Çimentoların katkı maddeleri ile birlikte veya ayrı öğütülmesinin beton dayanımı üzerindeki etkileri

Abstract

Bu tez kapsamında, Türk Standartlarınca çimentoya katılması uygun görülen puzolanlardan tras, cüruf ve kalkerin, çalışmaya ait deneylerin yapıldığı Lafarge Aslan Çimento Fabrikası da dahil olmak üzere çoğu çimento fabrikalarında olduğu gibi, klinkerle birlikte öğütülerek katkılı çimento elde edilişi yerine, bunların ve klinkerlerin ayrı ayrı öğütülüp, homojenizasyonu fikrinin sonuçta beton dayanımında göstereceği değişiklikler gözlenerek, daha yüksek dayanımlara ulaşma yolu araştırılmıştır. Tezin literatür kısmında çimento kavramı hakkında verilen bilgilerin ardından, çimentonun fiziksel ve kimyasal özellikleri belirtilerek, standartlarca belirlenen katkı maddelerinin çimentonun bir takım mühendislik özellikleri üzerindeki etkileri tartışılmıştır. Deneysel çalışmaların başlangıcında klinker, alçı, tras, kalker ve cüruf komponentlerinin XRF cihazında kimyasal analizi yapılmıştır. Üretilen çimentolar için hesaplanan yoğunluk değerleri portland, trash, kalkerli ve curuflu çimento için sırasıyla; 3.05, 2.83, 2.92 ve 2.95 g/cm3 olarak bulunmuştur. Çimentolardan hazırlanan çimento macunlarına uygulanan priz süresi testlerinde ayrı öğütmenin sadece curuflu çimento olmak üzere, birlikte öğütme priz sürelerine göre ortalama 40 dakikalık bir gecikmeye sebep olduğu görülmüştür. Ayrıca eklenen katkılarla çimentoda priz başlama ve sona erme sürelerinin ortalama 15 dakika geciktiği göze çarpmıştır. Hazırlanan çimento tipleriyle yapılan beton dayanım testlerinde trash ve kalkerli çimentoda, ayrı öğütmede dayanım kazançları elde edilmiş; curuflu çimento dayanımları açısından birlikte ya da ayrı öğütme arasında belirgin bir fark gözlemlenememiştir.

Today, cement is the most popular material for the construction industries. Especially, developing countries such as Turkey, are improving their cement production capacity for their growing amount of constructions which are kept on building. In 1911, the first Turkish cement factory was established in Danca with 200.000 tons/year cement capacity. This capacity was reached to 515.000 tons/year after the establishment of the Turkish Republic. As the years went on, the future role of cement seemed to be understood that in year 1960, Turkish cement capacity was increased to 2. 103.000 tons/year. As a recent capacity value for the year 1995 is about 47.000.000 tons of cement per year Especially after the energy crisis of 1970s, pozzolanic cements are started to be produced in an increasing capacity in Turkey, as it is in the whole word. Turkey is a lucky country with its large deposits of natural pozzolans and important artificial pozzolan potential. The main objective of replacing pozzolans in portland cement are to obtain some specific engineering properties such as, decrease in heat of hydration, permeability, thermal volume change, segregation bleeding and increase in resistance to chemical attack, long term strength freezing- thawing resistance and workability of fresh concrete. The other, equally important, objectives for using mineral admixtures in cement concrete include economic benefits environmental safe recycling of industrial and other types of waste by-products. Another objective is that the mineral admixtures are generally used as partial replacement of portland cement, an expensive and energy intensive material. Therefore, utilisation of mineral admixtures leads to considerable saving in cost and energy consumption. Utilization of increased volumes of industrial by-products (fly ash, silica füme, blast furnace slag,...) as mineral admixtures in cement and concrete will lead to conservation of energy and natural resources. Pozzolans concerning the resource they are obtained, are divided into two main groups such as natural pozzolanic materials and the industrial by-products as mineral admixtures. XII Natural pozzolans of volcanic origin are formed during explosive volcanic eruption when the quick cooling of magma composed mainly of aluminium silicates, results in the formation of amorphous (glass) or vitreous phases with disordered structure. Because of large surface area and disordered structure, the aluminium silicates present in pozzolans undergo chemical reaction with Ca4^ ions in the presence of water. This forms the basis of pozzolanic reaction with lime, and the resultant pozzolanic activity. Clays shales and diatomaceous earths need to be calcined at 540-900° to improve the pozzolanic reactivity. Fly ash from combustion of pulverised coal, granulated slag from both ferrous and non-ferrous metal industries, volatilized silica form silica metal or ferrosilicon alloy industries, red mud or bauxite waste from aluminium extraction industries, and rice hull (husk) ash from the combustion of rice husk, are some of the industrial by-products which are found suitable for use as mineral admixtures in portland cement mortar and concrete. All mineral admixtures added in cement is known to decrease the strength of concrete especially in early ages. In the scope of this study, pozzolans (trass, blast furnace slag, limestone) which are permitted by the Turkish Standards to be added in cement, are used. Many cement factories including Lafarge Asian Cement Factory where all tests for this thesis had been carried out, intergrind the mineral admixtures and the clinker for producing pozzolanic cement. The goal of the study is to separate grinding of mineral admixture and clinker before homogeneously mixing, instead of intergrinding the two components together. The effect of grinding type on the concrete strength difference between the two grinding systems were examined, and any change in the strength of concrete were determined as advantageous or disadvantageous. According to the new Turkish Standards, limestone is permitted to be added in cement up to 35 % of total cement mass. As a secondary step of this study the strength of limestone added cement (30 % by weight) is compared with other mineral admixtures (trass and slag) added cements and portland cement, in order to see limestone added cement gives the necessary strength values determined by the standards. This would be a benefit from the economical point of view because a cheaply costing pozzolanic cement could be produced with the use of limestone as an admixture. xm Throughout this study, the physical and the chemical properties of cement types are given, after giving information about cement concept beginning from the raw materials. Later on some specific engineering properties obtained by adding pozzolans are discussed. The test results for the intergrinding and the separate grinding of the clinker and the mineral admixtures, aregiven in terms of strengths. Finally, an industrial oriented example of (Akçimento) separate grinding of trass added cement is also presented. Chemical analysis of the samples of clinker, gypsum, trass, limestone, and slag used in the experiments is made by XRF, and Si02, A1203, Fe203, CaO, MgO, S03, Na20, K20, SCaO contents, and the amount of insoluble residue, lost in ignition, moisture are determined. Portland cement, trass, limestone, and slag added (30% by weight) cements are ground until the specific surface area of cement particles reach at 3600 cm2/g. Grinding is based on inter and separate grinding of clinker and mineral admixtures. Portland and trass, limestone, and slag added are interground for two hours in order to compare their pozzolanic reactivity. For this purpose, the specific surface area of portland and trass, limestone, and slag added cements are calculated as 3046 cm2/g, 3914 cm2/g, 4075 cm2/g, 3000 cm2/g respectively. Densities of ground cements, are also calculated as 3.05 g/cm3, 2.83 g/cm3, 2.92 g/cm3, 2.95 g/cm3 for portland, and trass, limestone, slag added cements respectively. During the calculation of electrical energy consumption, it was found that, the interground portland cement needed 0.590 kwh, interground trass added cement needed 0.343 kwh, interground limestone added cement needed 0.256 kwh, and slag added cement needed 0.420 kwh of electrical energy for each two kilograms of cement types. As a result of tests carried out with portland and trass, limestone, slag added cements, the following conclusions are made: 1. The comparison of portland cement with trass added cement has shown that trass added cement needed more water to reach the normal consistency for the concrete mortar. As an addition, separately ground trass added cement had a lower water demand than interground one. XIV As a general behaviour of all admixtures added in cements, trass caused a delay for both initial and final setting times of portland cement. No significant difference was observed between interground and separate ground trass added cements when setting times are concerned. Throughout the strength tests, trass caused a declivity for portland cement in both stress and bending strength characteristics. Separate grinding is proved to be more advantageous either in stress or in bending strength values, over intergrinding of trass added cement. 2. The water demand for normal consistency of concrete mortar of concrete mortar changed in the order beginning from highest water demand as, separately ground limestone added cement, portland cement, and interground limestone added cement Limestone seemed to make a retardation in the setting times of portland cement, but in the case of inter and separate grinding of limestone added cement, no significant changes for the setting time values were observed. Limestone had a decreasing effect on strength of portland cement. A remarkable difference in both stress and bending strength characteristics was determined when separate grinding was employed instead of intergrinding in the case of limestone added cement. 3. The tests showed that blast furnace slag added cement, needed more water than portland cement for the normal consistency of concrete mortar. There was no significant difference on the water demand between inter and separately ground slag added cements. Slag had a retardation effect on the setting times of portland cement. A remarkable, 45 minute delay for the initial setting time, and a 40 minute delay for the final setting time of separately ground slag added cement were observed when compared with interground one. Slag caused a declivity for portland cement strength characteristics. From the view point of stress strength, no useful benefits were achieved until 28* day of final setting, when separate grinding was employed against intergrinding of slag added cement. On the other hand, bending strength characteristics were higher for separately ground slag added cement at the 28ft day of final setting, when compared with interground one. XV As a result of comparison of two-hour interground portland and trass, limestone, slag added cements in terms of strength, an order beginning from the highest strength of portland cement, slag added cement, trass added cement, and limestone added cement was determined in both stress and bending strength characteristics. In the second part of the study for comparing four types of cements, limestone added cement showed as stress strength up to 31.1 N/mm2. This shows that if less than 30% of limestone added to the blended cement, a cheaply costing cement having sufficient strength characteristics according to the standards, could be achieved. Since strength characteristics could be improved by utilising the separate grinding in the production of limestone added cement, the strength conditions for this kind of cement can easily be improved by employing separate grinding process.