Utilization of waste-based sodium sulfates in alkali-activated materials

Abstract

Ordinary Portland cement (OPC) is one of the most used building materials in the world. However, the emissions caused by it cover up to 8% of all Greenhouse gas emissions caused by humans. Alkali activated materials (AAM) have been studied as a substitute for cement as they could be more environmentally friendly material. However, the production of typically used alkaline activators causes the main environmental issues like ozone layer depletion and human toxicity coming from AAM. The aim for this study was to investigate the use of waste-based activator to decrease environmental issues and increase the level of circular economy.

In this study, the activators used were sodium sulfates from lithium-ion batteries (BNS) production and fly ash from recovery boiler (RBFA). They were compared to samples activated with sodium hydroxide (NaOH). Blast furnace slag (BFS) was used as a precursor. All used BFS was from the same patch to ensure that the composition and properties of BFS affect all samples and tests in the same way. The concentrations of sodium sulfate and sodium hydroxide used were approximately 2% in the samples. Except for two RBFA samples with sodium sulfate concentrations of about 1% and 3% the comparison focused on the workability, microstructure and other properties like strength properties of the samples. For the samples, e.g. XRD, SEM, calorimeter and leaching analyses were done.

One of the most important tasks of the activator is to accelerate the settling of the mass and improve its compressive strength properties. These properties were significantly better with the sodium hydroxide comparison sample than with sodium sulfates. However, some of the waste-based sodium sulfate samples showed better results than the sodium hydroxide samples in some tests, which suggests that they could be used in some form, such as an additive.