Effect of burning temperature on alkaline reactivity of rice husk ash with lime

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<ul><li><p>This article was downloaded by: [Linnaeus University]On: 19 October 2014, At: 02:45Publisher: Taylor &amp; FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK</p><p>Road Materials and Pavement DesignPublication details, including instructions for authors andsubscription information:http://www.tandfonline.com/loi/trmp20</p><p>Effect of burning temperature onalkaline reactivity of rice husk ash withlimeLeonardo Behaka &amp; Washington Peres Nezba Geotechnical Department, Faculty of Engineering, University ofthe Republic of Uruguay, Montevideo, Uruguayb Post-Graduation Program in Civil Engineering, Federal Universityof Rio Grande do Sul, Porto Alegre, BrazilPublished online: 02 Apr 2013.</p><p>To cite this article: Leonardo Behak &amp; Washington Peres Nez (2013) Effect of burningtemperature on alkaline reactivity of rice husk ash with lime, Road Materials and Pavement Design,14:3, 570-585, DOI: 10.1080/14680629.2013.779305</p><p>To link to this article: http://dx.doi.org/10.1080/14680629.2013.779305</p><p>PLEASE SCROLL DOWN FOR ARTICLE</p><p>Taylor &amp; Francis makes every effort to ensure the accuracy of all the information (theContent) contained in the publications on our platform. However, Taylor &amp; Francis,our agents, and our licensors make no representations or warranties whatsoever as tothe accuracy, completeness, or suitability for any purpose of the Content. Any opinionsand views expressed in this publication are the opinions and views of the authors,and are not the views of or endorsed by Taylor &amp; Francis. The accuracy of the Contentshould not be relied upon and should be independently verified with primary sourcesof information. Taylor and Francis shall not be liable for any losses, actions, claims,proceedings, demands, costs, expenses, damages, and other liabilities whatsoever orhowsoever caused arising directly or indirectly in connection with, in relation to or arisingout of the use of the Content.</p><p>This article may be used for research, teaching, and private study purposes. Anysubstantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &amp;Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions</p><p>http://www.tandfonline.com/loi/trmp20http://www.tandfonline.com/action/showCitFormats?doi=10.1080/14680629.2013.779305http://dx.doi.org/10.1080/14680629.2013.779305http://www.tandfonline.com/page/terms-and-conditionshttp://www.tandfonline.com/page/terms-and-conditions</p></li><li><p>Road Materials and Pavement Design, 2013Vol. 14, No. 3, 570585, http://dx.doi.org/10.1080/14680629.2013.779305</p><p>Effect of burning temperature on alkaline reactivity of rice husk ashwith lime</p><p>Leonardo Behaka* and Washington Peres Nezb</p><p>aGeotechnical Department, Faculty of Engineering, University of the Republic of Uruguay, Montevideo,Uruguay; bPost-Graduation Program in Civil Engineering, Federal University of Rio Grande do Sul, PortoAlegre, Brazil</p><p>(Received 4 March 2012; final version received 10 February 2013)</p><p>The rice husk ash (RHA) is a by-product of rice milling, being used as a soil stabiliser to buildroads, an economical alternativewith environmental benefits.A researchof the influence of kindand temperature of burning on the reactivity of RHA andmixtures with sandy soil and lime wasmade. A no controlled temperature RHA andRHAs donewith different controlled temperatureswere used. X-ray diffraction analyses and loss on ignition tests were carried out onRHAs. X-raydiffraction analyses, unconfined compressive strength, and splitting tensile strength tests wereconducted on mixtures of sandy soil with different RHAs and lime. The results showed that theoptimal reactivity of the RHA is reached for a range of controlled temperature of 650800C,providing a significant increase on the strength and stiffness of mixtures.</p><p>Keywords: road material; soil stabilisation; rice husk ash; burning temperature</p><p>1. IntroductionThe rice husk is a by-product of the rice milling. About 108 tonnes of rice husk is generatedannually in the world (Alhassan &amp; Mustapha, 2007). In Uruguay, 1.5 106 tonnes of rice areproduced annually while in Brazil 107 tonnes are produced (Behak &amp; Nuez, 2008). Accordingto Haji Ali, Adnan, and Choy (1992), every 4 tonnes of rice produced, 1 tonne is rice huskwhich means that in Uruguay and Brazil approximately 375,000 tonnes and 2.5 106 tonnes aregenerated annually, respectively. The final disposition of such quantities of rice husk is a seriousproblem around the world.The rice husk is burned in order to reduce the volume to be deposited. To give an economical</p><p>benefit to this burning, the rice husk is used as fuel for furnaces to dry the rice, Portland cementproduction, power generation, etc. The rice husk contains about 80% volatile organic compoundsand water, and the balance 20% of the weight of this husk is converted into ash during the burningprocess, which is known as rice husk ash (RHA) (Juliano, 1985). The RHA is a new residue andits final disposition is also a serious problem.According to Malhotra and Metha (1996), the pozzolanas are defined as siliceous or siliceous</p><p>and aluminous materials, which in themselves possess little or no cementing property, but chem-ically reacts with calcium hydroxide, in the presence of water at ordinary temperature, to formcompounds possessing cementitious properties. The RHA contains the highest concentration ofsilica of all plant residues (Boateng&amp;Skeete, 1990), being around 90% amorphous silica (Juliano,1985). The calcium hydroxide required for chemical reactions can be provided by the lime. Soilstabilisation is obtained by the addition of RHA and lime for road pavements and is particularly</p><p>*Corresponding author. Email: lbehak@fing.edu.uy</p><p> 2013 Taylor &amp; Francis</p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>Lin</p><p>naeu</p><p>s U</p><p>nive</p><p>rsity</p><p>] at</p><p> 02:</p><p>45 1</p><p>9 O</p><p>ctob</p><p>er 2</p><p>014 </p></li><li><p>Road Materials and Pavement Design 571</p><p>attractive in countries where rice husk is abundant because it leads to cheaper construction andlesser disposal costs, reduces environmental damage and preserves the most highly qualifiedmaterials for priority use (Haji Ali et al., 1992). The stabilisation of sandy-silty soils with RHAand lime reduces building costs, particularly in rural counties of developing countries (Basha,Hashim, Mahmud, &amp; Muntohar, 2005).The reactivity of the RHA significantly depends on the burning process of husk. Houston (1972)</p><p>proposed to classify the RHA according to the burning conditions in high-carbon char (black),low-carbon ash (grey) and free-carbon ash (pink or white). The colours are associated with theevolution degree of the combustion process and with the structural changes of the silica in theash (Boateng &amp; Skeete, 1990). The white colour indicates the total oxidation of the carbon inthe ash, while very high temperatures and long periods of incineration produce pink ashes typicalof crystalline silica. The RHA quality depends on the temperature, incinerating time, cooling timeand milling conditions (James &amp; Rao, 1986). According to James and Rao (1986), the silica in theash suffers structural transformations with temperature conditions affecting the reactions betweenthe RHA and lime and the properties of the soil-RHA-lime mixtures. The type of ash suitable forthe pozzolanic reactivity is amorphous rather than crystalline (James &amp; Rao, 1986). Rice huskincineration at temperature ranging from 550C to 700C has been found to produce amorphoussilica while temperatures in excess of 900C produce unwanted crystalline structures. However,Smith and Kamwanja (1986) observed formation of crystalline silica in small proportions fortemperatures of about 800Cmaintained for 12 h. Metha (1978) established that a highly reactiveash can be produced by maintaining the combustion temperature below 500C under oxidisingconditions for relatively prolonged period or up to 680C provided the high temperature exposurewas less than 1min. Prolonged heating above this temperature may cause the material to convert(at least in part) into crystalline silica. Chopra, Ahluwali, and Laxmi (1981) have reported thatfor incineration temperatures up to 700C, the silica was predominant in the amorphous form andthat the crystals present in the ashes grew with burning time. Nehdi, Duquette, and El Darmatty(2003) state that silica in RHA can remain in the amorphous form at combustion temperaturesof up to 900C if the combustion time is less than 1 h, whereas crystalline silica is produced at1000C with combustion time greater than 5min. Other reports claim that crystallisation of silicacan take place at temperatures as low as 600C, 500C, or even at 350C with 15 h of exposure(Bui, 2001).The structural changes at several temperatures affect the reactivity of the RHA since the larger</p><p>the specific surface of silica the greater the extent of chemical reactions with lime (Boateng &amp;Skeete, 1990). The technologies of ash production vary from open-heap burning to speciallydesigned incinerators (Metha, 1979). When the rice husk is burned in open heaps or in theconventional oven, crystalline ash with low reactivity index is produced while when is incineratedin an oven with controlled temperatures, the residue is a highly reactive white ash that mixturedwith lime changes into a cement structurally as good as Portland cement (Metha, 1975). Therice husk incinerated in oven at controlled temperature conditions between 800C and 900Cverified a high reactivity of ash in comparison with the ash resulting from the open-heap burning(Boateng &amp; Skeete, 1990).Carbon content of RHA influences the stabilisation process, retarding the reactions and produc-</p><p>ing low increases of strength. The avidity of carbon by calcium ions interfere with the reactionsbetween calcium ions and amorphous silica (Petry &amp; Glazier, 2005). According to these authors,lime stabilisation of soils with 6% of carbon is economically impracticable. Rahman (1987) mea-sured a remaining carbon content less than 3% in an RHA obtained by burning in an oven atcontrolled temperature of 800C.The aim of this paper is to present a research of the effects of both type and temperature of</p><p>incineration on the RHA reactivity and stabilisation of a sandy soil of Uruguay with RHA and</p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>Lin</p><p>naeu</p><p>s U</p><p>nive</p><p>rsity</p><p>] at</p><p> 02:</p><p>45 1</p><p>9 O</p><p>ctob</p><p>er 2</p><p>014 </p></li><li><p>572 L. Behak and W.P. Nez</p><p>Table 1. Physical characteristics of used material.</p><p>Material</p><p>Physical characteristics Rice husk RHAr Soil Lime</p><p>Particle size distribution (%)Passing #4 100.0 99.6 98.4 100.0Passing #10 90.5 97.5 87.3 100.0Passing #40 3.9 71.0 28.5 99.5Passing #200 0.8 11.8 6.5 92.9&lt; 2m 0.8 6.0 1.6</p><p>Atterberg limits (%)Plastic index No plastic No plastic No plastic No plasticSpecific gravity 1.46 1.81 2.65 2.48</p><p>lime. For this scope, RHAmadewithout temperature control into a furnace (named in this paper asresidual RHA) and RHAsmade in a laboratory oven at different controlled temperatures (RHATC)were used.</p><p>2. Materials2.1. Residual RHA and rice huskThe residual RHA (RHAr) and rice husk for laboratory controlled temperature incineration werecollected from Arrozur, a rice parboiled plant sited in the city of Treinta y Tres, north-easternUruguay. The rice husk is used in Arrozur as a fuel for rice-dried furnaces. The incinerationprocess is done without temperature control and the temperature greatly varies in the furnace dueto its large size. A leaf-shaped and black RHAr results from rice dried which can be classified ashigh-carbon ash according to Houston (1972). Given these characteristics might be expected anash with low pozzolanic reactivity. The values of physical characteristics of used materials aregiven in Table 1.The particle size distribution of the rice husk and RHAr is shown in Figure 1. The RHAr is</p><p>coarse-sized, with 88% of weight retained on #200 sieve and 11% of the fine fraction greater than2m. A quite high content of organic of 18.7% was verified by loss on ignition analysis. Theparticle size distribution of RHAr is finer than that of the rice husk because of the volatilisation</p><p>Figure 1. Particle size distribution of residual RHA and rice husk.</p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>Lin</p><p>naeu</p><p>s U</p><p>nive</p><p>rsity</p><p>] at</p><p> 02:</p><p>45 1</p><p>9 O</p><p>ctob</p><p>er 2</p><p>014 </p></li><li><p>Road Materials and Pavement Design 573</p><p>Figure 2. X-ray diffractograph of residual RHA. Cr, cristobalite; C, carbon.</p><p>of coarse elements of rice husk during the incineration process. Among these, 99% of rice huskis retained on #200 sieve. The specific gravity of rice husk and RHAs grains was, respectively,1.46 and 1.81. During the incineration process of rice husk are volatilised their lighter elementssuch as organic matter, remaining the heaviest in the ash, as is the silica. As a result, the RHArspecific gravity is greater than that of the rice husk.Characteristic peaks of cristobalite are identified from the X-ray diffractograph of the RHAr</p><p>(Figure 2) which indicates that part of the silica which is in the crystalline state and, therefore,is not reactive. The peak of carbon confirms the presence of crystallised organic compounds inthe ash.</p><p>2.2. SoilA sedimentary sandy soil with low content of fines from the quaternary period was collected froma quarry sited 24 km west of Montevideo. This soil is constituted by 1% of gravel, 92% of sand,1% of silt and 6% of clay. The soil classifies as well-graded silty sand (SW-SM) according to theUnified Soil Classification System and classifies as A-1-b by the American Association of StateHighway and TransportationOfficials (AASHTO) classification system. TheX-ray diffractographof the sedimentary soil (Figure 3) shows the presence of quartz typical of the sandy fraction andthe main components of the clay fraction are kaolinite and montmorillonite.</p><p>2.3. LimeA commercial lime manufactured in Uruguay was used. This lime constituted 66% of calciumoxide, 5% of magnesium oxide and others elements like silica and ferric oxide. The lime was finewith 100% of weight passing the #10 sieve and 93% passing the #200 sieve, whereas 91% wasgreater than 2m.</p><p>3. Methodology3.1. RHA at controlled temperatureRice husk was incinerated into the oven at controlled temperatures of 500C, 650C, 800C and900C (RHA500, RHA650, RHA800 and RHA900, respectively). Due to the low-volume capacity</p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>Lin</p><p>naeu</p><p>s U</p><p>nive</p><p>rsity</p><p>] at</p><p> 02:</p><p>45 1</p><p>9 O</p><p>ctob</p><p>er 2</p><p>014 </p></li><li><p>574 L. Behak and W.P. Nez</p><p>Figure 3. X-ray diffractograph of sandy soil. Qz, quartz; K, kaolinite; Mm, montmorillonite.</p><p>of the oven and low specific density of the rice husk, 3040 g of rice husk were placed in aporcelain vessel and then burned for 4 h in turns. After the burning process, the produced ash wasair-cooled. The ash reactivity depends on the burning and cooling time (James &amp; Rao, 1986).Smith and Kamwanja (1986) have reported that temperatures of 800C maintained for 12 h givesmall proportions of crystalline silica. The complete burning took 79 h in an incinerator speciallybuilt by Boateng and S...</p></li></ul>


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