BCSA combines fast-setting calcium sulfoaluminates with slower-setting belite in a cement that has a lower carbon footprint than Portland cement and could be used in precast/prestressed concrete application.
Calcium sulfoaluminate (CSA) cements have been developed since the work of Alexander Klein of the University of California Berkeley in the 1960s. With a clinker mineralogy characterised by ye’elemite (also known as Klein’s compound) as the principal binding agent, CSAs have high early strengths and short setting times – although their long-term durability is lower than ordinary Portland cement.
Belite calcium sulfoaluminate (BCSA) cement is an extension of CSA cement technology. Combining the binding properties of ye’elemite with belite, the compound in Portland cement responsible for later strength development, BCSA was developed to improve the durability of CSA cements, while offering a lower environmental footprint than ordinary Portland cement.
These cements have much lower limestone requirements in the raw mix and lower clinkering temperatures, reducing both process and energy-related carbon dioxide (CO2) emissions by around 30% compared to ordinary Portland cement. In addition, BCSA cement clinker is much softer than Portland cement clinker, meaning it is much easier to grind, lowering energy consumption in the mill with consequent reductions in costs and CO2 emissions.
BCSA cement has been commercially produced in the USA for about four decades for mostly non-structure applications, although recent research has begun to investigate its use in the production of precast and prestressed concrete beams. In China, commercial production and application of BCSA cement has occurred for around five years with concrete showing higher early strength gain, lower dry shrinkage, and higher sulfate resistance.
There remain questions over the durability of BCSA cement, however, particularly its resistance to carbonation (a risk to carbon (black) steel reinforcement) and when exposed to high temperatures (>60°C) and fire. Raw materials costs are also higher than Portland cement, due to the need for higher amounts of aluminium-bearing materials (e.g. bauxite), although requirements are lower in BCSA cements than in standard CSA cements.