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Formulating Geopolymer Mortars through Construction and Demolition Waste (CDW) Recycling: A Comprehensive Case Study
Stefania Manzi1, Luca Baldazzi1, Andrea Saccani1
1Department of Civil, Chemical, Environmental and Materials Engineering, University of Bologna, Via Terracini 28, 40131 Bologna, Italy.
Materials (Basel, Switzerland)
|December 9, 2023
Summary
Alkali-activated metakaolin mortars with recycled concrete aggregates show reduced compressive strength due to adhered mortar layers. This study explores their properties as sustainable concrete alternatives.
Area of Science:
- Materials Science
- Civil Engineering
- Environmental Science
Background:
- Construction and demolition waste (CDW) is increasing globally, necessitating sustainable recycling practices.
- Ordinary Portland cement (OPC) production has high CO2 emissions, driving demand for alternative binders.
- Alkali-activated materials (AAMs) offer a promising eco-friendly alternative to OPC, especially when combined with recycled aggregates.
Purpose of the Study:
- To investigate the feasibility of using recycled concrete aggregates (RCAs) in alkali-activated metakaolin (AAM) mortars.
- To analyze the properties of fresh and hardened AAM mortars incorporating RCAs.
- To identify challenges and their impact on the performance of AAMs with RCAs.
Main Methods:
- Formulation of various mix designs for alkali-activated metakaolin mortars with different percentages of RCAs.
- Characterization of fresh properties (e.g., workability) and hardened properties (e.g., compressive strength, porosity) of the mortars.
- Microstructural analysis to understand the effect of adhered mortar on RCAs and the alkali-activation process.
Main Results:
- The adhered mortar layer on RCAs increased open porosity and hindered alkali activation of metakaolin.
- Compressive strength decreased with increasing RCA content: 20 MPa (12.5% RCA) and 15 MPa (25% RCA) at 28 days.
- Strength reduction was significant (35% and 50%) compared to mortars with natural aggregates.
Conclusions:
- While AAMs with RCAs show potential as sustainable materials, the adhered mortar layer poses a significant challenge.
- Further research is needed to mitigate the negative effects of adhered mortar on RCA properties for improved performance.
- Optimizing RCA treatment or AAM formulations is crucial for developing viable eco-friendly concrete alternatives.
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