Research On Performance Of RAP And Old Cement Stabilized Crushed Stone Composite Cold Recycled Mixture

At present,China’s highway construction has entered the stage of repair and maintenance,and the early roads are faced with renovation and reconstruction after long-term use.Due to the different damage levels of the pavement layers,the damage thickness of the base layer and the surface layer is different.Coupled with the positional relationship of the structural level,the surface layer needs to be completely removed after the base layer is damaged;if the base layer is partially damaged,a good thickness of the base layer should be retained,and the damaged base layer and surface layer should be removed to avoid the waste of resources,so two kinds of old materials with different quantities are obtained.In this paper,combined with two kinds of old materials with different mixing ratios produced by different road milling thicknesses,a composite cold regeneration study of RAP and old cement stabilized crushed stone materials is carried out.The main research results are as follows:1)At the beginning,seven different blending ratios of old materials are planned,and the test specimens are formed by using the heavy compaction method.Studying the influence of the dosage of binder and different ratios of old materials on the molding parameters of the mixture,it is concluded that the dry weight of the old material mixture with more RAP is greater at the same cement dosage.And the more cement dosage is in the same old material ratio,the greater the dry density of the mixture is.The analysis of variance shows that the dosage of binder and the ratio of different old materials have significant effect on the dry density of mixture.2)Improve the molding method of cement-emulsified asphalt mixture,and get method B: the first double-sided compaction is 50 times,and the second compaction is performed after 24 hours of curing at 60 ° C.After 25 times,the curing is continued for16 hours,and then cured at room temperature after 12 hours,the effect of forming test specimens is better.The AI regeneration method was used to estimate the amount of emulsified asphalt,and it was concluded that the proportion of more RAP predicted that the amount of emulsified asphalt was lower.Study the effect of cement dosages on the optimal emulsified asphalt dosage.It is concluded that the greater the cement dosages,the greater the reduction in the optimal emulsified asphalt dosage.But compared with the change of emulsified asphalt caused by different ratio of old materials,it can be neglected,and the best emulsified asphalt dosage for different old materials ratio is determined.3)Form the test specimens at the optimum moisture content to study the effects of different cement dosages and five different blending ratios on the strength and dry shrinkage of the cement stabilized recycled mixture.Summarize the performance index values to get the cement range corresponding to different old material ratios with better comprehensive performance.Form the test specimens at the best emulsified asphalt dosage and the best water content,and study the effects of different cement dosages and five different blending ratios on the strength and water stability and other properties of the emulsified asphalt stabilized recycled mixture.Summarize the various performance index values to get the cement range corresponding to different old material ratios with better comprehensive performance.4)The mechanism of cold regeneration was summarized and the microstructure between cement and asphalt was observed by SEM.It was found that the morphology of cement stone in the cement stabilizing RAP was similar to that of cement stone from new material stabilized by new cement.Some hydrates are inserted into the old asphalt membrane to form embedded link strength.Summarizing the influence of cement on the stabilized old materials of emulsified asphalt,it is concluded that the addition of cement greatly improves its strength and other properties.A small amount of unhydrated cement has the function of active mineral powder.5)Combined with the actual construction case,the plant mixing cold recycling construction process was studied,and the comprehensive benefit analysis of the cold recycling technology was concluded: the cost per kilometer was saved by 2.0904 million yuan,which can bring good economic benefits,social and environmental benefits.