# Compressive Behaviors of Prisms Made of Demolished Concrete Lumps and Fresh Concrete
## 1 Introduction  
The construction industry has developed strongly all over the world in recent decades, especially in the developing countries like China and India. More and more raw materials and energy have been consumed in this economic activity. In turn, wastes produced by the industry account for a majority of the overall amount of waste generated [1; 2; 3; 4]. It is estimated that the annual production of waste concrete in China has reached 239 million tons and that it accounts for about one-third of the total construction and demolition waste [5]. As conflicts between the desire to realize sustainable economic development and a shortage of natural resources get more serious, it is of great importance to reutilize waste concrete wherever possible. This can both reduce landfill utilization and provide inexpensive construction materials [6]. Recycled aggregate is widely regarded as a promising solution to the problem of waste concrete. Research on this subject started with basic observations of the effects of using recycled aggregate fill on the compressive strength of concrete, as well as its economic feasibility [7; 8]. Since then, research on recycled aggregate concrete (RAC) has become progressively more systematic. Mechanical properties, durability, and micro-characteristics of RAC have been experimentally investigated bymany scholars [6; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18]. New technologies have also been proposed to improve the quality of concrete filled with recycled aggregates in recent years [19; 20; 21]. Positive results from such research support and encourage the application of RAC in buildings and structures [22]. However, even though the use of recycled aggregates in place of natural aggregates has now received considerable attention as a sustainable method, it should be noted that RAC has not yet been widely adopted in practice. One reason is that technologies such as smart dismantling, demolition, crushing, and autogenous milling are needed to manufacture high-quality aggregate suitable for recycling [21; 23]. These processes obviously consume a lot of energy. In order to lessen that difficulty, a group led by [PERSON] has explored a more efficient approach to recycling waste concrete [24]. The innovation of their technique is to directly reuse large pieces of coarsely broken concrete from demolition (referred to as demolished concrete lumps, DCLs) with fresh concrete (FC) in new structural members. This recycling process is obviously superior to the traditional method of recycling concrete as aggregates in at least the following aspects [25]: (1) producing DCLs is much simpler than crushing concrete to small pieces and sieving; (2) an increased recycling ratio can be realized, because both the stones and the mortar of waste concrete are reused simultaneously in the new structural members; and (3) less hydration heat is generated in compound concrete consisting of DCLs and FC, due to the reduced amount of fresh cement employed. A series of experimental studies on structural members (beams, columns, slabs, and walls) containing DCLs have now been carried out to examine the feasibility of such recycling [26; 27; 28; 29; 30; 31; 32]. Test results show that the mechanical properties and seismic performance of structural members containing DCLs are similar to or only slightly lower than those of such members containing FC alone. In the past several years, structural members containing DCLs have been successfully employed in some real constructions, as depicted in Figure 1.  
It should be mentioned that before this recycling technique can be widely used, more research is still needed to comprehensively understand the behavior of compound concrete made with DCLs and FC. For instance, in order to reasonably design structural components containing DCLs, the compressive behavior of the compound concrete should be investigated carefully. In the past several years, uniaxial compressive properties of such compound concrete have been investigated.