A Comparative Study on the Degradation of Alkali-Activated Slag/Fly Ash and Cement-Based Mortars in Phosphoric Acid

Jie Ren,Lihai Zhang,Rackel San Nicolas,Yingcan Zhu,Zhenming Li

doi:10.3389/fmats.2022.845349

Abstract

This study compares the degradation behavior of the alkali-activated slag/fly ash (AASF) and ordinary Portland cement (OPC) mortars exposed to phosphoric acid with different pH values. The experimental results show that AASF mortars exhibit better resistance than OPC mortars against surface damage, although both systems get white deposits on the surface in phosphoric acid with a relatively high pH level. AASF mortars obtained lower mass loss than OPC mortars in phosphoric acid with pH at 2 and 3. The strength reduction in AASF mortars after immersion in phosphoric acid is more significant than that in OPC mortars. However, total degradation depth of AASF was smaller than that of OPC regardless of the pH of the acid solutions. Based on the experimental data, linear relationships were identified between the slope of degradation depth–mass loss curves and the Al/Si and Ca/Si ratios of the binders. This may indicate a new way to assess the degradation behavior of AASF and OPC based on their chemical compositions.

Highlights

Sewage wastewater environments containing various acids pose a significant threat to traditional ordinary Portland cement (OPC) concrete sewer pipes (De Belie et al, 2000; Bertron et al, 2004; Parande et al, 2006; Xiao et al, 2022a; Xiao et al, 2022b)
It is apparent that all mortar mixes obtained similar compressive strength (58 ± 2 MPa) after 56 days, based on which their durability can be reasonably compared. 65Slag_35OPC obtained the highest water absorption (10.11%) and volume of permeable voids (VPV) (20.79%), which is closely associated with the largest amount of water used for manufacturing followed by those of 100OPC specimens
The results indicate that activated slag/fly ash (AASF) mortars exhibited better resistance than OPC mortars against the ingress of phosphoric acid, while Figure 6 shows that the strength of OPC samples was higher

Summary

Introduction

Sewage wastewater environments containing various acids pose a significant threat to traditional ordinary Portland cement (OPC) concrete sewer pipes (De Belie et al, 2000; Bertron et al, 2004; Parande et al, 2006; Xiao et al, 2022a; Xiao et al, 2022b). Due to the alkaline nature of OPC binders, acid intrusion results in rapid neutralization reaction, leading to the dissolution and decomposition of some main components such as Portlandite, C-S-H gel, and ettringite (Oueslati and Duchesne, 2014) This causes an increase in porosity, decrease of mechanical strength of concrete, and corrosion of rebars embedded in concrete (Bertron et al, 2007; Aiken et al, 2018). In China, due to the rapid industrialization and urbanization, the structural integrity and security of the large number of OPC concrete sewer pipes produced every year is raising concerns (Yang et al, 2014). Another issue related to the damage of sewage systems is the possible

Methods

Results

Conclusion