Investıgatıon Of The Rheologıcal and Workabılıty Propertıes Of Constructıon and Demolıtıon Waste Based Geopolymer Mortars

Abstract

Being the most widely used construction material, concrete brings about considerable challenges. Portland cement (PC), main binding material for concrete, creates enormous negative impacts mainly due to the high energy requirement for its production and associated release of greenhouse gases. Production of PC and concrete encompasses a series of steps which require involvement of natural resources such as water, aggregates, clay, limestone and gypsum, which leads to detrimental effects for environment as well. Considering that, minimizing the usage of cementitious materials would clearly increase the environmental benefits such as reduced energy consumption, CO2 emissions and raw material use. This therefore has led researchers to search for the development of environmentally-friendly construction materials. Efforts within the recent years resulted in novel concepts of new generation binder materials termed as alkali-activated materials or geopolymers, that are successful candidates to partially or fully substitute PC. Geopolymers are inorganic polymers that are formed as a result of the reaction between aluminosilicate source materials (i.e. precursors) and alkaline activators (e.g. solutions of alkali-hydroxide/-silicate). Among different aluminosilicate precursors used in geopolymer technology, mineral admixtures such as blast furnace slag, fly ash, silica fume and metakaolin are prevalent while as different alkaline activators, sodium hydroxide potassium hydroxide, calcium hydroxide, sodium silicate are used more commonly. However, these precursors are highly demanded given their successful utilization concrete mixtures as mineral admixtures for years. Therefore, increasing attention was started to be paid on aluminosilicate precursors that are not strongly demanded by concrete industry. As a result of the urban transformation, which is mainly based on demolishment and reconstruction, millions of buildings are transformed each year upon completing their service life and/or reaching to a state that is dangerous to their dwellers and environment. What to do with the tremendous amounts of Construction and Demolition Waste (CDW) created is a question of huge debate globally and CDW mostly ends up being landfilled, which requires immense areas of storage and is very costly health-/economy-/environment-wise. One effective way for the proper CDW handling is to utilize CDW components in producing geopolymers. This is reasonable given the fact that CDW generation is a global problem and CDW can be easily found anywhere in the world. In this study, it was aimed to analyze effects of activators type, usage rates and combinations on rheological and workability performance of CDW based geopolymer matrix. In that context, at first, mortar phase composed of wall and roof members including bricks, tiles, glass waste and concrete waste in which recycled aggregate was utilized, was investigated with empirical test methods. For detailed investigation, rheometer was used to understand rheological and workability characteristic of CDW based geopolymer in addition to empirical test methods. In that way, know-how about rheological and workability performance of CDW based geopolymer was formed as well as mechanical performance and it was made possible to select the correct activator according to the application needs by using the results of the thesis study.