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316ABSTRACT Mineral and chemical admixtures are used today in most concrete mixtures to improve the recent and hardened properties of concrete and to increase the durability of concrete During this study four minerals and 4 chemical mixtures were studied in particular metacoline MK silica fume SF category F ash FA blast furnace slag BFS 2 high level water reducers SP water slow motion reducer WRD and inlet air AEA The objective of this study is to evaluate the consequences of mineral and chemical additives not used in concrete strength The properties studied here include setting time compressive strength and magnification when exposed to a sulfate solution The results of this study indicate that the inclusion of oxide fumes maintains greater strength than the opposing mineral mixtures considered here Up to 100 replacement levels have surpassed the opposing mixtures studied The ash showed an improvement in the workability of the mixtures however it had lower compression resistance results and could create challenges once the strength gain rate is crucial However the ash blends of category F showed a higher yield than non homogenized mixtures once exposed to a sulfate supply Metakaolin mixtures showed a greater heat evolution among all the mixtures studied here this will probably cause robustness problems particularly once the temperature increase can be a design problem Blast furnace scum additionally improved the workability of the mixes and therefore the later compressive strength however had mixed performances once examined for sulphate sturdiness
CHAPTER 2
LITERATURE REVIEW 2 1 Introduction In recent decades the characteristics of cement have changed considerably The propulsion for many of these changes is to extend the first resistance of concrete The change concerns chemicals and physical properties Mineralogical changes include a substantial increase in the tricalcium silicate content while physical changes include a substantial increase in cement fineness with a factor of 3 number 4 Concrete mixtures today incorporate many chemical and mineral additives while the surface unit of mineral mixtures evolves less many chemical additions accumulate in that area which are still regularly introduced on the market These additions will likely be problematic due to the potential present of an undesirable interaction between the various elements within the concrete mix Once water is added to Portland cement the hydration of the cement begins immediately The hydration of cement is of an exothermic nature and can be subdivided into 5 phases which are normally indicated in the literature as dissolution inactivity acceleration deceleration and stable state The reactions are chemical and controlled by diffusion The hydration of tricalcium aluminate is mainly controlled by phases of calcium sulfate 5 Insufficient amounts of calcium sulfate can cause configuration problems such as the flash set Various forms of calcium sulfate which are present in Portland cement include anhydrite hemihydrate and gypsum they have different solubilities and therefore their availability and their contribution to hydration kinetics can be different The SO3 A2O3 ratio in Portland cement is fundamental to optimize in order to control the hydration of C3A and subsequently the hydration of C3S to guarantee the correct regulation of the concrete mixtures For chemical and mineral additives incompatibility problems may arise when their presence within a specific concrete affects the ratio by increasing the sulphates or aluminates without making the appropriate adjustments 6 7 8 Therefore it is important to evaluate the effects of different combinations of chemical and mineral additives on the physical properties of concrete in addition to its effect on its durability
The duration of this study focuses on the potential of concrete to generate heat and its performance after exposure to a sodium sulphate environment 2 2 Chemical admixtures While chemical mixtures are now an integral part of concrete mixtures scientific data on many chemical additives and their interaction with concrete are not available This is partly due to the patented nature of the chemical formula and the continuous introduction of new mixtures The review presented here will focus mainly on the chemical additives used in this research ie air entraining admixtures water reducing and retarding admixtures and superplasticizers