Reactive Limestone as a Strategy Towards Low-Clinker Factor Cements
Ordinary portland cement production accounts for at least 5% of global CO2 emissions. As the principal component in concrete formulations in addition to the expansion, modernization and retrofitting of infrastructure in developed and developing countries, the share of greenhouse emissions is certain to expand. This environmental burden has brought questions with regard to cement as a sustainable material in the coming decades. The use of low-clinker factor cements has been thought as a means to a reduced CO2 footprint material, one way of achieving this is through the use of secondary cementitious materials (SCM’s) with pozzolanic properties (i.e., fly ash, furnace slag, silica fume, metakaolin, etc…), these materials have been widely used to reduce cement fractions while maintaining, sometimes even improving, mechanical properties of binders. However, availability of SCM’s, particularly a local scales, as well as durability related problems (i.e, carbonation, reinforcement corrosion, etc…) have hindered the increase of SCM’s use in cement. An attractive alternative is the use of limestone (calcite, CaCO3) as part of the binder formulation with or without SCM’s, while part of cement production as raw material and also present in commercially available cements, limestone fractions remain limited to 15% in the United States due to detrimental effects on durability and mechanical properties mainly due to dilution. This research work investigates the possibility of including limestone as a reactive part of the contentious binder. Rendering limestone as a reactive agent in hydration reactions can potentially induces a large increase in limestone replacement of OPC leading to concrete formulations with reduced cement content while keeping competitive mechanical properties.
Factors such as physical effects (i.e., filer effect), as well as chemical effects are analyzed in this research work while making emphasis in conditions that can increase or limit limestone reactivity in cementitious formulations, such as: quantity and/or characteristics of aluminous material present in the system, water-to-cement ratio, characteristics of the carbonate bearing source and ion exchange conditions for calcium carboaluminate mineral formation.