2. Background of lightweight concrete

Concrete is a relatively heavy building material; therefore many experiments have been conducted throughout the twentieth century to decrease its weight without impairing other properties. During the 1920s and 1930s, many different types of lightweight concrete were developed, e.g., Durisol, Siporex, Argex, and Ytong. Probably the most famous and first type of autoclaved gas concrete was Ytong. It was invented by the Swedish architect, Johan Axel Eriksson, assistant professor at the Royal Institute of Technology in Stockholm. In the early 1920s, Eriksson experimented with different samples of gas concrete and put the mixtures in an autoclave to speed up the curing process. In November 1929, the industrial production of Ytong blocks began. The name combines the y of Yxhult, the town where the first Swedish factory was located, and the end of betong, the Swedish word for concrete. The material was very popular in Sweden from 1935 onward, with a true breakthrough immediately after World War II, when it became one of the most important building materials in the country. Also, the manufacturing process was exported to other countries such as Norway, Germany, the UK, Spain, Poland, Israel, Canada, Belgium, and even Japan. The autoclaved gas concrete Siporex was developed in Sweden in 1935. The LWAC, Argex, was first produced in Denmark in 1939 under the international brand name Leca. Starting with an annual production in Copenhagen of 20,000 m<sup>3</sup> , the total production throughout Europe had increased by 1972 to nearly 6 million m<sup>3</sup> per year (adopted from postwar building materials "postwa rbuildingmaterials.be").

The later type of LWC which is called LWAC is one of the most popular one among them and from that time until today has been the subject of many research works around the word. Even today there are many ongoing extensive research programs on SLWC and NSLWC made of LWA. In the present chapter, we focus on LWAC, and for the case study, we will discuss a part of the ongoing research of the author on LWAC [1]. Categorized examples of the research works conducted recently have been discussed below:
