Influence Of Bentonite And Blast Furnace Slag To The Self Healing Behaviour Of Cracked Cement Paste - ITS Repository
FINAL PROJECT (RC14-1501)
INFLUENCE OF BENTONITE AND BLAST FURNACE
SLAG TO THE SELF HEALING BEHAVIOUR OF CRACKED CEMENT PASTE M. SAMSUL ANAM NRP. 31 11 100 076 Supervisor : Dr.Eng. Januarti Jaya Ekaputri, ST. MT. Prof. Dr. Ir. Triwulan, DEA. CIVIL ENGINEERING DEPARTMENT Faculty of Civil Engineering and Planning Institut Teknologi Sepuluh Nopember Surabaya 2016TITLE PAGE FINAL PROJECT (RC14-1501)
INFLUENCE OF BENTONITE AND BLAST FURNACE
SLAG TO THE SELF HEALING BEHAVIOUR OF CRACKED CEMENT PASTE M. SAMSUL ANAM NRP. 31 11 100 076 Supervisor : Dr.Eng. Januarti Jaya Ekaputri, ST. MT. Prof. Dr. Ir. Triwulan, DEA.
APPROVAL SHEET
CIVIL ENGINEERING DEPARTMENT Faculty of Civil Engineering and Planning Institut Teknologi Sepuluh Nopember Surabaya 2016
INFLUENCE OF BENTONITE AND BLAST FURNACE SLAG
TO THE SELF HEALING BEHAVIOUR OF CRACKED
CEMENT PASTE
Student Name : M. Samsul Anam NRP : 31 11 100 076Departement : Civil Engineering Department FTSP – ITS
Supervisor : Dr. Eng. Januarti J. E., ST. MT.Prof. Dr. Ir. Triwulan, DEA. ABSTRACT
Cracks, caused by shrinkage and external loading faciliates the
ingress of aggressive and harmful substance into concrete and
reduce the durability of the structures. It is well known that self –
healing of cracks can significantly improve the durability of the
concrete structure. In this reseach, self healing propertis of the
cement paste containing bentonite and blast furnace slag were
studied. The self healing properties were evaluated by using 4
indexparameters, including surface crack width (β ), crack depth
(α index ), tensile strength recovery, and flexural stiffness recovery.
In combination with microscopic obervation, a healing process
over time was drawn. The result show that bentonite can improve
healing properties, in term of surface crack width and crack
depth. In the other hand BFS also could also improve self healing
properties, in terms of crack depth, direst tensile regain, and
flexural stiffnes. Carbonation reaction still to be main mechanism
which contribute self healing process, althought continued
hydration still occure.
Keyword : cracks, self-healing, durability, bentonite, blast furnace slag
PREFACE
Thank to Almighty God who has given His favor to the author for finishing the research and completing the final project report entitled ""Influence of bentonite and blast furnace slag to the self-healing behavior in cracked cement paste". This research describe a solution to improve durability of the concrete structures which is due to a cracks in the concrete materials, by applying self-healing concrete approach. Since the durability is very important factor which is related to the age of buildings, the self-healing concrete is very important to develope. This reasearch focus on the influence of bentonite and blast furnace slag to the self-healing behaviour which is evaluated by using 6 parameters, i.e crack width, crack depth, tensile strength recovery, flexural stiffness recovery, pH, mineral closing crack, and cloride ion penetration to analyze the durability of the cracked cement paste. That 6 parameters are discused, both influence of each material and relationship between each parameter to the self-healing behaviour.
This research has been done for 8 months, which is started from March 2015 and fisnished on January 2016. Several testing, measurement, analysis and observation have been conducted in Laboratory of Concrete and Buiding Materials ITS, Cement Reseacrh Center PT. Semen Indonesia, Laboratory of Analysis and Instrumentation (Lab. TAKI) ITS, and Laboratory of Enviroment Quality ITS. Furthermore, the author likewise wish to express his profound and earnest appreciation for the individuals who have supported, guided and helped in finishing this research report, i.e :
1. The author’s beloved Parents, Supriyadi and Partutik. The author would like to thanks so much for their prayer, support, affection, advices, guidance, and help in all my life, their love is beyond any words.
2. Dr. Eng Januarti Jaya Ekaputri, ST., MT as first supervisor for his valuable guidance, encouragement, patient, correlation, advice, and suggestion which are very helpful in finishing this report. The author would like to thanks for for her time to share her great knowledge and great experiences to the author.
3. Prof. Dr. Ir. Triwulan, DEA as second supervisor, who has guided me with his worthy, valuable guidance, encouragement, patient, correlation, advice, suggestion and correction to improve the quality of this report. The author would like to thanks for for her time to share her great knowledge and great experiences to the author
4. Trieddy Susanto, ST, MT as external supervisor from PT.
Semen Indonesia. The author would like to thanks for his guidance, advice, suggestion, and correction to improve the quality of this report.
5. Mr. Basar, Mr. Hardjo, Mr. Totok, Mr. Supri, Mr. Ji as laboran in Laboratory of Concrete and Buidling Materials for their support and favor in conducting some testing and measurement of this reaseach.
6. The author’s Lab-mate, i.e Wawan, Alex, Novema, Luthfi Anas, James, Nizar, Ziad, Adi, Achsan, Henry, Kefi, Ila, Ruceh, Annisa, Inne, Like, Kiky, and Wuri, who have given beatiful and unforgettable memories as long as the author
conducted his research in the Laboratory of Concrete and Building Materials.
7. All lecturers of Civil Engineering Department ITS, who have transferred much knowledge to the author which very helpful in finishing final project report.
The author would like to thanks for guidance, instruction and help during
study at the Civil Engineering Departement
8. The author’s beloved friends in Civil Engineering Department’11 and S54. The author would like to thanks for togetherness and attention as long as the author study in Civil Engineering Departement ITS.
Big Familiy of Civil Engineering Department ITS 9.
Minister of Research and Higher Education which has fund the 10. Financial support for this research work.
11. PT. PT. Semen Indonesia for supporting cement materials, blast furnace slag, and supporting some experimen.
12. PT. Surya Beton Indonesia and PT. Varia Usaha Beton for supporting cement materials.
The last, this final project report is far from being perfect, but it is expected that this report will be useful not only for the researcher, but also the readers. For this reason, constructive thought full suggestions and critics are well come to make this report better.
. Surabaya, January 25, 2016
Author M. Samsul Anam 31 11 100076
TABLE OF CONTENTS
TITLE PAGE ................................................................................. i APPROVAL SHEET ..................................................................... i ABSTRACT .................................................................................. v PREFACE ...................................................................................vii TABLE OF CONTENT ............................................................... xi LIST OF FIGURE....................................................................... xv LIST OF TABLE ....................................................................... xxi
CHAPTER I INTRODUCTION .................................................. 1
1.1. Background ...................................................................... 1
1.2. Research Problems ........................................................... 4
1.3. Research Boundaries ........................................................ 5
1.4. Research Objective........................................................... 5
1.5. Benefits ............................................................................ 6
CHAPTER II LITERATURE REVIEW ...................................... 7
2.1. Crack on the Concrete Structures ..................................... 7
2.2. Conditions for Self-Healing ............................................. 8
2.3. Self-Healing Mechanism .................................................. 9
2.4. Self-Healing Mechanism with Continued Hydration ..... 11
2.5. The influence of Pozzoland to Ca(OH)
2 content ........... 13
2.6. Characteristics of Bentonite Clay ................................... 14
2.7. Chemical Structure of Montmorolinite .......................... 16
2.8. Autogenous Healing Concrete using Geomaterial ......... 18
2.9. Blast Furnace Slag as Autogenous Healing material ..... 23
CHAPTER III RESEARCH METHODOLOGY ....................... 35
3.1. Literature Riview ........................................................... 36
3.2. Preparation of Materials ................................................. 37
3.3. Analisys of Raw Materials Properties ............................ 37
3.3.1. Method to Determine Specific Gravity ..................... 37
3.3.2. Method to Determine Density ................................... 39
3.3.3. Method to determine SAI .......................................... 41
3.3.4. Flow Table Test ........................................................ 44
3.3.5. Particles Size Analyze .............................................. 45
3.3.6. X-Ray Fluoroscene ................................................... 46
3.3.7. X-Ray Diffraction ..................................................... 46
3.4. Mix Proportion Series .................................................... 47
3.5. Specimens Series ........................................................... 47
3.5.1. Dogbone/Briquet Specimen...................................... 48
3.5.2. Beam 10 x 10 x 40 .................................................... 48
3.6. Specimens Casting ......................................................... 51
3.7. Curing Condition ........................................................... 52
3.8. Introducing Artificial Crack .......................................... 53
3.9. Water Imersion Curing .................................................. 54
3.10. Self Healing Evaluation ................................................. 54
3.10.1. Ultrasonic Pulse Velocity Testing ......................... 54
3.10.2. Microscopic Investigation ...................................... 57
3.10.3. Four Point Bending Test ........................................ 62
5.10.4. Direct Tensile Strenght Test .................................. 63
5.10.5. Measuring pH of Specimens .................................. 65
5.10.6. Cloride Ion Penetration Test .................................. 67
5.10.7. XRD Analysis ........................................................ 69
CHAPTER IV RESULTS AND DISCUSSIONS ...................... 71
4.1. General Introduction ...................................................... 71
4.2. Testing Result of The Raw Materials ............................ 71
4.2.1. Spesific Gravity of Material ..................................... 71
4.2.2. Density of Material ................................................... 73
4.2.3. Strenght Activity Index ............................................ 75
4.2.4. XRD ......................................................................... 78
4.2.5. XRF .......................................................................... 82
4.2.6. Particles Size Distribution ........................................ 84
4.2.7. Spesific Surface Area (SSA) .................................... 86
4.2.8. Flowability of The Cement Paste Mixture ............... 87
4.3. Testing Result of Self Healing Evaluation .................... 92
4.3.1. Crack Width .............................................................. 92
4.3.2. Crack Depth ............................................................ 107
4.3.3. Direct Tensile Regain ............................................. 113
4.3.5. Alkalinity ................................................................ 127
4.3.6. XRD ........................................................................ 130
4.4. Discussions ................................................................... 138
4.4.1. Influence of Bentonite to the Self Healing .............. 138
4.4.2. Influence of BFS to the Self Healing ...................... 139
4.4.3. Correlation between w/c and healing ability ........... 140
4.4.4. Flexural - Tensile Strenght Relationships ............... 142
CHAPTER V CONCLUSIONS................................................ 143 BIBLIOGRAPHY ..................................................................... 145
LIST OF FIGURES
Figure 2. 1. Maximum crack width (functions of water pressure (h/d) according to Lohmeyer and Meichsner) ............. 9
Figure 2. 2. Causes of autogeneous self-healing ......................... 10 Figure 2. 3. Model for calculating the self-healing mechanism based on continued hydration ................................... 12 Figure 2. 4. Ca (OH)2 content based on cement type and additional pozzoland material ................................... 14 Figure 2. 5. Chemical structure of Montmorollonite .................. 17 Figure 2. 6. Self-healing [OPC90٪+CSA5٪+Geo 5٪] ................ 19 Figure 2. 7. A comparison X-Ray mapping between self healing zone and original zone .............................................. 19 Figure 2. 8. A comparison geopolimer gell in the self-healing zone with Hydrogarnet in original zone .................... 20 Figure 2. 9. Permeability Coefficient of Specimen using some mineral adimixture .................................................... 21 Figure 2. 10. γ Index value of Specimen using some mineral adimixture ................................................................. 22 Figure 2. 11. Flexural strength of cracked concrete using nanoclay for different curing conditions and precracking time ........................................................ 23
Figure 2. 12. Crack self-closing ratio .......................................... 24 Figure 2. 13. Cumulative heat production Q [J/g] for the different mixtures under investigation ..................................... 25 Figure 2. 14. Influence of carbonation degrees to the fillliing fraction of crack ........................................................ 26 Figure 2. 15. Faction minerals which close the crack ................. 27 Figure 2. 16. Influence of BFS replacement to Flexural strength concrete after cracking .............................................. 28 Figure 2. 17. Influence of BFS replacement to Splitting tensile strength concrete after cracking ................................ 28 Figure 2. 18. Influence of BFS replacement to compresif strength concrete after cracking .............................................. 29
Figure 2. 19. Maximum crack width for 100% healing .............. 30 Figure 2. 20. Crack healing percentage as a function of the initial crack width for A) fresh water and B) sea water ...... 31 Figure 2. 21. Chloride ion permeability of ECC mixtures using slag due to repetitive preloading ............................... 32 Figure 2. 22. Total crack closure rates of ECC mixtures with slag specimens due to self healing ................................... 33 Figure 3. 1. Flowchart of Research Methodology ...................... 36 Figure 3. 2. Measuring flow diamater of cement paste .............. 45 Figure 3. 3. Explanation of Sample Code ................................... 47 Figure 3. 4. Detail specification of briquet ................................. 48 Figure 3. 5. Dimension of Beam specimens ............................... 49 Figure 3. 6. Crack initiation by indtroducing teflon sheet as depth as 5 mm ........................................................... 49 Figure 3. 7. Detail of steel reinforcement ................................... 49 Figure 3. 8. Cylinder specimens ................................................. 50 Figure 3. 9. Coated specimens, a) cover side b) top side ........... 50 Figure 3. 10. Curing by covering specimens with wet burlap .... 52 Figure 3. 11. Introducing artificial crack, a) Cylinder specimens by using splitting test, b) beam specimens by using four point bending test .............................................. 53
Figure 3. 13. Water Imersion Curing .......................................... 54 Figure 3. 14. Schematic of Pulse Velocity Apparatus ................ 55 Figure 3. 15. Transmitter and receiver position for UPV measurement ............................................................. 56 Figure 3. 16. Typical arrangement for Measuring Crack Depth 57 Figure 3. 17. Example crack width graphic for calculating healing efficiency index ........................................................ 59 Figure 3. 18. Determine crack position ...................................... 59 Figure 3. 19. Choosing line button ............................................. 60 Figure 3. 20. Drawin line ............................................................ 60
Figure 3. 21. Showing crack width data ...................................... 60 Figure 3. 22 Determine crack position ........................................ 61 Figure 3. 23. Drawing poligon line ............................................. 61 Figure 3. 24. Typical arrangement for Four Point Bending Test 63 Figure 3. 25. Typical arrangement for direct tensile test according to CRD-C 260-01 ...................................................... 64 Figure 3. 26. a) Cylinder Specimens for cloride penetration,
b) Top Side, c) bottom side .................................... 67 Figure 3. 27. a) NaCl Flake, b) Dissolving NaCl flake in the water .......................................................................... 68 Figure 3. 28. a) Solution for Cloride penetration, b) Specimens were submerged in NaCl solution ............................. 68 Figure 3. 29. . Sampling for Cloride Ion Penetration Specimens 69 Figure 4. 1. SAI of OPC, Ca-Bentonite and BFS ....................... 77 Figure 4. 2. Diffractogram of BFS .............................................. 80 Figure 4. 3. Diffractogram of Bentonite ..................................... 81 Figure 4. 4. Particle Size Distribution of Bentonite .................... 84 Figure 4. 5. Cummulative Particle Size of Bentonite.................. 85 Figure 4. 6. Particle Size Distribution of BFS ............................ 85 Figure 4. 7. Cummulative Particle Size of BFS .......................... 86 Figure 4. 8. Flowability of the cement paste mixture ................. 89 Figure 4. 9. SEM image of BFS .................................................. 90 Figure 4. 10. Method to determine w/b for each mixture ........... 91 Figure 4. 11.Position of crack measurement point ...................... 93 Figure 4. 12. Evolution of the surface crack width over time for initial crack width 0 - 200 µm ................................ 94 Figure 4. 13. Evolution of the surface crack width over time for initial crack width 200 – 350 µm ............................ 95 Figure 4. 14. Comparison of material closing crack between mixture using BFS and mixture without BFS ........ 96 Figure 4. 15. . Evolution of crack width for B0S0 ...................... 98 Figure 4. 16. Evolution of crack width for B5S0 ........................ 99 Figure 4. 17. Evolution of crack width for B0S30 ...................... 99 Figure 4. 18. Evolution of crack width for B5S30 .................... 100
Figure 4. 19. β index for different mixtures on 28 days curing period ............................................................................. 103
Figure 4. 20. β index for different mixtures on 56 days curing period ................................................................... 103 Figure 4. 21. β index over time for each mixtures with initial crack width 0-200 µm .......................................... 105 Figure 4. 22. β index over time for each mixtures with initial crack width 200-350 µm ...................................... 105 Figure 4. 23. β index over the initial crack width ..................... 107 Figure 4. 24 Decrease in crack depth over time for each mixtures
............................................................................. 109 Figure 4. 25. Rate of Healing (α index ) over time for each mixtures
............................................................................. 110 Figure 4. 26. Side view of cracks on the concrete a). real crack pattern b) idealized crack pattern ......................... 112 Figure 4. 27. Tesile strenght before healing of some mixture on 28 age days after casting. ..................................... 115 Figure 4. 28. Tesile strenght regain after healing of some mixture on 56 age days after cracking ............................... 117 Figure 4. 29. Load – deflection curve of mixture B0S0 .......... 120 Figure 4. 30. Load – deflection curve of mixture B5S0 ........... 120 Figure 4. 31. Load – deflection curve of mixture B0S30 ......... 121 Figure 4. 32. Load – deflection curve of mixture B5S30 ......... 121 Figure 4. 33. Load – deflection curve of all mixtures .............. 122 Figure 4. 34. Model to analyze load – defelction curve ........... 123 Figure 4. 35. Crack occurence in load-deflection curve ........... 123 Figure 4. 36. Flexural stifness before (B) and after (A) healing process for different mixtures .............................. 126 Figure 4. 37. P cracking and P max for different mixtures ................ 127 Figure 4. 38. Ph value for each mixture ................................... 129 Figure 4. 39. Diffractogram of mineral closing crack for mixtures
B0S0..................................................................... 131 Figure 4. 40. Diffractogram of mineral closing crack for mixtures
B5S0..................................................................... 132
Figure 4. 41. Diffractogram of mineral closing crack for mixtures B0S30 ................................................................... 133
Figure 4. 42. Diffractogram of mineral closing crack for mixtures B5S30 ................................................................... 134
Figure 4. 43. Comparison diffractogram for different mixtures 135
LIST OF TABLES
Table 2. 1. Permitted Maximum Crack Width .............................. 8 Table 2. 2. Composition of Bentonite (٪) ................................... 16 Table 2. 3. Chemical Compounds of Bentonite .......................... 17 Table 3. 1. Mix proportion for SAI test ...................................... 42 Table 3. 2. Mixture composition for each cement paste series ... 47 Table 3. 3. Rate of Increase in Net Deflection ............................ 62 Table 4. 1. Specific Gravity Test Result of OPC ........................ 71 Table 4. 2. Spesific Gravity Test Result of Ca-Bentonite ........... 72 Table 4. 3. Spesific Gravity Test Result of BFS ......................... 72 Table 4. 4. Density Test Result of OPC ...................................... 73 Table 4. 5. Density Test Result of Ca - Bentonite ...................... 74 Table 4. 6. Density Test Result of BFS....................................... 74 Table 4. 7. Saturated water content for each raw material .......... 75 Table 4. 8. Mixture compostion for each raw material ............... 75 Table 4. 9. SAI Test Result of Some Raw Materials .................. 76 Table 4. 10. Mineral Compound of BFS ..................................... 78 Table 4. 11. Mineral Compound of Ca - Bentonite..................... 79 Table 4. 12. Chemical Compound of Bentonite .......................... 82 Table 4. 13. Chemical Compound of BFS .................................. 83 Table 4. 14. Spesific Surface Area Properties............................. 87 Table 4. 15. Flowability test result of cement paste mixtures ..... 88 Table 4. 16. W/b for each mixture at contant flow 22 cm .......... 91 Table 4. 17. β index over time for B0S0 ..................................... 96 Table 4. 18. β index over time for B5S0 ..................................... 97 Table 4. 19. β index over time for B0S30 ................................... 97 Table 4. 20. β index over time for B0S30 ................................... 98 Table 4. 21. Existing crack depth for different mixtures .......... 108 Table 4. 22.Corrected crack depth for different mixtures ......... 108 Table 4. 23. Tensile strength before cracking ........................... 114 Table 4. 24. Tensile strength before cracking ........................... 114
Table 4. 25. Calculation of flexural stiffness of beams specimens for each mixtures ...................................................................... 125 Table 4. 26. P cracking and P max ratiofor different mixtures .......... 127 Table 4. 27. Ph measurement result for different mixture inside cement paste ............................................................................. 128 Table 4. 28. Ph measurement result for different result inside Crack ........................................................................................ 128 Table 4. 29. Percentage of mineral closing crack ..................... 136
CHAPTER I INTRODUCTION
1.1. Background
Cracks are major problems, which always occur in buildings, such as reinforced concrete structures. Cracks occur because of some causes such as shrinkage, the differences in settlement, the difference in temperatures, chemical reactions, improper structural design, improper construction methods, and overloading (ACI 224.1R -07, 2007). Since the probability of crack occurrence is very high, the crack has to be repaired before it propagate widely. If there is no immediate repair, it can lead to the strength deterioration, corrosion of the concrete reinforcement, and also the decrease in concrete durability (Jaroenrat Prom, 2011).
If the crack’s position can be observed and reached, it can be repaired as soon as possible after its positions are detected. However, if the cracks occur on an undetected position such as the drainage channel/irrigation, dam structures, foundations, sheet piles, bridge abutments, tunnel structures and other underground structures, new approach is needed to solve this problem. The Self-healing concrete is a new approach which can solve crack problems on undetected structures (Ahn et al. 2009). Self-healing concrete is a type of concrete, which can heal cracks by its self automatically, when a crack occurs in the concrete structures.
Self-healing concrete approach has been widely studied by many researchers to solve crack problems on the concrete structure. Some mechanism such as swelling and recrystallization mechanism (Ahn, 2010), carbonation reaction, continued hydration (Tittleboom, 2012), bacteria metabolism to produce CaCO
3 (Jonkers, 2009), low
pozzolanic reaction (Hung, 2013) are common mechanisms, which have been proven to be able to generate self-healing properties. Generally, self-healing mechanisms can be divided into four principal mechanisms, including physical mechanism (swelling process), chemical mechanisms (hydration process and carbonation process), biological mechanism and mechanical mechanisms (Reinhardt et al, 2013). From the four principal mechanisms above, swelling process, carbonation process and hydration process have dominant effect to the self-healing process of cracks in concrete, in terms of crack width and water permeability.
Swelling process can generate self-healing properties in cracked concrete. Application of some clay minerals containing Montmorilonite mineral can be used for self- healing concrete application, in terms of swelling process (Ahn, 2010). It is caused by high ion-exchange capacity of Montmorilonite mineral, which can contribute swelling mechanism (Muurinen, 2011). Crack in concrete containing 5% geomaterial has high self-healing efficiency, compared to the normal concrete by using water immersion curing. It is due
3+ 4+
to diffusion of Al ion and Si Ion (Ahn, 2009). Furthermore, application of nanoclay in the concrete can decrease the water permeability coefficient on 28 age days and 60 age days after cracking up to 0.18 on 0.90 respectively. Besides that, it can decrease crack width up to 0.70 on 28 age days after cracking (Jiang, 2015). In the other case, nanoclay/bentonite has water retaining capacity. It means that bentonite can adsorb some water, and the water will be retained by bentonite in the concrete matrix. In the dry condition case, the montmorilonite will shrink and release some water. This water is very beneficial for carbonation reaction and continued hydration reaction to produce self-healing properties. In case of mechanical regain, crack in the concrete containing nanoclay has a high deflection capacity after cracking, compared to the normal concrete (Qian, 2010).
Besides the swelling process, the self-healing mechanism is also influenced by the carbonation reaction.
2+
This process occurs, when calcium ions (Ca ) from the
CO
2 dissolved in the water. This reaction produces CaCO
3 2+
crystals, which can fill up the cracks. The amount of Ca ion is very influenced by Ca(OH)
2 resulted from the cement
hydration (Edvarsen, 1996). The amount of Ca(OH)
2 is
influenced by the amount of pozzolan replacement and pozzolan reactivity used in cement (Reinhard et al, 2013). Thus, replacement some clinker cement with some materials such as pozzolan can decrease the amount of Ca(OH) and
2 2+
Ca ion. Furthermore, precipitation of CaCO
3 will decrease, and it can contribute decrease in self-healing properties.
However, some approach can be used to increase the amount
2+
of Ca ion. Application of nanoclay containing Ca-
2+ Montmorilonite can increase Ca ion (Fernandez, 2014). 2+
Increasing Ca ion can accelerate CaCO
3 precipitation. It was
proven by Muharam (2013), that combination of Ca-bentonite and Alkaline solution Ca(OH)
2 could adsorb more CO 2 gases,
compared to the conventional method. The absorption value of Ca-Bentonite containing Ca-Montmorilonite is 8.9-9.9%. Thus, Ca – bentonite is very beneficial to produce self-healing properties.
Besides the swelling process and carbonation process, the self-healing mechanism is also influenced by the hydration reaction, both continued hydrations of unreacted clinkers and hydration reaction of some latent hydraulic material such as Blast Furnace Slag (BFS). According to Zhong (2012), not all the clinker cement has been hydrated within the first 28 age days after mixing. Thus, the unhydrated clinker cement is available in the concrete matrix. If the crack occurs, unhydrated clinker cement reacts with water entering inside of crack to continue its hydration. The result of this reaction is C- S-H gel which can fill up the crack. Application of some byproduct materials such as Blast Furnace Slag (BFS) is potential used for self-healing concrete, because it has latent hydraulic properties. BFS has slow hydration reaction compared to clinker cement hydration (Lothenbach, 2012). BFS also has latent hydraulic properties. It means that, besides ph to activate its particles. High Ca(OH)
2 concentration
producing high ph can accelerate hydration reaction of BFS particles (Huang, 2012). Application of BFS as partial cement replacement of clinkers can contribute decrease in hydration heat rate, compared to the normal clinker. High replacement of BFS can contribute hydration heat rate more decrease (Nasir, 2014). Although hydration heat rate of clinker cement is higher than clinker cement containing BFS, but this process only occurs within the first 45 hours after casting. (Tittleboom, 2012). This property of BFS is very beneficial to produce self-healing properties, in terms of continued hydration mechanism (Oliver, 2013). This hydration product is mainly identified as C-S-H gel, Aft, and AFm. Hydration product can be increased by Ca(OH)
2 activation process
before BFS particle mixes together with other materials (Huang, 2012). The result shows that application of BFS as partial cement replacement can close crack completely with maximum crack width 408 um (Palin, 2015).
Based on problems above, bentonite and BFS have different mechanism to heal cracks. However, there is little information about self-healing properties of the cement paste incorporating bentonite and BFS, especially in terms of mechanical regain. In this research, self-healing property of cracked cement paste is discussed, including physical properties (decrease in crack width and crack depth), chemical properties (mineral of healing product), and mechanical regain properties (direct tensile strength and flexural strength). Thus, in this final project report will be discussed the research results that had been conducted, entitled "Influence of bentonite and blast furnace slag to the self-healing behavior in cracked cement paste."
1.2. Research Problems
The problems of this research are described as follows:
1. How bentonite and BFS influences self healing propertis of cracked cement paste? a. How the bentonite and BFS influences the crack width of cracked cement paste? b. How the bentonite and BFS influences the crack depth of cracked cement paste? c. How the bentonite and BFS influences the tensile strength recovery of cracked cement paste? d. How the bentonite and BFS influences the felxural stiffness recovery of cracked cement paste?
2. How about the self healing mechanisms occur in cement paste incorporating bentonite and BFS as a partial cement replacement?
1.3. Research Boundaries
In this research, there are a few problem's boundaries, include:
1. The self-healing is evaluated only by measuring four parameters, include crack width, crack depth, direct tensile recovery, and flexural stiffness recovery of the cement paste after cracking.
2. In this study, flow table test is conducted to determine w/c for each mixture series to get constant consistency with constant value 22 cm.
3. Cement which is used in this research is cement type 1 (Ordinary Pprtland Cement)
4. There’s no economical aspect, which is discussed in this final project report.
1.4. Research Objective
The objective of this research are described as follows:
1. To analyze the influence of bentonite and BFS to the self healing behavior in cracked cement paste.
a. To analyze the influence of bentonite and BFS to the crack depth of cement paste after cracking.
b. To analyze the influence of bentonite and BFS to crack width of cement paste after cracking.
c. To analyze the influence of bentonite and BFS to
d. To analyze the influence of bentonite and BFS to flexural regain of cement paste after cracking.
2. To analyze the self healing mechanisms occurre in cement paste incorporating bentonite and BFS as a partial cement replacement
1.5. Benefits
Benefits of this research are described as follows:
1. As a reference to next researchers about self-healing properties of cracked concrete.
2. This research is expected to reduce and solve crack problems, which occur in concrete structures, especially for undetected and unreached crack position.
3. As a supporting research to develop alternative cement products, which can be used to overcome the crack's problem in concrete structures.
CHAPTER II LITERATURE REVIEW
2.1. Crack on the Concrete Structures
Cracks can be classified as structural crack and non- structural crack. Structural cracks are due to improper structural design or also overload-capacity. Non-structural cracks are mostly due to the stress, which is induced internally in materials. This non-structural crack leads to weak the structures indirectly. Crack occurrence in the field can reach up to 50% from the total type of structure damage (Saputra et al, 2011).
According to Ghafur (2009), cracks can be identified by using three parameters, including crack width, crack length and crack pattern. Generally, crack width is very hard to be measured, because it has an irregular shape. In hardening concrete, micro crack is very hard to be measured because of the crack width is too small. To observe crack width of micro cracks, microscope is usually used with varies crack width between 0.125 - 1.0 μm (eight hour after casting). Minimum crack width which can be observed by the eye is 0.13 mm (0.005 in), and it is belonged to micro cracks. Micro cracks will propagate widely, when there’s no immediate repair.
Based on ACI 224 R – 01, permitted maximum crack width is determined based on type of concrete structures and environment condition of concrete. For the structures which are influenced by corrosion, greatest crack widths are limited 0.15 mm. For indoor and impermeable structures, maximum crack widths are limited 0.41 mm. Permitted maximum crack width can be seen in Table 2.1.
According to ACI 224 1R -07, cracks in concrete structures occur because of some causes such as shrinkage, the difference in temperature, chemical reaction, improper structural design and construction method, and overloading.
Table 2. 1. Permitted Maximum Crack Width Type of structure and Limit of crack No Enviroment width (mm)
0.41
1 Indoor strucrures, structure in dry
air enviroment, water impermeable structures
2 Structures contact with water
0.10
3 Outdoor structures, middle
0.30 humidity, no corrotion effect
0.18
4 Outdoor structures, high
humidity, structures are influenced by chemical reaction
5 Structures with high humidity,
0.15 structures are influenced by corrotion (snow/ice, sea water)
Source: ACI Commite 224R (2001)
2.2. Conditions for Self-Healing
According to Heide (2005), there are several condition which can contribute self healing process. Some conditions are very important for self healing process. Some conditions are: a. Water, water is very important to the all of self healing mechanisms. Thus if there’s no water, self healing process will not occure. It had been reported by Lauer (1956) that humidity enviroment 95٪ could decrease healing process in cracked concrete.
b. Cracks width, self-healing can occure for a small cracks width. Thus, in the large crack width, self healing prosess still occur, but crack close incompletely.
c. Water pressure, if the water enter throuh inside of the cracks rapidly, the self-healing process will not occure.
This condition is usualy described as a maximum ratio between water pressure head and thickness of the cracked concrete as shown in Figure 2.1.
Although, there are some requirement for self healing condition, but there is litlle information which is used to maximize self healing process, both for water pressure and cracks width. But Van Breugel (2003) reported that limit of a maximum cracks width is determined based on the water pressure which can enter inside of the cracks, such as shown in the Figure 2.1.
Figure 2. 1. Maximum crack width (functions of water pressure
(h/d) according to Lohmeyer and Meichsner) Maximum crack width 0.2 mm is limits of cracks width which can be healed perfectly for h/d less than 10. If cracks width greater than 0.2 mm, self healing process still occur, but crack close incompletely. In addition for h/d greater than 10, cracks width is limited between 0.05 - 0.20 mm, in order the self healing process occur completely.
2.3. Self-Healing Mechanism
Generally, there are 2 mechanisms of self healing on concrete, including autogeneous healing and autonomous
healing. Autogeneous healing is the self healing process that
the recovery process uses material components that could otherwise also be present when not specifically designed for self healing. In the other hand, Autonomous healing is the self healing process that the recovery process uses materials components that would otherwise not be found in the material. According to Reinhardt et al (2013), causes of autogeneous self-healing are divided into 3 causes, including physical cause, chemical causes, and mechanical causes. That three main mechanisms are shown in the Figure 2.2.
Figure 2. 2. Causes of autogeneous self-healing
Source: Reinhardt et al (2013) Physycal cause is due to the swelling process of
Hidrated Cement Paste (HCP) or other additives materials which have swelling ability. The swelling of HCP occur, when water molecules are adsorbed by HCP and fill up the gap between cracks surface. But this mechanism produce low healing effectiveness. This is proven by reinhard (2013), that permeability on the crack area decrease less than 10%, in term of swelling process of HCP. But for the specific material which have swelling ability, permeability on the crack area could decrease up to 90٪.
While in chemical process causes are devided into 2 mechanisms, including continued hydration of Unhidrated Cement Paste (UCP) and carbonation reactions. The continued hydration process of UCP needs water to continue its hydration. When cracks occur, water will go through inside of cracks and react with UCP, in term of hydration up to 2 times from diameter of clinker cement. Thus, continued hydration of UCP close cracks incompletetly. But if cracks width less than or equal to 0.1 mm and by the assumption that HCP can swell and hydrate simultaneously, cracks can close completely. But if cracks width greater than 0.10 mm, the effects of this mechanism is very small.
Beside continued hydration, self healing process based on chemical causes are also contributed by carbonation reaction. This carbonation reaction occur, when
2+ 2-
Ca ion react with carbonat (CO3 ) ion to precipitate
3 Calcium Carbonate (CaCO ) crystal. This Calcium
3 Carbonate (CaCO ) is white crystal which can fill up the 2+
2
cracks. This Ca ions are suplied from Ca(OH) which is
2-
resulted from cement hydration. And this carbonat (CO3 ) ions are came from water entering inside of crack. This carbonation reaction is influenced by temperature, ph, and reactants concentration. This carbonation reaction has high healing effectiveness, when compared to the other mechanisms (Edvarsen, 1996).
While mechanical causes are divided into 2 mechanisms, including particles which are carried by water and fracture of concrete particle which can blockage the cracks. But this two mechanisms give low effect to the self healing process of the cracked concrete.
2.4. Self-Healing Mechanism with Continued Hydration