Abstract
The expansion mechanism of magnesium oxide expansive hydraulic cement as a novel expansive hydraulic cement was reviewed. Anisotropic crystallization results in crystal growth pressure, causing volume expansion while also increasing the porosity of the whole system. The theoretical relationship between porosity and expansion was analyzed. A basic method is given for predicting the expansion rate considering the expansive agent content in MgO expansive hydraulic cement. A concise equation is proposed for calculating the ultimate expansion. A theoretical relationship between porosity and expansion is presented. The compressive strength and durability of magnesium oxide expansive hydraulic cement were analyzed considering porosity changes and compared with hydraulic cement. If the expansion rate exceeds 0.8%, the mechanical properties and durability changes caused by porosity should be considered. If magnesium oxide expansive concrete is used with restraining in real structure, extra compressive stress is generated and the porosity decreases, compared with that during free expansion. In particular, for strain‐hardening cementitious composites, expansion confined with the fibers present in the composite is beneficial for refining cracks and improving the self‐healing ability of these materials whenever exposed to humid environments. This paper describes the expansion mechanism and properties of magnesium oxide expansive hydraulic cement for engineering applications.
Highlights
Compared with CaO expansive agents, MgO expansive agents have a significant advantage owing to their designable expansion properties [17] because the hydration rate of MgO is relatively easier to control by controlling different calcination conditions during the manufacturing process
Erefore, the expansion mechanism and dynamics of MgO expansive hydraulic cement should be understood thoroughly to determine the optimal dosages of MgO for use during actual construction and avoid overdose to avoid damages to concrete structures. e mechanism for the expansion of dead-burnt MgO and CaO was first studied by Chatterji based on the crystal growth pressure, solubility of hydroxide crystals, their growth patterns, and diffusion of ions through the electrical double layer formed around the cement hydration products [25, 26]
MgO expansive hydraulic cement is a mixture of hydraulic cement and MgO expansive agent, which is responsible for expansion
Summary
MgO expansive hydraulic cement is a mixture of hydraulic cement and MgO expansive agent, which is responsible for expansion. E first and latest standard for MgO expansive agent for use in concrete was issued by the China Building Materials Federation and China Concrete and Cement-Based Products Association in 2017 [30]. For manufacturing MgO expansive hydraulic cement or shrinkage-compensating concrete, MgO expansive agent must be manufactured separately, complying with standards.
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