Thesis Type: Doctorate
Institution Of The Thesis: Yildiz Technical University, Graduate School of Natural and Applied Sciences, Turkey
Approval Date: 2018
Thesis Language: Turkish
Student: YURDAKUL AYGÖRMEZ
Consultant: Orhan CanpolatAbstract:
Today, cement is the most used binder material in the construction industry. But the energy used in the cement consumption also reveals economic and environmental problems. It is known that an average of 7% of the total CO2 emissions in the world originate from cement production. Therefore, producing alternative cements for Portland cement is among the current research topics. Geopolymer is a new generation construction material which is an alternative to traditional Portland cement and emits very little CO2. Geopolymers do not reveal CO2 in the chemical reactions and are known to be more energy-efficient and environmentally friendly than traditional Portland cements due to their production techniques. The total energy used in the production of geopolymer cements is approximately 40% less than the energy used in traditional Portland cement production. In this study, metakaolin was partially replaced up to 40% with silica fume and colemanite, and the effect of these materials on the behavior of the obtained geopolymer composites was investigated in terms of mechanical and durability properties. As a first step, unit weight, water absorption and void ratio values were investigated and then an experimental comparison was made with the compression and bending behavior, abrasion resistance and ultrasound velocity tests of polypropylene fiber and non-fibre samples. In general, the results have proven that substitute materials are useful. For comparison purposes, samples produced from CEM I 42.5R cement were used. In general, a significant improvement in terms of compression and bending strength has been achieved in all samples, for example, in 28-day results, compressive strength increase in the samples with 10% colemanite and 20% silica fume compared to 100% metakaolin based geopolymer samples was 2.02% and 11.48% while the increase in flexural strength was 14.61% and 29.44%. With respect to polypropylene fiber reinforced samples, a significant improvement in flexural strength was observed, but no significant increase in compressive strength was achieved. The addition of polypropylene fibers has often helped to improve the flexural strength and abrasion resistance of the samples. In addition to the mechanical properties of geopolymer mortars, durability properties were investigated. In this context, durability tests were carried out on samples with 100% metakaolin geopolymer and up to 20% silica fume and colemanite blended samples. In this study, the freezing-thawing test consisting of 56 cycles was applied. In the freezing thawing test, samples were produced in two forms, with and without air entraining agent. In the freezing-thawing effect of the geopolymer blends, there was an increase rather than a reduction in the strength results, which is mainly due to the fact that the geopolymeric matrix is compact and has a good adhesion which makes it resistant to freezing and thawing effects. In addition, a progression process of the matrix occurs through freezing-thawing cycles. The air entraining agent impacted less than Portland cements due to the compact nature of the geopolymer sample's internal structure. 300oC, 600oC, 900oC temperatures were applied to geopolymer mortar samples. Polypropylene fiber and non-fibre samples were produced for high temperature tests. As a result of the tests, the results of weight loss, compressive and flexural strength and ultrasound velocity were analyzed. According to the results, geopolymer mortars at high temperatures were better than Portland cement mortars. Even at 900oC, metakaolin-based geopolymer samples have shown a more stable structure. A slight decrease in compressive strength was observed in fibre reinforced samples while an increase in flexural strength was observed. In 10% sulfuric and hydrochloric acid, magnesium and sodium sulphate, sodium chloride solutions, the samples were kept for 3, 6 and 12 months and the results of weight change, compressive and flexural strength and ultrasound velocity were evaluated. In geopolymer samples, a significant decrease in strength was observed as a result of acid effect. But at the end of 1 year, while geopolymer specimens preserved their structure, Portland cement samples were dispersed after 3 months. Sulfuric acid is stronger than hydrochloric acid, resulting in more strength loss. When geopolymer samples were exposed to magnesium sulphate, sodium sulphate and sodium chloride effects, there was an increase in strength during 3 months and a decrease from 6 months. This is due to the fact that these solutions have contributed to the continuation of the geopolymerization process by entering the internal structure of the sample within 3 months. During the ongoing process micro cracks have started to occur and decrease in strength has begun to appear. Microstructural analysis with scanning electron microscopy (SEM) and XRD analyses generally showed a good geopolymerization bonding, a well-accepted compactness of the matrix, and materials that behave in harmony within the geopolymer system.