DEFORMABILITY AND CRACK RESISTANCE OF AIRFIELD SLABS

The results of experimental studies of deformability and crack resistance of models of airfield slabs made of reinforced concrete and steel fiber concrete are presented. Two series of plates were tested ‒ three models of reinforced concrete and three models with steel fiber added to the concrete mixture in amount of 1% of the total volume of the product. The load was applied in small steps, the instrument readings were recorded twice at each step, and the crack opening width was measured starting from the moment of the first crack formation. Dial gauges and deflectometers were used as measuring instruments. According to the normative documents acting in Ukraine, one of two possible loading schemes was considered ‒ with the loading by the concentrated force applied on the cantilever part of a plate. The plate models were tested on a specially made stand which consisted of four supporting struts connected in pairs by beams. The airfield slab was supported by the beams. The load was applied along the width of the plate in steps ‒ 0.05 of the destructive load, along two concentrated vertical strips. Each degree of load ended with a five-minute dwell time, at the beginning and end of which readings were taken on the measuring instruments. The deformations at the same levels were measured with dial gauges. The process of crack formation was observed with a Brinell tube in the places of the greatest crack opening. It follows from the obtained results that the process of cracking in the fiber concrete slab begins at higher loads than in the reinforced concrete slab. The final and initial crack opening widths of all cracks in the fiber concrete slab are significantly lower than in the reinforced concrete slab. The deformations in steel-fiber concrete slabs during the application of load in the cantilever part, both for compressed and stretched fibers are higher than in reinforced concrete slabs. At the initial stages of load application in the cantilevered part of the slabs, the deflections increase in a linear relationship. The curves get non-linear character for airfield slabs made of reinforced concrete when the load reaches the level of 10÷25 kN, for steel-fiber-concrete slabs ‒ 15÷30 kN. In reinforced concrete slabs, the non-linearity starts a little earlier and is expressed more clearly. Experimental studies show that dispersed reinforcement of airfield slabs with steel fiber leads to their higher crack resistance.