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sobre gestión deinfraestructurasd e l t r a n s p o r t e

Premio Internacional

Abertis de investigación

Rheological and mechanical characterization of portland cement

mixes containing micro and nano amorphous silica particles

Luis Eduardo Zapata Orduz

1- PUERTO RICO -

er

Pórtico

La red internacional de Cátedra Abertis convoca un año más, junto a prestigiosas universidades, los premios que reconocen a los mejores trabajos de final de carrera, tesinas o tesis doctorales relacionadas con la gestión de infraestructuras de transporte, desarrollados por universitarios de los distintos países en los que opera el grupo Abertis.

A partir de la creación en el año 2003 de la primera Cátedra Abertis junto a la Universitat Politècnica de Catalunya-UPC (BarcelonaTech), la red ha ido creciendo y ganando presencia internacional en Francia, Puerto Rico, Brasil y recientemente en Chile.

Este modelo de gestión del conocimiento tiene su origen en la firme voluntad de Abertis de colaborar con las universidades, los centros de excelencia y los expertos más destacados en cada materia con el fin de ayudar a generar y a divulgar el conocimiento, poniéndolo al servicio de la investigación y de toda la sociedad. El trabajo distinguido por los Premios Abertis de investigación que ahora tiene en sus manos, quiere ser una muestra más de esta vocación de servicio a los investigadores, a la comunidad educativa y de los profesionales con responsabilidades en el campo dela gestión de las infraestructuras.

Esta visión, que se integra en la responsabilidad social de Abertis, aspira también a ofrecer vías de progreso, de colaboración, de diálogo y de interacción en todos los territorios en los que Abertis está presente, ayudando a desarrollar de forma responsable y sostenible las actividades del Grupo. Más información sobre las actividades de la Cátedra Abertis en la web: www.catedrasabertis.com.

PresentaciónLa Cátedra Abertis de la Universidad de Puerto Rico (UPR) promueve la realización de seminarios y conferencias y la investigación sobre la gestión de infraestructuras del transporte estructurada en los ejes de actividad de la corporación: carreteras y autopistas, tráfico, seguridad vial y sistemas de transporte inteligentes. Asimismo, con objeto de potenciar el interés de los universitarios residentes en la isla, la Cátedra Abertis establece anualmente el Premio Abertis, al mejor trabajo de investigación inédito en gestión del transporte realizado por estudiantes en Puerto Rico.

Este año fue muy especial para nosotros ya que por primera vez la entrega del Premio Internacional se llevó a cabo en Puerto Rico, lo cual fue una oportunidad excelente para el intercambio de ideas con ejecutivos de Abertis, funcionarios del Gobierno de Puerto Rico, sector privado y de la Universidad de Puerto Rico. Esperamos continuar esta relación con la Fundación Abertis en los años venideros y estamos seguros que este premio redundará en mejoras en las infraestructuras de transporte en Puerto Rico y en motivar a futuros profesionales de la ingeniería y gerencia a cursar estudios en gestión de transporte.

Ha resultado ganador del 1er Premio Abertis 2013 en la categoría doctoral, la Tesis titulada “Rheological and Mechanical Characterization of Portland Cement Mixes Containing Micro and Nano Amorphous Silica Particles” por el Dr. Luis E. Zapata Orduz, Ingeniero de Ingeniería Civil por la Universidad de Puerto Rico- Recinto de Mayagüez.

La tesis emplea nano-SiO2 (nS), ceniza volante (FA), humo de sílice (SF) y superplastificantes tipo polycarboxilatos (SP) para determinar las características reológicas en estado fresco y las propiedades macro-mecánicas en estado endurecido. El estado fresco de las pastas de cemento usando el cono de Marsh (MCT) mostró que las adiciones minerales mejoraron la fluidez, pero los resultados mostraron que los análisis del MCT se deben interpretar cuidadosamente cuando hay adiciones minerales, por posibles distorsiones ocasionadas por la viscosidad plástica del material. Además, se estudió el estado endurecido de morteros a w/b=0.35 que contenían nano/micro-SiO2. Los análisis SEM mostraron que sistemas con nano-SiO2 presentaron mejoras por densificación y gradación. El estudio de concretos con nS, SF, FA y SP fue más complejo y requirió técnicas estadísticas (DOE) y redes neuronales (ANN). Los resultados DOE en compresión y tensión indicaron que las mezclas binarias de nS-SF son la mejor opción para ganar resistencia. Finalmente, desde ensayos de tensión indirecta en concretos se estimaron los parámetros de Weibull usando técnicas no-lineales. Los resultados estadísticos mostraron que algunos sistemas de silica amorfa exhibían valores del módulo Weibull mayores que las muestras de control. La novedad es que pese a la importancia del modulo Weibull en el análisis de materiales quebradizos, la mayoría de los estudios se basan en concretos simples.

En este categoría de tesis doctoral, se presentaron además, contribuciones técnicas relacionadas con el desarrollo de un modelo sistemodinámico para pronosticar, jerarquizar y distribuir cítricos durante operaciones de ayuda en caso de huracán, integración de sistemas de información geográfica, la síntesis, formación y caracterización de peróxido en la fabricación de explosivos caseros, el desarrollo de una tipología de los dos mecanismos de apoyo fiscal directo e indirecto e identificar las jurisdicciones donde se han empleado estos mecanismos y emplear el nano-SiO2, la ceniza volante , el humo de sílice y superplastificantes tipo de polucarboxilatos para determinar las características reológicas en estado fresco y propiedades macro-mecánicas en estado endurecido.

Dr. Benjamín Colucci RíosDirector de la Cátedra Abertis-UPR

RHEOLOGICAL AND MECHANICAL CHARACTERIZATION OF PORTLAND

CEMENT MIXES CONTAINING MICRO AND NANO AMORPHOUS SILICA

PARTICLES

By

Luis Eduardo Zapata Orduz

A dissertation submitted in partial fulfillment of the requirements for the degree of

DOCTOR OF PHILOSOPHY

IN

CIVIL ENGINEERING

UNIVERSITY OF PUERTO RICO

MAYAGÜEZ CAMPUS

2013

Approved by:

___________________________________ ____________

Arsenio Cáceres Fernández, PhD Date

Member, Graduate Committee

___________________________________ ____________

Omar I. Molina Bas, PhD Date


___________________________________ ____________

O. Marcelo Suárez, PhD Date


___________________________________ ____________

Genock Portela Gauthier, PhD Date

President, Graduate Committee

___________________________________ ____________

Ruben E. Díaz, PhD Date

Representative of Graduate Studies

___________________________________ ____________

Ismael Pagán Trinidad, MSCE Date

Chairperson of the Department

ii

ABSTRACT

In concrete technology, it is common to use fly ash (FA) and micro-SiO2 (SF) as mineral admixtures. This

has resulted in improvements in the fresh and hardened states. On the other hand, nano-SiO2 (nS) is

industrially produced for diverse applications due to their unique characteristics. Nevertheless, its use in

the concrete industry is not yet common and their physical-chemical effects as well as mechanical and

durability capacities are subject of interest in recent research. Thus, the current study employed nS, FA,

SF and polycarboxylate-type superplasticizer (SP) to determine their rheological characteristics at early

age and their macro-mechanical properties in the hardened state. The rheological properties of grouts

using the Marsh cone test (MCT) approach showed that mineral admixtures could improve the fluidity.

Nevertheless, results also showed that MCT must be interpreted carefully when mineral additions are

applied, because nonlinearities of the plastic viscosity could cause distortions in the MCT analyses. On

the other hand, the hardened state of mortar samples containing nano/micro-SiO2 at w/b=0.35 was

studied. SEM examinations in the ITZ suggested that compressive strengths of nano-SiO2-systems

presented densification and filler effects, whereas micro-SiO2-systems only showed filler effects.

Nevertheless, the study of concretes containing nS, SF, FA, and SP was more complex and statistical

tools (DOE) and artificial neural simulations (ANN) were required. DOE results of compressive and

tensile strength indicated that nS-SF binary mixes are the optimal choice to gain strength. However, DOE

results also showed lack-of-fit of the second-order. But, the ANN could effectively explain the lack-of-fit

inherit in the DOEs. Finally, splitting tensile failures were carried out on concretes to investigate the

accuracy of the Weibull models. The estimated Weibull parameters were obtained by using modern

advanced nonlinear methodologies. Statistical analysis indicated that some specific combinations of

amorphous silica exhibited Weibull modulus higher than the control case. The novelty in these analyses is

that despite the importance of the Weibull modulus in reliability analyses of brittle materials, the majority

of the studies are on plain concretes. The data is especially scarce for nano-SiO2 on binary, ternary, and/or

quaternary concretes mixes.

iii

RESUMEN

En tecnología del concreto, el uso de ceniza volante (FA) y humo de sílice (SF) como aditivo mineral es

muy común. Su implementación ha demostrado mejoras en el estado fresco y el endurecido. Además,

debido a sus propiedades únicas, el uso de nano-SiO2 (nS) ha presentado varias aplicaciones industriales.

Sin embargo, su uso en la industria del concreto no es común y sus efectos físico-químicos, capacidades

mecánicas y durabilidad son aún tema de investigación. Por consiguiente, el presente estudio emplea nS,

FA, SF y superplastificantes tipo polycarboxilatos (SP) para determinar las características reológicas en

estado fresco y las propiedades macro-mecánicas en estado endurecido. El estado fresco de las pastas de

cemento usando el cono de Marsh (MCT) mostró que las adiciones minerales mejoraron la fluidez. Pero

los resultados también mostraron que los análisis del MCT se deben interpretar cuidadosamente cuando

hay adiciones minerales, por posibles efectos de distorsión ocasionados por la viscosidad plástica en el

material. Por otra parte, se estudió el estado endurecido de morteros a w/b=0.35 que contenían

nano/micro-SiO2. Los análisis SEM en la interface mostraron que sistemas con nano-SiO2 presentaron

mejoras por densificación y gradación, mientras que en micro-SiO2 sólo la gradación fue importante. Sin

embargo, el estudio de concretos que contenían nS, SF, FA and SP fue más complejo y requirió usar

técnicas estadísticas (DOE) y redes neuronales (ANN). Los resultados desde DOE en compresión y

tensión indicaron que las mezclas binarias de nS-SF son la mejor opción para ganar resistencia. No

obstante, también se encontró falta-de-ajuste de segundo orden. Pero los análisis con ANN pudieron

eficazmente explicar esta falta-de-ajuste de los DOEs. Finalmente, desde ensayos de tensión indirecta en

concretos se estimaron los parámetros de Weibull usando modernas técnicas no-lineales. Los resultados

estadísticos mostraron que algunos sistemas de silica amorfa exhibían valores del módulo Weibull

mayores que las muestras de control. La novedad es que pese a la importancia del modulo Weibull en el

análisis de materiales quebradizos, la mayoría de los estudios se basan en concretos simples. Y los datos

son especialmente escasos para concretos que poseen nS en diseños binarios, terciarios y/o cuaternarios.

iv

Time ago Sir I. Newton said: “If I have seen further than others, it is by standing upon the

shoulders of giants”. To my parents Flor Elva and Eduardo, they patiently were my own giants during

these long academic years. Also, this thesis is dedicated to researchers in the field of concrete sciences,

because I used their shoulders.

v

ACKNOWLEDGEMENTS

I owe thanks to Prof. Genock Portela Gauthier, who trusted on my work four years ago and

accepted me as PhD student. Also, thanks by the supervision of the entire experimental and computational

process of this thesis and thanks by giving me much confidence to perform the cases studied. Also, I

would like to express my warm thanks to Drs. O. Marcelo Suárez, Omar I. Molina Bas, and Arsenio D.

Cáceres, who accepted to be co-examiners. In numerous discussions they helped to provide guidance to

this thesis and helped thoroughly reviewing this manuscript.

The materials employed in the present thesis were partially based on work supported by Essroc

San Juan, Puerto Rico, W. R. Grace & Co-Conn, Sika Corporation (PR-USA), and the staff of the

Construction Materials laboratory of the Department of Civil Engineering and Surveying of the

University of Puerto Rico at Mayagüez. The author would like to thank specially the National Science

Foundation (NSF) under Grant HRD 0833112 (CREST program) and Dr. O. Marcelo Suárez, because the

technical and financial support along these two last years of hard work. Without the help of CREST

program this work would not be as complete. I would like to extend me gratitude to the Geotechnical and

Structures Laboratory of the Engineer Research and Development Center, US Army Corps of Engineers

(Vicksburg, MS, USA), for supported at the beginning of the experiments and for advice during the

development of the majority of the topics in the present thesis.

I owe deep thanks to Dr. Ricardo López, who in numerous opportunities patiently advised me in

administrative situations. I am thankful to Dr. Luis E. Suárez, who inspired me as a Matlab® user during

the time involved in the course INCI-6029 and Dr. Antonio González-Quevedo who inspired me to read

papers on automation in construction during the time involved in the course INCI-6208. These two things

played an important role in a chapter of the present thesis. Special thanks are due to the construction

materials laboratory technician Mr. Monserrate Cruz, who spent much time finding solutions in the set up

devices required in the present investigation.

I thank to my graduate friends Fabio M. Upegüi, Diego Aguirre, Jorge A. Caro, and Ulises

Barajas, because they disinterestedly supported the present project in many ways. Finally, I am in

thankful with the entire undergraduate students who helped me with the cumbersome experimental

program carried out in the present thesis along the last four years.

vi

TABLE OF CONTENTS

ABSTRACT .................................................................................................................................................. ii

RESUMEN .................................................................................................................................................. iii

ACKNOWLEDGEMENTS .......................................................................................................................... v

TABLE OF CONTENTS ............................................................................................................................. vi

LIST OF FIGURES ..................................................................................................................................... ix

LIST OF TABLES ....................................................................................................................................... xi

LIST OF ABBREVIATIONS .................................................................................................................... xiii

CHAPTER I .................................................................................................................................................. 1

1 INTRODUCTION ..................................................................................................................................... 1

1.1 Justification ........................................................................................................................................ 1

1.2 Objectives .......................................................................................................................................... 2

1.3 Materials used in this research ........................................................................................................... 4

1.3.1 Portland cement type I ............................................................................................................... 4

1.3.2 Chemical admixtures ................................................................................................................. 4

1.3.3 Mineral admixtures .................................................................................................................... 4

1.3.4 Fine aggregate ............................................................................................................................ 5

1.3.5 Coarse aggregate ........................................................................................................................ 6

1.3.6 Water ......................................................................................................................................... 6

1.4 Literature review ................................................................................................................................ 6

1.4.1 Amorphous silica particles ........................................................................................................ 6

1.4.2 Fresh state properties in cementitious mixes ............................................................................. 8

1.4.3 Hardened state properties in mortar and concrete samples ........................................................ 9

1.4.4 Statistical design of experiments (DOE) ................................................................................... 9

1.4.5 Artificial neural networks (ANN) simulations ......................................................................... 10

1.4.6 Weibull statistical analysis ...................................................................................................... 11

1.5 General methodology ....................................................................................................................... 11

1.6 Scope of the research work .............................................................................................................. 13

1.7 General organization of the present thesis ....................................................................................... 14

1.7.1 Compatibility analyses and rheological performance between Portland cement Type I

and micro/nano-SiO2 particles in presence of polycarboxylate-type superplasticizers ....... 15

1.7.2 Fresh state analyses and compressive strength of superplasticized mortar containing

micro/nano-SiO2 particles .................................................................................................... 15

vii

CHAPTER II ............................................................................................................................................... 17

2 COMPATIBILITY ANALYSIS AND RHEOLOGICAL PERFORMANCE BETWEEN

PORTLAND CEMENT TYPE I AND MICRO/NANO-SIO2 PARTICLES IN PRESENCE

OF POLYCARBOXYLATE-TYPE SUPERPLASTICIZER ........................................................ 17

2.1 Introduction ...................................................................................................................................... 17

2.2 Theoretical background ................................................................................................................... 17

2.3 Methods used to analyze PC-SP systems ......................................................................................... 18

2.3.1 Marsh apparatus ....................................................................................................................... 18

2.3.2 Marsh test procedure ................................................................................................................ 19

2.4 Results and discussion ..................................................................................................................... 19

2.4.1 Marsh cone test analysis on plain grout mixtures .................................................................... 19

2.4.2 Marsh cone test analysis on PC-SP2-SF-0.35 system ............................................................. 22

2.4.3 Marsh cone test analysis on PC-SP2-SF-0.40 system ............................................................. 24

2.4.4 Marsh cone test analysis on PC-SP2-nS-0.35 system .............................................................. 26

2.4.5 Marsh cone test analysis on PC-SP2-nS-0.40 system .............................................................. 27

2.4.6 Marsh cone test: effects of the water-binder ratio ................................................................... 29

2.4.7 Marsh cone test: effects of the mineral admixture ................................................................... 30

2.5 Chapter final remarks ....................................................................................................................... 30

CHAPTER III ............................................................................................................................................. 32

3 FRESH STATE ANALYSIS AND MECHANICAL STRENGTH ON SUPERPLASTICIZED

MICRO/NANO-SiO2 SYSTEMS .................................................................................................. 32

3.1 Introduction ...................................................................................................................................... 32


3.3 Proportions, casting and testing for cementitious samples .............................................................. 33

3.3.1 Mortar samples: proportions, casting and testing .................................................................... 33

3.3.2 Concrete samples: proportions, casting and testing ................................................................. 34


3.4.1 Fresh state properties of mortar samples ................................................................................. 35

3.4.2 Hardened state properties of mortar samples ........................................................................... 38

3.4.3 Fresh concrete properties: validation of the MCT measurements ............................................ 42

3.4.4 Hardened concrete properties .................................................................................................. 44


CHAPTER IV ............................................................................................................................................. 48

viii

4 NONLINEAR STATISTICAL ANALYSIS IN COMPRESSIVE AND TENSILE STRENGTHS

OF CONCRETE CONTAINING AMORPHOUS SILICA ........................................................... 48

4.1 Introduction ...................................................................................................................................... 48


4.3 Proportions, casting and testing for concrete samples ..................................................................... 49

4.3.1 Concrete mixture proportions and specimen fabrication ......................................................... 49

4.3.2 Compressive and splitting tensile strength tests ...................................................................... 49

4.4 Development of the DOE and ANN models .................................................................................... 50


4.5.1 DOE analysis for compressive strength ................................................................................... 54

4.5.2 DOE analysis for tensile strength ............................................................................................ 60

4.5.3 ANN simulations ...................................................................................................................... 67


CHAPTER V .............................................................................................................................................. 78

5 WEIBULL ANALYSIS ON TENSILE STRENGTH OF CONCRETE CONTAINING

AMORPHOUS SILICA ................................................................................................................. 78

5.1 Introduction ...................................................................................................................................... 78

5.2 Proportions, casting and testing for concrete samples ..................................................................... 78

5.2.1 Concrete proportions ............................................................................................................... 78

5.2.2 Specimen fabrication ............................................................................................................... 79

5.2.3 Testing procedures ................................................................................................................... 79


5.3.1 Splitting tensile strength test .................................................................................................... 81

5.3.2 Statistical background .............................................................................................................. 81



CHAPTER VI ........................................................................................................................................... 101

6 GENERAL CONCLUSIONS AND RECOMMENDATIONS ............................................................. 101

6.1 Summary of the chapters ............................................................................................................... 101

6.2 Principal conclusions ..................................................................................................................... 102

6.3 Recommendations for future works ............................................................................................... 104

6.4 References ...................................................................................................................................... 106

ix

LIST OF FIGURES

Figure 1-1. XRD pattern of MA obtained with CuKα radiation. .................................................................. 5

Figure 2-1. Scheme of the Marsh cone apparatus. ...................................................................................... 18

Figure 2-2. Flow time as a function of SP-dosage at 5 min. ....................................................................... 21

Figure 2-3. Flow time as a function of SP-dosage at 60 min. ..................................................................... 21

Figure 2-4. Flow time as a function of SP2-dosage at 5 min (w/b=0.35). .................................................. 23

Figure 2-5. Flow time as a function of SP2-dosage at 60 min (w/b=0.35). ................................................ 23

Figure 2-6. Flow time as a function of SP2-dosage at 5 min (w/b=0.40). .................................................. 24

Figure 2-7. Flow time as a function of SP2-dosage at 60 min (w/b=0.40). ................................................ 25

Figure 2-8. Flow time for nS systems as a function of SP2-dosage at 5 min (w/b=0.35). .......................... 26

Figure 2-9. Flow time for nS systems as a function of SP2-dosage at 60 min (w/b=0.35). ........................ 27

Figure 2-10. Flow time for nS systems as a function of SP2 dosage at 5 min (w/b = 0.40). ...................... 28

Figure 2-11. Flow time for nS systems as a function of SP2-dosage at 60 min (w/b = 0.40). .................... 29

Figure 3-1. Constant contour plot for FA: (a) SF (wt%) and (b) nS (wt%). ............................................... 37

Figure 3-2. Constant contour plot for UW (kg/m3): (a) SF (wt%) and (b) nS (wt%). ................................. 37

Figure 3-3. Constant contour plot for AC (%): (a) SF (wt%) and (b) nS (wt%). ........................................ 38

Figure 3-4. Contour plots for Sc (MPa): (a) SF (wt%) and (b) nS (wt%). .................................................. 39

Figure 3-5. SEM micrographs of CA sample at SD=1, w/b=0.35 and t=90-days. ..................................... 40

Figure 3-6. SEM micrographs of S15A sample at SD=1, w/b=0.35 and t=90-days. .................................. 41

Figure 3-7. SEM micrographs of n3A sample at SD=1, w/b=0.35 and t=90-days. .................................... 41

Figure 3-8. Compressive and tensile strengths at w/b = 0.35. ..................................................................... 45

Figure 4-1. Schematic of a multilayer feed-forward/back-propagation network model. ............................ 51

Figure 4-2. Compressive strength of concretes at 3 days: (a) for DOE I and (b) for DOE II. .................... 55

Figure 4-3. Compressive strength of concretes at 7 days: (a) for DOE I and (b) for DOE II. .................... 55

Figure 4-4. Compressive strength of concretes at 28 days: (a) for DOE I and (b) for DOE II. .................. 56

x



Figure 4-7. Compression tests: DOE III (3-days): (a) principal effects and (b) interactive effects. ........... 58

Figure 4-8. Compression tests: DOE III (7-days): (a) principal effects and (b) interactive effects. ........... 58

Figure 4-9. Compression tests: DOE III (28-days): (a) principal effects and (b) interactive effects. ......... 58

Figure 4-10. Compression tests: DOE III (56-days): (a) principal effects and (b) interactive effects. ....... 59

Figure 4-11. Compression tests: DOE III (90-days): (a) principal effects and (b) interactive effects. ....... 59

Figure 4-12. Tensile strength of concretes at 3 days: (a) for DOE I and (b) for DOE II. ........................... 62

Figure 4-13. Tensile strength of concretes at 7 days: (a) for DOE I and (b) for DOE II. ........................... 63

Figure 4-14. Tensile strength of concretes at 28 days: (a) for DOE I and (b) for DOE II. ......................... 63



Figure 4-17. Tension analysis: DOE III at 3 days: (a) principal effects and (b) interactive effects. .......... 65

Figure 4-18. Tension analysis: DOE III at 7 days: (a) principal effects and (b) interactive effects. .......... 65

Figure 4-19. Tension analysis: DOE III at 28 days: (a) principal effects and (b) interactive effects. ........ 65



Figure 4-22. Actual compression and ANN-simulated-LMBP [12:15:1] (a) trained (b) tested. ................. 71

Figure 4-23. Actual tensile strength and ANN-simulated-LMBP [12:16:1] (a) trained (b) tested. ............. 71

Figure 4-24. Actual compressive strength and ANN-simulated-BRA [12:3:1] (a) trained (b) tested. ........ 72

xi

LIST OF TABLES

Table 1-1. Physical-chemical and mineralogical characteristics of the cement ............................................ 4

Table 1-2. Principal physical and chemical characteristics of FA, SF and nS .............................................. 5

Table 2-1. Results of saturation dosage and compatibility of the PC-SP systems ...................................... 19

Table 2-2. Physical and chemical properties of the chemical admixtures .................................................. 20

Table 2-3. Rheological parameters in PC-SP2-SF systems at w/b=0.35 and 0.40 ...................................... 26

Table 2-4. Rheological parameters in PC-SP2-nS systems at w/b=0.35 and 0.40 ...................................... 27

Table 3-1. MCT parameters in PC-SP (SD=1) at w/b=0.35 and 0.40 ......................................................... 33

Table 3-2. Mixtures proportions for the mortar cubes at w/b=0.35 ............................................................ 34

Table 3-3. Mix proportions of the concrete specimens ............................................................................... 35

Table 3-4. Fresh state properties for SF variable ........................................................................................ 36

Table 3-5. Fresh state properties for nS variable ........................................................................................ 36

Table 3-6. Compressive strength after 90 days ........................................................................................... 39

Table 3-7. Fresh properties of concrete binary mixtures (w/b=0.35) .......................................................... 42

Table 3-8. Fisher LSD for the difference in compressive and splitting tensile strength ............................. 45

Table 4-1. Concrete proportions, DOE compositions, and mechanical strengths of samples .................... 50

Table 4-2. Statistical results from DOEs in compression tests ................................................................... 54

Table 4-3. Summary from DOE analysis: optimized values for compressive strength .............................. 60

Table 4-4. Statistical results from DOEs in tension tests ............................................................................ 61

Table 4-5. Summary from DOE analysis of nS, SF and FA optimized values for tensile strength ............ 67

Table 4-6. Design parameters of ANN models ............................................................................................ 68

Table 4-7. Performance of ANN architectures (average of twelve simulations) ......................................... 68

Table 4-8. Results between the adjusted model from DOEs analyses and ANN-models ............................ 69

Table 4-9. Results between the predictive model from DOEs analyses and ANN-models ......................... 70

Table 4-10. Normalized ranking order from sensitivity analysis on ANN-simulations .............................. 73

xii

Table 4-11. Actual compression values and simulated ANN using LMBP [12:15:1] ................................. 74

Table 4-12. Actual compression values and simulated from ANN using BRA [12:3:1] ............................. 75

Table 4-13. Actual tension values and simulated from ANN using LMBP [12:16:1] ................................. 76

Table 5-1. Laboratory proportions and mechanical results of concrete samples ........................................ 80

Table 5-2. Statistical results and estimated parameters at 3-days ............................................................... 94

Table 5-3. Statistical results and estimated parameters at 7-days ............................................................... 95

Table 5-4. Statistical results and estimated parameters at 28-days ............................................................. 95



Table 5-7. Relationship between estimated Weibull parameters and average splitting strength ................ 98

Table 5-8. φ and λ estimated parameters versus r and the first order statistic ............................................ 99

xiii

LIST OF ABBREVIATIONS

ΔFT: fluidity loss

Ca(OH)2: Calcium hydroxide

C-S-H: Calcium silicate hydrate

CO: control or plain samples

C3A: tricalcium aluminate

C3S: tricalcium silicate

C4AF: tetracalcium ferroaluminate

GBFS: ground granulated blast-furnace slag

ITZ: interfacial transition zone

LSD: Fisher Least Significant Difference

MA: mineral admixtures

MSE: Error mean square

MCT: Marsh cone test

FT: flow time

FA: fly ash

NP: natural pozzolans

PC: Portland cement

XRD: x-ray diffraction

Na2O-eq: sodium oxide equivalent

nS: nano-SiO2

SD: saturation dosage

SEM: scanning electron micrographs

xiv

SG: specific gravity

SiO2: silica

SP: superplasticizer

SF: micro-SiO2

SSD: saturated surface dried

w/b: water-to-binder ratio

wt%: weight of cementitious materials (%)

1

CHAPTER I

1 INTRODUCTION

1.1 Justification

Increasing use of nano-modified high-performance materials in the construction industry such as

smart carbon nano-tubes, nano-titania, nano-calcium carbonate and nano-alumina produce systems with

higher strength, improved durability and reduced environmental impact (Gopalakrishnan et al., 2011).

Specifically, among recent advances in the concrete industry aiming to make concrete more sustainable

are the increasing use of binary, ternary, and quaternary binders. In effect, such modified cementitious

materials result not only in the production of high strength concretes but also in more durable, sustainable,

and economical concrete structures (Aïtcin and Mindess, 2011).

In concrete technology, it is common to use fly ash (FA) and silica fume or micro-SiO2 (SF) in

concrete mixes as mineral admixtures (MA) or supplementary cementitious materials (SCM). This has

resulted in improvements on the porosity, permeability, bleeding, and secondary C-S-H gel gained by the

reaction between the amorphous SiO2 with the calcium hydroxide in the cement hydration process

(Aïtcin, 1998; Mehta and Monteiro, 2003; Nazari and Riahi, 2011; Senff et al., 2010; Siddique and Khan,

2011). On the other hand, colloidal silica or nano-SiO2 (nS) particles are industrially produced for a

diverse array of applications. Nevertheless, the use of nS in concrete industry is not yet very common

practice because it is often too expensive (van de Griend et al., 2012) and their physical-chemical effects

as well as mechanical and durability capacities are being matter of recent research in concrete technology

(Jalal et al., 2012; Ltifi et al., 2011; Nazari and Riahi, 2011; Stefanidou and Papayianni, 2012; Zyganitidis

et al., 2011).

The present thesis is focused on the study of cementitious mixes containing amorphous silica at

both micro and nano scales. The samples contain replacement levels from zero to forty-six percent by

weight of cementitious material (wt%). The additions consist of Class F FA and SF as amorphous micro

particles and colloidal-silica as amorphous nS. In this thesis, the pertinent modifications for the binary,

ternary, and quaternary designs containing amorphous silica particles by the implementation of the

Absolute Volume Method are developed, adopting general plain concrete guides suggested by ACI 211.1

(1991).

2

The current study aims to employ nS in conjunction with other amorphous silica products (FA

and SF) at the micro scale and study the basic fresh characteristics and the principal hardened properties

in concrete samples. The cementitious systems will be experimentally analyzed to determine their

rheological characteristics at early age and their macro-mechanical properties (compressive and tensile

strength) in the hardened state at different maturity ages.

In the fresh state, the majority of the analyses are based on the Marsh cone test procedure. This

test has been widely supported by experiments on grouts without mineral admixtures hence, in the present

research a series of experimental programs incorporating SF and nS are developed. In addition, despite

the importance in reliability analyses of brittle materials, many studies in the literature evaluate the

Weibull modulus, only for plain concrete specimens while there are only a few studies in binary mixes.

Thus, concretes containing nano-SiO2 additions on binary, ternary and/or quaternary mixes are especially

scarce. Therefore, in the present thesis the accuracy of the two- and three-parameter Weibull models will

be investigated using the tensile strength of plain, binary, ternary and quaternary designs containing FA,

SF, and/or nS. The estimated Weibull parameters will be obtained by using modern nonlinear statistical

methodologies. Therefore, experimental and computational achievements will be provided to the concrete

technology area regarding the use of complex and novelty systems containing colloidal-amorphous silica

in conjunction with FA, SF and chemical polycarboxylate-type superplasticizers. On the other hand, in

the hardened state, results must reveal the effects on strength, strength gain and Weibull parameters

produced by additions of amorphous silica at micro and nano scales as well as the effects produced by

ternary and quaternary additions containing nano-SiO2 as an active ingredient.

1.2 Objectives

To study cementitious systems containing chemical and mineral admixtures via rheological and

mechanical characterization in the fresh and hardened states, respectively; in order to get mix proportions

classified as high-strength concretes as per the American Concrete Institute Committee ACI 363 R-92

(1997). The results will be analyzed by using advanced statistical tools including both theoretical

conditions and computational simulations.

The research work will focus on the following specific objectives:

Study the compatibility between Portland cement type I locally produced and a large range of

commercial polycarboxylate-type superplasticizers in grouts containing micro and nano particles of

SiO2 via the Marsh Cone Test procedure.

3

Study mortar specimens (ASTM C109, 2008) utilizing tested chemical and mineral admixtures

showing compatibility characteristics to be employed in mortar designs in order to both check the

rheological characteristics and investigate the water/binder range resulting most appropriate to cast

concrete samples.

Design plain, binary, ternary, and quaternary concrete mixes containing chemical and several

amorphous silica additions as mineral admixtures (fly ash, silica fume, and nano-SiO2) and

characterize their properties using the following techniques:

Fresh state: The entrapped air content (ASTM C138, 2010), the slump-cone test (ASTM

C143,2010), the flow table test (ASTM C1437), the fresh density or unit weight (ASTM

C138, 2010).

Hardened state: Compressive strength (ASTM C39, 2011) and tensile splitting test (ASTM

C496, 2004) for mechanical characterization, and scanning electron microscopy for the

microstructural properties.

Produce a computational model to simulate the behavior of the plain, binary, ternary, and quaternary

compressive strength of the concrete samples using Artificial Neural Networks based on Matlab®

script programs.

Produce a computational model to simulate the behavior of the plain, binary, ternary, and quaternary

splitting tensile strength of the concrete samples using Artificial Neural Networks based on Matlab®

script programs.

Obtain optimal design parameters from statistical analyses for the compression and tension states of

the plain, binary, ternary and quaternary high-strength concrete samples taking into account both

theoretical conditions and selected experimental ranges.

Obtain for the plain, binary, ternary, and quaternary high-strength concrete samples failed in splitting

tension test the Scale and Shape Weibull parameters via statistical analysis using script programs

developed in Mathematica® software to analyze the stochastic behavior of the samples containing fly

ash, micro and nano-SiO2.

4

1.3 Materials used in this research

In this thesis the materials listed below were employed for the experimental designs. The

proportions and recipes were varied for each particular experiment. Also, the source of fine and coarse

aggregate was the same through the experimental program to obtain comparative results. The brand and

source of the chemical and mineral admixtures as well as the Portland cement (PC) Type I was the same

for all the experimental programs. The exception is explained on Chapter I, where five different chemical

admixtures are used, but this variety of products was in fact the central axis of the experiment in that

chapter. Particular details are given below and additional information is provided through the chapters

when it is needed or relevant.

1.3.1 Portland cement type I

The cement is a PC Type I (ASTM C150, 2009). In the present thesis the grouts, mortars and

concrete samples were prepared using the same Portland cement type I. Table 1-1 shows the properties of

the cement.

Table 1-1. Physical-chemical and mineralogical characteristics of the cement

CHEMICAL COMPOSITION (wt%) BOGUE COMPOSITION (wt%)

SiO2 20.29 C3S 55.4

Al2O3 6.40 C2S 16.4

Fe2O3 3.51 C3A 11.0

CaO 65.13 C4AF 10.7

SO3 2.65 PHYSICAL PROPERTIES

MgO 1.03 Blaine (m2/kg) 394

K2O 0.48 Specific Gravity 2.90

Na2O 0.12 Normal consistency (%) 26.5

Loss of ignition 3.13 Compressive strength on cubes (MPa)

Alkalis Na2O eq.=0.44% 1 d 14.2

Free CaO 1.2 3 d 24.3

Insoluble residue 0.31 7 d 31.5

1.3.2 Chemical admixtures

This study employs five different polymer-based chemical admixtures of third generation (Rixom

and Mailvaganam, 2002). The doses vary in each particular experiment. All doses through the thesis are

expressed as the ratio by weight between the solid active matter and the cementitious content (wt%). The

physical-chemical properties of the admixtures were supplied by the manufacturers (Chapter II).

1.3.3 Mineral admixtures

The mineral admixtures employed were nano-SiO2 consisted of nanoparticles that were in the

form of opalescent amorphous silica dispersed in water (slurry). The nano-SiO2 particles were employed

5

at levels up to 6 (wt%). The micro-SiO2 powder (ASTM C1240, 2010) was in the form of uncondensed

particles, and it was employed at different levels from 5 to 20 (wt%). Finally, this thesis employed Class

F FA (low-calcium) (ASTM C618, 2008). Table 1-2 shows the principal physical-chemical characteristics

of nS, SF, and FA and Figure 1-1 shows results of X-ray diffraction (XRD) confirming the amorphous

nature of the materials.

Table 1-2. Principal physical and chemical characteristics of FA, SF and nS

FA SF nS

Chemical composition (wt%) SiO2 54.3 91.3 99.9 H2O 0.7 0.3 ---

pH value --- --- 9.0

Loss of ignition 1.28 --- 0.1

Physical properties

Specific gravity 2.1 2.3 2.1

Mean size (nm) 25000 200 25

Retained #325 (%) 15.5 --- ---

SSA* (m2/kg) 320 25000 109000

*SSA = specific surface area

Figure 1-1. XRD pattern of MA obtained with CuKα radiation.

1.3.4 Fine aggregate

The fine aggregate was in accordance to ASTM C33 (2003) with specific gravity (SSD) of 2.53,

and absorption capacity of 3.92%. The fine aggregate was oven dried before being used in the

experiments. Also, following recommendations for the design of high-strength concrete (Aïtcin, 1998;

Caldarone, 2009) the fineness modulus of the fine aggregate was 3.0.

5 15 25 35 45

Arb

itra

ry I

nte

nsi

ty U

nit

s

2θ

nS

SF

F

6

1.3.5 Coarse aggregate

The crushed gravel incorporated as coarse aggregate in the mixes has a maximum diameter of 9.5

mm, SSD specific gravity of 2.7, and absorption capacity of 4.2%. This material was in accordance to

ASTM C33 (2003). The coarse aggregate was oven dried before being used in the experiments.

1.3.6 Water

The water employed in the casting of grouts, mortar and concrete samples was tap water. The

source of the water was the system available at the University of Puerto Rico, specifically in the

construction materials laboratory located in Mayagüez, PR-USA.

1.4 Literature review

1.4.1 Amorphous silica particles

There are several studies on incorporation of SCM in cement-based composites; most of which

focus on FA and SF. These materials are used on different basis, for instance, environmental and energy-

related costs because they are cheaper than PC and its replacement helps to reduce the overall CO2

consumption (Mehta and Monteiro, 2003; Vejmelková et al., 2009). Also, SCM are attractive due to

improvements in the rheology, durability and strength of the concrete (Rao, 2003). Hence, FA and/or SF

additions are common in the production of high-strength concretes (Aïtcin, 1998; Caldarone, 2009; Rao,

2003). Nowadays the use of nS has gained special attention in civil engineering applications because

some improvements in chemical, physical and mechanical properties of concrete have been obtained

(Qing et al., 2007; Jalal et al., 2012; Nazari and Riahi, 2011; Li et al., 2004; Lin et al., 2008; Senff et al.,

2010; Stefanidou and Papayianni, 2012; Zhang and Islam, 2012; Zyganitidis et al., 2011).

FA is the most widely used SCM in concrete production (Kosmatka et al., 2003). FA is a finely

divided powder consisting of spherical glassy particles which resemble Portland cement. FA particles are

a by-product of the combustion of pulverized coal in electric power-generating plants collected by

electrostatic precipitators or bag filters. FA particles are primarily silicate glass containing silica, alumina,

iron, sodium, potassium, carbon and small amount of crystalline compounds. ASTM C618 (2008) Class F

and Class C FA are commonly used as pozzolanic admixture for concrete. Class F FA is often used at

dosages of 15 to 25 wt% and Class C FA is used at dosages of 15 to 40 wt% (Kosmatka et al., 2003).

During the last decade, considerable attention has been given to the use of SF as a partial

replacement of cement to produce high-strength concrete. Silica fume is also referred as micro-silica (or

micro-SiO2) is a mineral addition by-product of the ferrosilicon alloy industries obtained in an electric arc

7

furnace. SF rises as an oxidized vapor from 2000 °C furnaces. When it cools it condenses and is collected.

The condensed silica fume is then processed to remove impurities and to control particle size which is

extremely fine, about 100 times smaller than average cement particles (Kosmatka et al., 2003). SF is

essentially amorphous silica (usually more than 85%). SF is used in amounts between 5 and 10 wt%

where a high degree of impermeability and/or high-strength concrete is required.

In comparison to normal Portland cement-concretes, the addition of SF provide the following: i)

particles with two orders of magnitude finer than Portland cement, ii) highly pozzolanic reactive

chemistry, iii) increase the water requirement in concrete unless SPs are used (Siddique and Khan, 2011).

In addition, SF in concrete results in lower: porosity, permeability, and bleeding because amorphous SiO2

react and consume calcium hydroxide from the hydration process (Mindess et al., 2003). Silica fume

concrete has been found to be extremely strong, impermeable, and very durable against freezing-thawing,

salt water, and abrasion resistance. In concrete technology incorporation of SF is one of the methods of

enhancing the strength of concrete, particularly when the aggregates are of low quality (Almusallam et al.,

2004).

On the other hand, nano-SiO2 particles are industrially produced for a diverse array of

applications such as, paper treatment, anti-corrosion, painting, coatings, and textile industry among

others. In general, the variety of applications are due to their unique characteristics such as large surface

area, binding capacity, basic pH, heat resistance, large quantities of amorphous silica and high free

energy. Nowadays, the use of nS particularly has gained attention in civil engineering applications

because the potential improvements produced in chemical, physical and mechanical properties of concrete

(Björnström et al., 2004; Chen and Lin, 2009; Jalal et al., 2012; Jo et al., 2007; Li et al., 2004; Lin et al.,

2008; Nazari and Riahi, 2011; Zhang and Islam, 2012; Stefanidou and Papayianni, 2012; Zyganitidis et

al., 2011).

Results have shown that, like SF particles, addition of nS provide potentially enlarged strength,

lower porosity, improved permeability, and reduced bleeding. The reaction of the amorphous silica with

the Ca(OH)2 induces formation of secondary C-S-H (Jo et al., 2007; Mehta and Monteiro, 2003; Mindess

et al., 2003; Siddique and Khan, 2011). Therefore, since the major reactivity with the Ca(OH)2 phase and

the better improvement in the interfacial transition zone (ITZ), the potential effect of nS has been found to

be more efficient in enhancing strength than SF particles (Qing et al., 2007; Sanchez and Sobolev, 2010).

8

1.4.2 Fresh state properties in cementitious mixes

Polycarboxylate-type superplasticizers (SP) represent one of the most employed chemical

admixtures for concrete. The SP presence is related to its capacity of producing concrete with: i) high-

fluidity, ii) high-strength, and iii) superior dispersing force and retention effects even at low w/b ratios

(Yamada et al., 2001). However, the dispersing force of the SP and its power of retention seem to be

affected by some components of the PC or even by variations in the sequence of the mixing conditions

(Hallal et al., 2010).

Specifically, the behavior of the blended systems formed by PC and SPs may be altered due to

changes in the sequence in which the SP admixture is added (Agulló et al., 1999; Aïtcin, 1998; Hallal et

al., 2010). Even when a particular kind of cement and a particular SP is satisfactory with respect to the

specifications of an adopted standard (e.g. ASTM) the resultant PC-SP couple may not be necessarily

compatible from a rheological point of view (Aïtcin, 1998; Dodson and Hayden, 1989). Hence, one

approach to amend this problem is to select the most efficient PC-SP couple between the different brands

of cements and/or SP available in a particular location (Hallal et al., 2010).

In technical literature, rheology studies the laws governing the flow behavior (de Larrard, 1999).

In this sense, the Marsh cone test (MCT) is a “dynamic” indicator of rheological behavior in a particular

PC-SP couple by studying the performance of the grout (Aïtcin, 1998). The Marsh cone method is widely

used as a preliminary test before calibrating particular mixture designs with trial batches or with

quantitative studies by employing more complex instrumentation based on shear stress and plastic

viscosity measurements (Agulló et al., 1999; Aïtcin, 1998; Hallal et al., 2010). This procedure becomes

significant when high-performance concrete is the target, since its low w/b ratios require (usually w/b≤

0.35) the use of compatible PC-SP systems as an initial step (Aïtcin, 1998; Hallal et al., 2010).

In addition to the MCT procedure, in this research the slump cone, air content, unit weight and

flow table test are proposed on the fresh state of cementitious samples. The slump-cone test (ASTM

C143, 2010) is a measure the consistency. The literature (Li, 2011) defines consistency as a property

which describes how easily fresh cementitious mixes flows. The flow table test is described in ASTM

C1437 (2007). In general the flow area of a cementitious material is related to the degree in dispersion of

the cement particles (Chandra and Björnström, 2002); the fresh density or unit weight, as defined in

ASTM C138 (2010), is a measure of compactness (Chandra and Björnström, 2002); and the entrapped air

content (ASTM Standard C138) is a measure of the voids in concretes.

9

1.4.3 Hardened state properties in mortar and concrete samples

At any stage of hydration, the hardened cement paste of concrete or mortar samples consists of

(Illston and Domone, 2001): (1) a residue of unhydrated cement, at the center of the original grains; (2)

the hydrates, primarily calcium silicates hydrates (C-S-H) but also some calcium aluminates,

sulfoaluminates and ferrites; (3) crystals of calcium hydroxide; (4) the unfilled residues of the spaces

between the cement grains, called the capillary pores. The strength of the hardened cement paste derives

from van der Waals type forces between the hydrate fibers. Although these forces are of relatively low

magnitude, the integrated effect over the enormous surface area is considerable.

The compressive strength at a specified age, usually 28 days, measured on standard test

specimens, has traditionally been the criterion of acceptance of concrete. Also, the compressive strength

of concrete is, in most cases, the most suitable and effective tool for the control of concrete quality, even

when the compressive strength is not the most important quality to be controlled in a mix design. On the

other hand, indirect tensile test on concrete such as the splitting tensile test (ASTM C496, 2004) are

carried out in lieu of performing direct tensile test on brittle materials because the samples tend to break

where they are gripped by the testing machine. This is due to contact stresses exceed the fracture strength

of the material, leading to premature failure at the grips (Ashby and Jones, 2005).

1.4.4 Statistical design of experiments (DOE)

The statistical designed experiments which will be referred from now on as DOE are very useful,

because with a minimum of well-planned and developed experimental trials using an specialized software

it is possible to detect the principal and/or interactive effects between the factors under study (Aïtcin and

Mindess, 2011; Akalin et al., 2010; Caldarone, 2009; Senff et al., 2010). In civil engineering applications,

Senff et al. (2010) reported the effects of w/b, nS and SF on rheology, spread on flow table, compressive

strength, water absorption, apparent porosity, unrestrained shrinkage and weight loss of mortars up to 28

days using a 22 factorial design experiment with central points. Specifically, when values of compressive

strength were analyzed, the results showed that the curvature was statistically significant, suggesting that

the compressive strength variation did not follow a linear model. By using a robust statistical treatment

(32 factorial), they showed that the concavity of curve is positive when w/b varies and nS or SF was kept

constant, while negative curve concavities were obtained when nS or SF vary and w/b was kept constant.

In addition, when the above models were tested for lack-of-fit, the result was statistically significant. In a

similar study (Senff et al., 2009), the authors showed that it is possible to adjust the data to a second order

model reducing the range of the w/b ratio, thus the lack-of-fit condition could be successfully overcome.

10

Finally, the authors also could identify the interactive effects between the factors (w/b, SF o nS) which

were explained in detail in the document (Senff et al., 2009).

Ayan et al. (2011) carried out a parameter optimization of compressive strength of steel fiber

reinforced high-strength concrete (SFRHSC) by statistical design of experiments. The results showed that

among several factors affecting the compressive strength, five parameters that maximize all the responses

were: age of testing, binder type, binder amount, curing type and steel fiber volume fraction. In this study

was clearly demonstrated that current factors used in concrete technology, except steel fiber, significantly

contributed to the compressive strength being the age and binder type the most significant contributors.

Akalin et al. (2010) stated that concrete design is a hard and expensive job which takes too much time,

being the selection of an appropriate chemical admixture a very important criterion to achieve the desired

specification for concrete. Therefore, the cited authors proposed statistical mixtures experiments in order

to study the effects of admixture components and admixture dosage on the response variables examined.

In their experiments, the target was to reach an optimum point by obtaining maximum compressive

strength and maximum water reduction for concrete with minimum cost of the admixture. The results

from the statistical treatments were validated in laboratory experiments on mortar and concretes showing

that application of mixture experiments in concrete industry can result in lower product costs, shorter

product design and development time, and product with enhanced field performance.

1.4.5 Artificial neural networks (ANN) simulations

Artificial neural networks simulations (ANNs) are a powerful tool extremely useful in situations

for which the rules are unknown or when response surfaces are highly complex. Hence, the use of ANN is

especially advantageous when traditional predictive mathematical models are not feasible (El-Kassas et

al., 2002). However, the ANN flexibility is linked to one of the most important of their disadvantages:

they are not able to provide explanations and justifications for their answers (El-Kassas et al., 2002).

Therefore, ANN are often called “black box” (Arsenovic´ et al., 2013; Lee and Hsiung, 2009) but a

mathematical treatment on the trained network called sensitivity analysis can clarify considerably the

behavior of the parameters involved (Das and Basudhar, 2006; Guler and Artir, 2007; Lee and Hsiung,

2009; Madandoust et al., 2012).

In civil engineering, ANN approach has been widely used to model and analyze a diversity of

topics, such as soil behavior (Khanlari et al., 2012), torsion in concrete beams (Arslan, 2010), and the

effects of ground-granulated blast furnace slag and calcium nitrite-based corrosion inhibitor on the

chloride ion permeability and the compressive and tensile strength of concrete specimens (Boğa et al.,

11

2013). Also, flexural capacity of fiber-reinforced polymer concrete columns were determined, the ANN

predictions were more satisfactory than approaches used currently in the literature (Köroğlu et al., 2012).

Finally, the split tensile strength and water permeability of concrete containing Fe2O3 nanoparticles was

studied by Nazari et al., (2011) using ANN and genetic programming. According to their results, both

models have strong predicting potential, although ANN exhibited better performance. Nevertheless, the

computational work of the ANNs was more difficult to be carried out.

1.4.6 Weibull statistical analysis

In concrete technology the Weibull statistic has been used in research dealing with failure

analysis and fatigue tests. For example, Man and van Mier (2011) studied the size effect of concrete

subjected to three-point bending using the lattice model. The numerical analyses showed that a size effect

can be approximated with a Weibull model, where the Weibull modulus, depends on the concrete

composition. Also, in Germany Toasa Caiza and Ummenhofer (2011) stated that there are several

methods to determine the Weibull parameters. Nevertheless, they emphasized that there is no consensus

about which is the most appropriate method. The authors presented a general formulation of the

Probability Weighted Moments to estimate the three-parameter Weibull distribution. The study also

contains an application with experimental and simulated data from concrete specimens.

Similarly, a research dealing with the probability of failure of concrete components under

multiaxial stress states was developed in Japan by Li et al. (2003). This work presented a simplified

measurement method for determining the parameters of the governing Weibull distribution. Finally, a

recent study developed by Peiying et al. (2012) where the damage probability in concrete was analyzed

based on detection test and numerical simulation. In their research the authors assumed that concrete

strength obeyed a two parameter Weibull distribution and based on the results of numerical simulation,

the local damage probability analyses were developed.

1.5 General methodology

To estimate the rheological behaviors of PC-SP systems, two simplified methods are widely used

(Aïtcin, 1998): i) the mini-slump test and ii) the Marsh cone test. The present thesis will employ the

Marsh cone test (MCT) due to the dynamic characterization of the systems. Thus, typical water-to-binder

(w/b) ratios for experiments in high-strength concrete will be adopted in the grouts to obtain rheological

parameters indicating an acceptable chemical compatibility between the local Portland cement Type I and

the available chemical admixtures for this thesis. Also, in order to be consistent with Aïtcin (1998) it is

12

important to define a grout as a material different to mortar or concrete, that is, the combination of water,

PC, and mineral admixtures (when applied).

Specifically, in the fresh state the MCT would assist in the design of grouts with several chemical

admixtures to obtain a chemically compatible Portland cement and superplasticizers couples, which

permits to study mineral additions (fly ash, micro-SiO2 and nano-SiO2) in posterior stages. Thus, by using

the MCT, the effects of the following parameters are studied: i) type and dosage of the mineral

admixtures, ii) dosage of polycarboxylate-based superplasticizer, and iii) at two different w/b ratios

typical for high-strength concrete: 0.35 and 0.40.

Since the incorporation of amorphous silica in different size particles (micro and nano) could

have different rheological results, as a second stage the rheological behavior of the best PC-SP selected in

the previous stage will be studied but now with micro and nano-SiO2 additions. This posterior stage aims

to estimate the effects of different dosage levels of SP and the potential w/b ratios to be adopted in the

design of concrete mixes containing SF and/or nS.

Once the chemical couples (PC-SP) and the most adequate w/b ratios are tested and selected in

the fresh state, the next step consists in the design of more complex cementitious mixes, using a series of

fresh tests commonly employed in concrete technology to characterize the PC-SP-SF/nS systems. In this

stage, the experimental program will address the relationship between the fresh and hardened states in

mortar cements, which include superplasticized mineral admixtures in the range of micro and nanometer

scales. In this case, the SP levels will vary in dosage to characterize the behavior of the systems in their

rheological properties and their mechanical compressive strengths in mortar specimens.

Once the rheological analyses between PC-SP-SF/nS have been carried out in the fresh state and

the mortar samples studied in the hardened state by means of compressive strength, the results will be

analyzed to design more complex systems but now using concrete mixes and incorporating Class F FA as

a third amorphous silica product to produce binary, ternary and quaternary mixes: PC-SP, FA-PC-SP, SF-

PC-SP, nS-PC-SP, FA-SF-PC-SP, FA-nS-PC-SP, and FA-SF-nS-PC-SP.

In the hardened state, the mechanical test of the concrete samples will be carried out using both

compressive and tensile strength analyses. Different ages of failure will be conducted to monitor the

strength gained over time, which is an important issue when mineral admixtures are employed. In this

stage, statistical tools such as designs of experiments are employed in order to analyze in a more efficient

way the complex systems formed.

13

The next and final steps include the incorporation of experimental results as input data in

computational models, based on both artificial intelligence and advanced failure analyses based on the

Weibull statistics. The purpose is to understand the effects of the amorphous silica and correlate

theoretical concepts with experimental results.

As a final remark, it is important to clarify a couple of points in the fresh and hardened states. For

the fresh state: even though a particular system (mortar or concrete) would be cast without

superplasticizer (SP) based on its fresh behavior during the earlier minutes; all mortars and concretes in

this thesis will include SPs. The use of SP is based on two main reasons: first, validation in the prediction

of SP content in concrete from the MCT methodology based on grouts. Second, when validation

experiments are not the topic being studied, the environmental conditions and the high reactivity of the

materials employed (SF and nS) could affect retention effects of the fresh state; therefore the casting

process would be disadvantageous for some mixes in comparison with superplasticized-mixes.

Respect to the hardened state, the general objective of this study is related to the high-strength

concrete based on the ACI 363 (1997). The official document (ACI 363-97) states that a concrete is

referred as high strength when it reaches 40 MPa at 28 days in 6x12 inches cylinders. Nevertheless, the

present thesis is based on 2x4 inches cylinders. In order to reduce the geometrical-scale effects in

unpublished trials carried out in the laboratory at the beginning of the experimental program, 6x12 inches

cylinders were cast and the strength values were recorded. For calibration purposes, 2x4 inches cylinders

were cast in the same mixes and the loading rate was changed to obtain similar results as those obtained

using 6x12 inches cylinders. Notice from Chapter III how the strength gain rate of the 2x4 cylinders is in

the middle of the expected ranges from literature when using the larger 6x12 inches molds.

1.6 Scope of the research work

This research is restricted to the study of grouts at w/b=0.35 and 0.40, mortars at w/b=0.35 and

concretes at w/b=0.35 using Portland cement Type I and Polycarboxylate-type superplasticizers.

Nanoparticles of silica and silica fume are employed as mineral admixtures in grouts and mortars,

whereas micro- and nano-particles of silica and fly ash are employed in concrete samples. The principal

idea in the implementation of computational tools in this thesis is in assisting the analyzer in the physical

phenomenon, i.e., in determining and understanding the role of the mineral additions and aging effects on

concrete samples.

14

The activities to be performed as part of this thesis include:

(1) Perform the Marsh cone test method to study the rheological properties in the fresh state of the

cementitious systems. In addition to the Marsh cone test procedure, in this research the slump cone, air

content, unit weight and flow table test are used on the fresh state of cementitious samples.

(2) Perform compression and scanning electron micrographs (SEM) tests in mortar samples at 90

days and compressive and tensile strength measurements on concrete samples at specified ages of 3, 7,

28, 56 and 90 days. The compressive strength of mortar and concrete samples are treated as both an

output research variable and an indicator for the control of concrete quality. On the other hand, the

indirect tensile tests on concrete samples are performed using the splitting tensile test. The measurements

of this test are used only as an output research variable.

(3) Execute factorial experiments on mortar samples at 90 days and response surface analyses

from designed experiments on concrete specimens at 3, 7, 28, 56 and 90 days. These treatments are

carried out since the analyses of the nonlinear effects between the studied variables are more efficient

using statistical tools. Also, the response surface methodology permits determine the optimal dosages of

mineral admixtures in order to gain compression and tension strength in the concrete specimens.

(4) Develop artificial neural networks models for concretes failed in compression and tension

tests at 3, 7, 28, 56 and 90 days. The aim of incorporating artificial neural simulations in this study is to

correlate fresh and hardened concrete properties, as well as, to predict compressive and tensile strength of

concrete samples containing nano-particles of silica along with micro silica and/or fly ash in presence of

polycarboxylate-type superplasticizer as a tool complementary to response surface analyses.

(5) Address experiments in both plain and binary-ternary-quaternary systems in tension test

failures to determine Weibull parameters in concretes containing amorphous silica, especially, nano-

particles of silica as an active ingredient of the concrete samples.

1.7 General organization of the present thesis

The present thesis assesses the rheological and mechanical characterization of PC mixes

containing amorphous-SiO2 in presence of polycarboxylate-type SP. The present thesis is organized in six

chapters, where the first is being discussed in this section, and a summary of Chapter II-VI is presented as

follows:

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1.7.1 Compatibility analyses and rheological performance between Portland cement Type I and micro/nano-SiO2 particles in presence of polycarboxylate-type superplasticizers

In Chapter II, five PC-SP systems are analyzed at w/b=0.40 and the best PC-SP couple on

rheological basis using the MCT is selected. Once the best PC-SP is found, it is now cast at w/b=0.35 and

0.40 but adding SF(5,10,15 wt%) and nS(1,2,3 wt%). The rheological properties of these grouts

containing mineral admixtures are discussed.

1.7.2 Fresh state analyses and compressive strength of superplasticized mortar containing micro/nano-SiO2 particles

In Chapter III, the best PC-SP previously found in Chapter II is now used in the casting of mortar

and concrete specimens at w/b=0.35 containing SF(5,10,15 wt%) and nS(1,2,3 wt%). For mortar

specimens, the saturation dosage (SD) for each system was obtained according to MCT results previously

found in Chapter II. Furthermore, two overdose levels consisting of two times (SD=2) and four times

(SD=4) the SD from the MCT were used to study the compressive behavior of mortar samples containing

mineral admixtures. Statistical experimental designs at w/b=0.35 on mortar samples are conducted to

study the fresh state properties. In the hardened state of the mortar samples, compressive strength and

SEM examinations in the ITZ are carried out. Also, validation of the results of Chapter II from the MCT

in plain and mineral grouts is carried out using concrete mixes based on several trials with the best PC-SP

couple found in Chapter II on mortar samples, but now acting in binary concrete blends of PC-nS(1,2,3

wt%)/SF(5,10,15 wt%) at w/b=0.35. Finally, mechanical tests of these concrete samples are analyzed in

compression and tension conditions. Compressive and tensile strength of concretes containing amorphous

silica analyzed by designed experiments and artificial neural networks simulations

In Chapter IV mechanical and rheological applications of Chapters II and III is carried out using

the best PC-SP (Chapter II) in plain, binary, ternary, and quaternary concrete blends containing PC-SP-

FA/SF/nS at w/b=0.35. This chapter also presents experimental and computational treatments related to

compressive and tensile strength of concrete specimens. At different ages (3, 7, 28, 56 and 90 days), three

different central-composite experimental designs (DOE) are performed. Also, by ANN, the compressive

and tensile strength of the systems are modeled and additional mathematical analyses of the ANNs are

carried out to explain complex mathematical phenomena presented in the DOEs. Failure statistical

analysis on tensile strength of concretes containing amorphous silica

Chapter V investigates the tensile strength of concrete compositions tested in Chapter IV: PC-SP-

FA/SF/nS at w/b=0.35. Splitting tensile failures are carried out to investigate the accuracy of two and

three-parameters Weibull models. Finally, the estimated Weibull parameters are obtained by using

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different advanced nonlinear methodologies. Summary, conclusions and recommendation for future

studies

In chapter VI, summary, final conclusions and recommendations for future researches are

developed, according to the results obtained on chapters II through V. Finally, the literature cited through

chapters I to V is shown.

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CHAPTER II

2 COMPATIBILITY ANALYSIS AND RHEOLOGICAL PERFORMANCE BETWEEN

PORTLAND CEMENT TYPE I AND MICRO/NANO-SIO2 PARTICLES IN PRESENCE

OF POLYCARBOXYLATE-TYPE SUPERPLASTICIZER

2.1 Introduction

The present chapter assesses the interaction between a locally-produced PC type I and five

commercial polycarboxylate type SP in grouts containing SF or nS. The experimental procedure

comprises the evaluation of five PC-SP systems analyzed at w/b=0.40 and the best PC-SP couple on

rheological basis using the MCT methodology is selected. Once the best PC-SP couple at w/b=0.40 is

known, the rheological behavior is evaluated at w/b=0.35 and 0.40 but adding 5, 10 and 15 wt% and 1, 2,

and 3 wt% of SF and nS, respectively. Thus, by using the MCT, the effects of the following parameters

were studied: i) type and dosage of the MA, ii) dosage of carboxylate-based SP, and iii) two w/b ratios.

2.2 Theoretical background

The MCT is a “dynamic” indicator of rheological behavior in a particular PC-SP couple by

studying the performance of the paste (Aïtcin, 1998). The MCT is considered to reveal the same trends as

the yield shear stress, by assuming that the cement paste under study follows a Bingham model (Agulló et

al., 1999; Banfill, 1991; de Larrard, 1999; Tattersall, 1991). This becomes relevant when high-

performance concrete is the target, since its low w/b (generally, w/b ≤ 0.35) require the use of compatible

PC-SP systems (Hallal et al., 2010). Nevertheless, this method must be used as a preliminary test prior to

calibrate particular mixture designs incorporating aggregates with field trial batches.

The term compatibility is understood as that which characterizes the PC-SP-SF/nS interaction

reflected in: low flow time (FT) at 5 min, low saturation dosage (SD) and negligible fluidity loss (ΔFT) at

60 min. Where, the difference between the FT at 60 and 5 min is defined as the ΔFT (Hallal et al., 2010).

Plain compatible couples require an FT between 60 and 90 sec in combination with ΔFT tending to zero

and values of SD in the 0.0-1.0 range by mass of solid content (wt%) of SP with respect to the cement

weight (Aïctin, 1998). SD is defined as the point beyond which at 5 min age there is no significant

18

increase in fluidity (Agulló et al., 1999; Aïctin, 1998; Hallal et al., 2010). Furthermore, under ideal

conditions the intersection of the curves describing the rheological behavior reflected in the FT at 5 and

60 min corresponds to the SD (Aïctin, 1998). Nevertheless, when the ideal conditions of the intersection

are not reached, the break point in the curve FT vs. SP dosage at 5 min is commonly accepted as the SD.

Polycarboxylate-type SPs are one of the most employed chemical admixtures for concrete. This is

due to its capacity of producing concrete with: i) high fluidity, ii) high strength, and iii) superior

dispersing force and retention effects even at low w/b (Yamada et al., 2001). However, the dispersing

force of the polycarboxylate-type SPs and its power of retention seem to be affected by some components

of the cement (Hallal et al., 2010; Yamada et al., 2001) or even by variations in the sequence of the

mixing conditions (Agulló et al., 1999; Aïctin, 1998; Hallal et al., 2010; Yamada et al., 2001). Recently,

the reasons for the incompatibility between cement and some SPs have been of interest in concrete

technology (Felekoğlu et al., 2011; Plank, 2009; Plank, 2010; Zingg, 2009).

2.3 Methods used to analyze PC-SP systems

2.3.1 Marsh apparatus

The Marsh funnel viscometer (1.5 L) is shown in Figure 2-1. The calibration of the viscometer

was conducted as part of each experimental scheme following the manufacturer´s instructions.

Figure 2-1. Scheme of the Marsh cone apparatus.

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2.3.2 Marsh test procedure

During the process 1.2 L of cement paste is employed (Aïctin, 1998). The pastes were mixed in a

1.7 L Hamilton-Beach blender with 550 Watt peak-power motor 120V, 60Hz, and 3.5A. Following

literature recommendations (Aïctin, 1998; Ferraris et al., 2001; Helmuth et al., 2006) a blender is used

instead of a Hobart mixer. The sample preparation comprised the following steps (Aïctin, 1998):

Step 1: Record the water temperature before starting the mixing process, as it must range between

20-23 °C in order to represent normal initial hydration conditions. Step 2: Pour the water, SP and nS (if

used) into the jar and start the mixing process during 10 sec. Step 3: Progressively, add the amount of

cement within a time interval not exceeding 2 min. In the case of PC-SP-SF systems, the cement and the

SF were previously mixed by hand in dry conditions for 3 min. Step 4: Stop the mixing process for 15 sec

in order to clean the cement adhered to the jar. Step 5: Mixing For 60 sec and then monitor the

temperature: 20-23 °C. If the temperature is not within the range, the experiment had to be repeated from

step 1. Step 6: Fill the Marsh cone to about 1.4 L, and then proceed to record the time it takes to fill the

1.2 L beaker with grout.

2.4 Results and discussion

2.4.1 Marsh cone test analysis on plain grout mixtures

Table 2-1 summarizes the results obtained from the rheological analysis of the systems. Results

show that SD, FT and ΔFT present important variations among the systems studied even though the same

cement was employed and all five SP employed rely on the latter polymer technology (Rixom and

Mailvaganam, 2002). Table 1.2 (Zapata et al., 2013a) shows the principal properties of the SP used in the

present couples. In general, a poor compatibility was observed in these PC-SP couples. In order to save

efforts, an adequate SP in conjunction with a particular kind

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