As Gypsum reacts with C_(3)A(tri-calcium aluminate) and C_(4)AF(tetra calcium alumino ferrite) at initial hydration of cement, assists the hydrolysis of C_(3)S(tri-calcium silicate), the producing rate of ettringite (3C_(3)Aㆍ3CaSO_(4)ㆍ32H_(2)O) an...
As Gypsum reacts with C_(3)A(tri-calcium aluminate) and C_(4)AF(tetra calcium alumino ferrite) at initial hydration of cement, assists the hydrolysis of C_(3)S(tri-calcium silicate), the producing rate of ettringite (3C_(3)Aㆍ3CaSO_(4)ㆍ32H_(2)O) and C-S-H gel is accelerated. Therefore it was certain that compressive strength of cement and concrete was improved due to the effect of Gypsum.
The purpose of this study is to utilize waste phosphogypsum into Admixture for high strength concrete at steam curing.
For the study, waste phosphogypsum is made use of 5 types by specific gravity distribute which is simple and physical dry process and 4 foams (Dihydrate, Hemihydrate, TypeⅢ-Anhydrite and TypeⅡ-Anhydrite) which is changed to in low temperature.
Also, various admixtures were made of waste phosphogypsum(PG) and Pozollanic fine poweders(Fly-ash, Blat Furnace Slag), and the basic porperties of the cement mortars incorporating with these admixtures were examined and analyzed under a verity of experimental conditions.
Also, based on the study of cement mortars, properties of compressive strength of OPC and alternative admixture(specimen name PG2-2MF) for High-Strength Concrete at steam curing air-dry, were compared with each other.
The conclusion obtained from this study can be summarized as follows:
(1) As additives for high strength, waste phosphogypsum content was found properly out 7.5% and being harmful to later age strength for added more large content. This reason is that formation of needle-like ettringite crystals.
(2) By specific gravity distribute all the types of compressive strenth is higher than OPC. In hemihydirat and typeⅢ-anhydrite cases, these is similar to typeⅡ-anhydrite from compressive strength and are greate in the effect of strength improvement.
(3) Compressive strength value in steam cured mortars at water binder ratio 45%, mortars with PG2-1(M), PG2-2(MB), PG2-3(MF) manufactured in present study developed 668, 688, 712.8 kgf/㎠ at 28 days, respectively. Therefore, it is possible to manufacture of high strength mortar in order to get compressive strength of 650kgf/㎠.
(4) Alternative admixture PG2-2(MB), which was determined form the results of cement mortar test, is able to manufacture of high strength concrete up to 495.1 kgf/㎠ by only steam curing at 7days.
(5) As a result of this study, it was proved that specimens made on type Ⅲ-anhydrite of waste phosphogypsum and flyash increased on the compressive strength of mortar and concrete was as good as concrete with type Ⅱ-anhydrite.
Consequently, it was proved that a high strength concrete was able to be made with such alternative admixture.