Coal-Combustion Bottom Ash for Reducing Shrinkage of Concrete

Center for By-Products Utilization

Coal-Combustion Bottom Ash for Reducing Shrinkage of Concrete Made

With Portland Cement and Sulfoaluminate Cement

By Tarun R. Naik, Rudolph N. Kraus, Yoon-moon Chun, and Samuel O. Nageotte

Presented at the Jean Pera Symposium on Recent Advances in Concrete Technology, Warsaw, Poland, May 2007.


Calcium Sulfoaluminate Cement

Innovative developments and uses of calcium sulfoaluminate cement has been reported by J. Pera, including:

• development of concrete with high-early strength,• design of self-leveling screed with limited curling,• design of self-leveling topping mortar with low drying

shrinkage, and• glass-fiber-reinforced cement with high-ductility and

durability.


Coal-Combustion Bottom Ash

• Coal-combustion bottom ash has been successfully used as a surface material on service roads, park trails, and driveways, as an alternative to stone. Bottom ash particles have interlocking characteristic.

• It has also been reported that bottom ash can be used as a pozzolanic material, by grinding it until the material retained on a 45-µm sieve is less than 5%.

• It is also possible to produce lightweight concrete using bottom ash to reduce the dead load of a structure.


Research Objective and Tests Conducted

• This research was conducted to develop uses of coal-combustion bottom ash for reducing the autogenous shrinkage of concrete made with and without sulfoaluminate cement.

• Concrete mixtures were tested for time of initial set (ASTM C 403), autogenous shrinkage, compressive strength (ASTM C 39), splitting tensile strength (ASTM C 496), and other properties.


Cements, Fly Ash, Aggregates

• ASTM Type I portland cement• Sulfoaluminate cement• ASTM Class C fly ash• Natural sand• Crushed quartzite stone with a nominal maximum size

of 19 mm• Bottom ashes P4, WPS, and MGE, from three different

sources of boilers (two pulverized coal and one RDF + coal)


Bottom Ash P4 (97% PRB* coal)

• As-received condition was wet.• It resembled dark rough sand with some

coarse particles and few large particles.• Bottom ash P4 was sieved and only the

portion passing 4.75-mm sieve was used to replace part of natural sand in concrete.

*Subbituminous


Bottom Ash WPS (PRB coal)

• Except for its brown color, Bottom ash WPS was similar to Bottom ash P4 in appearance, gradation, and moisture content.

• Only the portion of Bottom ash WPS passing 4.75-mm sieve was used to replace part of natural sand in concrete.


Bottom Ash MGE (RDF + Coal)

• The size of particles ranged from very fine to coarse, most of the particles being coarse.

• Bottom ash MGE was received in dry condition.• The particles had soft round surface and were generally

easily breakable, friable.• Only the portion retained on 4.75-mm sieve was used to

replace part of natural coarse aggregate in concrete.


Properties of Bottom Ashes

The portions of the bottom ashes P4 and WPS finer than 4.75-mm sieve, and the portion of the bottom ash MGE coarser than 4.75-mm sieve, were tested for gradation by sieve analysis, moisture content, specific gravity, and absorption.


Properties of Aggregates

17.515.813.60.41.4SSD Absorption (%)

1.18 -1.63

2.102.092.652.62Bulk specific gravity at SSD

N. A.15.015.0--As-received moisture content (%)

Bottom Ash

MGE

Bottom Ash WPS

Bottom Ash P4

StoneSand


Sieve Analysis of Bottom Ash P4

0102030405060708090

100

0.1 1 10Sieve opening (mm)

% p

assi

ng

Sample 1Sample 2Sample 3ASTM C 330 MINASTM C 330 MAX


Sieve Analysis of Bottom Ash WPS

0102030405060708090

100

0.1 1 10Sieve opening (mm)

% p

assi

ng Sample 1Sample 2ASTM C 330 MINASTM C 330 MAX


Sieve Analysis of Bottom Ash MGE

0

10

20

30

40

50

60

70

80

90

100

1 10 100Sieve opening (mm)

% p

assi

ng MGE bottom ashASTM C 330 MINASTM C 330 MAX


• Oven-dry samples and wet-samples of the bottom ashes showed approximately the same gradation.

• The bottom ashes P4 and WPS finer than 4.75-mm sieve met the gradation requirement for lightweight fine aggregateper ASTM Standard Specification for Lightweight Aggregates for Structural Concrete (C330).


• The gradation of the bottom ash MGE retained on the 4.75-mm sieve approximately coincided with the upper limit of the gradation requirement for lightweight coarse aggregate per ASTM C 330.

• Thus, the bottom ash MGE was treated as a lightweight coarse aggregate.


Preparation for Mixing

• The fine bottom ashes P4 and WPS were used in their as-received wet condition in making concrete mixtures.

• Bottom ash MGE was soaked for 24 hours and allowed to dry for one hour before it was used in concrete mixtures.

• The moisture content of the soaked bottom ash MGE was 20%.


Replacement Rates of Natural Aggregate with Bottom Ash

• The bottom ashes P4 and WPS were used to replace75% of natural sand by volume, and the bottom ash MGE was used to replace approximately 30% and 75% of natural coarse aggregate by volume.

• Due to the relatively low specific gravity of all bottom ashes, the percentage of replacement was calculated based on volume.


Cementitous Materials and HRWRATwo groups of concrete mixtures were made using different blends of cementitious materials:

• 70% portland cement + 30% Class C fly ash• 52% portland cement + 18% sulfoaluminate cement +

30% Class C fly ash.To achieve a slump of 50 to 100 mm, high-range water-reducing admixture (HRWRA) was used, as needed, in some of the mixtures containing fine bottom ash.


Mixture Proportions of Concrete without Sulfoaluminate Cement

260680990940100010401040Quartzite coarse aggregate (kg/m3)003.90000HRWRA (L/m3)

42819900000MGE coarse bottom ash (kg/m3)00535520000WPS fine bottom ash (kg/m3)000054700P4 fine bottom ash (kg/m3)

816913198197207859859Natural sand (kg/m3)169155154178166157157Water (kg/m3), W9210810199105104104Class C fly ash (kg/m3)0000000Sulfoaluminate cement (kg/m3)

211251230230244243243Type I portland cement (kg/m3)MGEMGEWPSWPSP4--Bottom ash source

I-M75

I-M30

I-W75-2

I-W75

I-P75I-repeat

IMixture Designation


Slump test of fresh concrete

Testing for air content of fresh concrete


Wet-sieving of concrete through a

4.75-mm sieve for obtaining a ample for initial setting time test of

concrete

Testing for initial setting time

of concrete by penetration resistance

S


Fresh Properties and Time of Setting of Concrete without Sulfoaluminate Cement

10.89.011.59.79.0N.Av.8.5Time of initial set (hr)1990231022102160227024002400Density (kg/m3)6.12.81.52.71.71.21.1Air content (%)70655050508565Slump (mm)

0.560.430.470.540.480.450.45W/CmMGEMGEWPSWPSP4--Bottom ash source

I-M75

I-M30

I-W75-2

I-W75

I-P75I-repeat

IMixture Designation


Mixture Proportions of Concrete Containing Sulfoaluminate Cement

65010109609601050Quartzite coarse aggregate (kg/m3)08.84.300HRWRA (L/m3)

1860000MGE coarse bottom ash (kg/m3)0539000WPS fine bottom ash (kg/m3)005405400P4 fine bottom ash (kg/m3)

942200210202862Natural sand (kg/m3)157151163184150Water (kg/m3), W109101107104100Class C fly ash (kg/m3)6459605858Sulfoaluminate cement (kg/m3)

192172185180173Type I portland cement (kg/m3)MGEWPSP4P4-Bottom ash source

S-M30S-W75S-P75-2S-P75SMixture Designation


Fresh Properties and Time of Setting of Concrete Containing Sulfoaluminate Cement

2.23.51.82.82.5Time of initial set (hr)22902240223022302390Density (kg/m3)2.82.82.91.81.5Air content (%)50100555070Slump (mm)

0.430.460.460.540.45W/CmMGEWPSP4P4-Bottom ash source

S-M30S-W75S-P75-2S-P75SMixture Designation


Time of Initial Set

• The time of initial set of the concrete mixtures without sulfoaluminate cement ranged from 8.5 to 11.5 hours.

• In contrast, the time of initial set of the concrete mixtures containing sulfoaluminate cement was much shorter, ranging from 1.8 to 3.5 hours.


Comparator for autogenous shrinkage test

Autogenous shrinkage test setup

while beams are in molds


Autogenous shrinkage test setup

Storage of autogenous shrinkage

beams, sealed with aluminum adhesive tape, following removal

from molds


Autogenous Shrinkage of Concrete Without Sulfoaluminate Cement

-200

-150

-100

-50

0

50

100

0 7 14 21 28

Age (days)

Aut

ogen

ous

leng

th c

hang

e (µ

m/m

)

II-P75I-W75I-W75-2I-M30I-M75


Autogenous Length Change of Concrete Containing Sulfoaluminate Cement

-500

-450

-400

-350

-300

-250

-200

-150

-100

-50

00 7 14 21 28

Age (days)

Aut

ogen

ous

leng

th c

hang

e (µ

m/m

)

SS-P75S-P75-2S-W75S-M30


AUTOGENOUS SHRINKAGE

• Bottom ashes used in the mixtures reduced theautogenous shrinkage of concrete.

• This may be explained by the porosity of the bottom ash particles and the moisture contributed from them to the cementitious matrix during the curing and hydration process.


• Mixtures I-W75, I-W75-2, and I-M75 showed a slight expansion up to the age of at least 28 days.

• Mixtures I-M30 and I-P75 did not showautogenous shrinkage until 10 and 17 days, respectively.

• Thus, it was possible to eliminate the earlyautogenous shrinkage of concrete by replacing either 75% of natural sand or 30 to 75% of natural stone with coal-combustion bottom ash.


• The mixtures with sulfoaluminate cement showed higher autogenous shrinkage because of the rapid hydration reaction.

• But still, the use of bottom ash reduced theautogenous shrinkage.

• The mixture S-P75-2 showed relatively small autogenous shrinkage.


Compressive strength test of concrete

Splitting tension strength test of

concrete


Compressive Strength of Concrete Without Sulfoaluminate Cement

0

10

20

30

40

50

60

1 d 3 d 7 d 14 d 28 d 91 d

Age

Com

pres

sive

str

eng

th (M

Pa)

I

I-P75I-W75

I-W75-2I-M30I-M75


Compressive Strength of Concrete Containing Sulfoaluminate Cement

0

10

20

30

40

50

60

1 d 3 d 7 d 14 d 28 d 91 d

Age

Com

pres

sive

str

eng

th (M

Pa)

SS-P75

S-P75-2S-W75

S-M30


Splitting Tensile Strength of Concrete Without Sulfoaluminate Cement

0

1

2

3

4

5

6

1 d 3 d 7 d 14 d 28 d 91 d

Age

Spl

ittin

g te

nsile

str

engt

h (M

Pa)

I-repeat

I-P75I-W75

I-W75-2I-M30I-M75


Splitting Tensile Strength of Concrete Containing Sulfoaluminate Cement

0

1

2

3

4

5

6

1 d 3 d 7 d 14 d 28 d 91 d

Age

Spl

ittin

g te

nsile

str

engt

h (M

Pa)

SS-P75

S-P75-2S-W75

S-M30


Compressive Strength and Splitting Tensile Strength

• Use of bottom ash reduced the compressive strength of concrete by 24 to 65% (average 45%) and the splitting tensile strength by 13 to 55% (average 32%).

• The reduction in compressive strength was especially noticeable for mixtures withoutSulfoaluminate cement upon replacement of a portion of stone with higher amount of bottom ash.


CONCLUSIONS

• By replacing 75% of either natural sand or natural stone with coal-combustion bottom ash, several concrete mixtures did not showed autogenous shrinkage .

• Thus, it is possible to develop concrete mixture proportions to achieve none or negligible autogenous shrinkage of concrete.


CONCLUSIONS (cont’d)

• Use of bottom ash reduced the strength of concrete.

• Improvement of mixture proportions should improve the strength of concrete.


ACKNOWLEDGEMENTS• The authors would like to thank We Energies

(Milwaukee, WI), Wisconsin Public Service Corporation (Green Bay, WI), and Madison Gas and Electric Company (Madison, WI) for supplying the bottom ashes used in this research.

• Samuel Nageotte’s travel and living expenses for his summer research at the University of Wisconsin-Milwaukee (UWM) were provided by INSA (Institut National des Sciences Appliquees), Lyon, France.


More information at<www.cbu.uwm.edu>.


Thank you very much for your

interest.

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Coal-Combustion Bottom Ash for Reducing Shrinkage of Concrete

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