Experimental investigation of the beams behavior made by conventional concrete and geopolymer concrete beams having openings under static and impact loading

The issue of whether geopolymer concretes can replace cement concrete, which is the basic building block of the construction sector, due to its low carbon emission is one of the most intensively researched issues today. The production principles of geopolymer concrete, which is still a very new material, have not yet been fully determined. In addition, studies revealing the structural behaviour of geopolymer concretes in a reinforced structural element are quite limited. Structures under static loads may be subjected to a dynamic impact load due to explosion or impact. These effects such as shocks caused by explosions, earthquakes, explosions in natural gas systems, rock impacts, and rocket impacts, which have an acceleration, cause damage to the carrier system. Impact load, which is one of the dynamic loads, is one of the least known and studied loads, and especially in recent years, experimental, numerical, and theoretical investigations have been carried out to determine the strength and behaviour of structures against impact load. The most important feature of the structural elements that make up the structure is its ductility, that is, its susceptibility to deformation. The area under the stress-strain curve expresses the energy absorption capacity of the element, in other words, its ductility. Since the static and dynamic loads acting on the structural elements have different characteristics, the deformations that they will create in the element, that is, their energy absorption capacities will be different from each other. Within the scope of this thesis, the impact and flexural strengths of beam elements formed with geopolymer concrete, whose usage area is increasing day by day, and conventionally used Portland cement concrete was experimentally investigated. Especially in reinforced concrete beams, uncontrolled gaps are formed in the beam bodies during the installation of plumbing, heating pipes and ventilation ducts through the ceiling. The effects of these holes on beam behaviour are important. For this purpose, the mechanical and physical properties of geopolymer mortars were determined by creating 10 different mixtures with Fly Ash (UK), Blast Furnace Slag (YFC), and Waste Stone Powder (PTT) wastes using the Mixture Design method for geopolymer concrete design. Compressive strength, flexural strength, impact strength, unit volume weight, water absorption, setting times and flow table were performed on the mixtures. Then, in order to produce a geopolymer concrete with the desired properties, different waste materials such as silica fume, metakaolin, etc. were added and additional mixtures were prepared and the optimum mixing ratios of geopolymer concrete were determined. Then, geopolymer concrete was produced by using the ideal mixture ratio in terms of mechanical, physical and workability. Using geopolymer and conventional concrete with similar mechanical properties, a total of 32 beam specimens with rectangular cross-sections without holes and with different hole diameter/beam height ratios (D/H= 25%, 41.5% and 55%) opened in the beam bearing areas were produced. The behaviour of the beams under static and dynamic loading, their strength, damage conditions, crack patterns, stiffness and energy absorption capacities were investigated in detail. As a result of the study, the increase in the amount of Class C fly ash used in the pre-mix tests increased the water absorption value, decreased the compressive flexural impact strengths, unit volume weight and flow table test values, shortened the setting start and end times considerably and negatively affected the workability of the mortar. Again, in the pre-mix tests, it was observed that the compressive, flexural and impact strengths and unit volume weight values increased with the increase in the YFC ratio, and at the same time, the setting start and end times and flow table values were adversely affected by the increase in the amount of YFC. However, with the addition of PTT to the mixtures, it was observed that the workability, i.e. setting start and end times and flow table test values reached ideal conditions in terms of application. However, a decrease was observed in the mechanical properties (compressive, flexural and impact strengths) of the mortars with increasing PTT ratio. The use of silica fume in the mixtures contributed positively to the compressive strength and setting start time. When holes are opened in geopolymer and conventional reinforced concrete shear and flexural beams, the load carrying capacities of the holes opened above 50 mm diameter (D/H=25%) decreased significantly and at the same time the ductility rate increased. These decrease and increase rates are compatible with the hole diameters. The load carrying capacity reductions due to holes in geopolymer and conventional reinforced concrete shear beams were much higher than in flexural beams. Therefore, the stirrup spacing is a very important factor in reinforced concrete hollow beams—lower compressive strength. Geopolymer concrete generally has a lower compressive strength than Portland cement concrete. This may mean geopolymer concrete may crack or deform more easily under a given load. The study demonstrates that traditional reinforced concrete beams are more affected by applied fixed-energy impact loading than geopolymer beams, experiencing greater displacement and more permanent plastic deformation, thereby absorbing more energy. These results indicate that the performance of geopolymer beams under impact loading is superior, as evidenced by higher maximum acceleration values compared to traditional reinforced concrete beams. This finding highlights the improved performance of geopolymer beams under impact loading conditions.