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Similaire à Kingsten - Honors Thesis Defense
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Kingsten - Honors Thesis Defense
- 1. NOVEL CEMENT REPLACEMENT MATERIALS FOR SUSTAINABLE INFRASTRUCTURE By Kingsten Banh Honors Thesis Defense Honors Thesis Committee Dr. Narayanan Neithalath – Dr. Subramaniam Rajan – Dr. Barzin Mobasher
- 2. INTRODUCTION Honors Thesis Defense Every tonne of cement (U.S. Geological Survey, 2009) → consumes nearly 4 GJ of energy → releases almost one tonne of CO2 • Rapid population growth leads to more demand for cement → actively in search for sustainable alternatives → merit similar characteristics and properties • Geopolymer is an intensive area of interest → utilized industrial wastes and by-products → activated by alkaline solutions
- 3. GEOPOLYMER – INGREDIENTS Honors Thesis Defense Binders Alkali Activators Aluminosilicates contain high silicon (Si) and aluminum (Al) oxides. → Slags (high calcium) → Fly ash • Class F (low calcium) • Class C (high calcium) → Metakaolin Activating agents consist of alkali metal compounds → Alkali hydroxides (MOH) • NaOH → Weak acid salts → Alkali silicates (M2O∙nSiO2) • Na2O∙nSiO2
- 4. Honors Thesis Defense STRUCTURE OF GEOPOLYMER Tetrahedral [SiO4]4- and [AlO4]4- anions united by oxygen atoms Abbreviated as Poly(Sialates) (Davidovits, 2005) Empirical formula → 𝐌 𝐧 − 𝐒𝐢𝐎 𝟐 𝐳 − 𝐀𝐥𝐎 𝟐 𝐧 ∙ 𝐰𝐇 𝟐 𝐎 Al SiO Al Si Si Poly(sialate) z = 1 (-Si-O-Al-O-) Poly(sialate-siloxo) z = 2 (-Si-O-Al-O-Si-O-) Poly(sialate-disiloxo) z = 3 (-Si-O-Al-O-Si-O-Si-O-) Al Si Si Al Si Si Si
- 5. Honors Thesis Defense GEOPOLYMERIZATION PROCESS Fernandez et 2005
- 6. PHYSICAL PROPERTIES OF FLY ASH Honors Thesis Defense Gray, very fine, and glassy like particles Particle size between 1 to 100 𝝁m Regularly shaped particles → cenospheres, plerospheres, and ferrosphers Irregularly shaped particles → quartz, unburned coal particles cenosphere plerosphere ferrosphere diatomite Komljenovi, 2010
- 7. ACTIVATOR PARAMETERS Honors Thesis Defense Sodium hydroxide (NaOH) → varying the molarity concentration Sodium silicates → n = Na2O/Binder → Ms = Silica modulus = moles of SiO2/moles of Na2O Liquid sodium silicate (waterglass) with Ms = 3.26 Ms value needs to be reduced to increase the alkali content
- 8. GEOPOLYMER – INGREDIENTS Honors Thesis Defense Binder – Class F fly ash (ASTM C 618) → 100% fly ash → liquid/powder = 0.40 Alkali activators – Sodium hydroxide (NaOH) → 4 M and 8 M – Liquid sodium silicates (Waterglass) → n-values of 0.04 and 0.07 → Ms-values of 2.0 and 1.0 sodium hydroxide waterglass
- 9. MIXING PROCEDURES Honors Thesis Defense Select Activator Waterglass Sodium Hydroxide NaOH + Water NaOH Solution + Waterglass Fly Ash + Sand Paste
- 10. EXPERIMENTAL PROGRAMS Honors Thesis Defense Compressive strength • 50 mm size cubical mortars – 6 cubes per matrix • cured 40oC, 60oC, and 80oC • under dry or moist heat curing condition • duration of 24 and 72 hours Factorial statistical analysis • to evaluate the effects of investigating factors • to determine the most influential factor(s)
- 11. COMPRESSIVE STRENGTH TEST Honors Thesis Defense • in compliance with ASTM C109 Standard • 6 cubes per matrix • allow to the samples to cool down to ambient temperature before performing the test
- 12. COMPRESSIVE STRENGTH OF SODIUM HYDROXIDE ACTIVATED FLY ASH MORTARS Honors Thesis Defense 0 5 10 15 20 25 30 35 40 45 50 40 60 80 CompressiveStress,MPa Curing Temperature, oC 4M - Dry - 24 Hours 4M - Moist - 24 Hours 8M - Dry - 24 Hours 8M - Moist - 24 Hours 0 5 10 15 20 25 30 35 40 45 50 40 60 80 CompressiveStress,MPa Curing Temperature, oC 4M - Dry - 72 Hours 4M - Moist - 72 Hours 8M - Dry - 72 Hours 8M - Moist - 72 Hours
- 13. Honors Thesis Defense 0 5 10 15 20 25 30 40 60 80 CompressiveStress,MPa Curing Temperature, oC 24 Hours Ms=2, n=0.04, Dry Ms=2, n=0.04, Moist Ms=2, n=0.07, Dry Ms=2, n=0.07, Moist COMPRESSIVE STRENGTH OF SODIUM SILICATES ACTIVATED FLY ASH MORTARS 0 5 10 15 20 25 30 40 60 80 CompressiveStress,MPa Curing Temperature, oC 72 Hours Ms=2, n=0.04, Dry Ms=2, n=0.04, Moist Ms=2, n=0.07, Dry Ms=2, n=0.07, Moist
- 14. Honors Thesis Defense COMPRESSIVE STRENGTH OF SODIUM SILICATES ACTIVATED FLY ASH MORTARS 0 5 10 15 20 25 30 35 40 60 80 CompressiveStress,MPa Curing Temperature, oC 72 Hours Ms=1, n=0.04, Dry Ms=1, n=0.04, Moist Ms=1, n=0.07, Dry Ms=1, n=0.07, Moist 0 5 10 15 20 25 30 35 40 60 80 CompressiveStress,MPa Curing Temperature, oC 24 Hours Ms=1, n=0.04, Dry Ms=1, n=0.04, Moist Ms=1, n=0.07, Dry Ms=1, n=0.07, Moist
- 15. Honors Thesis Defense ECONOMIC EFFICIENCY OF ALKALI ACTIVATORS To determine how much energy consumed per MPa of compressive strength 𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑡 = 𝐸𝑛𝑒𝑟𝑔𝑦 𝐶𝑜𝑛𝑠𝑢𝑚𝑡𝑖𝑜𝑛 𝑀𝑃𝑎 = 𝑘𝑊 𝑀𝑃𝑎
- 16. Honors Thesis Defense ENERGY USAGE AND ASSUMPTION Power Usage 𝑃 = 𝑅 × 𝐼2 Resistivity 𝑅(𝑇) = 𝑅 𝑜[1 + 𝛼 𝑇 − 𝑇𝑜 ] P = Power usage R = Resistance I = Current Ro = initial resistance R(T)= temperature dependent resistance To = initial temperature T = final temperature 𝛼 = temperature coefficient
- 17. Honors Thesis Defense ASSUMPTIONS & CALCULATIONS Resistivity Due to the lack of manufacture information Simplicity of calculation → 𝑹 𝒐 = 𝟏 𝜴 → 𝜶 = 𝟏 → 𝑻 𝒐 = 𝟐𝟑 𝒐 𝑪 𝑹 𝑻 = 𝑹 𝒐[𝟏 + 𝜶 𝑻 − 𝑻 𝒐 ] At T = 40OC, R = 1[1+1(40 – 23)] → 𝑹 𝟒𝟎 𝒐 𝑪 = 𝟏𝟖 𝜴 At T = 60OC, R = 1[1+1(60 – 23)] → 𝑹 𝟔𝟎 𝒐 𝑪 = 𝟑𝟖 𝜴 At T = 80OC, R = 1[1+1(80 – 23)] → 𝑹 𝟔𝟎 𝒐 𝑪 = 𝟓𝟖 𝜴
- 18. Honors Thesis Defense ASSUMPTIONS & CALCULATIONS Power Consumption – assuming current, I = 5 A 𝑷 = 𝑹 × 𝑰 𝟐 Temperature Resistance Power consumption, kWh 1 Hour 24 Hours 72 Hours 40 18 0.45 10.8 32.4 60 38 0.95 22.8 68.4 80 58 1.45 34.8 104.4
- 19. Honors Thesis Defense EFFICIENCY OF SODIUM HYDROXIDE ACTIVATED SYSTEMS 0 1 2 3 4 5 6 7 8 40 60 80 Efficiency,kWh/MPa Curing Temperature, 24 Hours 4M - Dry 4M - Moist 8M - Dry 8M - Moist 0 1 2 3 4 5 6 7 8 40 60 80 Efficiency,kWh/MPa Curing Temperature, 72 Hours 4M - Dry 4M - Moist 8M - Dry 8M - Moist
- 20. Honors Thesis Defense EFFICIENCY OF SODIUM SILICATES ACTIVATED SYSTEMS 0 1 2 3 4 5 6 7 8 40 60 80 Efficiency,kWh/MPa Curing Temperature, Ms = 2.0 - 24 Hours n=0.04, Dry n=0.04, Moist n=0.07, Dry n=0.07, Moist 0 1 2 3 4 5 6 7 8 40 60 80 Efficiency,kWh/MPa Curing Temperature, Ms = 2.0 - 72 Hours n=0.04, Dry n=0.04, Moist n=0.07, Dry n=0.07, Moist
- 21. Honors Thesis Defense EFFICIENCY OF SODIUM SILICATES ACTIVATED SYSTEMS 0 1 2 3 4 5 6 40 60 80 Efficiency,kWh/MPa Curing Temperature, Ms = 1.0 - 24 Hours n=0.04, Dry n=0.04, Moist n=0.07, Dry n=0.07, Moist 0 1 2 3 4 5 6 40 60 80 Efficiency,kWh/MPa Curing Temperature, Ms = 1.0 - 72 Hours n=0.04 - Dry m=0.04 - Moist n=0.07 - Dry n=0.07 - Moist
- 22. SUMMARY OF INFLUENCE OF THE INVESTIGATING FACTORS Honors Thesis Defense NaOH Similarities Low strength development at low temperature and early age Higher strength as temperature increases and under moist curing Higher strength → energy consumption Differences Waterglass → significant difference between moist and dry curing √ → demonstrated higher compressive strength √ → lowest energy per MPa of compressive stress 8M (24 & 72 hours) Ms= 1.0 (24 hours)
- 23. 2K FACTORIAL DESIGN Honors Thesis Defense To evaluate the influence of the investigating factors and optimize the compressive strength 25-1 – One-half factorial design (A, B, C, E) Factors Description Low level (-1) High level (+1) A Ms 2 1 B n 0.04 0.07 C Curing condition Dry Moist D Temperature 60 80 E Alumina 0.1 0.2 Objective Useful when there are several variables in the systems
- 24. 24 FACTORIAL DESIGN Honors Thesis Defense Run # Treatment Combination Main Effect A B C D 1 (1) -1 -1 -1 -1 2 a 1 -1 -1 -1 3 b -1 1 -1 -1 4 ab 1 1 -1 -1 5 c -1 -1 1 -1 6 ac 1 -1 1 -1 7 bc -1 1 1 -1 8 abc 1 1 1 -1 … … … … … … 16 abcd 1 1 1 1
- 25. 24 FACTORIAL DESIGN Honors Thesis Defense Categories Model Term Main Effects A B C D Two-factor Interactions AB AC AD BC BD CD Three-factor Interactions ABC ABD BCD
- 26. 25-1 ONE-HALF FACTORIAL DESIGN Honors Thesis Defense Run # Treatment Combinati on Main Effect Generator A B C D E 1 e -1 -1 -1 -1 1 2 a 1 -1 -1 -1 -1 3 b -1 1 -1 -1 -1 4 abe 1 1 -1 -1 1 5 c -1 -1 1 -1 -1 6 ace 1 -1 1 -1 1 7 bce -1 1 1 -1 1 8 abc 1 1 1 -1 -1 … d … … … … … 16 ade 1 1 1 1 1
- 27. Honors Thesis Defense Initial Regression Model 𝒚 = 𝜷 𝟎 + 𝜷 𝟏 𝒙 𝟏 + 𝜷 𝟐 𝒙 𝟐 + 𝜷 𝟑 𝒙 𝟑 + 𝜷 𝟒 𝒙 𝟒 + 𝜷 𝟓 𝒙 𝟓 + 𝜷 𝟏𝟐 𝒙 𝟏 𝒙 𝟐 + ⋯ + 𝜷 𝟏𝟐𝟑𝟒𝟓 𝒙 𝟏 𝒙 𝟐 𝒙 𝟑 𝒙 𝟒 𝒙 𝟓 25-1 ONE-HALF FACTORIAL DESIGN Defining relation – 𝑰 = 𝑨𝑩𝑪𝑫𝑬 Aliases Main Effects A = BCDE B = ACDE C = ABDE D = ABCE E = ABCD Interaction Effects AB = CDE AC = BDE AD = BCE AE = BCD CD = ABE CE = ABD DE = ABC BC = ADE BD = ACE BE = ACD
- 28. 25-1 ONE-HALF FACTORIAL DESIGN Honors Thesis Defense Run # Treatment Combination Main Effect Generator Response A B C D E 24 Hours 72 Hours 1 e -1 -1 -1 -1 1 8.40 10.14 2 a 1 -1 -1 -1 -1 3.26 4.00 3 b -1 1 -1 -1 -1 22.84 25.14 4 abe 1 1 -1 -1 1 17.83 20.74 5 c -1 -1 1 -1 -1 10.20 11.99 6 ace 1 -1 1 -1 1 5.56 6.80 7 bce -1 1 1 -1 1 26.67 28.91 8 abc 1 1 1 -1 -1 22.98 24.59 … d … … … … … … … 16 ade 1 1 1 1 1 31.78 33.48
- 29. ANALYSIS OF VARIANCE Honors Thesis Defense 24 Hours 72 Hours Model Term Effect Estimate SS % Contribution Effect Estimate SS % Contribution A -0.54 1.15 0.07 -0.84 2.86 0.16 B 19.01 1446.09 88.84 20.26 1642.54 89.54 C 2.33 21.77 1.34 2.23 19.87 1.08 D 2.43 23.57 1.45 2.40 23.03 1.26 E -0.31 0.37 0.02 -0.20 0.17 0.01 AB 1.14 5.22 0.32 0.82 2.69 0.15 AC -0.44 0.76 0.05 -0.84 2.79 0.15 AD 4.09 66.75 4.10 4.17 69.48 3.79 AE 0.27 0.29 0.02 0.64 1.62 0.09 BC 1.49 8.86 0.54 1.38 7.61 0.42 BD 3.29 43.20 2.65 3.65 53.39 2.91 BE -0.89 3.16 0.19 -1.09 4.79 0.26 CD -0.94 3.50 0.21 -0.84 2.82 0.15 CE 0.87 3.03 0.19 0.17 0.12 0.01 DE -0.10 0.04 0.00 -0.42 0.71 0.04 SSTotal 1627.77 SSTotal 1834.47
- 30. ANALYSIS OF VARIANCE (24 HOURS) Honors Thesis Defense Source Effect Estimate SS DF Mean Square F value f(𝜶, n, d) Prob > F Model - 1601.38 5 320.27 121.40 0.05,5,10 3.71 0.0000 B 19.01 1446.09 1 1446.09 548.14 0.05,1,10 4.96 0.0000 C 2.33 21.77 1 21.77 8.25 0.05,1,10 4.96 0.0167 D 2.43 23.57 1 23.57 8.93 0.05,1,10 4.96 0.0137 AD 4.09 66.75 1 66.75 25.30 0.05,1,10 4.96 0.0005 BD 3.29 43.20 1 43.20 16.37 0.05,1,10 4.96 0.0023 Residual 26.38 10 2.64 SSTotal 1627.77 15 R2 0.984 Adj R2 Final Regression Model 𝒚 = 𝟏𝟓. 𝟗𝟑 + 𝟗. 𝟓𝟏𝒙 𝟐 + 𝟏. 𝟏𝟕𝒙 𝟑 + 𝟏. 𝟐𝟏𝒙 𝟒 + 𝟐. 𝟎𝟒𝒙 𝟏 𝒙 𝟒 + 𝟏. 𝟔𝟒𝒙 𝟐 𝒙 𝟒
- 31. ANALYSIS OF VARIANCE (24 HOURS) Honors Thesis Defense -3 -2 -1 0 1 2 3 4 0 10 20 30 40 Residuals Predicted Compressive Stress, MPa 0 5 10 15 20 25 30 35 0 10 20 30 40 ActualYield,MPa Predicted Yield, MPa
- 32. ANALYSIS OF VARIANCE (24 HOURS) Honors Thesis Defense 0 5 10 15 20 25 30 35 Low High CompressiveStress,MPa B - Ms Values 0 5 10 15 20 25 30 35 Low High CompressiveStress,MPa C - Curing Conditions 0 5 10 15 20 25 30 35 Low High CompressiveStress,MPa D - Temperature To increase compressive strength B at high level C can be at either low or high D can be at either low or high
- 33. ANALYSIS OF VARIANCE (24 HOURS) Honors Thesis Defense 0 5 10 15 20 25 30 Low High CompressiveStress,MPa B - n values D- D+ 0 5 10 15 20 25 30 35 Low High CompressiveStress,MPa A - Ms value D- D+ A and D should be at high level B and D should be at high level
- 34. ANALYSIS OF VARIANCE (72 HOURS) Honors Thesis Defense Source Effect Estimate SS DF Mean Square F value f(𝜶, n, d) Prob > F Model 1808.31 5 361.66 138.24 0.05,5,10 3.71 0.00000 B 20.2641 1642.54 1 1642.53 627.88 0.05,1,10 4.96 0.00000 C 2.22859 19.87 1 19.86 7.59 0.05,1,10 4.96 0.02028 D 2.39952 23.03 1 23.03 8.80 0.05,1,10 4.96 0.01412 AD 4.16774 69.48 1 69.48 26.55 0.05,1,10 4.96 0.00043 BD 3.6535 53.39 1 53.39 20.40 0.05,1,10 4.96 0.00111 Residual 26.16 10 2.62 SSTotal 1834.47 15 R2 0.986 Adj R2 Final Regression Model 𝒚 = 𝟏𝟕. 𝟕𝟒 + 𝟏𝟎. 𝟏𝟑𝒙 𝟐 + 𝟏. 𝟏𝟏𝒙 𝟑 + 𝟏. 𝟐𝟎𝒙 𝟒 + 𝟐. 𝟎𝟖𝒙 𝟏 𝒙 𝟒 + 𝟏. 𝟖𝟑𝒙 𝟐 𝒙 𝟒
- 35. ANALYSIS OF VARIANCE (72 HOURS) Honors Thesis Defense 0 5 10 15 20 25 30 35 40 0 10 20 30 40 ActualYield,MPa Predicted Yield, MPa -3 -2 -1 0 1 2 3 4 0 10 20 30 40 ActualYield,MPa Predicted Yield, MPa
- 36. ANALYSIS OF VARIANCE (72 HOURS) Honors Thesis Defense 0 5 10 15 20 25 30 35 Low High CompressiveStress,MPa B - Ms Values 0 5 10 15 20 25 30 35 Low High CompressiveStress,MPa C - Curing Conditions 0 5 10 15 20 25 30 35 Low High CompressiveStress,MPa D - Temperature To increase compressive strength B at high level C can be at either low or high D can be at either low or high
- 37. ANALYSIS OF VARIANCE (72 HOURS) Honors Thesis Defense 0 5 10 15 20 25 30 35 Low High CompressiveStress,MPa A - Ms value D- D+ 0 5 10 15 20 25 30 35 Low High CompressiveStress,MPa B - n values D- D+ A and D should be at low level B and D should be at high level
- 38. CONCLUSION Honors Thesis Defense • Sodium hydroxide activated fly ash mortars demonstrated higher compressive strength. • 8M NaOH activated systems and Ms of 1.0 provides the most efficient usage of energy • Factorial design assists in design the experiment runs • Na2O/binder ratio, n, is the most influential factors to the compressive strength of waterglass activated systems
- 39. THANK YOU Honors Thesis Defense QUESTIONS & COMMENTS
Notes de l'éditeur
- The production of cement is energy intensive and causing environment impact. For every tonne of cement, about 4 GJ of energy is consumed and one tonne of CO2 is released. With a rapid population growth, the demand for cement is increasing and reaching nearly 3 Gtonnes annually according to U.S Geological survey in 2009. To reduce both energy consumption and greenhouse gas emissions, the cement industry is under pressure to search for sustainable alternatives that merit similar characteristics and mechanical properties. For decades of research, geopolymer consists of alkali-activated aluminosilicates materials has been developed and refined to obtain a better understanding of the materials.
- So what ingredients are used to make geopolymer ? The two main ingredients involve in the formation of geopolymer are the aluminosilicate binder and alkali activating agent. The binders are composed of high aluminosilicates contain such as slags and fly ash, while the alkaline activating agents are compounds of alkali metals. For the scope of this thesis, class F fly ash was activated by various concentration of sodium hydroxide and liquid sodium silicates solutions.
- The structure of geopolymer is composed of tetrahedral negatively charge [SiO4]4- and [AlO4]4- connected by the oxygen ions in which is named “poly(sialates)”. The word “poly” means many, and “sialate” is an abbreaviation for silicon-oxo-aluminate. Due to the presense of negatively charged Al in the 4-fold coordination, dissolution of alkali metal compounds will provide a positive cation to balance out the charge. The reaction product of the geopolymer is quite complex, but it has been simplified in this empirical formula accounting for the main components, where M is a cation from alkali metal compound, n is the degree of polycondensation, and z is commonly known as 1, 2, and 3. to indicate the numbers of [SiO4]4- present in the compound. At z = 1, one [SiO4]4- connects to [AlO4]4-. At z = 2, two [SiO4]4- connects to [AlO4]4- , and so on.
- Different aluminosilicate-based materials produces different geopolymer properties and microstructure as well as different reaction mechanism. Solid aluminosilicate particles is being attacked by the alkali species in the system. At high pH level, the amorphous aluminosilicates dissolve very rapidly and quickly reach the equilibrium state. In this supersaturated aluminosilicate solution, the formation of gel creates larger networks by condensation and release water that was consumed during the dissolution. The system continue to rearrange and reorganize as the connectivity of the gel increases resulting in the three-dimensional aluminosilicate network The structural reorganization determine the microstructure and pore distribution of the materials that governs many physical properties of the materials.
- Now, let’s take a look at the formation and physical properties of typical fly ash. At high temperature and pressure, the combustion of coal in power stations produces different types of ash depending on the constituent within the coals. While the organic matter and carbon are evaporated, many mineral impurities such as clays and quartz melt at high temperature. The resulting molten impurities quickly transported to the low-temperature zones to solidify into fine, gray, and glass particles of ash Although fly ash appears as homogenous materials within human eyes, it is indeed a heterogeneous material comprising particles of different dimension various shapes. Cenosphere is light and hallow sphere made of silica and alumina that filled with air. Plerosphere is a large sphere covering smaller particles inside Ferrosphere has a rough surface
- Figure A present together with the unreacted spheres (point 3) along with the existing amorphous aluminosilicate gel (points 4 and 5). The considerable amount of unreacted or not totally consumed spheres is indicating a moderate degree of reaction in the system. Point 6 of Figure B show the main matrix of reaction product and some deposits of crystalline material. In Figure C, some fly ash spheres partially covered with reaction product as indicated by the arrows. This picture might be suggesting that the precipitation of the reaction products forms out of the supersaturated dissolution of aluminosilicate. This fact could justify the moderate degree of reaction already taken place in this type of systems. Finally, Figure D indicates that the interfacial area between the aggregate and the aluminosilicate gel matrix is almost non-existent which could mean that the adherence of the cementitious material with the aggregates is really good.
- Two different alkali activators are used to activate the formation of geopolymer. For sodium hydroxide, various molarity concentration of the solution will be used. On another hand, two different activator parameters for liquid sodium silicates. “n” indicates the sodium dioxide-to-binder ratio and “Ms” is the Silicon dioxide-to-sodium dioxide ratio. Since the moles ratio of the Ms (60/62) is 0.97 which can be assumed to be 1:1 ratio. So, every 1,000 g of fly ash having a n-value of 0.05 and Ms-value of 1.0 requires a total of 50 g of Sodium dioxide and 50 g silicon dioxide. Ultimately, the Ms and n values are additional alkali solution and soluble silicate that will be added to the systems.
- For the investigation within the thesis, class F fly ash conforming ASTC C 618 was used as the sole binding material in the formation of geopolymers. 4M and 8M concentration of sodium hydroxide solutions with a liquid to binder ratio of 0.4 were prepared to activate the binder. On another hand, liquid sodium silicates or waterglass with n-values of 0.04 and 0.07 along with MS values of 2.0 and 1.0 were used to activate the binder for another study in this thesis.
- Although there are two different alkali activators, the mixing procedures are very similar. If the activator is sodium hydroxide, NaOH salt is mixed with the required amount of water to achieve the desired molarity. For Waterglass as the activating agent, the desired Ms value is often smaller then the one from the actual waterglass. So, additional NaOH solution is required to add into the waterglass solution to bring the value down. Because both activators are composed of sodium, the dissolution of each activators with water is exothermal in which heat is released. Therefore, the solutions require about 2 to 3 hours to cool down to the ambient temperature. Prior mixing the solution with binder, the required amount of fly ash and sand are first dry mixed together for two minutes to prevent the formation of clump when the liquid is added. Then, the solution is added into the binders and further mixed for another three minutes until obtain a uniform mixture.
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- As it can be observed in the figures, the highest compressive strength are reached at 8M activator concentration. In early age, the compressive strength development of the mixtures were equal or slightly higher at very low temperature regardless the concentration of NaOH solutions. Moist heat curing provides higher compressive strength over convectional dry curing, the effect was not as much as the effect of curing temperature and the concentration of NaOH. Under moist heat curing, the samples are surrounded by high relative humidity compared to dry heat curing in which will prevent the occurrence of carbonation that will lower the pH level and lead to a reduction in reaction rate. At 24 hours curing, the higher concentration of NaOH shows a boost in compressive strength from 4M to 8M, but not as much when compared to the increase of strength due to the increase of NaOH concentration for 72 hours cured samples. When more curing time was allowed, the newly formed aluminosilicate network had more “time” rearranging and reorganizing by utilizing the available sodium cations in the system to form a more complex and stronger network. The compressive strength of this set of data reached about 50 MPa at 80oC under moist curing for three days. The lowest strength occurred below 5 MPa for 24 hours at 40oC regardless the NaOH concentrations.
- Now, let’s investigate how the compressive strength be influenced by the silica modulus, Na2O/binder ratio, and the curing parameters (conditions, durations, and temperatures). Effect of curing condition Early age – regardless anything Ms value – high value -> lower strength N value – high value -> higher strength Temperature – increase -> increase strength Max and min compressive strength Curing duration
- Similar for the Ms of 1.0, at low temperature and early age, there are also not a distinguishable difference between the compressive stress of the mixtures. But as temperature, high concentration of Na2O in the systems favor the mechanical strength development of the samples. At Ms of 1 and n of 0.07, as temperature increases, there is a huge difference in compressive strength of moist cured samples compared dried cured. On another hand, at Ms of 1 and n of 0.04, the difference between moist and dry curing is not very significant. This set of data also shows similar trends obtained from previous slide. The lowest strength development at low temperature and early age in which the compressive stress is about 10 ± 3 MPa. The highest compressive stress can be obtained from moist cured sample at Ms = 1 and n = 0.07, which is about 35 MPa.