Pirinç kabuğu külünün puzzolanik özellikleri ve külün çimento harcının dayanıklılığına etkisi

Abstract

ÖZET Günümüzde sanayileşme ve şehirleşmenin sonucu olarak inşaat sanayii gelişmekte, buna bağlı olarak çimento üretimi ve çeşidi artmakta dır. Çimento üretiminde puzzolanların kullanımı da gün geçtikçe önem kazanmaktadır. Tras gibi doğal puzzolanların yanısıra, silis dumanı, uçucu kül, cüruf gibi endüstriyel atıklardan yapay puzzolan olarak çimento üretiminde yararlanılmaktadır. Bu çalışmada yapay puzzolanlar arasında tarımsal ürün atığı olan pirinç kabuklarından elde edilen pirinç kabuğu kül ünün özelikleri ve harçlardaki durabıliteye etkisi araştırılmıştır. Pirinç kabukları 400û ve 500°C de sıcaklığı kontrol edilebilen, LPG ile çalışan fırında 1,5 saatte yakılmıştır. Elde edilen küllerin fiziksel, kimyasal özellikleri incelenmiş, puzzolanik karakteri de kimyasal, mekanik deneylerle saptanmıştır. Küllerin özellikleri, silis dumanı, uçucu kül, cüruf ve tras gibi puzzolanlarla da karşılaştırılmıştır. Küller çimentoya %10, 20, 30 oranında ikame şeklinde katılarak küllü harçlar ve şahit, külsüz harç üretilmiştir. Harç karışımlarında bileşim ağırlıkça (çimento+puzzolan):(su+süperplas- tifiyan):kum=l:0,57:3 oranındadır, üretilen harçlar üretimden 28 gün sonra saf su ve saf su ile hazırlanmış sodyum sülfat çözeltisine kon muştur. Harçlarda belirli kür süreleri sonunda eğilme ve basınç dayanımı ağırlık ve boy değişimi, kılcallık, su emme, birim ağırlık deneyleri yapılmıştır. Ayrıca X ışını difraktometresi ve elektron mikroskobu ile harçların mikroyapısı incelenmiştir. Çalışmadan elde edilen belli başlı sonuçlar şöyledir: Su içinde bekletilen küllü harçlarda eğilme ve basınç dayanımı şahit harca ve zamana göre artmıştır. Sülfat çözeltisinde bekletilen küllü harçların eğilme ve basınç dayanımı 8'ci kür haftasından sonra azalmıştır. Küllü harçlarda ise dayanımlar zamanla, şahit harca göre daha fazla artmıştır. Sülfat çözeltisinde bekletilen küllü harçların eğilme dayanımı, su için de bekletilen küllü harçların dayanımına göre daha yüksek; aynı harçların basınç dayanımı ise su içinde bekleyenlerinkine denktir. Su içinde bekletilen tüm harçların ağırlık ve boy değişimi de 28 günde artış şeklinde az miktarlardadır. 28 günden sonraki kür haftalarında ise şahit harcın ağırlık ve boy değişimi sülfat çözeltisinde sürekli ve büyük miktarlarda artmıştır. Küllü harçlarda ağırlık değişimi sülfat çözeltisinde ağırlık kaybı, su içinde çok az ağırlık artışı şeklindedir; kılcallık ve su emme, değerleri suda kür için kül miktarının artmasıyla artmış, birim ağırlık, kül miktarının artmasıyla azalmıştır. XRD incelemelerine göre su ve sülfat çözeltisinde bekletilen harçlardan şahit ve »10 kül içerenlerde Ca(0H)2 saptanmıştır. Sülfat çözeltisinde bekletilenlerde ise Ca(0H)2'in yanında ettrengit görülmüş, oysa %20 ve %30 küllü harçların yapısında bu bileşiklere rastlanmamış tır. Araştırma sonuçlarına göre 20 ve %30 oranında kül katılmasının sodyum sülfatlı ortamda harcın dayanım ve dayanıklılığını arttırdığı kanısına varılmıştır. xii

POZZALANIC PROPERTIES OF RICE HUSK ASH and ITS EFFECT on DURABILITY of CEMENT MORTAR SUMMARY In our day, types and varieties of concrete structures are in creasing continuously, and depending on this situation types of cement and their production are also increasing. Pozzalanic cement addives are used to improve properties of cement and to decrease cost. Pozzalanic cements are especially used in the production of chemical resistant concretes. Besides natural pozzalans such as trass, also industrial by-products such as silica fume, fly ash and rice husk ash are used. This usage of industrial by products in cement production also prevents environmental polution. Rice husk ash is an artificial pozzalan and is an agricultural waste. Rice husk ash is gaining more importance inrural areas of agricultural countries. In the present work the pozzalanic charactber of rice husk ash (RHA) and its effect on the sülfat durability of mor tar is investigated. The work consists of five chapters which are as follows: The first chapter is introduction, the second chapter covers the experimental part of the study, the third chapter presents the experiment results, the fourth chapter is devoted, to the evaluation, of the experimental results, and the fifth chapter gives the conclusions derived from the study and the proposals for further, investigations. In the introduction there is given general knowledge, about pozzalans, the structure of silica in pozzalans, the pozzolanic activity, the rice husk and its burning, the rice husk ash, the durability of concrete against corrosion in detrimental environments, the effect of pozzalans on durability, previous studies on the subject, and finally the purpose. and scope of the present study. In the second chapter, the materials such as Portland cement rice husk ash (at 400°C and 500°C), silica fume, fly ash, blast fur nace slag, trass and superplastifiers which are used in the experi mental part of the study are defined. Physical, chemical and pozza lanic activities of the pozzalans are determined. In pozzalanic activity tests mechanical and chemical methods are used. In addition heat of hydration of pozzalanic cements and portand cement were mea sured and as a result of these experiments the pozzalans are compared to each other. xi i iThe rice husk used in this work is burnt in a cylindirically shaped furnace covered by heat resistant brick internally, and with its interior temparature being measurable and controllable. In the furnace LPG is used to burn the husk. Two burning temparatures of 400° and 500°C were used for periods of 1,5 hours. The reason for the choice of those temparatures being to obtain an amorphous state of the silica in the ash. The ash obtained as a result of this bur ning process was cooled in air to room temparature (18-20°C) in a few minutes. Finally this ash is ground in a disc mill to a fineness of 0-200 um. Physical and chemical properties and pozzalanic activity of the ground ash were determined. The existence. of amorphous silica in ash is proved by chemical analysis, X-Ray Diffraction (XRD) and by pozza lanic activity test. When the ash is compared with other pozzalans, it is observed that the rice husk ash gives better results in regard to pozzalanic activity, than the other ones. RILEM mortar mixtures were prepared by the addition of rice husk ash in the percentages of %0, 10, 20 and 30 as a replacement by weight of cement. Since the water requirement of the ash was increased, %Z superplasti fiying admixture by weight of cement plus ash (RHA) is ad ded to thfr mixing water. The water+superplastifier/cement+rica husk ash ratio was kept 0,57 for all the mortars. On the mortars produced in this study properties in the fresh and hardened state and durability were investigated. Sodium sulphate (Na2S04.10H2&) solution was selected as corrosive environment for durability. At the age of 28 days the mortar prisms (4x4x16 cm) were immer sed in distilled water and in sodium sulphate solution of 0,35 M for the durability test. The sodium sulphate solution was prepared using distilled water. The dH of the sodium sulphate solution was constant at 6+2. To keep the pH value at 6 when it tended to increase, the solution was titrated with, H2SO4 solution through a dozimeter connected to the pH meter. Following tests were performed comparatively on samples kept in distilled water and in sodium sulphate solution after predetermi ned durations of exposure-. Flexural and compressive strength tests were made at 0, 4, 8, and 12th exposure weeks. Weight and length measurements were made at 1, 3, 7, 14, 21 and 28th day and after the end of 28th day at 4, 6, 8 and 12th exposure weeks. Also weight and length measurement on samples kept in air at room temparature were made at 1, 3, 7, 14, 21 and 28 days, and 8, 10, 12, 16 weeks. Capillarity, water absorption, and unit weight determination were made after 4th and 12th exposure weeks. xivThe nicrostructures of the mortars kept in distilled water and in sodium sulphate solution were examined by X Ray Oiffractometer (XRO). The samples keept in sodium sulphate solution were examined additionally by Scanning Electron Microscopy (SEM). In the third chapter calculated experimental results were pre sented m tables. In the fourth chapter the experimental results were evaluated and discussed. The evalution of the results is divided in the follo wing 3 titles: 1- Properties of the fresh mortar such as unit weight and flow. 2- Mechanical properties of the hardened mortar such as flexural and compressive strength after curing in distilled water. 3- Durability of mortar stored in ^SOa solution and comparison of durability with control samples cured in distilled water. Parame ters compared were: - Volume stability (weight and length changes) - Porosity (Capillarity, water absorption, unit weight, microstruc- ture) - Loss in strength (flexural and compressive strengths) In the fifth chapter general results are summarized. Important results obtained in this study can be summarized as follows: 1- Results related to properties of the fresh mortar: In the fresh mortar unit weight and flow decrease in proportion to the increase in amount of rice husk ash. 2- Results related to properties of the hardened mortar:. Flexural and compressive strengths of plane mortar samples kept in distilled water were less than those of samples with rice husk ash mortar. In other words rice husk ash increased the strengths of the mortar.. Flexural strengths of the two series with 4Q0.OC and 500°C rice husk ash mortars, kept in distilled water were ^ery close to each other. This situation was also true for compressive strengths. xv3- Results related to the durability a. Results related to volume stability a.l. Result related to the change of weighth Unit weight decrease as the amount of ash in mortar increases,. The weight change of both the ash and the control mortars, kept in distilled water, were in the form of an increase in weight.. The change in weight of specimens kept in sodium sulphate so lution occured in the form of an increase of weight for the control mortar, and in the form of a decrease of weight for the ash mortar. The decrease in the weight of the ash mortar kept in sodium sulphate solution became stronger as the burning temparature of husk, and the amount of ash increased.. The change in the weight of control mortar kept in sodium sulphate solution was much more than the one kept in distilled water. The increase in the weight of control mortar kept in distilled water was %Q 1,2 after 12 week, and the same value in the case of storage in sodium sulfate solution was %Q 7,3. At the end of Î2 weeks, change in weight for %30 ash mortar kept in distilled water were %0. +0,7 for 400°C ash, and %Q+0,5 for 500°C ash. For storage in Na2S04 solution the same values were 350-2,1 for 400°C ash and 540-4,4 for 50Q°C ash.. In the mortars kept in air the weight losses increased with the increase in the amount of ash in mortar and was allways greater than that of control mortars. Further more the weight loses of the 500°C ash mortar was greater than that of the 400°C ash mortar. a. 2. Results related to the change* of length. The increase in the length for all of mortars kept in distil led water was very small and comparable to each other.. Increases in the length are observed in all of the mortars kept in sodium-sulphate solution. When a comparison for the lengths of mortars kept in distilled water and with those of mortars kept in sodium sulphate solution is to be made, it will be seen, that the length increases in sodium sulphate solution were greater than those in distilled water. Also the increase in the length of control mor tar in NaoSC^ solution was continous and greater than that of ash mortar. At the 12th week of cure, the increase in the length of control mortar kept in distilled water was 30x10-3 y/mra, and the observed value of the control mortar kept in sodium sulphate solution was around 1072xl0`3 u/mm. The increase in the length of ash mortars in sulphate solution was much less than that of the control mortar in xvisodium sulphate solution, and this increase became less as the amount of ash increased. It was also observed that the increase in length of ash mortars having a rice husk burning temparature of 40Q°C was greater than the those of 500aC ash mortars. At the end of 12 weeks, change in length for %30 ash mortar kept in distilled water were 30x10-3 u/mm for 400°C ash, and 45xl0-3 u/mm for 500°C ash. for storage in NaoSOa solution the same values were 45x10-3 u/mm for 400°C ash and IHxlO`-3 p/mm for 500°C ash. Results of the weight and length measurements showed that the lengths and the weights of control mortars containing no ash and stored in Na2SÛ4 solution increased 30 times and 6 times recpectively more than the weights and lengths of control mortars stored in distilled water. But for the test mortars containing %30 ash and stored in Na2S04 solution the increase in the length was only -v3-5 times of that of the increase in length of mortars stored in distilled water; and a decrease was observed in the weight which was equal to 1/8 of that stored in distilled water for 5QQ°C ash These results prove that the control mortar has suffered severly from the sulphate solution as a result of certain compounds causing volume increase. But the test mortars containing %30 ash suffered much less or even none for the length of a storage applied in this investigation.. In the mortars kept in air, the drying schrinkage increased with the increase in the amount of ash and was all ways greater than that of control mortars. Further more the schrinkage of the 500°C ash mortar was greater than that of the 40Q°C mortar. b- Results related to porosity and micro structure b.l. Results related to capillarity, water absorption and unit weight.. The value of capillarity coefficient of the ash mortar kept in distilled water increased in relation to the increase in the amount of ash.. As a result of increase in the amount of ash the capillarity coefficient of ash mortar increased. Also the capillarity coefficient of ash mortars kept in Na2S04 solution was greater in comparison with the ones kept in water. But at the end of the 12th week the capilla rity coefficient.of %30 ash mortar kept in ^SCty solution, decreased xvi iwith time whereas that of the control mortar increased.. Water absorption of the ash mortar kept in water increased in relation with amount of ash.. As a result of increase in the amount of ash, water absorption values of ash mortar kept in Na2SC>4 solution increased for the first 4 weeks of storage but started to decrease after 12 weeks (at 400OC). Mo such change occured for mortar cured in distilled water.. Unit weight of mortars decreased as the amount of the ash in mortar increased. Unit weight did not vary appreciably for both mor tars kept in distilled water and sodium sulphate solution. b.2. Results related to X Ray Oiffraction (XRO). While Ca(0H)2(=Portlandite) was observed in the diffractogram of the control mortar and the %10 husk ash mortars kept in water, it was impossible to make the same observation in the case of %30 ash mortar.. Ca(0H)2 and ettring ite were observed in the diffractogram of the control mortar and of the %10 ash mortar kept in Na2S04 solution, but not in the %2G and %30 ash mortar. XRO test result; showed that Ca(0H)2 is decreasing as a result of increase in the amount of ash in the ash mortar kept in distilled water, or in other words, amorphous silica in ash is holding Ca(0H)2 that is liberated as a result of hydration of cement. But Ca(0H)2 and ettringitte were not seen in ash mortar kept in ^SCfy solution. This proves that rice husk ash blocks the formation of ettringitte and holds the Ca(0H)2. Among these results weight and, length increases in the control mortar and observation of ettringite in XRO were the signs of destruc tion in the structure of mortar containing no ash. In addition to these external apperence, control and %10 ash mortars showed signs of distruption,but no external changes were observed in the %2Q and 30 ash mortans. c- Results related to the strength changes. Flexural and compressive strengths of ash mortars kept in Ha2S04 solution were higher than those of the control mortar. xvi n. A decrease is observed in compressive strengths of mortars kept in Na2SÛ4 in comparison with those of in mortars kept in dis tilled water.. Flexural strengths of control mortars kept in sodium sulphate solution decreased at the end of the 12tn test week, whilst the va lues of flexural strength of control mortars and ash mortars kept in distilled water increased %10 and %2Q respectively. The increase turned out to be %AQ for ash mortar stored in Ma2`S04 solution. The values of compressive strengths of control mortars and ash mortars kept in distilled water increased $10 and %25 respectively. The same values for storage in Na2SC>4 solution turned out to be a decrease of %2 for the control mortar and an increase of %20 for the ash mortar.. The flexural strength of ash mortar kept in NaoSCfy solution was greater than that of the ash mörtar kept in distilled water. However, the compressive strengths of ash mortars kept in Ma2S04 solution were very near to the ones kept in distilled water. As a final result it is concluded that rice husk ash is a profitable pozzalanic cement additive material. It is specially effective in increasing the durability of mortars in corrosive environments like a sodium sulphate solution. xix