Abstract
In mass concrete, shrinkage resulting from temperature drop and drying leads to cracking, which can seriously affect the strength and durability of cement-based materials. Fortunately, expansion agents can deter or prevent these effects, especially MgO expansion agents (MEAs). In this study, the effects of four MEAs of different activity on the expansion properties, strength, and hydration of cement paste were explored. The different expansion phenomena between the high activity and low activity MgO was especially explained by the hydration model and dynamic theory. The results indicate that when the other conditions were the same, higher curing temperature and dosage could improve the expansion to some extent. Moreover, the hydration of high activity MgO and the expansion behavior occurred mainly in the early hydration stage, while the hydration of low activity MgO and the expansion behavior had a high contribution rate in the later stage, and the final expansion of cement mixed with low activity MgO was larger.
Highlights
The expansion behavior occurred mainly in the early hydration stage, while the hydration of low activity MgO and the expansion behavior had a high contribution rate in the later stage, and the final expansion of cement mixed with low activity MgO was larger
Gypsum was mixed into tionship between various conditions and hydration expansion was discussed, with the the cement system at a concentration of 5% weight of cement to adjust the cementation aim of serving as a guide for the application of MgO expansion agents
It was obvious that any specimens without active MgO expand slightly in the first 7 days, but after 7 days the expansion curve levels off or even falls—namely, cement specimens no longer expand or even begin to shrink
Summary
In the nineteenth and early twentieth centuries, a lot of structural damage to bridges and dams took place not long after being put in service due to the high content of MgO contained in cement used in Europe [1,2]. Much more research has been undertaken to investigate the soundness of dead-burned MgO in cement. Standards for limiting the content of MgO in cement have been established in many countries. The content of MgO should be below 5% in cement and can be 6%. When passing soundness testing under autoclaving according to Chinese standards [3]. It has been found that the expansion produced by MgO could be utilized to compensate for the shrinkage of cementitious material under certain conditions.
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