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Resources, Conservation and Recycling 72 (2013) 20– 32
Contents lists available at SciVerse ScienceDirect
Resources, Conservation and Recycling
journa l h o me pag e: www.elsev ier .com/ locate / resconrec
eview
ffect of coal bottom ash as partial replacement of sand on properties of concrete
alkit Singha, Rafat Siddiqueb,∗
Thapar University, Punjab 147004, IndiaDepartment of Civil Engineering, Thapar University, Punjab 147004, India
r t i c l e i n f o
rticle history:eceived 29 September 2012eceived in revised form3 December 2012ccepted 14 December 2012
eywords:
a b s t r a c t
Coal bottom ash (CBA) is formed in coal furnaces. It is made from agglomerated ash particles that aretoo large to be carried in the flue gases and fall through open grates to an ash hopper at the bottomof the furnace. Bottom ash is mainly comprised of fused coarser ash particles. These particles are quiteporous and look like volcanic lava. Bottom ash forms up to 25% of the total ash while the fly ash formsthe remaining 75%. One of the most common uses for bottom ash is as structural fill.
Published literature shown that there is a strongly possibility of coal bottom ash being used as substi-
oal bottom ashompressive strengthoncreteorkability
lexural strengthurability
tute/replacement of fine aggregate (sand). Its use in concrete becomes more significant and important inview of the fact that sources of natural sand as fine aggregates are getting depleted gradually, and it is ofprime importance that substitute of sand be explored.
This paper presents an overview of the published literature on the use of coal bottom ash in concrete.Effect of coal bottom ash on the properties of concrete such as workability, bleeding, setting times,compressive strength, split tensile strength, flexural strength, shrinkage, and durability are presented.
© 2012 Elsevier B.V. All rights reserved.
ontents
. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211.1. Uses of coal bottom ash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
. Properties of coal bottom ash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212.1. Chemical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212.2. Physical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212.3. Mineralogy characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
. Properties of fresh coal bottom ash concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213.1. Workability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213.2. Bleeding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243.3. Setting times . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243.4. Plastic shrinkage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
. Properties of hardened coal bottom ash concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254.1. Density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254.2. Compressive strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264.3. Flexural strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284.4. Split tensile strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284.5. Microstructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294.6. Modulus of elasticity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294.7. Drying shrinkage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
. Durabilty properties of coal bottom ash concrete . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.1. Permeability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.2. Freeze–thaw resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
∗ Corresponding author. Tel.: +91 175 239 3207; fax: +91 175 239 3005.E-mail address: siddique [email protected] (R. Siddique).
921-3449/$ – see front matter © 2012 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.resconrec.2012.12.006
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
M. Singh, R. Siddique / Resources, Conservation and Recycling 72 (2013) 20– 32 21
5.3. Resistance to sulfate attack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315.4. Abrasion resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315.5. Behavior of bottom ash concrete under high temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
6. Observations and conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32. . . . . .
1
totbEadtbbptrmmbhomdopwmrastflTamhfictbtBmuprsto
1
tb
••
References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. Introduction
On burning of coal in furnace of coal fired thermal power plants,he non combustible material present in it results in productionf coal ash. The finer and lighter particles of coal ash escape withhe flue gases and are extracted in the Electrostatic Precipitatorsefore reaching the environment. The coal ash collected from thelectrostatic Precipitators is named as fly ash. Some melted ashccumulates on the boiler walls and against steam tubes and soli-ifies to form masses called clinkers. The clinkers build up and fallo the bottom of boiler/furnace and are cooled in the water sumpefore passing through clinker grinder. The coal ash collected atottom of furnace is called bottom ash. Bottom ash particles arehysically coarse, porous, glassy, granular and grayish in color. Bot-om ash forms up to 25% of the total ash while fly ash forms theemaining 75%. In India, coal fired thermal power plants are theain source of power generation and about 70% electricity require-ents are fulfilled by them. About 360 million tons of coal is burnt
y the coal fired thermal power plants every year. Indian coals haveigh amount of inorganic inclusions with varying properties andn combustion result in high ash content up to 46%. About 100illion tones of fly ash and 25 million tone of bottom ash is pro-
uced by these thermal power plants annually. With the additionf 59,000 MW of power generation by the end of year 2012, annualroduction of bottom ash will shoot up to 50 million tones. World-ide fly ash is used in large volume in production of cement asineral additive and in construction industry as partial cement
eplacement in concrete. Bottom ash is used as land fill materialnd as base material in road construction. In India up till now amall volume of fly ash is utilized in production of cement but bot-om ash is not used in any form. Bottom ash along with unutilizedy ash is disposed off in ponds spread over thousand acres of land.he disposal of bottom ash in ponds poses risk to human healthnd the environment. The hazardous constituents in bottom ashigrate and can contaminate ground water or surface water, and
ence living organisms. Also there is danger of ash dyke spill andlling the surrounding area of pond with ash. Environment con-erns are increasing day by day and land fill space is declining,herefore it becomes essential to initiate the effort to utilize theottom ash. Bottom ash has the appearance and particle size dis-ribution similar to that of natural fine aggregate i.e. river sand.ecause of these properties it attracted to be used as sand replace-ent in concrete. Recently research works have been focused on
sage of bottom ash as partial sand replacement in concrete. Theublished research data indicate that bottom ash is a viable mate-ial as sand replacement in concrete. Therefore its suitability asand replacement material in concrete and the ways in which bot-om ash affects the fresh, hardened as well as durability propertiesf concrete has been critically evaluated in this review.
.1. Uses of coal bottom ash
Bottom ash can be beneficially utilized in a variety of manufac-uring and construction applications. At present in America, coal
ottom ash is predominantly used for the following applications:Road base and sub-baseStructural fill
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
• Backfill• Drainage media• Aggregate for concrete, asphalt and masonry• Abrasives/traction• Manufactured soil products
2. Properties of coal bottom ash
2.1. Chemical properties
Bottom ash is mainly composed of silica, alumina, and ironwith small amounts of calcium, magnesium, sulfate, etc. Its chem-ical composition is controlled by the source of the coal. Table 1shows the comparative study of Chemical composition of bottomash obtained from different sources of coal.
2.2. Physical properties
The particles of coal bottom ash are angular, irregular andporous and have rough surface texture. The particle size rangesfrom fine gravel to fine sand. Coal bottom ash particles have inter-locking characteristics. Bottom ash is lighter and more brittle ascompared to natural sand. The specific gravity of the bottom ashvaries from 1.39 to 2.33 depending upon its chemical composi-tion. Table 2 shows the specific gravity of various bottom ashesinvestigated worldwide. The low specific gravity of bottom ash isexplained by its low iron oxide contents. It is believed that for ironcontent greater than 10%, the specific gravity value is directly pro-portional to iron content but for lime content greater than 15%, thespecific gravity value is more irrespective of iron content. Bottomash with a low specific gravity has a porous texture that readilydegrades under loading or compaction. Bottom ash derived fromhigh sulfur coal and low rank coal is not very porous and is quitedense. Bottom ash is usually a well-graded material although vari-ations in particle size distribution may be encountered from thesame power plant. Figs. 1 and 2 show the SEM of coal bottom ashesfrom two different thermal power plants.
2.3. Mineralogy characteristics
Results of XRD analysis of pure bottom ash carried out byMuhardi et al. (2010), show that mullite, silicon oxide, and sili-con phosphate are the predominant crystalline form substances.Mineralogical examination showed that silica is present partly inthe crystalline forms of quartz and in combination with the alu-mina as mullite. The iron appears partly as the oxide magnetiteand hematite. Figs. 3 and 4 present the XRD of coal bottom ashfrom two different sources.
3. Properties of fresh coal bottom ash concrete
3.1. Workability
Water demand to achieve desired workability of concrete
mainly depends on the number of fines and properties of fine aggre-gate in it. Natural river sand particles are dense and its shape,surface becomes smooth due to weathering affects. Weak miner-als like mica are removed from it. Whereas bottom ash particles
22 M. Singh, R. Siddique / Resources, Conservation and Recycling 72 (2013) 20– 32
Table 1Chemical properties of bottom ash.
Chemicalcomposition (%)
Yuksel andGenc (2007)
Andrade et al.(2009)
Bai et al.(2005)
Kasemchaisiri andTangtermsirikul (2007)
Sani et al.(2010)
Ghafoori and Bucholc(1997)
SiO2 57.90 56.0 61.80 38.64 54.80 41.70Ai2O2 22.60 26.70 17.80 21.15 28.50 17.10Fe2O3 6.50 5.80 6.97 11.96 8.49 6.63CaO 2.00 0.80 3.19 13.80 4.20 22.50MgO 3.20 0.60 1.34 2.75 0.35 4.91Na2O 0.086 0.20 0.95 0.90 0.08 1.38K2O 0.604 2.60 2.00 2.06 0.45 0.40TiO2 – 1.30 0.88 – 2.71 3.83 (P2O5, TiO2, etc.)P2O5 0.20 – 0.28SO3 0.10 0.79 0.61 – 0.42LOI 2.40 4.60 3.61 7.24 2.46 1.13
Table 2Physical properties of bottom ash.
Physical properties Yuksel andGenc (2007)
Topcu and Bilir(2010)
Bai et al. (2005) Kim and Lee (2011) Naik et al. (2007) Ghafoori andBucholc (1997)
SD) 1.87 (SSD) 2.09 (SSD) 2.47 (SSD)(1-h) 5.45 13.6 (SSD) 7.0
2.36 – 2.8
ampafiiifwoacwurdmra
Fa
Specific gravity 1.39 1.39 1.5 (SWater absorption (%) 6.10 12.10 30.4
Fineness modulus – – –
re angular and rough textured and are porous. Bottom ash hasore number of particles of size smaller than 75 �m as com-
ared to that in natural river sand. Therefore on use of bottomsh as replacement of natural sand in concrete, the number ofnes and irregular shaped, rough textured and porous particles
ncreases and thereby increasing the inter particles friction. Thencreased inter particle friction hinders the flow characteristics ofresh concrete. Secondly since the bottom ash has much higherater absorption ratio as compared to that of natural sand, part
f water is absorbed internally by the porous bottom ash particlesnd as such quantity of water available for lubrication of parti-les to achieve desired workability is reduced. Hence for the fixedater cement ratio, the workability of concrete reduces with these of bottom ash as sand replacement. The published researcheports also show that to achieve same slump of concrete, wateremand increases on use of coal bottom ash as sand replace-
ent in concrete. The following examples are the independenteports of decreased workability of concrete imparted by bottomsh.
ig. 1. Scanning electron microscopy (SEM) secondary-electron images of Bottomsh (Fernandez-Turiel et al., 2004).
Fig. 2. SEM photomicrographs of Tanjung Bin bottom ash (Muhardi et al., 2010).
Ghafoori and Bucholc (1997) examined the effect of high cal-
cium bottom ash as natural sand replacement on the properties offresh concrete mixtures of proportions to develop 28 days strengthof 3000 psi, 4000 psi, 5000 psi, and 6000 psi. They found that in caseFig. 3. PXRD patterns of the bottom ash samples from the Power Units I (Kantiraniset al., 2004). C: calcite, Q: quartz, Cl: clays (kaolinite), F: feldspars, G: gehlenite.
M. Singh, R. Siddique / Resources, Conservation and Recycling 72 (2013) 20– 32 23
Table 3Fresh properties of bottom ash and natural sand concrete (Ghafoori and Bucholc, 1997).
Mix No. Type of concrete Slump, (in.) Bleedingpercent
Initial settingtime (h)
Final settingtime (h)
Air temp.(F)
Conc. temp.(F)
Air contentpercent
Early shrinkagepercent
A1 Natural sand concrete 4 1/4 2.2 4.05 5.58 75 75 1.90 −0.49B1 Bottom ash concrete 4 1/4 4.0 4.2 5.95 65 65 1.80 −0.29C1 Bottom ash + sand concrete 4 1/4 2.8 3.81 5.55 72 90 1.85 −0.40D1 C1 + 12.5 oz ADM 4 1/4 2.0 3.63 5.21 72 84 1.80 −0.42A2 Natural sand concrete 4 1/4 1.0 3.75 5.08 78 82 1.80 −0.47B2 Bottom ash concrete 4 1/4 2.7 3.93 5.58 74 74 1.65 −0.30C2 Bottom ash + sand concrete 4 1/4 2.0 3.74 5.32 72 75 1.73 −0.39D2 C2 + 12.5 oz ADM 4 1/4 0.8 3.24 4.52 72 85 1.65 −0.42A3 Natural sand concrete 4 1/4 0.47 3.30 4.38 79 84 1.70 −0.49B3 Bottom ash concrete 4 1/4 1.7 3.56 4.95 68 72 1.50 −0.31C3 Bottom ash + sand concrete 4 1/4 1.2 3.33 4.72 72 75 1.60 −0.37D3 C3 + 12.5 oz ADM 4 1/4 0.45 3.06 4.04 72 78 1.55 −0.40A4 Natural sand concrete 4 1/4 0.08 3.06 4.08 78 84 1.50 −0.46B4 Bottom ash concrete 4 1/4 0.84 3.33 4.41 67 75 1.40 −0.31C4 Bottom ash + sand concrete 4 1/4 0.54 3.01 4.12 72 75 1.50 −0.39D4 C4 + 12.5 oz ADM 4 1/4 0.36 2.82 3.66 72 80 1.40 −0.45
owcrtcwiatw
brm7cwtartTrdWw
was replaced with bottom ash. As shown in Fig. 5, they observedthat for fixed water cement ratios of 0.45 and 0.55 and cement con-tent of 382 kg/m3, the slump increased with increase in bottom ash
0
50
100
150
200
250
0.45 0.55
Slu
mp (
mm
)
0% 30% 50% 70% 100%
Fig. 4. X-ray diffractogram of the bottom ash (Cheriaf et al., 1999).
f bottom ash concrete mixture with 100% sand replacement theater cement ratio for fixed workability is higher than that of the
ontrol mixture. For combined mixture (50% BA + 50% sand) waterequirement reduced significantly. When water reducing admix-ure was used, it further improved but was still higher than theontrol concrete mix except in case of 6000 psi mix in which itas lower than that of control concrete mix. For fixed workabil-
ty, the difference in water cement ratio of bottom ash concretend sand concrete narrows down with the increase in cement con-ent. Table 3 presents the properties of fresh bottom ash concreteith partial or full replacement of river sand.
Ghafoori and Bucholc (1996) investigated the effect of ligniteased bottom ash as sand replacement and impact of use of watereducing admixtures on properties of fresh structural concreteixtures with varying cement content of 500 lb/yd3, 600 lb/yd3,
00 lb/yd3, and 800 lb/yd3. They noted that when identical waterement ratios were used, the concrete containing bottom ashas fairly stiff and displayed far less workability than the con-
rol concrete. They demonstrated that for the same slump, bottomsh concrete required higher mixing water, however when watereducing admixture was used, the water requirement reduced. Bot-om ash concrete yielded an average of 7% higher volume of mix.he increase in volume dropped to 4% when low dosage of watereducing admixture was used. Also the gap in volume narrowed
own with the increase in cement content in bottom ash concrete.hen high dosage of water reducing admixture was used, actualater/cement reduced than that of control concrete.Aramraks (2006) examined the water requirement of concretemixes with 50% and 100% bottom ash as sand replacement. Lignitebased bottom ash used in his investigations was classified into twotypes normal grain (passing through No. 4 sieve) and coarse grain(passing through No. 4 and retained on No. 50 standard sieve). Heobserved that the mixes using bottom ash required approximately25–50% more mixing water content than normal concrete to obtainsuitable workability.
Aggarwal et al. (2007) found that the workability measuredin terms of compaction factor, decreases with the increase of thereplacement level of the fine aggregates with the bottom ash. Thecompaction factor reduced from 0.9 to 0.82 when the replacementlevel increased from 0% to 50%. Chun et al. (2008) observed thatslump decreases with increase in content of pond-ash, indicatinglower workability and the air content also shows a decline whenthe pond-ash content increases.
However, there is some contrary data in the published literaturewhich does not support the above concept of decreased workabilityon use of bottom ash as sand replacement in concrete. The pub-lished research reports which indicate increase in workability ofconcrete on use of bottom ash are illustrated below:
Bai et al. (2005) observed the reverse results, when natural sand
Water - Cement Ratio
Fig. 5. Slump of fresh concrete at fixed W/C (Series A) (Bai et al., 2005).
24 M. Singh, R. Siddique / Resources, Conservation and Recycling 72 (2013) 20– 32
0
50
100
150
200
250
10 60
Fre
e W
ater
Conte
nt
( K
g/m
3
Concr
ete)
Target Slump (mm)
0% 30% 50% 70% 100 %
F2
cadtkbc
maacmtisw
aaidwdth
ctatcw
F2
0
3
6
9
12
15
0% 25 % 50 % 75 % 100 %
wat
er lo
ss/
tota
l wat
er %
Bottom ash con tent
CRT3 CRT4
ig. 6. Free water content of concrete at fixed slump range (Series B) (Bai et al.,005).
ontent. For the controlled slump in the slump range of 0–10 mmnd 30–60 mm, as shown in Fig. 6, the requirement of free waterecreased with increase in bottom ash content. Correspondingly,he free W/C decreased due to the fact that the cement content wasept the same for all the mixtures. They considered it to be due toall bearing effect of the spherical shape of bottom ash particles asompared to irregular natural sand particle.
Yuksel and Genc (2007) observed that workability of concreteixtures containing varying percentage from 10% to 40% of bottom
sh as sand replacement, 35 kg/m3 of fly ash, 350 kg/m3 of cementnd 167 l of mixing water, improved with reference to control con-rete. With 50% bottom ash as sand replacement, the workabilityarginally decreased than that of the control concrete. When bot-
om ash used in combination (natural sand + GBFS + BA), there wasmprovement in workability at all sand replacement levels. Table 4hows the observed values of slump of fresh bottom ash concreteith different sand replacement levels.
Shi-Cong and Chi-Sun (2009) examined the effect of bottom ashs sand replacement at levels of 0%, 25%, 50%, 75% and 100% by masst fixed water cement ratio of 0.53 and fixed slump, on workabil-ty of concrete with mix proportions based on saturated surfaceried condition. They observed that the slump values increasedith increase in bottom ash content in the concrete mix. This wasue to the fact that bottom ash made more free water availableo increase the fluidity of fresh concrete because bottom ash hasigher water absorption values than that of river sand.
Kim and Lee (2011) found that the slump flow values of freshoncrete were not changed as the replacement ratio of fine bot-om ash was increased. They observed that FBA absorbed smallermount of cement paste and water on the surface of particles due
o its lower porosity and water absorption (5.45%) and higher vis-osity of cement used. Pores size of FBA used in their research workas around 0.1–10 �m. Fig. 7 presents the effect of bottom ash on300
350
400
450
500
550
600
0.0 20.0 40.0 60.0 80.0 100.0
Slu
mp f
low
(mm
)
Replacement of bottom ash(vol.%)
FBA replacement
CBA replacement
FBA+CBA replacement
ig. 7. Effect of bottom ash on flow characteristics of fresh concrete (Kim and Lee,011).
Fig. 8. Water loss by bleeding in relation to total water added in the mix (Andradeet al., 2009).
the slump vales of fresh bottom ash concrete with different sandreplacement levels.
3.2. Bleeding
The quantity of water loss through bleeding in concrete dependslargely on the water cement ratio, the properties of cement and thephysical properties of fine aggregate especially finer than 150 �msieves.
It is believed that when bottom ash is used as sand replacementin concrete, its porous particles absorb some water internally inaddition to water absorbed in inter particle voids present in theconcrete mix. Also bottom ash particles have a lesser water reten-tion capacity as compared to natural river sand. With the passage oftime, the internally absorbed water by the bottom ash particles isreleased to the concrete. This results in higher loss of water throughbleeding in bottom ash concrete as compared to that in natural sandconcrete. Research data also indicates that water reducing chem-ical admixtures had a profound effect on the amount of bleedingexhibited by the bottom ash concrete.
Andrade et al. (2009) found that the presence of bottom ashas sand replacement in concrete increased the quantity of waterloss by bleeding, the bleeding time and also the water release rate.Higher the bottom ash contents in the concrete the greater thiseffect. As shown in Fig. 8 the total loss of water for 25% and 50%bottom ash content concrete mixes were very close to the controlmix but in case of concrete mixes containing 75% and 100% bottomash there was remarkable increase in loss of water.
Ghafoori and Bucholc (1996) demonstrated that because ofincreased water demand of mixing water, the bottom ash mixturesdisplayed higher degree of bleeding than the control mixture. Theincrease in accumulated bleeding water for bottom ash concrete,over that of control concrete was about 84% in low cement contentmixes and was about 1000% for concrete mixes containing highcement content. The magnitude of bleeding decreased with the useof low dosage of admixture and was approximately 50% of thoseobtained for bottom ash concrete without admixtures. When highdosage of admixtures was used, the magnitude of bleeding was sig-nificantly lower than that of equivalent control concrete. Ghafooriand Bucholc (1997) observed that bleeding varied between 2.79%and 0.54% for concrete mix containing combined bottom ash andsand and was slightly higher than that of control concrete. Whenwater reducing admixture was used, bleeding was nearly identicalto that of control concrete (2.0–0.36%).
3.3. Setting times
The initial setting time of concrete is the moment at which themix shows certain level of stiffness. The investigations carried out
M. Singh, R. Siddique / Resources, Conservation and Recycling 72 (2013) 20– 32 25
Table 4Mix proportions of specimens and measured slump values (Yuksel and Genc, 2007).
Code C kg (lb) W. l (gal) FAkg (lb) M. kg (lb) F. kg (lb) GBFSkg (lb) FBAkg (lb) CA kg (lb) Measured slump,cm (in.)
Ref 350 (772) 167 (44.1) 35 (77.2) 1120 (2469) 720 (1587) 0 0 2.45 (5.40) 6 (2.36)C10 350 (772) 167 (44.1) 35 (77.2) 1120 (2469) 648 (1429) 72 (159) 0 2.45 (5.40) 8 (3.15)C20 350 (772) 167 (44.1) 35 (77.2) 1120 (2469) 576 (1270) 144 (318) 0 2.45 (5.40) 9 (3.54)C30 350 (772) 167 (44.1) 35 (77.2) 1120 (2469) 504 (1111) 216 (476) 0 2.45 (5.40) 11 (4.33)C40 350 (772) 167 (44.1) 35 (77.2) 1120 (2469) 432 (952) 288 (635) 0 2.45 (5.40) 10 (3.94)C50 350 (772) 167 (44.1) 35 (77.2) 1120 (2469) 360 (794) 360 (794) 0 2.45 (5.40) 12 (4.72)K10 350 (772) 167 (44.1) 35 (77.2) 1120 (2469) 648 (1429) 0 72 (159) 2.45 (5.40) 8 (3.15)K20 350 (772) 167 (44.1) 35 (77.2) 1120 (2469) 576 (1270) 0 144 (318) 2.45 (5.40) 9 (3.54)K30 350 (772) 167 (44.1) 35 (77.2) 1120 (2469) 504 (1111) 0 216 (476) 2.45 (5.40) 8 (3.15)K40 350 (772) 167 (44.1) 35 (77.2) 1120 (2469) 432 (952) 0 288 (635) 2.45 (5.40) 7 (92.76)K50 350 (772) 167 (44.1) 35 (77.2) 1120 (2469) 360 (794) 0 360 (794) 2.45 (5.40) 5 (1.97)CK10 350 (772) 167 (44.1) 35 (77.2) 1120 (2469) 648 (1429) 36 (79) 36 (79) 2.45 (5.40) 8 (3.15)CK20 350 (772) 167 (44.1) 35 (77.2) 1120 (2469) 576 (1270) 72 (159) 72 (159) 2.45 (5.40) 9 (3.54)CK30 350 (772) 167 (44.1) 35 (77.2) 1120 (2469) 504 (1111) 108 (238) 108 (238) 2.45 (5.40) 9 (3.54)CK40 350 (772) 167 (44.1) 35 (77.2) 1120 (2469) 432 (952) 144 (318) 144 (318) 2.45 (5.40) 8 (3.15)CK50 350 (772) 167 (44.1) 35 (77.2) 1120 (2469) 360 (794) 180 (397) 180 (397) 2.45 (5.40) 7 (2.76)
N gate;
F
srTcwtpibtbstr
ahirdtd1i32
mwttw1
vtitoioaps
ote: C = cement; W = water; FA = fly ash; M = (4–7 mm [0.157–0.276 in.]) aggreBA = furnace bottom ash; and CA = chemical admixture.
o far in this respect reveal that the addition of bottom ash as sandeplacement in concrete increases the setting times of concrete mix.he main reason of increase in setting time of bottom ash con-rete is the increased demand of mixing water to achieve desiredorkability. The increased mixing water lowers the pH value of
he medium and increases the distance between cement hydrationroducts and thus results in delay or decrease in hydration activ-
ties of the cement particles. The delay in hydration of cement inottom ash concrete results in increase in its initial and final set-ing times. The use of low dosage of water reducing admixtures inottom ash concrete of low cement content has little effect on itsetting times but in case of concrete mix of higher cement content,he setting times decrease with the increase in dosage of watereducing admixtures.
Ghafoori and Bucholc (1996) observed that the average initialnd final setting times for bottom ash concretes were 6.3% and 9.5%igher than the control mixture respectively. When a water reduc-
ng admixtures was incorporated into the mixture, the setting timeemained unaffected in the mixtures of low cement content andecreased slightly in the high cement content concrete. For mix-ures having cement content of 800 lb/yd3, the initial setting timesecreased from 3.3 h to 3.0 h on use of 12.5 oz of admixture per00 lb of cement and 2.5 h when 25 oz per 100 lb of cement were
ntroduced. The final setting times decreased from 4.4 h to 4.0 h to.7 h as dosage rate of admixture increased from 0 oz to 12.5 oz to5 oz respectively.
Ghafoori and Bucholc (1997) observed that in case of concreteix with partial sand replacement, the initial and final setting timesere identical to that of control concrete. As shown in Table 3,
he initial setting times of concrete mixtures containing 50% bot-om ash and 50% sand dropped approximately by 9% on use ofater reducing admixtures. The final setting time dropped by about
3.5%.Andrade et al. (2009) investigated the influence of addition of
arying proportions from 0% to 100% of bottom ash on settingimes of concrete mixes. They observed that there was delay innitial and final setting times of the bottom ash concrete mix-ures. Jaturapitakkul and Cheerarot (2003) found that setting timesf cement paste delayed as the bottom ash replacement levelncreased. At 30% replacement level, initial and final setting times
f cement paste were longer than that of control paste by 23 minnd 30 min respectively. The reduction in Tricalciumsilicate in theaste on replacement of cement by bottom ash resulted into longeretting times.F = fine (0–4 mm [0–0.157 in.]) aggregate; GBFS = granulated blast-furnace slag;
3.4. Plastic shrinkage
The volumetric contractions or plastic shrinkage of the freshconcrete is caused by the loss of water by evaporation from its sur-face. Greater the water evaporation greater is the plastic shrinkage.From the research data published, it can be inferred that bottom ashhas a significant influence in relation to plastic shrinkage of bottomash concrete. Bottom ash concrete exhibits greater dimensional sta-bility as compared to natural sand concrete. The porous particlesof bottom ash act as water reservoir in the concrete mix. With thepassage of time, the absorbed water by the bottom ash particlesis released to the concrete, and thus helps in reducing the plasticshrinkage. Greater bleeding capacity and higher bleeding rate ofthe bottom ash concrete also plays an important role in reducingplastic shrinkage.
Ghafoori and Bucholc (1996) observed that the bottom ash con-crete mixtures exhibited greater dimensional stability than thecontrol mixture. This may be due to increased water requirementfor achieving the similar consistency. Higher bleeding displayed bybottom ash concrete resulted in an average shrinkage of 35% belowthan that of control concrete. With a low dosage of admixture,average early shrinkage of bottom ash mixtures remained approxi-mately the same as that of control concrete. When a high dosage ofadmixture was used, the plastic shrinkage increased but remained13% less than that of the control mixes. Ghafoori and Bucholc (1997)found that early plastic shrinkage of combined bottom ash and sandconcrete was lower than that of control concrete and increasedon use of water reducing admixtures. It was 50% higher than thatof bottom ash concrete. Andrade et al. (2009) concluded that bot-tom ash concrete resulted in lesser total deformations. As shownin Table 5, the maximum deformation for CRT3 mix reduced from0.031 mm/m to 0.009 mm/m on increase in sand replacement levelsin concrete.
4. Properties of hardened coal bottom ash concrete
4.1. Density
The research data reported by various researchers’ show thatthere is an appreciable decrease in unit weight of concrete when
natural sand is substituted with bottom ash. The decrease in den-sity of bottom ash concrete is attributed to the lower unit weightand porous structure of bottom ash as compared to natural sand.Another factor which is also responsible for lower density is the
26 M. Singh, R. Siddique / Resources, Conservation and Recycling 72 (2013) 20– 32
Table 5Maximal plastic shrinkage deformation (Andrade et al., 2009).
Concrete(%)
Maximumdeformation(mm/m)
Time to maximumdeformation after initialsetting time (h)
0 0.031 2.7CRT3 25 0.015 6.8
50 0.009 10.075 0.009 1.8
100 0.013 10.0
CRT4 25 0.005 7.850 0.088 6.2
hlpr
hao
tiptrmotdbTww
7qigmida
cc1
0
1000
2000
3000
4000
5000
6000
0 20 40 60 80 100 120 140 160 180
Com
pre
ssiv
e S
trength
(psi
)
Curing Age (Days)
Bottom ash (B.A.)
50% B.A. + 50% N.S.
50/50 +12 .5 oz. ADM
Natural Sand
75 0.088 4.1100 0.065 3.5
igher demand of mixing water by the bottom ash concrete whicheaves behind more number of pores, larger size pores and thusorous structure. As the percentage of lighter bottom ash as sandeplacement in concrete increases the unit weight decreases.
Andrade et al. (2007) demonstrated that the use of bottom ashaving specific gravity of 1.67 g/cm3 and fineness modulus of 1.55s sand replacement in concrete resulted in decrease in densitiesf concrete by 25% from 2170 kg/m3 to 1625 kg/m3.
Kim and Lee (2011) studied the effect of fine and coarse bot-om ash on density of concrete. The mix proportions used in theirnvestigations consisted 143 kg/m3 of silica fume, 14 kg/m3 of superlasticizer, 187 kg/m3 of water and 607 kg/m3 of cement in allhe specimens with varying percentages of bottom ash as sandeplacement, coarse aggregate replacement and combined replace-ent of both sand and coarse aggregate. As shown in Fig. 9, they
bserved that densities of hardened concrete decreased linearly ashe replacement ratio of fine and coarse bottom ash increased. Theensity of high strength concrete was less than 2000 kg/m3 whenoth 100% fine bottom ash and 100% coarse bottom ash were used.he decrease in density was 109 kg/m3 (4.6%) and 228 kg/m3 (9.6%)hen sand was replaced with fine bottom ash and coarse aggregateas replaced with coarse bottom ash respectively.
Topcu and Bilir (2010) investigated the effect of bottom ash on days and 28 days densities of mortars having proportions of fixeduantities of 500 kg/m3 cement, 3 kg/m3 high range water reduc-
ng admixtures and varying percentages of bottom ash of specificravity of 1.39 g/cm3 as natural sand replacement in all the speci-ens. They observed that the weight of specimens decreased with
ncrease in bottom ash content. The unit weight at the age of 7ays and 28 days ranged between 1.23 kg/dm3 and 2.23 kg/dm3
nd 1.35 kg/dm3 and 2.28 kg/dm3 respectively.Ghafoori and Bucholc (1996) observed that bottom ash con-
retes displayed lower unit weight when compared to theontrol sample. One day unit weight of bottom ash concrete was41.3 lb/ft3 as compared to 146.3 lb/ft3 of control sample. They
1900
2000
2100
2200
2300
2400
2500
0.0 20.0 40.0 60.0 80.0 100.0
Den
sity
[K
g/m
3 ]
Replacement of bottom ash (vol. %)
FBA replacement
CBA replacement
FBA+CBA replacement
Fig. 9. Effect of bottom ash on density of concrete (Kim and Lee, 2011).
Fig. 10. Compressive strength of concrete containing 500 lb/yd3 cement (Ghafooriand Bucholc, 1997).
observed that usage of water reducing admixtures has influence onthe unit weight of bottom ash concrete. The unit weight increasedby an average of 0.8% when dosage of 12.5 oz per 100 lb of cementwas used and an additional 0.25% when high admixture dosage of25 oz per 100 lb of cement was applied. Arumugam et al. (2011)observed that with increasing replacement of fine aggregate withpond-ash, the average density of concrete shows linear reductiondue to lower specific gravity.
4.2. Compressive strength
The strength development of concrete is influenced by porosityof hydrated paste which is controlled by water/cement ratio and thepresence of bond cracks at the interface of aggregate and hydratedpaste. The strength of individual constituent material of concretealso has influence on the strength of concrete mix. The investiga-tions show that bottom ash particles are more porous and weakthan natural sand particles. The demand of mixing water increasedon its use in concrete as sand replacement. The higher demand ofwater is responsible for increased volume of all pores: pores left bywater, fissures formed by bleeding etc. The higher water cementratio results in low density of bottom ash concrete mix. Since bot-tom ash concrete has higher bleeding, there are more chances ofmore bleeding water getting trapped below the aggregates. Thistrapped water results in the formation of the more number ofsmall pores close to the aggregate surfaces. These pores preventthe excellent bonding of cement paste with the aggregate. There-fore the transition zone between the aggregate and cement pastebecomes weak and porous which ultimately results in reductionin strength of bottom ash concrete mix. The weak microstructureobtained with the use of bottom ash is responsible for the decreasein compressive strength.
Ghafoori and Bucholc (1997) found that compressive strength ofcombined bottom ash and sand mix was lower than that of controlconcrete. The average differences in compressive strength at theage of 3 days and 7 days were 12% and 14.5% respectively. As shownin Fig. 10, when high range water reducing admixture was used incombined mixture, compressive strength surpassed those of con-trol sample at all levels of age. At 28 days of age the compressivestrength increased by 24%.
Andrade et al. (2007) observed that concrete mixes preparedwith addition of bottom ash as equivalent volume replacement,correcting bottom ash quantities according to the moisture con-tent showed very significant loss in compressive strength. However
in case of concrete mix prepared with the addition of bottom ashas non equivalent volume replacement, without correcting bottomash quantities according to the moisture content the compressive
M. Singh, R. Siddique / Resources, Conserv
0
20
40
60
80
100
0.0 25.0 50.0 75.0 100.0
Com
m. S
tr.[
Mpa]
Replacement of of FBA(%)
7 d
28 d
F2
sc
tcwcidwf
basbacFmams
1sTodom
s
F2
ig. 11. Effect of bottom ash on compressive strength of concrete (Kim and Lee,011).
trength of bottom ash concrete was similar to that of referenceoncrete.
Shi-Cong and Chi-Sun (2009) demonstrated that at a fixed W/C,he compressive strength decreased with the increase in the FBAontent at all the ages. However when concrete was designedith a fixed slump range, bottom ash concrete showed higher
ompressive strength than that of the control at all the ages. Themprovement in compressive strength could be attributed to theecrease in free W/C due to the fact that for a given slump, the highater absorption properties of FBA lead to reduction in demand of
ree water to produce the target slump value.Kim and Lee (2011) investigated the effect of fine and coarse
ottom ash on compressive strength at 7 days and 28 days curingge. As demonstrated in Fig. 11, they observed that compressivetrengths were not strongly affected by the replacements of fineottom ash. Sani et al. (2010) found that the compressive strengtht day 3 for 20% and 30% sand replacement levels is the highestompared to other washed bottom ash concretes. As presented inig. 12, washed bottom ash sand concrete with 30% sand replace-ent level recorded highest compressive strength at all the curing
ges up to 60 days. They concluded that 30% of WBA as sand replace-ent in concrete is the optimum amount in order to get favorable
trength, environment saving and a lowering cost.Topcu and Bilir (2010) examined the effect of addition of
0–100% bottom ash as fine aggregate replacement on compres-ive strength of cement mortar at the age of 7 and 28 days.hey observed that there was decrease in compressive strengthf cement mortar with the increase of bottom ash content and theecrease rate in 7 days compressive strength was similar to thatf 28 days compressive strength. Compressive strength values of
ortar were lower than that of control sample.Ghafoori and Bucholc (1996) observed that compressivetrength of bottom ash concrete was lower than that of control
0
5
10
15
20
25
30
35
40
45
50
0% 10 % 20 % 30 % 40 % 50 %
Co
mp
ress
ive
Str
eng
th(N
/mm
2)
% age of WBA
Compress ive Streng th vs Perce ntage o f WBA
3 DAYS 7 DAYS 28 DAYS 60 DAYS
ig. 12. Effect of % age replacement of WBA on compressive strength (Sani et al.,010).
ation and Recycling 72 (2013) 20– 32 27
concrete but with increased curing age compressive strength wasalmost same. The mean compressive strengths of bottom ash con-crete were 30% and 25% lower than those of control concrete atthe curing age of 3 days and 7 days respectively. This differencedropped to 17% and 7% at 28 days and 180 days curing age. When alow dosage of admixture was used, compressive strength of bottomash concrete at all levels of cement content improved. Compressivestrength of bottom ash concrete at the age of 28 days increased bynearly 20% than that of the mix produced without admixture andby 3.5% than that of control concrete. However when a high rangewater reducing admixture was used in combined mixture of 50%bottom ash and 50% natural sand, compressive strength surpassedthose of control mixture.
Ghafoori and Cai (1998a,b) demonstrated that compressivestrength development of bottom ash roller compacted concrete issimilar to that of conventional concrete. Nearly 75% of the 28 daysstrength attained after 7 days of curing. For mixtures containing 9%,12% and 15% cement, 90 days compressive strength exceeded the28 days compressive strength by an average of 19%, 15% and 12%respectively. At end of 180 days curing, the 28 days compressivestrength was surpassed by 26%.
Yuksel and Genc (2007) investigated the possibilities of usinggranulated blast-furnace slag, bottom ash and their combinationas fine aggregate in concrete. They found that 28 days compres-sive strength decreased with increase in bottom ash content andmaximum decrease for 50% sand replacement was 31.8%. With 10%sand replacement by bottom ash, 90 days compressive strength ofconcrete decreased by 6.9%.
Aramraks (2006) demonstrated that the compressive strengthof 50% and 100% replacement bottom ash concrete was found to beapproximately 20–40% lower than that of natural sand mixtures.
Aggarwal et al. (2007) investigated the effect of bottom ash withvarying levels from 20% to 50% as sand replacement on propertiesof concrete and observed that compressive strength of bottom ashconcrete specimens was lower than control concrete specimens atall the ages. The strength difference between bottom ash concretespecimens and control concrete specimens became less distinctafter 28 days. Compressive strength of bottom ash concrete con-tinued to increase with the age for all the bottom ash contents.Mix containing 30% and 40% bottom ash, at 90 days, attained thecompressive strength equivalent to 108% and 105% of compressivestrength of normal concrete at 28 days.
Bai et al. (2005) studied the effect of bottom ash as fine aggregatereplacements varying from 0% to 100% in concrete on compressivestrength at the age of 3, 7 and 28 days at the fixed water cementratio and slump range. As presented in Fig. 13, they observed that atfixed W/C ratio, compressive strength decreased with the increasein bottom ash content in concrete mix, while at fixed slump range of30–60 mm, there was improvement in compressive strength overthat of control concrete at all the ages. The improvement in com-pressive strength could be attributed to water reduction effect ofbottom ash.
Arumugam et al. (2011) observed that concrete samples having20% sand replaced with pond-ash showed improved compressivestrength over the control sample at all the curing ages. Compres-sive strength reduced with further addition of pond-ash as sandreplacement from 20%.
Chun et al. (2008) noticed that the strength of concrete dif-fered by the content of pond-ash collected from each disposal site.With increase in content of pond-ash, there was relatively greaterincrease in compressive strength compared to normal concrete andsuch trend might be a consequence of decreased water/cement
ratio induced by the absorption of mixing water.Kurama and Kaya (2008) studied the effect of bottom ash aspartial replacement of cement in concrete and observed that com-pressive strength increased with increase in amount of bottom ash
28 M. Singh, R. Siddique / Resources, Conservation and Recycling 72 (2013) 20– 32
0
20
40
60
3 7 28
Co
mp
ress
ive
Str
eng
th(N
/mm
2)
Age (days)
FBA Level 0% 30% 50% 70% 100%
(a) W/C 0.45
0
20
40
60
3 7 28
Com
pre
ssiv
e S
tren
gth
(N/m
m2)
Age (Days)
FBA Level 0% 30% 50% 70% 100%
F0
rsasco
4
flscflcuwas
tscta7Fis
oost
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
10 20 30 40 50 60 70 80 90 10 0
Fle
xu
ral
stre
ss (
MP
a)
No of Days
M1 (0%)
M2(20 %)
M3(30 %)
M4(40 %)
M5(50 %)
(b) W/C 0. 55
ig. 13. Compressive strength at fixed W/C (Bai et al., 2005). (a) W/C 0.45; (b) W/C.55.
eplacement up to 10%. At 10% replacement level, 56 days compres-ive strength increased by 5%, compared to control concrete. Thedditions of higher ash than 10% lead to decrease in compressivetrength at lower age such as 7 days and 28 days. However 56 daysompressive strength at all replacement levels was higher than thatf control mix except at 25% replacement level.
.3. Flexural strength
Bottom ash concrete displays similar trend in development ofexural strength and compressive strength. The published datahows that on inclusion of bottom ash as sand replacement in con-rete, flexural strength of concrete decreased at all the ages. Theexural strength of concrete mainly depends upon the quality ofement paste in concrete mix. Bottom ash being porous material,pon its use as sand replacement in concrete, the paste becomeseak and porous. Volume of all pores in concrete increases
nd as such bottom ash concrete mix displays lower flexuraltrength.
Ghafoori and Bucholc (1996) found that flexural strength of bot-om ash mixtures was lower than that of reference sample. When auper plasticizer admixture was incorporated into the bottom ashoncrete, flexural strength equaled or slightly exceeded that of con-rol concrete. The strength improvement over that of the bottomsh concrete without super plasticizer was 29.76%, 20.3%, 11.4% and.5% as the cement content increased from 500 lb/yd3 to 800 lb/yd3.lexural strength of bottom ash concrete decreased with increasen bottom ash content but with the addition of super plasticizer, itlightly improved at almost all the curing ages.
Yuksel and Genc (2007) demonstrated that flexural strength
f bottom ash concrete is lower than that of control mix. Theybserved that for 10% bottom ash replacement, the decrease in ten-ile strength is almost 10% and with replacement more than 10%,here was almost no change in tensile strength values of bottomFig. 14. Flexural strength of the concrete with age (Aggarwal et al., 2007).
ash concrete compared to control concrete. Topcu and Bilir (2010)observed that when bottom ash was used as sand replacement,there was decrease in flexural strength with the increase of bottomash content and the decrease rate in 7 days flexural strength wassimilar to that of 28 days flexural strength. The values of flexuralstrength were lower than that of control sample at all the curingages.
Ghafoori and Cai (1998a,b) studied the effect of bottom ashincorporating it in roller compacted concrete on its mechanicalproperties. They investigated that flexural strength of bottom ashconcrete increased with the curing age and at the end of 90 daysit surpassed its 28 days strength by about 17%. The ratios of flex-ural strength and compressive strength are fairly uniform with anaverage value of 1.55.
Kim and Lee (2011) demonstrated that the flexural strengthof concrete decreased linearly as the replacement ratio of fineand coarse bottom ash was increased. The modulus of rupturedecreased by 19.5% and 24.0% on 100% replacement of normalaggregates with fine and coarse bottom ash respectively.
Aggarwal et al. (2007) found that flexural strength of bottom ashconcrete specimens were lower than control concrete specimensat all the ages. As shown in Fig. 14, they observed that at 90 days,concrete mix containing 30% and 40% bottom ash, attained flexuralstrength in the range of 113–118% of flexural strength of normalconcrete at 28 days. Arumugam et al. (2011) observed that pond-ash concrete showed similar behavior in flexural strength to that ofcompressive strength. Concrete samples having 20% sand replacedwith pond-ash showed improved flexural strength over the controlsample at all the curing ages. With the increase in sand replacementlevel from 20%, flexural strength reduced.
Kurama and Kaya (2008) observed that 28 days flexural strengthof bottom ash concrete was almost equal to that of control speci-men. At the curing age of 56 days flexural strength of bottom ashconcrete exceeded that of control sample, except mix containing25% cement replacement. The reduction in strength of mix con-taining 25% bottom ash is due to low activity of bottom ash at theearly curing ages.
4.4. Split tensile strength
The split tensile strength of bottom ash concrete progresses inthe similar manner as in the case of normal concrete. Bottom ashhas more influence on the development of split tensile strengththan compressive strength of concrete. When bottom ash is usedas sand replacement in concrete there is reduction in split tensile
strength. One of the reasons for reduction in tensile strength isthe increase in porosity and distribution of pores in bottom ashconcrete. The chemical admixtures reduce the water requirement
M. Singh, R. Siddique / Resources, Conservation and Recycling 72 (2013) 20– 32 29
F(
ar
mcdmts6acistb
csdscscao0
ts
F
0.0
10.0
20.0
30.0
40.0
50.0
0.0 20.0 40.0 60.0 80.0 100.0
Modulu
s of
ela
stic
ity [
GP
a]
Replacement of bottom ash (vol. %)
FBA replacement
CBA replacement
FBA+CBA replacement
ig. 15. Splitting tensile strength of concrete containing 800 lb/yd3 cementGhafoori and Bucholc, 1996).
nd improve the microstructure of bottom ash concrete and henceesult in improvement in the splitting tensile strength.
Yuksel and Genc (2007) observed that up to 10% sand replace-ent, there was no change in split tensile strength and it decreased
onsiderably with increase in bottom ash content. The maximumecrease in the split tensile strength was 58% for 50% FBA replace-ent. Ghafoori and Bucholc (1996) in their investigation observed
hat bottom ash concrete displayed an identical splitting tensiletrength compared to control concrete and in case of mixture with00 pounds of cement or higher, it exceeded the reference mixturet all the ages of curing. The splitting tensile strength of bottom ashoncrete improved by 12% above reference concrete, when chem-cal admixtures was used. On use of water reducing admixtures,plitting tensile resistance of bottom ash concrete improved at allhe ages. Fig. 15 presents the splitting tensile strength developmentehavior of bottom ash concrete.
Ghafoori and Cai (1998a,b) demonstrated that when the per-entage of cement content was kept same, the splitting tensiletrength decreased with increase in bottom ash content. After 7ays curing, concrete gained 65–76% of its 28 days splitting ten-ile for the mixtures containing 9–15% cement content and 50–60%oarse aggregate. At the end of 90 days and 180 days of curing,plitting tensile strength of mixtures containing 15%, 12%, and 9%ement content surpassed its 28 days strength by 11%, 20%, and 18%nd 18%, 32%, and 36% respectively. 28 days and 180 days ratiosf splitting tensile to compressive strength range from 0.101 to.153.
Aggarwal et al. (2007) found that flexural strength of bot-om ash concrete specimens were lower than control concretepecimens at all the ages. As shown in Fig. 16, at 90 days of age,
0
1
2
3
4
10 20 30 40 50 60 70 80 90 100
Spli
ttin
g t
ensi
le s
tres
s (
MP
a)
No of Days
M1
M2
M3
M4
M5
ig. 16. Splitting tensile strength of the concrete with age (Aggarwal et al., 2007).
Fig. 17. Effect of bottom ash on modulus of elasticity of concrete (Kim and Lee,2011).
bottom ash concrete attains splitting tensile strength in the rangeof 121–126% of splitting tensile strength of normal concrete at 28days. Arumugam et al. (2011) observed that Split tensile strength ofconcrete of samples containing 20% WBA as sand replacement washigher than the control concrete. Split tensile strength decreasedwith increase in sand replacement level from 20%.
4.5. Microstructure
Yuksel and Genc (2007) investigated that when natural sandis replaced with bottom ash in the concrete, the microstructurechanges its network structure. Instead of irregular grains in case ofnatural river sand, the grains becomes circular and pores becomesmaller and more distributed on use of bottom ash. As the replace-ment of sand with bottom ash increases, the detachment of grainsin the network structure increases. These discrete grains are themicrostructure of bottom ash.
4.6. Modulus of elasticity
From the literature published it is evident that use of bottom ashstrongly affects the modulus of elasticity of concrete. With increasein level of sand replacement with bottom ash in concrete the mod-ulus of elasticity concrete decreases. Bottom ash particles are lessstiff and dense than natural sand particles and its use in the con-crete results into weak and porous paste which results in reductionof modulus of elasticity of concrete. The application of chemicaladmixtures results in improvement in the modulus of elasticity ofconcrete because of lowering the water cement ratio.
Ghafoori and Bucholc (1996) found that bottom ash concretemixtures with all unit weights of cement displayed lower modu-lus of elasticity than that of reference sample. Kim and Lee (2011)found that the modulus of elasticity decreased with the increase inreplacement of fine and coarse bottom ash aggregates. As shownin Fig. 17, when 100% sand was replaced with fine bottom ash, themodulus of elasticity of concrete decreased by 15.1% from 41.1 MPato 34.9 MPa. It was 31.8 MPa i.e. 77.5% of control specimen, when100% coarse bottom ash was used as coarse aggregate. Topcu andBilir (2010) observed that Modulus of elasticity of bottom ash con-crete decreased from 60 GPa to 17 GPa with the increase from 0% to60% of bottom ash content. The Values of Modulus of elasticity ofsamples incorporating 60–100% of bottom ash were closer to eachother. The porous structure obtained on use of bottom ash in con-
crete is responsible for decrease in modulus of elasticity. Andradeet al. (2009) demonstrated that the modulus of elasticity of con-crete at 28 curing age, decreased from 25.8 GPa to 8.9 GPa whenthe replacement ratio of bottom ash increased to 100%.
30 M. Singh, R. Siddique / Resources, Conservation and Recycling 72 (2013) 20– 32
0
200
400
600
800
1000
0 25 50 75 100 125 150
Dry
ing S
hri
nkag
e (x
10
-6 )
Age (Days)
FBA Level0% 30% 50%
75% 100%
W/C 0.45
(a) W/C 0. 45
0
200
400
600
800
1000
0 25 50 75 10 0 12 5 15 0
Dry
ing
Sh
rin
kag
e (x
10
-6 )
Ages (Days)
FBA Level0% 30% 50%
75% 100%
W/C 0.55
(b) W/C 0. 55
F
4
ppiao
0tiptostsd
ycvcpocc2
Table 6Chloride permeability test of concrete at 56 days (Aramraks, 2006).
Mix No Bottom ash W/C Electrical Chloride
F.M % by wt. Charge (Coulomb) Penetrability
1 – 0 0.6 4178 High2 1.83 50 0.81 3040 Medium3 1.83 100 0.89 1975 Low4 3.07 50 0.74 3224 Medium5 3.07 100 0.85 2080 Low
ig. 18. Drying shrinkage at fixed W/C (Bai et al., 2005). (a) W/C 0.45; (b) W/C 0.55.
.7. Drying shrinkage
A limited literature has been published on drying shrinkageroperties of bottom ash concrete. It is believed that the porousarticle structure of bottom ash is beneficial for reducing the dry-
ng shrinkage of concrete. It is considered that the porous bottomsh particles slowly release the moisture during the drying phasef concrete and therefore result in reduced shrinkage.
Bai et al. (2005) observed that at fixed W/C ratio of 0.45 and.55, drying shrinkage values of all bottom ash concrete were lowerhan that of control concrete, while at fixed workability, the dry-ng shrinkage values were higher. At fixed W/C, the quantity oforous material in concrete increases with the increase of bot-om ash content, which slowly release the water during dryingf concrete and thus result in reduced drying shrinkage. At fixedlump range, with the increase in Bottom ash content, they foundhat drying shrinkage increased contrary to the decrease in dryinghrinkage on reduction of free water content. Fig. 18 presents therying shrinkage behavior of bottom ash concrete.
Ghafoori and Cai (1998a,b) in their study found that the oneear drying shrinkage strain of bottom ash roller compacted con-rete varies from 203 × 16−6 to 298 × 10−6 nearly half that ofibratory placed conventional concrete mixtures. Similar to that ofonventional concrete, drying shrinkage of bottom ash roller com-acted concrete increased with time. Ghafoori and Bucholc (1996)bserved that despite higher water cement ratio, bottom ash con-
rete displayed less drying shrinkage in comparison with that ofontrol concrete. Swelling properties of bottom ash concrete were00% higher than the volume increase exhibited by the equivalent6 3.07 50 0.6 2621 Medium7 3.07 100 0.80 1860 Low
natural sand concrete. Water reducing admixtures had negligibleeffect on the swelling characteristics of the bottom ash.
Shi-Cong and Chi-Sun (2009) demonstrated that at the fixedslump range, the drying shrinkage values of all the FBA concretesare lower than that of the control. This was due to the fact thatwith the increase in FBA content, the required free water contentdecreased.
5. Durabilty properties of coal bottom ash concrete
5.1. Permeability
The permeability of concrete depends upon the size, distributionand continuity of pores present in cement paste and permeability ofaggregates. The reports published by various researchers indicatethat bottom ash concrete has higher permeability as compared tonatural sand concrete. With the increase in bottom ash contentin concrete its permeability increases. The main factors respon-sible for the increased permeability of bottom ash concrete areporous microstructure of bottom ash, increased demand of mixingwater and higher loss of water through bleeding. The replacementof sand with bottom ash in concrete results in porous microstruc-ture. Due to increased water demand and bleeding in bottom ashconcrete, number of pores and their continuity increases. Concreteswith lower water to binder ratio and longer curing age’s exhibitsmarginally lower permeability.
Ghafoori and Bucholc (1996) found that as per AASHTO T-277specifications, the chloride permeability of bottom ash concrete ishigher than that of control concrete. The permeation of chlorideions into the bottom ash concrete decreases drastically when a lowdosage of super plasticizer is used. The bottom ash concrete with-out admixtures allowed on average 120% greater current flow thanthe control concrete and with the use of admixture it reduced to61% above the control concrete. The results of accelerated chloridepermeability of their research show that bottom ash concrete ismore permeable than the control concrete at all levels of cementcontents.
Aramraks (2006) found that Chloride permeability of bottomash concrete was better than that of normal concrete. As shownin Table 6, the concrete mix of 100% coarse grain (passing no. 4and retaining on no. 50 standard sieves) bottom ash replacementwith 2% super plasticizer showed the lowest chloride permeability.Shi-Cong and Chi-Sun (2009) demonstrated that at the same W/C,the resistance to chloride-ion penetration of the concrete mixesdecreased with increasing percentages FBA replacement of riversand. The more free water available in bottom ash concretes thanthe control concrete lead to a looser microstructure.
5.2. Freeze–thaw resistance
Limited research data in this respect has been reported whichmay not be sufficient to draw conclusion. The reported researchdata indicates that bottom ash concrete exhibits resistant to
M. Singh, R. Siddique / Resources, Conservation and Recycling 72 (2013) 20– 32 31
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
0 20 40 60 80 10 0 12 0 14 0 16 0 18 0
Ex
pan
sio
n (
%)
Age (Days)
Natural Sand (N.S.)
50% B.A./N.S.
Bo�om ash (B.A.)
50% B.A. + ADM
Fig. 19. Sulfate expansion of natural sand and bottom ash concretes containing6
fcf
bfim9lBtdmstitei
5
iicriaslwwcauetccs
aobeio
Table 7Weight loss of concrete surface by abrasion (Aramraks, 2006).
Mix No Bottom ash W/C Weight loss (gm/sq cm)
F.M % by wt. 28 days 56 days
1 – 0 0.6 0.0535 0.03152 1.83 50 0.81 0.1305 0.08083 1.83 100 0.89 0.1758 0.10324 3.07 50 0.74 0.1318 0.07855 3.07 100 0.85 0.1681 0.10516 3.07 50 0.6 0.0993 0.0649
00 lb/yd3 cement (Ghafoori and Bucholc, 1997).
reezing and thawing similar to that of the normal control con-rete. The water reducing admixtures have insignificant effect onreezing and thawing resistant of bottom ash concrete.
Ghafoori and Cai (1998) observed that the non air entrainedottom ash RCC performs well in an environment with repeatedreezing and thawing cycles. They reported that the tested spec-mens completed 300 rapid freezing and thawing cycles with a
aximum mass loss of 2.3% and a minimum durability factor of1.2%. Both cumulative mass loss and durability factor exhibited
inear relationship with freezing and thawing cycles. Ghafoori anducholc (1996) observed that despite a higher W/C Ratio, bot-om ash concrete containing cement content of 356 kg/m3 or moreisplayed a remarkable performance when exposed to an environ-ent with repeated freezing and thawing cycles. The addition of
uper plasticizers has minimal effect on freezing and thawing resis-ance of the bottom ash concrete. Chun et al. (2008) noticed thatncreased content of pond-ash leads a relatively lower freezing andhawing resistance than normal concrete, while the trend of low-ring resistance was mainly due to a decrease in air content and annfluence of absorption water.
.3. Resistance to sulfate attack
Ghafoori and Cai (1998a,b) studied the effect of bottom ashncorporation in concrete on its long term durability. From thenvestigation carried out by them they concluded that rollerompacted concrete containing dry bottom ash exhibit excellentesistance to external sulfate attacks. During first 28 days of curingn sodium sulfate solution, the bottom ash RCC prisms displayed
mean expansion value of 0.0017%. After a year exposure to 5%odium sulfate solution, RCC containing bottom ash experience aength change ranging from 0.00203% to 0.0388%. No mass loss
as detected during this period. 180 days compressive strength ofater cured samples was identical to that of the equivalent samples
ured in a 5% sodium sulfate solution for 6-month period. Ghafoorind Bucholc (1996) observed that bottom ash concrete and nat-ral sand concrete exhibit similar expansion characteristics underxternal sulfate attack. They found that after 6 months of exposure,he largest expansion of bottom ash concrete containing 600 lb/m3
ement without admixture was 0.035%. However bottom ash con-rete containing 800 lb/m3 cement displayed expansion almostimilar to that of control concrete.
Ghafoori and Bucholc (1997) observed that expansion of bottomsh concrete when subjected to sulfate attack was higher than thatf control concrete. As shown in Fig. 19, bottom ash and combined
ottom ash and sand concrete exhibited largest expansion. How-ver when cement content increased to 800 lb/yd2, expansions wasdentical to one another. This may be due to improvement in qualityf paste of the matrix.7 3.07 100 0.80 0.1452 0.0855
5.4. Abrasion resistance
Published literature indicates that bottom ash concrete showdecreased abrasion resistance. Resistance to abrasion is greatlyinfluenced by the cementitious paste and fine aggregate of top mor-tar, which is highly susceptible to moisture. Bottom ash particlesare porous and less stiff as compared to dense and stiffer particlesof natural sand. Due to its porous microstructure, bottom ash ismore venerable to moisture than natural sand, as such its use inconcrete as sand replacement result in reduction in abrasion resis-tance. However with the addition of water reducing admixtures inbottom ash concrete, it’s the abrasion resistance increases.
Ghafoori and Cai (1998a,b) found that resistance to abrasionof RCC containing bottom ash is far superior under air-dry con-ditions to that obtained under wet conditions. For RCC containing9% cement, the depth of wear under wet conditions was 7.25 timesof those under dry conditions. This ratio dropped to 6.42 and 6.00when cement content increased to 12% and 15% respectively. Thisindicates that higher cement content produces stronger paste andsmoother surface layer.
Ghafoori and Bucholc (1996) found that the bottom ash concretewas 40% worse than the control concrete in abrasion resistance.However, with the use of water reducing admixtures, a superiorabrasion resistant bottom ash concrete was produced.
Aramraks (2006) noticed that the weight loss of normal concretesurface by abrasion test was 53–30% of weight loss of bottom ashconcrete. The mix of 50% coarse grain (passing no. 4 and retaining onno. 50 standard sieves) bottom ash replacement and with the useof 2% super plasticizer was the most suitable mix regarding bothabrasion resistance and compressive strength properties. Table 7presents the weight loss of concrete surface at the age of 28 daysand 56 days.
5.5. Behavior of bottom ash concrete under high temperature
The main factors which affect the fire resistance of concrete arethe type of aggregate and cement used in its composition, temper-ature and duration of fire, size of structural member and moisturecontent of concrete. At temperature of about 500 ◦C calcium sili-cate hydrate in hardened cement paste starts to dehydrate and atabout 900 ◦C calcium silicate hydrate decompose completely. Dueto dehydration of C–S–H gel concrete loses its compressive strengthand modulus of elasticity and cracks develop. When the tempera-ture exceeds 100 ◦C, water present in concrete starts vaporizingand builds up pressure within the concrete. The excessive inter-nal pressure results in spalling of concrete. At high temperature,Quartz based aggregate increase in volume where as limestonebased aggregate began to decompose.
Bottom ash is porous material and its inclusion as sand replace-ment in concrete results in porous structure. The higher porosity ofconcrete can be considered beneficial when concrete is subjectedto high temperature. Yuksel et al. (2011) investigated the influence
32 M. Singh, R. Siddique / Resources, Conserv
0
10
20
30
40
50
60
0 10 20 30 40 50
Com
pre
ssiv
e st
rength
(M
Pa)
Replacement ratio (%)
C Series after high temp
C Series before high temp
K Series after high temp
KSeries before high temp
Fs
oroillrFurwattctr
6
aioaaiscicoiet
•
•
•
ig. 20. Alteration of compressive strength before and after high temperature expo-ure (Yuksel et al., 2011).
f high temperature on properties of bottom ash concrete. In theiresearch work concrete samples were subjected to 800 ◦C at the agef 90 days. They observed that loss in weight increased with thencrease in replacement levels. At 50% replacement level, weightoss was 6% as compared to 4.5% weight loss at 0% replacementevel. Residual strength decreased with increase in replacementatio. Fig. 20 shows the residual strength of bottom ash concrete.or samples containing 50% bottom ash as sand replacement, resid-al strength decreased by 74% as compared to decrease of 63% ofeference concrete. Surface crack pattern in bottom ash concreteas similar to that of in reference concrete. Crack widths in bottom
sh were narrower than the reference concrete. They also observedhat residual dynamic modulus of elasticity decreased by about 10imes with respect to initial dynamic modulus of elasticity. Theyonsidered that when concrete was subjected to high temperature,he decrease in dynamic modulus of elasticity was due to the dete-ioration of concrete matrix and not due to inclusion of bottom ash.
. Observations and conclusions
The properties of fresh as well as hardened concrete are closelyssociated with the characteristics and relevant proportioning ofts constituent materials. The research reports show that inclusionf bottom ash as sand replacement in concrete influences the work-bility, setting times, loss of water through bleeding, bleeding ratend plastic shrinkage of fresh concrete and density, strength, poros-ty, durability of hardened mass. The published research literaturehows that the strength development pattern of bottom ash con-rete is similar to that of conventional concrete but there is decreasen strength at all the curing ages. The decrease in strength of con-rete is mainly due to higher porosity and higher water demandn use of bottom ash in concrete. The compressive strength can bemproved by reducing the water demand by using super plasticiz-rs. From the review of published research work, it is concludedhat:-
Bottom ash is the potential viable material to be used as fineaggregate to produce durable concrete.
Its use as fine aggregate in concrete will help in alleviating thepotential problem of dwindling natural resources.Its use will also help in protecting the environment surroundingthe thermal power plants.ation and Recycling 72 (2013) 20– 32
Till date a very limited research work on bottom ash as fineaggregate in concrete has been carried out. Therefore furtherinvestigations to study the ways in which bottom ash as sandreplacement in concrete affects the rheological properties of freshconcrete, mechanical and durability properties of hardened massare needed.
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