Optimisation of Cementitious Lining Adhesion for Protection and Rehabilitation of Concrete Sewer Systems

Abstract

Rehabilitation of sewers by spray-lining calcium aluminate cement (CAC) and geopolymer-based protective mortars have gained interest as they can restore structural integrity and provide a barrier against microbially induced concrete corrosion (MICC). However, there appears to be a knowledge gap regarding their adhesion properties, resulting in the lack of industry guidelines and implementation. Improper adhesion induces premature failure and compromises MICC resistance. To address this, this study aimed to provide tools to optimise their adhesion. 11 commercial mortars were evaluated, utilising both laboratory tests and field trials. The field trials were undertaken in five water utilities, with 14 access chambers and two man-entry pipes. In the field, the mortars were applied by shotcrete. The study examined the application and placement properties in the field. Surface preparation, including methods and surface properties, were examined in the laboratory and verified in the field. The study of the residual unconfined compressive strength (UCS) of the mortar and asset concrete in the field was used as a basis to develop failure models to predict residual UCS. Through this study, several innovative tools and new knowledge to the scientific and industrial community on controlling the interaction and adhesion of protective mortar lining consisting of surface repair material on corroded assets were established: 1. Placement specification for selection of fit-for-purpose mortar and post-application tests. 2. Quality assurance around surface preparation guidelines and post-surface preparation condition assessments. 3. Service life models that predict the cohesive strength of fit-for-purpose mortar under given corrosive classification conditions. The guidelines based on the outcomes of this study have been implemented in the updated WSA- 201 code of practice and WSA-160 & 161 product standards for the use of protective mortars in extending the life of concrete sewers.