Flexural behavior investigation of composite reinforced concrete structural elements

ABSTRACT Because world sources of raw materials are getting depleted continuously, mankind is forced to exploit the existing reserves as economically as possible and to explore new materials. Hence, research on usability of locally available materials, especially in civil engineering applications, has became more important in the recent years. Because of widespread volcanic formations, among other geologic peculiarities of such zones, light-weight aggregates of pumice type is found abundantly at various places of Anatolia. Recently, research on practicability of using these rich natural reserves of pumice aggregates as the major constituent of either structural or nonstructural light-weight concrete has gained momentum both in academic and industrial fields in Turkey. In this study, usability of "composite reinforced concrete" (CRC) slab units as structural elements consisting of an upper layer of light- weight concrete underlaid by a lower layer of normal-weight concrete, produced using the pumice aggregates of the Develi region, which is a district of Kayseri lying in the southern foothills of the Erciyes Mountain, is investigated. For this purpose, a total of 24 number of slab units of 120x220xh cm dimensions each are produced at varying composite depths, which had 5+5, 5+8, and 5+1 Ocm combinations, the first 5 cm being the height of the normal-weight concrete layer and the second value being the height of the lightweight concrete layer, respectively. Some of these slabs are designed and produced to be under-reinforced, some as balanced, and some others as over-reinforced. With the purpose of comparing the behavior of all these various CRC slab units versus the conventional ones, three more normal-weight reinforcete concrete (RC) slaps of 10 cm, 13 cm, and 15 cm thickness are produced using normal- weight concrete only. As a result of experiments subjecting these slabs to simple bending moments in a two-point-loading setup, it is observed that the behaviors of the CRC slab units are reasonably satisfactory with considerable savings in dead weight as compared to those of normal- weight concrete; and It is calculated that a reduction of about 20-30% in overall dead weight of a structure will result if such CRC slabs are used. In conclusion, it is experimentally determined that the ratio of elasticity modulus of the structural light-weight concrete produced with the suitably graded Develi pumice XVIIIaggregates with a cement dosage of 400 kgf/m3 to that of normal-weight concrete having a cement content of 300 kgf/m3 is about 1/3, and the ratio of flexural stiffnesses of the CRC to RC slabs is around 1/2, respectively. The shear strength of CRC units is observed to be a little less than that of RC elements. It is determined that producing protrusions of approximately 5mm heights by manual trimming of top of the lower normal-weight concrete layer in fresh form is sufficient to provide sufficient bonding between the light weight and normal-weight concrete layers. XIX