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Prospect of Bangladeshi Fly Ash in Concreting Works

Md. Moinul Islam*
Department of Civil Engineering, Chittagong University of Engineering &Technology, Chittagong-4349, Bangladesh

Md. Saiful Islam
Department of Civil Engineering, Chittagong University of Engineering &Technology, Chittagong-4349, Bangladesh

Abstract/ Executive Summary:

Sustainability issues in the construction sector came forward in the last two decades due to concerns regarding using virgin materials as well as the emission of greenhouse gases from the production of raw materials. The use of fly ash in concrete construction has become of increasing importance because of not only its ability to improve the fresh and hardened properties of concrete but also its environmental credentials. Fly ash is a by-product produced from pulverized coal combustion in power generation and formed from the non-combustible minerals found in coal. In the year 2006, two units of 125 MW coal-based power plant has started generation in Barapukuria, Bangladesh. Around 65 thousand tons of fly ash is being produced from those thermal power plants. This study aimed to explore the possibility of using fly ash in concrete construction produced from the only coal-based power plant in Barapukuria, Bangladesh. Two different grades of concrete (M28 and M38), each with eight different cement replacement levels 0, 10, 20, 30, 40, 50, 60 and 70% were used for the experimental program. Among all the concretes studied, the optimum amount of cement replacement is reported as 30%, which provides around 12% higher compressive and 53% higher tensile strength as compared to OPC concrete.

Keywords: Climate Cement, Compressive strength, Environmental pollution, Fly ash, Tensile strength.

Location: Bangladesh

Start Date:

End Date:

Program Area: Resource Development and Management

Commodity: Ash

Objectives:

The beneficial use of coal-burning power plant fly ash in concrete has increased the interest of researchers for the evaluation of the performance of such concrete. The relevant studies indicate that the percentage of cement replaced with fly ash and their relative proportion for making concrete is very important. Concrete mixes made by replacing cement with fly ash are reported to show better results for compressive, tensile as well as flexural strength, freezing and thawing resistance, shrinkage, permeability, and abrasion resistance than conventional concrete mixes (Tarun, 1996). Fly ash has dual effects in concrete i.e. as a micro-aggregate and as a pozzolana. Fly ash improves the interfacial bond between the paste and the aggregates in concrete (Poon, 2000). According to Malhotra (2000), the concrete incorporating moderate and high volumes of fly ash showed superior resistance against strength deterioration, rebar corrosion and the penetration of chloride ions compared to the control concrete specimen.

Methodology:

The experimental program was planned to quantify the compressive strength and tensile strength of concrete using fly ash as a partial replacement of cement. Cement replacement at various percentage levels was used in this investigation to observe the effects of different fly ash levels in concrete in contributing strength at various ages of curing.

2.1 Materials Used (a) Cement: ASTM Type I Portland Cement was used as binding material. Chemical compositions of OPC which was determined as per BS EN 196-2.

(b) Fly ash: A low calcium ASTM Class F fly ash was used in this investigation. Chemical analysis of the fly ash which was determined as per BS EN 196-2. (c) Aggregate: Locally available natural sand passing through 4.75 mm sieve and retained on 0.075 mm sieve was used as fine aggregate. The coarse aggregate was crushed stone with a maximum nominal size of 12.5 mm.

2.2 Mix Design and Sample Preparation Two different grades of concrete namely M28 and M38 were used in the program. Seven different mix proportions of cement fly ash (90:10, 80:20, 70:30, 60:40, 50:50, 40:60, 30:70) were used as cementitious material. Cement fly ash mix ratio of 100:0 i.e. plain concrete specimens were also cast as reference concrete for comparing the properties of fly ash concrete. Thus the fly ash concrete means the concrete made by using cement and fly ash as cementitious material with sand, stone chips, and water.

Around 300 no’s of cubical specimens of 100 mm size were prepared according to the mix proportion as described for both compressive and tensile strength test. The small size of the specimen i.e. 100 mm cube was taken in order to accommodate a large number of specimens in the limited-sized curing tanks. The specimens were demoulded after 24 hours of casting and cured in plain water at 27±2°C. The concrete test specimens were designated keeping concrete grade and replacement as the variable. Thus M38FA40 concrete means the grade of concrete is M38 and the cement fly ash mix ratio is 60:40.

2.3 Experimental Procedures The compressive strength and tensile strength of various water cured concrete specimens were tested at the ages of 3, 7, 28, 56, 90 and 180 days in accordance with the BS EN 12390-3:2009 for compressive strength and BS EN 12390-6:2000 for tensile strength. In each case, the reported strength is taken as the average of three tests results.

Source of Information: Journal of Engineering Science 03(1), 2012 59-67

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Based on the results of the investigation conducted on different fly ash concrete made with various levels of cement replacement as mentioned and cured for various curing periods up to 180 days, the following conclusions can be drawn: (1) At the early ages of curing, the rate of gain in strength of fly ash concrete specimens is observed to be lower than the corresponding OPC concrete. (2) Fly ash concrete mix having various cement replacement levels up to 40% exhibited satisfactory results for both compressive and tensile strength. (3) The study reveals that the optimum fly ash content is 30% of cement. Fly ash concrete with 30% cement replacement shows around 12% higher compressive strength as well as 53% higher tensile strength than OPC concrete after 180 days of curing. (4) Use of high volume fly ash in any construction work as a replacement of cement, provides lower impact on the environment (less CO2 (5) Use of fly ash reduces the amount of cement content as well as generation of heat due to hydration of concrete mix. Thus, the construction work with fly ash concrete is economical and environmentally safe. Based on the results of the investigation conducted on different fly ash concrete made with various levels of cement replacement as mentioned and cured for various curing periods up to 180 days, the following conclusions can be drawn: (1) At the early ages of curing, the rate of gain in strength of fly ash concrete specimens is observed to be lower than the corresponding OPC concrete. (2) Fly ash concrete mix having various cement replacement levels up to 40% exhibited satisfactory results for both compressive and tensile strength. (3) The study reveals that the optimum fly ash content is 30% of cement. Fly ash concrete with 30% cement replacement shows around 12% higher compressive strength as well as 53% higher tensile strength than OPC concrete after 180 days of curing. (4) Use of high volume fly ash in any construction work as a replacement of cement, provides lower impact on the environment (less CO2 (5) Use of fly ash reduces the amount of cement content as well as generation of heat due to hydration of concrete mix. Thus, the construction work with fly ash concrete is economical and environmentally safe.

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