Detection of iron sulfide-bearing aggregates by chemical tests and accelerated mortar bar method

Iron sulfide mineral is a highly reactive compound, which rapidly reacts with oxygen and water. This mineral is commonly found in natural rocks which are used as aggregates for concrete. The oxidation of iron sulfide-bearing aggregate can cause damage to concrete surfaces. Testing methods still do not exist that can be used to effectively detect the presence of iron sulfide-bearing aggregates, as well as to evaluate the possibility of visible damage on concrete surface. Two types of qualitative testing that are based on the mechanism of oxidation have been studied, i.e. chemical testing and accelerated mortar bar testing. This research investigates and improves the quick detection of iron sulfide-bearing aggregates by using existing chemical test methods (Quick test and Cation Group III test) and modified methods (H2O2 test, and Sulfate test). The results obtained from the chemical test methods were used to correlate with the modified accelerated mortar bar test, to indicate the potential reactivity of iron sulfide-bearing aggregate in concrete. In this paper, two types of pure minerals (pure pyrrhotite and pure pyrite), one type of iron sulfide-bearing aggregate, and two types of normal limestone aggregate without iron sulfide mineral were used to investigate the performance of the test methods and also to verify the oxidation reactivity of each type(2)of aggregate. Experimental results obtained from chemical tests (Quick test, Cation Group III test, H2O2 test, and Sulfate test) showed that the combination of the Cation Group III test or H2O2 test and the Sulfate test can be used to detect iron sulfide minerals in aggregates within 1 hour. The severity of the oxidation reaction in aggregates obtained from chemical tests correlated well with the results of the accelerated mortar bar test. By using the modified ASTM C 1260 mortar bar test to accelerate the oxidation reaction, the mortar bars prepared from iron sulfide minerals reached almost 0.15% expansion within 1 month. In contrast, the non-sulfide aggregates showed insignificant expansion at 60℃ and 80% RH and submersion in 6% NaOCl solution, supplying oxygen 7 times per two weeks. A combination of the Cation Group III test, H2O2 test, Sulfate test, and accelerated mortar bar test can be used to investigate the presence of iron sulfide-bearing aggregates that have the potential to cause deleterious effects in concrete.