Abstract
Slag cement is a hydraulic cement formed when granulated blast furnace slag (GGBFS) is ground to suitable fineness. It is a recovered industrial by-product of an iron blast furnace and its carbon footprint is significantly lower than that of Portland cements. Lafarge has been producing and supplying this material in Canada since the late 1970s for the ready-mix industry and later in the 1990s for the mining industry. It currently has 4 production facilities in Ontario and Quebec.
The cemented paste backfill (CPB) is a widely adopted technology that allows the mining industry to reutilize mineral tailings in a safe way. GGBFS has been used in the cemented paste backfill (CPB) since the late 1980’s in Canada. Lafarge first commercially supplied Slag majority blends (Terraflow®) to the mining market in early 1990s. The product was sourced from our Spragge grinding plant located 140km west of Sudbury, ON.
A summary of +7 years experimentation at Lafarge Canada is presented in order to highlight the mechanical properties of cemented paste backfill (CPB) when substituting Portland cements with Slag majority blends.
When compared with Slag blends pure Portland mixes usually develop a higher unconfined compressive strength (UCS) at early age (1 to 7 days). However, its strength development reaches a peak at about 28 days and does not continue beyond that point. Data shows Slag majority blends mixes start developing a higher strength than pure Portland mixes at as early as 7 days and its development continues until after 90 days. At 14 days of age, UCS of Slag majority blends mixes is typically double the strength of pure Portland mixes and, on average, Slag majority blends produce a UCS of 2.5 to 3 times higher than pure Portland at 28 days and beyond.
Replacing Portland cement with Slag majority blends in the CPB reduces the total CO2 emissions because it intrinsically has a much lower carbon footprint. Since 2017, Lafarge Canada’s mining partners in Eastern Canada have saved approximately 1.3M tons of CO2 by using Slag majority blends instead of pure Portland cements. Slag majority blends also help improve the unconfined compressive strength of CPBs specially at mid to long-term (> 14 days). Other advantages of Slag majority blends include its resistance to sulphates.