@phdthesis{01GMAY9S11KCFNJ078YNEVD6BP,
  abstract     = {{Eco-efficiency of concrete is essential for sustainable development given the huge amounts of concrete used every year by mankind. Three aspects are fundamental in this regard: low carbon emission, limited use of non-renewable resources, and extended service life. First, concerning carbon emissions, reducing the clinker factor in concrete is essential due to the high carbon intensity of this constituent. Even though alternative binder materials have successfully proven to be sustainable alternative binders, the versatility of Portland cement (PC) makes it a hard-to-fully-replace binder. Production of Portland clinker is however responsible for about 6 to 8% of the global CO2 emissions, so more environmentally friendly alternative binders are still needed to take action on climate change. Interesting alternatives are binders based on industrial by-products, e.g. ferrous slags (FS) such as blast furnace slag (BFS), or fly ash (coal combustion by-product). A wide range of studies have already discussed in detail the reactivity and reaction products of binders based on fly ash and BFS but these industrial by-products are not available in sufficient quantities to cover the needs. An interesting alternative to investigate is the applicability of non-ferrous slags (NFS). NFS are industrial by-products synthesized during the production of non-ferrous metals such as copper (Cu), lead (Pb), Zinc (Zn) and others. There is a large production of NFS and usually, these slags are stockpiled or used in low-value applications. NFS can find a high-value application as a sustainable binder for concrete. In this research, Modified Ferro Silicate (MFS) slag, one kind of cleaned NFS is used as a PC replacement.
These MFS slags can be used as a PC replacement, whereby in this work three different binder systems have been applied: binder systems with MFS as supplementary cementitious material (SCM), hybrid binder systems and quaternary binder systems. In the SCM binder series, for instance, MFS slags are added together with PC in a mortar or concrete mix, and the amorphous slag phase reacts with the alkaline pore solution (enriched in calcium hydroxide CH, resulting from the PC hydration) precipitating hydrates of calcium silicates (C-S-H). These MFS slags can be used as SCM without modification and can satisfy the requirements of demanding construction applications. However, these binders are slow in reactivity and do not allow for high
PC replacement levels. In the second set of series, hybrid systems are a solution that can provide higher strengths at an early age, and also at higher PC replacement levels. In such a case, the MFS slag is mixed with a small proportion of PC and an additional alkali-activator is applied, allowing for the production of concrete with a similar performance to more conventional concrete types. By adding activators in combination with PC the slag hydration is more complete via a complex mechanism, which involves increased pH from the equilibration of portlandite in the presence of reduced Ca2+ activity. Reduced Ca2+ activity appeared to promote slag dissolution by increasing the under-saturation of the slag. The third set of the series is a novel quaternary system where MFS slag is mixed with PC, as well as with additives. In this thesis, the combined usage of BFS and dolomite as additives was tested. By adding dolomite and BFS into the system, the synergetic effect of latent hydraulic and dedolomitization tend to increase the hydration and reactivity of the MFS slag. Since all these binders contain also a large concentration of Fe in the system, the role of Fe is also a vital factor in influencing its reactivity. XRD analysis of the MFS slag model paste indicated the participation of Fe in the hydration mechanism, as well as the formation of Fe-AFm, besides other hydrated phases in the SCM binder system.
Second, related to the extended service life of structures, good durability performance is required for eco-efficient concrete to prevent the early need for intervention or replacement of structures, hence extended service life. Amongst other, important durability properties of concrete are related to carbonation, frost scaling and chloride ingress. Usually, the durability properties such as frost scaling and carbonation of the PC replacement binders might be less good, due to their different pore structure and CO2 buffer capacity and also possible coupling of the deterioration mechanisms. Thus, as an important scope of the thesis, for the three different binder systems (SCM, hybrid and quaternary binder) concrete compositions were designed and further tested, including durability. The durability properties such as carbonation resistance, chloride resistance and frost scaling of the concrete were thoroughly assessed. All series of concrete showed positive chloride binding capacity, this is likely due to the binding of Cl ions in calcium alumina silicate hydrates (C-A-S-H), ettringite and Fe-AFm phases. However, SCM and hybrid concrete showed an increased carbonation rate compared to quaternary binder concrete. This positive result of the quaternary system is believed to be due to the synergetic effect of BFS and dolomite. As expected, all series also showed poor frost scaling resistance, when no air entraining agent was applied.
Third, depletion of non-renewable resources is also a growing environmental concern globally. Aggregates are a major ingredient of concrete. Depending on its geographic location, the construction industry mainly uses non-renewable sources, such as marine sand, dredged gravel or crushed rocks, often granite or limestone, as aggregates. By using recycled aggregates as a primary source for the inert skeleton in concrete, a contribution can be made to the development of a circular economy. Promoting the recycling of waste concrete into high-value applications is key to developing such a circular economy. However, the attached mortar in recycled aggregate particles is a specific feature that limits structural applications. The water absorption and porosity of the recycled aggregates are higher than for most natural aggregates. The durability performance of recycled aggregate concrete can be affected unless transport properties are controlled by embedding the recycled aggregate in a compact matrix that isolates their pore structure. In this scope, novel hybrid binder concrete with MFS slag (as partial replacement of PC, rather or not in combination with BFS) and alkali activator was successfully produced containing 50% recycled aggregates. The presence of recycled aggregates had an adverse effect on early age strength whereas after 91-day no difference could be observed between concrete with or without recycled aggregates. A positive effect on chloride binding capacity could be observed in the BFS/MFS slag system with recycled aggregates. However, BFS/MFS slag concrete with recycled aggregates showed an increased carbonation rate and frost scaling compared to the system with virgin aggregates. Durability properties such as sorptivity and water penetration were positively affected by a longer curing time for the BFS/MFS system.
Finally, the usage of the MFS slag for the production of large-scale elements under realistic conditions was investigated and proven to be successful. The PC replacement by binders such as BFS and MFS slag could be easily introduced in the silos of the concrete plants without the need for significant changes in the mixing protocol. Thus, large-scale reinforced concrete (RC) slabs applying MFS slag-based concrete were manufactured to test their flexural performance. Flexural behaviour was investigated in terms of deformations under increasing load, crack patterns, load bearing capacity and failure aspect.}},
  author       = {{Sivakumar, Pithchai Pandian}},
  isbn         = {{9789463556545}},
  language     = {{eng}},
  pages        = {{XXXII, 207}},
  publisher    = {{Ghent University. Faculty of Engineering and Architecture ; Catholic University Leuven. Faculty of Engineering Technology}},
  school       = {{Ghent University}},
  title        = {{Mix development and performance of concrete with treated slag from copper production as cement and sand replacement}},
  year         = {{2022}},
}