Experimental Study On Durability Of Red Mud-based Cementitious Material Stabilized Base

As a new type of road base material,red mud-based cementitious material can completely replace traditional cement in the field of traffic engineering to prepare stable macadam base.It can not only realize the large-scale utilization of red mud with high added value,but also promote the green and low-carbon development of road engineering construction.In this paper,the performance of red mud-based cementitious materials stabilized macadam under long-term service conditions in the process of engineering application is systematically studied.The longterm evolution law of working performance of red mud-based cementitious materials stabilized macadam is revealed.The evaluation model of fatigue performance of red mud-based cementitious materials stabilized macadam pavement structure is established,and it is successfully applied to expressway construction projects.The main research contents and research results of this paper mainly has the following four:(1)The changes in mechanical properties and quality of red mud-based cementitious materials stabilized macadam under freezing and thawing cycles are investigated.revealing the mechanism by which the temperature and number of freezing and thawing cycles affect the mechanical properties and mass loss of materials.Under the conditions of 20℃～-20℃ and 28 d,the maximum mass loss rate of 5%cementitious materials is 1.85%.The mass loss rate of stabilized macadam with 5%and 6%red mud-based cementitious materials is higher than that with 7%and 8%,and the rate of quality loss is constantly increasing with the increase of freezethaw cycles.Through industrial CT and SEM-EDS microscopic analysis,with the increase of freeze-thaw cycles,the porosity of stabilized macadam increases.After 20 freezing and thawing cycles with 6%content and and 28 d,the porosity increases by 1.53%,and the internal crack damage increases and accumulates continuously,showing a changing law from less to more and from narrow to wide.(2)The change law of shrinkage performance of red mud-based cementitious materials stabilized macadam is revealed.As the experimental age increases,the cumulative water loss rate and cumulative dry shrinkage strain of stabilized crushed stone gradually increases to no longer increase;And when the content of red mud based cementitious material is 8%,the dry shrinkage coefficient and dry shrinkage strain of stable crushed stone are much higher than other additives;Under different amounts of red mud based cementitious materials,the temperature shrinkage coefficient of stable crushed stone shows a trend of first increasing and then decreasing with the decrease of the experimental temperature range.With the increase of the content of red mud based cementitious material,the average temperature shrinkage coefficient of stabilized crushed stone shows a trend of first decreasing and then increasing.As the curing age increases,the temperature shrinkage coefficient of stable crushed stone gradually decreases.Through grey correlation analysis,it was determined that the dry shrinkage crack resistance index and temperature shrinkage coefficient are the optimal evaluation indicators for the crack resistance performance of red mud based cementitious material stabilized crushed stone.And under the same mix design conditions,the 7%cementitious material content has the best crack resistance performance.Through grey relational analysis,the dry shrinkage energy anti-cracking coefficient and the temperature shrinkage energy anti-cracking coefficient are determined as the best evaluation indexes of the anti-cracking performance of stabilized macadam with red mud-based cementitious materials.(3)The anti-scour evaluation test shows that the increase of curing age and the content of red mud-based cementitious materials is helpful to improve the anti-scour performance of red mud-based cementitious materials stabilized macadam.Increasing the content of red mudbased cementitious materials can increase the internal friction angle and effective bonding area between particles,and increase the amorphous gel in hydration products,thus improving the erosion resistance.The impact of erosion frequency on the quality and strength loss of stable crushed stone is mainly manifested in the early stage of erosion,with the strength loss at 4500 cycles being 55%of the strength loss at 27000 cycles.A numerical model of erosion quality damage of red mud-based cementitious materials stabilized macadam is established.With the increase of erosion times,the quality loss tends to decrease,and the cumulative erosion amount increases slowly,and finally tends to be stable.The erosion amount in the freezing and thawing erosion test is significantly greater than that in the erosion test.As the number of freezing and thawing cycles increases,the loss of erosion quality continues to increase,and the anti erosion performance of stable crushed stones continues to decrease.(4)Based on four-point bending fatigue,the fatigue equation under 95%guarantee rate is obtained and the law of fatigue performance variation is revealed.The structural model of red mud-based cementitious material stabilized macadam pavement is established through ABAQUS.By analyzing the stress characteristics of red mud based cementitious material stabilized crushed stone base,the fatigue life of pavement structure is estimated.At the most unfavorable load position,the asphalt surface layer failed after loading 3.51964×1012 cycles.Based on this research result,the engineering application test of red mud-based cementing material stabilized macadam was carried out.Within one year after the test section was opened to traffic,the pavement structure was stable,and there were no diseases such as potholes and cracking,which indicated good durability of the structure.