التحقيق في السلوك الإنشائي للبلاطات الخرسانية المسلحة والمعززة بالألياف تحت تأثير الحمل الصدمي

Investigation the Structural Behaviour of Fibrous Reinforced Concrete Slab Subjected to Impact Load

Abstract

Current research investigates experimentally the behavior of high-strength fibrous reinforced concrete slabs (HSFCS) under dynamic load. Thirteen specimens were cast during the experimental work, including one control sample. The main twelve specimens were categorized into two groups based on the slab’s thickness, 70 and 100 mm.
Six different mixtures were prepared, each two samples with two different thicknesses have the same concrete mixture. Two types of fiber were used in addition to micro silica to improve the mechanical properties of HSFCS. Steel and polypropylene fibers were used with various percentages to study their effect on concrete properties under impact load.
The impact frame was designed to apply the impact load by falling 14.5 kg projectile on the center of the slab. All samples were tested under the effect of impact load. A load cell with 10 Ton capacity and a laser sensor was used to measure the impact capacity of the midspan deflection. The relations between load with time in addition to displacement with time were produced. The crack patterns were noticed and recorded. The primary parameters studied in current research were the thickness of the slab, type of fibers, percentage of fibers and height of drops for the projectile.
The results showed that the midspan displacement and impact capacity for all tested slabs under the effect of impact load tended to be larger with a percentage of (11.8% to 43.5%) and (12.1% to 24.8%) respectively with the increase in the falling height. When the slab thickness was increased, the central displacement decreased significantly with a percentage ranged between (33% to 133%) due to the increment in the stiffness of the slab, which leads to an increase in the maximum impact capacity by a percentage of (28% to 50%) compared to control specimen.

The effect of fibers was clearly monitored in the experimental results. The steel fibers have a clear effect on enhancing all concrete properties, while the polypropylene fibers improved the tensile and the flexural strength only. The presence of steel fiber leads to reduce the maximum deflection by a percentage of (13.5% to 51.2%) and increase the load capacity by (3.5% to 16.8%) compared to control samples. In contrast, the presence of polypropylene fibers increased the deflection by (1.5% to 21.2%) and reduced the maximum load by (3.6% to 7.8%). The hybrid samples showed a reasonable result, the displacement was increased compared to control samples by a percentage of (3.6% to 23%), while the load was slightly decreased by (1.1% to 5.3%) due to the reduction in compressive strength of concrete.
Also, results showed that the clamped support condition leads to high stiffness for all tested slabs and the cracks on the bottom faces of all slabs appear first, followed by cracks on the top faces. These cracks tend to take on random shapes, and directions start from the center of the bottom face of the tested slabs.