Abstract: In order to effectively inhibit the shrinkage of concrete for hybrid girder bridges,a new admixture of cementbased materials for hybrid girder bridges was developed. Calcined dolomite-sludge was prepared by calcining dolomite and sludge at 800 ℃ for 0. 5 h after mixing them at mass ratios of 1 ∶2,1 ∶1 and 2 ∶1,respectively. The effects of calcined dolomitesludge on the hydration reaction,mechanical properties and volume stability of composite cement were analyzed,and the influence mechanism was clarified by analyzing the product composition of composite cement paste. The results show that calcined dolomite-sludge can delay the hydration exothermic reaction of composite cement,reduce the early strength,but improve the later strength. Moreover,when the ratio of dolomite to sludge in calcined dolomite-sludge is 1 ∶2,the strength of composite cement mortar is the highest at 60 d. The metakaolin in the calcined dolomite-sludge composition has pozzolanic activity, and the CaCO3 and dolomite in the mineral composition also react with the tricalcium aluminate in the cement to form carbon aluminate,thereby improving the strength. The hydration of magnesium oxide in calcined dolomite-sludge also causes the expansion of composite cement. 

Key words: calcined dolomite-sludge,hydration reaction,intensity,cement-based materials