JultikaUniversity of Oulu repository

Abstract

The metamorphic rock (soapstone) has been used since Stone age, even it plays a significant role in the economy of numerous countries. Currently, it is often used for architectural applications such as artefacts, cooking appliances, countertop and slab. Apart, it produces a massive amount of waste powder during the extraction phase and plant processing which is unavoidable. Resulting in a large amount of recyclable material landfilled or released to the environment annually that could be problematic in terms of environmental perspective.

To diminish its adverse impacts and ensure sustainability; it would be beneficial to thrive a new technique to recycle these industrial wastes in construction applications.

Based on previously published results; soapstone (Mg3Si4O10(OH)2) is poorly reactive in alkaline-activation owing to its chemical structure and a lack of amorphous components. As a result low mechanical properties which cannot be used for construction applications. Therefore, these types of materials necessitate co-binder, thermal curing at high temperature and high alkalinity to achieve high strength alkali-activated material.

Experimental and statistical investigates were conducted to observe the effects partially replacing of soapstone (talc) with co-binders (i.e., metakaolin, lime, stone wool, and silica fume), and fibers on the hardened-state properties. The variables used in the analyses were the concentration of virgin steel fibers or basalt fibers (dosages = 0.5% and 1%), the proportion of metakaolin, stone wool or silica fume used to replace soapstone (20 wt. %) and lime by 5 wt. %. The effects of employing fibers at two dosages with co-binders in 20 mix compositions were investigated. The designed mixtures were activated by using an alkali solution, which contains NaOH (10M) and sodium silicate (molar ratio of SiO2/Na2O = 2.5). The samples were treated by thermal curing at 60 °C for 24 hours, and placed under ambient conditions (24°C and 35% RH).

The findings showed that using co-binders and fibers were different behaviors on the hardened-state properties, however, the metakaolin reinforced mix composition with 0.5% basalt fibers improved compressive strength about 25 MPa after 28 days. This strength enables the use of the proposed binders for construction applications.