This research study comprises of concrete cubes made with Ordinary Portland Cement and with different configurations of fly ash by replacing cement and fine aggregate. To achieve the aim of this study, total 81 concrete cubes were cast. Among 81 cubes, 9 cubes were made with normal concrete, 36 cubes were made by replacing 25%, 50%, 75% and 100% of fine aggregate with fly ash and 36 cubes were made by replacing 10%, 25%, 50%, and 75% of cement with fly ash. The cubes were 6" x 6" in cross-section, and the mix design was aimed for 5000 psi. After proper curing of all 81 cubes, they were tested at 3, 7 and 28 days curing age. The cubes were tested in Forney Universal Testing Machine in the Concrete Laboratory of Civil Engineering Department, Mehran University Jamshoro. By analyzing the test results of all the concrete cubes, the following main findings have been drawn.
The compressive strength of concrete cubes made by replacing 100 % fine aggregate by fly ash was higher than the concrete cubes made with Ordinary Portland Cement at all 3, 7 and 28 days curing ages. On the other hand, the compressive strength of concrete cubes made by replacing 10 % and 25 % cement by fly ash were slightly lower than the concrete cubes made with Ordinary Portland Cement at all curing ages, whereas the compressive strength of concrete cubes made by replacing 50 % and 75 % of cement by fly ash were quite lower than the concrete cubes made with Ordinary Portland Cement at all curing ages.
Key Words: Ordinary Portland Cement, Fine Aggregate, Fly Ash, Compressive strength of Concrete.
Concrete is a composite material which is being used in variety of structures. More commonly cement, steel bars as well as coarse and fine aggregates are to be transported from distant places to the site which is quite expensive. Therefore the aggregates are preferably to be used from whatever is available locally.
Fly ash (also known as a Coal Combustion By-Product) is the finely divided mineral residue resulting from the combustion of powdered coal in electric generating plants. Large quantities of industrial by-products are produced every year. These waste by-products must be effectively disposed to eliminate air, soil, and surface, as well as ground water pollution at added cost to the industry and thus to the society [1- 3].
Fly ash is generally used as partial replacement of Portland Cement and/or fine aggregate, an expensive and energy intensive material. Therefore use of fly ash leads to considerable saving in cost and energy consumption. Utilization of increased volumes of fly ash in concrete will lead to conservation of energy and natural resources. Bulk quantities of some industrial by-products such as fly ash, bottom ash and slag have been used as aggregates for concrete, road embankment as well as sub base construction, but such bulk uses represents low value applications. On the other hand, their use as mineral admixtures in cement and concrete due to their pozzolanic and cementitious properties represents high value applications. [4]
Addition of finely divided pozzolanic and cementitious materials like fly ash, can affect the properties of cement mortar/concrete both in fresh and hardened state. In fresh or plastic state, mix proportions, water requirements for specified consistency, setting characteristics, workability, and heat of hydration are some of the properties influenced by mineral admixtures. In the hardened state, the rate of strength development and ultimate strength, permeability, durability against frost attack, sulfate attack, alkali-silica reaction, carbonation, and resistance to thermal cracking are significantly affected with the incorporation of mineral admixtures in cement concrete. Over the years, extensive research has been conducted all over the world to investigate the influence of fly ash on the strength of plain cement concrete. In this study the fly ash produced at Lakhra Coal Power Plant is used as a replacement of cement / fine aggregate, in order to investigate its effects on the strength of concrete.
With the boom in population and industrial growth, the need for power has increased manifold. It has been observed that the power generation plants running through coal fuel are producing huge amount of ashes, which is being treated as waste. If this waste is left unutilized, it can pollute various phases of human environment like air, food, land, shelter and water [5]. However, if this waste is disposed of properly, it can be a new source of useful material.
Researchers have been attempting to convert this waste into the wealth by exploring viable avenues for use of fly ash. It has been reported that this waste stuff is being used as fine aggregate in concrete construction and higher strengths are being achieved [5]. This will inevitably reduce the cement content, which is one of the expensive item in concrete construction. Hence the use of fly ash as a construction material in those areas where it is cheaply available would be a feasible step in construction industry rather than transporting standard hill sand from a far distant source.
It is reported that fly ash has cementitious properties; hence fly ash is an inexpensive replacement for various contents of concrete construction. When fly ash is employed with portland cement, then hydrated lime combines with the fly ash forming stable cementitious compound which contributes strength. [2, 10].
Fly ash refers to the finely divided material which is added to obtain specific engineering properties of cement mortar and concrete. The other, equally important, objective of using fly ash in cement concrete include economic benefits and environmentally safe recycling of waste by products. Fly ash is generally finer than Portland Cement. Because of its fineness, pozzolanic properties and self- cementitious nature, it is widely accepted as mineral admixture in mortar and concrete [4].
Fly ash in concrete is used to enhance the performance of concrete. The various advantages of fly ash in concrete largely depend on mix proportions, mixing procedure and field conditions. Although fly ash creates environmental problems, never the less it improves the quality of concrete. It also lowers the heat of hydration. Fly ash increases strength of concrete, reduces the permeability and corrosion of reinforcing steel, increases sulphate attack resistance and reduces alkali-aggregate reaction [10].
Lakhra Power Plant is very near to Jamshoro and Hyderabad and is the only coal fuel powered plant in Pakistan. It is about 35 km form Jamshoro and 55 km from Hyderabad. Lakhra coal field encompasses an area of 250 square kilometers. Fly ash produced through this power plant is very fine powder recovered from gases created by coal fired electric power generation. This power plant produces about 2 million tons of fly ash annually, which is being dumped like a land fill. It has been reported that dumped fly ash has occupied huge considerable space of land in the vicinity of power plant which has created environmental problem to the inhabitants who are living in this area. This alarms researchers to consume this land fill fly ash which is producing great environmental impact in the surrounding society.
There may be differences in the fly ash from one plant to another, day-to-day variations in the fly ash from a given power plant are usually quite predictable, provided plant operation and coal source remain constant. The effective utilization of fly ash in concrete requires adequate knowledge of characteristics of fly ash defined by its physical, chemical and mineralogical properties.
The various materials used in concrete mix are given in Table 1.
Cement
Dada Bhai Cement Factory
Fine Aggregatge
Bolhari sand
Coarse Aggregatge
Petaro crushing plant
Fly ash
Lakhra Power Plant
Water
Concrete laboratory, Civil Engineering Department
3.2 Properties of Materials used in Concrete mix
Standard test procedure as prescribed by ASTM C128-93 was used for this test. The specific gravity of fine aggregate used in this research study was found to be 2.61.
Standard test procedure as prescribed by BS: 812 Part 107: (Draft) and ASTM C 127- 93 was used for this test. The specific gravity of coarse aggregate used in this research study was found to be 2.66.
Standard test procedure as prescribed by ASTM C128-93 was used for this test. The specific gravity of Fly ash was found to be 2.54.
Standard test procedure as described in BS 812: Part 107: (Draft) was used for this test. The water absorption of fine aggregate was found to be 1.69 %.
Standard test procedure as described in BS 812: Part 107: (Draft) was used for this test. The water absorption of coarse aggregate was found to be 1.38 %.
Standard test procedure as described in BS 812: Part 107: (Draft) was used for this test. The water absorption of Fly ash was found to be 16.92 %.
Standard test procedure as described in BS 812: Part 2: 1975 and ASTM C 29-91a was used for this test. The unit weight of fine aggregate was found to be 103.47 lb/ft3.
Standard test procedure as described in BS 812: Part 2: 1975 and ASTM C 29-91a was used for this test. The unit weight of coarse aggregate was found to be 98.48 lb/ft3.
Standard test procedure as described in BS 812: Part 2: 1975 and ASTM C 29-91a was used for this test. The unit weight of Fly ash was found to be 44.52 lb/ft3.
The British method of concrete mix design, popularly referred to as the "DoE method", was used for design purpose. After having few trials to check the mix design for the required strength of 5000 psi, the ratio was used as: 1 : 1.25 : 2.50 @ 0.39 w/c ratio.
In this research study total 81 concrete cubes were cast. Among 81 cubes, 9 cubes were made with normal concrete, 36 cubes were made by replacing 25%, 50%, 75% and 100% of fine aggregate by fly ash and 36 cubes were made by replacing 10%, 25%, 50%, and 75% of cement by fly ash. The cubes were 6" x 6" in cross-section, and the mix design was aimed for 5000 psi. After proper curing of all 81 cubes, they were tested at 3, 7 and 28 days curing ages. The cubes were tested in Forney Universal Testing Machine in the Concrete Laboratory of Civil Engineering Department Mehran University Jamshoro.
4. TEST RESULTS AND DISCUSSION
After proper curing of all 81 cubes, these were tested at 3, 7 and 28 days curing ages. The cubes were taken out from the water tank and left for surface saturated drying condition. The cubes were then tested in Forney Universal Testing Machine in the Concrete Laboratory of Civil Engineering Department Mehran University Jamshoro. The test results of all the concrete cubes are summarized in Table 2, whereas their graphical presentation is shown in figure 1.
01.
Cubes made with Normal cement concrete
3241
4594
5129
02.
Cubes made by replacing 25% of Fine Aggregate by Fly ash
3033
4287
4896
03.
Cubes made by replacing 50% of Fine Aggregate Fly ash
3128
4381
4975
04.
Cubes made by replacing 75% of Fine Aggregate by Fly ash
3377
4561
5041
05.
Cubes made by replacing 100% of Fine Aggregate by Fly ash
3608
4614
5197
06.
Cubes made by replacing 10% of Cement by Fly ash
3146
4409
4989
07.
Cubes made by replacing 25% of Cement by Fly ash
2925
4428
5076
08.
Cubes made by replacing 50% of Cement by Fly ash
1872
1931
2283
09.
Cubes made by replacing 75% of Cement by Fly ash
1038
1090
1323
The compressive strength of concrete cubes made by replacing 100 % Fine aggregate by Fly ash was higher than the concrete cubes made by Ordinary Portland Cement at all 3, 7 and 28 days curing ages as shown in Figure 1. The compressive strength of concrete cubes made by replacing 75 % of Fine aggregate by Fly ash was higher at 3 days but it was slightly lower than the O.P.C made normal cubes at 7 and 28 days as presented in Figure 2.
The compressive strengths of concrete cubes made by replacing 10 % and 25 % cement by Fly ash were slightly lower than the concrete cubes made by Ordinary Portland Cement at all curing ages. The compressive strengths of concrete cubes made by replacing 50 % and 75 % of cement by Fly ash were quite lower than the concrete cubes made by Ordinary Portland Cement at all curing ages as shown in Figure 3.
5. CONCLUSIONS AND RECOMMENDATIONS
By analyzing the test results of all the concrete cubes with Ordinary Portland Cement concrete and with different configurations of fly ash made concrete by replacing fine aggregate and Ordinary Portland Cement, the following conclusions have been drawn.
As the compressive strength of concrete cubes, made by replacing 100 % fine aggregate with fly ash is more higher than the concrete cubes, made by using Ordinary Portland Cement and common fine aggregate, therefore the use of fly ash is recommended in plain cement concrete as a replacement of fine aggregate.
As the compressive strength of concrete made by replacing 10% and 25% cement with fly ash is relatively same as made with Ordinary Portland Cement at 7 & 28 days, therefore the use of fly ash as a replacement of Ordinary Portland Cement in plain cement concrete is recommended up to 25 %.
This paper emphasizes on the suitability of fly ash to replace the fine aggregate and cement in plain concrete. Further extensive research is required to use fly ash for design and construction of R.C.C members which may be economical for our construction industry.
The first author is extremely thankful to honorable project supervisor Professor Dr. Ghous Bux Khaskheli, Chairman, Department of Civil Engineering, and Director Post Graduate Studies, Mehran University of Engineering & Technology, Jamshoro, Pakistan, for his encouragement and necessary help at each and every stage of this research work.
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