This paper presents a study on the strength and corrosion resistance of mortars made with binary blends of ordinary Portland cement (OPC) and ground rice husk ash (RHA) or ground palm oil fuel ash (POA).This paper presents a study on the strength and corrosion resistance of mortars made with binary blends of ordinary Portland cement (OPC) and ground rice husk ash (RHA) or ground palm oil fuel ash (POA). The mortar mixtures were made with Portland cement Type I containing 0-40% RHA and POA. RHA and POA with 1-3% by weight retained on a sieve No.325 were used. The water to binder ratio was kept constant at 0.5 and the flow of mortar was maintained at 110±5% with the aid of superplasticizer (SP). Scanning electron microscopy (SEM) was used for analysis. The compressive strength, chloride penetration and corrosion resistance of the mortar were determined. The results show that strength as well as the resistance of mortar to chloride and corrosion can be improved by blending with RHA and POA. Thus, RHA and POA have a high potential to be used as a good pozzolanic material

Chindaprasirt, Prinya

Rukzon, Sumrerng

Intellectual Repository at Rajamangala University of Technology Phra Nakhon

Original ArticleUse of waste ash from various by-product materialsin increasing the durability of mortarSumrerng Rukzon a,* and Prinya Chindaprasirt ba Rajamangala University of Technology,Phra Nakhon, Dusit, Bangkok, 10300 Thailand.b Department of Civil Engineering, Faculty of Engineering,Khon Kaen University, Khon Kaen, 40002 Thailand.Received  29 October 2007; Accepted  12 July 2008AbstractThis paper presents a study on the strength and corrosion resistance of mortars made with binary blends of ordinaryPortland cement (OPC) and ground rice husk ash (RHA) or ground palm oil fuel ash (POA). The mortar mixtures were madewith Portland cement Type I containing 0-40% RHA and POA. RHA and POA with 1-3% by weight retained on a sieveNo.325 were used. The water to binder ratio was kept constant at 0.5 and the flow of mortar was maintained at 110±5% withthe aid of superplasticizer (SP). Scanning electron microscopy (SEM) was used for analysis. The compressive strength,chloride penetration and corrosion resistance of the mortar were determined. The results show that strength as well as theresistance of mortar to chloride and corrosion can be improved by blending with RHA and POA. Thus, RHA and POA havea high potential to be used as a good pozzolanic material.Keywords: rice husk ash, palm oil fuel ash, corrosion, chloride penetration, mortarSongklanakarin J. Sci. Technol.30 (3), 485-489, May - Jun. 20081. IntroductionRice husk is one of the major agricultural wastes.When rice husk is burnt at temperatures lower than 700oC,rice husk ash with a cellular microstructure is produced. Ricehusk ash has a high silica content, in the form of non-crystal-line  or  amorphous  silica.  Therefore,  rice  husk  ash  is  apozzolanic material and can be used as a supplementarycementitious materials (Metha, 1979).Palm oil fuel ash is one promising pozzolan and isavailable  in  many  parts  of  the  world.  It  is  a  by-productobtained from a small power plant, which uses the palm fiber,shells and empty fruit bunches as a fuel and burnt at 800-1000oC. Palm oil fuel ash continues to garner more attentionbecause it is shown to generally improve the properties ofblended  cement  concrete  and  its  use  poses  a  comparablymilder environmental hazard. The main chemical composi-tion of palm oil fuel ash is silica which is a main ingredient ofpozzolan (Chindaprasirt et al., 2008).One of the main causes of corrosion of reinforcementstructures in concrete is chloride. When the chloride concen-tration  of  mortar  or  concrete  exceeds  a  certain  thresholdvalue,  depassivation  of  steel  occurs  and  reinforced  steelstarts to corrode (Thomas, 1996; Alonso et al., 2000). Theobjective of this research is to study the strength, chloridepenetration and corrosion resistance of blended cementmortar containing ground rice husk ash and ground palm oilfuel ash. The results of the study will be beneficial for futureapplications of the material in increasing the durability ofmortar and concrete.*Corresponding author.Email address: rerng197@rmutp.ac.thhttp://www.sjst.psu.ac.thS. Rukzon & P. Chindaprasirt / Songklanakarin J. Sci. Technol. 30 (3), 485-489, 20084862. Experimental details2.1  MaterialsOrdinary Portland cement (OPC), local rice husk,palm oil fuel ash from a thermal power plant in southern ofThailand, river sand with specific gravity of 2.63 and finenessmodulus of 2.82, and type-F superplasticizer (SP) were thematerials used in this study. Rice husk ash was obtained fromopen burning in small heaps of 20 kg rice husk with maxi-mum temperature of burning of 650oC. Ground palm oil fuelash (POA) and ground rice husk ash (RHA) were obtainedusing ball mill grinding until the percentage retained on asieve No. 325 (opening 45 mm) was 1-3%. Scanning electronmicroscopy (SEM) and grading analysis were used to study.2.2  Mix proportions and curingOPC  is  partially  replaced  with  pozzolans  at   thedosage of 0-40% by weight of cementitious materials. Asand-to-binder ratio of 2.75 by weight and a water to binderratio (W/B) of 0.5 were used. SP was incorporated in orderto obtain mortar mixes with a similar flow of 110±5%. Thecast specimens were covered with a polyurethane sheet anddampened cloth in a 23±2oC chamber. They were demouldedat the age of 1 day and moist cured at 23±2oC until the testages.2.3  Compressive strength50 × 50 × 50 mm cube samples were used for the com-pressive strength test of mortar. They were tested at the ageof 7, 28 and 90 days. The test was done in accordance withthe ASTM C109 (2001). The reported result is the averageof two samples. The mix proportions of mortar are given inTable 1.2.4  Rapid chloride penetration test (RCPT)Cylindrical samples of 100 mm diameter and 200 mmheight were prepared in accordance with ASTM C39 (2001).They were demoulded at the age of 24 hours. After beingcured  in  water  until  the  age  of  27  days,  the  cylindricalsamples were cut into 50 mm thick slices with the 50 mmends discarded. They were tested with the RCPT as shownin Figure 1. The 100 mm diameter and 50 mm thick epoxy-coated cylindrical specimens were conditioned and tested atthe age of 28 and 90 days with the RCPT in accordance withthe method described in ASTM C1202 (2001). The reportedresult is an average of two samples.2.5  Open circuit potential (OCP)The OCP test for the different systems was perio-dically monitored using a voltmeter with a high input imped-ance  of  10  MÙ.  The  half-cell  potential  of  the  rebar  wasmeasured versus immersion time using a saturated calomelelectrode (SCE) as a reference electrode. The correspondingpotentials were recorded. A sponge soaked with distilledwater was placed between the tip of reference electrode andthe surface of the mortar, to provide ionic conduction. Themeasurements were made at sites on the surface, at a mini-mum distance from the rebar.Mortar prisms 40 × 40 × 160 mm with embedded steelrebar of 10 mm in diameter and 160 mm in length were used.The steel rebar was secured such that it protruded from thetop surface of the prism by 15 mm, thus provided sufficientmortar cover of 15 mm at the bottom and the sides of theprism. The mortar bar was cast in two layers and compactedusing a vibrating table. After 28 days of curing, the mortarbars were placed in the environmental chamber. The mortarbars in the chamber were sprayed with a 5% NaCl solutionevery 3 days. The tests were continued over a period of 180days. In this study, specimens in triplicate were used for eachsystem and the average of these values was reported andinterpreted based on ASTM C876 (2001). The mixed propor-tions of mortar are given in Table 1.3. Results and discussions3.1  Characteristics of OPC, POA and RHAThe chemical constituents are given in Table 2. Themain chemical components of POA are 63.6% of SiO2, 7.6%of CaO and 6.9% of K2O. The high CaO and K2O contentsare most likely from lime and fertilizer (Chindaprasirt et al.,Table 1. Mortar mix proportions   Mix OPC POA RHA SP (%)OPC 100 - - 2.020POA 80 20 - 2.140POA 60 40 - 3.220RHA 80 - 20 2.240RHA 60 - 40 3.9Figure 1. The rapid chloride penetration test (RCPT).487S. Rukzon & P. Chindaprasirt / Songklanakarin J. Sci. Technol. 30 (3), 485-489, 20082008). The loss on ignition (LOI) is 9.6%, which is not toohigh, indicating a reasonable burning temperature and time.The sum of SiO2, Al2O3 and Fe2O3 is 66.6% which is slightlyless than 70% as required for natural pozzolan, according toASTM  C618  (2001).  RHA,  on  the  other  hand,  consistsmainly of SiO2, and the other components are not signific-ant.  The  SiO2  content  of  93%  satisfies  the  ASTM  C618(2001) requirement as a natural pozzolan and a LOI of 3.7%indicates complete burning (Chindaprasirt et al., 2008). Thefineness characteristics of Portland cement and pozzolanicmaterials are given in Table 2. The Blaine fineness of OPCis 3600 cm2/gm. The finenesses of POA and RHA are 11800and 11200 cm2/gm, respectively. The specific gravity of theOPC, POA and RHA are 3.14, 2.25 and 2.23, respectively.The percentage of POA and RHA retained on a 325 sieve is1-3%. The particle size distribution of Portland cement andpozzolanic  materials  are  given  in  Figure  2.  The  medianparticle sizes of the POA, RHA and OPC are 7.0, 10.0 and15.0 µm, respectively.3.2  Compressive strengthThe compressive strength and normalized (strengthactivity index) of mortars are given in Figure 3. The strengthdevelopment of OPC mortar is rather good. The 7, 28 and90 day strengths are 43.5, 57.0 and 60.0 MPa, respectively(Figure 3a). At a replacement dosage of 20%, the strengthsof mortar containing POA and RHA are also high, between102% and 106% of those of OPC mortar at the same age (Fig-ure  3b).  For  a  40%  replacement  dosage,  reductions  instrength at 7 days are apparent for mixes containing eitherPOA or RHA. The 7 day strengths are 76-77% of that of OPCmortar at the same age. At the age of 90 days, strengths ofPOA and RHA mortar are 103% of that of OPC mortar atthe same age (Figure 3b). The low early strength and laterage strength development exhibited by the 40% replacementdosage mortar samples is a common feature of pozzolanicmaterials. The results of the compressive strength test of themortar suggest that POA and RHA have a high potential forbeing  used  as  a  pozzolanic  material  in  a  ternary  blendedcement system when the material is ground and classified asa fine particle size. The increased fineness of the pozzolansresulted in a greater pozzolanic reaction efficiency. In addi-tion,  smaller  particles  are  more  effective  at  filling  in  thevoids of mortar mixture, thus increasing the compressivestrength of mortar3.3  RCPT resultsThe RCPT method usually causes the temperature ofthe mortar specimens to rise. However, for the specimens usedhere, the temperature rise is not large as the mortar speci-01020304050607080901000.01 0.1 1 10 100 1000Particle size (micron)Cummulative Passing (%)POARHAOPCTable 2. Chemical composition and characteristics of OPC, RHA and POAPhysical properties and oxides OPC RHA POAMedian particle size (µm) 15.0 10.0 7.0Retained on a sieve No. 325 (%) - 1-3 1-3Specific Gravity 3.14 2.23 2.25Blaine Fineness (cm2/gm) 3,600 11,200 11,800SiO2 20.9 93.2 63.6Al2O3 4.8 0.4 1.6Fe2O3 3.4 0.1 1.4CaO 65.4 1.1 7.6MgO 1.3 0.1 3.9Na2O 0.2 0.1 0.1K2O 0.4 1.3 6.9SO3 2.7 0.9 0.2LOI 0.9 3.7 9.6SiO2+ Al2O3+ Fe2O3 - 93.7 66.6Figure 2. Particle size distributions of POA, RHA and OPC.S. Rukzon & P. Chindaprasirt / Songklanakarin J. Sci. Technol. 30 (3), 485-489, 2008488mens exhibit relatively high compressive strengths of 55-59.5MPa (Figure 3a). The results of the RCPT are shown in Fig-ure 4. From the results, it is shown that the resistance tochloride penetration of mortar is significantly increased withthe  incorporation  of  pozzolanic  materials.  This  result  isconfirmed by other research (Chindaprasirt et al., 2008;Gastaldini et al., 2007). The increased chloride penetrationresistance is due to reduced average pore size of the pasteand the improved interfacial zone. RHA is the most effective,followed by POA and OPC. The relatively high resistance ofthe mortars (with pozzolanic materials) to chloride penetra-tion can be partly explained by its expected lower medianpore diameter and porosity values. Furthermore, normal OPCmortar will have a higher Ca(OH)2 content in the hydratedstructures.3.4  Results of OCPThe results of the OCP tests are interpreted to accord-ing to ASTM C876 (2001), which provides general guide-lines for evaluating corrosion in concrete structures as out-lined  in  Table 3.  The  potential-time  behavior  of  steel  inmortars is shown in Figure 5. At 120180 days of exposure,mortar with and without various pozzolans replacementlevels, namely OPC and 40POA, showed potential valuesranging from -350 to -450 mV vs. SCE, indicating a 90%probability of depassivation of rebar embedded in mortar.From this figure it was inferred that initially up to 30 days ofexposure, almost all the systems showed potential valuesranging from 0 to -300 mV vs. SCE, reflecting the passivecondition of the embedded steel anode. On the other hand,the rebar embedded in 20% POA (20POA), 20% RHA(20RHA) and 40% RHA (40RHA) replacement levels do notcross  the  threshold  limit  even  after  180  days  of  exposureperiods.4. ConclusionsFrom these tests, it can be concluded that POA andFigure 4.  Results of the rapid chloride penetration tests (RCPT).Table 3. Probability of corrosion according to half-cell readings [8]Half-cell potential reading vs. SCE Corrosion activityless negative than -200 mV 90% probability of no corrosionbetween -200 mV and -350 mV an increasing probability of corrosionmore negative than -350 mV 90% probability of corrosion0204060801001207 d 28 d 90 dNormalized (%) OPC20POA40POA20RHA40RHA(a)(b)Figure 3. Results of (a) compressive strength and (b) normalized(normalized or strength activity index).Figure 5.  Potential corrosion of mortars.0102030405060707 d 28 d 90 dCompressive strength (MPa)OPC20POA40POA20RHA40RHA010002000300040005000600070008000OPC 20POA 40POA 20RHA 40RHACharge passed (Coulomb)28 d90 d-500-450-400-350-300-250-200-150-100-5000 30 60 90 120 150 180 210OCP vs. SCE 40RHA20RHA20POA40POAOPC489S. Rukzon & P. Chindaprasirt / Songklanakarin J. Sci. Technol. 30 (3), 485-489, 2008RHA can be used as pozzolans to replace part of Portlandcement in making mortar of relatively high strength and goodresistance to chloride penetration and corrosion. The RCPTis effective for measuring the resistance to chloride penetra-tion of relatively high strength mortars containing pozzolans.The incorporations of POA and RHA decreases the chloridepenetration  of  mortar  by  increasing  nucleation  sites  forprecipitation of hydration products, reducing Ca(OH)2 andimproving  the  permeability  of  mortar.  RHA  is  the  mosteffective followed by POA and OPC. The incorporation ofPOA and RHA can significantly improve the mortar corro-sion resistance. RHA is the most effective followed by POAand OPC. RHA is the most effective and increases the corro-sion resistance at 40% replacement levels. POA and RHAhave high potentials to be used as a good pozzolanic materi-als.AcknowledgementsThe authors would like to acknowledge the financialsupports of the office of the National Research Council ofThailand (NRCT), the Sustainable Infrastructure Researchand Development Center Khon Kaen University (SIRDC),and the Deapartment of Civil Engineering of RajamangalaUniversity of Technology, Phra Nakhon (RMUTP).ReferencesASTM C39, Standard Test Method for Compressive Strengthof Cylindrical Concrete Specimens, ASTM C 39M-01, Annual Book of ASTM Standard 04.02 2001 pp.18-22.ASTM C109, Standard Test Method for Compressive Strengthof Hydraulic Cement Mortars (Using 2-in or [50 mm]Cube Specimens), ASTM C109M-99, Annual Book ofASTM Standard 04.01 2001 pp. 83-88.ASTM C 618, Standard Specification for Coal Fly Ash andRaw or Calcined Natural Pozzolan for Use as a Min-eral Admixture in Concrete, ASTM C 618-00, AnnualBook of ASTM Standard 04.02 2001 pp. 310-313.ASTM C876, Standard Teat Method for Half Cell Potentialsof Reinforcing Steel in Concrete, ASTM C876-91,Annual Book of ASTM Standard 04.02 1998 pp. 430-435.ASTM C 1202, Standard Test Method for Electrical Indica-tion  of  Concrete’s  Ability  to  Resist  Chloride  IonPenetration, ASTM C1202-97, Annual Book of ASTMStandard 04.02 2001 pp. 646-651.Alonso, C., Andrade, C., Castellote, M., Castro, P.  2000.Chloride threshold values to depassivate reinforcingbars  embedded  in  a  standardized  OPC  mortar.Cement and Concrete Research; 30: 1047-1055.Chindaprasirt, P., Rukzon, S., Sirivivatnanon, V. 2008. Resis-tance  to  chloride  penetration  of  blended  Portlandcement mortar containing palm oil fuel ash, rice huskash and fly ash. Construction and Building Materials;22:932–938.Gastaldini. A.L.G., Isaia, G.C., Gomes, N.S., Sperb, J.E.K.2007.  Chloride  penetration  and  carbonation  inconcrete with rice husk ash and chemical activators.Cement and Concrete composite; 21: 356-361.Metha, P.K. 1979. The chemistry and technology of cementmade from rice husk ash, In UNIDO/ESCAP/RCTT.Proceeding of work shop on rice husk ash cement,Peshawar, Parkistan, Regional Center for technologytransfer, Bangalor, India.  113-122.Thomas, M. 1996. Chloride thresholds in marine concrete.Cement and Concrete Research; 26: 513-519.

Use of waste ash from various by-product materials in increasing the durability of mortar

This paper presents a study on the strength and corrosion resistance of mortars made with binary blends of ordinaryPortland cement (OPC) and ground rice husk ash (RHA) or ground palm oil fuel ash (POA). The mortar mixtures were madewith Portland cement Type I containing 0-40% RHA and POA. RHA and POA with 1-3% by weight retained on a sieveNo.325 were used. The water to binder ratio was kept constant at 0.5 and the flow of mortar was maintained at 110±5% withthe aid of superplasticizer (SP). Scanning electron microscopy (SEM) was used for analysis. The compressive strength,chloride penetration and corrosion resistance of the mortar were determined. The results show that strength as well as theresistance of mortar to chloride and corrosion can be improved by blending with RHA and POA. Thus, RHA and POA havea high potential to be used as a good pozzolanic material

Sumrerng Rukzon

Prinya Chindaprasirt

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Use of waste ash from various by-product materials in increasing the durability of mortar

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