Curing temperatures effect on explosive spalling in alumina cement-based concretes

Abstract

Alumina cement (AC) based refractory concretes are the primary building materials for steel, cement, glass, ceramics, and chemical industries. Those advanced materials are efficient at high operation temperatures (up to 1500 °C), conforming to thermal shock and mechanical and slag resistance requirements. For these purposes, fine-grade or ultra-fine powders partially replace the cement. However, that increases the material density and, depending on the first heating cycle regime, the evaporated steam pressure can cause cracking and even explosive spalling of the concrete. The coarse aggregates and temperature-melting fibers can regulate the water evaporation process—the melted fibers form micro-channels, allowing excessive water removal from the heated material. However, the concrete curing conditions also affect the hydration products’ structure (density) and chemical composition, altering the water removal kinetics from the refractory material. This investigation focuses on the hardening conditions’ effect on the hydration process and explosive spalling resistance of the AC refractory concretes. The research object is the refractory concrete with a 130 MPa target compressive strength and 7wt% of AC. The alternative mixture contains polypropylene fibers (0.1wt%). The cylinder samples were cured at different temperatures, representing “normal” (20 °C), “summer” (35 °C), and “winter” (10 °C) conditions. The test results demonstrate the fiber efficiency in preventing the spalling failure characteristic of the samples produced without fibers. On the other hand, the curing temperature was the essential parameter, affecting the water removal kinetics of the refractory material with fibers—the “winter” concrete samples tend to explosive spalling due to the formed hydrates.