Farklı çimento tiplerinde süper akışkanlaştırıcı ve rötre azaltıcı kimyasal katkıların performansının incelenmesi

Abstract

Along with standard Portland Cement, many new cement types have become the reason for preference and need in the construction sector. In particular, the aesthetic and architectural expectations in the sector have increased the demand for white cement. In addition, mechanical and physical properties of white cement provide to the composite structure have increased the requirements for white cement in the production of construction chemicals. The demand for calcium aluminate cement has been increasing recently in our country as well as in many countries around the world. The main reason is that it is preferred due to its special phase structure like early high strength and fast setting time. The physical and mechanical properties of cement can be improved with the help of chemical additives in line with the expectations of the end user. Super plasticizer admixtures provide additional value for the mixture in terms of workability and ultimate strength. Shrinkage reducing admixtures contribute to the durability of the composite structure thanks to its shrinkage compensation feature. In this thesis, consistency, setting times, bending strengths, compressive strengths, shrinkage and vertical height change of different cement types produced in Turkey in two different phases were tested according to related standards. The chemical properties of cement types and chemical admixtures were tested according to TS EN 197-1 by the quality control team in advance and had been added in the beginning of chapter 3. Cem I 42.5 R Portland Cement, Cem I 52.5 R White Cement, Calcium Aluminate Cement and Ternary System Binder were used in the mixtures. Ternary systems are mainly created by mixing calcium aluminate cement, standard portland cement and gypsum. In addition to this mix, some other raw materials such as sands, mineral admixtures and specific chemicals are added in order to finalize the design. The rate of raw materials including cements are decided accorrding to expectations of projects. For instance, in cases where early strength is required, quantity of calcium aluminate cement in design would be higher. Also, gypsum is important in determining the setting time of designs. The study was first started with the cement paste stages. The mechanical and physical properties of these binders tested by adding shrinkage reducing admixture. In this phase, a constant flow 20±2 was aimed in all mixtures. Water reduction had been made in the mixtures, especially in cases where shrinkage reducing admixtures were added to ensure constant flow. The use of shrinkage reducing admixtures incrased the initial and final setting time in all binder types. Especially, these periods were almost doubled in white cement and ternary system. Although the use of shrinkage reducing admixtures increased flexural strengths, it decreased the ultimate compressive strengths. The second part was continued with the mortar. In this phase, the performance of 4 different cement types with shrinkage reducing admixture and super plasticizer admixtures were measured. Castings were started with mixtures without any admixtures, as reference mortars. Afterwards, the castings were continued by adding only shrinkage reducing admixture, only super plasticizer admixture, and both shrinkage reducing admixture and super plasticizer admixture at the same time. Since there is a super plasticizer as raw material input in the ternary system design, only castings with reference and shrinkage reducing admixture are made in this binder type. Again, at this stage, in order to examine the retardation in setting time of the calcium aluminate cement type, mortar castings were made with different kinds of super plasticizer based on polycarboxylate ether, and setting time and compressive strength were measured. Also in this phase, a constant flow 20±2 was aimed at all mixtures. Water reduction has been made in the mixtures, especially in cases where shrinkage reducing admixtures and super plasticizer admixtures were added to ensure constant flow. Target flow could not be achieved due to rapid hydration in ternary system mortars. The use of shrinkage reducing admixture in the mortar phase also slightly reduced the compressive strength. The use of super plasticizer admixtures provided high ultimate compressive strength in all binder types owing to its high range water reduction property. Super plasticizer admixture used in experiments caused the retardation of setting time in calcium aluminate cement; therefore, compressive strength could not be obtained at the 6th hour. Because of this situation, other super plasticizer admixtures which had got different raw materials were used in order to obtain 6th hour compressive strength. However, the sufficient early compressive strength value could not be reached in the 6th hour. Also, the use of other super plasticizer admixtures could not change the retardation of setting time. In the last part, shrinkage and vertical height change measurements were made in these 4 different binder types listed below: 1. Cem I Portland Cement 2. Cem I Portland Cement and superplasticizer 3. Cem I Portland Cement, superplasticizer and shrinkage reducing admixture 4. White Cement and superplasticizer 5. White Cement, superplasticizer and shrinkage reducing admixture 6. Calcium Aluminate Cement 7. Calcium Aluminate Cement and superplasticizer 8. Calcium Aluminate Cement, superplasticizer and shrinkage reducing admixture 9. Ternary System Binder (mix design has already superplasticizer) 10. Ternary System Binder (mix design has already superplasticizer) and shrinkage reducing admixture The use of shrinkage reducing admixtures in portland cement compensated for the shrinkage by almost 38% compared to the witness mortar. Vertical height changes were compensated by more than 50% thanks to shrinkage reducing admixture. In white cement, shrinkage reducing admixture could not show sufficient advantage in terms of reducing shrinkage. The use of shrinkage reducing admixture in calcium aluminate cement compensated for the shrinkage by more than 50% compared to the witness mortar. Vertical height changes were compensated by more than 60% thanks to shrinkage reducing admixture. In ternary system binder, shrinkage reducing admixtures enabled with decreasing the shrinkage by almost 50%. Super plasticizers caused the retardation of setting time in all designs. As a result of the experiments, it was observed that super plasticizer reduced water content and provided strength contribution in all cement types except the ternary system. As mentioned before, since the ternary system design has super plasticizer, no additional mixing which has super plasticizer was made. A It has been observed in experiments that shrinkage reducing admixtures significantly restrict the deformation in all cement types except white cement. The combination of white cement and shrinkage reducing admixtures should be reconsidered and retested.