Lime based steam autoclaved fly ash bricks

Lime based steam autoclaved fly ash bricks

Construction and Building MATERIALS Construction and Building Materials 21 (2007) 1295–1300 www.elsevier.com/locate/conbuildmat Lime based steam a...

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Construction and Building

MATERIALS

Construction and Building Materials 21 (2007) 1295–1300

www.elsevier.com/locate/conbuildmat

Lime based steam autoclaved fly ash bricks Tayfun Cicek *, Mehmet Tanrıverdi Dokuz Eylu¨l University, Faculty of Engineering, Department of Mining Engineering, 35160 Buca, Izmir, Turkey Received 5 June 2005; received in revised form 26 January 2006; accepted 31 January 2006 Available online 28 August 2006

Abstract About 10 million tonnes of fly ash are produced yearly as waste from coal fired thermal power plants in Turkey. Only a small portion of this waste is utilized as a raw material in the production of cement and concrete. In this study, Seyito¨mer power plant fly ash was investigated in the production of light weight bricks. Fly ash, sand and hydrated lime mixtures were steam autoclaved under different test conditions to produce brick samples. An optimum raw material composition was found to be a mixture of 68% fly ash, 20% sand and 12% hydrated lime. The optimum brick forming pressure was 20 MPa. The optimum autoclaving time and autoclaving pressure were found 6 h and 1.5 MPa, respectively. The compressive strength, unit volume weight, water absorption and thermal conductivity of the fly ash–sand–lime bricks obtained under optimum test conditions are 10.25 MPa, 1.14 g/cm3, 40.5% and 0.34 W m 1 K 1 respectively. The results of this study suggested that it was possible to produce good quality light weight bricks from the fly ash of Seyito¨mer power plant. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Fly ash; Bricks; Lime; Sand; Steam autoclave

1. Introduction A large amount of fly ash is produced from the coal fired power plants as waste. In Turkey, over 10 millions of tonnes of fly ash are produced yearly. This waste material is considered an environmental problem in Turkey because only a portion of it can be utilized. Characterization results of the fly ash samples received from the different Turkish coal fired power plants have shown that the majority of them was found suitable for use in different section of the industry [4]. In Turkey and abroad studies on characterization and industrial utilization of fly ash have increased substantially over the years. As a result of these studies, fly ash can now be utilized in many different areas like cement, ceramic, paint, plastic, agriculture, environmental and construction [5,7,11–13]. In Turkey, fly ash has been mainly used in cement and concrete production. However, the fly ash usage is much lower than in other countries due to difficulties of obtaining the fly ash product with consistent quality. *

Corresponding author. Tel.: +90 232 4127548; fax: +90 232 4530868. E-mail address: [email protected] (T. Cicek).

0950-0618/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2006.01.005

Lack of research and development studies aiming the utilization of fly ash in other industrial fields also contributes to this low usage. The production of the construction materials like sand/ lime or silica/lime bricks is based on mainly CaO–SiO2– H2O (C–S–H) formation [2,3,9,10]. Calcium–silicate– hydrate is formed by the reaction of Ca(OH)2, SiO2 and H2O under pressurized steam at 125–200 °C. In the beginning of this reaction, a lime-rich Tobermorite gel is formed. The composition of this gel is probably C7S4Hn. This phase reacts with residual SiO2 to form C5S4Hn and finally the low-lime C2S3H2 phase [1]. The steam autoclaved fly ash bricks based partly on the formation of this C–S–H phase. CaO–Al2O3–SiO2–H2O (C–A–S–H), Hydrogarnet is also found to be formed in the presence of Al2O3 [6,8]. Thus, mainly C–S–H and C–A–S–H phases contribute to the hardening of fly ash/lime materials since fly ash contains considerable amounts of Al2O3 and SiO2. 2. Material and test procedure In this study, a fly ash sample from Seyito¨mer power plant/Turkey, hydrated lime and sand were used for

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making bricks. Physical and chemical properties of the fly ash sample are presented in Table 1. The particle size distribution of the fly ash is shown Fig. 1. As silica additives, quartz sand with 99% SiO2 and washed river sand with 78% SiO2 were used. The Ca(OH)2 content of the hydrated lime was 95.4%. Firstly, optimum fly ash–sand–lime mixing ratio, brick forming pressure, steam pressure and autoclaving time were determined. Twenty-two different types of brick specimens were produced under the conditions given in Table 2. Brick specimens of about 100 g were prepared with 14% moisture and formed with the aid of a hydraulic press into cylinders with B = 45 mm. The specimens were pre-cured for about 24 h prior to autoclaving. The specimens were steam autoclaved in an autoclave brand ELE with max. operating pressure of 4 MPa. Autoclaved specimens were tested for their volume weight, compressive strength and water absorption according to Turkish Standards TS 705

Table 1 Physical and chemical properties of Seyito¨mer fly ash Lignite

Bulk density (g/cm3) SiO2 (%) Al2O3 (%) Fe2O3 (%) CaO (%) MgO (%) K2O (%) Na2O (%) TiO2 (%) Loss on ignition (%) Cd (ppm)a Pb (ppm)a Zn (ppm)a Cu (ppm)a Cr (ppm)a Ni (ppm)a Mn (ppm)a

0.90 57.21 20.39 10.89 2.75 4.96 1.36 0.40 0.81 0.94 – 79.0 112.6 98.8 454.5 1975.9 790.4

100 80

Passing, cum. %

3.1. The effect of sand addition on compressive strength The specimens T1–T5 (Table 2) were prepared to determine the effect of quartz sand addition on compressive strength. The results of compressive strength tests are given in Fig. 2. The compressive strength of the specimens was increased from 2.2 to 3.74 MPa by increasing the amount of quartz sand. The highest compressive strength of 3.74 MPa was achieved at 40% quartz sand addition. Sand addition of 20% was accepted as optimum, because the value of the compressive strength was slightly lower than that of 40% quartz. The improved mechanical strength of the specimens by addition of quartz can be explained to a greater extend by the increased amount of free SiO2 which is more readily reacting with lime than the fly ash.

The results of compressive strength tests conducted on specimens T6–T9 in order to determine the effect of lime addition and to obtain the optimum lime addition percentage are given in Fig. 3. The specimens were prepared at 20% quartz sand addition. Lime addition of 12% gave the highest compressive strength of 4.75 MPa. Higher lime addition had no significant effect on the mechanical strength of the specimens. Hence, 12% lime was accepted as the optimum lime addition. This amount of lime is comparable with the amount of lime addition in sand/lime bricks production process. 3.3. Effect of brick forming pressure on the compressive strength The specimens T10–T14 containing 68% fly ash, 20% quartz sand and 12% lime were formed under pressures of <0.5 , 10, 20, 25 and 30 MPa. The compressive strengths of these specimens are given in Fig. 4. The highest compressive strength of 6.17 MPa was achieved at 20 MPa forming pressure. The compressive strength of the bricks deteriorated above 20 MPa forming pressure. This can be explained by the mechanical deformation of the bricks under very high forming pressures.

Ref. [4].

60

3.4. The effect of autoclaving pressure on compressive strength

40 20 0 0.01

3. Experiments

3.2. The determination of the optimum lime addition

Coal type

a

[14]. For compressive strength tests eight specimens were used for each brick type.

0.1 Particle Size (mm)

Fig. 1. Particle size distribution of Seyito¨mer fly ash.

1

To determine the effect of autoclave pressure on compressive strength of the bricks, specimens T15– T18 were prepared and cured at different autoclave pressures. The results of the compressive strength tests of these samples are shown in Fig. 5. As seen from the figure, the compressive strength of the bricks at autoclave pressures 1.5 and

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Table 2 Test parameters Bricks code

Quartz sand (wt%)

Fly ash (wt%)

Lime (wt%)

Moisture (wt%)

Forming pressure (MPa)

Autoclaving pressure (MPa)

Curing time (h)

Number of bricks

T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T12 T13 T14 T15 T16 T17 T18 T19 T20 T21 T22 T23 T24a

0 10 20 30 40 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20

90 80 70 60 50 72 70 68 66 68 68 68 68 68 68 68 68 68 68 68 68 68 68 68

10 10 10 10 10 8 10 12 14 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12

14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14

<0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 10 20 25 30 20 20 20 20 20 20 20 20 20 20

1 1 1 1 1 1 1 1 1 1 1 1 1 1 0.5 1 1.5 2 1.5 1.5 1.5 1.5 1.5 1.5

9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 3 6 9 12 6 6

10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 20

a

Five bricks for each size fraction of river sand ( 0.1,

0.2,

0.5 and

1 mm).

12

Compressive Strength (MPa)

Compressive Strength (MPa)

12 10 8 6 4 2

10 8 6 4 2 0

0 0

10

20

30

40

Quartz Sand (%)

8

10

12

14

Lime (%)

Fig. 2. The effect of quartz sand addition on compressive strength of fly ash–sand–lime bricks.

Fig. 3. The effect of lime addition rate on compressive strength of the bricks.

2 MPa are almost the same. Therefore, 1.5 MPa pressure was considered as optimum autoclaving pressure. The 1.5 MPa autoclaving pressure is on the high side of the pressures applied in the production processes of sand/lime bricks and aerated cellular concrete.

curing time of 6 h was found sufficient for producing bricks with the highest mechanical strength. The curing time is comparable with the curing times of sand/lime bricks production process.

3.5. Effect of curing time on the compressive strength

3.6. The effect of river sand addition and sand particle size on the compressive strength

To determine the effect of curing time on compressive strength of the bricks, specimens T19–T22 were prepared and autoclaved at different curing times. The results of the compressive strength tests are presented in Fig. 6. A

The usability of the river sand with low SiO2 was investigated. For this purpose, specimens with 1, 0.5, 0.2, and 0.1 mm river sand (T24) were prepared and cured under previously determined optimum test conditions.

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12

C o m p r e s s iv e S tr e n g t h (M P a )

Compressive Strength (MPa)

12 10 8 6 4 2 0

0.4 0.8 0.6 Particle Size (mm)

1.0

8 6 4 2

5

10

15

20

30

25

35

0.0

0.2

Forming pressure (MPa) Fig. 4. The effect of the brick forming pressure on the compressive strength.

1.2

Fig. 7. Effect of river sand addition and sand particle size on the compressive strength.

quartz sand. This can be explained by the low SiO2 content of the river sand. An increase of the mechanical strength of the bricks toward coarser size of river sand was observed.

12

Compressive Strength (MPa)

Quartz Sand

0

0

10 8

3.7. Water absorption test 6 4 2 0 0.0

1.0 1.5 2.0 Autoclave Pressure (MPa)

0.5

2.5

Fig. 5. The effect of the autoclave pressure on the compressive strength.

The compressive strength test results are presented in Fig. 7. As seen from Fig. 7, the bricks made with river sand show lower compressive strength than that of bricks with

The results of the water absorption tests conducted on specimens T23–T24 are given in Table 3. The water absorption values of fly ash–sand–lime specimens were ranging from 33% to 40% depending on the sand particle size. The specimens with quartz sand gave higher water absorption values than the specimens with river sand. The water absorption values of the specimens are quite high which is in general not preferred in construction bricks (max. 18% for solid clay bricks, TS 705). This high water absorption values indicate that most of the pores of the specimens are open to outside. 3.8. Determination of the thermal conductivity The thermal conductivity of the fly ash–sand–lime bricks were determined using Hot-wire method with a Showa Denko Shotherm QTM thermal conductivity measuring device according to Turkish Standards of TS 825. The thermal conductivity of the fly ash specimens with quartz sand and river sand were measured as 0.34 and 0.36 W m 1 K 1 respectively.

12

Compressive Strength (MPa)

River Sand 10

10 8 6 4

Table 3 Results of water absorption tests

2

Particle size and sand type

0 0

3

6 8 Curing Time (hour)

12

15

Fig. 6. The effect of the curing time on the compressive strength.

0.2 mm (Quartz sand) 0.1 mm (River sand) 0.2 mm (River sand) 0.5 mm (River sand) 1 mm (River sand)

Water absorption (%) 40.5 34.7 34.5 34.1 32.8

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Table 4 Properties of the ash–sand–lime bricks produced under optimum conditions Quartz sand ( 0.2 mm) Sand (%) Fly ash (%) Lime (%) Moisture (%) Forming pressure (MPa) Autoclave pressure (MPa) Curing time (h) Volume weight (g/cm3) Thermal conductivity (W m 1 K 1) Compressive strength (MPa) Water absorption (%)

River sand ( 1 mm) 20 68 12 14 20 1.5 6

1.14 0.34 10.25 40.5

4. Summary of the results and conclusion The properties of the fly ash–sand–lime specimens (named as T23 and T24) produced under optimum conditions are summarized and compared with the properties of solid clay bricks type 1.8/100 according to Turkish Standard TS 705 in Table 4. In this study, the following results were obtained:  Steam autoclaved bricks can be produced using the fly ash from the Seyito¨mer power plant, sand and lime.  Positive effects of sand addition on the compressive strength of the bricks were observed. Twenty percent of sand addition was estimated as optimum.  The optimum lime addition was determined as 12%.  Brick forming pressure has a great positive influence on the mechanical strength of the bricks. However, forming pressures above 20 MPa have an adverse effect.  The optimum autoclave pressure and curing time were determined as 1.5 MPa and 6 h, respectively.  The compressive strength of the bricks prepared with quartz sand is higher than that of the bricks produced with river sand.  The unit volume weight of the fly ash bricks prepared with quartz sand addition is 1.15 g/cm3, whereas the unit volume weight of the bricks with river sand addition is 1.27 g/cm3. Thus, the unit volume weights of the fly ash bricks are much lower than that of the traditional clay bricks.  The water absorption of the fly ash–sand–lime bricks ranges from 30% to 40%.  The thermal conductivity of the fly ash–sand–lime bricks with the value of 0.34–0.36 W m 1 K 1 is much lower than that of the traditional clay bricks. The fly ash–sand–lime bricks produced in this study seem to be suitable for use as construction material. The production of this type of bricks will certainly contribute to the recycling of the fly ash and hence minimize the negative impact of the fly ash land fills on the environment. On the other hand, the reduction in clay usage for the produc-

Solid clay bricks TS 705 Brick type: 1.8/100

1.27 0.36 7.8 32.8

– – – – 1.8 0.7 min. 7.8 max. 18

tion of conventional clay bricks will help to protect the environment. Furthermore, the hazardous emissions from the clay brick burning kilns will be reduced. The considerably low volume weight and low thermal conductivity of the fly ash bricks will reduce the construction and heating/cooling costs of the buildings Acknowledgement ¨ ztu¨re Holding A.S./Izmir The authors acknowledge O for their support. References [1] Al-Wakeel EI, El-Korashy SA, Uossef HN. Promotion effect of C–S–H phase nuclei on building calcium silicate hydrate phase. Cem Concr Res 1999;21:173–80. [2] Ball MC, Carroll RA. Studies of hydrothermal reactions of UK pulverized ashes. Part 1: reactions between pulverized fuel ash and calcium hydroxide. Adv Cem Res 1999;11(2):53–61. [3] Baoju L, Youjun X, Shiqiong Z, Jian L. Some factors affecting early compressive strength of steam-curing concrete with ultra fine fly ash. Cem Concr Res 2001;31:1455–8. [4] Bayat O. Characterization of Turkish fly ashes. Fuel 1998;77(9–10): 1059–66. [5] Baykal G, Do¨ven AG. Utilization of fly ash by pelletization process; theory, application areas and research results. Resour Conserv Recy 2000;30:59–77. [6] Goni S, Guerrero A, Luxan MP, Macias A. Activation of the fly ash pozzolonic reaction by hydrothermal conditions. Cem Concr Res 2003;33:1399–405. [7] Iyer RS, Scott JA. Power station fly ash-a review of value-added utilization outside of the construction industry resources. Conserv Recy 2001;31:217–28. [8] Klimesch DS, Ray A. Effect of quartz particle size on hydro garnet formation during autoclaving at 180 °C in the CaO–Al2O3–SiO2–H2O system. Cem Concr Res 1998;28:1309–16. [9] Ma W, Brown PW. Hydrothermal reactions of fly ash with Ca(OH)2 and CaSO4 2H2O. Cem Concr Res 1997;27:1237–48. [10] Peng G, Feng N, Chan SYN. Formation and strength of crystalline calcium silicate hydrate prepared by single autoclaving process. Adv Struct Eng 1999;2(3):191–7. [11] Pimraksa K, Wilhelm M, Kochberger M, Wruss W. 2001. A new approach to the production of bricks made of 100% fly ash, International ash utilization symposium. Available from: http:// www.flyash.info/agenda.html.

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[12] Poon CS, Kou SC, Lam L. Use of recycled aggregates in molded concrete bricks and blocks. Constr Build Mater 2002;16:281–9. [13] Toktay, M. C ¸ etin, B. Mechanical strength and water absorption properties of autoclaved fly ash-lime bricks, TMMOB.

Chamber of Civil Engineers’ Publication, vol-1;1991: p. 385– 394. [14] TS 705 for solid and vertically perforated clay bricks, Turkish Standard Institute, UDK 691.421; March 1985.