Influence of Coal Fly Ash on

Mechanical Properties of Mortar

Consisting of Total Dissolve Solids

By

Bijoy Krishna Halder, Vivek Tandon, Anthony Tarquin,

Ramana V. Chintalapalle

The University of Texas at El Paso

Agenda

Introduction

Challenges

Objective

Material Used

Micro Scale Test

Experimental Design

Compressive Strength Test

Conclusion

Introduction

Introduction

• Water is an important resource.

• Mark et al. (2002) (Global Water Outlook 2025 Averting an

Impending Crisis)

Year

Global Water

Demand (billion

gallon/day)

Increase

1995 3000 25 %

2025 3750

Introduction (Cont.)

• Dependency on Nontraditional source

• Technique like Desalination is used to produce 50-90%

potable water.

• Remaining is byproduct brine

• Problem is sustainable disposal of this brine (containing TDS*)

• Is it possible to use TDS as construction material?

* TDS=Total Dissolved Solids

Challenges

Challenges

TDS contains high corrosive elements (Na, Cl) which needs

stabilization.

Barberon et al. (2005)* found that

*Barberon, F., Baroghel-Bouny, V., Zanni, H, Brsson, B., Caillerie, J., Malosse, L., Gan, Z., Interactions between chloride and cement paste materials, Magnetic Resonance

Imaging, V. 23, 2005, pp. 267-282.

Objective

• Evaluate the feasibility of using TDS in mortar by stabilizing

salt using fly ash.

Objective

Material Used

Material Used

• Cement (Type I/II OPC, ASTM C-150)

• Quickrete all purpose sand (ASTM C 33 )

• Water & Sodium phosphate buffer (50mM Na3PO4, 8.2g/l of

water)

• TDS (passing #16 sieve )

• Class F fly Ash

• Analytical report of final concentration of brine

• All concentration in mg/l, conductivity (µs/cm) and pH in (pH unit)

Material Used (Cont.)

1

Parameter Final concentration

Calcium 1432

Iron 5.5

Magnesium 438

Potassium 216

Sodium 8,640

Chloride 26,600

Sulfate 8,140

Silica 72

Electrical Conductivity 99,000

TDS 57,800

pH 3.6

Source: Tarquin, A. J. (2010). “High Tech Methods to Reduce Concentrate Volume Prior to Disposal”, El Paso Water Utilities Public Service Board, El Paso, p. 23.

• Fly ash Property (Collected from Boral Material Technology)

Material Used (Cont.)

Component Results

SiO2 50.69 %

Al2O3 23.68 %

Fe2O3 4.68 %

SiO2+ Al2O3+ Fe2O3 79.05 %

CaO 13.19 %

MgO 1.62 %

SO3 1.78 %

Na2O 0.05 %

K2O 0.90 %

Total Alkalies (as Na2O) 0.64 %

Loss of Ignition, % LOI 1.69 %

Specific gravity 2.29 1

MICRO SCALE TEST

XRD Analysis of TDS

• Bruker D8 X-ray diffractometer

• Rock salt, Halite

Laser Diffraction Particle Sizing

0

2

4

6

8

10

12

14

0.1 1 10 100 1000

Volu

me

In (

%)

Particle Size (µm)

Mean diameter

=34.065 µm

0

10

20

30

40

50

60

70

80

90

100

0.1 1 10 100 1000

Cu

mu

lati

ve

Vo

lum

e In

(%

)

Particle Size (µm)

Median Dia =24.062 µm

Laser Diffraction Particle Sizing (Cont.)

• The key findings of laser diffraction analysis are

Parameter Outcome

D (0.1) 3.825 µm

D(0.5) 24.062 µm

D(0.9) 80.24 µm

Surface weighted mean D[3,2] 7.359 µm

Volume weighted mean D [4,3] 34.065 µm

Specific surface area 815 m2/kg

Particle size larger than 45 µm in

volume 25 %

Particle size larger than 10 µm in

volume 70 %

1

Laser Diffraction Particle Sizing (Cont.)

XRD Analysis of Fly Ash

• Predominant crystalline phases Q & M (Al4.44Si1.56O9.78).

SEM Analysis of Fly Ash

1

(a) (b)

(c) (d) Irregular

Shape

• Fig a, b & c showed irregular and larger particle > 45 μm.

• Yield due to collision of the flame-borne particles of silica ash

and sulfate fume in pulverized-coal-fired boilers.

• Does not have smooth texture.

• Significant amount of small solid sphere particles (Figure 5 d).

SEM Analysis of Fly Ash (Cont.)

• EDS analysis of a single solid sphere particle at 20 kV and

10000 magnification

• Si/Al=1.5 is low, may cause formation of lower strong bonds

of Al-O-Al or Si-O-Al than strong bonds Si-O-Si.

• MgO induce formation of mullite.

SEM Analysis of Fly Ash (Cont.)

Element Si Al Fe K Ca Na Mg S O

Weight (%) at

10,000

magnification

26 17 2.8 0.6 4.9 2.4 1.2 0.3 45

Experimental Design

Sample Preparation (Cont.)

ASTM* C-109 (2008)

Cement: Sand: Mixing Liquid= 1:2.75:0.49

Samples were prepared in 2 × 2 × 2 in..

*American Society of Testing material

Specimen

Size

Mortar

Components

Material Amount

Cement

(C),

grams

Fly

Ash(F),

grams

Sand (S),

grams

Salt

(s),

grams

Phosphate

Buffer (P),

ml

Amount

of

Materials

required

for Six-50

mm. Cube

Specimens

CSP 500 --- 1,375.0 --- 242.5

CSF(5%)P 475 25 1,375.0 --- 242.5

CSF(10%)P 450 50 1,375.0 --- 242.5

CSF(20%)P 400 100 1,375.0 --- 242.5

CSF(30%)P 350 150 1,375.0 --- 242.5

CSF(40%)P 300 200 1,375.0 --- 242.5

CSs(5%)P 475 25 1306.3 68.7 242.5

CSs(5%)F(5%)P 475 25 1306.3 68.7 242.5 1

Sample Preparation (Cont.)

*C: Cement; S:Sand; s: TDS/salt; F:Fly Ash; P:Sodium Phosphate Buffer; W: Water

Curing Process

• Tap Water (For standard samples)

• Cured at 25 ̊ C, submerging under water.

Compressive Strength

Test (ASTM C 109-08)

Compressive Strength Test

*C: Cement; S:Sand; s: TDS; F:Fly Ash; P:Sodium Phosphate Buffer; W: Water

• Fly ash sample strength reduction

• From micro scale test

1. Particle size larger that 45 µm = 25% in vol. (Cheerarot suggested only 5%)

2. Mean particle size = 34 µm (Li (2005)* found that fly ash coarser than 12 µm

lower strength ratio of 28 day compressive strength in mortar comparing no fly

ash added sample)

3. Formation of non glassy phase mullite that chemically inactive.

4. EDS analysis showed low Si/Al ratio, may form more C-A-S-H gel (Walairat

(2009)** mentioned C-A-S-H is weak binder)

5. Larger particle present in fly ash will remain inert.

Compressive Strength Test

*Li, Gengying & Wu, Xiaozhong," Influence of fly ash and its mean particle size on certain engineering properties of cement composite mortar.", Cement & Concrete Research, Vol 35, p. 1128-

1134, 2005.

**Walairat, B., Richard, L. “A figure of merit for fly ash replacement of Portland cement.” World of Coal Ash Conference, May 4-7, 2009.

• For TDS (s) added Sample CSs(5%)P

Addition of salt considerably decreased the strength for CSs(5%)P sample.

For >5 % replacement with TDS, sample failed by crumbing under

loading.

Berke* reported that chloride ions presence in solution may weaken the

integrity of cement matrix.

Barberon found free Cl- ion form Friedel’s salt; thus, Al substituted in C-

S-H gel does not contribute towards strength gain.

• CSs(5%)F(5%)P improved the ultimate strength (30.6 MPa)

by 6 MPa.

• Gained strength at higher rate from 7-28 days by 23 percent.

*Berke, N.S., Pfeifer, D.W., and Weil, T.G., Protection against Chloride Induced Corrosion; Concrete International, V.10, No.12, 1988,

pp. 45-55.

Compressive Strength Test

Strength Growth Rate (%)

*C: Cement; S:Sand; F:Fly Ash; s:TDS; P:Sodium Phosphate Buffer; W: Water

Only 30 & 40 % fly ash replacement showed higher pozzolanic reaction rate,

though some fly ash will remain inert due to lack of hydration product Ca(OH)2

Conclusion

Conclusion

• Fly ash with mean particle size larger than 10 µm, inactive

mullite and lower calcium oxide and Si/Al ratio content will

cause slower pozzolanic reaction to yield lesser strength

(ultimate compressive strength) of Mortar.

• Total dissolve solid (TDS) or salt can raise the pozzolanic

reaction rate, so use of brine partially with water can be an

option to produce cement mortar. However still it does require

lot of research to dispose it as construction material in

sustainable way.

• Ternary blends of this type of fly ash can be investigated to

use it effectively.

• Alternative approach for this type of fly ash with

biocementation may further improve strength and durability,

that is under investigation.

Future Recommendation