Evaluation of the long-term compressive strength development of the sewage sludge ash/metakaolin-based geopolymer

D Istuque,L Soriano,M.M Tashima,J Payá,J.L Akasaki,M.V Borrachero,J.L.P Melges

doi:10.3989/mc.2021.13220

Abstract

This paper aimed to evaluate the long-term compressive strength development of the sewage sludge ash/metakaolin (SSA/MK)-based geopolymer. SSA/MK-based geopolymeric mortars and pastes were produced at 25ºC with different SSA contents (0 - 30 wt.%). Compressive strength tests were run within the 3-720 curing days range. A physicochemical characterisation (X-ray diffraction and scanning electron microscopy) was performed in geopolymeric pastes. All the geopolymeric mortars presented a compressive strength gain with curing time. The mortars with all the SSA evaluated contents (10, 20, 30 wt.%) developed a compressive strength over 40 MPa after 720 curing days at 25ºC. The maximum compressive strength of the mortars with SSA was approximately 61 MPa (10 wt.% of SSA), similarly to the reference mortar (100% MK-based geopolymer). The microstructure analyses showed that the SSA/MK-based geopolymer presented a dense microstructure with N-A-S-H gel formation.

Highlights

This paper aimed to evaluate the long-term compressive strength development of the sewage sludge ash/metakaolin (SSA/MK)–based geopolymer
Compressive strength In Step 1, three different NaOH concentrations (8 mol.kg-1 (ε=1.6), 10 mol.kg-1 (ε=1.3), 12 mol.kg-1 (ε=1.0)) in the activating solution were evaluated in the geopolymeric mortars with 10 wt.% SSA and 90 wt.% MK
The increasing NaOH concentration lowered the compressive strength of the SSA/MK–based geopolymeric mortars for both curing times (3 and 7 days)

Summary

Introduction

This paper aimed to evaluate the long-term compressive strength development of the sewage sludge ash/metakaolin (SSA/MK)–based geopolymer. The literature has pointed out the incorporation of sewage sludge ash (SSA) into the geopolymer based on its physicochemical characteristics [17], apart from its environmental-friendly immobilization needed. Such residue, SSA, comes from incinerating sewage sludge generated during wastewater treatment. The average bulk density of SSA is 805 kg/m3, which is a low value due to its porous particles [21] Given these physicochemical characteristics, SSA has been evaluated as raw material to produce blended PC, mortars, bricks, ceramics and glass [19, 22,23,24,25,26,27,28]. Such an SSA application has not yet been properly explored, being found a few studies focused on this field [29,30,31]

Objectives

Results

Conclusion