Application of Bituminous Fly Ash for Partial Replacement of Cement in Producing Hollow Concrete Blocks

Transcription

1 Asia Journal of Public Health Journal homepage: Original Articles Application of Bituminous Fly Ash for Partial Replacement of Cement in Producing Hollow Concrete Blocks Nipapun Kungskulniti* Naradol Thaisuchart ** Udomsak Kongmuang * Chaovayut Phornpimolthape * Naowarut Charoenca* *Department of Sanitary Engineering, Faculty of Public Health, Mahidol University, Bangkok,Thailand and Center of Excellence on Environmental Health, Toxicology and Management of Chemicals (ETM), Bangkok, Thailand. ** Papop Company Limited, Bangkok, Thailand ARTICLE INFO Article history : Received September 2011 Received in revised form October 2011 Accepted October 2011 Available online January 2012 Keywords: Bituminous fly ash Cement Hollow concrete block Compressive strength Heavy metals Corresponding Author: Kungskulniti N, Department of Sanitary Engineering, Faculty of Public Health, Mahidol University, 420/1 Ratchavithi Road, Bangkok 10400, Thailand. phnks@mahidol.ac.th Asia J Public Health 2011;2(3):15-21 ABSTRACT Objective: Bituminous coal is one type of coal which has been increasingly used for energy generation. However, its waste, bituminous fly ash is of concern due to the need for its disposal. Hence, this research aimed to investigate the application of bituminous fly ash as a useful material to partially replace Portland cement for producing hollow concrete blocks. Materials and Methods: Production of hollow concrete blocks with various fly ash mixtures was used to experimentally determine the usability of fly ash. The ratio 1:5 (by weight) of cement to limestone crushed rock was used. Replacement of cement with bituminous fly ash was tested at 0%, 20%, 40%, 50%, 60% and 70%, respectively. Samples were measured for compressive strength at 3, 7 and 14 days to assess appropriate curing time. Water absorption, thermal conductivity and leaching of heavy metals from hollow concrete blocks were measured to select the optimum bituminous fly ash proportion. Results: It was found that the compressive strength at all curing times decreased (p<0.05) when the bituminous fly ash proportion increased. The appropriate curing time was found to be 7 days. The optimum replacement of cement by bituminous fly ash was 70% (by weight). The properties of hollow concrete blocks met the requirements of Thai industrial standard No. TIS They had a compressive strength of 45 kg/cm 2 and water absorption of 14.5%. Regarding the leaching of heavy metals, tested parameters were acceptable as specified in the standards of the Notification of the Thai Ministry of Industry. Conclusion: Various mixtures of fly ash and cement show that hollow concrete blocks with a maximum proportion of 70% bituminous fly ash replacement for cement can be considered an optimum proportion for hollow concrete block production. 15

2 INTRODUCTION Coals are important power resources used worldwide to generate electricity and heat production. There are four types of coals: lignite, sub-bituminous, bituminous and anthracite coal. Lignite coal is the lowest quality coal whereas anthracite coal has highest quality. Bituminous and anthracite coals have been used increasingly since they are inexpensive and of high quality. On the one hand, the use of coal is useful for generating energy, but on the other hand, it also generates wastes of coal fly ash, causing disposal problems. Therefore, environmentally conscious management of coal fly ash should be used. Coal fly ash has been investigated as a replacement for cement in producing concrete 1-6. Compressive strength has been compared between fly ash added concrete and non-fly ash added concrete. It was found that partial fly ash replacement of cement is feasible for producing concrete. Presently, bituminous coals are used in most industries. Hence, bituminous fly ash is of concern due to the large amount needing disposal. Bituminous fly ash is mainly composed of silica (SiO 2 ) and alumina (Al 2 O 3 ) 7. Utilization of bituminous fly ash as an alternative to replace cement and aggregate in construction materials is of interest in recycling this waste material. In this study, the optimum proportion of bituminous fly ash to replace cement in hollow concrete block production was investigated. Moreover, leaching of heavy metals from the hollow concrete block was also determined. Production of hollow concrete block using fly ash will reduce the amount of bituminous fly ash needing disposal, and therefore add benefits from this recycled product. MATERIALS AND METHODS Hollow concrete blocks were produced from mixing a proportion of cement (plus bituminous fly ash), aggregate and water in a mechanical concrete mixer and then pouring it into a 7x19x39 cm mold 8. The hollow concrete blocks were stored 3 days indoors for air drying. Commercial Portland cement, type I (elephant brand) was used in the study. Bituminous fly ash was obtained from a textile factory. Its physical properties and chemical composition were analyzed according to the ASTM C and the ASTM C , and by X-ray fluorescence spectrometry, scanning electron microscope, and atomic absorption spectrophotometer 9, 10. Bituminous fly ash was used to replace cement at 0%, 20%, 40%, 50%, 60%, and 70% respectively by weight. Water to cement ratios of 0.5, 0.6, 0.65, and 0.7 respectively, were used. After shape forming, these hollow concrete blocks were cured with water for 3, 7, and 14 days. Limestone crushed rock with the particle size distribution in accordance with the Thai Industrial Standard No. TIS was used as aggregate 11. The ratio of cement and limestone crushed rock was 1:5 by weight 12. The experiment was divided into 2 phases. Phase I was the study of different mixing proportions of bituminous fly ash, cement, limestone crushed rock, and water for producing hollow concrete blocks. The optimum curing time was based on the best compressive strength found from the different bituminous fly ash proportions. In Phase II, the properties of hollow concrete blocks were determined for water absorption, thermal conductivity and the leaching of heavy metals (Cr, As, Ni and Zn). RESULTS AND DISCUSSION The research was conducted to investigate the potential use of bituminous fly ash as a cement replacement to produce hollow concrete blocks. The results of the experiments of this study are presented as follows: Characteristics of bituminous fly ash The specific gravity of bituminous fly ash was 2.25, whereas that of Portland cement type I was Hence, the density of bituminous fly ash particles is less than that of cement (Portland cement type I). As a result, bituminous fly ash added to hollow concrete blocks makes them lighter than 100% cement hollow concrete blocks. In terms of fineness 10, bituminous fly ash retained using sieve No. 325 was 39% which is greater than the standard requirement of not more than 34%. It is obvious that the bituminous fly ash particles are larger than those of cement (5.7%). Therefore bituminous fly ash is not pozzolan like cement because it does not meet the standard. Scanning Electron Microscope (SEM: Model JSM 5800 LV/ JEOL Ltd.) with 500 times magnification was used to analyze the surface image and particle size of bituminous fly ash and cement as shown in Figure 1. The size of bituminous fly ash was rather larger than the cement. Bituminous fly ash particle size was in the range of micrometers whereas cement particle size is in the range of micrometers. The texture appearance of cement is non-uniform with rough surface whereas that of bituminous fly ash consists of many types of heterogeneous particles such as spherical, edged and spongy 16

3 shapes. The interesting characteristic of bituminous fly ash is its porosity. Its texture is close to spongy. Figure 2 shows the spongy shape of bituminous fly ash particles. It has a greater porosity surface area than that of cement. This property has an effect on the loss of compressive strength when bituminous fly ash replaces cement. Results from the experiments showed that the more bituminous fly ash replaced cement, the more water is needed for mixing in the production of hollow concrete block. (A) (B) Figure1. Microstructure of bituminous fly ash (A) and cement (B) with 500x magnification like a replacement material for limestone crushed rock instead of cement. Bituminous fly ash was also analyzed for heavy metals including arsenic, chromium, nickel and zinc by atomic absorption spectrophotometer 14. All aforementioned parameters were found much below the standards for total threshold limit concentration according to the Notification of the Thai Ministry of Industry 15. Therefore, bituminous fly ash in this study does not pose potential adverse effects to the environment. Characteristics of hollow concrete block Figure 3 shows the hollow concrete block produced. Its size is 7x19x39 cm. Bituminous fly ash replaced cement at 0%, 20%, 40%, 50%, 60%, and 70%, respectively by weight to produce hollow concrete blocks or non-loadbearing concrete blocks. The curing time used for the hollow concrete blocks was 3, 7 and 14 days. Figure2. Microstructure of spongy shape of bituminous fly ash The chemical composition of bituminous fly ash was examined by X-ray fluorescence spectrometry (Model ED 2000 /Oxford Instruments). It was found that the total amount of SiO 2, Al 2 O 3, and Fe 2 O 3 in bituminous fly ash was 43.49%. The standard of pozzolan in accordance with ASTM C (Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use in Concrete) specifies the summation of total amounts of SiO 2, Al 2 O 3, and Fe 2 O 3 in Class F and Class C fly ash as not less than 70 and 50 percent respectively 13. The results show that the physical and chemical properties were less than those values specified by ASTM C Hence, the bituminous fly ash in this research was not identified as pozzolan in accordance with ASTM C In other words, bituminous fly ash in this study is an inert substance, and does not bind well when mixed with cement. When its replacement for cement increases, it results in a decrease of the resulting compressive strength of the hollow concrete block. So, the bituminous fly ash acted much Figure3. Shape of the hollow concrete block Compressive strengths (Figure 4.) with different portions of bituminous fly ash added to hollow concrete blocks at different curing times were determined following the Thai Industrial Standard No. TIS (Referenced from ASTM C Standard Methods of Sampling and Testing Concrete Masonry Units) 16. It was found that the mean compressive strength value for all curing times was decreased when the replacement of cement by bituminous fly ash was increased proportionally (p-value <0.001). These results show that compressive strength is inversely related to bituminous fly ash proportion. This means, when the bituminous fly ash proportion increases, the compressive strength will decrease. The results showed the same trend as other researchers studying the effect of fly ash in replacement of cement on the compressive strength 17, 18. The mean compressive strength (Figure 4.) for different curing times was also determined and their differences and correlations determined. It was found that there were no statistical differences in compressive strength at 17

4 different curing times. However, the correlation analysis demonstrated that the correlation between curing time and the compressive strength was significant, r = 0.206, p-value = Using stepwise regression analysis to analyze compressive strength, it was found that 88.7% of bituminous fly ash proportions influenced changes in compressive strength, whereas 4.2% of curing time influenced change in compressive strength. Results indicate that bituminous fly ash proportions have more effect than curing time on compressive strength. The compressive strength could be predicted using a linear combination of bituminous fly ash proportion and curing time (p-value < 0.001) as follows 19 : Y = (1.348 X 1 ) + (1.547 X 2 ) (R 2 = 0.923) When Y = Compressive strength (kg/cm 2 ) X 1 = Bituminous fly ash proportion (%) X 2 = Curing time (days) Remark : The prediction was within the limits of possible conditions: bituminous fly ash proportion (X 1 ) at 0 70 % and curing time (X 2 ) at 3 14 days. The non-pozzolan property as well as the spongy shape of the bituminous fly ash may have effects on reduction of compressive strength. In addition, water porosity during the mixing process might result in voids in the hollow concrete block which possibly reduced the compressive strength. Compressive Strength (Kg/cm 2 ) % Bituminous fly ash 3 day 7 day 14 day Safety factor 37.5 kg/cm 2 Std. 25 kg/cm 2 TIS Figure 4 The compressive strength of hollow concrete block in different bituminous fly ash proportions at 3, 7 and 14 day curing times. The longer curing time resulted in increasing the compressive strength of the hollow concrete block with all fly ash proportions. When curing time was increased, so was the hydration and pozzolanic reaction (reaction between CaO with water and CaO with SiO 2 ) 20. SiO 2 reacted with calcium oxide and was converted to calcium silicate. The combination of calcium silicate and water turned to calcium silicate hydrate, which improved cementitious function between molecular structures and age hardening of concrete, rendering the increase of compressive strength of hollow concrete block. However, the compressive strength with a maximum proportion of bituminous fly ash at 70% at all curing times was acceptable when compared to the Thai Industrial Standard No. TIS The required compressive strength is specified at more than 25 kg/cm 2. As shown in Figure 4, the compressive strength of hollow concrete block increased as the curing time was longer: 3, 7 and 14 days, accordingly. The percent increase of average compressive strength over the curing time from 3 days to 7 days and 7 days to 14 days was and 4.81 respectively. The compressive strengths at the maximum proportion (70%) of bituminous fly ash replacement for cement at 18

5 curing times of 3, 7 and 14 days were 32.1, 45.0 and 50.3 kg/cm 2, respectively. Other studies also reported that the longer curing time yielded the better compressive strength of concrete 4, 21. For this study, the optimum curing time was selected based on the safety factor of compressive strength. The safety factor of compressive strength was specified as not less than 37.5 kg/cm 2 (25 x 1.5), which was 1.5 times of the standard compressive strength, according to the TIS (not less than 25 kg/cm 2 ). The compressive strength at the maximum proportion (70%) of bituminous fly ash replacement for cement at a curing time of 3 days was less than 37.5 kg/cm 2 (the safety factor), whereas, at a curing time of 7 and 14 days, it was more than 37.5 kg/cm 2, meeting the safety factor. However, a curing time of 14 days does not provide any advantage, so would be a waste of time. Therefore, the optimum curing time was chosen at 7 days for producing hollow concrete blocks. Water absorption for the hollow concrete blocks with different proportions of bituminous fly ash at 7 days curing time was determined 16. Correlation analyses demonstrated that the correlation between bituminous fly ash proportion and the water absorption at 7 days curing time was significant, r = (p-value < 0.001). The results show a highly positively correlation between the bituminous fly ash proportion and the water absorption, which means, when the bituminous fly ash proportion increases, the water absorption also increases. As delineated by Figure 5, water absorption of hollow concrete block will be increased as fly ash replacement of Portland cement increases (water absorption varied directly with fly ash replacement). This phenomenon induced hollow concrete block to increase water absorption. Bituminous fly ash surface is rough; and it is porous in shape, water molecules are able to pass through it easily. Results show more water absorption due to its high porosity. However, water absorption of bricks with a maximum proportion of bituminous fly ash at 70% is quite acceptable when compared to the Thai Industrial Standard No. TIS The requirement for water absorption is that it should be less than 25 %. Thermal conductivity for hollow concrete blocks was performed for different bituminous fly ash proportions at 7 days curing time 22. The control unit (0% of bituminous fly ash) had the highest thermal conductivity at W/mk; whereas the maximum proportion (70% bituminous fly ash) had the lowest thermal conductivity at W/mk. Correlation analyses found that there was a highly inverse correlation (r = , p-value < 0.001) between the bituminous fly ash proportion and thermal conductivity; which means that when the bituminous fly ash proportion increases, the thermal conductivity will decrease. Water absorption (%) control 20% 40% 50% 60% 70% % bituminous fly ash Std. < 25 % TIS Figure 5 The water absorption of hollow concrete block in different bituminous fly ash proportions with a 7 day curing time The reason could be that bituminous fly ash has lower specific gravity than cement; in addition, its particle shape looks spongy with high porosity. Thus, when more volume of bituminous fly ash replaces cement, the weight of hollow concrete block is lighter (Molecules of hollow concrete block would be less compressed and more porous: therefore, it should be lighter). This results in a decrease of heat transfer from one side to the other. So, thermal conductivity of hollow concrete block will be decreased when bituminous fly ash replacement of cement increases. These hollow concrete blocks have higher thermal conductivity when compared with other construction materials. Since hollow concrete blocks are made of hard material with compressed and crowded molecules, thus, the transmission of heat from side to side of hollow concrete block is excellent. But generally, the material that has lower thermal conductivity will be better for heat protection 23. Leaching of heavy metals The heavy metals tested for leaching out of hollow concrete blocks using proportions of bituminous fly ash of 0%, 20%, 40%, 50%, 60% and 70% respectively, included arsenic, chromium, nickel and zinc ions (see Table 1.). The leaching of heavy metals tested in this study at all proportions was less than the standard of Soluble Threshold Limit Concentration specified in the Notification of the Thai Ministry of Industry (B.E. 2548) 15. Therefore, the hollow concrete block products with bituminous fly 19

6 ashpartial replacement of cement should not pose potential adverse effects to the environment. Table1. Average highest concentrations of leached heavy metals from hollow concrete blocks Conditions Concentrations of heavy metals (mg/l) Cr Zn Ni As Control ND With bituminous fly ash 20-70% ND Standard (STLC) STLC = Soluble Threshold Limit Concentration (Notification of Ministry of Industry (B.E. 2548)) ND = Not Detected (limit of measurement for heavy metal concentration of AAS = mg/l) Optimum proportion of bituminous fly ash The optimum proportion of bituminous fly ash for hollow concrete block products was selected based on all of the experimental results and very careful analysis of all critical factors. The main parameters were compressive strength and water absorption, under the criteria established in the Thai Industrial Standard (TIS), Ministry of Industry, TIS Table 2 Comparison of the properties from hollow concrete block (with 70% bituminous fly ash) and the standards of TIS Comparison Hollow concrete block (Bituminous fly ash 70%) Std. TIS Compressive strength (kgf/cm 2 ) The properties Water absorption (%) Not less than 25 Not more than 25 In short, results showed that both the compressive strength and water absorption with a maximum portion of 70% bituminous fly ash replacement for cement was comfortably within the requirements of TIS Comparisons of properties for hollow concrete block with 70% bituminous fly ash and the standard of TIS are presented in Table 2. Moreover, leaching of all tested heavy metals from hollow concrete blocks with a maximum portion of 70% bituminous fly ash replacement for cement was also within acceptable levels of the Soluble Threshold Limit Concentration, a standard specified in the Notification of the Thai Ministry of Industry (B.E. 2548) 15. Therefore, from this study, +hollow concrete blocks with a maximum proportion of 70% bituminous fly ash replacement for cement can be considered an optimum proportion for hollow concrete block production which shall not pose any adverse effects to the environment from heavy metals. Acknowledgements The authors would like to thank the facilities of the central laboratory of Chulalongkorn University as well as the laboratories of the Department of Civil Engineering, Faculty of Engineering, and the Department of Sanitary Engineering, Faculty of Public Health, Mahidol University. This research work was supported in part by the grant from the Centre for Environmental Health, Toxicology and Management of Chemicals (ETM) under Science & Technology Postgraduate Education and Research Development Office (PERDO) of the Ministry of Education. Additionally, the article publication is also supported by the China Medical Board (CMB) References 1. Naik TR, Ramme BW. Effects of highlime fly ash content on water demand, time of set and compressive strength of concrete. ACI Materials Journal 1990; 87: Ghosh RS, Timusk J. Creep of fly ash concrete. ACI Materials Journal 1981; 78: Cuijuan S, Lousha G, Haimin W. Concrete made with calcium - enriched fly ash. Proceeding of the Second International Conference on Fly Ash, Silica Fume, Slag, and Natural Pozzolans in Concrete. ( Ed: Malhotra VM ). ACI SP Madrid, Spain. 1986; Naik TR, Ramme BW, Tews JH. Pavement construction with high-volume class C and class F fly ash concrete. ACI Materials Journal 1995; 92: Siddique R. Effect of fine aggregate replacement with class F fly ash on the mechanical properties of concrete. Department of Civil Engineering, Thapar Institute of Engineering and Technology, Deemed University, India Naik TR, Chun YM. Use of class C fly ash cement - based construction materials. Department of Civil Engineering and Mechanics, College of Engineering and Applied Science, the University of Wisconsin, USA

7 7. American Coal Ash Association.Coal com- Bustion product - production and use. Alexandria, Virginia, USA Thai Industrial Standard. Standard for Hollow non-load-bearing concrete masonry units. TIS Thai Industrial Standard Institute, Ministry of Industry. Thailand American Society for Testing and Material. Standard test method for density, relative density (specific gravity), and absorption of fine aggregate. ASTM C , Annual Book of ASTM Standard USA American Society for Testing and Material. Standard test method for fineness of hydraulic cement by the 45 - μm (No. 325) sieve. ASTM C , Annual Book of ASTM Standard USA Thai Industrial Standard. Standard for concrete aggregates. TIS Thai Industrial Standard Institute, Ministry of Industry. Thailand Pipatsamut W. Cement blocks. Section of Industrial Services, Center for Northern Industrial Promotion, Chiangmai, Thailand American Society for Testing and Material. Standard specification for coal fly ash and raw or calcined natural pozzolan for use in concrete. ASTM C , Annual Book of ASTM Standard USA APHA. Standard Methods for the examination of water and wastewater. 21st ed. APHA, AWWA, WEF, Washington DC, USA Notification of Ministry of Industry B.E on the Disposal of Waste or Unused Materials. Based on the Factory Act. B.E Ministry of Industry. Thailand Thai Industrial Standard. Sampling and testing concrete masonry units. TIS Thai Industrial Standard Institute, Ministry of Industry. Thailand Chindaprasert P, Horvichit I. Portland cement mixed with fly ash from Mae Moh. Division of Technology for Rural Development, Khon, Kaen Univeristy, Khon Kaen, Thailand Nontananan S, Wangtian S. Selection of lignite fly ash for concrete works. Division of Research and Knowledge Development, Electricity Generating Authority of Thailand, Nonthaburi, Thailand Ott RL, Longnecker M. An introduction to statistical methods and data analysis. Thomson Learning, Duxbury, Australia Soroka I. Concrete in hot environments. 1 st ed. E&FN Spon. 1993; 13-8, 25-8, , Demirboga R. Thermal conductivity and compressive strength of concrete incorporation with mineral admixtures. Department of Civil Engineering, Faculty of Engineering, Ataturk University, Turkey American Society for Testing and Material. Method for determination of thermal conductivity of soil and soft rock. ASTM C , Annual Book of ASTM Standard USA Kulkarni SP, Vipulanandan C. Thermal conductivity of insulators. Department of Civil., Environmental Engineering, University of Houston, USA