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Research on Mechanical and Drying Shrinkage Properties of Cement Cold-recycled Base Based on the Vibration Molding

Author: FuXingChun
Tutor: DongRuiZuo
School: Chongqing University
Course: Traffic and Transportation Engineering
Keywords: cement cold regeneration base compaction characteristics strength andstiffness dry shrinkage property
CLC: U414
Type: Master's thesis
Year: 2013
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A large number of roads in our country have entered a period when medium-sizedand large road maintainance is undergoing, waste and old base course materialsgenerated every year are more than waste and old materials for asphalt pavement.Although our country has been long studying asphalt pavement recycling and madecertain achievements, researches completely for old base course material recycling isscarcely found. In this paper, the author made a detailed research on the compaction,mechanics and drying shrinkage performance of cement cold regeneration and cementstabilized base waste material, in an attempt to provide an experimental and theoreticalbase for future practice.The author made an analysis on raw materials from waste materials of cementstabilized base. After which has been used for years, coarse aggregate is brokenseverely, leading that the grading curve tends upper bound. Coarse aggregate crushingvalue and density meet the standardized requirements. Old cement mortar contained infine aggregate leads to lower density. Old materials have higher water absorption rateand larger sediment percentage.Heavy compaction and vibration compaction are respectively used for compactionexperiment on old sandstone and limestone materials. Heavy compaction curve for oldlimestone materials conforms to curve characteristics. Maximum dry density of oldsandstone material heavy compaction goes up with the increase of contained water.Old sandstone and limestone materials forms sag vertical curve under vibrationcompaction. The compaction method and characteristics of raw materials are bothimportant factors to consider. The study confirms proper compaction parameters for oldmaterial vibration compaction are determined. Grey relational analysis is put forwardto determine optimum water content for cement cold recycled mixture.Research on the strength and stiffness properties of cement cold regeneration basewith different cement dosages, curing duration, forming ways, degrees of compactionand curing temperatures is carried out. The cement dosage should be under6%, and thedesign duration for the compressive modulus of resilience and splitting strength ofcement cold regeneration base should be50to60days. The strength and stiffness ofvibratory compaction should be higher than static pressure molding. Higher the degreeof compaction is, it’s more favorable for stiffness. Standard curing temperature is recommended. Though the residual strength of cement cold regeneration base is higherthan new materials, this can not be taken as assessment criteria, for the absolute valueof new material’s secondary strength is larger than old materials’.Dry shrinkage energy anti-cracking evaluation index can be used for goodevaluation on the shrinkage anti-crack property of semi-rigid base in terms of energy.In this paper, evaluation on cement cold regeneration base’s dry shrinkageanti-cracking property is based on improved dry shrinkage property evaluation index.According to the influence of different cement dosages, degrees of compaction andcuring temperatures on cement cold regeneration base’s dry shrinkage, dry shrinkageenergy is the lowest at the end of dry shrinkage exposure period, in other words, dryshrinkage crack happen easily during this period, therefore, moisturizing and curing forbuilt base should be strengthened, or asphalt surface should be put on it as soon aspossible. Too low or high cement dosages will weaken dry shrinkage energy, and thebest proportion is5%. The higher the compaction degree is, the larger the dryshrinkage energy is, which is the largest during standard curing period. Too low or highcuring temperature will increase the risk of dry shrinkage and crack.Through study on the effects of admixture including water reducer, fly ash andardealite on the dry shrinkage energy of cement cold regeneration base shows that:water reducer will increase dry shrinkage and careful usage is recommended; fly ashwill increase the maximum dry shrinkage strain, but ultimate dry shrinkage energy risealong with the increase of dosage; ardealite makes it appear tumefacient at thebeginning, the maximum dry shrinkage strain reduces, and dry shrinkage energy goesdown. Admixture of ardealite and fly ash causes no greater changes compared withtheir single dope. It’s better to make the proportion of ardealite and fly ash smaller than1; the mixture of lime, ardealite and fly ash will greatly increase its dry shrinkageenergy.The author makes a study on the strength of the mixture of these three admixtures.Low dosage of water reducer will slightly decrease the intensity, and greatly decreasewhen making it4.5%.10%to15%dosage of fly ash will increase its intensity duringearly and late period; the strength goes down when the dosage of ardealite increases,but can still satisfy the strength standard for expressway subgrade; mixture of lime,ardealite and fly ash brings higher compressive and splitting strength than the mixture ofardealite and fly ash.

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