Many developments in shotcrete technology during the 1980s have enhanced shotcreting capabilities. Today, both dry- and wet-mix shotcretes often contain supplementary cementing materials, which improve shotcrete workability and performance. A high-volume fly-ash, wet-mix shotcrete is one recent development. This shotcrete has good volume stability, good freeze-thaw durability, and very low chloride permeability. Silica fume usage also made some progress in the 1980s. Research done in 1983 showed even more pronounced benefits when silica fume was used in dry-mix shotcrete than when it was used in wet-mix shotcrete. Another improvement came along with high-early-strength cements. Tests show that shotcretes containing these cements develop higher early- and later-age strengths than chemically accelerated shotcretes.
Developments have also been made in reinforcement materials. Prior to the 1980s, most shotcrete was reinforced with conventional concrete reinforcing steel or welded-wire mesh. Now steel and polypropylene fibers are increasing in use because they offer some performance advantages. Steel-fiber-reinforced shotcrete (SFRS) is particularly useful for remedial applications in aggressive chemical or marine environments because it resists corrosion better than shotcrete with conventional steel reinforcement. Polypropylene fibers produce a pseudoductile material with load versus deformation characteristics equal to some mesh and steel-fiber-reinforced shotcretes. The extra fiber reinforcement also reduces cracking potential.
