Comparison Of Performance Of Road Base Materials Made From Red Mud With Different Storage Time And Its Strength Mechanism

By a series of performance comparison experiments and orthogonal experiments, mechanical properties of three road base materials made from red mud by sintering process with different storage time (three years, five years and over ten years respectively) are compared. The orthogonal experiments using degree of compaction, lime and fly ash as factors are designed and carried out to investigate the effects of the factors on strength. Moreover, by means of microscopic analysis methods of X-ray diffraction (XRD), scanning electron microscope(SEM) and energy dispersive X-ray analysis (EDXA), the strength formation mechanism of red mud road base material and the effects of additives on the strength are investigated by raw material composition comparison experiment and additives (32.5 portland cement andβsemi-hydrated gypsum) comparison experiment.The results of performance comparison experiments and orthogonal experiments indicate that as follows: Under the condition of high content (over 70%) of red mud, the 7 days compressive strength of all of three red mud road base materials can satisfy the requirement of speedway and first-class highway. On the whole, all of the three red mud road base materials have the property of high early strength, and with an increase in the storage time of red mud, the engineering performance of red mud road base is getting better. Under the ordinary construction condition—degree of compaction is 95%, taking account of high compressive strength and high content of red mud, the optimal raw material mixture ratio of the road base material containing three years storage aged red mud is red mud : fly ash : lime=75 : 15 : 10, the optimal raw material mixture ratio of road base material containing five years or over ten years storage aged red mud is 75 : 10 : 15. Moreover, the effect of lime on the strength of red mud road base is the most remarkable, the more amount of lime added (less than 15%), the higher compressive strength. The results of strength optimization additives comparison experiments indicate that the optimal addition amount of 32.5 portland cement is 1%, and the suitable addition amount ofβsemi-hydrated gypsum is 1~3%. The early effect ofβsemi-hydrated gypsum is better than that of 32.5 portland cement.The results of microscopic analysis show that as follows: The strength formation of red mud road base material is an interaction of complicated chemical reaction, physical chemistry process and physical mechanics process. Thereinto, gels (mainly hydrated calcium silicate gels) and crystals formed by hydration reaction and crystallization are the main contributors to strength. As the age of red mud road base increases, gels and crystals formed continually increase and grow up, then they gradually interlace, fill and join together, and cohere those grains which don't participate in the reactions to form a dense spacital network and skeleton structure. As a result, the road base acquires stable strength.In general, in actual construction, for the road base material containing three years storage aged red mud, because the strength of red mud agglomerations are low, the reactions among the three raw materials are the main contributors to strength. Although the active cement ingredients like dicalcium silicate in red mud gradually decrease as the storage age of red mud increases, the red mud particles consolidate to form macroaggregates with certain strength which can partially act as aggregates, as a group, gelation created by the reaction among the three raw materials consolidates red mud macroaggregates to form strength.