An evaluation and suggestion for a sustainable concrete industry Green Concrete Evolutionary Cement An evaluation and suggestion for a sustainable concrete industry John Anderson CEE, UC Berkeley Spring 2007

Overview of Green Concrete Environmental aspects of concrete CO2 in Ordinary Portland Cement Alternative binders Alkali activated cements Calcium sulfoaluminate cements Other alternatives Challenges and opportunities for green cement green cement

Environmental aspects CO2 emissions Water use Raw material extraction Responsibility of engineers green cement

CO2 in Ordinary Portland cement ~50% from the calcination of limestone CaCO3 → CaO + CO2 (3CaCO3 + SiO2  Ca3SiO5 + 3CO2) ~40% from fossil fuels to heat kiln (1450 ºC) alternative fuels- Cement Sustainability Initiative (tires, plastic insulation, paper) green cement

Alternative binders (1) Cement compound Raw material used Quantity of RMCO2* generated (g/g) M (magnesia, periclase) Magnesite 1.092 C (calcia, quicklime) Limestone 0.785 C3S (alite) Limestone + silica 0.578 β-C3S (belite) 0.511 C3A (tricalcium aluminate) Limestone + alumina 0.489 C4AF (calcium aluminoferrite) As above + iron oxide 0.362 NS (sodium metasilicate) Soda + silica 0.361 CA (monocalcium aluminate) 0.279 C4A3S (calcium sulfoaluminate) As above + anhydrite 0.216 * RMCO2- raw material CO2 FDCO2- fuel derived CO2 green cement

Alternative binders (2) Alkali activated cements Calcium sulfo-aluminate cements Other options (calcium sulfate, magnesia, and blended OPC cements) green cement

Alkali activated cements Alumino-silicate bonding phase (alumina rich source material and an alkali silicate solution) Termed geocements, aluminate cements Source materials can be either pozzolanic or non-pozzolanic Fly ash, blast furnace slag, metakaolin green cement

Alkali activated cements Environmental + Waste as source material (fly ash, blast furnace slag) Low RMCO2 (except metakaolin) Low FDCO2 (except metakaolin) Environmental - High RDCO2 and FDCO2 for alkali activator Elevated curing temps Alkali runoff Limited source materials green cement

Alkali activated cements Fly ash alkali activated Curing (> 30° C) Activator (10% by mass) green cement

Alkali activated cements Fly ash alkali activated Strength development 7 days 28 days green cement

Alkali activated cements Fly ash alkali activated Compressive strength (MPa) Activator Curing temperature (° C) Activator/fly ash ratio 0.25 (time of curing) 2 h 5 h 24 h Solution 1 65 0.0 21.2 85 9.3 22.0 34.6 Solution 2 8.7 1.4 9.4 23.3 Solution 3 4.3 31.7 52.7 39.8 48.2 54.5 Solution 4 9.5 38.7 7.7 34.3 63.0 NaOH 12 M (solution 1), KOH 18 M (solution 2), NaOH + sodium silicate (solution 3), and KOH + potassium silicate (solution 4). green cement

Alkali activated cements Slag alkali activated Similar advantageous as fly ash Influencing factors Activator, curing temp, specific surface Production decreasing Rapid setting time and high shrinkage Metakaolin alkali activated Human-made Thermal decomposition of kaolin High costs Significant RMCO2 and FDCO2 green cement

Calcium sulfoaluminate cements Known as sulfoaluminate, ettringite, or belite-sulfoaluminate cements High alumina, low energy, high early strength, rapid setting, long-term durability Source material Limestone, bauxite or alumina clays, and gypsum Clinker result of calcinated source materials Hydration products Early strength: ettringite, long-term strength: C-S-H green cement

Calcium sulfoaluminate cements Environmental appeal No elevated curing temperature Use outside of precast Reduced limestone used Reduced kiln temperatures (1160-1200° C) Lower grinding energy Gypsum not fired in kiln High sulfur industrial byproducts Slag, flue gas desulfurisation sludge, low calcium FA No alkali solution/ alkali runoff green cement

Calcium sulfoaluminate cements Strength Higher long-term strength than OPC Cured at room temp (20°C), compression strength of ~80MPa SAC-calcium sulfoaluminate cement, FAC-ferroaluminate cement, PC-portland cement CAC-calcium aluminate cement green cement

Additional alternative binders Calcium sulfate-based cements Gypsum based mortars Hydration of calcium sulfate hemihydrate Zero RMCO2, low FDCO2 Natural and byproduct source material Durability weakness of gypsum Use dense gypsum (alabaster) or additives (calcium aluminates) No corrosion protection Use fibers green cement

Additional alternative binders Magnesia cements Binding phase- magnesium oxide Family Sorel, magnesium oxysulfates, magnesia phosphate, magnesia carbonate CO2 sink Recycling Calcinate at 1000°C, high RMCO2 Possible water durability issues $, unproven properties green cement

Additional alternative binders Blended OPC OPC plus replacement (pozzolan) material Fly ash, slag, rice husk ash Initiated by lime Low heat of hydration, improved workability 90% of market needs < 3,000 (20 MPa) 80% of SCMs go to landfill, low-value applc. Low early strengths Characterization of source material Coal not sustainable product green cement

Future of green cement Opportunities Challenges Market system for CO2 PC faces mechanical challenges Low strength/ low risk applications Challenges OPC well established Conservative nature of construction/design industry More research green cement