The Implementation of Wood Waste Ash as a Partial Cement Replacement Material

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Please cite this article in press as: Cheah CB, Ramli M. The implementation of wood waste ash as a partial cement replacement material in the

production of structural grade concrete and mortar: An overview. Resour Conserv Recy (2011), doi: 10.1016/j.resconrec.2011.02.002

ARTICLE IN PRESSGModel

RECYCL-2381; No.of Pages 17

Resources, Conservation and Recycling xxx (2011) xxxxxx

Contents lists available atScienceDirect

Resources, Conservation and Recycling

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / r e s c o n r e c

Review

The implementation of wood waste ash as a partial cement replacement material

in the production of structural grade concrete and mortar: An overview

Cheah Chee Ban , Mahyuddin Ramli

School of Housing, Building and Planning, Universiti Sains Malaysia, 11800 Penang, Malaysia

a r t i c l e i n f o

Article history:

Received 7 September 2010

Received in revised form 3 February 2011Accepted 10 February 2011

Keywords:

Cement replacement material

Wood waste ash

Blended cement

Hazardous waste management

Green concrete material

Reuse and recycling

a b s t r a c t

Thetimber manufacturingand powergeneration industryis graduallyshifting towards theuse of biomass

such as timber processing waste for fuel and energy production and to help supplement the electri-

cal energy demand of national electric gridlines. Though timber processing waste is a sustainable and

renewable source of fuel for energy production, the thermal process of converting the aforementioned

biomass into heat energy produces significant amounts of fine wood waste ash as a by-product material

which, if not managed properly, may result in serious environmental and health problems. Several cur-

rent researches hadbeen carried out to incorporate wood waste ash as a cementreplacementmaterialin

the production of greener concrete material and also as a sustainable means of disposal for wood waste

ash. Results of the researches have indicated that wood waste ash can be effectively used as a cement

replacement material for the production of structural grade concrete of acceptable strength anddurabil-

ity performances. This paper presents an overview of the work carried out by the use of wood waste ash

as a partial replacement of cement in mortar and concrete mixes. Several aspects such as the physical

and chemical properties of wood waste ash, properties of wood waste ash/OPC blended cement pastes,

rheological, mechanical and the durability properties of wood waste ash/OPC concrete mix are detailed

in this paper.

2011 Elsevier B.V. All rights reserved.

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

1.1. Factors influencing the quantity and quality of wood waste ash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

1.2. Uses of wood waste ash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

2. Physical properties of wood waste ash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

3. Chemical properties and leachate of wood waste ash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

3.1. Chemical composition and phases of wood waste ash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

3.2. Chemical properties of leachate from wood waste ash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

4. Properties of wood waste ash blended cement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

4.1. Standard consistency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

4.2. Initial and final setting time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

4.3. Soundness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

4.4. Calorimetric and heat evolution characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

4.5. Microstructure of cement paste matrix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

5. Rheological properties of wood waste ash/OPC concrete and mortar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

6. Bulk density and mechanical strength of hardened wood waste ash/OPC concrete and mortar. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

6.1. Bulk density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

6.2. Compressive strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

6.3. Split tensile strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

6.4. Flexural strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

Corresponding author. Tel.: +60 0164846502; fax: +60 046576523.

E-mail addresses:[email protected],ccb09 [email protected](C.B. Cheah).

0921-3449/$ see front matter 2011 Elsevier B.V. All rights reserved.

doi:10.1016/j.resconrec.2011.02.002
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7. Durability properties of wood waste ash/OPC concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

7.1. Resistance against acid attack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

7.2. Water absorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

7.3. Chloride permeability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

7.4. Alkali silica reaction (ASR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

7.5. Corrosion current and electrical resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

8. Resistance of wood waste ash concrete against freezethaw action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

9. Drying shrinkage of concrete containing wood ash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

10. Reuse and recycling of wood waste ash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

10.1. Use of wood waste ash in the production of controlled low strength material (CLSM) .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0010.2. Use of wood ash for improvement of soil alkalinity and as fertilizer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

10.3. Use of wood ash as a pollution control agent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

11. Conclusions and summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

1. Introduction

In thecurrent trend of power generation, emergence of biomass

(forestry and agricultural waste) fuelled power plant seems to be

a promising source of renewable energy with low operational cost

coupled with continuously renewable fuel. Additionally, the use of

forestry andtimber product manufacturing waste such as sawdust,woodchips, wood bark, sawmill scrapsand hard chips as fuel source

for production of electrical power offers a highly efficient method

of disposal for the aforementioned waste materials. In Portugal,

two units of pilot biomass fuelled power plants have been con-

structed for production of electricity in order to supplement the

power demand of the national electric gridlines alongside with

other conventionalpower plants which use fossilfuels.Both instal-

lations implement forestry biomass as the main fuel for production

of heat energy to operate steam turbine systems for subsequent

production of electric power (Rajamma et al., 2009).Moreover, it

has been a common practice in the timber product manufacturing

industry to develop small scale boiler units that utilize wood waste

as their main source of fuel as a cost effective means to recover

heat energyfor the industrialprocessesespecially for drying timberproducts. Wood wastes are the more preferable fuels for biomass

furnaces because the incineration of wood waste produces rela-

tively less fly ash and other residual materials in comparison to

other biomasses such as herbaceous and agricultural wastes.

A major problem arising from the widespread use of forestry

biomass and timber processing waste as fuel is related to the ash

produced in significant quantities as a by product from the incin-

eration of such biomasses. A major portion (approximately 70%) of

the wood waste ash produced is land-filled as a common method

of disposal (Campbell, 1990; Etiegni and Campbell, 1991; NCASI,

1993).As wood waste ash consists of highly fine particulate mat-

ters, which can be easily rendered airborne by winds, such a means

of waste disposal may result in subsequent problems, namely, res-

piratory health problems to residents dwelling near the disposalsite of the ash material. Moreover, contamination of ground water

resources can also be expected to occur from leaching of heavy

metal contents of ash or by seepage of rain water ( Udoeyo et al.,

2006).Hence, disposal of wood waste ash by means of land-filling

require a properly engineered land fill which have implications in

terms of the cost of disposal. Therefore, such a method of disposal

is uneconomical over long term. These problems require a new and

a more economical means of wood waste ash disposal as a solution.

In addition, the current boom in the construction industry has

caused a massive elevation of the demand for cement which is

the main constituent material in the production of concrete. The

production of cement involves an intensive use of raw material

(limestone) andenergy, while atthe same time, releases high quan-

tities of carbon dioxide into the atmosphere. Research reveals that

forthe production of every 600 kg of cement, approximately 400kg

of carbon dioxide gas is released. The increased demand of cement

implies a higher rate of environmental deterioration due to the

limestone extraction activities, a higher requirement of fossil fuels

and higher rate of green house gas discharge.

Recent research (Udoeyo and Dashibil, 2002; Elinwa and Ejeh,

2004; Udoeyo et al., 2006; Naik et al., 2003) was performedto investigate the feasibility of the use of wood waste ash as

a partial replacement material for the energy intensive process

of hydraulic cement for concrete production. The tests showed

promising results in that wood waste ash can suitably used as

constituent material in during the production of structural grade

concrete with acceptable mechanical and durability properties.

These findings provide a solution for the waste management prob-

lems of wood waste ash and also contribute towards minimizing

the consumption of energy intensive hydraulic cement production

of greener concrete material supplying the ever growing demand

of the construction industry. Hence, incorporation of wood waste

ash as cement replacement material in blended cement and con-

cretewill be beneficialnot onlyin environmentalterms for concrete

material but also in production costs of the aforesaid materials.

1.1. Factors influencing the quantity and quality of wood waste

ash

There are several factors which have a significant effect on the

qualitative and quantitative aspects of wood waste ash produced

from theincinerationof rawwoodwaste. This mandates theproper

characterisation of wood waste ash prior to being used as con-

stituent material in production of concrete and blended cement

paste. These factors include heat treatment temperature, types and

the hydrodynamics of the furnace and the species of trees from

which the wood wastes were derived.

Combustion temperature of raw wood waste inside the fur-

nace strongly governs both yield and chemical compositions ofresulting wood waste ash. In terms of ash yield, the combustion of

wood waste at higher temperatures generally resulted in a lower

amount of wood waste ash produced. The reduction in wood waste

ash yielded up to 45% with a combustion temperature increase

from 538 C to 1093 C. Combustion of wood waste at higher tem-

peratures beyond 1000 C also resulted in a profound decrease in

carbonate content due to the chemical decomposition of the afore-

said chemical compound at such temperatures. Carbonates and

bicarbonates compound especially calcite (CaCO3) are predomi-

nant in wood ash produced from an incineration at temperature

lower than 500 C. However, at higher incineration temperatures

greater than 1000 C which is the typical operational temperature

for most wood fired boiler units, oxide compounds such as quick

lime (CaO) become predominant in the chemical phase of wood
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Table 1

Chemical composition of wood ash from several species of timber (Vassilev et al., 2010).

Biomass group, sub-group and variety SiO2 CaO K2O P2 O5 Al2O3 MgO Fe2O3 SO3 Na2O TiO2

Wood and woody biomass

Alder-fir sawdust 37.49 26.41 6.1 2.02 12.23 4.04 8.09 0.83 1.81 0.98

Balsam bark 26.06 45.76 10.7 4.87 1.91 2.33 2.65 2.86 2.65 0.21

Beech bark 12.4 68.2 2.6 2.3 0.12 11.5 1.1 0.8 0.9 0.1

Birch bark 4.38 69.06 8.99 4.13 0.55 5.92 2.24 2.75 1.85 0.13

Christmas trees 39.91 9.75 8.06 2.46 15.12 2.59 9.54 11.66 0.54 0.37

Elm bark 4.48 83.46 5.47 1.62 0.12 2.49 0.37 1 0.87 0.12Eucalyptus bark 10.04 57.74 9.29 2.35 3.1 10.91 1.12 3.47 1.86 0.12

Fir mill residue 19.26 15.1 8.89 3.65 5.02 5.83 8.36 3.72 29.82 0.35

Forest residue 20.65 47.55 10.23 5.05 2.99 7.2 1.42 2.91 1.6 0.4

Hemlock bark 2.34 59.62 5.12 11.12 2.34 14.57 1.45 2.11 1.22 0.11

Land clearing wood 65.82 5.79 2.19 0.66 14.85 1.81 1.81 0.36 2.7 0.55

Maple bark 8.95 67.36 7.03 0.79 3.98 6.59 1.43 1.99 1.76 0.12

Oak sawdust 29.93 15.56 31.99 1.9 4.27 5.92 4.2 3.84 2 0.39

Oak wood 48.95 17.48 9.49 1.8 9.49 1.1 8.49 2.6 0.5 0.1

Olive wood 10.24 41.47 25.16 10.75 2.02 3.03 0.88 2.65 3.67 0.13

Pine bark 9.2 56.83 7.78 5.02 7.2 6.19 2.79 2.83 1.97 0.19

Pine chips 68.18 7.89 4.51 1.56 7.04 2.43 5.45 1.19 1.2 0.55

Pine pruning 7.76 44.1 22.32 5.73 2.75 11.33 1.25 4.18 0.42 0.17

Pine sawdust 9.71 48.88 14.38 6.08 2.34 13.8 2.1 2.22 0.35 0.14

Poplar 3.87 57.33 18.73 0.85 0.68 13.11 1.16 3.77 0.22 0.28

Poplar bark 1.86 77.31 8.93 2.48 0.62 2.36 0.74 0.74 4.84 0.12

Sawdust 26.17 44.11 10.83 2.27 4.53 5.34 1.82 2.05 2.48 0.4

Spruce bark 6.13 72.39 7.22 2.69 0.68 4.97 1.9 1.88 2.02 0.12

Spruce wood 49.3 17.2 9.6 1.9 9.4 1.1 8.3 2.6 0.5 0.1

Tamarack bark 7.77 53.5 5.64 5 8.94 9.04 3.83 2.77 3.4 0.11

Willow 6.1 46.09 23.4 13.01 1.96 4.03 0.74 3 1.61 0.06

Wood 23.15 37.35 11.59 2.9 5.75 7.26 3.27 4.95 2.57 1.2

Wood residue 53.15 11.66 4.85 1.37 12.64 3.06 6.24 1.99 4.47 0.57

Mean 22.22 43.03 10.75 3.48 5.09 6.07 3.44 2.78 2.85 0.29

ash produced.The reductionof carbonates andbicarbonates chem-

ical species which contribute to alkalinity of wood ash at higher

combustion temperatures resulted in a corresponding decrease in

alkalinity of ash. Moreover,therewas a decline in composition light

metallic elements such as potassium, sodium and zinc in wood

waste ash with increasing temperature of combustion (Etiegni and

Campbell, 1991).

Types of combustion technology used in thermal the conver-sion of wood waste into ash has had a significant influence on the

physical and chemical properties of ash produced. Different types

of furnaces and incinerators may have varied thermal conversion

temperatures which have resulted in corresponding variations in

chemical and ash yieldproperties as discussed earlier. Additionally,

differenttypes of combustion technologyhave significanteffects on

the physical properties of ash produced. Typically, in a grate fired

furnace, the wood ash produced is coarser in nature and tend to

settle inside the combustion chamber as bottom ash. On the con-

trary, for more advanced and efficient fluidised bed furnaces, the

ash produced is predominantly fine fly ash with a finer particle size

grading with only a small fraction of coarse ash retained within the

combustion chamber.

Some species of trees from which thewood wasteswere derivedhas shown to be a dominant factor governing the chemical prop-

erties of wood waste ash produced. The chemical composition of

essential oxide compounds which governs the suitability of wood

ash as a cement replacement material such as silica (SiO2), alumina

(Al2O3), iron oxide (Fe2O3) andquicklime (CaO) varies significantly

with various species of trees. Variations in the chemical composi-

tion of ash produced from different species of trees can be seen in

Table 1.

1.2. Uses of wood waste ash

Currently, ash by-products fromthe combustion of woodwastes

are commonly used as a soil supplement to improve the alkalinity

of soil for agriculture applications. Wood waste ash is also used as

a filler material in the construction of flexible pavements for roads

and highways (Etiegni and Campbell, 1991).Recent research find-

ings confirm the suitability of wood waste ash as a partial cement

replacement materialin the production of structural gradeconcrete

and self compacting concrete for applications in building construc-

tion (Elinwa and Mahmood, 2002; Elinwa et al., 2008; Abdullahi,

2006).

2. Physical properties of wood waste ash

Wood ash is reported to consist of a heterogeneous mixture of

variable size particles which are generally angular in nature. These

particles were unburned or partiallyburned wood or bark. In terms

of fineness, average amount of wood fly ash passing sieve #200

(75m) and retained on sieve #325 (45m) were 50% and 31%

respectively. The bulk density of wood fly ash was determined to

be relatively low at 490 kg/m3 with a specific gravity value of 2.48.

Wood fly ash was found to have low average autoclaved expansion

value of 0.2% (Naik, 1999).

Naik et al. (2003) evaluated the physical properties of woodashes from five different sources which concluded that wood

ash samples have varying values of unit weight that range from

162kg/m3 to a maximum of 1376kg/m3. The specific gravity of

wood waste ash samples investigated ranged between 2.26 and

2.60. The low unit weight and specific gravity of wood ashes rel-

ative to neat cement indicate a possibility of the reduction in the

unit weight of concrete material produced by the partial substitu-

tion of cement using wood ash. A higher degree in the variation of

wood ash fineness was observed whereby the percentage of wood

ash retained on a 45m sieve varied between 23% and 90%.

A sieve analysis results showed that the mean diameter, d50,

of sawdust waste incineration fly ash (SWIFA) obtained from an

open incineration of sawdust in a drum to be 150m. The corre-

sponding surface area of SWIFA was determined to be relatively


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high (150m2/g) which, is possibly due to the increasedash surface

porosity. Other physical properties of SWIFA namely specific grav-

ity, loose bulk density and moisture content were found to be 2.29,

830kg/m3 and 0.37% respectively (Elinwa and Mahmood, 2002;

Elinwa and Ejeh, 2004).Abdullahi (2006)reported similar results

whereby thespecific gravity andthe bulk density of wood ashwere

found to be 2.13 and 760 kg/m3 respectively.

A micrograph obtained from a scanning electron microscopy

(SEM) analysis on residual ash produced from the incineration of

wood waste ash at a temperature of 1000 C indicated that wood

waste ash consists of two dominating phases, namely a fibre-like

continuous layer and particle like aggregates. The fibre like con-

tinuous layer is highly carbonaceous in nature with high carbon

content. On the contrary, carbon content in the particle like aggre-

gates phase is low and the consists mainly of silica and alumina

compounds as per energy dispersive X-ray (EDX) results illustrated

inFig. 1(Udoeyo et al., 2006).

A commonfinding whereby wood waste flyash consistsof parti-

cles which arehighly irregularin shape with a highlyporoussurface

was reported by Wang et al. (2008a). In addition, crystal like spikes

were also observed to be present on the surface of wood waste fly

ash particles, as can be seen inFig. 2, which may contribute sig-

nificantly to the high surface area of the ash particles. A specific

gravity of wood waste fly ash was determined to be 2.40 and par-ticle size grading analysis results indicated that most of the ash

particles have diameter within 30130m.

The specific gravity of wood fly ash collected from a forestry

biomass fired power plant was found to be 2.54. Wood fly ash from

the same source consisted of fine ash particles with an average

diameter below 50m. SEM images of wood fly ash reveals that

wood fly ash consists mainly of highly angular particles with a high

extentof surface porosity.Specific surface areas of wood fly ashcol-

lectedfromtwo differentsources hadreported valuesof 40.29m2/g

and 7.92m2/g respectively. A higher specific surface area of thefor-

mer is due to higher degree of irregularity in particle shape and

porosity of its surface as shown inFig. 3(Rajamma et al., 2009).

As physical properties of wood waste ash have significant effect

on pozzolanic and hydraulic reactivity, high degree in variation ofphysical properties of wood ash obtained from different sources

mandate proper characterisation of wood ash prior to being incor-

porated as cement replacement material in production of concrete

material for construction.

3. Chemical properties and leachate of wood waste ash

3.1. Chemical composition and phases of wood waste ash

The chemical composition of biomass fly ash is an important

property governing its suitability for use as pozzolanic material in

blended cement and concrete. ASTM C618 (ASTM, 1998)defines

pozzolana as a siliceous and aluminous material which possesseslittle or no cementitious properties but in finely divided form may

react with portlandite from the hydration of cement to form a

product with cementitious properties. By definition of ASTM C618

(ASTM, 1998), the presence of significant quantities of silica and

alumina compounds in biomass fly ash or other type of finely

divided powder is mandatory in order to qualify as pozzolana.

Wood waste ash obtained from an uncontrolled incineration

of sawdust under an open burning condition is highly alkaline in

nature with pH values ranging between 9.5 and 10.1 have been

found to have a significant quantity of volatile matter of between

4.63 and 8.4% expressed as mass loss upon ignition of the ash at

temperature of 75050 C(Elinwa and Mahmood, 2002; Udoeyo

and Dashibil, 2002; Elinwa and Ejeh, 2004). An ignition loss of

27% was reported for wood waste ash acquired from uncontrolled

Fig.1. EDXanalysison (a)fibre-likecontinuousphaseand(b) particle-likeaggregate

phase (Udoeyo et al., 2006).

burning of a wood biomass within the furnace of a local bakery

possibly due to the presence of external contaminants ( Abdullahi,

2006). XRD analysis results of the wood waste ash confirmed pres-

ence of silica and calcium carbonates as the main phases of the

chemical compound within the ash (Elinwa and Mahmood, 2002;

Elinwa and Ejeh, 2004).In addition to silica and calcium carbonate

phases, the XRD analysis performedby Campbell (1990) and Etiegni

and Campbell (1991) detected the presence of additional dominant

phases, namely portlandite (Ca(OH)2) and lime (CaO), in the wood

waste ash samples examined.

XRF analysis performed by several researchers (Elinwa and

Mahmood, 2002; Udoeyo and Dashibil, 2002; Elinwa and Ejeh,

2004; Abdullahi, 2006)found significant amounts of silica in the

ash samples obtained from incinerated wood waste sawdust under


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Fig. 2. Particle morphology of wood fly ash (Wang et al., 2008a).

Fig. 3. Particle morphology of wood fly ash (Rajamma et al., 2009).

an uncontrolled burning condition. A total chemical composition of

pozzolanic essential compounds, namely silica, alumina and ferric,

was reported to have a range from 62.14 to 80.67% with a mean

value of 72.78% which is similar to those of class N and F coal flyashes.In an effort to characterize the chemical composition of wood

waste ash obtained from five distinct sources for use as a binder in

a controlled low strength material, Naik et al. (2003) found a wider

range of a total chemical composition of silica, alumina and fer-

ric compounds between 18.6 and 59.3% for the wood ash samples

examined. Chemical compositions of wood waste ash determined

by several researchers above are summarized inTable 3.An eval-

uation of pozzolanicity wood waste ash byElinwa and Mahmood

(2002)indicated that wood waste ash is chemically reactive with

the pozzolanic activity index (PAI) value of 75.9% when exceeding

the minimum 70% specified by ASTM C618 for all classes of coal fly

ash to be suitable as pozzolan.

Co-firing of 20% wood waste with 80% coal in the coal power

plant was observed to yield a resulting fly ash with a similar chem-

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5 6

Extentofreaction(%)

Months

SAW

Class C

10P

Fig. 4. Extent of reactions for various fly ash samples (Wang and Baxter, 2007).

ical composition and organic matter content in comparison with

class C fly ash. Further evaluation on pozzolanicity using the 70:30

ash mixture-the portlandite ratio indicated wood waste-coal co-

fired ash possesses similar pozolanic reactivity in comparison to

class C fly ash at a later age of tests, beyond 6 months, though the

rate of pozzolanic reaction at early age were relatively lower in

comparison tothe class C flyash ascan beseen in Fig. 4 (Wang and

Baxter, 2007).

Rajamma et al. (2009) performed X-ray diffractometry (XRD)analysis on samples of wood waste fly ash collected from an elec-

trostatic precipitator unit of two separate forestry biomass fuelled

power plants. Results of XRD analysis indicated that two main

chemical compounds present in the ash samples are silica and

calcite. Loss on ignition (LOI) of both the fly ash samples was

determined to be 14% and 7% respectively. Relatively high LOI in

comparison to other type of cement replacement material namely

silica fume and metakaolin implies a certain degree of inefficiency

in theconversion of carbondue to kinetic andmass transfer restric-

tions in the biomass power plant when wood wastes were at

sufficiently high temperature between 750 C and 1000 C.

X-ray fluorescence (XRF) analysis results of both wood waste fly

ash samples, as shown in Table 2, confirmed the presence of essen-

tial chemical compounds governing pozzolanic reactivity namelySiO2, Al2O3 and Fe2O3 in significant amounts within the wood

waste fly ash samples examined. Wood waste fly ash samples with

higherSiO2 + Al2O3 + Fe2O3 chemical compositions (F1)were deter-

mined to have stronger pozzolanic reactivitys in comparison to

the wood waste fly ash F2 which have lower SiO2 + Al2O3 + Fe2O3chemical compositions hence lower pozzolanic reactivity as can be

seen from pozzolanic reactivity results shown in Fig. 5. In Fig. 5,

it can be observed that concentrations of OH ions and a corre-

sponding CaO concentration of wood waste fly ash F1 which plot

Table 2

Chemical composition of wood waste fly ash (Rajamma et al., 2009).

Element F1 (wt.%) F2 (wt.%)

SiO2 41 28

Al2O3 9.3 6.2

Fe2O3 2.6 2.2

CaO 11.4 25.4

MgO 2.3 5

Na2O 0.9 3.3

K2O 3.9 3.2

TiO2 0.4 0.3

MnO 0.3 0.7

P2O5 0.9 0.9

Cd 1.0 mg/kg 1.3 mg/kg

Pb 191 mg/kg 12 mg/kg

Cu 99 mg/kg 27 mg/kg

Cr 47 mg/kg 73 mg/kg

Hg


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Table 3

Summary of chemical composition of wood waste ash.

Chemical compound SiO2 Al2O3 Fe2O3 CaO MgO TiO2 K2O Na2O SO3 C P2O5 LOI (%)

Elinwa and Mahmood (2002) 67.20 4.09 2.26 9.98 5.80 0.08 0.45 0.48 4.67

Udoeyo and Dashibil (2002) 78.92 0.89 0.85 0.58 0.96 0.43 17.93 8.40

Elinwa and Ejeh (2004) 67.20 4.09 2.26 9.98 5.80 0.08 0.45 0.48 4.67

Abdullahi (2006) 31.80 28.00 2.34 10.53 9.32 10.38 6.50 27.00

Naik et al. (2003)

W1 32.40 17.10 9.80 3.50 0.70 0.70 1.10 0.90 2.20 31.60

W2 13.00 7.80 2.60 13.70 2.60 0.50 0.40 0.60 0.90 58.10W3 50.70 8.20 2.10 19.60 6.50 1.20 2.80 2.10 0.10 6.70

W4 30.00 12.30 14.20 2.20 0.70 0.90 2.00 0.50 2.10 35.30

W5 8.10 7.50 3.00 25.30 4.50 0.30 2.70 3.30 12.50 32.80

far below the saturation curve indicate strong pozzolanicity while

concentrations of OH ion and corresponding CaO concentrations

of wood waste fly ash F2 plot slightly above the saturation curve

implying negative pozzolanicity. Hence, there exists a strong cor-

relation between pozzolanicity of wood waste fly ash with its total

chemical content of SiO2, Al2O3 and Fe2O3. Generally, pozzolanic-

ity of wood waste fly ash varies proportionately with sum of SiO2,

Al2O3and Fe2O3chemical content of the ash.

Quantitative elemental analysis of the wood waste fly ash sam-

ples showed that quantities of Ca, Si, Al and Mg elements present

on the surface of the wood waste fly ash particles are comparable

to those present on the surface of cement particles and the find-

ing further supports the analysis results of energy dispersion X-ray

spectrometry performed on the wood waste fly ash samples.

3.2. Chemical properties of leachate from wood waste ash

For non conventional material such as wood waste ash there

have been no adequate environmental specifications developed for

its use as a construction material. In the absence of proper specifi-

cation, regulatory evaluators tend to use contaminant leachability

levels of pure wood waste ash in their judgement on the suitability

of wood waste ash as construction material.

Udoeyo et al. (2006) studied the chemical content especially

heavy metal content of leachate produced from the batch leach-

Fig. 5. Result of pozzolanicity of F1 and F2 wood waste fly ash (Rajamma et al.,

2009).

ing of wood waste ash. De-ionized water acidified using nitric acid

to adjust the pH to 4 and 5 for leaching of metals from pure wood

waste ash to produce a leachate then analysed using an atomic

absorption spectrophotometer. Analysis of the leachate from wood

waste ash indicated the presence of heavy metal ions such as

chromium,iron, zincand arsenic whenusing an acidifiedsolutionof

both pH 4 and 5. It was observed that arsenic exhibited the highest

leachability due to its high concentration in the leachate exam-

ined while iron had the least leachability as it was only detected in

trace amounts. The leachability of chromium, iron, copper and zinc

were observed to have significant dependence on the pH value of

the leaching agent. The aforementioned metal exhibited a higher

degree of leachability with a higher acidity of leaching agent used.

Apparently, the mineralogical phase of the metal oxides present

in the ash had a significant influence on their susceptibility to the

reaction of H+ ions present in theleachingagent. More H+ ions were

available in a higher acidity leaching agent to react with the min-

eral phases containing metal ions within wood waste ash hence

resulted in a higher leachability of the metals.

A similar trend of higher metal leachability with an increas-

ing acidity of leaching agents has been observed by several other

researchers (Fytianos and Tsaniklidi, 1998; Karuppiah and Gupta,

1997).They also found that a leaching agent of pH 5 did not have

an adequate quantity of H+ ions to react with iron oxide phases

produced from the combustion of wood waste.The concentration of the metallic ions namely arsenic,

chromium, iron and zinc in the leachate of wood waste ash were

found to be higher than the EPA fresh water acute criteria. In the

consideration that wood ash from fresh wood would not normally

have a high chemical composition of these metals, the recorded

high concentration of these metallic ions in the leachate produced

from wood waste ash are attributable to wood preservatives used

during processing of timber. Hence, it is important to screen wood

waste asa part oftheirselection process foruse in concrete(Udoeyo

et al., 2006).

4. Properties of wood waste ash blended cement

Blending of wood waste ash and ordinary Portland cement

(OPC) at various levels of cement replacement produces a new

type of blended cement with altered physical properties and

heat kinetic properties in comparison to neat OPC. Wood waste

ash/OPC blended cement exhibit significant difference in terms of

the standard consistency, setting times, soundness, heat evolution

characteristics and the microstructure of hardened cement paste

with respect to OPC.

4.1. Standard consistency

Laboratory investigation findings of several researchers (Elinwa

and Ejeh,2004; Elinwa and Mahmood,2002; Abdullahi, 2006) were

in common agreement that the inclusion of wood waste ash as a


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partial cement replacement material in blended cement resulted

in a higher requirement for water in order to achieve a standard

level of cement paste consistency. Water demand of wood waste

ash/OPC blended cement paste increases proportionately with the

level of cement replacement by wood waste ash expressed as a

percentage of total binders weight. Higher water demand of wood

waste ash/OPC blended cement relative to OPC is mainly due to a

higher specific surface area of porous wood waste ash particles in

comparison to OPC particles.

4.2. Initial and final setting time

The inclusion of wood waste ash as a partial cement replace-

ment material in wood waste ash/OPC blended cement resulted in

a delay of cement setting hence the need for longer initial and final

setting times of blended cement paste. The effects of setting time

delays become more significant with the increase in the level of

cementsubstitutions with wood waste ash (Elinwa andEjeh, 2004;

Elinwa and Mahmood,2002; Udoeyo and Dashibil, 2002; Abdullahi,

2006). At the level of cement replacementwithwoodwaste ash up

to 30% by total binders weight, both initial and final setting time

of the blended cement paste are still in compliance to the limits

prescribed in standard code of practice BS 12: 1978 (Udoeyo and

Dashibil, 2002).Delaysin theinitial andfinal setting of cementpastein thepres-

ence of wood waste ash is largely due to the dilution of cement

content as part of the OPC was used as a substitute with wood

waste ash (Elinwaand Ejeh, 2004). Thepresenceof wood waste ash,

which is less reactive than OPCin blended cementpaste, resulted in

the retardation rate of cement hydration which also contributes to

the delay in the blended cement paste setting. A prolonged time

of setting for cement pastes is a desirable attribute of blended

cement which implicates longer times in which the paste is work-

able. A corresponding lower hydration heat of the blended cement

due to the lower hydration rate as aforementioned rendered wood

waste ash/OPC blended cementpaste suitable for applications. This

allowed a desired low heat development which offsets the stress

induced by temperature differential such as mass concreting work.

4.3. Soundness

Thepresenceof wood waste ashas a partial cementreplacement

material in blended cement paste generally resulted in a higher

magnitude of cement paste soundness. Varying levels of cement

replacement using wood waste ash from 0 to 30% causes a corre-

sponding increase in the soundness of blended cement paste. At a

replacement level of 30%, the most sound blended cement paste

reported was 1.45 mm which was still in good compliance with the

maximum allowablesoundnessof 10 mm specified by BS 4550-Part

3 (Elinwa and Mahmood, 2002; Udoeyo and Dashibil, 2002; Elinwa

and Ejeh, 2004).

4.4. Calorimetric and heat evolution characteristics

The evaluation of heat development characteristics was per-

formed byRajamma et al. (2009) on samples of wood waste fly

ash (WWFA)/OPC blended cement containing 030% of WWFA as

a partial substitution of OPC. All blended cement paste samples

tested were observed to reach a steady state temperature of 24 C

within 3 days upon mixing. In addition, the time taken to reach

their peak hydration temperature was observed to be shorter for

cement pastes containing WWFA.

In the absence of WWFA, neat OPC paste tested was found to

reach peak hydration temperature at 40 C. Peak hydration tem-

peratures attainable by WWFA/OPC blended cement pastes were

recorded to be lower with increasing levels of cement replace-

Fig. 6. Calorimetric evaluation of the hydration process of WWFA/OPC blended

cement pastes (Rajamma et al., 2009).

ment with WWFA. Moreover, peak hydration temperatures of all

WWFA/OPC blended cement paste within WWFA levels of cement

replacement between 5% and 30% were lower in comparison with

neat OPC paste as can be observed in Fig. 6.

The difference in the hydration rate and the shift in the peak of

hydration temperature with respect to the neat OPC pastes were

probably caused by variations of alkali and chlorine content of

WWFA used. Additionally, dilutions of OPC content in the presence

of WWFA as a partial substitution of OPC in the blended cement

paste also contribute towards lowering the hydration rate of thecement pastes and the corresponding decrease in peaktemperature

attainable by WWFA/OPC blended cement pastes.

4.5. Microstructure of cement paste matrix

Elinwa et al. (2008)performed a microstructural analysis on

concrete mixes containing 0% (PC-01N) and 10% (PC-03N) of wood

waste ash by total binder weight and observed a significant reduc-

tion in porosity of hardened mortar for the latter concrete mix.

Additionally, the incorporation of 10% of wood waste ash as sub-

stitution of ordinary Portland cement (OPC) in the formulation

of concrete mix was found to significantly reduce the percentage

of non-hydrated cement and portlandite amount while increasing

the quantity of CSH gel present within the concrete mix producedafter a given curing age as summarized in Table 4. These obser-

vations imply a strong pozzolanic reaction between the reactive

silica present in wood waste ash with the portlandite compound

generated from the hydration of cement.

Pozzolanic reactions, which produced additional CSH gels in the

concrete mix with 10% wood waste ash of total binder weight,

were observed to continue beyond the hydration age of 28 days

up to90 days. Itcan be noted in Table 4 that the production of CSH

gel within an equivalent concrete mix containing neat OPC with-

out wood waste ash content (PC-01N) had virtually stopped at the

age of 28 days and beyond as indicated by the stagnant amount of

CSH gel after curing age of 28 days. Continuous production of CSH

gel within a concrete mix with 10% wood waste ash content con-

tributed towards the microstructure densification of the cement


8/17






Table 4

Result of micrograph analysis (Elinwa et al., 2008).

Mix no. Property (%) Age (days)

3 7 28 60 90

PC-01N (control) Porosity 25 18 15 15 15

Unhydrated cement 14 12 10 10 10

Ca(OH)2 10 12 14 14 14

CSH 39 58 61 61 61

PC-03N (SCC) Porosity 18 12 9 7 6Unhydrated cement 9 8 6 6 6

Ca(OH)2 14 8 7 6 4

CSH 59 72 78 81 84

paste matrix, lowered degree of mixporosity, improved the quality

of the cement-aggregate interfacial transition zone and increased

theuniformity of pore distributionwithin thecementpaste matrix.

These enhancements of the microstructural properties of cement

paste matrices were beneficial for mechanical strength and dura-

bility of hardened concrete mix produced.

The XRD analysis performed on hardened wood waste fly ash

(WWFA) blended cement paste indicated that calcium silicates

peaks in blended cement paste with 10% WWFA of total binder

weight was more intense than those with 30% WWFA while theintensityof thecalciumsilicatepeakof neat OPCpaste is thehighest

at 28 days of curing. Theobservationimplicates that theproduction

rate of calcium silicate hydrate (CSH) gel which is also the hydra-

tion rate of cement paste was retarded by the inclusion of wood

waste fly ash as a partial cement substitution material in blended

cement paste (Rajamma et al., 2009).

Micrographs of hardened cement paste after 24h of curing indi-

cated extensivegrowth ofCSH gelin neat OPCand 10% WWFA (both

type F1 and F2 WWFA) substituted cement paste as can be seen in

Fig. 7ac. For blended cement paste specimens with type WWFA

content of 30%, an active formation of ettringite needles within the

cement paste matrix was noted for the same duration of curing as

in Fig. 7d and e.After 30days ofhydration ofneatOPCpaste and the

blended cementpastes containing 10% and30%, WWFA was almostcompletedwhereby silicate hardening phases could be observed in

the micrographs of their respective hardened cement paste matri-

cesasin Fig.8. In Fig.8d ande, it canbe noted that ettringite needles

observed at earlier age of hydration in the blended cement paste

containing 30% of WWFA remained in the paste even after 30 days

(Rajamma et al., 2009).

5. Rheological properties of wood waste ash/OPC concrete

and mortar

Elinwa and Mahmood (2002)reported that utilization of wood

waste ash obtained from open burning for sawdust as cement

replacement material in the production grade 20 concrete has hadadverse effects on the workability of freshly producedconcrete mix.

While the water binder ratio of the concrete mix were maintained

at a constant at 0.565, increment level of cement replacement by

wood waste ash from 5% to 30% of the total binder weight at 5%

intervals resulted in a corresponding gradual decrease in theslump

value of the concrete mix by 540mm with reference to the con-

trol concrete mix without wood waste ash content. Similar trends

in the reduction of concrete workability in terms of slump were

reported by Udoeyo and Dashibil (2002) who attempted to pro-

duce grade 25 concrete mixes containing a similar range of cement

replacement (530%) of cement using wood waste ash also pro-

duced from open burning for sawdust. Corresponding decrease in

value of compacting factor of concrete mix with increasing level of

cement replacement with wood waste ash was also observed.

A drastic reduction in the slump of concrete mix, from 62 mm

for a control concrete to merely 8 mm for a concrete mix with only

5% wood waste ash, was reported byUdoeyo et al. (2006). Zero

slump mixes were produced when wood waste ash was used at

a cement substitution level of 2030%. Such a significant impair-

ment of mix workability was probably due to high organic content

of wood wasteash used in theproductionof themixes. Wood waste

ash used in the study was reported to have high value for ignition

loss (LOI 10.46%), which may implicate the presence of significant

combustible organic content within the ash that renders, in nature,a high water absorption of ash. The nature of high water absorp-

tion of wood waste ash is further justified by the research findings

ofAbdullahi (2006) that show the inclusion of wood waste ash col-

lectedfrom a local bakeryas a partial cementreplacement material

at replacement levels of 10%, 20%, 30%and 40% resulted in increase

water requirements by 10%, 11.7%, 13.3% and 15% respectively in

order to achieve similar values of slump as the control concrete

mixes without wood waste ash content.

Elinwa et al. (2008)investigated the effects of partial substi-

tution of cement by wood waste ash in the formulation of self

compacting concrete (SCC) and mortar (SCM) mixes. At a constant

mix proportion of cement, sand, water binder ratio and dosage of

superplasticizer, the mortar spreads of SCM mixescontaining wood

waste ash (from open burning of sawdust) at a cement replace-ment level ranging from 0% to 20% of binder weight were observed

to undergo consistent reduction from 270 mm to 200mm. In addi-

tion, the fresh SCM mix flow times were found to increase from

4 s to 18 s. This occurred when the level of cement replacement

of wood waste ash in the mix was increased from 0% to 20% by

total binder weight as summarized in Table 5. SCC mixes con-

taining 20mm coarse aggregates, wood waste ash as a partial

cement replacement material at 10% binder weight were tested

using a slump flow, V-funnel, T-5 minutes, U-Box and L-Box pro-

cedures. They each exhibited good compliance with specifications

in EFNARC (EFNARC, 2002)as summarized inTable 6.The SCC mix

with 10% wood waste ash content was in EFNARC compliance with

their specified flowand V-Funnel values. This implies adequatemix

stability and self-deaeration properties. Moreover, compliance ofthe actual T5minutes test time, within EFNARC specifications, also

showed that the mix had no segregation. The mix therefore satis-

fied the EFNARC requirement because of the good compactibility

achieved as shown by the U-Box and L-Box values.

Rajamma et al. (2009)investigated the effects of incorporation

of wood waste fly ash from a biomass power plant in mortar mixes

on fresh and hardened properties in the produced mixes. The addi-

tion of wood waste fly ash as a partial substitution of OPC (10%)

by total binders weight in mortar mixes had no adverse effect on

the water demand of wood waste fly ash mortar mixes. This was

compared to the control mortar mix in order to achieve a similar

level of workability using solely OPC as binder material. It had also

been observed that mortar mixes with wood waste fly ash as a par-

tial replacement material, using 10% binder weight, had prolonged


9/17






Fig. 7. Microstructure of cement paste after 24 h of hydration: (a) neat OPC paste; (b) 10% type F1 WWFA blended cement paste; (c) 10% type F2 WWFA blended cement

paste; (d) 30% type F1 blended cement paste; (e) 30% type F2 blended cement paste (Rajamma et al., 2009).

setting times in comparison to an equivalent control mortar mix.

Shortenedmix setting times recordedwhen wood wastefly ashwasused at a higher cement replacement level at 20% and 30% binders

weight. Higher setting rates were observed when there was a high

rate of absorption when mixing water by organic content of the

wood waste ash in the mix. An unexpected retardation occurred

within the mix setting rate. By incorporating the wood waste ashat a cement 10% replacement level, as mentioned earlier, proba-

bly caused a dominating effect over the relatively lower fineness of

wood waste ash in comparison to OPC over its organic content.

Table 5

Mix proportion and workability of SCM mixes (Elinwa et al., 2008).

Mix no . Cemen t ( kg/ m3) SDA, % (kg/m3) Sand (kg/m3) Water (kg/m3) SP dosage (%) w/c Mortar spread (cm) Flow time (s)

PC-01M 441 0 (0) 662 265 2.5 0.6 27 4

PC-02M 419 5 (22) 662 265 2.5 0.6 25 7

PC-03M 397 10 (44) 662 265 2.5 0.6 24 7

PC-04M 375 15 (66) 662 265 2.5 0.6 23 12

PC-05M 353 20 (88) 662 265 2.5 0.6 20 18


10/17






Fig. 8. Microstructure of cement paste after 30 days of hydration: (a) neat OPC paste; (b) 10% type F1 WWFA blended cement paste; (c) 10% type F2 WWFA blended cement

paste; (d) 30% type F1 blended cement paste; (e) 30% type F2 blended cement paste (Rajamma et al., 2009).

6. Bulk density and mechanical strength of hardened wood

waste ash/OPC concrete and mortar

6.1. Bulk density

Generally, the utilization of wood waste ash as a partial cement

replacement material in concrete mixreduces bulk density of hard-

ened concrete. Reduction in bulk density becomes more significant

at higher levels of cement replacement using wood waste ash. Bulk

density of grade 20 concrete mixes was observed to be reduced

from2482 kg/m3 at0%woodashcontentto2281kg/m3 when wood

ash content was increased up to 40%. The bulk density reduction

effect is attributed to a lower specific gravity wood waste ash in

comparison to OPC (Elinwa et al., 2005).

6.2. Compressive strength

Several researchers (Elinwa and Mahmood, 2002; Udoeyo and

Dashibil, 2002; Elinwa and Ejeh, 2004; Abdullahi, 2006)had com-

mon findings that show the use of wood waste ash as a partial

cement replacement material in concrete at all level of cement

replacement ranged between 5% and 30% it reduces the compres-

sive strength of the concrete mix produced relative to neat OPC

concrete for all curing times. Udoeyo et al. (2006) justified that

the trend observed is most probably due to the mechanism that

wood waste ash particles act more like filler material within the

cement paste matrix than as binder material. Thus, increasing ash

content as replacement of cement resulted in an increased surface

area of filler material to be bonded by decreasing the amount of


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Table 6

Fresh property of SCC mixes with 10% wood waste ash (Elinwa et al., 2008).

Measurement Mix Standard (EFNARC, 2002)

FC-01M FC-01N

Experimental value Experimental value

Flow 680 mm 665 mm 650800 mm

V-funnel 8.4 s 8.2 s 812 s

T5 minutes 9.8 s 9.9 s 815 s

U-Box 29 mm 28.5 mm 030 mm

L-Box 0.85 0.85 0.81.0

cement which caused a decline in strength. However,Elinwa and

Mahmood (2002) observed a marginal difference of compressive

strength between wood waste ash concrete and neat OPC control

concrete mix. This tends to decrease with prolonged curing dura-

tions, especially beyond 28 days. In addition,Udoeyo and Dashibil

(2002) observed a higher rate of compressive strength gain for

concrete mix with wood waste ash content ranging between 15%

and 25% total binder weight. This was true for increments of 5%

at later curing ages of 56 and 90 days. Both observations are evi-

dence of increased CSH gel formation within cement paste matrix

microstructure of wood waste ash concrete by pozzolanic activity.

This wasdone between an amorphoussilicacontent of wood wasteash and portlandite from the hydration of cement.

Elinwaand Ejeh (2004)studied the compressivestrength devel-

opment of mortar mixes containing wood waste ash as a cement

replacement between 5 and 30% at stepped increments of 5%

observed that mortar mixwith 10%wood waste ash content exhib-

ited highest compressive strength atall ages of curingup to 60days.

Ata 60daycuring age the mortarmixwith 10%of woodwasteashas

partial cementreplacementmaterialexhibited similar compressive

strength as equivalent mortar mix with only OPC as binder.

Naik et al. (2002)investigated the compressive strength devel-

opment behaviour of a concrete mixture made with wood fly ash

used as a partial cement substitution material for curing age up to

365 days. Wood fly ash was included in the mix at binder substitu-

tionlevels of5, 8 and 12% bytotalbinder weightwhile a quantityof

binder, aggregate and water/binder ratios remained constant for all

mixes produced. From the compressive strength results acquired,

they concluded that (i) control concrete mixture (without wood

waste ash content) achieved a strength of 34 MPa at 28 days and

44MPa at 365 days. The strength of (ii) concrete mixtures contain-

ing wood fly ash ranged from 33 MPa at 28 days and between 42

and 46MPa at 365 days. (iii) The inclusion of wood flyash in a par-

tial substitution of cement in concrete up to a replacement level of

12% had a significant contribution to the strength development of

concrete mixtures produced. Continuous strength was gained from

the wood fly ash concrete mixes upon prolonged curing durations.

This indicated a presence of pozzolanic reactions between wood

waste ash and the cement hydration product.

Elinwaet al.(2005) attempted to improve compressivestrength

of wood waste ash/OPC concrete by the including trace amountsof metakaolin as an additive in the concrete mixes. The concrete

mixes produced had 20 MPa target strength. This mix included

wood waste ash as a cement replacement using a 5% step incre-

ments between 0 and 40%. Metakaolin was used as an additive

material at a constant dosage of 3% by total binder weight. It was

observed that the inclusion of metakaolin though at small dosage,

contributed towards the enhancement of an early rate of com-

pressive strength gain of wood waste ash/OPC concrete. SDA/OPC

concrete with 10% wood waste ash total binder weight exhibited a

compressive strength and modulus of rupture which was respec-

tively 37% and 7% higher in comparison to the neat OPC concrete

though bothmixes hadsame content of metakaolin. Concrete mixes

with wood waste ash at cement replacement levels of 5%, 10%, 15%

and 20% and 3% metakaolin as additive reached target strength of

20 MPa after 28 days of curing period.

Further evidence of pozzolanic characteristic of wood waste ash

was reported byElinwa et al. (2008) that incorporation of wood

waste ash as partial cement replacement material by 10% of total

binderweight in self a compacting mortarmix resulted in improve-

ment in compressive strength of mix relative to control the mortar

mix containing neat OPC as binder. Self compacting mortar mixes

with wood waste ashbeyond 10%total binderweight wasobserved

tohavelowercompressivestrengththanneatOPCmortarforcuring

ages up to 28 days. At a prolonged curing age up to 90 days, mortar

mixes with wood waste ash content of 15% exhibited compressivestrength similar to neat OPC mortar. Similar trends of a higher rate

of compressive strength development at later curing ages beyond

28 days up to 90 days relative to neat OPC mortar were exhibited

by all mortar mixes which had wood waste ash contentof 5, 10, 15

and 20% of total binder weight.

Rajamma et al. (2009) investigated the compressive strength

of cement mortar mixes containing wood waste fly ash obtained

from a wood biomass fired power plant. Wood waste fly ash was

used as cementreplacementmaterialat replacement level of 10, 20

and 30% of total binder weight. It was observed that mortar mixes

with a wood waste fly ash content of 10% exhibited higher 28-day

compressive strength but lower flexural strength in comparison

with equivalent neat OPC mortar. The use of wood waste fly ash as

a partial cement replacement material at higher replacement level

of 20and 30% of total binder weight was observed to reduce 28day

compressive strength relative to equivalent neat OPC mortar mix.

Utilization of very finely ground ash from the co-combustion of

wood waste, sugarcane bagasse and rice husks (BRWA) as partial

cement replacementmaterial in concrete was foundto significantly

improve the compressive strength of the concrete mix produced.

Horsakulthai et al. (2011)investigated the strength development

characteristic of concrete mixes produced by incorporation of

BRWA as cement replacement material. BRWA used were obtained

from a biomass power plant which used themixtureof wood waste,

sugarcane bagasse and rice husk as fuel and ground to a very fine

dust (2% of total mass of ash retained on 45m sieve). Concrete

mixes produced had BRWA content of 0%, 10%, 20% and 40% total

binder weight as a partial cement replacement material. After 28

days curing, the concrete mixes with BRWA contents of 10% and20% totalbinder weightweredeterminedto have a highercompres-

sive strength of 103%and 108%normalized against the compressive

strength of the control concrete mix. Concrete mixes with 40%

BRWA content total binder weight, though exhibited lower com-

pressive strength as early as 7 and 28 days relative to control

concrete mix, had a similar compressive strength as the control

concrete at prolonged curing period of 91 days. Concrete mixes

with 10%, 20% and 40% of concrete mixes exhibited higher rates of

strength beyond 28 days relative to control concrete mix with only

OPC as binder. Compressive strengths with a given curing time for

all the mixes examined are summarized inTable 7.Enhancements

in thecompressive strength ofconcretewithBRWAcontent asearly

as 7 and28 days were attributed to themicrofiller effectof theultra


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Table 7

Compressive strength of concrete at various curing duration (Horsakulthai et al.,

2011).

Mix Compressive strength (MPa)normalized

7 days 28 days 91 days 180 days

PC1 19.0100 24.0100 29.0100 31.5100

10BRWA1 18.597 24.5103 33.4116 36.5116

20BRWA1 21.0111 26.0108 38.5133 40.5129

40BRWA1 16.084 20.585 29.0100 34.5110

Table 8

Split tensile strength of sawdust ash concrete (Udoeyo and Dashibil, 2002).

SDA (%) Split tensile strength (N/mm2 )

7 days 28 days

0 2.14 2.8

10 2.05 2.76

15 1.83 2.69

20 1.79 2.61

25 1.44 2.53

30 1.14 1.91

1.2

0.4

0.6

0.8

1

7 Days

28 Days

0

0.2

30252015100

Splittensilestregthratio

Sawdust ash content (%)

Fig. 9. Splittensilestrength ratio versus sawdustash content (Udoeyo andDashibil,

2002).

fine particles of ash which contributed to the denser packing of

the cement paste matrix. A higher compressive strength of BRWA

mixes at later age of curing (91 and 180 days) were largely due

to continuous formation of CSH gels within cement paste matrix

by pozzolanic reaction between amorphous silica composition of

BRWA with portlandite from hydration of cement. High rates of

thepozzolanicreactionwhichwas initiatedon the28 days of curing

period were largely due to very fine particle size of the ash.

6.3. Split tensile strength

Udoeyo and Dashibil (2002)reported a reduction in both the

compression and split tensile strength of concrete produced by

partial replacement of cement with wood waste ash. Split tensilestrength of concrete mixes at 7 and28 days wasobservedto decline

with increasing level of cement replacement with wood waste ash.

The effects of reduction in split tensile strength of concrete by the

use of wood waste ash as partial cement replacement material

was less pronounced in comparison with reduction in compres-

sive strength. It was observed that the marginal difference in split

tensile strength of SDA/OPC concrete mixes with reference to neat

OPC concrete were more significant at 7 days. However, at 28 days

the SDA/OPC concrete mixes with a cement replacement level up

to 25% total binder weight exhibited a split tensile strength values

of over 90% of split tensile strength of neat OPC concrete as seen in

Table 8.The graphical correlation between a split tensile strength

ratio (split tensile strength of SDA concrete to neat OPC concrete)

and sawdust ash content in Fig. 9 illustrates a further reduction

in marginal differences between split tensile strength of sawdust

ash/OPC concrete with neat OPCconcrete at prolongedcuring 728

days.

Naik et al. (2002) studied the influence of wood ash on the

splitting tensile strength of concrete when used as partial cement

replacement material in production of concrete. Wood fly ash

was used in the partial replacement of cement to produce several

batches of concrete mix at replacement level of 5%, 8% and 12%

total binder weight. A corresponding control concrete mix with-

out wood fly ash content was cast for comparison. The tensile split

strength of the concrete specimens produced was monitored at 3,

7, 28, 91, 182 and 365 days. (i) From the laboratory results analy-

sis, it was reported that control concrete mixtures achieved a split

tensile strength of 3.8 MPa at 28 days and 4.3 MPa at 365 days; (ii)

the split tensile strength of concrete mixtures with wood fly ash

content varied between 3.6 and 4.0 MPa at 28 days and between

4.3 and 5.3 MPa at 365 days. It was also observed that for ages of

concrete beyond 28 days up to 365 days, the concrete mix with

wood ash content of 8% total binder weight exhibited the best split

tensile strength development behaviour with a magnitude of split

tensile strength consistently exceeded those of other test mixes.

6.4. Flexural strength

Naik et al. (2002)investigated the effects of the incorporation

of wood ash in partial replacement of cement in concrete mix

on flexural strength of hardened concrete. In this study, wood fly

ash was incorporated in a concrete mix at a cement replacement

level of 0 (control concrete), 5, 8 and 12%. The flexural strength

results obtained indicated that (i) control mixture achieved flex-

ural strength of 4.1 MPa at 28 days and 4.4 MPa at 365 days; (ii)

the strength of concrete mixtures with wood fly ash content varied

between 3.9 and 4.4 MPa at 28 days and between 4.3 and 5.3 MPa

at 365 days (iii) and at 7 days, all mixes with wood fly ash content

exhibited superior flexural strength relative to the control concrete

mix. The mix which had 5%woodfly ash exhibited the highest flex-

ural strength. (iv) At 28365 days, the concrete mix containing 8%

of wood fly ashexhibited optimal flexural strength among allmixesexamined.

Udoeyo et al. (2006)studied the flexural strength development

behaviour of concrete mixes produced with the use of wood waste

ash as a partial cement replacement material at varying levels of

cement replacement; (0 (control concrete), 5, 10, 15, 20, 25 and

30% binder weight. Flexural strengths of concrete specimens pro-

duced were recorded at 3, 7, 14, 21 and 28 days. Analysis of the

results indicatedthatat allagesthe concretetherewas an increased

level of cement replacement with wood waste ash that resulted

in a decreased magnitude of flexural strength. For instance, at 28

days, the flexural strength of the concrete mix with 5% wood waste

ash content was recorded at 5.20 MPa as compared to 5.57MPa of

control concrete specimens. A gradual reduction occurred in the

flexural strength over 28 days. Results revealed a decrease from5.20MPa with 5% wood waste ash concrete to 3.74 MPa with 30%

total binder mass with wood waste ash content in the mix was

observed. By performing a regression analysis of flexural strength

and compressive strength data acquired, they also found a strong

direct linear proportional correlation between flexural strength and

the compressive strength of wood waste ash concrete mixes pro-

duced for up to 28 days as presented in the following equation.

ff = 0.234fcu 0.908(R2= 0.94) (1)

Rajamma et al. (2009)evaluated the 28 days flexural strength

of mortarmixes produced by partial replacement of cement binder

using fly ash from two distinct wood biomass power plants. Mor-

tar bars specimens fabricated for flexure testing were produced

with the use of wood fly ash at 0 (control mortar), 10, 20 and 30%


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Fig.13. Chloridediffusion coefficientof concreteat theage of 28days (Horsakulthai

et al., 2011).

of water absorption below 10% which has been an acceptable value

for most construction material.

7.3. Chloride permeability

Wang et al. (2008b) investigated the chloride penetration resis-

tance of air entrained in a concrete mix with a partial replacement

of cementbinder using wood fly ashand wood/coalblended fly ash.Level of cement replacement by several types of fly ash was main-

tained at 25% total binder weight. Various types of fly ash used as a

partial cementreplacementmaterialwere, to name a few, combus-

tion of wood (Wood), class C coal/woodblended fly (Wood C), class

F coal/wood blended fly ash (Wood F), class C and class F coal fly

ash and fly ash from co-combustion of coal and switch grass (SW1

and SW2). Wood C and Wood F blended fly ash were produced by

blending class C and class F coalfly ash withpure woodashata mass

ratio of 80% coal fly ash and 20% wood waste fly ash. All concrete

mixes produced were moist cured for 56 days prior to being sub-

jected to a rapid chloride permeability test which was performed in

accordance to ASTM C1202-91. Based on the test results obtained,

they observed that (i) the incorporation of wood waste ash at a

cement replacement level of 25% in air entrained concrete mix didnot result in a significant impairment of the chloride permeabil-

ity property of concrete. (ii) The utilization of wood waste/class F

coal blended fly ashin partial substitutionof cementhad significant

contribution towards lowering of chloride permeability property of

concrete mix. A slight increase in chloride permeability of concrete

mixwith25% wood wasteash used in partial substitutionof cement

relative to control concrete mixwith pure OPCbinder observed was

probably attributed to coarse particle size (30130m) of wood

waste ash used.

Horsakulthai et al. (2011)studied the effects of incorporating a

very finely ground ash from the co-combustion of wood, rice husk

and sugarcane bagasse waste (termed as BRWA) as partial cement

replacement material on the chloride permeability property of con-

crete mixproduced. The accelerated salt ponding methodwas usedto evaluate chloride permeability of two different grades (grade 20

and 35) of concrete mixes produced by the incorporation of BRWA

at a cement replacement level of 0, 10, 20, and 40% total binder

mass. The test results concluded that the incorporation of finely

ground BRWA as partial cement substitution in concrete resulted

in the enhancement of resistance against chloride penetration and

lowered the chloride diffusivity coefficient. The presence of BRWA

in a concrete mix at a cement substitution level of 10, 20 and 40%

resulted in the reduction of the chloride diffusion coefficient by

3040%,6570%and 75%respectively in comparison to control con-

crete mixes with only OPC as binder. The gradual reduction trend

of the chloride diffusion coefficient for two different grades of con-

crete was examined. The increasing level of cement replacement

by BRWA is presented inFig. 13.

7.4. Alkali silica reaction (ASR)

Wang and Baxter (2007)investigated the alkali silica reaction

(ASR) expansion behaviour of mortar mixes containing a reactive

aggregate (opal), high alkali cement and three different type of fly

ash. Three types of fly ashes used were C, SAW and 10P. They were

obtainedfromthe combustion ofclassC coal,co-firingof classC coal

with sawdust at mass ratio of 80%coal/20% sawdust andco-firingof

class C coal with switch grass at mass ratio of 90% coal/10% switch

grassrespectively. Four batches of mortar mix with similar binders:

aggregate: water proportion was made. They included a batch of

control mortars (with only OPC as binder) and three other batches

with the three different types of fly ash used at a constant level

of cement replacement with 35% total binder weight. The change

in length of the mortar bars were designed from the four different

mortarmixesandmonitoredat 1 day,14 days, 1,2, 3,4, 6,9 and 12

months. The test results indicated that although sawdust-coal co-

fired fly ash(SAW)had much higheralkali content in comparison to

class C flyash, it performedbetter in thereduction of ASRexpansion

than class C fly ash. The use of sawdust-coal co-fired fly ash in the

mortar mix was found to be able to reduce ASR expansion at 6

months below 0.1% (maximum expansion specified in ASTM C33)

from 0.28%. This occurred with the control mortar mix having only

OPC as binder. Among the fly ash examined, sawdust-coal co-firedashwas observed tohave best performance in themitigation of ASR

expansion.

7.5. Corrosion current and electrical resistance

Horsakulthai et al. (2011) investigated the effects of partial

substitution of cement with very finely ground ash from co-

combustion of chop wood, rice husks and sugarcane bagasse

(termed as BRWA). These substitutions were tested in two dif-

ferent grades of concrete on the corrosion current and electrical

resistance of hardened concrete mixes. The two concrete mixes

had a target strength grade of 20 MPa and 35MPa respectively. For

grade 20 mixes, BRWA was used as partial cement replacement

material at a replacement level of 0 (control mix), 10, 20, and 40%.Meanwhile, for the grade 35MPa mix, BRWA was used at a cement

replacement level of 0 (control mix), 10 and20%.The corrosioncur-

rent and electrical resistance of mixes produced were evaluated by

an accelerated corrosion test using the impressed voltage (ACTIV)

method. From the test results they observed that increased levels

of cementreplacementusing BRWA resulted in increasedelectrical

resistance of the mix. This is indicated by a lowered value of initial

corrosion current passing the mix. For grade 20 concrete, values of

initial corrosion current of the mixes with BRWA content of 0, 10,

20 and 40% were recorded to be 27.4, 18.8, 7.9 and 4.0 mA respec-

tively. While for the grade 35 concrete mix, with BRWA content of

0, 10 and 20%, currents reported were to be 26.1, 14.5 and 6.4 mA

respectively. The enhancement in electrical resistance of the con-

crete mix with the use of BRWA as partial cement replacementmaterial was largely attributed to the effect of the overall reduc-

tion of the average pore size. There was a quality improvement of

the interfacial transition zone between the cement paste matrix

and the aggregates formed by the additional CSH compounds from

the pozzolanic reaction. This reaction, in turn occurred between

the amorphous silica content of BRWA with portlandite formed

during the OPC hydration stage. Test results of the accelerated cor-

rosion test, by impressed voltage, also

Documents

The Implementation of Wood Waste Ash as a Partial Cement Replacement Material