الإستدامة الإنشائية للبلاطات الخرسانية السندويجية خفيفة الوزن

Structural Sustainability of Light Weight Sandwich Concrete Slabs

    Concrete sandwich structure is rather modern and inventive construction system based on the best use of materials. The simplest type of sandwich slabs consists of two concrete layers confine low weight material. The two concrete layers are connected by steel shear connector trusses. The shear connectors are essential functions to transmit the shear and to ensure that when the panel is bent, the faces do not slide over each other and to connect the concrete layers so that they behave as a single one unit.

     The present study involves experimental investigation on the behavior of one-way simply supported sandwich slabs and solid slab. The effect of using sandwich principle was studied. The concrete wythes were normal weight aggregate concrete or lightweight concrete; Therefore, the main variable of this study was; aggregate type that used to produce concrete. The other studied variable was the optimum position of shear connectors via using different shear connectors steel ratio at the two ends a fourth of span as compared with the middle section of the span. On the other hand, in this study, the effect of the inclined bent angle of shear connector truss was investigated by using two different bent angles (27˚and 45˚) with different shear connectors steel ratios. Moreover, the effect of using discrete W-shaped shear connector, as compared with continuous truss shear connector by using the same shear connectors steel ratio was examined.

    In the present work, two types of lightweight aggregate (waste crushed bricks and Attapulgite which is natural stones are broken and burned at a specified temperature) were used to produce structural lightweight aggregate concrete. Cylinders and cubes, for each type of concrete, were tested to observe the mechanical properties of concrete.

     The results indicate that the structural lightweight aggregate concrete (SLWAC) of Attapulgite (as a coarse aggregate), with using natural sand and high performance superplasticizers (PC-200), produces an average cylinder compressive strength of about 21 MPa and air dry density of 1940 kg/m3, which agree with the requirements of SLWAC according to ACI 213R-03 and ASTM 330-05.

When Attapulgite is replaced with the waste crushed bricks, with the same mix proportion, the average cylinder compressive strength and air dry density are 25.2 MPa and 1954 kg/m3, respectively.

     All sandwich slabs behave as one structural unit. Also, all sandwich slabs exhibit more ductility and toughness than solid slab. Additionally, they have low total weight by about (42.75%- 31.21%) of the weight of solid slab.

     In sandwich slabs, using crushed bricks as aggregate in slabs shows increment in the deflection, ductility, and toughness by about 62.96%, 8.62%, 54.04% when is compared with slab with normal coarse aggregate accompany with decreeing total weight by 11.70%. On the other hand, when using Attapulgite as course aggregate in slab, the increment in the max deflection value, ductility index (μΔ), toughness was 73.48%, 38.75%, 43.82%, respectively. Additionally, gaining another benefit which is decreasing the total weight by 14.31 %.

     It is clear that the presence of shear connectors in the ends one-fourth (1/4) of span has significant performance than in the center of the panel, therefore.

    Also, the results indicate that using a continuous truss shear connector with 27˚ is better than using discrete W-shaped shear connectors with 45˚.