Sodium monofluorophosphate, chemically known as Na2PO3F and from here on referred to as Na-MFP, has long been known as a surface applied corrosion inhibitor in the concrete industry. Over the past decade, Na-MFP has gained large interest as an inorganic self-healing agent, particularly on blast furnace slag cement (BFSC) concrete. BFSC is an important product of the cement industry, especially in Northern European countries. In the Netherlands it holds a market share of more than 50% and besides many technical advantages it is an environmentally friendly product. However, its carbonation rate is a huge drawback compared to ordinary Portland cement (OPC) performances and requires a large-scale industrial and feasible solution to keep BFSC equally attractive for the building industry.
Numerous experimental and theoretical studies, embedded within the framework of the innovative research program of self-healing materials (IOP-SHM), have investigated the influence of Na-MFP as self-healing agent on BFSC systems upon carbonation. Results of these studies have shown that Na-MFP has the potential to “heal” the microstructure of carbonation-attacked cementitious material surfaces rich in BFS. Under the presence of water Na-MFP reacts with the slag-bearing carbonated concrete matrix to form amorphous calcium phosphates (ACPs), which increase the mechanical quality of the material surface, decrease the pore volume, the capillary water uptake and decelerate the carbonation rate. As a consequence damage through micro coarsening of pore structure and related cracking can effectively be compensated and the frost salt scaling durability of the BFSC products can significantly be increased.
This chapter summarizes research results generated over the past couple of years and gives an outlook towards the development of an autogenous inorganic self-healing mechanism induced by Na-MFP in BFSC systems.