The use of supplementary cementitious materials (SCM) has become a major trend in concrete technology with effective utilization of industrial by-products (IBP) such as fly ash, ground granulated blast furnace slag and silica fume. Many types of industrial by-products (IBP) such as fly ash, silica fume, rice husk ash and waste glass are becoming the predominant source of mineral components with pozzolanic properties required to improve the performance of portland cement based materials. The availability of decent quality SCM has almost reached its limits and cannot offset the need for higher volumes of concrete required by developing markets. The use of alternative supplementary cementitious materials, including off-spec products and less-investigated by-products can be a viable alternative. However, there are many obstacles and limitations which hinder the utilization of such products. These are related to the lack of long-term results related to strength and durability, the potential variability in terms of composition and the presence of undesirable substances including heavy metals. These limitations dictate the need for higher production control and product consistency. This report presents the state of the art experience with utilization of modern technologies and potential SCM such as steel slag, pulverized bottom ash, sugarcane bagasse ash, waste glass and low-grade silica fume. Certainly, the current economic conditions make recycling feasible for only a limited number of by-products. Waste materials can be used only when they can be collected, processed, and reused at a cost the same or less than natural raw materials. To increase the rates of recycling, cement and concrete manufacturers need a uniform supply of quality waste; this would require better sorting and also the development of waste identification technology. On the other hand, it is also evident that innovative technologies capable of tolerating multiple contaminants are needed to boost the recycling of industrial by-products and waste beyond the current limits. © RILEM 2018.