Durability of Concrete Incorporating Blended Binders and Alkali-Activated Materials to Sulfuric Acid Environments By Mohamed Ramadan Hussien Mahmoud A Thesis submitted to the Faculty of Graduate Studies of The University of Manitoba In partial fulfillment of the requirements of the degree of Master of Science Department of Civil Engineering University of Manitoba Winnipeg, MB, Canada Copyright © 2018 by Mohamed Hussien Mahmoud Abstract Acidic attack on concrete imparts unique set of damage mechanisms and manifestations compared to other durability issues of concrete. Sulfuric acid attack limits the service life of concrete elements and, thus, results in increased expenditures for the repair or in some cases replacement of the whole structure. To date, there is lack of standardized tests for specifically evaluating the resistance of concrete to sulfuric acid attack, which has caused great variability, for example in terms of solution concentration, pH level/control, etc., among previous studies in this area. Accordingly, there are conflicting data about the role of key constituents of concrete (e.g. supplementary cementitious materials [SCMs]), and uncertainty about building codes’ stipulations for concrete exposed to sulfuric acid. Hence, the first objective of this thesis was to assess the behaviour of the same concretes, prepared with single and blended binders, to incremental levels (mild, severe and very severe) of sulfuric acid solutions over 36 weeks. The test variables included the type of cement (general use [GU] or portland limestone cement [PLC]) and SCMs (fly ash, silica fume and nano-silica). The severe (1%, pH of 1) and very severe aggression (2.5%, pH of 0.5) phases caused mass loss of all specimens, with the latter phase providing clear distinction among the performance of concrete mixtures. The results showed that the penetrability of concrete was not a controlling factor, under severe and very severe damage by sulfuric acid attack, whereas the chemical vulnerability of the binder was the dominant factor. Mixtures prepared from PLC performed better than that of counterparts made from GU. While the quaternary mixtures comprising GU or PLC, fly ash, silica fume and nanosilica showed the highest mass losses after 36 weeks, binary mixtures incorporating GU or PLC with fly ash had the lowest mass losses. i Several studies reported that the improved chemical resistance of alkali-activated materials (AAMs) over concrete based on portland cements. However, AAMs have technical limitations, which might deter its widespread use in cast-in place applications. These limitations include need for heat curing, slow setting, and slow strength development, which might be mitigated by further improving the reactivity of AAMs during early-age with nanoparticles; however, this area remains largely unexplored. Hence, the second objective of this thesis was to develop innovative types of AAMs-based concrete [alkali activated fly ash (AAFA), alkali activated slag (AAS) and their blends incorporating nanosilica] and evaluate their resistance to two different sulfuric acid exposures over 18 weeks for potential use in repair of concrete elements vulnerable to acidic attack. While AAFA specimens, produced without heat curing, experienced rapid ingress of the acidic solution and a significant reduction in the bond strength with substrate concrete, fly ash based AAMs comprising slag and or nanosilica (AAFA-S and AAFA-S-NS) had improved performance due to discounting the ingress of acidic solution and continued geopolymerization reactivity. Comparatively, specimens from the slag group exhibited high levels of swelling, internal cracking and mass loss due to chemical deterioration. The overall results suggest that AAFA-S and AAFA- S-NS mixture, without heat curing, may be a viable option for repair applications of concrete elements in acidic entrainments, but field trials are still needed to further verify their performance. ii To Mom and Dad, I hope this achievement gets me a step closer to making you proud of me. iii Acknowledgements I would like to express my sincere gratitude and appreciation to my supervisor Dr. Mohamed T. Bassuoni, P.Eng., Associate Professor, Department of Civil Engineering, University of Manitoba, for his unremitting guidance and cordial support in all stages of this research accomplishment. I do also deeply convey my sincere thanks to him for his encouragement and help to organize my ideas and interests, and also express my deep appreciation for what I have learned from him during my study. I highly appreciate the financial support from Natural Sciences and Engineering Research Council of Canada (NSERC), John Glanville Memorial Scholarship, and Graduate Enhancement of Tri- Council Stipends (GETS). The IKO Construction Materials Testing Facility at the University of Manitoba in which these experiments were conducted. Many thanks to Chad Klowak, P.Eng., W.R. McQuade Heavy Structures Laboratory Manager, University of Manitoba, for his technical assistance and valuable guidance. I would like to thank my colleagues for their continuous support specially Ahmed Gaber, Mohammad Tiznobaik, Mohamed Sakr and Mohamed El Gendy whose comments and suggestions were remarkable. Finally, I would like to thank my mother and my father for their endless support throughout this significant part of our life. Thank you all, without your sincere support I would not be here to make this achievement. iv Table of Contents Abstract ............................................................................................................................................ i Acknowledgements ........................................................................................................................ iv Table of Contents ............................................................................................................................ v List of Tables ................................................................................................................................ vii List of Figures .............................................................................................................................. viii Abbreviations/Nomenclature ......................................................................................................... xi Chapter 1: Introduction ................................................................................................................... 1 1.1. Overview .............................................................................................................................. 1 1.2. Need for Research ................................................................................................................ 2 1.3. Objectives ............................................................................................................................. 6 1.4. Scope of Work ...................................................................................................................... 7 1.5. Thesis Outline ...................................................................................................................... 8 Chapter 2: Literature Review .......................................................................................................... 9 2.1. General Features of Sulfuric Acid Attack ............................................................................ 9 2.2 Standardized Test Methods and Methods of Quantifying Degradation .............................. 13 2.3. Role of the Type of Cement, SCMs, Nanoparticles and Limestone Fillers in Resisting Acidic Attack............................................................................................................................. 15 2.3.1 Role of the Type of Cement ......................................................................................... 15 2.3.2 Role of SCMs and Nanoparticles ................................................................................. 16 2.3.3 Role of Limestone Filler ............................................................................................... 17 2.4. Alkali-Activated Materials ................................................................................................. 18 2.4.1 Review .......................................................................................................................... 18 2.4.2 Alkali-Activated Fly Ash .............................................................................................. 19 2.4.3 Alkali-Activated Slag ................................................................................................... 20 2.4.4 Alkaline Activator ........................................................................................................ 21 2.4.5 Curing, fresh and Hardened Properties ......................................................................... 24 2.4.6. Durability of AAMs to Sulfuric Acid Attack .............................................................. 28 2.5. Code Provisions.................................................................................................................. 29 2.6. Closure ............................................................................................................................... 33 Chapter 3: Experimental Program ................................................................................................ 35 3.1 Experimental Program for Concrete Mixtures Incorporating SCMs and Nanosilica under Incremental Acidic Attack ........................................................................................................ 35 v 3.1.1 Materials and Mixtures ................................................................................................. 35 3.1.2 Acid Exposure .............................................................................................................. 37 3.1.3 Tests .............................................................................................................................. 39 3.2 Experimental Program for Concrete with AAMs under Different Acidic Exposures ........ 44 3.2.1 Materials and Mixtures ................................................................................................. 44 3.2.2 Procedures of Mixing ................................................................................................... 46 3.2.3 Acid Exposure .............................................................................................................. 48 3.2.4 Tests .............................................................................................................................. 50 Chapter 4: Results and Discussion for Concrete Mixtures Incorporating SCMs and Nanosilica under Incremental Acidic Attack .................................................................................................. 54 4.1 Penetrability and Porosity ................................................................................................... 54 4.2 Visual Assessment............................................................................................................... 56 4.3 Mass Loss ............................................................................................................................ 58 4.4 Thermal and Microstructural Analyses ............................................................................... 63 Chapter 5: Results and Discussion for Concrete with AAMs under Different Acidic Exposures 72 5.1 Absorption Test ................................................................................................................... 72 5.2 Visual Assessment............................................................................................................... 73 5.3 Neutralization Depth ........................................................................................................... 75 5.4 Mass Loss and Pull-off Test ................................................................................................ 77 .5 Discussion ............................................................................................................................. 80 Chapter 6: Summary, Conclusions and Recommendations .......................................................... 90 6.1. Summary ............................................................................................................................ 90 6.1.1 Conclusions of Concrete Mixtures Incorporating SCMs and Nanosilica under Incremental Acidic Attack ........................................................................................................ 90 6.1.2. Conclusions of Concrete with AAMs under Different Acidic Exposures ...................... 92 6.2 Recommendations for Future Work .................................................................................... 93 References ..................................................................................................................................... 95 vi List of Tables Table 2. 1: Typical Ms and Na2O dosage based on sodium silicate activators for AAFA .......... 23 Table 2. 2: Typical Ms and Na2O dosage based on sodium silicate activators for AAS ............. 24 Table 3. 1: Chemical and physical properties of cement and SCMs ........................................... 36 Table 3. 2: Proportions of mixtures per cubic meter of concrete ................................................. 37 Table 3. 3: Chemical composition and physical properties of fly ash, slag and nanosilica ......... 44 Table 3. 4: Proportions of the mixtures per cubic meter .............................................................. 46 Table 4. 1: Results from RCPT and MIP ..................................................................................... 55 Table 4. 2: Portlandite (420-440ºC) contents in specimens stored in the curing chamber .......... 64 Table 4. 3: Enthalpies (J/g) of the main phases in the cementitious matrix after acid exposure . 65 vii List of Figures Fig. 2. 1: a) gypsum depositions and b) aggregate disintegration after exposure to 2.5% concentration of sulfuric acid in a laboratory test. .......................................................................... 1 Fig. 3. 1: Incremental aggression of the sulfuric acid exposure: phase I, II and III ....................... 1 Fig. 3. 2: Incremental aggression of the sulfuric acid exposure: phase I, II and III ....................... 1 Fig. 3. 3: RCPT apparatus. ............................................................................................................. 1 Fig. 3. 4: MIP apparatus. ................................................................................................................ 1 Fig. 3. 5: Drying the specimens in laboratory conditions after taking them out of the solution. ... 1 Fig. 3. 6: Weighing the specimens after drying to calculate the relative mass change. ................. 1 Fig. 3. 7: The DSC instrument........................................................................................................ 1 Fig. 3. 8: The sample chamber of SEM where the fracture pieces were mounted. ........................ 1 Fig. 3. 9: Spraying the top surfaces of the mixtures after casting by a curing compound. ............ 1 Fig. 3. 10: Wire brushing the surface of the substrate slabs after casting. ..................................... 1 Fig. 3. 11: Casting the repair layer (AAMs) on the substrate slabs and spraying the top surface of the mixtures with the curing compound.......................................................................................... 1 Fig. 3. 12: Test set-up for the slabs before ponding with the sulfuric acid solution. ..................... 1 Fig. 3. 13: Partial coring of the slabs. ............................................................................................. 1 Fig. 3. 14: The pull-off test. ............................................................................................................ 1 Fig. 3. 15: XRD instrument in which the powder samples were test ............................................. 1 Fig. 4. 1: Features of damage of GU specimens immersed in the sulfuric acid solutions after Phases: (a) I, (b) II, and (c) III. ....................................................................................................... 1 Fig. 4. 2: Neutralization depth of concrete specimens immersed in the sulfuric acid solutions after: a) Phase I (pH of 4.5), and b) Phase III (pH of 0.5) .............................................................. 1 viii Fig. 4. 3: Average mass loss with time for specimens from groups: a) GU, and b) PLC. ............. 1 Fig. 4. 4: Cumulative mass loss for GU and PLC groups after: a) 24 weeks, and b) 36 weeks. .... 1 Fig. 4. 5: Penetrability of specimens vs. their total mass losses after: a) Phase II, and b) Phase III ......................................................................................................................................................... 1 Fig. 4. 6: Exemplar micrographs from a GU specimen after Phase I showing gypsum in the reaction zone infilling air voids with higher magnification (x 3000). ............................................ 1 Fig. 4. 7: Micrographs of SEM and EDX analyses for a GUSF specimen after Phase II: (a) deteriorated surface, and (b) gypsum formation in the reaction zone (left) with corresponding EDX (right). .................................................................................................................................... 1 Fig. 4. 8: SEM and EDX analyses after Phase III for a GU specimen: (a) deteriorated surface showing gypsum formation in the reaction zone (left) with corresponding EDX (right), and (b) ettringite rosettes growing in an air void away from the surface (left) with corresponding EDX (right). ............................................................................................................................................. 1 Fig. 4. 9: SEM and EDX analyses after Phase III for a PLCFSFNS specimen showing: (a) large gypsum crystals in the reaction zone, (b) deteriorated surface, and (c) cracks extending into the inner core................................................................................................................................... 1 Fig. 4. 10: Unreacted fly ash particles within the reaction zone of a PLCF specimen (left) with corresponding EDX (right). ............................................................................................................ 1 Fig. 5. 1: Absorption trends of all mixtures.................................................................................... 1 Fig. 5. 2: Appearance of concrete specimens after 18 weeks of immersion in 10% sulfuric acid: (a) fly ash based AAMs, and b) slag based AAMs ......................................................................... 1 Fig. 5. 3: Degradation of slabs at the end of the cyclic exposure with the sulfuric acid. ............... 1 Fig. 5. 4: Neutralization depth versus time for the specimens in the full immersion exposure. ... 1 ix