Study On Preparing Dry-mixed Mortar With Steel Slag

Conventional in-situ mixed mortar is prone to inaccuracy of measurement, highly energy consuming and polluting, it also has a poor performance and limited types, difficult application of industrial solid waste and admixture, failing to meet the requirement of modern project development. Dry- mixed mortar is of a high quality, environmentally friendly, full range and of excellent workability, but the high cost prevents its rapid development. Accordingly, a large amount of steel slag brings grave environment load. It shows high theoretical and practical value for research on high added-value application of steel slag and dry-mixed mortar with high replacement ratio of cement, making it highly cost efficient with high performance.In the paper, the hydration characteristics, hydration products of steel slag and also its influence on cement hydration in mix cements were investigated with combined methods of alkalinity, bound water, SEM and XRD, etc. Results indicate that steel slag itself has the hydrating capacity to some degree, with hydrates of C-S-H, Ca(OH)₂ and a small amount of CaCO₃, FeCO₃ attributed to carbonization. Moreover, its incorporation into cement system promotes cement hydration and there is a little Fe₆(OH)₁₂(CO₃) in the hydrates, different from ones of the pure cement system. It is noted that the microstructure is looser along with the increase of steel slag dosage.Influence of several chemical and mineral activators on the activation of steel slag, and also the related mechanism were explored. It shows that the seperate or compound addition of chemical activators (e.g. gypsum, water glass, sodium carbonate, and sodium sulfate)and mineral activator (e.g. slag) can activate steel slag , but slag has a better activating effect, without noticeable negative effect, so it is a proper candidate for activation and the optimal dosage is also specified.The mixing proportion of steel slag dry-mixed mortar is designed and the activation index of steel slag is put forward as an indicator of the cementitious effect of steel slag. Excessive replacement coefficient regression equation of steel slag is established, based on the relation between its activation index and excessive replacement coefficient, in order to specify the optimal dosage and Excessive replacement coefficient, and also the proper water demand of steel slag mortar and steel slag-slag mortar by experiments. Finally, orthogonal experiment is used to select proper types and dosages of admixtures and proportion a series of dry-mixed mortars with strength degrees of M5, M10 and M20.The durability of steel slag, steel slag-slag and cement mortars were compared . The results indicate that steel slag-slag mortar performs best in resisting carbonation, shrinkage, cracking and sulfate acid corrosion. And the properties of steel slag mortar can meet requirements for durability.At the end of the paper, the in-situ construction was monitored and results indicate that steel slag dry-mixed mortar consumes a large amount of industrial wastes such as steel slag, slag in replacement of cement and holds great potential of social and economic profits.