Stefania Manzi

Superplasticizer Addition to Carbon Fly Ash Geopolymers Activated at Room Temperature

Present concerns about global warming due to the greenhouse emissions in the atmosphere have pushed the cement industry to research alternatives to ordinary Portland cement (OPC). Geopolymer binder may constitute a possible breakthrough in the development of sustainable materials: understanding the effectiveness and the influences of superplasticizers on geopolymer systems is one of the essential requirements for its large-scale implementation. This study aims to investigate the possibility of using commercially available chemical admixtures designed for OPC concrete, to improve fresh properties of fly ash-based geopolymers and mortars. A special emphasis is laid upon evaluating their influence on mechanical and microstructural characteristics of the hardened material realized under room-temperature curing conditions. Results indicate that the addition of a polycarboxylic ether-based superplasticizer, in the amount of 1.0 wt. % by mass of fly ash, promotes an improvement in workability without compromising the final strength of the hardened material. Moreover, the addition of the polycarboxylic ether- and acrylic-based superplasticizers induces a refinement in the pore structure of hardened mortar leading to a longer water saturation time.

Mechanical Performances and Corrosion Resistance of Reinforced Fly Ash Geopolymer Mortars

The growing focus on issues related to the control of CO2 emissions, energy conservation and waste recycling pushes the construction industry to tackle the challenge of sustainable development. The production of ordinary Portland cement (OPC), main product of the sector, is one of the most polluting in terms of CO2 emissions, thus finding alternative binder is becoming an urgent matter. Geopolymers are largely investigated for this purpose, but studies concerning the durability of reinforced conglomerates prepared with alkali activated binders are only few. The present work aims at investigating the durability performances of steel reinforced geopolymer mortar samples based on carbon fly ash in comparison with OPC mortar. The effect of different Na2O/SiO2 molar ratios in the geopolymer mixes is evaluated in terms of mechanical and microstructural properties as well as corrosion resistance in a chloride rich environment. The obtained results show that under the same severe environmental conditions more limited chloride amounts penetrate in reinforced fly-ash geopolymers where a better corrosion behaviour is also detected up to a week of exposure for samples with a nominal Na2O/SiO2 molar ratio equal to 0.12 and 0.14. Instead, the corrosion resistance is quite similar to that of reinforced OPC mortar when a period of three months is considered.

Preliminary Studies on the Effect of C&DW on the Long-Term Properties of Sustainable Self-Compacting Concrete

The mix-design of self-compacting concrete (SCC) with both fine and coarse concrete waste from construction and demolition (C&DW) is investigated. The effects of concrete recycled aggregates on fresh state behavior and short- and longterm mechanical and physical properties of new structural SCC are investigated to ascertain the feasibility of SCC with medium-high mechanical strength. A reference SCC mix, prepared with natural aggregates and the same water/powder ratio as those prepared with recycled aggregates, is reported for comparison. An integrated approach involving porosimetric analysis and mechanical characterizations has been carried out. Porosity measurements and mechanical investigations combined with time-dependent properties, such as shrinkage and creep are reported as fundamental features to assess structural SCC behavior.