Durability to chemical attacks and life cycle assessment of alkali-activated binders based on blast furnace slag and sugar cane straw ash

Abstract

Alkali-activated binder (AAB) is a new material that is being researched as an alternative to the use of Portland cement due to technical and environmental advantages. However, further studies on the durability and environmental impacts of this kind of binder are required to confirm its potential. Therefore, in this work, the durability to chemical attacks and life cycle assessment (LCA) of alkali-activated binders composed of blast furnace slag (BFS) and sugar cane straw ash (SCSA) with BFS/SCSA mass ratios of 100/0 and 75/25 were studied. AAB samples were produced with a solution composed of only NaOH (Na+ concentration of 4 mol kg−1). Portland cement (PC) samples were also produced to compare with AAB samples. For the durability study, the samples were maintained in five different environments to perform durability attacks: sodium sulphate, hydrochloric acid, acetic acid, ammonium chloride, and deionised water. Additionally, unattacked samples were left in a wet room as a reference environment. The compressive strength variation, mass variation, expansion/shrinkage behaviour, visual analysis after application of phenolphthalein, H+ consumption (only for acetic acid, hydrochloric acid and ammonium chloride attacks), thermogravimetric analysis, and powder X-ray diffraction (only for sodium sulphate attack) tests were carried out to analyse the performance of the samples. Results showed that AAB samples presented better resistance to chemical attacks than PC samples based on compressive strength variation for sodium sulphate (−12.1%), hydrochloric acid (−71.8%), acetic acid (−83.7%), and ammonium chloride (−50.1%). The use of SCSA in AAB was more beneficial under sodium sulphate attack (−12.1%). Finally, LCA results showed that the AAB sample with SCSA yielded lower Climate Change impact in kg of equivalent CO2 per kg of produced mortar (0.153 kg CO2-eq). Therefore, the study concludes that using SCSA blended with BFS is a sustainable option to produce AAB.