The floor of apartment houses is constituted of a layer of slab, which bears the load, a layer of lightweight foamed concrete for the purpose of heat storage and sound insulation, and a layer of floor mortar, which fixes and protects heating pipes and releases the heat upward. Notably, floor mortar plays the role of conveying working load to the lightweight foamed concrete layer and slab layer, but it is prone to cracks. Such vulnerability of floor mortar causes problems such as the increase in crack maintenance costs, and discoloration and damage of the floor finishing material. However, when alpha-calcium sulfate hemihydrate whose setting begins earlier and whose expansion deformation occurs in the early age is used as the floor mortar, it can restrict the occurrence of cracks owing to shrinkage, while also shortening the construction period owing to faster setting.
The setting of alpha-calcium sulfate hemihydrate is delayed in the same way as calcium sulfate dehydrate at a certain addition rate, but when the rate exceeds this level, its setting begins with the immediate precipitation of calcium sulfate dehydrate from the supersaturated solution. Furthermore, as the space between cement particles and hydrate is widened by the pressure from the growth of ettringite needle-shaped crystals generated in the process of the reaction between C3A and alpha-calcium sulfate hemihydrate, expansion deformation is caused in the early age.
Alpha-calcium sulfate hemihydrate is produced via a pressurized-steam process and pressurized-solution process, which use an autoclave with calcium sulfate dehydrate, and via an atmospheric steam process and atmospheric solution process, which do not use an autoclave. However, these processes have complicated manufacturing methods, which are not appropriate for continuous mass production and raise the unit cost of raw material. Therefore, alpha-calcium sulfate hemihydrate produced in these processes has low value for practical use as construction material. More recently, an economical method of manufacturing alpha-calcium sulfate hemihydrate using flue gas desulfurization gypsum released from the flue gas desulfurization equipment of thermoelectric power plants was used practically. Flue gas desulfurization gypsum was used only as a hydration retarder for the purpose of securing the liquidity of cement, or it was modified into beta-calcium sulfate hemihydrate to be used as plaster or gypsum board. Currently, owing to the wider use of the technology of manufacturing alpha-calcium sulfate hemihydrate from flue gas desulfurization gypsum, more research on its practical application to construction is required.
This study focuses on the properties of alpha-calcium sulfate hemihydrate whose setting begins earlier and whose expansion deformation occurs in the early age. It examines the mechanical properties and microstructural analysis of mortar with alpha-calcium sulfate hemihydrate by analyzing the setting and compressive strength properties, and the drying shrinkage of ordinary Portland cement and Portland blast-furnace slag cement mortar with 10, 20, and 30 wt.% of alpha-calcium sulfate hemihydrate content. Based on such analysis, the setting and hardening properties, drying shrinkage, and drying shrinkage cracks of non-sintered binder based slag type mortar and clay type mortar are reviewed. They were used at the site of an apartment house construction to examine the shrinkage properties of floor mortar under exposure to outdoor air. The purpose of this study is to develop non-sintered binder based floor mortar containing alpha-calcium sulfate hemihydrate.

Chapter 1 provides the introduction of the setting and shrinkage properties of mortar containing alpha-calcium sulfate hemihydrate, the background, objective, and the scope of the study.
Chapter 2 is a literature review on the alpha-calcium sulfate hemihydrate and the floor mortar of apartment houses. It provides the basic information and describes the reaction mechanism of alpha-calcium sulfate hemihydrate. It also explains the cracks caused in floor mortar among the three layers of floors of apartment houses, the factors affecting its shrinkage deformation, and the recent trend of research on floor mortar of apartment houses.
Chapter 3 describes the mechanical properties and microstructural analysis of mortar with alpha-calcium sulfate hemihydrate. It evaluates the setting and compressive strength properties and drying shrinkage properties of ordinary Portland cement and Portland blast-furnace slag cement mortar with 10, 20, and 30 wt.% of alpha-calcium sulfate hemihydrate content. Subsequently, it reviews the value of these mortars for practical use as construction materials.
Chapter 4 describes the mechanical properties of non-sintered binder based floor mortar containing alpha-calcium sulfate hemihydrate. The setting and hardening properties and drying shrinkage of cement type mortar, slag type mortar, and clay type mortar are evaluated and compared to the compressive strength criteria of the floor mortar in which dry cement mortar is used. Furthermore, the feasibility of its practical application to construction is examined.
Chapter 5 describes the results of a study on the practical application of the non-sintered binder based floor mortar containing alpha-calcium sulfate hemihydrate. Cement type mortar, slag type mortar, and clay type mortar were used for the construction of apartment houses to evaluate the shrinkage properties of floor mortar under exposure to outdoor air. The effect of the use of non-sintered binder based floor mortar containing alpha-calcium sulfate hemihydrate on the process of building the apartment houses is analyzed.
Chapter 6 presents the comprehensive conclusion of the study, and describes the setting and shrinkage properties of mortar containing alpha-calcium sulfate hemihydrate.

This study reviews the mechanical properties of mortar with alpha-calcium sulfate hemihydrate and evaluates the setting and hardening properties, drying shrinkage, and drying shrinkage cracks of non-sintered binder based slag type mortar and clay type mortar. They were used for the construction of apartment houses to examine the shrinkage properties of the floor mortar under exposure to outdoor air. The conclusions of this study are as follows.

1) When alpha-calcium sulfate hemihydrate is present in ordinary Portland cement mortar and Portland blast-furnace slag cement mortar, the initial setting time is shortened. Mortar with a greater content of alpha-calcium sulfate hemihydrate exhibits lower compressive strength. In addition, the shrinkage deformation in the early age is reduced by the pressure from the growth of needle-shaped crystals of ettringite generated from the mixing of alpha-calcium sulfate hemihydrate. The result demonstrates a clear restriction of shrinkage deformation in the early age owing to the mixing of alpha-calcium sulfate hemihydrate, but such an effect diminishes in the later age.
2) When alpha-calcium sulfate hemihydrate is present in mortar with a mixing ratio over a certain value, setting is accelerated, which affects the formation of ettringite and leads to a reduction in the strength and occurrence of expansion deformation. Hence, this study proposes that alpha-calcium sulfate hemihydrate can be useful as a mixing material for mortar in terms of accelerated setting and restricted shrinkage deformation of mortar, despite the reduction of strength to some extent.
3) The initial and final setting times of non-sintered binder based slag type mortar containing alpha-calcium sulfate hemihydrate and clay type mortar are shorter than those of cement type mortar. Furthermore, the time elapsed between the initial setting and final setting of slag type mortar and clay type mortar is 86 % and 59 % shorter, respectively, than that of cement type mortar. Such a result suggests that, when non-sintered binder based slag type mortar containing alpha-calcium sulfate hemihydrate is used for construction, it is possible to shorten the duration of the finishing process of floor mortar.
4) Non-sintered binder based slag type mortar and clay type mortar containing alpha-calcium sulfate hemihydrate undergoes expansion deformation in the early age owing to the calcium sulfate dehydrate crystals generated during the hydration reaction of alpha-calcium sulfate hemihydrate, thus reducing their shrinkage deformation rate as compared to that of cement type mortar. The shrinkage deformation behavior occurring after expansion deformation in the early age of slag type mortar demonstrates a similar trend to that of cement type mortar. On the contrary, clay type mortar shrinks gradually after expansion deformation, but the degree of its shrinkage deformation is smaller than those of cement type mortar and slag type mortar.
5) The degree of deformation under exposure to outdoor air is not significant for slag type mortar and clay type mortar. As a wide area of floor mortar is structurally exposed to outdoor air, air temperature, humidity, and wind factor have substantial effect on its shrinkage deformation. However, the dimensional stability of slag type mortar and clay type mortar is believed to be greater than that of cement type mortar, according to the result of the experiment in this study.
6) The initial and final setting times of slag type mortar and clay type mortar applied to non-sintered binder based floor mortar containing alpha-calcium sulfate hemihydrate are shorter than those of cement type mortar. Furthermore, the result of the experiment confirms the shortening of the time elapsed between initial setting and final setting. Therefore, the duration of the floor finishing process can be shortened when alpha-calcium sulfate hemihydrate is applied to floor mortar.

After developing non-sintered binder based floor mortar containing alpha-calcium sulfate hemihydrate, it was used for the construction of apartment houses to examine the deformation behavior of floor mortar under exposure to outdoor air. The result of the experiment confirms the shortening of setting time and restriction of shrinkage deformation of slag type mortar and clay type mortar containing alpha-calcium sulfate hemihydrate. However, as clay type mortar has lower compressive strength than slag type mortar, the latter is believed to be better for practical use in construction than the former, owing to its shortened setting time, higher compressive strength, and restricted shrinkage deformation. Therefore, the use of slag type mortar instead of cement type mortar for the floor mortar of apartment houses can restrict the shrinkage deformation and shorten the duration of the floor finishing process.