Evaluation of class C and class F fly ash by xft76262

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									Evaluation of class C and class F fly ash as precursors
    for a corrosion resistant geopolymer coating




                    Carlos Montes
                    Erez Allouche

              Trenchless Technology Center
                Louisiana Tech University
                    GEOPOLYMERS

   Powder phase:                     Fly ash


   Liquid phase:                 Alkaline      Alkaline
                                  hydroxide +   silicate
                            GEOPOLYMERIZATION REACTION




J. Davidovits, Geopolymer Chemistry and Sustainable Development. The Poly(sialate) Terminology : A Very Useful and Simple Model for the Promotion
and Understanding of Green-Chemistry. Geopolymer Institute. Proceedings of the World Congress Geopolymer. 9-15 (2005).
GEOPOLYMER STRUCTURE




    [ (Si O
 Mn [-(Si-O2)z – Al – O]n + wH2O

     Geopolymer’s general formula
                PORTLAND CEMENT HYDRATION
                                           Calcium silicate reactions
C        CaO
                                           2C3S + 6H  C3S2H3 + 3CH
S        SiO2                              2C2S + 6H  C3S2H3 + CH
Ŝ        SO3                               Calcium aluminate reactions
F       Fe2O3
                                       C3A + 3CŜH2 + 26H  C6AŜ3H32 ,
A       Al2O3
                                      2C3A + C6AŜ3H32 + 4H  3C4AŜH12
H        H2O
                                 C4AF + 3CŜH2 + 21H  C6(A,F)Ŝ3H32 + (A,F)H3

                          C4AF + C6(A F)Ŝ3H32 + 7H  3C4(A F)ŜH12 + (A F)H3
                                   (A,F)Ŝ        H      (A,F)ŜH     (A,F)H

Portland cement phases:                             Portland cement hydrated phases:


C3S        Tricalcium silicate                      C3S2H3     CSH
C2S        Dicalcium silicate                       CH         Calcium hydroxide
C3A        Tricalcium aluminate                     C6AŜ3H32 Ettringite
C4AF       Ferrite h
           F it phase                                        Calcium monosulfoaluminate
                                                    3C4AŜH12 C l i         lf l   i t

3CŜH2      Gypsum (added to the clinker)            (A,F)H3    Aluminum and iron hydrates
                 PROBLEM # 1: BY-PRODUCTS
             1

 Ca(OH)2 + H2SO4  CaSO42H2O

             2

  C3A + 3CŜH2 + 26H  C6AŜ3H32 ,

 2C3A + C6AŜ3H32 + 4H  3C4AŜH12

C4AŜH12 + 2CŜH2 + 16H  C6AŜ3H32
                             SOLUTIONS

                                  1

     Use cements low in calcium aluminate (C3A), also called Type V

                                  2

             Ca(OH)2 + SiO2, SiO2Al2O3 + H2O  C3S2H3
           PROBLEM # 2: MAIN PRODUCT

CSH Decalcification:
C3S2H3 + 2H2SO4  CS2H3 + 2CŜH2  CŜH2 + CŜ + 2S(aq)

Geopolymer cation replacement:

Hn
Nan [-(Si-O2)z – Al – O]n + H2SO4


NaSO4


Al2H2(SO4)48H2O
                                       H
                                       H H

                                           H
 ACTUAL MATERIALS USED IN TT PROJECTS

EPOXY/POLYMERS                       CEMENTITIOUS
Advantages:                          Advantages:
Corrosion resistance                 Lower costs
Smooth surface                       Easy application
                                             li i
High strength                        Good adhesion
                       GEOPOLYMER!


Disadvantages:                       Disadvantages:
Adhesion                             Low corrosion resistance
Cost                                 Rougher surfaces
Thermal expansion
    OBJECTIVES OF CURRENT PROJECT
MAIN:

Develop and test a geopolymeric coating for concrete sewer pipes.

SPECIFIC:

•          p g p y                g         g     p             g    (
     Develop a geopolymer mix design with high compressive strengths (>60
     MPA).

•    Obtain setting times and pot life so that geopolymer can be applied with
             technology.
     current technology

•    Develop a geopolymeric mix design with corrosion resistance
     superior to actually used cementitious coatings.

•    Determine the optimal workability to use in the field.

•    Study the adhesion and wettability of geopolymer slurries to the parent
     concrete surface.
                CHEMICAL COMPOSITION

                Fly Ash,     Fly Ash,   OPC, %
   Oxide
                Class C %    Class F%
    SiO2          48 7
                  48.7         50.25
                               50 25      6
                                         26.12
   Al2O3          16.6        22.56      4.25
   Fe2O3          6.93         20.0      3.65
    CaO           18.72        2.1       58.51
    MgO           3.91         0.00      1.59
    SO3           0 85
                  0.85         0.50
                               0 50      2.36
                                         2 36
    LOI           0.49         2.48      2.67
   Na2O           0.00         0.00      0.14
    K2O           0.00         0.00      0.52
   Total          96.2        97.89      99.8
 SiO2/Al2O3
     /            2.93
                    93         2.23      6.15
SiO2 + A l2O3     65.30       72.81     30.37
                                     COMPRESSIVE STRENGTH RESULTS

                                            COMPRESSIVE STRENGTH


                             12000




                             10000
                       si)
             TRENGTH (ps




                              8000
                                                                       Class C Fly ash
                                                                       Class F Fly ash
  MPRESSIVE ST




                              6000
                                                                       OPC


                              4000
COM




                              2000




                                0
                                     1      2          3           4

                                                DAYS
                             CORROSION TEST RESULTS
                             Class ‘C’ FLY ASH Geopolymer



                                                                120.00
               RESSIVE



                                                                100.00
       RENGTH (%)
REMAINING COMPR




                                                                80 00
                                                                80.00
                                  0.6
                                  1                             60.00
                                  2
                                                                40.00
                                                                40 00
    STR




                                  3

                                                                20.00
R




                                                                0.00
                         0    1         2           4   6   8

                                            WEEKS
                                   CORROSION TEST RESULTS
                                     OPC & SF Binary Blend




                                                                     120.00
                                                                     120 00
               RESSIVE



                                                                     100.00
               %)




                                                                     80 00
                                                                     80.00
       RENGTH (%
REMAININ COMPR




                                                                     60.00
       NG




                             0.6
    STR




                                                                     40 00
                                                                     40.00
                             1
                             2
                             3
                                                                     20.00

                                                                     0.00
                                                                     0 00
                         0          1       2           4    6   8
                                                WEEKS
                     CORROSION TEST RESULTS
                    Class ‘C’ FLY ASH Geopolymer


                                                       30.00
                    0.6
                    06
                    1                                  25.00
                    2
 ASS LOSS (%)




                    3                                  20.00
        S




                                                       15.00


                                                       10.00
MA




                                                       5.00


                                                       0.00
                                                       0 00
                0   1        2           4    6    8

                                 WEEKS
                        CORROSION TEST RESULTS
                             OPC & SF Binary Blend



                                                         80 00
                                                         80.00
                                                         70.00
                         0.6
MASS LOSS (%)




                         1                               60.00
                         2
        S




                                                         50.00
                         3
                                                         40.00
                                                         30.00
                                                         20.00
                                                         10.00
                                                         0.00
                                                         0 00
                0   1            2           4   6   8
                                     WEEKS
                   CORROSION RESULTS for pH = 0.6



                                                                  120.00
               RESSIVE



                                                                  100.00
       RENGTH (%)
REMAININ COMPR




                                                    Class F
                                                    Fly ash       80.00
                                                                  80 00
                                                    Class C
                                                    fly ash
                                                    OPC
                                                                  60.00
       NG




                                                                  40.00
    STR




                                                                  20.00

                                                                  0.00
                         0   1   2          4   6             8
                                     WEEK
pH   3    2    1    0.6




     pH       0.6
  STUDY ON THE EFFECT OF THE MIX DESIGN PARAMETERS ON
            THE PROPERTIES OF GEOPOLYMERS

• The previous steps helped to determine geopolymer’s suitability as
rehabilitation materials for underground pipes.
• It was also decided that Class F ash would be the best option for the
design of the coating.
• Now it was necesary to study the effect of the different research
parameters on geopolymer’s properties to create a suitable mix
design for the coating.
• A 33 design of experiments was created for this purpose.
• The research variables were: silicate type, hydroxide concentration
                       ratio.
and silicate/hydroxide ratio
• The response variables were: compressive strength, remaining
compressive strength, mass loss and flow.
     SPRAYABLE GEOPOLYMER FORMULATION
• A suitable formulation was created starting from the results of
the previous tests.
• Three 12” sections of concrete pipe were coated using this
formulation.


                                Observations:
                                   h ili      /h d id       i had
                                • The silicate/hydroxide ratio h d to
                                be changed to allow sufficient
                                setting time.
                                • Curing after a 24 hrs rest period
                                produced higher compressive
                                strength and reduced sagging.
                       CONCLUSIONS
• Class C Fly ash performs better than Class F Fly ash in
terms of compressive strength. Both achieve higher early
compressive strengths than Portland cement.
• In terms of corrosion resistance, Class F fly ash’s absence
                                p
of calcium oxide results in a superior pperformance.
Therefore the use of this fly ash is recommended for
applications under acidic conditions. The workability and
                                          superior
setting time of this type of ash are also superior.
• Mix design formulations are critical to the final properties
of the geopolymer matrix. An optimal solution have been
              spray-
developed for spray-on applications.

								
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