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Resources, Conservation and Recycling 67 (2012) 27– 33

Contents lists available at SciVerse ScienceDirect

Resources, Conservation and Recycling

journa l h o me pa ge: www.elsev ier .com/ locate / resconrec

eview

tilization of wood ash in concrete manufacturing

afat Siddique ∗

enior Professor of Civil Engineering, Thapar University, Patiala 147004, Punjab, India

r t i c l e i n f o

rticle history:eceived 7 June 2012eceived in revised form 10 July 2012ccepted 19 July 2012

eywords:ompressive strength

a b s t r a c t

Solid waste management is the prime concern globally due to ever increasing quantities of waste mate-rials and industrial by-products. Scarcity of land-filling space and because of its ever increasing cost,recycling and utilization of industrial by-products and waste materials has the only option. There areseveral types of such materials. The utilization of such materials in concrete not only makes it eco-nomical, but also helps in reducing disposal concerns. One such material is wood ash (WA). Wood ash(WA) is the residue generated due to combustion of wood and wood products (chips, saw dust, bark,

oncretelumptrength propertiesurability propertiesater absorption capacityood ash

etc.). It is the inorganic and organic residue remaining after the combustion of wood or unbleachedwood fiber.

This paper details about the physical, chemical, elemental and mineralogical composition of wood ash.It highlights the influence of wood ash on the slump, water absorption, compressive strength, splittingtensile strength, flexural strength, freezing and thawing resistance, and shrinkage of concrete. It alsodeals with the leaching behavior of wood ash.

© 2012 Elsevier B.V. All rights reserved.

ontents

. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281.1. Applications of wood ash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

1.1.1. Land application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281.1.2. Pollution control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281.1.3. Construction materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

. Properties of wood ash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282.1. Physical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282.2. Elemental analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292.3. Chemical composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292.4. Mineralogical analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

. Properties of concrete containing wood ash. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303.1. Slump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303.2. Water absorption capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303.3. Compressive strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303.4. Splitting tensile strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313.5. Flexural strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313.6. Drying shrinkage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323.7. Freezing and thawing resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

3.8. Batch leaching of wood ash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

∗ Tel.: +91 175 239 3207; fax: +91 175 239 3005.E-mail address: siddique 66@yahoo.com

921-3449/$ – see front matter © 2012 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.resconrec.2012.07.004

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

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8 R. Siddique / Resources, Conser

. Introduction

Wood ash (WA) is the residue generated due to combustion ofood and wood products (chips, saw dust, bark, etc.). It is the inor-

anic and organic residue remaining after the combustion of woodr unbleached wood fiber. Hardwoods usually produce more ashhan softwoods and the bark and leaves generally produce moresh than the inner woody parts of the tree. On the average, theurning of wood results in about 6–10% ashes. Wood ash composi-ion can be highly variable depending on geographical location andndustrial processes.

.1. Applications of wood ash

Approximately, 70% of the wood ash generated is landfilled; 20%s applied on land as a soil supplement, and remaining 10% haseen used for miscellaneous applications (Etiegni, 1990; Campbell,990; Etiegni and Campbell, 1991; NCASI, 1993) including con-truction materials, metal recovery, and pollution control.

.1.1. Land applicationWood ash applications should be limited to a level that main-

ains the soil pH within the optimum range for the intended croprowth. The liming ability of wood ash is generally estimated bysing a laboratory measured parameter called the calcium carbon-te equivalent (CCE). The CCE indicates how well the wood ash willaise the soil pH compared to lime (calcium carbonate). As withhe nutrient composition of wood ash, the CCE of different woodsh may vary considerably, however, most are within the range of5–60%.

Etiegni and Campbell (1991) reported the use of wood ash as angricultural soil supplement and liming material. For that investi-ation, two types of plants (winter wheat and poplar) were grownn a greenhouse on six different Idaho (United States) soils amended

ith varying amounts of wood ash. The results indicated a substan-ial increase in the wheat biomass and in the diameter and height ofhe poplar at ash concentrations of up to 2% (16 tons/acre). Based onhe results obtained, the author indicated that wood ash could besed as a low-grade fertilizer containing potassium and as a liminggent. Meyers and Kopecky (1998) reported that use of wood ashesulted in a higher yield compared to those obtained with limednd fertilized control treatments. No adverse effects were noted atood ash application rates of up to 20 tons/acre.

Nguyen and Pascal (1997) measured tree growth responsessing two sources of wood ash as a forest soil amendment. Theddition of wood ash affected all the measured growth responsesheight, diameter, and total leaf area) within the tested range.owever, 2% (i.e., 16 tons/acre) application rate was found to beptimum. Bramryd and Frashman (1995) reported a decrease incidity and aluminum concentration when wood ash was appliedo the soil having 35-year old pine trees in Sweden. Except Cu, noignificant increase in heavy metal concentrations was found dueo the addition of wood ash.

Naylor and Schmidt (1986) evaluated wood as a fertilizer andiming material. Wood ash was mixed with two acidic soils at ratesf 0, 0.4, 1.8 and 2.4 tons/acre to assess changes in extractableutrients and soil pH. Concentrations of extractable P, K, and Ca

ncreased with increasing ash application rate. The same trend waslso noticed for soil pH. The neutralizing capability of the ash wasound to be half of that achieved by using agricultural limestone.

.1.2. Pollution control

Wood ash has been used as a replacement of lime or cement

iln dust in the solidification of hazardous wastes (NCASI, 1993). Itas also been used for odor as well as pH control of hazardous andon-hazardous wastes. Wood ash has been added to compost as a

and Recycling 67 (2012) 27– 33

color and odor control. Wood ash has been found to capture severalwater borne contaminants (NCASI, 1993).

1.1.3. Construction materialsNot much work has been reported relating to the applications of

wood ash as a construction material, particularly in cement-basedmaterials. Due to high carbon content in wood ash, its use is limitedto low- and medium-strength concrete materials. In Europe, woodash has also been used as a feedstock in the manufacture of Portlandcement (Etiegni, 1990). Naik (1999) reported that wood ash has asubstantial potential for use as a pozzolanic mineral admixture andan activator in cement-based materials. He further indicated thatwood ash has significant potential for use in numerous other mate-rials including controlled low strength materials (CLSMs), low- andmedium-strength concrete, masonry products, roller-compactedconcrete pavements (RCCPs), materials for road base, and blendedcements.

2. Properties of wood ash

Physical and chemical properties of wood ash are important indetermining their beneficial uses, and vary significantly dependingon many factors. These properties are influenced by species of tree,tree growing regions and conditions, method and manner of com-bustion including temperature, other fuel used with wood fuel, andmethod of wood ash collection (NCASI, 1993; Etiegni, 1990; Etiegniand Campbell, 1991).

2.1. Physical properties

Etiegni and Campbell (1991) studied the effect of combustiontemperature on yield and chemical properties of wood ash. Theresults showed that wood ash yield decreased by 45% when com-bustion temperature were increased from about 550 to 1100 ◦C.The average particle size of the wood ash was found to be 230 �m.The pH of wood ash was found to vary between 9 and 13.5.

Naik (1999) determined the physical and chemical propertiesof wood ashes derived from different mills. The average moisturecontent values for the wood ash studied were about 13% for flyash and 22% for bottom ash. The average amount of fly ash pass-ing sieve #200 (75 �m) was 50%. The average amount of fly ashretained on sieve no. 325 (45 �m) was about 31% for wood fly ash.Test results for unit weight or bulk density (ASTM C 29) exhibitedaverage density values of 490 kg/m3 for fly ash and 827 kg/m3 forbottom ash. Wood fly ash had an average specific gravity value of2.48. Specific gravity for bottom ash showed an average of 1.65.The average saturated surface dry (SSD) moisture content valueswere 10.3% for fly ash and 7.5% for bottom ash. The average cementactivity index at the age of 28 days for fly ash was about 66% ofthe control. The average water requirement for fly ash exhibited avalue of 116%. Autoclave expansion tests for fly ash exhibited a lowaverage expansion value of 0.2%.

Naik et al. (2003) evaluated the wood ashes from five differentsources for possible use in making controlled low-strength mate-rials (CLSMs). They used wood ashes from five different sources inWisconsin (USA) and were designated as W1–W5. Physical prop-erties of all the five sources of wood ash are presented in Table 1.Fineness of the wood ash (% retained on 45 �m sieve) varied from23 to 90%. Specific gravity of wood ash sources ranged from 2.26 to2.60.

Udoeyo et al. (2006) reported the physical properties of waste

wood ash (WWA), used as additive in concrete. The WWA had aspecific gravity of 2.43, a moisture content of 1.81%, and a pH valueof 10.48. The average loss on ignition of the ash was found to be10.46.

R. Siddique / Resources, Conservation and Recycling 67 (2012) 27– 33 29

Table 1Physical properties of wood ash used (Naik et al., 2003).

Test Source

W1 W2 W3 W4 W5

Retained on no. 325 sieve (%) 23 60 90 40 12Strength activity index with cement, % of control

3 days 88 38 102.0 53.8 112.37 days 84 39 83.3 59.3 72.028 days 88 34 78.7 59.4 67.0

Water requirement, % of control 115 155 115 126 130Autoclave expansion, % 0.2 0.5 −0.6 −0.22 0.12Unit weight, kg/m3 545 412 1376 509 162

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Abdullahi (2006) determined the properties of wood ash to besed as partial replacement of cement. The wood ash used wasowdery, amorphous solid, sourced locally, from a bakery. Theood ash was passed through BS sieve 0.075 mm size. The spe-

ific gravity of wood ash was found to be 2.13. The bulk density ofood ash was found to be 760 kg/m3.

.2. Elemental analysis

Typically, wood ash contains carbon in the range of 5–30%Campbell, 1990). The major elements of wood ash include cal-ium (7–33%), potassium (3–4%), magnesium (1–2%), manganese0.3–1.3%), phosphorus (0.3–1.4%), and sodium (0.2–0.5%). Den-ity of wood ash decreases with increasing carbon content. Thehemical and physical properties depend upon the type of wood,ombustion temperature, etc. (Campbell, 1990; Mishra et al., 1993).n elemental metal and other analysis for various types of wood arehown in Table 2.

Mishra et al. (1993) investigated the elemental and molecularomposition of mineral matters in ash from five types of woodnd two types of barks as a function of temperature. The massoss occurred in the range of 23–48% when the combustion tem-erature was increased from 500 to 1300 ◦C. This was attributedo decreased elemental mass concentrations of K, S, B, Na, andu resulting from increased temperature. Steenari and Lindqvist1998) characterized fly ashes derived from co-combustion ofood chips and fossil fuels, and compared their properties with

hose obtained from combustion of wood ash alone. The fly ashes

erived from the co-combustion of wood with coal or peat exhib-

ted lower concentrations of calcium, potassium, and chlorine, andigher concentrations of aluminum ion and sulfur relative to pureood ash.

able 2lemental metals and other analyses for ash from wood (mg/kg).

Elemental metal Normal wood fuel Particle/plywood Cr

Arsenic 42–53 22.5–26.9

Aluminum 4000–4500 4400–4800 3Barium 220–300 280–400

Copper 41–46 50–59

Chromium 12–14 12–15

Cadmium 5.5–6.1 7.3–7.9

Manganese 2440–2750 2430–2740 2Mercury 0.05–0.08 0.06–0.10

Iron 5900–6100 3700–4300 14Lead 29–35 73–78

Nickel 6–8 6–7

Silver 0.2–0.4 0.3–0.4

Selenium 0.53–064 0.55–0.64

Zinc 380–420 530–610

PH 11.31–11.67 10.64–10.85 1Alkalinity (%) 12.0–13.2 13.4–14.6

2.60 2.26 2.33

Naik et al. (2002) studied the elemental analysis of woodobtained from Rothschild, Wisconsin in United States, and com-pared it with that of the Type-I cement. Analysis was done usingInstrumental Neutron Activation Analysis. The elemental compo-sition of the cement and wood ash differed considerably. Thepredominate elements contained in the wood ash (>5000 ppm)were Aluminum, Cadmium, Calcium, Iron, Magnesium, Manganese,Potassium, Sodium, and Titanium. Primary elements in the cementwere Aluminum, Calcium, Iron, and Potassium. The wood ash hadmuch higher amounts of Magnesium, Manganese, Potassium, Alu-minum, and Sodium than the cement.

2.3. Chemical composition

Etiegni (1990) and Etiegni and Campbell (1991) reported thatmajor oxides detected in the wood ash were lime (CaO), calcite(CaCO3), portlandite (Ca (OH) 2) and calcium silicate (Ca2SiO4). Theauthors reported that swelling of wood ash occurred due to thepossible hydration of silicates and lime present in the ash. Naiket al. (2003) studied the chemical composition of wood ashes fromfive different sources for their possible use in making controlledlow-strength materials (CLSMs). Chemical composition of all thefive sources of wood ash is presented in Table 3. The LOI obtainedfor the wood ashes ranged from 6.7 to 58.1%.

Udoeyo et al. (2006) reported the chemical composition of wastewood ash (WWA). The results of the oxide concentrations of theash, measured using an X-ray diffraction (XRD) test, showed thatits major oxide components are: CaO, SiO2, Al2O3, K2O, Fe2O3, MgO,

SO3, TiO2, and P2O5. Other substances, such as Na2O, ZnO, Cl, MnO,SrO, Cr2O3, CuO, ZrO2, and Rb2O, were found in trace amounts. Thechemical analysis showed that the ash has silicon dioxide (SiO2),aluminum oxide (Al2O3), and iron oxide (Fe2O3) values of 20.8, 11.6,

eosote-treated Construction/demolition wood CCA-treated

51–64 78–98 8570–9390600–5000 4900–5800 3900–4500200–280 480–590 220–280

49–52 71–93 2610–282014–17 34–39 1710–18505.1–5.7 7.1–8.1 10.7–11.7

040–2140 2030–2230 2610–27200.12–0.14 0.36–0.52 0.03–0.32,900–17,100 6900–7400 6400–6900

47–50 920–1010 58–738–10 7–10 6–8

0.4–0.4 0.1–0.1 0.7–0.80.74–0.81 0.84–0.97 1.18–1.45450–510 1420–1520 520–6200.69–11.09 10.76–11.12 10.68–10.8410.2–11.6 11.7–12.5 11.1–12.2

30 R. Siddique / Resources, Conservation and Recycling 67 (2012) 27– 33

Table 3Chemical composition of wood ash used (Naik et al., 2003).

Analysis parameter Source

W1 W2 W3 W4 W5

Silicon dioxide, SiO2 (%) 32.4 13.0 50.7 30.0 8.1Aluminum oxide, Al2O3 (%) 17.1 7.8 8.2 12.3 7.5Iron oxide, Fe2O3 (%) 9.8 2.6 2.1 14.2 3.0Calcium oxide, CaO (%) 3.5 13.7 19.6 2.2 25.3Magnesium oxide, MgO (%) 0.7 2.6 6.5 0.7 4.5Potassium oxide, K2O (%) 1.1 0.4 2.8 2.0 2.7Sodium oxide, Na2O (%) 0.9 0.6 2.1 0.5 3.3LOI (1000 ◦C) (%) 31.6 58.1 6.7 35.3 32.8

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Table 5Slump test results of wood ash concrete (Abdullahi, 2006).

Replacement of OPC by WA (%) 0 10 20 30 40Water/binder actual ratio 0.6 0.66 0.67 0.68 0.69

achieved strength of 34 MPa at 28 days and 44 MPa at 365 days; (ii)strength of concrete mixtures containing wood fly ash ranged from33 MPa at 28 days and between 42 and 46 MPa at 365 days and; (iii)

Moisture (%) 2.4 0.5 0.2 0.4 3.3Available alkali, Na2O (%) 0.9 0.4 0.8 1.1 4.2

nd 5.37, respectively. A combination of the percentage masses ofhese three oxides gives a total of 37.8%, which is less than the 70%imit specified for pozzolan in ASTM C 618 (1994).

Abdullahi (2006) determined the chemical composition ofood ash to be used as partial replacement of cement. The totalercentage composition of iron oxide (Fe2O3 = 2.34%), aluminumxide (Al2O3 = 28.0%) and silicon dioxide (SiO2 = 31.80%) was foundo be 62.14%. This is less than 70% minimum required for pozzolanaASTM C 618, 1994). This reduces the pozzolanic activity of theood ash. The loss on ignition obtained was 27%. The value isore than 12%; the maximum as required for pozzolana (ASTM

618-94). This means that the wood ash contain appreciablemount of un-burnt carbon which reduces its pozzolanic activity.he un-burnt carbon is not pozzolanic and its presence serves asller to the mixture. The alkali content (Na2O) was found to be.5%. This value is higher than the maximum alkali content of 1.5%equired for pozzolana.

.4. Mineralogical analysis

Campbell (1990) presented data on major and trace elements inood ash. The major elements were calcium (7–33%), potassium

3–4%), magnesium (1–2%), phosphorus (0.3–1.4%), manganese0.3–1.3%), and sodium (0.2–0.5%). The trace elements were zinc,oron, copper, molybdenum, and others at parts per million levels.arbon content in wood ash was found to vary between 4 and 34%y mass.

Naik et al. (2002) studied the mineralogical analysis of woodsh obtained from Rothschild in Wisconsin in United States. Theredominant crystalline phase present in the wood ash sampleas quartz (SiO2). Additional trace amounts of crystalline phasesetected in wood ash included gypsum (CaSO4·H2O), magnetiteFe3O4), microcline (KAlSi3O8), mullite (Al2O3·SiO2), periclaseMgO), and plagioclase (NaCa). The mineralogical analysis also indi-ated large amounts of amorphous material present in the woodsh (46.9%). The calcite, hematite, magnetite, microcline, mullite,lagioclase, and quartz present in the wood ash are generally noteactive when used in concrete.

. Properties of concrete containing wood ash

.1. Slump

Udoeyo et al. (2006) reported slump test results of concrete con-aining varying percentages (5, 10, 15, 20, 25, and 30% by weight of

able 4lump of concrete with WWA as additive (Udoeyo et al., 2006).

WWA content (%) 0 5 10 15 20 25 30Slump (mm) 62 8 5 2.5 0 0 0

Slump (mm) 30 35 40 40 35

cement) of waste wood ash (WWA) used as additive in concrete. Thetest results are presented in Table 4. It is evident from the resultsthat WWA concrete mixes exhibited less workability than that ofplain concrete of the same water–cement ratio, and it increasedwith higher content of WWA ash. At 20, 25, and 30% additive levelsthe concrete was insensitive to slump.

Abdullahi (2006) studied the influence of wood ash (WA) onthe slump of concrete. He used wood ash as partial replacement ofcement in varying percentages (0, 10, 20, 30, and 40%) in concretemixture proportion of 1:2:4. The result for the slump test is givenin Table 5. Test result showed that mixtures with greater woodash content require greater water content to achieve a reasonableworkability.

3.2. Water absorption capacity

Udoeyo et al. (2006) evaluated the water absorption capacityof concrete made with varying percentages (5, 10, 15, 20, 25, and30% by weight of cement) of waste wood ash (WWA) as additive(Fig. 1). It can be seen that concrete specimens absorbed more wateras the ash content increased. The water absorption at 5% WWAcontent was 0.4% and increased to 1.05% at 30% WWA content.However, these values are less than 10% which is the percentagewater absorption value accepted for most construction materials.

3.3. Compressive strength

Naik et al. (2002) investigated the compressive strength of con-crete mixtures made with wood ash up to the age of 365 days. Woodash content was 5, 8 and 12% of the total cementitious materials.Fig. 2 shows the compressive strength results. Based on the results,they concluded that: (i) control mixture (without wood fly ash)

Fig. 1. Percentage water absorption versus ash content of WWA concrete (Udoeyoet al., 2006).

R. Siddique / Resources, Conservation and Recycling 67 (2012) 27– 33 31

Table 6Compressive strength of concrete with WWA as additive (Udoeyo et al., 2006).

WWA content (%) Compressive strength (N/mm2)

3 days 7 days 14 days 28 days 90 days

0 16.24 ± 0.10a 16.85 ± 0.05 23.40 ± 0.46 28.35 ± 2.64 31.48 ± 0.50b

5 14.23 ± 1.04 15.31 ± 0.87 18.32 ± 0.67 24.61 ± 0.51 28.66 ± 0.70d

10 14.01 ± 0.86 15.31 ± 0.37 16.92 ± 0.75 21.86 ± 1.11 27.54 ± 0.34d

15 13.75 ± 0.62 14.18 ± 0.26 15.78 ± 0.68 21.73 ± 0.84 23.70 ± 0.81c

20 13.25 ± 0.47 14.10 ± 0.39 15.78 ± 0.68 20.55 ± 0.79 22.68 ± 0.81c

25 13.17 ± 0.36 14.05 ± 0.58 15.03 ± 0.88 20.35 ± 1.16 19.62 ± 0.56b

30 12.83 ± 0.30 13.88 ± 0.76 14.85 ± 0.25 19.52 ± 0.57 19.52 ± 0.57b

a Standard deviations.b Not significant.c � < 0.05.d � < 0.05.

Fe

ioaa

c3ae

omitseh6

TC

ig. 2. Compressive strength of concrete mixtures containing wood fly ash (Naikt al., 2002).

nclusion of wood fly ash contributed to the strength developmentf concrete mixtures, even as the cement content was decreased bybout 15%. This indicates contribution of wood fly ash to pozzolanicctivity.

Udoeyo et al. (2006) determined the compressive strength ofoncrete made with varying percentages (5, 10, 15, 20, 25, and0 by weight of cement) of waste wood ash (WWA). Tests resultsre given in Table 6. There was significant compressive strengthnhancement in strength due to a longer duration of curing.

Abdullahi (2006) reported the compressive strength test resultsf wood ash (WA) concrete. He used wood ash as partial replace-ent of cement in varying percentages (0, 10, 20, 30, and 40%)

n concrete mixture proportion of 1:2:4. Tests were conducted athe age of 28 and 60 days. Results are given in Table 7. The results

howed that the specimens containing 0% wood ash had the high-st compressive strength. The mixture containing 20% wood ashad higher strength than that containing 10% wood ash at 28 and0 days. This was due to the fact that the silica provided by 10%

able 7ompressive strength of wood ash concrete (Abdullahi, 2006).

WA content (%) Compressive strength (N/mm2)

28-day 60-day

0 23.96 24.1510 13.09 14.0620 14.13 18.6030 9.02 7.9140 8.59 7.82

wood ash was inadequate to react with the calcium hydroxideproduced by the hydration of cement. Increase in wood ash con-tent beyond 20% resulted in a reduction in strength at 28 and60 days. In this case, the silica present in the mix was in excess ofthe amount required to combine with the calcium hydroxide fromthe hydrating cement. The excess silica had no pozzolanic value butonly served as filler. At 60 days hydration period, the compressivestrength of concrete containing 20% wood ash increased consider-ably indicating that greater strength can be obtained at later ages.The optimum replacement of cement by wood ash was 20%.

3.4. Splitting tensile strength

Naik et al. (2002) investigated the influence of wood ash on thesplitting tensile strength of concrete. Wood ash content was 5, 8and 12% of the total cementitious materials. They concluded that(i) control mixture (without wood fly ash) achieved a strength of3.8 MPa at 28 days and 4.3 MPa at 365 days; (ii) strength of concretemixtures containing wood fly ash varied between 3.6 and 4.0 MPaat 28 days and between 4.2 and 5.1 MPa at 365 days and; (iii) split-ting tensile strength generally followed a similar pattern as for thecompressive strength.

3.5. Flexural strength

Naik et al. (2002) studied the effect of wood ash on the flexuralstrength of concrete. Three percentages (5, 8 and 12) of wood ashof the total cementitious materials were used. Flexural strengthresults of concrete mixtures are shown in Fig. 3. Based on theinvestigation, they concluded that (i) control mixture (withoutfly ash) achieved a strength of 4.1 MPa at 28 days and 4.4 MPa at365 days; (ii) strength of concrete mixtures containing wood flyash varied between 3.9 and 4.4 MPa at 28 days and between 4.3 and5.3 MPa at 365 days and;(iii) test results indicated that inclusion ofwood fly ash enhanced the flexural strength of concrete mixturesdue to pozzolanic contribution of the wood fly ash.

Udoeyo et al. (2006) reported flexural strength results of con-crete made with varying percentages (5, 10, 15, 20, 25, and 30% byweight of cement) of waste wood ash (WWA), used as additive inconcrete. The results of the flexural strength of concrete contain-ing WWA are presented in Table 8. The flexural strength decreasedwith the increase in WWA content but at a slower rate than that ofcompressive strength. The 28-day flexural strength of samples con-

taining 5% WWA was 5.20 N/mm2, and it decreased to 3.74 N/mm2

at 30% WWA content. The flexural strength magnitudes of WWAconcrete ranged between 67% and 93% of the control concrete atcorresponding ages and additive levels.

32 R. Siddique / Resources, Conservation and Recycling 67 (2012) 27– 33

Table 8Flexural strength of concrete with WWA as additive (Udoeyo et al., 2006).

WWA content (%) Flexural strength (N/mm2)

3 days 7 days 14 days 21 days 28 days

0 4.45 ± 0.04a 4.93 ± 0.15 5.44 ± 0.42 5.46 ± 0.03 5.57 ± 0.055 4.34 ± 0.02 4.67 ± 0.27 5.04 ± 0.20 5.18 ± 0.01 5.20 ± 0.01

10 3.81 ± 0.02 3.92 ± 0.07 3.99 ± 0.03 4.08 ± 0.09 4.28 ± 0.0915 3.75 ± 0.06 3.91 ± 0.03 3.97 ± 0.04 4.01 ± 0.15 4.04 ± 0.0420 3.64 ± 0.04 3.76 ± 0.04 3.79 ± 0.05 3.80 ± 0.05 3.85 ± 0.0825 3.51 ± 0.02 3.53 ± 0.07 3.55 ± 0.04 3.57 ± 0.03 3.73 ± 0.0330 3.65 ± 0.06 3.66 ± 0.02 3.69 ± 0.03 3.71 ± 0.05 3.74 ± 0.03

3

masat2aa2

3

ifim

cTs

u9w

p

Fe

a Standard deviations.

.6. Drying shrinkage

Naik et al. (2002) investigated the drying shrinkage of concreteixtures made with wood fly ash. Wood ash content was 5, 8

nd 12% of the total cementitious materials. They reported that (i)hrinkage of control mixture (with out wood ash) was −0.0092%t 7 days and −0.052% at 232 days; (ii) shrinkage of concrete mix-ure with 5% wood ash, ranged from 0.012% at 7 days to −0.027% at32 days; (iii) shrinkage for mixture with 8% wood ash was 0.014%t 7 days and −0.013% at 232 days; and (iv) mixture with 12% woodsh had shrinkage between −0.0051% at 7 days and −0.044% at32 days.

.7. Freezing and thawing resistance

Naik et al. (2002) studied the influence of wood ash on the freez-ng and thawing resistance of concrete. It was evaluated by testingor changes in relative dynamic modulus, pulse velocity, and changen length. Wood ash content was 5, 8 and 12% of total cementitious

aterials.There is no significant effect of freezing-thawing cycles (300

ycles) on the relative dynamic modulus of the concrete mixtures.he inclusion of wood ash in concrete mixtures did not make aignificant difference in relative dynamic modulus.

For control mixture (without wood ash), relative dynamic mod-lus was 97.7% and it was 95.7% for mixture (with 5% wood ash),

7.8% for mixture (8% wood ash), and 95.7% for mixture (with 12%ood ash).

There is no significant effect from inclusion of wood ash on theulse velocity of concrete mixtures. At 300 cycles, the pulse velocity

ig. 3. Splitting tensile strength of concrete mixtures containing wood fly ash (Naikt al., 2002).

Fig. 4. Flexural strength of concrete mixtures containing wood fly ash (Naik et al.,2002).

of concrete mixtures (without wood ash) was 5425 m/s, 5480 m/sfor mixture (5% wood ash), 5560 m/s for mixture (8% wood ash),and 5435 m/s for mixture (12% wood ash).

3.8. Batch leaching of wood ash

Udoeyo et al. (2006) reported the leachate results of waste woodash (WWA) used in varying percentages (5, 10, 15, 20, 25, and 30%),by weight, of cement as additive in concrete. Analyses of leachatefrom WWA, which are presented in Fig. 4, show the presence ofchromium, copper, iron, zinc, and arsenic in the leachates at almostall pH values. As evident in the results, arsenic exhibited the high-est leachability, while iron exhibited the lowest leachability. It wasfurther noted that apart from leaching of chromium, leaching ofall other metals from WWA showed significant dependence on pH.The leachability of the metals increased with decrease in pH. Appar-ently, the mineralogical phase of the metal oxides present in theash affected their susceptibility to attack by H+ ions present inthe leachant. At a lower pH, there was an increase in the inten-sity of attack of these ions on WWA mineral phases containingthese elements, thus the increase in leachability. A similar trend hasbeen observed by other researchers (Fytianos and Tsaniklidi, 1998;Karuppiah and Gupta, 1997). Their results also indicated that a pHof 5 does not provide enough concentration of H+ to attack ironoxide phases that are produced during incineration of wood waste.

The leachate concentrations of almost all the metals were higherthan the EPA fresh water acute criteria. Considering that wood ashwould not normally contain high concentrations of these metals,the recorded high concentrations in the leachate are attributable

R. Siddique / Resources, Conservation

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4

•

•

•

•

•

University of Technology, Goteborg, Sweden, Report no. ISSN 0366-8746 OCLC

Fig. 5. Metal concentration of WWA (Udoeyo et al., 2006).

o the wood preservatives used. It is therefore important to screenood waste as part of their selection process for use in concrete

Fig. 5).

. Conclusions

As such there is no separate code of practice for utilization ofwood ash, but its properties indicates that ASTM C 618, “Standardspecification for coal fly ash and raw or calcined natural pozzolanfor use as a mineral admixture in concrete”, could be suitable usedin case of wood ash.Inclusion of wood ash partial replacement of cement adverselyaffects the slump of the concrete.Water absorption capacity of the concrete increases with increasein wood ash content.Strength properties of concrete mixtures decreases marginally

with increase in wood ash contents, but increases with age dueto pozzolanic actions.Wood ash can be used for making precast products and structuralgrade concrete.

and Recycling 67 (2012) 27– 33 33

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