Effect of Aggressive Environment on Durability of Metakaolin Based Cement Mortar

Abstract

In all sectors of society there are growing demands for improvement in the quality of manufactured products and this demand is more so in construction industry. Concrete is the major product used in the construction industry. It has to constantly face challenges of aggressive environment either from within or from external sources during its service life. Concrete immersed in a wet or moist aggressive medium tend to suffer damages; and exhibits so in the form of microcracks and spalling on its surface. This aggressive environment may be the acid content in surrounding environment that leads to reduction of pH of concrete i.e. during carbonation, or the acid attack due to the various gases present in the atmosphere which deteriorate the concrete. Even the marine structures are affected by the continuous salt crystallization and scaling damage. In the present scenario, concrete is not only the mixture of cement, aggregates and water but now some smart materials i.e mineral admixtures like silica fume, fly ash, metakaolin, rice husk etc are also being used within the concrete to increase its durability and strength. These mineral admixtures due to their fineness not only increase the cohesiveness of mix but also improve the impermeability of concrete to various salt solutions. Concrete subjected to repeated cycles of freezing and thawing may deteriorate rapidly, or it may remain in service far many years without showing signs of distress. Failure of the material be in the form of loss of strength, crumbling or a combination of the two. It is likely that due to varied behavior of climatic conditions in cold weather regions, the fresh concrete or hardened concrete gets subjected to freezing and thawing cycles. The durability of concrete gets greatly impaired due to this alternate freezing and thawing. It exerts fatigue in concrete. Similarly, alternating cycles of wetting and drying during the curing process is also extremely harmful to the concrete surface and may result in surface crazing and cracking. Keeping in view the large coastal line of our country, the concrete used in coastal structures are also susceptible to distress due to several factors some of which are common and they affect the durability of concrete in general. In the present study, the mortar specimens containing 0%, 5% and 10% metakaolin are cast at two water-cement ratios of 0.46 and 0.5. Then the detailed effect of various deicing solutions (3%) and corrosion inhibitors (1%) on the mortar samples subjected to freezing thawing cycles and wetting drying cycles have been studied. Four salt solutions including sodium chloride with and without corrosion inhibitor and calcium chloride with and without corrosion inhibitor have been used. Triethanolamine is used as a corrosion inhibitor in the present research work. The samples are tested for compressive strength, scaling, and mass change after 14, 28 and 42 cycles of freezing and thawing and alternate wetting and drying cycles. Non destructive tests like ultrasonic pulse velocity test have also been conducted to check the quality of mortar samples.