Study On Surface Modification And The Interfacial Transition Zone Between Ferrochromium Slag Lightweight Aggregate And Cement Paste

Nowadays, the burgeoning modern industries produce a large amount of solid wastes, harmless resource utilization of these industrial solid wastes is hence imperative. At the same time, the raw material source of lightweight aggregate(LWA) still relies on natural mineral resources in great quantities, which is not conducive to the sustainable development of LWA. Moreover, with modern architectural structure constantly being develped towards a direction of high-level, large span and lightweightness, the market demands for high performance lightweight aggregate concrete(HPLAC) are steadily on the increase. However, the preparation of high-performance light aggregate(HPLWA) with high strength, low water absorption becomes the key problem for the further development of HPLAC.Based on above, in this study we used the ferrochrmium slag, a tipically industrul byproduct to prepare the HPLWA with high strength and low water absorption by adding proper amount of fly ash and bauxite. Simultaneously a modified layer, also known as high-belite sulphoaluminate clinker with outstanding chemical reactive ability was designed and coated on the surface of the HPLWA to further improve the interfacial transizion zone(ITZ) between HPLWA and cement paste. Furthermore, the improvement mechanism and effects of HPLWA on ITZ was syntheticly investigated. This study consequently provides experimental foundation and theoretical basis for preparation and modification of HPLWA as well as harmless resource utilization of ferrochromium slags.The main conclusions of this study include the following;(1) the HPLWA is successfully prepared by using 50~60 w% ferrochromium slags, 40~32 w% fly ash and 10~8 w% bauxite as raw materials. The sintering temperature of HPLWA ranges from 1250~1300 ?, and the furnace cooling or repaid cooling in air under 800 ? is adoped to get the HPLWA with a water absoption within 2 w% and an individual pellet compressive strength of about 7 MPa. The prepared ferrchromium slag HPLWA has a glazed outer shell and a three-dimensional porous internal frame structure. Inside the frame structure, the prismatic cordierite and granular spinel grains grows well each other;(2) the optimal technological process for surface modification of ferrchromium slag LWA is as follows; the high-belite sulphoaluminate clinker raw meal powder is initially coated on the surface of the ferrochromium slag LWA green pellet by using carboxymethylcellulose(CMC, 40 w%) as binding agent, and then the green pellet toghter with the raw meal powder is sintered at furnace by one sintering technique. The “twice powder coating” method is chosed as the best way of coating, and the optimal mass ratio of surface modified layer and internal ferrochromium slag LWA green pellet is set to 24~36 w%;(3) being compared with the the unmodified ferrochromium slag LWA, the surface modified ferrochromium slag LWA(MLWA) has denser and thinner ITZ, and the interfacial bonding strength between MLWA and cement paste is much higher than that between LWA and cement paste at the same hydration age. In facat, the results show that the thickness of ITZ between MLWA and cement paste is only about 80%, 62.5% and 50% of that between LWA and cement paste at 28 d, 56 d and 90 d respectively, and the interfacial bonding strength between MLWA and cement paste is about 17.4%, 28.0% and 39.1% higher than that between LWA and cement paste at 3 d, 28 d and 90 d, respectively.