Study On Composition, Structure And Properties Of Reactive Powder Concrete Containing Steel Slag Powder

Reactive powder concrete (RPC), otherwise known as high-performance concrete, has high durability and excellent mechanical properties, so the application of RPC has good prospects. In this paper, aiming at the main problems in application of RPC, i.e., high production costs and energy consumption, steel slag powder (SS) and ultra-fine fly ash (UFFA) were used as reactive powder component to product RPC, and meanwhile, fine river sand was used as aggregate instead of quartz sand. Based on systematic study of the physical and mechanical properties, durability, microstructure and hydration as well as hardening of RPC containing SS, the relationship among the composition, structure and performance of RPC containing SS was revealed and the design methods and preparation technology for RPC containg SS were grasped, which provided important references for preparation and application of RPC containing SS.The main research and achievements accomplished in this paper are as follows:In order to propel the application of RPC, taking three aspects, i.e., development strategies, technical requirements and economy of material into account, it was pointed out that the design of RPC containing SS must flollow the principle that RPC prepared in this paper should have high strength (RPC 200), excellent durability, good economy and environmental compatibility. Based on the centroplasm theory developed by Wu ZhongWei, the ideal microstructure model of RPC containing SS was built, which provided theoretical guidance for design and preparation of RPC. On this basis, the design methods of RPC were proposed: In the component design, compound mineral admixture containing SS and UFFA was utilized as reactive powder component and the particle size distribution (PSD) of SS was optimized by gray correlation method in order to improve the hydration activity of SS; in the dense microstructure design, on one hand, a mix design method based on the maximum density theoretical model (i.e., Dinger-Funk equation) was developed in order to enhance the packing density of compound system of RPC containing SS, on the other hand, superplasticizer having good compatibility with compound system was utilized to reduce the water-cement ratio of compound system and thus to increase the paste density. By the design methods mentioned above, dense microstructure of cement paste could be formed through dynamic hydration filling effect and stastic dense packing effect of the compound system, which were brought out by ordered hydration owing to the different hydration activity of mineral admixture particles with different chemical compositions and particles size. Therefore, RPCs with high-performance would be obtained.The mix design based on the Maximum Density Theoretical Model was carried out through Matlab and Microsoft Excel 2003, which had the following 4 steps: Firstly, the value of distribution modulus, n, in Ding-Funk equation sutiable for RPC was chosen according to some principles of powder engineering; secondly, the target and adjustable value of mix design was defined on the basis of particle size distribution (PSD) of each raw material; thirdly, the constrains were determined according to the circumstances; Finally, an optimization algorithm is programmed in Microsoft Excel and Matlab. The mix proportion of RPC obtained by this method was verified by experimental programs for minimum water requirement of paste and orthogonal experimental design for RPC.The influence of chemical composition, specific surface area and curing temperature on hydration activity of SS and the effect of the amount of and specific surface area of SS on mechanical properties of RPC were studied. The effect of PSD characteristics of SS on mechanical properties of RPC was analysed by gray correlation method. Based on these findings, the PSD of SS would be optimized in order to improve RPC performance. Moreover, the influence of water cement ratio, sand-cement ratio and steel fiber content on mechanical properties of RPC was researched and the effect of heat-curing regime on both mechanical properties and microstructure of RPC was analysed systematically. Therefore, the preparation technology for high-performance RPC containing SS was grasped. RPCs with excellent-durability as well as high mechanical properties were prepared by utilizing 42%～48% (by weight of binder) compound mineral admixtures, which included SS, silica fume and UFFA, and other raw materials and through curing in a proper heat-curing procedure. The hydration, hardening mechanism and microstructure were systematically studied through XRD, IR, thermal analysis (TG-DTG-DSC), SEM-EDXA, micro-hardness, steel fibers pull-out test and pore structure analysis. Therefore, the process of microstructure forming and structural characteristics of RPCs containing SS were discovered and the excellment mechanical properties and high durability of RPCs containing SS resulted from 3 aspects: the higher packing density and very low water-binder ratio of RPCs; the static dense packing and dynamic hydration filling effect of the compound system, which included silica fume, SS and UFFA; the cracking resistance, enhancing and toughening effect of steel fibers in RPCs.