Use of nano CaCO3 in sustainable cement production
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Cement industry is the second largest leading contributor of greenhouse gases after power plant industries. Several efforts such as the use of Supplementary Cementitious Materials (SCMs), Carbon Capture and Storage (CCS), alternative fuels, and new innovations for replacing cement clinkers are being investigated and practiced in an effort to reduce the environmental impacts from cement industries. All existing technologies have their own limitations and may not be adequate moving forward in the current form. For example, the use of limestone powder helps reduce the amount of clinker; however, it has shown to compromise the later age strength and durability of the concrete; likewise, fly ash is the other commonly used environment friendly SCMs. However, the future availability and quality of fly ash has already become a concern. Similarly, CCS approach has its own limitations in all regards – technical, economic, and societal. Lately, the use of nanomaterials has emerged as a promising way to fill the gap in existing technologies and engineering. Several studies have already shown that nanomaterials such as nano SiO2, nano TiO2, CNTs, and CNFs among several others help improve the performance of concrete by changing the concrete matrix at nano levels. Yet, the high cost and limited availability of nanomaterials have restricted the use of nanomaterials only for research purpose. To overcome the obstacles in the use of nanomaterials, this research aims to investigate the commercial applicability of nanotechnology in cement industries. In this study, nano CaCO3 - a relatively low-cost nano material, but with similar performance to other high-cost nanomaterials- was used as partial replacement to cement in Ordinary Portland Cement (OPC) and Portland Limestone Cement (PLC). First, the effects of nano CaCO3 on OPC and PLC (with replacement rates of 1, 2 and 3%) were investigated through a comprehensive testing on fresh, hardened, and durability properties. Next, the results were compared with those of concretes with fly ash (Class F and C). The results confirmed that both OPC and PLC with 1% nano CaCO3 exhibited significantly superior (in most cases) or at least comparable performance to OPC and PLC concretes with or without fly ash. Lastly, an integrated approach is proposed for sustainable and economic cement production. This approach integrates existing major techniques - SCMs, CCS, and nanotechnology, where CO2 emitted will be captured and used for nano CaCO3 production within a cement plant. This approach will help address some major pitfalls of using nanotechnology as it ensures proper dispersion of nanomaterials in cement as the nanomaterials are incorporated into cement in the final production process of cement. More importantly, it will help reduce the environmental impacts of cement industries as CO2 will be captured and utilized, whilst generating economic revenues for the cement industries. This approach, however, needs further consideration in an overall social, economic, and environmental context of benefits and risks, as a part of an optimally efficient, sustainable, and economic approach.