Proposition of a methodology for the evaluation of adhesiveness (pull-off test) of aggregate−geopolymer binder interfaces

Abstract

Portland cement concrete is the most used material in civil construction, but it is a source of greenhouse gases emissions. In addition, its Interfacial Transition Zone (ITZ) is a point of weakness, which limits its performance and application, generating pathological manifestations throughout its service life, decreasing mechanical and durability properties. In this context, geopolymer concretes arise for as a potentially sustainable building material with a much reduced and denser ITZ, when compared to ordinary cement Portland concrete. However, there is a lack of methodology to evaluate the aggregate-geopolymer interface and objectively evaluate compatibility between such new binder and aggregate particles. In other materials, adhesion tests are performed to obtain parameters related to adhesiveness. Provided that context, this work aims to propose a methodology to evaluate the adhesiveness of aggregates and geopolymer binders. For this, a pull-off test based on AASHTO TP 361 (T 361: Standard method of test for determining binder bond strength by means of the binder bond strength (BBS) test, 2022) is proposed, with particular adaptation with respect to specimens’ preparation. The main proposed modifications were: (i) the application method of the binder over a wider surface; and (ii) the use of epoxy glue to attach the pull-off elements (dollies) to ensure the bonding to the geopolymer binder film. Modifications allowed to test the geopolymer adhered to the rock in order to obtain the necessary experimental results. For validation, interfaces composed of a geopolymer binder based on fly ash and steel slag glued onto two granitic rocks (biotite) were prepared and tested. For the test according to AASHTO TP 361 (2022), without the proposed modifications, the adhesion between the geopolymer binder and the equipment proved to be insufficient. Then, with the proposed modified methodology the results were more consistent, in which the specimens showed suitable adhesion for the test. Then, this work contributed to an empirical characterization of adhesiveness for aggregate-geopolymer binder interfaces, enabling adequate analyses regarding the durability, to avoid future pathologies resulting from a weak ITZ and evaluations without huge costs in time and resources.