Alkali Activated Materials (AAMs) as Concrete Repair Materials

Abstract

Alkali Activated Materials (AAMs) is a new cement technology utilizing waste products to produce cementitious binders. The main precursors are activated with an alkali activator for the hardening process. The reaction between precursors and alkali activator will create hydrated gels of calcium aluminate silicate hydrates, C-A-S-H and/or sodium aluminate silicate hydrates, N-A- S-H for binding phases. FA and GGBFS contain a high amount of silica and alumina in their chemical components, thus making them suitable sources as aluminosilicate precursors for cement binders.

AAMs are traditionally employed in the two-part system where the activator is liquid and activated dry precursor powder. However, it has handling problems due to corrosive activators that may affect worker safety, besides some performance issues such as rapid setting time and higher shrinkage issues that limit their application at real-site construction. Including ordinary Portland cement (OPC) mixed with aluminosilicate precursors, also known as hybrid, is an effort to modify the engineering properties of the dry mixture materials in one-part AAMs (dry activator system) in this study, diversifying its potential application.

One-part AAMs technology mainly focuses on concrete product purposes as an alternative to conventional OPC-based cementitious. A hybrid one-part AAMs mortar is being developed to reduce dependency on OPC in the form of mortar and cut the OPC volume as low as possible. Interestingly, the mechanical strength of the hybrid one-part AAMs mortar developed in this research is comparable to the OPC concrete, providing extra added value where no coarse aggregate is used, which the construction sector responsible for the waning of natural resources and environmental imbalances due to mining activities/rock excavations.

In this studies, all mortar samples were tested in the laboratory with controlled room temperature (18 – 22°C) and relative humidity, RH > 90%, to comply with EN1504–3:2005 standard, part 3: structural and non-structural concrete repair materials. The novel mix design formulation confirms it successfully replaces 30% of OPC volume with industrial by-product precursors as the first step in diminishing reliance on the OPC and another effort to reduce clinker production, reuse waste products, and control CO2 emissions. Nevertheless, using a less reactive alkaline activator with a low concentration level is beneficial for a cheaper cost, lower health risks and is not harmful to the environment. The hybrid one-part AAMs mortar in this study has mechanical strength that complies with European standards, EN-1504 specifications for Class R4 – Structural concrete repair materials. It has also had improved pore volume structures that reduce the porosity level – main drawbacks for one-part AAMs system while providing better engineering properties and durability for long-term applications.

One-part AAMs repair mortar as new innovative construction materials achieved another milestone as an effort to improve the construction sector towards the goal of sustainable construction to keep global warming increased to no more than 1.5 Celsius as called for in the Paris Agreement – emissions need to be reduced by 45% by 2030 and reach net zero by 2050 and also particularly for the zero carbon target in New Zealand - for domestic targets under the Climate Change Response Act (CCRA) Net zero emissions of all greenhouse gas (GHG) emissions other than biogenic methane by 2050.