Lightweight aggregate concrete with an open structure and a porous matrix with an improved ratio of compressive strength to dry density Katrin Schumacher, Nils Saßmannshausen, Christian Pritzel, Reinhard Trettin Institute for Building and Material Chemistry, University of Siegen, Paul-Bonatz-Str. 9-11, 57076 Siegen, DE, Germany highlights  Successful combination of foam concrete and lightweight aggregates.  Lightweight aggregate concrete with open structure and porous matrix.  Nanoscale view on the texture of the lightweight aggregates.  Improved ratio between compressive strength and dry density/thermal conductivity.  Reduction of drying shrinkage due to the aggregates of almost 80%. article info Article history: Received 12 May 2020 Received in revised form 2 July 2020 Accepted 6 July 2020 Keywords: Lightweight concrete Foam concrete Microstructure of lightweight aggregates Embedding of lightweight aggregates Compressive strength Drying shrinkage Thermal conductivity abstract In this study the combination of foam concrete and lightweight aggregates was investigated in order to develop a lightweight aggregate concrete with open structure and porous matrix (LACPM). For this pur- pose the recipe of a foam concrete was combined with the following lightweight aggregates: pumice, expanded glass, foam glass, expanded clay, and expanded perlite. The successfully produced concretes showed a homogenous microscopic structure and arrangement of the aggregates. A nanoscale view on the texture of the aggregates helped to understand the different embedding in the foamed cement paste matrix and their interaction at the interface. The best embedding was shown by pumice, expanded perlite and expanded clay. The ratio between compressive strength and dry density as well as the ratio between compressive strength and thermal conductivity has been improved respectively. Compared to conven- tional foam concrete an improvement of the compressive strength by almost 40 % was measured. The same applied for the drying shrinkage, the change in length was reduced by the addition of the aggregates to almost 80 %. Ó 2020 Elsevier Ltd. All rights reserved. 1. Introduction Lightweight concrete is an important field of concrete technol- ogy, because it combines constructive and insulating properties of building materials. Normally the reduction of weight is imple- mented by the intrusion of air, either into the matrix, into the aggregates or both. One kind of lightweight concrete has an open structure, which can be obtained by normal or lightweight aggre- gates. A possibility to enhance the properties of such a concrete with lightweight aggregates is to fill the cavities with a porous cement paste matrix, which provides the opportunity to decrease the dry density while keeping the compressive strength constant [1,2,3]. This is due to the more homogeneous stress distribution. In concrete with open structure stress transfer is just from one aggregate to another in the contact points, but if the voids in between are filled the transfer area is higher and the stress is evenly distributed [3]. An additional advantage is the improved workability for the concrete with an open structure. The consis- tency is not stiff anymore and the use of a roller compaction which is unusual equipment for precast plants is unnecessary. In addition the production process is less complicated, since there is only one silo necessary for the aggregate and one for the cement. Another type of lightweight concrete is foam concrete, which consists of a cement paste with a large quantity of air pores inside [4,5]. One way to produce such a foam concrete is the addition of preformed foam to a cement paste or mortar. To reduce the dry density of foam concrete different approaches can be chosen, e.g. aerogel foam concrete [6,7]. A serious problem of foam concrete is the high degree of drying shrinkage, due to the lack of inert admixtures [8,9]. The addition of lightweight aggregates could pre- https://doi.org/10.1016/j.conbuildmat.2020.120167 0950-0618/Ó 2020 Elsevier Ltd. All rights reserved. E-mail addresses: schumacher@chemie.uni-siegen.de (K. Schumacher), pritzel@- chemie.uni-siegen.de (C. Pritzel) Construction and Building Materials 264 (2020) 120167 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat