Early-age hydration and strength formation mechanism of composite concrete using molybdenum tailings

Abstract

With the aim of reducing the land occupation and environmental pollution caused by accumulation of molybdenum tailings, and to promote the use of molybdenum tailings as building materials, molybdenum tailings, fly ash, and cement were used as composite cementitious materials to prepare concrete. The effect of molybdenum tailings replacement on the working performance of fresh concrete, as well as early-age mechanical properties and the hydration reaction of the concrete at different ages were studied. The results show that with higher replacement amounts of molybdenum tailings, slump, and air content of fresh concrete both increase first and then decrease; when the age is less than 3 d, the molybdenum tailings increase the compressive strength of concrete. After 7 d, with higher replacement ratios of molybdenum tailings, the compressive strength of concrete gradually decreases. Higher amounts of molybdenum tailings also cause the internal water content of concrete to gradually increase during 28 d hydration reaction; and with greater curing age, the internal water content of concrete gradually decreases. The compressive strength of concrete increases faster in the curing stage when the internal water consumption rate of the concrete is faster. In the later hydration reaction of the molybdenum tailings composite cementitious system, which mainly produces C-S-H gels and ettringite (AFt) intertwined with other hydration products, the fine grains that are not involved in the reaction fill the pores of the system, which promotes the compressive strength of the concrete.

Keywords

• Molybdenum tailings
• Compressive strength
• Nuclear Magnetic Resonance (NMR)
• Hydration
• Early-age