Abstract

     The recycling process of construction and demolition waste, which started with brick pieces and brick dust used in the production of binder thousands of years ago, gained momentum after the second world war. Nowadays, the recycling activities of waste materials are sustained much more effectively by developing technology, machinery, and equipment. The obtained material by recycling waste concrete is called recycled concrete aggregate. And it has been stated in many experimental, analytical studies in the literature and more than one international material code that the recycled concrete aggregate, which meets specific material criteria, is an alternative to natural aggregate. This current study is carried out to give a different perspective and contribute to the literature on a not researched topic. Therefore, within the scope of this recent study, the structural topology optimization of structural members was performed by the isoline topology design method. The concrete properties of these members are considered with the natural concrete and the recycled aggregate concrete with four different recycled concrete aggregate ratios (25%, 50%, 75%, 100%). Besides, the structural topology optimization was performed by considering multi-material and single-material properties under similar loading conditions. As a result of the optimization process, the quantified optimization shapes indicated that the structural optimization behavior of multi-material structural members exhibits different optimization behavior depending on the recycled concrete aggregate ratios.

Introduction

     The construction industry is one of the leading industries that play a critical role in developing and developed countries. The primary material of the construction industry is concrete. With the developing technology, concrete finds many usage areas in the world [1–۳]. Nowadays, most of the structures are constructed from concrete with conventional methods. However, concrete is not material with eternal life. Therefore, it is essential to eliminate the waste concrete that has completed their life. In addition, regional and global wars, natural disasters (especially earthquakes), restoration works, urban transformation programs can be stated as the factors that cause concrete to turn into waste materials [4, 5]. The waste concrete resulting from these effects through the 4Rs rule: Reduce, Recycle, Reuse, and Resell or Rebuy have been eliminated very quickly and effectively from the beginning of the 2000s with increasing knowledge, experience, machinery, and equipment. As a result of recycling and reuse (waste treatment) activities, millions of tons of waste concrete are eliminated in European countries by contributing to countries’ society, environment, and economy (Fig. 1).

     Recycled concrete aggregates (RCA) are obtained from the recycling activities of construction and demolition waste concrete. With increasing awareness of RCA in the production of new structures, the number and scope of related studies have reached a significant level in recent years [1–۳, ۶, ۷]. Within the scope of these studies, while previously only RCA and the characteristics of recycled aggregate concrete (RAC) produced with RCA have been investigated [3, 6–۸], different performance values of significant structural members with different scales containing RAC are now being investigated [3–۱۱]. Furthermore, many international documents are stating that these RCA and RAC are alternative products to natural aggregate (NA) and Natural aggregate concrete (NAC) [3, 7, 11].

Conclusions

     This paper presents the results of an optimization study conducted on full-scale single short corbels and columns to investigate the effects of RCA on structural topology optimization behaviors. Particular attention was paid to the impacts of single-material and multi-material conditions on the characteristics of optimization behavior. The following conclusions can be drawn from the global optimization performance of the structural members:

۱٫ The multi-material RAC25 and RAC50 members exhibited similar structural topology optimization behavior to the NAC member. The RAC75 and RAC100 members behaved differently from their counterparts. Because, as the RCA ratio in the new concrete increases (in this case, both the concrete compressive strength and the modulus of elasticity decrease), these members’ structural topology optimization behavior may change under similar loading conditions.

۲٫ The optimization results revealed that the structural topology optimization behavior of the single-material RAC members is similar to this of the NAC member.