Durability Properties of an Alkali Activated Cementitious Material

The utilization of Portland cement as a construction material is unsustainable due to the huge amount of CO2 emissions coupled with the high energy demand during its production. New innovations in low impact construction materials require a reduction in the use of Portland cement with alternative binders, preferably utilising industrial waste materials and aggregates made from recycled waste. Alkali activated cementitious materials (AACMs) shows potential benefits when used in place of Portland cement in the construction industry. However, market forces mitigating against the acceptance of AACMs are fomidable. This is partly because of the limited knowledge of the in-service life of AACM concrete, which is linked to the inadequate durability investigations available in literature. This research project investigates the durability properties of AACM concrete by exposing it to deleterious substances that cause deterioration and damage to reinforced concrete structures. The durability properties of AACM concrete were investigated under long term exposure to chloride and CO2 environments which are the two main corrosion initiators in reinforced concrete structures. Four series of AACM concrete mixes were studied with a parallel OPC concrete mix used for the comparative analysis. Mix parameters investigated in the research included factors such as activator dilution and liquid/binder ratios which are given in relevant chapters. Chapter 1 provides an Introduction to the thesis. Chapter 2 gives an overall Literaure Review and also provides information on the materials used in the research. A chapter specific literature review is given at the start of each chapter. The third chapter presents the investigation of the microsrtucture of AACM and OPC mortar mixes which shows that AACM mortar has less porosity than OPC mortar. However, a greater capillary pore volume was observed in AACM mortar than OPC mortar but the reverse was the case for gel pore volume. The fourth and fifth chapters investigate the physically bound, chemically bound and free chloride concentrations in both AACM and OPC concrete. The results show a lower degree of physically and chemically bound chlorides but a higher degree of free chloride in AACM concrete compared with OPC concrete. The free chloride/hydroxyl ion ratio which is an index for corrosion initiation in concrete is lower in AACM concrete than OPC concrete due to the higher pH of the former. The sixth chapter investigates the carbonation in AACM and control OPC concrete. The depth of carbonation is higher in AACM concrete than OPC concrete but the phenolpthlain test method has limitations for use in AACMs. Investigations on the pH of carbonation specimens gave a greater insight to carbonation in AACMs. The influence of mix design parameters of AACMs are reported in each chapter 3, 4, 5 and 6. The seventh chapter reports the monitoring of the corrosion activity of steel reinforcing bars embedded in AACM and OPC concrete until 860 days of cyclic exposure in a 5% NaCl solution and air. The corrosion potentials and current densities were higher in AACM concrete than OPC concrete under wet cycles, which is likely due to the insufficient oxygen concentration at the steel interface. The visual inspection of the reinforcing steel bars in AACM and OPC concrete to detect when corrosion begins will confirm the insufficient oxygen concentration at the steel interface. Generally, AACM concrete shows better durability properties than OPC concrete except the carbonation aspect which requires further investigation. The likehood that the phenolpthalein indicator method which is a standard testing method for carbonation of OPC concrete might not be suitable for AACM concrete.