Alçı sünger taşı cam lifi kompoziti

Abstract

VI ÖZET Ülkemizde önemli boyutlara ulaşmış olan konut sorununun çözümünde nitelikli ve yerli kaynaklara dayanan malzeme kullanımının ve endüstri- leşmiş yapım sistemlerine geçişin, sorunu hafifletici etkisi olacağı açıktır. Ayrıca özellikle son yıllarda enerji tasarrufu da zorunlu hale gelmiştir. Bu çalışmada, yukarıda sözü edilen sorunları hafifletmeye yönelik olarak, zengin doğal rezervlerimize dayalı doğal sünger taşı agregası ve alçı bağlayıcısı ile üretilen hafif malzemenin cam lifleri ile donatı larak, özeliklerinin iyileştirilmesinin olanakları araştırıldı. Çalışmanın ikinci bölümünde, alçı bağlayıcı, iki fazlı malzeme olarak hafif beton ve liflerle donatılı kompozit malzeme konularında yayın tara masına yer verildi. Alçının bugünkü kısıtlı kullanım alanları dışında da bir takım imkanlara sahip olduğu, literatürde cam lifleri ile donatılı çimento konusunda birçok çalışmaya rastlanmasına karşın, cam lifleri ile donatılmış alçı konusundaki çalışmaların az olduğu görüldü. Ayrıca, alçı bağlayıcı ile üretilen kompozitlerin sıcaklık karşısındaki özelik değişi mine dair verilere de literatürde rastlanmadı. Yayın taraması sonucunda, alçı bağlayıcı ile üretilen hafif agregalı karışımlarda cam lifi donatı kullanılmasının kompozit özeliklerine etki sinin araştırılması ve bu malzemenin yüksek sıcaklık karşısındaki özelik değişikliklerinin belirlenmesi konularında bir deneysel çalışma, III. Bölümde düzenlendi. Deneysel çalışmanın birinci aşamasında, alçı bağlayıcının bazı fizik sel ve mekanik özelikleri araştırılarak, priz geciktiricinin etkileri üzerinde duruldu. Ancak çalışmanın ileri safhalarında değişkenlerin arta cağı dikkate alınarak, priz geciktirici kullanılmasından vazgeçildi. İkinci aşamada, sünger taşı hafif agrega olarak alçı ile birlikte kulla nıldı. 1 - 8 mm arası hafif agrega kullanılarak iki fazlı kompozit olarak değerlendirilen karışımda matris su/bağlayıcı oranı, agrega hacım oranı ve agrega dane boyutu değiştirilerek özelikler üzerindeki etkileri ince lendi. Kırılgan yapıya sahip alçı hamurunun mekanik özeliklerinin iyileş tirilmesi amacı ile, üçüncü aşamada alçı hamurlarının E-camı lifleri ile donatılması ele alınarak, lif hacım oranı ve lif boyu değiştirildi. Ça lışmanın dördüncü safhasında, sünger taşı hafif agrega kullanılarak hafif- leştirilen malzemenin cam lifleri katılması ile çeşitli özeliklerinde görülen değişmeler izlendi. Bu aşamada matris hacım oranı ve lif hacım oranının nihai özelikler üzerindeki etkileri araştırılırken, konuyu tamamlayıcı olarak, agrega ve lif boyutlarındaki değişmelerin etkileri üzerinde de duruldu. Çalışmanın her aşamasında üretilen numunelerin dinamik elastiklik modülleri, birim ağırlıkları, basınç, eğilme ve çarpma mukavemetleri belirlendi. Seçilen numuneler üzerinde sıcaklık etkileri de araştırıldı. Dördüncü bölümde değerlendirmeye tabi tutulan sonuçlar, iki bölüm halinde özetlendi.VII 1. Fiziksel ve mekanik özelikler ile ilgili sonuçlar Karışıma katılan hafif agreganın daneli bir malzeme olması, agrega boşluklarından kaynaklanan kritik bir agrega-matris hacım oranını oluş turdu. Bu orana kadar bağlayıcı hamur, agrega ve liften üçlü bir kom- pozit malzeme oluşabilmesine karşın, bu oranın aşılması özelikler ile ilgili değerlerin düşmesine neden oldu. Birim ağırlık, rezonans frekansı, elastiklik modülü, basınç mukavemeti gibi özeliklerde agrega daha belirleyici rol oynadı, liflerin etkisi tali kaldı. Ancak eğilme, çarpma mukavemetleri, deformasyon oranları, kırılma sonrası davranışlar, kırıl ma işi değerleri lif miktarı ile doğrudan ilişkili olarak elde edildi, agrega etkisi tamamlayıcı anlamda kaldı. Lif boyunun artması ile, lifler ile belirlenen özelikler üzerindeki lif etkinliğinin arttığı görüldü, agrega ortalama boyutunun artması ise, özelikle elastiklik modülü, birim ağırlık, eğilme ve basınç mukavemetlerinde düşüşe neden oldu. 2. Yüksek sıcaklık etkisi ile ilgili sonuçlar Uzun süreli yüksek sıcaklık etkisi sonucunda kompozit boyutlarında önemli deformasyonlar oldu, agrega varlığı bu deformasyonları arttırır ken, lifler nisbeten engelledi. Sıcaklık etkisi ile numunelerin ağırlık ları düştü. Ancak hacmin da hızlı azalması ile birim ağırlıklarda bağıl bir artış izlendi. Agreganın bu durumda belirleyici olduğu, özellikle deney sonucu mukavemetlerini önemli ölçüde arttırdığı, liflerin mukave metle ilgili etkilerini nisbeten güçlendirdiği görüldü. Sonuçlar, malzemenin yapıda bölme, pano ve kabuk olarak kullanımına elverişli olduğunu, yaygın kullanım halinde yapıyı hafifleştirerek ve sünekliği arttırarak deprem açısından olumlu karakter kazandıracağını, agrega konsantrasyonu ve lif miktarının ayarlanması ile kısmen taşıyıcı elemanlar üretilebileceği gibi, çok boşluklu yalıtım malzemesi olarak da kullanılabileceğini, yangın direncini arttıracağını ve prefabrikasyona elverişli olduğunu gösterdi. Bu konuda ilerki çalışmalarda priz geciktiricilerin etkilerinin ve donatı türünün özelikler ile ilişkisinin incelenmesi, ayrıca yorulma ve yangındaki davranış üzerinde çalışılması tavsiye edildi.

VIII THE GYPSUM-PUMICE- GLASS FIBER COMPOSITE SUMMARY In this study, the possibility of improvement of the properties of lightweight composites made with pumice aggregate and gypsum cement has been investigated. Part II of the study starts with a literature survey on a. gypsum cement, b. lightweight concrete as a multiphase material, c. fiber reinforced composites. In section (a) dealing with gypsum cement production, physical and mechanical properties of gypsum have been shortly discussed. In section (b) studies on concrete and lightweight concrete as a composite material are outlined and general relations, developed for particle reinforced composites, are discussed by assuming concrete as a two phase material. In section (c), dealing with fiber reinforced composites, studies on fiber reinforced cement and gypsum composites are outlined. In this section, the basic relations involving mechanical properties such as stress transfer between fiber and matrix, fiber length and orientation, elastic constants and stresses, first crack stresses, critical fiber volume ratio, critical ultimate composite strength and behaviour in flexure are discussed. As a result of this literature survey it has been seen, that the matrix of the fibrous concrete exhibits a relatively low elongation at rupture. The fibers check the formation of cracks and /or have an effect on elongation by of breaking the crack pattern up into very fine and consequently invisible and harmless cracks. Fibrous concrete exhibits therefore a much more favorable extencibility than the matrix. The inclusion of fibers increases also the modulus of elasticity of the composite, the tensile and bending tensile strengths and their maximum strains, the first crack stresses and strains in flexure and the impact strengths. On the other hand the effect of fibers at the compressive strength is not positive. From this literature survey and evaluation, it has been seen that the most of studies on fiber reinforced composites have been done on cement base matrices and that there were very few studies on fiber reinforced gypsum composites. With the exception of one study made with perlite lightweight aggregate and gypsum cement and glass fibers, no other work dealing with the reinfor cement of gypsum cement-lightweight aggregate composites with fibers has been incountered. Also no studies have been incountered involving the behaviour of such composites under high temperatures. As a result of this literature survey,which showed that the effect of fiber reinforcement on properties of gypsum cement - lightweight aggregate composites has not been fully investigated, it was decided to plan an experimental investigation this subject, which will be outlined in Part III below.IX In the experimental investigation in Part III, gypsum cement, containing 92.92 % CaS04'l/2H20 and conforming to the gypsum standards has been used. As lightweight aggregate a pumice stone from the central Anotolia, containing 84.3 % insoluble Si02 and having a bulk unit weight of 0.407 kg/dm3 and fibers of E-glass of 13 m diameter and in the form of bundels of 80 filaments have been used. Taking into account that the unit weight of the aggregate fraction below 1 mm particle size was rather high, the aggregate size has been kept above this limit. The lengths of the glass fibers have been varied between 17, 34 and 50 mm. The experimental work has been planned in four stages : In the first stage, physical and mechanical properties of the gypsum cement and the effects of set retarders on it have been investigated. But finally it was decided not to use any set retarder in order to reduce the number of the variables. In the second stage of the experimental investigation, pumice stone has been used as lightweight aggregate together with gypsum cement. The maximum particle size has been selected in the range 1 mm to 8 mm, the water/gypsum ratio of the matrix, the volume fraction of the aggregate and the maximum particle size have been varied and their effect on the properties have been evaluated as a two phase composite material. In the third stage of the experimental investigation, it was decided to reinforce pure gypsum paste with E-glass fibers in order to reduce its fragility and to improve its mechanical properties. The fiber volume fraction and the fiber length were varied and their effects have been investigated. In the fourth stage of the investigation, fiber reinfor cement was added to mixtures of pumice aggregate and gypsum cement and its effect on the properties of this lightweight composite has been observed. The volume fraction of the matrix was varied between the limits of 1.0 and 0.2 and the volume fraction of the fibers was varied between the limits of 0.0 and 0.025 and their effects of final properties have been investi gated. Also the variation of the maximum particle size of the lightweight aggregate from 2 to 4 mm and 8 mm and of the fiber length from 17 mm to 34 mm and 50 mm were investigated. Prismatic samples with square cross-section and of 4x4x16cm dimensions for the static tests and of 3.5x3.5x30.0 cm dimen sions for the Charpy Impact test have been used. After casting, all specimens have been cured for one day in the laboratory, followed by 7 days of drying in an oven 40 °C + 2 oc temperature. After this drying, the samples were kept in a room with 18-20 °C temperature and 60 % ± 5 % relative humidity until they were tested at the age of 13 to 15 days. In every phase of the investigation the dynamic modulus of elasticity and the unit weight of the samples have beendetermined. Afterwards tests such as compressive strength, flexural strength and Charpy impact test were performed as required. Also the effect of heating to high temperatures up to 1260 °C and cooling has been investigated on some selected samples. The results of these experimental studies have been shown in tables given in the appendix, in tables III. 4 through III. 17. In Part IV of the study, experimental results are evaluated and conslusion drawn from these results are outlined under two subsections : a. Conclusion related to physical and mechanical properties There exist a critical volume fraction of the aggregate, up to which the matrix, the aggregates and the fibers may create a three phase composite. If this critical volume fraction is exceeded, the matrix becomes insufficient to fill all the voids in the aggregates and additional air voids start to remain in the mixture, with the result of a lowering of all properties. For volume fractions below this critical volume limit, following conclusions may be drawn : 1. Upon properties like unit weight, resonnant frequency, dynamic modulus of elasticity and compressive strength, the aggregates have a dominant effect and the fibers show only a secondery effect. The effect of the fiber show themselves more on the flexural strength, modulus of rupture, Charpy Impact strengths, maximum strains, post fracture behaviour and fracture energies. 2. With increasing fiber lengths the efficiency of the fibers increase, with increasing avarage particle size of the lightweight aggregates, modulus of elasticity, unit weight, compressive and flexural strenths decrease. 3. The bulk density of the composite decreases with increasing aggregate volume fraction and water /gypsum ratio. However this effect is lower for the gypsum-aggregate-fiber composites. 4. With decreasing matrix volume fraction, the dynamic modulus of elasticity decreases. Exceeding of the critical matrix volume fraction accelerates this decrease. 5. The increase of the water /gypsum ratio, decreases the dynamic modulus of elasticity, whereas the existance of the fibers increases this property. 6. The dynamic modulus of elasticity increase with increasing of fiber volume fraction and fiber length. Meanwhile decrease of the maximum aggregate particle size has the some effect.XI 7. The addition of aggregates, decreases the compressive strength and the existance of fibers accelerates this effect. 8. The compressive strength of the composite decreases with the increasing water /gypsum ratio, maximum aggregate particle size and fiber length. 9. The flexural strength of the composite increase with increasing fiber volume fraction and matrix volume fraction. The existance of fibers, makes the accelerating effect of the critical volume fraction on flexural strength disappear. 10. The flexural strength increases with decreasing water/ gypsum ratio and increasing fiber length. 11. The first crack stress of the composite in flexure increases with increasing fiber volume fraction. This effect being stronger in gypsum-aggregate-fiber composites. 12. The first -crack stress increases with fiber length too. 13. The fiber-matrix interfacial bond strengt decrease with existance of aggregate. 14. Compressive strength and flexural strength of the gypsum-aggregate-fiber composites with matrix volume fraction Vm=0.60, equaled each other for a fiber volume fraction of about 0.015-0.020. 15. The Charpy impact strength of the composite increases with increasing fiber volume fraction and fiber length. The existance of aggregates decreases this effect. The increase of the matrix volume fraction have a secondary positive effect too. 16. The maximum deflections of the composite in flexure, increase suddently with addition of the first fibers into the mixture. Their further increase with increasing fiber volume fraction being at a slower rate. 17. The area under the load deflection curve increases with increasing fiber volume fraction. 18. Fiber reinforced lightwei-ght aggregate-gypsum composites show a good correlation between the factor ( `/j A3 öbc' ) and their dynamic modulus of elasticity. b. Conclusion dealing with the results of high temperatures As a result of a standard heating test to high temperatures it was observed that the dimensions of the samples showed great reductions. The addition of aggregates increase these reduction, whereas the existance of fibers decrease them. Also the weights of the samples were reduced under the effect of high temperatures. Results of mechenical tests after cooling, showed that the pure gypsum paste was comletely deteriorated after this heatingXII and the existance of pumice aggregate or the existance of glass fibers gave to the samples some strength proportionnel to their volume concentrations. Further conclusion are as follows : 1. The existance of the aggregate increases the after cooling compressive and flexural strengths and the addition of fibers have a similar effect. 2. The after cooling dynamic modulus of elasticity increases with increasing fiber volume fraction. 3. Results of heating tests conducted at different temperatures, varying from 20 °C to 1260 °C showed, that the behaviour of gypsum composites with or without pumice aggrega tes were similar. 4. In al mixtures, compressive strength decreased considerably during the first heating up to 200 °C. Further increase of the temperature up to 1200 °C changed this result very little. An increase of the temperature above 1200 °C indicated some improvement of the after cooling strengths for the aggregate-gypsum composites. Part V of the study gives a brief outline of the experimen tal results and discusses the possibility of their utilization in practical applications. As shown in this discussion, this type of composite material is suitable for use in buildings in the form of panels and shells. In bulk utilization it will make the structure lighter and increase its ductility and create thereby a positive character in respect to eartquake resistance. By suitable selection of aggregates and fiber volume fractions it is possible to build structural elements, as well as very porous insulation elements from it. Which will also have increased fire endurance. Finally it is recommended that the effects of set retarders and of the types of fibers on properties of the composite should be studied in future investigations, as well as the fatigue strength and behaviour during the application of high temperatures.