A Task Group of ASTM Subcommittee Section C09.03.08.05 has developed laboratory tests for lightfastness, alkali resistance, water wettability, and curing stability of pigments to be used to integrally color concrete. A general purpose carbon black, which was hydrophobic, did not pass the water wettability test, but a hydrophilic concrete-grade carbon black readily mixed with water. Many otherwise attractive pigments, such as chrome yellow and iron blue, did not pass the alkali resistance test. Ultramarine blue is resistant to most alkalies, but calcium hydroxide gradually decomposes it, especially at elevated temperatures; therefore, ultramarine blue did not pass the curing stability test. None of the organic pigments tested passed the lightfastness test. Of the pigments tested, only iron oxide (natural and synthetic), chromium oxide, cobalt blue, and carbon black (concrete grade) passed all four tests.
Paper ID: CCA10185J