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This paper presents an experimental work to study the effect of dune sand as an alternative to sand on the mechanical properties of hybrid fiber reinforced concrete. 24 concrete mixes were prepared, 6 of them without fibers and containing different proportions of dune sand, and 18 concrete mixes with the same proportions of dune sand but containing long and short single and hybrid steel fibers. For the purpose of studying the properties of hybrid concrete, including measuring the workability of fresh concrete, examining the compressive strength, dry density, split tensile strength, Flexural strength, ultrasonic pulse velocity testing, water absorption of hardened concrete. The main parameters were the proportions of dune sand (20 %, 40 %, 60 %, 80 %, and 100 %) in addition to the ratio 0 % without dune sand. Two types of steel fibers were used: straight steel fibers (short) with a length of 13 mm and hook end steel fibers (long) with a length of 50 mm, It is added to concrete (single or hybrid) with a total volume ratio of 1 % of the concrete volume. The tests that were conducted showed that sand dunes affect the compressive strength, especially when the percentage increased by more than 40 %, where the compressive strength of concrete decreases by 39 % when the replacement ratio reaches 100 %, but it improves with the addition of single or hybrid fibers. Also, the workability from high to medium level decreases by 30 % with increasing dune sand content, the addition of steel fibers along with dune sand significantly reduced the workability. The tensile and flexural strength decreases with the increase in the sand dune rate, but at a lower rate than the compressive strength, which was 29.3 %, 21.1 % for splitting and flexural tensile strength, respectively. The addition of steel fibers improved the mechanical properties of the hybrid concrete, which can compensate for most of the lost strength due to the increase in sand dunes ratios. The study also showed that the use of long fibers (hook end) gives better results than straight fibers. But in the case of using hybrid fibers, we can get an improvement in the mechanical properties more than using one type of fiber.

The mud is considered as one of the oldest construction materials in Iraq and is still used in the country regions for farmer’s houses or animal shelters. In Iraq, there are different types of mud constructions, including adobe, unfired bricks and cob. The presented study has focused on unfired clay brick where the clay is the main material. To ensure that the clay is pure and clean, it was excavated from the depth of 2 m below the natural ground level. Different types of unfired clay bricks produced by adding different materials to the clay to improve its properties and especially large deformation due to shrinkage. The added materials are classified into three concepts, the first additives are the natural fibers (straw, sawdust, and rice husk) and they are used to improve the tensile strength of brick and reduce the cracking due to shrinkage. The second additives included added the fine and coarse sand as a stabilizer to reduce the volumetric changes. The third additives are adding cement to increase the adhesive and cohesion of the mud matrix. The measurements included compressive strength of brick, mortar, and masonry and the flexural strength of bricks alone. The behaviour of unfired masonry prisms was also compared to the traditionally fired clay brick prisms. The results indicate that higher compressive strength of bricks was got for the mix that included clay, coarse sand and straw. The maximum flexural strength of bricks was got for the mix that included clay and sawdust, while for unfired masonry prism the higher compressive strength was obtained with a mix that included clay, coarse sand and straw. Finally, a proposed formula to obtain the compressive strength of unfired brick masonry from the compressive strength of brick and mortar is presented.

In this study, the binary bat algorithm (BBA) for structural topology optimization is implemented. The problem is to find the stiffest structure using a certain amount of material and some constraints using the bit-array representation method. A new filtering algorithm is proposed to make BBA find designs with no separated objects, no checkerboard patterns, less unusable material, and higher structural performance. A volition penalty function for topology optimization is also proposed to accelerate the convergence toward the optimal design. The main effect of using the BBA lies in the fact that the BBA is able to handle a large number of design variables in comparison with other well-known metaheuristic algorithms. Based on the numerical results of four benchmark problems in structural topology optimization for minimum compliance, the following conclusions are made: (1) The BBA with the proposed filtering algorithm and penalty function are effective in solving large-scale numerical topology optimization problems (fine finite elements mesh). (2) The proposed algorithm produces solid-void designs without gray areas, which makes them practical solutions that are applicable in manufacturing.