couplers were assembled using two different epoxy products. One was the product specified by the reinforcing bar coupler manufacturer; the other was a similar product that had already shown susceptibility to long-term failure in its intended application. The difference in the creep perfor-mance of the epoxy-bonded reinforcing bar couplers assembled with different epoxy products was significant—the manufacturer-specified epoxy product produced acceptable creep performance and the other epoxy product was shown to creep extensively. Keywords: adhesive; anchorage; coupler; creep; epoxy; reinforcing bar; splice.

INTRODUCTION

Reinforcing bar couplers are used to transfer load between reinforcing bars in concrete structures in situations for which a typical lap splice would be inconvenient, inefficient, or inappropriate. Epoxy-bonded reinforcing bar couplers are one type of reinforcing bar coupler that are commercially available and unique in that they transfer load via an epoxy-filled sleeve. Although not all adhesives are epoxies, only epoxy has been used in adhesively bonded reinforcing bar couplers; therefore, the term “epoxy-bonded reinforcing bar coupler” is used to describe a class of construction products, although the mechanisms it refers to would be applicable to any adhesively bonded reinforcing bar coupler.

Adhesives, although commonly used in other branches of engineering, are relatively new to civil engineering (compared to materials such as steel and concrete). Conse-quently, their long-term degradation mechanisms are not as well-understood by the civil engineers responsible for their design as part of a reinforced concrete structure.

Epoxies, like many adhesives, are typically vulnerable to moisture and elevated temperature—two environmental conditions that are commonly found inside reinforced concrete structures, such as bridge decks.

RESEARCH SIGNIFICANCE

Epoxy-bonded reinforcing bar couplers are commercially available and have been installed in numerous reinforced concrete structures. Due to their reliance on an adhesive to transfer load—unique among reinforcing bar couplers— they may be susceptible to the same type of creep fail-ures that have been seen in epoxy anchorage to concrete. This research demonstrates the difference in performance between two commercially available epoxy systems. The results show that the creep performance of epoxy-bonded reinforcing bar couplers varies widely, depending on the epoxy system used.

EXPERIMENTAL INVESTIGATION

Reinforcing bar coupler specimens were assembled using two different types of epoxy. The only variable in their assembly was the epoxy system used. No standardized creep

(5)

creep of reinforcing bar couplers, the results of this test were compared to the results of a test on cementitiously grouted reinforcing bar couplers by Jansson.3

ANALYTICAL PROCEDURE

The results of the test were used to evaluate the perfor-mance of epoxy-bonded reinforcing bar couplers. The analytical procedure for extrapolation of the creep data was taken from ASTM E1512. Data were recorded for 42 days and the results for each system were averaged between the specimens. Figure 3 shows the displacement time test data for both epoxy systems on a logarithmic time scale and fits the data to

( )

ln

y c= ⋅ x b+ (1)

where y is displacement; c is a curve-fitting constant; x is time; and b is a curve-fitting constant.

The curves developed from the data are extrapolated to a time of 600 days, as per ASTM E1512. Figure 4 shows the displacement time test data and associated curve fits extrap-olated to 600 days on a linear time scale.

ACI member Griffin Brungraber is an Assistant Bridge Engineer at T.Y. Lin

Interna-tional. He received his BS from Bucknell University, Lewisburg, PA, and his MS and PhD from the University of California, San Diego, La Jolla, CA. He is a member of ACI Committee 355, Anchorage to Concrete. His research interests include the long-term performance of adhesives for concrete construction, infrastructure durability, and the seismic performance of bridges.

setup for the epoxy-bonded reinforcing bar couplers adapted ASTM E1512 wherever possible. The testing procedure for ASTM E1512 is to apply constant load to the test specimens and measure displacement. The load was initially applied over the course of 1 minute and then maintained for 42 days. The 42-day length of the test, the extrapolation of data to a time of 600 days, and the stress level of the test—40% of reinforcing bar ultimate strength—were all adapted from ASTM E1512. Although no specific standard exists for the Fig. 1—Schematic figure of reinforcing bar coupler test setup.

Fig. 2—Photograph of reinforcing bar coupler test setup.

Fig. 3—Displacement time creep test data and fitted curves.

Fig. 4—Displacement time creep test data and fitted curves extrapolated to 600 days.

(6)

EXPERIMENTAL RESULTS AND DISCUSSION Extrapolated predictions of creep results

The extrapolated creep displacements at 600 days are 0.26 and 3.2 mm (0.010 and 0.124 in.) for Systems C and F, respectively. ASTM E1512 recommends comparing creep displacement to ultimate displacement during a tensile test; however, ICC-ES Acceptance Criteria 58 (AC58)4 is more

explicit in its creep displacement limits. AC584 specifies

displacement at 600 days to be below the lesser of displace-ment at ultimate load or 3.05 mm (0.12 in.). Taking 3 mm (0.12 in.) as the limit, it can be seen that System C meets the requirements of AC584 but that System F slightly exceeds

them. The disparity between the extrapolated creep results of the two systems is significant and these results provide another example of the large disparities in the long-term performance of different ASTM C881/C881M systems. The difference in the performance of the two epoxy systems can be seen in Fig. 5, which compares the specimens after the conclusion of creep testing. An arrow indicates the location of visible, permanent creep displacement on the System F specimen. Creep comparison to other types of reinforcing bar couplers

Epoxy-bonded reinforcing bar couplers are similar to cementitiously grouted reinforcing bar couplers; the only difference is the type of material used to grout the reinforcing bars into a steel sleeve. In one published creep test, cementi-tiously grouted reinforcing bar couplers were found to have creep displacements extrapolated to 600 days of approxi-mately 0.75 mm (0.030 in.).3 This value is less than the

maximum displacement recommended by AC58 of 3 mm (0.12 in.) and also matches the performance of System C evaluated in this research.

FURTHER RESEARCH

Because epoxy degrades more quickly in moister and/or higher-temperature environments, additional research to inves-tigate the creep performance of epoxy-bonded reinforcing bar couplers at a range of temperatures and moist environments should be undertaken. To understand the potential impact of heat and moisture on the creep performance of epoxy-bonded reinforcing bar couplers, the environmental condi-tions that can be expected during service inside a reinforced concrete structure should be used.

CONCLUSIONS

Based on the results of this experimental investigation of creep loading, the following conclusions are drawn:

1. Epoxy-bonded reinforcing bar couplers do creep measurably due to the creep of the epoxy grout under sustained load. This phenomenon is similar to the creep behavior of epoxy when used for anchorage to concrete.

2. The extrapolated creep performance of epoxy-bonded reinforcing bar couplers can vary widely, depending on which epoxy system is used to assemble them.

3. Epoxy-bonded reinforcing bar couplers, if assembled with a well-suited epoxy system, have adequate creep performance in dry, room-temperature conditions.

4. Epoxy-bonded reinforcing bar couplers, if assembled with a well-suited epoxy system, have similar creep perfor-mance to other types of nonadhesive, grouted reinforcing bar couplers.

ACKNOWLEDGMENTS

The author wishes to express his gratitude and sincere appreciation to the California Department of Transportation for financing this research, V. Karbhari for overseeing the research, and A. Pridmore and the staff of the UCSD Powell and SRMD Laboratories for their assistance.

REFERENCES

1. ASTM C881/C881M-02, “Standard Specification for Epoxy-Resin-Base Bonding Systems for Concrete,” ASTM International, West Conshohocken, PA, 2002, 6 pp.

2. ASTM E1512-01(2007), “Standard Test Methods for Testing Bond Performance of Bonded Anchors,” ASTM International, West Conshohocken, PA, 2001, 5 pp.

3. Jansson, P. O., “Evaluation of Grout-Filled Mechanical Splices for Precast Concrete Construction,” Report No. TI-2094, Michigan Depart-ment of Transportation, Construction and Technology Division, Lansing, MI, 2008, 68 pp.

4. ICC-ES Acceptance Criteria 58 (AC58), “Acceptance Criteria for Adhesive Anchors in Concrete and Masonry Elements,” International Congress of Building Officials Evaluation Services (ICBO ES), 2001, 17 pp.

Fig. 5—Photograph of reinforcing bar coupler specimens after conclusion of testing.

(7)
(8)

Title no. 109-M48

ACI MATERIALS JOURNAL

TECHNICAL PAPER

ACI Materials Journal, V. 109, No. 5, September-October 2012.

MS No. M-2011-033.R3 received December 6, 2011, and reviewed under Institute publication policies. Copyright © 2012, American Concrete Institute. All rights reserved, including the making of copies unless permission is obtained from the copyright proprietors. Pertinent discussion including author’s closure, if any, will be published in the July-August 2013 ACI Materials Journal if the discussion is received by April 1, 2013.

Effect of Na

2

SiO

3

/NaOH Ratios and NaOH Molarities on

Compressive Strength of Fly-Ash-Based Geopolymer

by A. M. Mustafa Al Bakri, H. Kamarudin, M. Bnhussain, A. R. Rafiza, and Y. Zarina

and moldable paste) and stored at mild temperatures (T < 100°C [212°F]) for a short period of time to produce a mate-rial with good binding properties. At the end of this process, an amorphous alkaline alumino-silicate gel is formed as the main reaction product. In addition, Na-herschelite-type zeolites and hydroxysodalite are formed as secondary reac-tion products.4-6

The most-used alkaline activators are a mixture of sodium or potassium hydroxide (NaOH or KOH) with sodium water glass (nSiO2Na2O) or potassium water glass

(nSiO2K2O).1,7-9 One of the factors that influences the

compressive strength of geopolymer is the Na2SiO3/NaOH

ratio.10,11 Rattanasak and Chindaprasirt12 concluded that the

use of an Na2SiO3/NaOH ratio of 1.0 produced a product

with a compressive strength as high as 70 MPa (10.15 ksi). A study conducted by Hardjito et al.10 showed that the use

of an Na2SiO3/NaOH ratio of 2.5 gave the highest

compres-sive strength of 56.8 MPa (8.24 ksi), whereas a ratio of 0.4 resulted in a lower compressive strength of 17.3 MPa (2.51 ksi).

The concentrations of NaOH solution that can be used are in the range of 8 to 16 M.8 Some researchers7,12,13 have

studied the effects of different molarities of NaOH on the geopolymer. Puertas et al.13 stated that, at 28 days of

reac-tion, a mixture of equal parts FA and slag activated with 10 M NaOH and cured at 25°C (77°F) develops a compressive strength of approximately 50 MPa (7.25 ksi). Rattanasak and Chindaprasirt12 concluded that a geopolymer mortar strength

of up to 70 MPa (10.15 ksi) is obtained when the mixture is formulated with 10 M NaOH and an Na2SiO3/NaOH ratio of

1.0. Palomo et al.7 reported that a 12 M activator

concentra-tion leads to better results than an 18 M concentraconcentra-tion. In this study, the effects of various Na2SiO3/NaOH ratios

and NaOH molarities on FA geopolymer paste were studied. Six different Na2SiO3/NaOH ratios (0.5, 1.0, 1.5, 2.0, 2.5,

and 3.0) and six different NaOH molarities (6, 8, 10, 12, 14, and 16 M) were used in this study. The geopolymer properties, such as compressive strength, water absorption, porosity, and density, were used as indicators to prove that the geopolymer has similar properties to PC.

RESEARCH SIGNIFICANCE

The Na2SiO3 and NaOH solution requires different mass

proportions with different FAs to obtain high compressive strength. Most of the studies on geopolymer concentrated Carbon dioxide (CO2) emissions from the production of 1 ton

(2204.62 lb) of cement vary between 0.05 and 0.13 tons (110.23 and 286.60 lb). It is important to reduce CO2 emissions by the greater use of substitutes for portland cement (PC), such as fly ash (FA), clay, and other geo-based materials. This paper studies the processing of geopolymers using FA and alkaline activators. The factors that influence the early-age compressive strength, such as the sodium hydroxide (NaOH) molarity and Na2SiO3/NaOH ratios, were studied. Sodium hydroxide and sodium silicate solutions were used as alkaline activators. The geopolymer paste samples were cured at 70°C (158°F) for 1 day and kept at room temperature until testing (the seventh day). The compressive strength was measured after 7 days. The results show that the geopolymer paste with a combination of an Na2SiO3/NaOH ratio of 2.5 and a 12 M NaOH concentration produces the highest compressive strength. The density obtained for geopolymer for PC is in the range of 1760 to 1855 kg/m3 (0.064 to 0.067 lb/in.3). The porosity of the geopolymer was in the range of 12.16 to 26.19%, and the water absorption was in the range of 5.03 to 8.13%. The results of scanning electron microscopy (SEM) indicated that the samples with a denser matrix and less unreacted FA contributed to the maximum compressive strength. In the X-ray diffraction (XRD) patterns, the intensity of quartz content at 12 M was highly detected compared to the 6 and 10 M solutions.

Keywords: alkaline activation; compressive strength; geopolymer;

Na2SiO3/NaOH ratio; NaOH molarity; scanning electron microscopy;

X-ray diffraction.

INTRODUCTION

The term “geopolymer” was first applied by Davido-vits1 to alkali alumino-silicate binders formed by the

alkali-silicate activation of alumino-silicate materials. Geopolymers (green polymeric concrete) are amorphous to the semi-crystalline equivalent of certain zeolitic mate-rials with excellent properties, such as high fire and erosion resistances, as well as high strength. Recent works2 have

shown that the addition of moderate amounts of minerals to a geopolymer can yield significant improvements in the geopolymer’s structure and properties.

The alkaline liquid could be used to react with the silicon (Si) and aluminum (Al) in a source material of natural minerals or in by-product materials, such as fly ash (FA) and rice husk ash, to produce binders.1 The alkaline activation of

materials can be defined as a chemical process that provides a rapid change of specific structures—partial or completely amorphous—into compact cemented frameworks.3 The

alkali activation of FA is a process that differs widely from portland cement (PC) hydration and is very similar to the chemistry involved in the synthesis of large groups of zeolites.4 Some researchers5,6 have described the alkali

activation of FA (AAFA) as a physicochemical process in which this powdery solid is mixed with a concentrated alkali solution (in a suitable proportion to produce a workable

(9)

A. M. Mustafa Al Bakri is a Senior Lecturer and PhD Candidate at Universiti

Malaysia Perlis (UniMAP), Perlis, Malaysia. He received his BS in civil engineering and his MS in material engineering from Universiti Sains Malaysia (USM), Penang, Malaysia. His research interests include green and construction materials.

H. Kamarudin is a Vice Chancellor at UniMAP. He received his BS, MS, and PhD in

chemistry from USM. His research interests include chemistry reaction and sustain-able material.

M. Bnhussain is a Director of the Program of Advanced Material at the King

Abdu-laziz City for Science and Technology, Riyadh, Saudi Arabia. He received his BS in civil engineering from King Abdulaziz University, Jeddah, Saudi Arabia, and his PhD in civil engineering materials from the University of Leeds, Leeds, UK. His research interests include construction materials, including green polymeric concrete.

A. R. Rafiza is a Researcher at UniMAP. She received her BS and MS in civil

engi-neering (structural engiengi-neering) from USM. Her research interests include seismic modeling, structural analysis, and green polymeric concrete.

Y. Zarina is a Researcher at UniMAP. She received her BS and MS in civil

engi-neering (structural engiengi-neering) from USM. Her research interests include seismic modeling, structural analysis, and green polymeric concrete.

Table 1—Chemical composition of FA

Chemical composition Percentage, % SiO2 52.11 Al2O3 23.59 Fe2O3 7.39 TiO2 0.88 CaO 2.61 MgO 0.78 Na2O 0.42 K2O 0.80 P2O5 1.31 SO3 0.49 MnO 0.03

Table 2—Mixture design details for various ratio of Na2SiO3/NaOH

FA/alkaline

activator ratio NaOH ratioNa2SiO3/ lb (g)FA, Nalb (g)2SiO3, NaOH,lb (g)

2.5 0.5 1.33 (605) 0.18 (80) 0.35 (160) 1.0 0.26 (120) 0.26 (120) 1.5 0.32 (145) 0.21 (95) 2.0 0.35 (160) 0.18 (80) 2.5 0.37 (170) 0.15 (70) 3.0 0.40 (180) 0.13 (60)

on only two different molarities of NaOH. This study deals with more details on different NaOH molarities (6, 8, 10, 12, 14, and 16 M) of geopolymer pastes. The research data presented in this paper are useful to understand the effect of various Na2SiO3/NaOH ratios and different molarities on

the geopolymer, which influence the compressive strength results. The compressive strength of specimens decreases with increasing porosity and water absorption. The scanning electron microscopy (SEM) and X-ray diffraction (XRD) tests are also important to understand the microstructural characteristics and phases involved in geopolymer.

EXPERIMENTAL PROCEDURE Materials

In this research, low-calcium Class F dry FA14 obtained

from the Sultan Abdul Aziz Power Station in Kapar, Selangor, Malaysia, was used as a base material to make the geopolymers. The chemical composition of FA is shown in Table 1. The table shows that this FA consists of a high composition of silicon and aluminum oxide of 75.7%.

The mixture of sodium silicate (Na2SiO3) and sodium

hydroxide (NaOH) was used as an alkaline activator in this study. NaOH in pellet form with 97% purity8,15,16 and

Na2SiO3 consisting of Na2O = 9.4%, SiO2 = 30.1%, and H2O

= 60.5% (with a weight ratio of SiO2/Na2O of 3.20 to 3.30 and

a specific gravity of 20°C [68°F] = 1.4 g/cm3 [0.05 lb/in.3])

were used in this study. Mixing method

The ratio of FA to alkaline activator was 2.5 and was kept fixed for all mixtures. The use of this ratio is due to the work of Hardjito et al.,10,17 which states that a ratio of FA

to alkaline activator of 2.5 produces the highest compres-sive strength on the 28th day of testing. In this study, various Na2SiO3/NaOH ratios (0.5, 1.0, 1.5, 2.0, 2.5, and 3.0) were

used to determine the highest compressive strength. It should be noted that Na2SiO3 is a quick-setting chemical

and binding material that requires a different combination of proportions with NaOH molarities. The NaOH molarity was kept constant at 10 M. The total mass of each dry and solutions material used is shown in Table 2. The best ratio of the Na2SiO3/NaOH result (highest compressive strength)

was further used in this study.

To prepare the NaOH solution, NaOH pellets were dissolved in 1 L (0.26 gal.) of distilled water in a volumetric flask for six different NaOH concentrations (6, 8, 10, 12, 14, and 16 M) with different masses of NaOH, as shown in Table 3. The best mixture design (the FA/alkaline activator and Na2SiO3/NaOH ratios were fixed as 2.5 as their highest

compressive strength result obtained previously) was used to determine the best NaOH molarity solution. The total mass of each of the dry and solutions materials used was kept constant for the geopolymer paste for all samples (6, 8, 10, 12, 14, and 16 M) with different molarities.

An alkaline activator consisting of a combination of NaOH and Na2SiO3 was prepared just before mixing with FA to

ensure the reactivity of the solution. The addition of sodium silicate is to enhance the geopolymerization process.18 The

FA and alkaline activator were mixed together in the mixer until a homogeneous paste was achieved. This mixing process could be handled for up to 10 minutes for each mixture with different NaOH molarities, as shown in Fig. 1. Table 3—Details of preparing NaOH solutions

NaOH molarity, M 1 L (0.26 gal.) of distilled water, lb (g)Masses of NaOH pellets dissolved in 6 0.53 (240) 8 0.71 (320) 10 0.88 (400) 12 1.06 (480) 14 1.23 (560) 16 1.41 (640)

(10)

Casting and curing

The geopolymer paste was placed in a 50 x 50 x 50 mm (1.97 x 1.97 x 1.97 in.) cube mold and cured in an oven for 1 day1 at 70°C (158°F).1,19 After the samples were cured

in an oven, the molds were removed from the furnace and left to cool to room temperature before demolding.1 The

samples were then left to room temperature until they were loaded in compression at the seventh day.1

Testing

The compressive strength test was performed on geopolymer paste samples in accordance with BS 1881-116:198320 using a mechanical testing machine to obtain

the ultimate strength of the geopolymer. The samples were loaded with 50.00 kN (11.24 kips) and the speed rate of loading was 5.00 mm/min (0.20 in./min). The loading pace rate was 0.1 kN/s (22.48 lb/s. The reported compressive strength values are an average of three samples for each ratio.

The sample densities were determined by the mass and volumes of the cubes in accordance with BS 1881-114:1983.21 The results of densities are taken as an average

of three samples for each ratio.

The water absorption test was performed in accordance with ASTM C140 to determine the porosity of the samples. The sample masses were measured before and after immer-sion in water. The difference in weight was calculated to determine the water absorption of the samples, as shown in Eq. (1). Water Absorption S D 100 D M M M − = • (1)

where MS is saturated mass, units; and MD is dry mass, units.

A scanning electron microscope was used to reveal the microstructure of the geopolymer paste. The test was carried out using secondary and backscattered electron detectors.

XRD patterns were performed using an X-ray diffractom-eter. The XRD test was held for phase analysis of the orig-inal FA and to investigate the crystallinity of the geopolymer samples that gave high compressive strength. The samples were prepared in powder form. For the prepared geopolymer samples, the samples were first cut into 0.5 mm (1.97 in.) thick slices and then ground into powder form as required.

EXPERIMENTAL RESULTS AND DISCUSSION Compressive strength

The Na2SiO3/NaOH ratio and NaOH molarity affects the

compressive strength of the geopolymer. The compressive strengths for different Na2SiO3/NaOH ratios are shown in

Fig. 2. The highest compressive strengths of 57.00 MPa (8.27 ksi) were observed at an Na2SiO3/NaOH ratio of 2.5,

which is 18% higher than an Na2SiO3/NaOH ratio of 3.0 on

the seventh day of testing. Hardjito et al.10 and Sathia et

al.22 stated that compressive strength increases as FA content

and concentration of the activator solution increase. This is due to the increase in the sodium oxide content, which is mainly required for the geopolymerization reaction. The compressive strength of the product for an Na2SiO3/NaOH

ratio of 3.0 was low, however, which could be due to the excess OH– concentration in the mixtures.18 Furthermore, the

excess sodium content can form sodium carbonate by atmo-spheric carbonation and this may disrupt the polymerization

process.23 The lowest compressive strength was found at an

Na2SiO3/NaOH ratio of 0.5 with 40.00 MPa (5.80 ksi).

The compressive strength results for various NaOH molar-ities on the seventh day of testing are shown in Fig. 3. For the seventh day of testing, the 12 M NaOH samples produced the highest compressive strengths of 94.59 MPa (13.72 ksi). This is due to the increase of Na ions in the system, which was important for the geopolymerization because Na ions were used to balance the charges and formed the alumino-silicate networks as the binder in the mixture.24 At a low

Fig. 1—Mixture of FA with alkaline activator.

Fig. 2—Compressive strength of various Na2SiO3/NaOH

ratios.

(11)

which reduced the compressive strength of the sample. The amount of liquid in the systems affects the saturation rate of the ionic species and the strength of the geopolymer. The geopolymer microstructures with different NaOH molarities are shown in Fig. 5(a) through (f).

As the NaOH molarity increases from 6 to 16 M, the microstructure of the resultant geopolymer contains a smaller proportion of unreacted FA microspheres. As can be seen from Fig. 5(a) and (b), a large proportion of FA still did not completely dissolve. Figure 5(d) shows the least unreacted FA for the alkaline activator that gave the highest compressive strength of 94.59 MPa (13.72 ksi) on the seventh testing day. This suggests that the dissolution of silica and alumina in the geopolymerization process that formed the alumino-silicate gel in the 12 M NaOH sample was higher, contributing to the stability of the geopolymer during the hardening process and giving a high compressive strength of geopolymer.29 The pores are indicated on the figures by

arrows, and cracks are also found in the matrix (Fig. 5(a), (b), (c), (e), and (f)), which would limit the binding capacity and lead to a lower compressive strength.

XRD pattern

The results of the XRD of FA and geopolymer pastes with 6, 10, and 12 M NaOH concentrations are shown in Fig. 6. The original FA and the 6, 10, and 12 M NaOH molarity pastes had a similar diffraction pattern and did not signifi-cantly alter the degree of amorphous and crystallization of FA. For 12 M NaOH molarity, the XRD pattern showed that the intensity of quartz content was highly detected at 2q = 26.5 degrees compared to the 6 and 10 M solutions. This also indicated that the new crystalline phases were detected in the geopolymer paste and that the 12 M NaOH solution contains the highest amount of crystalline and had a higher compres-sive strength compared to FA. Alvarez-Ayuso et al.30 stated

that the increase in the crystalline product increased the compressive strength of the geopolymer. The formation of crystallines in the samples—studied by quantitative XRD— depended strongly on the NaOH concentration. The crystal-lization rate increased with increasing NaOH content and the proportion of the crystalline phase gradually increased with a longer curing time.31

The obtained results suggest that the composition of the alumino-silicate gel formed by the reaction between FA and NaOH molarity, the geopolymerization is low due to the

low concentration of base and, hence, less leaching of silica and alumina from the source material.25 The lowest

compressive strength was found for the 6 M NaOH tion with 40.00 MPa (5.8 ksi). After 12 M of NaOH solu-tion, the compressive strength decreased. The high viscosity hinders the leaching of the silica and alumina, resulting in a lesser degree of geopolymerization26 as compared to that

of the 12 M NaOH paste. Palomo et al.27 also found that

a 12 M NaOH solution produced better results than the corresponding 18 M activator.

The compressive strength of PC paste was in the range of 17 to 20 MPa (2.47 to 2.90 ksi) at 28 days of testing; however, geopolymer paste can achieve a better performance of compressive strength of 94.59 MPa (13.72 ksi) at 7 days of testing. This clearly shows that geopolymer paste can achieve a higher compressive strength than PC paste. Density, porosity, and water absorption

The densities of the geopolymer samples are in the range of 1760 to 1855 kg/m3 (0.064 to 0.067 lb/in.3) for 7 days

of testing. Higher alkali contents in the mixture yield better reactivity with the FA, resulting in a denser microstruc-ture.28 The density of normal PC paste is 1750 to 2400 kg/m3

(0.063 to 0.087 lb/in.3). Because the density obtained from

the geopolymer samples is in this range, the samples possess the same properties as PC paste.

The porosity of the geopolymer was in the range of 12.16 to 26.19%, and the paste specimen produced water absorption in the range of 5.03 to 8.13% for the seventh day of testing. According to Thokchom et al.,28 the compressive

strength of specimens decreases with increasing porosity and water absorption.

SEM analysis for geopolymer paste

The microstructure of FA-based geopolymer for different mixture designs was observed with SEM, as shown in Fig. 4(a) and (b). It showed that the materials are hetero-geneous, with partially reacted and unreacted FAs existing on the dense, gel-like matrix geopolymer. The sample with the FA/alkaline activator and an Na2SiO3/NaOH ratio of 2.5

(Fig. 4(a)) showed a more dense matrix and less unreacted FA, which contributed to a maximum compressive strength of 8.27 ksi (57 MPa). Figure 4(b) shows the microcracks that exist on the sample with an FA/alkaline activator ratio of 2.5,

Fig. 4—SEM pictures of geopolymer paste with various mixture designs: (a) FA/alka-line activator of 2.5 and Na2SiO3/NaOH of 2.5; and (b) FA/alkaline activator of 2.5 and

(12)

the alkaline activator is variable and depends on the reac-tivity and the type and concentration of the activators.32

CONCLUSIONS

Based on the experimental work reported in this paper, it can be concluded that the Na2SiO3/NaOH ratios and NaOH

molarities affect the compressive strength of FA-based geopolymer. The Na2SiO3/NaOH ratio of 2.5 contributed to

the high compressive strength of 57.00 MPa (8.27 ksi). The highest NaOH molarity does not necessarily give the highest compressive strength. The FA-based geopolymer with 12 M NaOH showed excellent results, including a high compres-sive strength of up to 94.59 MPa (13.72 ksi) on the seventh testing day. This was proven by the XRD results, which show that the intensity of the quartz content at 12 M was highly detected and contributed to the highest compressive strength compared to the 6 and 10 M solutions. The density obtained for the geopolymer (1760 to 1855 kg/m3 [0.064 to

0.067 lb/in.3]) was in the range for PC of 1750 to 2400 kg/m3

(0.063 to 0.087 lb/in.3). The samples with a denser matrix

and less unreacted FA contributed to the maximum

compres-Fig. 5—SEM image of geopolymer with: (a) 6 M; (b) 8 M; (c) 10 M; (d) 12 M; (e) 14 M; and (f) 16 M of NaOH solution.

Fig. 6—XRD patterns of FA and geopolymer paste samples with 6, 10, and 12 M NaOH concentrations.

(13)

15. Buchwald, A., and Schulz, M., “Alkali-Activated Binders by Use of Industrial By-Products,” Cement and Concrete Research, V. 35, No. 5, May 2005, pp. 968-973.

16. Wallah, S. E., “Drying Shrinkage of Heat-Cured FA-Based Geopolymer Concrete,” Modern Applied Science, V. 3, No. 12, Dec. 2009, pp. 12-21.

17. Hardjito, D.; Cheak, C. C.; and Lee Ing, C. H., “Strength and Setting Time of Low Calcium FA-Based Geopolymer Mortar,” Modern Applied

Science, V. 2, No. 4, July 2008, pp. 3-11.

18. Xu, H., and Deventer, J., “The Geopolymerisation of Alumino-Sili-cate Minerals,” International Journal of Mineral Processing, V. 59, No. 3, 2000, pp. 247-266.

19. Van Jaarsveld, J. G. S.; Van Deventer, J. S. J.; and Lukey, G. C. C., “The Effect of Composition and Temperature on the Properties of Fly Ash and Kaolinite-Based Geopolymers,” Chemical Engineering Journal, V. 4001, 2002, pp. 1-11.

20. BS 1881-116:1983, “Testing Concrete. Method for Determination of Compressive Strength of Concrete Cubes,” British Standards Institution, London, UK, 1983, 8 pp.

21. BS 1881-114:1983, “Testing Concrete. Methods for Determination of Density of Hardened Concrete,” British Standards Institution, London, UK, 1983, 8 pp.

22. Sathia, R.; Ganesh Babu, K.; and Santhanam, M., “Durability Study of Low Calcium FA Geopolymer Concrete,” The 3rd ACF International

Conference ACF/VCA, 2008, pp. 1153-1159.

23. Barbosa, V. F. F.; Mackenzie, K. J. D.; and Thaumaturgo, C., “Synthesis and Characterisation of Materials Based on Inorganic Poly-mers of Alumina and Silica: Sodium Polysialate PolyPoly-mers,” International

Journal of Inorganic Materials, V. 2, 2000, pp. 309-317.

24. Sathonsaowaphak, A.; Chindaprasirt, P.; and Pimraksa, K., “Work-ability and Strength of Lignite Bottom Ash Geopolymer Mortar,” Journal of

Hazardous Materials, V. 168, No. 1, Aug. 2009, pp. 44-50.

25. Alonso, S., and Palomo, A., “Alkaline Activation of Metakaolin and Calcium Hydroxide Mixtures: Influence of Temperature, Activator Concen-tration and Solid Ratio,” Materials Letters, V. 47, No. 1-2, 2001, pp. 55-62.

26. Chindaprasirt, P.; Jaturapitakkul, C.; Chalee, W.; and Rattanasak, U., “Comparative Study on the Characteristic of FA and Bottom Ash Geopolymer,” Waste Management, V. 29, No. 2, Feb. 2009, pp. 539-543.

27. Palomo, A.; Blanco, M.; Granizo, M.; Puertas, F.; Vazquez, T.; and Grutzeck, M., “Chemical Stability of Cementitious Materials Based on Metakaolin,” Cement and Concrete Research, V. 29, No. 7, July 1999, pp. 997-1004.

28. Thokchom, S.; Ghosh, P.; and Ghosh, S., “Effect of Water Absorp-tion, Porosity, and Sorptivity on Durability of Geopolymer Mortars,” ARPN

Journal of Engineering and Applied Sciences, V. 4, No. 7, Sept. 2009, pp. 28-32.

29. Bakharev, T., “Resistance of Geopolymer Materials to Acid Attack,”

Cement and Concrete Research, V. 35, No. 4, 2005, pp. 658-670. 30. Alvarez-Ayuso, E.; Querol, X.; Alastuey, A.; Moreno, N.; Izqui-erdo, M.; Font, O.; Moreno, T.; Ramonich, E. V.; Diez, S.; and Barra, M., “Environmental, Physical and Structural Characterisation of Geopolymer Matrixes Synthesised from Coal (Co-)Combustion FAes,” Journal of

Hazardous Materials, V. 154, 2008, pp. 175-183.

31. Zhang, B.; MacKenzie, K. J. D.; and Brown, I. W. M., “Crystalline Phase Formation in Metakaolinite Geopolymers Activated with NaOH and Sodium Silicate,” Journal of Materials Science, V. 44, 2009, pp. 4668-4676.

32. Duchesne, J.; Duong, L.; Bostrom, T.; and Frost, R., “Microstructure Study of Early In Situ Reaction of FA Geopolymer Observed by Environ-mental Scanning Electron Microscopy (ESEM),” Waste and Biomass

Valo-rization, V. 1, No. 3, 2010, pp. 367-377.

sive strength. A higher dissolution of silica and alumina in the geopolymerization process that forms alumino-silicate gel contributes to the higher compressive strength of the geopolymer; however, different FAs from other countries may need different ratios to achieve high compressive strength. FA-based geopolymer has excellent properties due to the very high compressive strength obtained in this study. Further studies need to be conducted to find the best mixture design to achieve the highest compressive strength of FA-based geopolymer concrete.

ACKNOWLEDGMENTS

A grant from the King Abdulaziz City for Science and Technology (KACST) for this research project is gratefully acknowledged.

REFERENCES

1. Davidovits, J., “High-Alkali Cements for 21st Century Concretes,”

Concrete Technology: Past, Present, and Future, SP-144, P. K. Mehta, ed., American Concrete Institute, Farmington Hills, MI, 1994, pp. 383-397.

2. Hu, M.; Zhu, X.; and Long, F., “Alkali-Activated FA-Based Geopoly-mers with Zeolite or Bentonite as Additives,” Journal of Cement and

Concrete Composites, V. 31, No. 10, Nov. 2009, pp. 762-768.

3. Fernández-Jiménez, A., and Palomo, A., “Characterisation of FAes. Potential Reactivity as Alkaline Cements,” Fuel, V. 82, No. 18, Dec. 2003, pp. 2259-2265.

4. Criado, M.; Palomo, A.; and Fernández-Jiménez, A., “Alkali Activa-tion of FAes. Part 1: Effect of Curing CondiActiva-tions on the CarbonaActiva-tion of the Reaction Products,” Fuel, V. 84, No. 16, Nov. 2005, pp. 2048-2054.

5. Fernández-Jiménez, A.; de la Torre, A. G.; Palomo, A.; Lopez-Olmo, G.; Alonso, M. M.; and Aranda, M. A. G., “Quantitative Determina-tion of Phases in the Alkaline ActivaDetermina-tion of FA. Part II: Degree of ReacDetermina-tion,”

Fuel, V. 85, No. 14-15, Oct. 2006, pp. 1960-1969.

6. Fernández-Jiménez, A., and Palomo, A., “Composition and Micro-structure of Alkali Activated FA Binder: Effect of the Activator,” Cement

and Concrete Research, V. 35, No. 10, Oct. 2005, pp. 1984-1992. 7. Palomo, A.; Grutzek, M. W.; and Blanco, M. T., “Alkali-Activated FAes: A Cement for the Future,” Cement and Concrete Research, V. 29, No. 8, Aug. 1999, pp. 1323-1329.

8. Rangan, B. V., Concrete Construction Engineering Handbook, Taylor and Francis Group, LLC, London, UK, 2008, pp. 1-19.

9. Pacheco-Torgal, F.; Castro-Gomes, J.; and Jalali, S., “Alkali-Activated Binders: A Review. Part 2. About Materials and Binders Manufacture,”

Journal of Construction and Building Material, V. 22, No. 7, July 2008, pp. 1315-1322.

10. Hardjito, D.; Wallah, S. E.; Sumajouw, D. M. J.; and Rangan, B. V., “On the Development of FA-Based Geopolymer Concrete,” ACI Materials

Journal, V. 101, No. 6, Nov.-Dec. 2004, pp. 467-472.

11. Mustafa Al Bakri, A. M.; Kamarudin, H.; BnHussain, M.; Khairul Nizar, I.; Rafiza, A. R.; and Zarina, Y., “Microstructure of Different NaOH Molarity of Fly Ash-Based Green Polymeric Cement,” Journal of

Engi-neering and Technology Research, V. 3, No. 2, 2011, pp. 44-49.

12. Rattanasak, U., and Chindaprasirt, P., “Influence of NaOH Solution on the Synthesis of FA Geopolymer,” Minerals Engineering, V. 22, No. 12, Oct. 2009, pp. 1073-1078.

13. Puertas, F.; Martinez-Ramirez, S.; Alonso, S.; and Vazquez, T., “Alkali-Activated FA/Slag Cement: Strength Behaviour and Hydration Products,” Cement and Concrete Research, V. 30, No. 10, Oct. 2000, pp. 1625-1632.

14. Chindaprasirt, P.; Chareerat, T.; and Sirivivatnanon, V., “Work-ability and Strength of Coarse High Calcium FA Geopolymer,” Cement and

(14)

Title no. 109-M49

ACI MATERIALS JOURNAL

TECHNICAL PAPER

ACI Materials Journal, V. 109, No. 5, September-October 2012.

MS No. M-2011-042.R3 received January 3, 2012, and reviewed under Institute publication policies. Copyright © 2012, American Concrete Institute. All rights reserved, including the making of copies unless permission is obtained from the copyright proprietors. Pertinent discussion including author’s closure, if any, will be published in the July-August 2013 ACI Materials Journal if the discussion is received by April 1, 2013.

Effect of Using Mortar Interface and Overlays on Masonry

Behavior by Using Taguchi Method

by Mariam Farouk Ghazy

to out-of-plane and in-plane vertical and lateral stresses was investigated.4 A significant strength increase was observed

for all strengthened specimens.

Experimental investigations that studied the rehabilita-tion of masonry walls with reinforced mortar overlays were carried out.5,6 The general conclusion was that the

applica-tion of mortar overlays is a powerful rehabilitaapplica-tion technique for masonry constructions.

The results of a series of axial compression tests on concrete block wallets coated with cement mortar overlays were presented. Different types of mortars and combina-tions with steel welded meshes and fibers were tested.6,7 The

main conclusion was that the application of mortar overlays increases the wall strength, but not in a uniform manner; the strengthening efficiency of wallets loaded in axial compres-sion is not proportional to the overlay mortar strength because it can be affected by the failure mechanisms of the wall. Steel mesh-reinforced overlays, in combination with high-strength mortar, show better efficiency because the steel mesh mitigates the damage effects in the block wall and in the overlays themselves.7

A relationship between the masonry prism compressive strength and bond strength was obtained.8 The results clearly

indicate that an increase in bond strength, while keeping the mortar strength constant, leads to an increase in the compres-sive strength of masonry.

The various influences on masonry behavior caused by brick-mortar interface properties were investigated.9 The

brick-mortar interface is characterized by a central bonded area of variable size and shape surrounded by fissures near the masonry surface. The interface is usually the weakest spot during bending and shear. At the fissure tip (10 to 15 mm [0.39 to 0.59 in.] deep from the surface), the bricks split, showing that high strain levels develop around the central brick-mortar contact area. In stack-bonded masonry prisms, the fissures close before the bricks notice-ably deform. Only after closing of the horizontal fissures, which occurs at considerable loads, do the outer sides of the bricks become stressed.

The behavior of lime-based renders on the masonry walls made from solid clay bricks and parallel tests of the characteristics of fresh and hardened lime-based mortars was studied.10 The tests were carried out on five different

lime-based mortar mixtures. The results show that in cases when higher ductility of the hardened lime-based renders The effect and optimization of using different types of mortar for

both interface and overlays on masonry behavior was investi-gated by using the Taguchi method. The experimental studies were conducted under varying types of mortar. The mortar was rein-forced with a polypropylene (PP) fiber with a volume fraction (0, 1, and 2%) by volume of mortar. An orthogonal array (OA), the signal-to-noise ratio (S/N), and the analysis of variance (ANOVA)

were employed to study the performance characteristics of the masonry prisms and walls.

The conclusion revealed that the number of overlays and the type of interface mortar were the most influential factors on the masonry prism’s compressive strength and flexural bond strength, respectively. Moreover, the application of mortar over-lays increases the wall compressive strength.

Keywords: compressive strength; flexural bond strength; masonry walls;

overlay; polypropylene fibers; signal-to-noise ratio; Taguchi method.

INTRODUCTION

Masonry—specifically brick and mortar—requires much more than knowledge of the brick or mortar individually to fully understand its properties. Why would two materials of very different strengths combine to form a composite system that displays a yield strength intermediate to both and not that of the lower-strength material? This materials interaction is being reviewed at the University of Colorado, Boulder.1 Recent advances in masonry technology brought

new materials, building techniques, and rational methods of structural analysis; however, the structural behavior of masonry walls is still a complex matter. A concrete masonry wall is made of at least two different materials that are assembled under diverse conditions of execution and quality control. If the masonry wall is coated on both sides with cement mortar overlays, these overlays become part of the composite element. In this case, the wall can be seen as a sandwich panel where the overlays are the covering sheets and the concrete masonry wall is the core.2

The use of fiber-reinforced polymers (FRPs) as external wraps for the structural rehabilitation of buildings and bridges has taken tremendous strides forward over the past decade. In particular, extensive use of this structural rehabili-tation system has been made in the area of masonry struc-tures.2,3 The glass fiber-reinforced polymer (GFRP) wrap

system provided adequate tension reinforcement to develop the compressive strength of the masonry, thus substantiating its utility in this application.

Epoxy-bonding a thin layer of composite materials to the exterior surfaces of unreinforced masonry (URM) walls forces the individual brick or block elements to act as an integrated system. The high tensile strength of composite materials can be used to significantly increase the shear and flexural capacity of URM walls. The application of GFRP laminates in strengthening the concrete block walls subjected

(15)

has been made to investigate the effect of using mortar interface and overlays on masonry behavior by using the Taguchi11 method. Furthermore, the analysis of variance

(ANOVA) was used to discuss the relative importance of all control factors.

RESEARCH SIGNIFICANCE

The effect and optimization of using different types of mortar for both interface and overlays on masonry behavior was investigated in this study by using the Taguchi11 method as

a new technique in experimental design. Taguchi’s11 method

of experimental design was used in this study to provide a simple, efficient, and systematic approach for the optimi-zation of experimental designs. The experimental studies were conducted under varying types of mortars to study the masonry behavior. Three basic control factors were taken into consideration: the type of mortar interface (A), the type of mortar overlays (B), and the number of overlays (C).

EXPERIMENTAL WORK Materials and means

The constituent materials used in this study were locally available materials specified by the following:

1. Brick units: Perforated shale brick units (10 vertical holes) were obtained from various manufacturers to select the brick with the best performance (with a higher compres-sive strength and low absorption). The absorption proper-ties of the brick may affect the mortar structure and, conse-quently, the mechanical behavior.9 The mechanical

prop-erties of the brick units are given in Table 1, according to ES 4763/200513 and ECP 204-2005.14 A hydraulic testing

machine with a total capacity of 348.2 kips (1550 kN) was used to test brick units. No. 3 brick was used to complete the experimental program, and the area of the holes was less than 25% of the total surface area of the brick units. Thus, the loading area was taken as equal to the gross area.

2. Cement: Grade 4700 psi (32.5 N) ordinary portland cement was used in this investigation. Cements conform to ES 4756-1/2007.15

3. Fine aggregates: Medium well-graded sand with a fineness modulus of 2.2 and 2.5 was used for mortar and concrete, respectively.

4. Coarse aggregates: Natural well-graded gravel with a maximum nominal size of 0.787 in. (20 mm) was used for casting the concrete beam. It included a combination of round and angular particles. The surface of the particles was more or less smooth. The fine and coarse aggregates conformed to ES 1109/2002.16

5. Chemical admixtures: A high-range water-reducing admixture (HRWRA) was used in fiber-reinforced mortar mixtures to keep a plastic consistency of mortar that satisfies the requirements of ASTM C494/C494M-99a17 Type F and

BS 5075-3:198518 for HRWRA. Its dosage ranged between

0.6 and 2.5% of cement weight, as given by the manufacturer. 6. Fibers: The polypropylene (PP) fibers used in this inves-tigation are commercially available. The length of the fibers was approximately 0.75 in. (19 mm) and the equivalent diameter was 0.0016 in. (0.04 mm).

Specimen preparation and testing

The mortar mixtures were weighed and mixed manually in a container with a capacity of 250 L (66.04 gal.) for a period of 10 minutes. The perforated shale brick units were kept in water before they were built to lead to better bond Mariam Farouk Ghazy is an Assistant Professor in the Faculty of Engineering

in the Department of Structural Engineering at Tanta University, Tanta, Egypt. Her research interests include concrete technology, fiber-reinforced concrete, inspection and quality control of reinforced concrete, and composites.

is demanded, the incorporation of fine, flexible, and evenly distributed fibers in the lime-based mortar could be a solution.

To investigate the effects of various process parameters on the final results and then to suggest the near-optimum (the best) process settings, statistically designed experi-ments were used in this study. The Taguchi11 method, a

powerful experimental design tool, uses a simple, effective, and systematic approach for setting suitable process param-eters to effectively control the amount of final results and to easily determine what parameters have the most significant effects on the final results. Further, this approach requires minimum experimental cost and efficiently reduces the effect of the source of variation. Taguchi11 has developed

a system of tabulated designs (arrays) that allow for the maximum number of main effects to be estimated in an unbi-ased (orthogonal) manner, with a minimum number of runs in the experiment.

In this study, three parameters were taken with three different levels of each. Thus, a total of 27 (33) different

combinations were considered according to full factorial design. According to Taguchi,11 however, the samples

could be organized into only nine groups. If they were considered separately, they would still yield results with the same confidence.

Taguchi’s11 method of experimental design provides a

simple, efficient, and systematic approach for the optimi-zation of experimental designs for performance quality and cost.12 The traditional experimental design methods are too

complex and difficult to use. Additionally, large numbers of experiments have to be carried out. Traditional experimen-tation involves one-factor-at-a-time experiments, wherein one variable is changed while the rest are held constant. The major disadvantage of this strategy is that it fails to consider any possible interactions between the parameters. It is also impossible to study all the factors and determine their main effects—that is, the individual effects in a single experiment. The Taguchi11 technique overcomes all of these drawbacks.

Compared to the conventional approach to experiments, this method drastically reduces the number of experiments that are required to model the response functions.

In this study, a new application of Taguchi’s11 method was

employed to design the experimental work and determine the effect of using different types of mortar for both interface and overlays on masonry behavior. The Taguchi11 method

of offline quality control has been successfully used in the design and selection of near-optimum process parameters in many areas of manufacturing processes; however, no effort Table 1—Brick unit properties

Manufacturer No. Dimensions, in. (mm) Absorption, % Compressive strength of brick, psi (MPa) 1 9.1 x 4.25 x 2.44(230 x 108 x 62) 9.53 1435.5(9.9) 2 (229 x 108 x 65)9 x 4.25 x 2.56 11.69 1261.5(8.7) 3 9.65 x 4.57 x 2.6(245 x 116 x 66) 9.41 1450(10)

(16)

between brick and mortar. The mortar proportions were in accordance with ECP 204-2005.14 The ratio by volume was

1:3 for cement:sand, and the water-cement ratio (w/c) was 1.3 for plain mortar while adding HRWRA for PP fiber-reinforced mortar to improve the workability. Mortar cubes with dimensions of 2.8 x 2.8 x 2.8 in. (70 x 70 x 70 mm) were made during construction of the test specimens to record the compressive strength of mortar after 28 days (refer to Table 2). For the masonry prisms, three courses of brick units were made to measure the compressive strength and seven vertical courses of brick units were made to measure the flexural bond strength after 28 days in accordance with ASTM C1314-00a19 and ASTM E518-00a,20 respectively.

Figure 1 shows the specimen’s preparation and testing. Eighteen specimens were made and cured in the laboratory condition. After 2 days, masonry prisms were covered with various layers of mortars—approximately 0.4 in. (10 mm) of thickness for each layer. Masonry prism strengths were calculated using the gross area under loading. Masonry prisms were tested using a universal testing machine with a total capacity of 67.4 kips (300 kN).

Nine wall specimens 30 in. (750 mm) long, 30 in. (750 mm) high, and 4.64 in. (116 mm) wide—the width of the brick unit—were constructed using the same perfo-rated shale brick units and mortar to build brick prisms. Bed and head joint mortar had overlays approximately 0.4 in. (10 mm) thick, which were added to the walls after running bond and mortar joint pointing 2 days after construction. The walls were capped with 0.4 in. (10 mm) thick concrete beams to distribute the applied load uniformly (refer to Fig. 2). All of the walls were air-cured inside the laboratory (at a temperature of approximately 77°F [25°C] and 70% rela-tive humidity) for 28 days. A hydraulic load cell with a total capacity of 112.4 kips (500 kN) was used to test the walls after 28 days. During testing, applied loads and midheight longitudinal strain (with a gauge length of 10 in. [250 mm]) were recorded at each load stage for each specimen. The compressive strength of masonry walls was calculated by using the gross area under loading.

Plan of experiments

In experimental investigations, the statistical design of experiments is used quite extensively. The statistical design of experiments refers to the process planning the experiment so the appropriate data can be analyzed by the statistical method, resulting in valid and objective conclu-sions. The design of experimental methods such as facto-rial design, response surface methodology (RSM), and the Taguchi11 method are now widely used in place of the

one-factor-at-a-time experimental approach, which is time-consuming and exorbitant in cost.

Design of experiment based on Taguchi’s11 technique

The major steps required for the experimental design using the Taguchi11 method are 1) establishment of the objective

function; 2) identification of the factors and their levels; 3) selection of an appropriate orthogonal array (OA); 4) experi-mentation; 5) analysis of the data and determination of the near-optimum level of each factor (optimum combination); and 6) confirmation of experiment.

Taguchi11 designed certain standard OAs by which the

simultaneous and independent evaluation of two or more parameters for their ability to affect the variability of a particular product or process characteristics can be done in a minimum number of tests. While there are many standard OAs available, each array is meant for a specific number of independent design variables and levels. In this study, the behavior of three control factors each at three levels was investigated. Therefore, an L9 OA was selected for this

inves-tigation. The three independent variables (control factors) and their three levels are presented in Table 3. Table 4 shows the layout of the L9 OA according to Taguchi.11 A loss

func-Table 2—Characteristics of used mortars and concrete

Material Mixture proportion PP fiber,* % w/c HRWRA, % Compressive strength, psi (MPa)

Mortar 1 C:S = 1:3 (by volume) 0 1.3 0 2320 (16) Mortar 2 1 1 2247.5 (15.5) Mortar 3 2 1.5 2247.5 (15.5)

Concrete C:S:G = 1:1.7:3.4 (by weight) 0 0.5 1 4350 (30)

*Percentage by volume of mortar. Percentage by weight of cement.

Fig. 1—Masonry prism specimens’ preparation and testing.

References

Related documents

We then select the points around the linear feature for each fault plane, and we automatically obtain the suggested geometry parameters of the fitted plane as shown in Table 1,

Tour de France 102nd edition - Pyrenean Stages 2015..

The reliability of EMU’s fiscal indicators has been questioned by recent episodes of large upward deficit revisions. This paper points out that EMU’s deficit

(motorists parking where they should not). As a result, inadequate parking supply can create problems to both users and nonusers. However, excessive parking can also

 The procedure of issuing digital Certification for users and host in Grid 9.. Some Goals of MPI

In the short-run models, the rental adjustment process in Shanghai is affected by both supply and demand; in Beijing, only the vacancy rate has significant impact on rental

Table 24 Effect of Light Rail and Toll on Employment Characteristics, Combined Anticipatory Model, Comparison Group I Proximity.. Measurement

between adults), to provide care for disabled or vulnerable people, to provide emergency assistance, to attend a support group (of up to 15 people), or for respite care where that