The Relationship Between Shrinkage Of Blast Furnace Slag Cement And Composites Of Hardened Cement Pastes

Shrinkage is one of the chief durability index of cement concrete. The characteristic of cement hydration is a main reason for resulting concrete shrinkage. The shrinkage of cementitious material is controlled by capillary tension, disjoining pressure, surface tension and removal of interlayer water. Incorporating ground granulated blast furnace slag(GGBS) is an effective approach for adjusting cement shrinkage. Performance of hardened cement pastes depends on its microstructure and composites.Fineness and content of GGBS are processing parameters for manufacturing blast furnace slag cement(BFSC). Three fineness of GGBS (fineness=396, 502, 605 m~2/kg) are chosen for mortar shrinkage experiments. Adding two fineness of GGBS (396, 502 m~2/kg) can remarkably improve shrinkage of mortars with GGBS dose ranging from 10 to 70 percent. But shrinkage factor of cement mortars with low GGBS content is greater than that of Portland cement, when the specific surface area of GGBS is too great(605m~2/kg) . Among the three fineness of GGBS, the shrinkage of cement mortar is the smallest, which GGBS content is 50%.Shrinkage factor of cement pastes is greater than shrinkage factor of mortars 4-6 times at 60d The time for paste to reach volume steady is shorter than that of mortars'. Shrinkage trend of cement containing 10% GGBS is similar to Portland cement. Cements containing 30-70% GGBS have similar shrinkage characteristics, and the shrinkage factor is smaller than that of Portland cement.The amount of banded water and CH content in cement paste are reduced after GGBS is incorporated into cement. The amount of banded water in Portland cement paste and the cement paste containing 10% GGBS are almost equal. In contrast with Portland cement, the development of the amount of banded water in BFSC is slower at the early period and faster during the later period.CH content in hardened cement paste decreases with the increase of GGBScontent.CH content fluctuates within 35d in BFSC. Incorporating GGBS in cement decreases porosity of hardened cement paste, and the varied scope increases with GGBS content.Specific surface area, hydration degree, characteristic pore size, and small pore content are closely related to shrinkage. The shrinkage factor increases with the increase of specific surface area and the amount of banded water in hardened cement pastes. Analyzing correlations between shrinkages and pore content of different pore size range, the conclusion is that the smaller the pore size be, the better the correlation be. The decrease of bur on the surface of C-S-H gel was observed using SEM in cement incorporating GGBS. C-S-H gel surface presents honeycombed. CH crystal is corroded in cement paste incorporating 10% GGBS, and crystal edge takes on irregularly. New C-S-H gel forms on CH surface which adhered to original gel forcefully.