Full Title: Geopolymer Cements: Resistance-Engineered Sewer Infrastructure for Longevity using Innovative, Energy-efficient, Synthesis Techniques (RESILIENT)
Year: 2016-21
Participants: Mohammad Matar, Xu Chen, JP Gevaudan
Primary Investigator: Wil Srubar III (CU Boulder)
Co-Investigator: Claire White (Princeton University)
Summary: The primary objective of this Extremely Durable Cementitious Materials project is to engineer an ultra-acid-resistant low-calcium alkali-activated (geopolymer) cement paste specifically for wastewater (i.e., sewer) infrastructure applications to address the critical need for concrete materials with enhanced biogenic sulfuric acid resistance compared to ordinary portland cement (OPC) concrete.
In the United States, local governments spend approximately $50 billion annually on the construction, operation, and maintenance of over 800,000 miles (1,300,000 km) of concrete sewers – $13.8 billion of which is specifically used to prevent and mitigate the effects of microbial-induced concrete corrosion (MICC). While sulfuric acid destabilizes and dissolves the calcium-rich phases in OPC, yielding weak, gypsiferous reaction products and deterioration severe enough to cause collapse, low-calcium geopolymers laden with polyvalent cations (i.e., Mg(OH)2, Fe(OH)3, and, in some cases, Ca(OH)2) have been shown by the PI, Co-PI, and others to exhibit exceptional acid resistance to sulfuric acid compared to OPC.
The resulting geopolymer cement paste formulations will exhibit 80% reductions in steady-state biodeterioration rates compared to OPC concrete (from ~5 mm/year (0.20 in.year) to ~1 mm/year (0.04 in/year)), which will extend the service life of concrete sewer infrastructure ~5X and will yield reductions in total life cycle environmental (i.e., embodied energy and embodied carbon) costs of mitigating biogenic sulfuric acid degradation by ~75%.
Microbial-induced concrete corrosion. Sulfur oxidizing bacteria (SOB) generate sulfuric acid on the crowns and in the headspaces of concrete pipes, converting Ca-rich binder phases to weak, gypsiferous reaction products.
Metal cation additions effect on improving the sulfuric acid resistance of geopolymer cements: Prof. Srubar’s team has shown that (a) Mg2+, (b) Fe3+ and (c) Cu2+ additions show improved acid resistance in highly acidic (pH ~ 2) H2SO4 (i.e., dimensional stability in (a) and (b) and no evidence of dealumination in (c)); Prof. White (Princeton) has utilized DFT to show (d) atomic rearrangements and changes in total energy that occur as Ca2+ is replaced by Na+ in the interlayer of C-S-H gel; a similar technique will be used to identify best-performing polyvalent cations for binder stabilization.