Abstract

This thesis investigates the effects of aggressive sulfuric acid attack on the concrete mixtures prepared with metakaolin (MK) and limestone filler (LF) at various replacement levels. In addition, rapid chloride permeability (RCPT), water sorptivity, water porosity and rapid freezing and thawing tests were also performed on the concrete samples. Three sulphuric acid solutions with concentrations of 3%, 5% and 7% were used for examining the resistance of concrete specimens for a total exposure period of eight weeks. The performance of the degraded specimens was evaluated by measuring the weight loss, change in strength and visual assessment. The results of the weight loss and visual assessment reveal that the increase in the amount of MK would enhance the performance of concrete, while inclusion of LF into MK concretes has shown positive results in terms of resistance against sulphuric acid attack. The mixtures with ternary binders of OPC, MK and LF experienced the lowest strength loss after exposure to high concentrations of sulphuric acid. Measuring the change of weight was found to be a better way to evaluate the resistance of concrete specimens immersed in sulfuric acid solutions as the results of the load bearing capacity can be affected by several parameters such as the variable geometry of degraded specimens. The rate of the water absorption of concrete with MK and LF was lower than the reference mixture with only Portland cement. The RCPT results also showed that the reference mixture had considerably higher permeability than other concrete mixtures. The results of the water porosity on degraded samples indicate that the inner parts of the concrete (not in contact with sulfuric acid) have remained sound and maintained their original pore structure after different exposure periods.

Highlights

  • According to the U.S Geographic Service in 2006, approximately 7.5 cubic kilometres of concrete is produced every year, and it is the most used human made construction material in the world

  • It is important to note that immersing specimens into sulfuric acid solutions for specified time periods may not represent the real condition of the sewer pipes where bacteria corrosion is involved

  • The results of the preliminary studies on the resistance of different concrete mixtures to sulfuric acid intrusion indicates that, in terms of weight loss (WL), specimens that contain acrylic latex polymer perform better than other mixtures, which could have resulted from the obstruction by the polymer film on water transport which subsequently slows the ingression of sulfuric acid in concrete

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Summary

Introduction

According to the U.S Geographic Service in 2006, approximately 7.5 cubic kilometres of concrete is produced every year, and it is the most used human made construction material in the world. It is interesting to note that the word ‘concrete’ comes from the Latin word ‘concretus’ which means compact or condensed This material is generally highly durable and can be made to possess superior mechanical properties, such as high compressive and flexural strengths. Most concrete structures have considerable long life expectancies, there are a significant number of infrastructures in the world, such as wastewater systems, which are constantly under corrosion from different types of chemicals, such as sulfuric acid This continuous invasion and ingression of acidic ions into concrete can lead to serious damages to structures, which will result in costly repairs or in some cases, complete replacement of the whole structure

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