Development of corn cob ash blended cement

Available online at www.sciencedirect.com

Construction and Building

MATERIALS

Construction and Building Materials 23 (2009) 347–352

www.elsevier.com/locate/conbuildmat

Development of corn cob ash blended cement D.A. Adesanya a, A.A. Raheem b,* b

a Building Department, Obafemi Awolowo University, Ile-Ife, Nigeria Civil Engineering Department, Ladoke Akintola University of Technology, Ogbomoso, Nigeria

Received 11 April 2007; received in revised form 26 November 2007; accepted 26 November 2007 Available online 31 January 2008

Abstract In an attempt to convert waste product into useful material for the construction industry, this research considered the use of corn cob ash (CCA) as a pozzolan in cement production. The study investigated the chemical composition of CCA. Factory production of the CCA – blended cement was carried out by replacing 0%, 2%, 4%, 6%, 8%, 10%, 15%, 20% and 25% by weight of Ordinary Portland Cement clinker with CCA. The 0% replacement serves as the control. The results showed that CCA is a suitable material for use as a pozzolan as it satisfied the minimum requirement of combined SiO2 and Al2O3 of more than 70%, which a good pozzolan for manufacture of blended cement should meet. The blended cements produced also satisfied both NIS 439:2000 and ASTM C 150 requirements especially at lower levels (<15%) of CCA percentage replacement. Based on the test results, it was concluded that CCA could be suitably used in blended cement production. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Corn cob ash (CCA); Pozzolan; Blended cement; Chemical composition

1. Introduction The need for affordable building materials cannot be over emphasized in the provision of adequate housing for the teaming populace of the world, especially those in third world countries. The cost of building materials continues to increase as the majority of the population continues to fall below the poverty line. As prices increase sharply, there is the need to search for local materials as alternatives for the construction of functional but low-cost buildings in both the rural and urban areas [1]. Astronomical price increases of conventional building materials have been identified as one of the constraints to effective housing delivery in Nigeria [2]. Since materials cost accounted for two-third of the building production cost [3], a reduction in its cost would definitely bring about a huge saving in the overall building production cost. This study focuses on Portland Cement, which is one of the most widely used building materials. *

Corresponding author. Tel.: +234 8033928991. E-mail address: [email protected] (A.A. Raheem).

0950-0618/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2007.11.013

Portland Cement as an ingredient in concrete is one of the main construction materials widely used, especially in developing countries. The current cement production rate of the world is approximately 1.2 billion tons/year [4]. This is expected to grow to about 3.5 billion tons/year by 2015. This increasing demand for cement is expected to be met by partial cement replacement [4]. The search for alternative binder or cement replacement materials led to the discovery of the potentials of using industrial by-products and agricultural wastes as cementitious materials. If these fillers have pozzolanic properties, they impart technical advantages to the resulting concrete and also enable larger quantities of cement replacement to be achieved [5]. This research focuses on the use of agricultural wastes as cementitious materials. The use of agricultural waste product in cement production is an environmental friendly method of disposal of large quantities of materials that would otherwise pollute land, water and air. The waste products which possess pozzolanic properties and which have been studied for use in blended cement are Rice husk ash [4,6–8], Saw dust ash [9], Waste burnt clay [10,11] and Corn cob ash [12–14].

348

D.A. Adesanya, A.A. Raheem / Construction and Building Materials 23 (2009) 347–352

The waste product that is of concern in this study is corn cob ash (CCA). Corn cob is the waste product obtained from maize or corn, which is the most important cereal crop in sub-Saharan Africa. According to food and agriculture organisation (FAO) data, 589 million tons of maize were produced worldwide in the year 2000 [15]. The United States was the largest maize producer having 43% of world production. Africa produced 7% of the world’s maize [16]. Nigeria was the second largest producer of maize in Africa in the year 2001 with 4.62 million ton. South Africa has the highest production of 8.04 million ton [15]. Previous research efforts on the use of corn cob ash (CCA) as a pozzolan [12–14] did not consider the chemical composition of CCA, which makes it suitable for use as a pozzolan. Also, these previous works involved mixing of the CCA with Ordinary Portland Cement at the point of need. An attempt is being made in this study to produce CCA-blended cement in the controlled environment of a factory as it is being done for Ordinary Portland Cement. This study considered the determination of the chemical composition of CCA as well as the physical and chemical properties of the blended cement produced by intergrinding CCA with Portland Cement clinker at varying percentage replacement during the cement manufacturing process. 2. Experimental procedure 2.1. Materials The CCA used was produced by grinding dried corn cobs to about 4.00 mm diameter to enhance adequate combustion and to reduce the carbon content which affects the pozzolanic properties of the CCA. The ground cobs were burnt in open air using a local blacksmith furnace that uses charcoal as fuel. The burning was continuous, with temperature increasing to 650 °C in about 8 h, when the corn cobs turned to ashes [17]. The analysis of the ash was carried out using X-ray Fluorescence Analyser (Model QX 1279). The chemical composition of the CCA is presented in Table 1. The clinker used for producing the blended cements was obtained from West Africa Portland Cement Company (WAPCO) Table 1 Chemical composition of corn cob ash (CCA) Chemical constituents

Percentage composition (%) Sample 1

Sample 2

Sample 3

SiO2 Al2O3 Fe2O3 CaO MgO SO3 Na2O K2O Total SiO2 + Al2O3

67.33 7.34 3.74 10.29 1.82 1.11 0.39 4.20 74.67

65.39 9.14 5.61 12.89 2.33 1.10 0.48 4.92 74.53

66.41 5.97 3.97 11.53 2.02 1.01 0.36 5.64 72.38

Average

66.38 7.48 4.44 11.57 2.06 1.07 0.41 4.92 73.86

Table 2 Chemical composition of the clinker used Constituents

SiO2 Al2O3 Fe2O3 CaO MgO SO3 K2O Na2O LOI LSF SR AR Free lime

Percentage composition (%)

Average

Sample 1

Sample 2

Sample 3

22.83 3.9 3.11 66.36 1.79 0.11 0.12 0.27 0.38 93.84 2.84 1.27 0.95

22.46 4.62 2.90 66.54 1.77 0.18 0.15 0.28 0.34 93.99 2.98 1.55 0.84

22.39 4.63 3.10 66.71 1.91 0.31 0.11 0.25 0.37 94.30 2.90 1.60 0.92

22.56 4.40 3.04 66.54 1.82 0.20 0.13 0.27 0.36 94.04 2.91 1.47 0.90

Sagamu Plant in Ogun State, Nigeria. This is the clinker used by the company to produce Ordinary Portland Cement (OPC). Table 2 shows the chemical composition of the clinker. 2.2. Cement mixtures Eight series of mixtures and one reference mixture were prepared for the cement milling. The milling involves the replacement of 0%, 2%, 4%, 6%, 8%, 10%, 15%, 20%, and 25% by weight of Ordinary Portland Cement clinkers with corn cob ash (CCA) during the manufacturing process. The 0% replacement serves as the reference specimen. As it is the practice in WAPCO Sagamu Works, 5% gypsum was used for the milling. The milling machine used is a Laboratory Ball Mill (Model R. PM 1400/50, Serial Number 93021.A). The mill was charged with media balls following the order and distribution given below: 90 mm – 8.2 kg 80 mm – 10.0 kg 60 mm – 10.0 kg 50 mm – 14.0 kg 30–40 mm – 12.8 kg The ball mill was charged with the required weight of clinker, CCA and gypsum after which it was firmly tightened and put in operation for about 1 h, testing the specific surface area (SSA) of the cement midstream to ensure that it is not less than 250 mm2/kg in line with NIS 439:2000 requirements [18]. The milling was done in batches of 5 kg each. Table 3 shows the mix proportion for each batch and the percentage CCA replacement. 2.3. Testing procedure The physical characteristics of the blended cements produced considered are fineness, consistency, soundness, initial and final setting times, and residue on 45 lm sieve. The

D.A. Adesanya, A.A. Raheem / Construction and Building Materials 23 (2009) 347–352 Table 3 Mix proportion for charging ball mill Percentage CCA replacement (%)

Percentage of clinker (%)

Weight of clinker (g)

Weight of CCA (g)

Weight of gypsum (g)

0 2 4 6 8 10 15 20 25

95 93 91 89 87 85 80 75 70

4750 4650 4550 4450 4350 4250 4000 3750 3500

– 100 200 300 400 500 750 1000 1250

250 250 250 250 250 250 250 250 250

Notes: (i) Gypsum is 5% of total weight throughout. (ii) Total weight charged per batch is 5000 g.

chemical characteristics of the blended cements produced considered are chemical composition, loss on ignition (LOI), free lime, and insoluble residue (IR). All the tests were carried out in accordance with the practice at WAPCO Sagamu Works. The standards applied for all the tests in the study are NIS 439:2000, BS 12:1991 and ASTM C150:1994. 3. Results and discussion 3.1. Chemical composition of CCA and clinker Table 1 shows the elemental oxides present in the corn cob ash (CCA) samples. The results indicate that all samples of CCA had combined percentages of silica (SiO2) and Alumina (Al2O3) of more than 70%, a requirement which a good pozzolan for manufacture of blended cement should meet [10,11,19,20]. The requirements of ASTM C 618 for a combined SiO2 + Al2O3 + Fe2O3 of more than 70% was also satisfied [21]. Thus, CCA is a suitable material for use as a pozzolan. Table 2 shows the chemical composition of the clinker used. Values obtained for the elemental oxide are in agree-

349

ment with the range of values reported in literature [5,22,23]. The composition also satisfied the requirement in the available standards [18,24,25]. Thus the clinker is quite suitable for cement production. 3.2. Chemical composition of the blended cements The chemical composition of the blended cements produced using the clinker mentioned above are presented in Table 4. The silica content of the blended cements increased from 21.53% for 2% CCA replacement to 23.69% for 25% CCA replacement. A similar trend was observed for the alumina and ferric oxide contents which increased from 4.44% to 5.20% and 3.86% to 4.17%, respectively. The silica and alumina content are responsible for the formation of cementitious products – calcium silicate hydrates and calcium aluminate hydrates when they react with lime [Ca(OH)2] in the presence of water [11]. Thus, as the CCA percentage increases, more silicate and alumina were available to react with the lime produced during hydration of cement to produce additional cementitious products. The calcium oxide content decreased from 63.49% for 2% CCA replacement to 61.46% for 25% CCA replacement. Similarly, the lime saturated factor (LSF) decreased from 92.07% to 72.40% for 2% to 25% CCA replacement. This shows that addition of CCA led to a reduction in the lime content of the cements. With reduced lime, the free lime content is lower, thus enhancing the soundness of the cement. All the cement produced satisfied the limiting value of 2–3% free lime content as specified by available standards [18,24,25]. The minor compounds of Na2O and K2O known as alkalis, ranges from 0.31–0.36% and 0.71% to 0.83%, respectively for the CCA-blended cements. These values are higher than those for the control, which are 0.26% for Na2O and 0.19% for K2O. Higher alkalis content may affect the rate of gain in strength of cement [5]. The limiting value of 0.3% to 1.2% per mass of cement was

Table 4 Chemical composition of CCA-blended cement Constituents

SiO2 Al2O3 Fe2O3 CaO MgO SO3 K2O Na2O LOI LSF SR AR Free lime IR

Percentage composition (%) 0% CCA

2% CCA

4% CCA

6% CCA

8% CCA

10% CCA

15% CCA

20% CCA

25% CCA

21.48 4.54 3.80 63.65 1.94 2.11 0.19 0.26 0.99 93.04 2.65 1.37 1.33 0.59

21.53 4.44 3.86 63.49 1.95 2.19 0.71 0.33 1.38 92.07 2.69 1.38 1.24 0.77

21.64 4.49 3.86 63.41 1.96 2.03 0.75 0.32 1.41 87.09 2.62 1.41 1.07 0.96

21.72 4.48 3.89 62.80 2.03 2.21 0.78 0.34 1.42 85.49 2.70 1.40 1.10 1.31

21.93 4.49 3.91 62.21 2.26 2.09 0.79 0.35 1.40 83.04 2.66 1.24 1.10 1.67

22.15 4.51 3.94 62.18 2.47 2.12 0.76 0.36 1.44 81.76 2.71 1.30 1.03 1.94

22.45 4.59 3.97 62.01 2.48 2.02 0.76 0.35 1.30 80.83 2.76 1.20 1.08 3.02

22.67 4.75 4.10 61.90 1.42 2.45 0.80 0.30 1.35 72.05 2.96 1.18 1.10 4.19

23.69 5.20 4.17 61.46 1.57 1.64 0.83 0.31 1.47 72.40 2.96 1.36 1.14 5.28

350

D.A. Adesanya, A.A. Raheem / Construction and Building Materials 23 (2009) 347–352

Percentage Composition (%)

70

SiO2

yCaO = -0.0869x + 63.437

60

R2 = 0.8534

AL2O 3

50

Fe2 O3 CaO

40 ySiO2 = 0.0714x + 21.382

30

R2 = 0.9808 20

yFe2O 3 = 0.014x + 3.8044

10 yAl2O3 = 0.024x + 4.3698 R2 = 0.7185

R2 = 0.9713

0 0

5

10

15

20

25

30

Replacement (%) Fig. 1. Effect of CCA percentage replacement on the chemical composition of blended cement.

satisfied. The loss on ignition (LOI) of the CCA-blended cements were higher than that of the control. The LOI ranges from 1.30% to 1.47% for the blended cements as against 0.99% for the control. This indicates that the addition of CCA increases the organic content, which has a negative effect on the binding properties of cement. However, the recommended limit of 5% by NIS 439:2000 requirements was satisfied. The insoluble residue (IR) of the blended cement increases steadily from 0.77% for 2% CCA replacement to 5.28% for 25% CCA replacement against the control value of 0.5%. The increase is as a result of the excess organic content incorporated by the CCA. Beyond 20% CCA replacement, the recommended limit of 5.0% maximum by NIS 439:2000 requirements could not be satisfied. Fig. 1 shows the variation in the percentage composition of the four main components of cement – CaO, SiO2, Al2O3 and Fe2O3 oxides as the CCA percentage replacement in the blended cement increases. It could be observed from Fig. 1 that the incorporation of CCA led to an increase in the percentage composition of SiO2, Fe2O3 and Al2O3 and a reduction in that of CaO. This finding agrees with the previous observations on the effect of pozzolan addition on oxide composition of the cement produced

[22,23,26]. These results indicate that the blended cements are adequate in terms of chemical composition. 3.3. Physical properties of the blended cements The physical properties of the laboratory produced blended cements are presented in Table 5. The table indicates that the fineness decreases from 385 m2/kg at 0% CCA replacement to 272 m2/kg at 25% CCA replacement. All the cement satisfied the 250 m2/kg minimum fineness specified by NIS: 439:2000. The incorporation of CCA has a diminishing effect on the fineness of the blended cement when grinding time was kept constant. As expected, the blended cements were generally coarser than Ordinary Portland Cement as the residue on 45 lm sieve increases from 29% to 44.6% as the CCA percentage replacement increases from 0% to 25%, respectively. The coarseness, according to [23] was attributed to the clinker component, which was harder to grind compared with the pozzolan (CCA in this case). Thus, it could be concluded that the relative hardness of the pozzolan significantly influences the particle size distribution of blended cement due to the interactions between blended components during intergrinding. The implication of the coarseness of the blended cements is

Table 5 Summary of physical characteristics of CCA-blended cement Parameters

Percentage of CCA replacement 2

Fineness (m /kg) Soundness (mm) Consistency (%) Initial setting time (min) Final setting time (min) Residue on 45 lm sieve (%)

0

2

4

6

8

10

15

20

25

385 1.00 27.00 120 220 29.00

380 2.00 26.80 142 251 30.00

367 2.50 26.50 164 277 30.50

343 2.00 26.00 180 298 31.00

320 3.50 26.20 193 306 31.60

306 3.00 25.60 208 328 32.00

291 3.50 25.10 211 333 34.50

285 4.00 24.00 245 374 38.00

272 4.50 23.00 296 441 44.60

D.A. Adesanya, A.A. Raheem / Construction and Building Materials 23 (2009) 347–352

351

Final setting time (min)

350 300 y = 0.8081x - 58.467 R2 = 0.9983

250 200 150 100 50 0 0

50

100

150

200

250

300

350

400

450

500

Initial setting time (min) Fig. 2. Relationship between initial and final setting times of CCA-blended cement.

increase in the setting times of the cements. Table 5 also revealed that the soundness of the cement ranges between 1.00 mm and 4.50 mm when the CCA percentage replacement increases from 0% to 25%. These values are far less than the 10 mm limiting value recommended by NIS 439:2000. Hence, the cements do not show any appreciable change in volume after setting. The consistency diminishes from 27% to 23% as CCA substitution increases from 0% to 25%. The decrease in consistency was attributed to the reduction of cementitious binder in the mixture as the pozzolan content increases [5]. This can be observed from Table 4 as the lime content (CaO) decreases from 63.65% to 61.46% when CCA percentage replacement increases from 0% to 25%. Also, the specific gravity of CCA is less than that of cement, which resulted in larger volume of CCA compared with the cement clinker replaced as the replacement was made by mass. Thus, the overall volume was increased needing more water to form a paste of same consistency for different percentage of CCA in the mixture. Only blended cements with maximum of 15% CCA replacement satisfy the NIS 439:2000 requirement for consistency of between 25% and 27%. The initial and final setting times increased from 120 to 296 min and 220 to 441 min, respectively when the percentage CCA replacement increased from 0% to 25%. All the cement satisfy the NIS 439:2000 requirement of 45 minutes minimum initial setting time and maximum of 10 h final setting time. However, the 25% CCA replacement could not satisfy the ASTM C 150 requirements for final setting time of 375 min maximum. The variation of setting times with percentage CCA replacement shows that both initial and final setting times increase as the CCA content increases. This is reasonable as increase in CCA content reduces the surface area of the cement as discussed above. As a result of this, the hydration process is slowed down, thus causing setting times to increase. The slow hydration means low rate of heat development, which is one of the notable characteristics for which pozzolan cements are known. This is of great importance in mass concrete construction where low rate of heat development is very essential as it reduces thermal stresses.

A plot of the initial setting time against the final setting time as shown in Fig. 2 indicates that there is a very strong linear relationship between the parameters as the coefficient of correlation (r) was calculated to be 0.9991. A strong linear relationship exists between two variables when 0.5 < |r| < 1 [27]. Thus, an estimate of the final setting time can be calculated from Eq. (1) when the initial setting time has been obtained. y ¼ 0:8081x  58:467

ð1Þ

Where y = final setting time; x = initial setting time. 4. Conclusions From the results of the various tests performed, the following conclusions can be drawn: (i) Corn cob ash (CCA) is a suitable material for use as a pozzolan, since it satisfied the requirement for such a material by having a combined SiO2 and Al2O3 of more than 70%. (ii) The addition of CCA as pozzolan in blended cement increases marginally the oxide composition of SiO2, Fe2O3 and Al2O3; and decreases slightly that of CaO, in line with previous findings. (iii) The CCA-blended cements satisfied BS 12:1991, ASTM C 150:1994 and NIS 439:2000 requirements especially at lower levels (<15%) of CCA substitution. (iv) All the CCA-blended cements have higher setting times than the control, thus, they are most applicable where low rate of heat development is required such as in mass concreting. This shows that CCA-blended cement is good as low heat cement. Acknowledgements The authors acknowledge the management of West Africa Portland Cement Company (WAPCO) Sagamu Works, Ogun State, Nigeria; for the opportunity given to perform the various laboratory tests using their facilities.

352

D.A. Adesanya, A.A. Raheem / Construction and Building Materials 23 (2009) 347–352

References [1] Osunade JA. Effect of replacement of lateritic soils with granite fines on the compressive and tensile strengths of laterized concrete. Build Environ 2002;37:491–6. [2] Olusola K, Adesanya DA. Public acceptability and evaluation of local building materials for housing construction in Nigeria. J Prop Res Construct 2004;1:83–98. [3] Ayangade JA, Olusola KO, Ikpo IJ, Ata O. Effect of granite dust on the performance characteristics of Kernelrazzo floor finish. Build Environ 2004;39:1207–12. [4] Coutinho JS. The combined benefits of CPF and RHA in improving the durability of concrete structures. Cement Concrete Comp 2003;25:51–9. [5] Hossain KMA. Blended cement using volcanic ash and pumice. Cement Concrete Res 2003;33:1601–5. [6] Waswa-Sabuni B, Syagga PM, Dulo SO, Kamau GN. Rice husk ash cement – an alternative pozzolana cement for Kenyan building industry. J Civil Eng JKUAT 2002;8:13–26. [7] Nehdi M, Duquette J, El-Damatty A. Performance of rice husk ash produced using a new technology as a mineral admixture in concrete. Cement Concrete Res 2003;33:1203–10. [8] Bui DD, Hu J, Stroeven P. Particle size effect on the strength of rice husk ash blended gap-graded Portland cement concrete. Cement Concrete Comp 2005;27:357–66. [9] Udoeyo FF. Sawdust ash as concrete materials. J Mater Civil Eng 2002;14(2):173–6. [10] Syagga PM, Kamau SN, Waswa-Sabuni B, Dulo SO. Potentials of using waste burnt clay as a pozzolanic material in Kenya. J Discovery Innovat 2001;13(3/4):114–8. [11] Shihembetsa LU, Waswa-Sabuni B. Burnt clay waste as a pozzolanic material in Kenya. J Civil Eng JKUAT 2002;7:21–8. [12] Adesanya DA. Evaluation of blended cement mortar concrete and stabilized earth made from ordinary Portland cement and corn cob ash. Construct Build Mater 1996;10(6):451–6. [13] Adesanya DA. The characteristics of laterite bricks and blocks stabilized with corn-cob fillers. The Professional Builder 2000;June/ July:47–55.

[14] Adesanya DA. The effects of thermal conductivity and chemical attack on corn cob ash blended cement. The Professional Builder 2001;June:3–10. [15] FAO. Records, Retrieved December 15, 2002, from http://apps.fao.org/default.htm. [16] IITA. Maize, Retrieved December 15, 2002, from http://intranet/ iita4/crop/maize.htm. [17] Raheem AA. An investigation of corn cob ash blended cement for concrete production, Unpublished Ph.D thesis, Department of Building, Obafemi Awolowo University, Ile-Ife, Nigeria; 2006. [18] Standards Organisation of Nigeria. Standard for Cement, NIS 439, Lagos, Nigeria; 2000. [19] Pekmezci BY, Akyuz S. Optimum usage of a natural pozzolan for the maximum compressive strength of concrete. Cement Concrete Res 2004;34:2175–9. [20] Justnes H, Elfgren L, Ronin V. Mechanism for performance of energetically modified cement versus corresponding blended cement. Cement Concrete Res 2005;35:315–23. [21] Siddique R. Performance characteristics of high-volume class F fly ash concrete. Cement Concrete Res 2004;34(3):487–93. [22] Bouzoubaa N, Zhang MH, Malhotra VM. Mechanical properties and durability of concrete made with high-volume fly ash blended cements using a coarse fly ash. Cement Concrete Res 2001;31: 1393–402. [23] Turanli L, Uzal B, Bektas F. Effect of material characteristics on the properties of blended cements containing high volumes of natural pozzolans. Cement Concrete Res 2004;34:2277–82. [24] British Standard Institution. Specification for Portland Cements, BS 12, London, British Standard Institution, 1991. [25] American Society for Testing and Materials. Specification for Portland Cement, ASTM C 150, 1994. [26] Antiohos S, Maganari K, Tsimas S. Evaluation of blends of high and low calcium fly ashes for use as supplementary cementing materials. Cement Concrete Comp 2005;2:349–56. [27] Johnson RA. Miller and Freund’s probability and statistics for engineers. 5th ed. New Jersey: Prentice Hall; 1994.