Experimental Study On Strength And Deformation Characteristics Of Unbound Granular Fill Materials Recycled From Building Demolition Waste

With the increasing emphasis on green and sustainable transportation infrastructure construction and the implementation of the zero net carbon emission strategy,the recylcing and high-value reutilization of bulk solid wastes,including building demolition waste(commonly known as BDW),have received increasing attention.Under the combined applications of vehicular and environmental loads,the unbound aggregate layers recycled from BDW could suffer from permanent deformation accumulation due to particle rearrangement and breakage,and the excessive permanent deformation could lead to surface rutting,cracking,and many other pavement distresses.Therefore,it is necessary to study the single particle crushing strength of aggregates recycled from BDW and the shear strength and elasto-plastic deformation characteristics of unbound granular fill materials derived from BDW under long-term cyclic vehicular loading to provide theoretical basis and technical reference for the design of unbound BDW granular fill layers.Supported by the National Key R&D Program of China and the National Natural Science Foundation of China,this thesis study presented research results from a compherensive laboratory testing program aimed to investigate compaction behavior by using the newly-developed flat plate vibration compactor,particle breakage,and resilient modulus and accumulated plastic deformation characteristics of unbound granular fill materials recycled from BDW under monotonic and cyclic loading conditions.The main research tasks and conclusions drawn are as follows.(1)The effect of vibratory parameters on the macroscopic compaction characteristics of recycled fill materilas with different gradations was investigated from laboratory plate vibration compaction tests,and the motion characteristics of coarse particles inside the fill materials under typical vibration compaction conditions were monitored and recorded in real time by customized smart sensors(termed as Smart Rocks),and the meso-scale vibration compaction mechanisms of unbound granular fill materials recycled from BDW were disclosed.The results showed that the time history curves of the achieved dry density values obtained from plate vibration compaction show obvious three-stage characteristics,and the optimal excitation frequency is in the range of 25–30 Hz.The particle motion pattern is also affected by the density of the fill materials,which also shows typical staged characteristics.(2)The crushing strength and compression deformation characteristics were studied by carrying out single particle crushing tests on recycled aggregates and one-dimensional confined compression tests(or oedormeter tests)on recycled granular fill materials and by combining digital image processing techniques.The effects of particle size and material type on single particle crushing strength,Weibull modulus,compression index,yield stress and crushing index were analyzed,and a characteristic strength prediction model was established to consider the particle size effect and the inter-correlation between relative crushing rate and normal stress.(3)Through laboratory repeated load triaxial tests,the effects of different combinations of stress states and physical conditions on resilient modulus characteristics of unbound granular fill materials recycled from BDW with different gradationswere studied,and a unified prediction model of resilient modulus was established by considering the effects of stress state,particle breakage level,the degree of compaction,and moisture content.(4)Through laboratory repeated load triaxial tests,the influences of stress states and gradations on accumulated plastic axial strain of unbound granular fill materials recycled from BDW were studied,and the prediction model of accumulated plastic axial strain was developed by with the particle breakage level considered properly.Based on the shakedown theory,the critical dynamic stress levels separating plastic shakedown and plastic creep behaviors of unbound granular fill materials recycled from BDW with different gradations were determined,and the related prediction model of such critical dynamic stress levels were developed by considering the gradation variations due to particle breakage.