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Long-term performance simulation of geopolymer concrete under coupled carbonation and chloride transport

Periodic Reporting for period 1 - GEOCRETE (Long-term performance simulation of geopolymer concrete under coupled carbonation and chloride transport)

Reporting period: 2016-06-15 to 2018-06-14

The main aim of this project is long-term performance simulation of geopolymer concrete (GPC) under coupled chloride and carbonation transport. GPC has received extensive attention as an interesting alternative for ordinary Portland cement (OPC)-based concrete as a step forward to eco-friendly construction and to reduce the environmental impacts of conventional construction materials. Climate change is one of the biggest environmental problems affecting Europe in the past decades and has been widely acknowledged as one of the major challenges for Europe and a key policy issue. In the construction sector, approximately 12 billion tonnes of OPC is approximately produced yearly. Portland cement, the main binder of OPC, emits substantial amount of CO2 (0.94 tonnes for each tonne of cement) and consumes a large amount of natural limestone. Cement manufacturing also releases large amounts of SO3 and NOx that can cause the greenhouse effect and acid rain. These issues have lightened up the need for green replacements, such as GPC, for OPC concrete in the construction sector. Structural components made of GPC are also expected to be more durable due to the low permeability, and satisfactory chemical and fire resistance of geopolymers. Moreover, geopolymer mortars are of great interest as a sustainable matrix for conservation and strengthening of existing and historical structures.
GPC concrete is still at scientific development stage and, before it becomes acceptable by the industry, obtaining a clear understanding of its service life behaviour is needed. For the past decade, the research has been focused on understanding the chemistry, reaction processes and structure of GPC. Future studies need to target the structural behaviour, durability, and long-term performance under different environmental conditions. Carbonation and chloride transport are the main factors affecting the long-term performance of RC structures and therefore should be critically addressed for these materials as well.
The main research areas that have been addressed in this project are:
• State of the art review and training on geopolymer material, chemistry of material, multi-scale modeling, transport phenomenon in porous media, reactive transport simulations.
• Successful investigation of the carbonation mechanism in these composites under natural and accelerated carbonation mechanisms.
• Successful investigation of the role of curing conditions on the stability of the pastes, stability of the pore solution pH and carbonation resistance.
• Successful conceptualization and implementation of the carbonation mechanism in binary systems of geopolymer concrete.
• Successful implementation of a multi-phase reactive transport code for simulation of the carbonation phenomenon in porous media (applicable to OPC-based, ternary-based on geopolymer-based concrete).
• Successful simulation of alkali leaching phenomenon in geopolymer concrete as one of the main mechanisms in instability of the pore solution pH.
The main tasks followed in the framework of this project are all beyond the state of the art. The obtained results are expected to provide a new understanding on the carbonation mechanism in geopolymer concrete. The developed numerical models are expected to provide a basis in accurate simulation of complex degradation mechanisms in new materials including geopolymer concrete.