The effects of fly ash on the permeability of concrete culvert pipes.

• Main Authors: Reynoso, Carlos Martin Antonio P., Romualdez, Alberto Christian Estanislao H., Santos, Karyl Pauline V.
• Format: text
• Published: Animo Repository 2001
• Online Access: https://animorepository.dlsu.edu.ph/etd_bachelors/10346
• Institution: De La Salle University

Abstract. The primary objective of the thesis is to develop a more economical mix design by the use of substituting a percentage of cement with a by-product that is cheaper yet still effective in contributing to the concrete mix and improving other characteristics. The study aims to use fly ash in addition to cement in the manufacturing of concrete culvert pipes. These pipes will be used to transport wastewater to treatment facilities, so it is impeccable that the fly ash additive should not greatly decrease the strength nor increase the permeability of the culvert walls. Strength and permeability are the two most important characteristics monitored in culvert manufacturing. The culverts should be able to withstand a constant head of pressure while being able to prevent contaminated water from seeping through its walls. The experiment was designed for 35MPa concrete. Six different mixes according to varying percentages of fly ash in the mix (0%, 10%, 20%, 30%, 40%, and 50%) were made. Permeability was tested using a pressure pump to provide a constant head of water with 172kPa (25psi) applied to cylinders with an average diameter of 4cm and an average height of 3.3cm. represents the minimum thickness of walls used in culvert pipes. The constant head is applied for 30 minutes after which we break the cylinder and measure the depth of the penetration of water inside the cylinders. The data reveals that the more fly ash there is in the mix, the less permeable the concrete becomes. Based on our graphs, substituting 22% of the cement with fly ash in the mix will decrease the permeability by 59%, with only a 5% decrease in the strength. This will definitely result into less expense for cement since fly is about half the price.