|M.Sc Student||Ulka Simon|
|Subject||Upcycling of Chemical Waste Containing Linear|
in Cementitious Systems
|Department||Department of Civil and Environmental Engineering||Supervisors||Professor Konstantin Kovler|
|Assistant Professor Charles E. Diesendruck|
|Full Thesis text|
For the production of each ton of the commonly used linear alkylbenzene sulfonate (LABS), 3 kg of highly acidic, chemical waste (LABSW) are produced. This hazardous waste has to be purified and incinerated in an emission heavy and expensive process and no possibility for recycling has been found to date. LABSW contains large quantities of LABS, which has been suggested in the past as a possible admixture to cementitious systems. LABS is similar to other known admixtures and, as such, can have plasticizing, air entraining and in addition corrosion inhibiting properties. However, due to uncertain environmental and financial feasibility LABS has not been studied further. LABSW on the other hand, as a waste, can be considered a candidate for admixture production, as the high environmental and financial cost of its disposal justifies treatment and further application.
The goal of this thesis was, to study the possibility of turning LABSW into a feasible admixture for cementitious systems as an air-entraining admixture (AEA), improving rheological behaviour of the fresh mix, entraining additional air, while still reaching appropriate levels of compressive strength. For this purpose waste samples were studied, identified and neutralized using four different neutralization agents: (a) NaOH, (b) Ca(OH)2, (c) CaCO3 and (d) Fe2O3. The resulting non-water soluble admixtures were dry-milled at different dosages with Portland Cement (PC) for preparation of binders with incorporated admixtures. Subsequently, these binders were tested in regards to their rheology, kinetics of hydration, porosity and strength to evaluate the impact of the processed LABSW admixtures on the cementitious system.
The results show that in contrast to commercial admixtures, the properties of the cementitious system change non-proportionally with the dosage of the LABSW-based admixtures. All tested admixtures caused a plasticizing effect starting beyond 0.5% except the Ca-based one, which starts at 1% addition. In terms of hydration, all admixtures accelerated hydration at dosages below 0.5% and retarded at quantities beyond. The air-entraining properties changed non-proportionally with a high increase in porosity of 10-15% at low dosages (0.25%). The addition of 1% only marginally increased porosity by 1 - 3 %. Beyond this dosage, the porosity increased greatly once again. In terms of compressive strength, Na-LABSW showed the least reduction of all LABSW-based admixtures at similar porosity levels.
Based on these results, the environmental feasibility of using LABSW-based admixtures was studied using the methodology of life-cycle assessment (LCA) to quantify the environmental impact in the categories of (a) global warming potential (GWP), (b) depletion of the ozone layer (OD) and (c) terrestrial and oceanic acidification (AP) in comparison to generic commercially available admixtures. The reduction in compressive strength at similar porosity levels turned out to be the most significant factor in establishing ecological feasibility due to the emission-heavy production of cement, which is required to offset the strength loss. The results of the LCA model show that LABSW-based admixtures are preferable over generic commercial ones that exhibit strength losses great than ~15% at similar porosities.