Flow Properties of Green Cementitious Binders: Influence of Superplasticizer on Flowability of Clay Containing Cementitious Binders

Abstract

With increasing populations worldwide, building new constructions and infrastructures grows to fulfill societal demands. But at the same time, discussions around the topic of sustainable development, and the concerns with greenhouse gas emissions assigned to building material production has been a major focus. Constructions industry in Sweden is responsible of the CO2 emissions, the major CO2 is assigned to the employed construction materials, mainly due to the production process (Boverket, 2021). The most popular structural construction materials are concrete, timber and steel. Concrete has been used in the construction industry for a long time because of so many good advantages assigned to it. The modern developed societies require a built environment that is unimaginable without the widespread use of concrete which enables construction anywhere, at low cost, of complex and massive shapes from water, gravel, sand, and cementitious powder. Although other common building materials such as timber or steel, when available can replace fraction of construction needs, however many structures such impressively engineered bridges and dams, architecturally innovative skyscrapers, roads and railways, high-rise apartments cannot be constructed without concrete. But cement as one of the main constituents of concrete is the third largest source of anthropogenic emissions of carbon dioxide, accounting for approximately 8% of global emissions in the world (Andrew, 2018). Although, use of industrial wastes like coal combustion fly ash or ground granulated blast furnace slag as cement replacement materials for manufacturing concrete with lower cement clinker content has been an answer to tackle this challenge but expected lower availability of these materials in the near future has been another recent obstacle. This has brought a lot of attention to natural resources like clays to be considered as future alternative cement replacements. However, industrial application of these new alternative binders is still dependent on further research mainly in terms of performance, and durability of these new engineered binders. Therefore, aiming to demonstrate the potentials of activated clays as a clinker replacement (future green binders) to reduce greenhouse gas emissions and environmental impact when constructing infrastructure buildings made from concrete. This project is performed to study the fresh properties of calcined clay containing concrete. In this context the water demand and consequently, the effect of using superplasticizers (SP) on the workability of clay blended cements is investigated. Two kinds of clays obtained from separate geographical locations in Sweden were studied in this project for their rheological behaviour as a potential future of supplementary cementitious material (SCM). The results showed that the flow properties of the clay were affected by the particle size distribution of the clays and the state of the clay (uncalcined or calcined). Further, it was also found that the SP requirement varied with the water demand of clays. Out of the two kinds of PCE superplasticizers studied, one type was found to disperse the clay particles for longer durations while one was observed to retard the workability beyond a certain duration. Finally, it was observed that calcinated clays did not require superplasticizer for particle separation or for achieving a target flow spread in the mixes with high water to solid ratios.