Optimization Design And Performance Evaluation Of Sulfur Aluminate–based Cement Treated Aggregate With High Early Strength

Cement treated aggregate（CTA）is widely used in the base and subbase of high-grade roads because of its strong bearing capacity and good durability.With the extension of service time,cracks and other distresses appear in the CTA base,which needs to be repaired by excavation.Traditionally,the construction of overlying structure is carried out after CTA is cured for at least 7 days,which seriously affects public transportation.Therefore,after the optimization design of sulfur aluminate cement,CTA with high early strength was prepared and its performance was then evaluated.The strength standard suitable for sulfur aluminate–based CTA was proposed.The main research conclusions are as follows:（1）The influences of composite retarder and composite early strength agent on the setting time and the compressive strength of sulfur aluminate cement system were performed,based on which the best dosages of composite early strength agent and composite retarder were determined to be 0.25%Li₂CO₃+0.6%Ca（HCOO）₂ and 0.4%polycarboxylate superplasticizer+0.6%borax.The hydration process and the interaction between hydration products and microstructure of sulfur aluminate cement were analyzed by TAM air isothermal calorimeter,scanning electron microscope（SEM）and X-Ray diffraction（XRD）.（2）Sulfur aluminate–based CTA was prepared,and its mechanical performances such as unconfined compressive strength,indirect tensile strength and resilience modulus of compression were tested.The results show that the 1d strength of sulfur aluminate–based CTA is approximately equal to the 7d strength of ordinary CTA when using the same cement content.The delay time,drying shrinkage,bonding strength and anti-scour performance of sulfur aluminate–based CTA were tested.The results show that sulfur aluminate–based CTA had excellent performance and could meet the requirement of fast traffic opening.（3）Finite element calculation model was established for sulfur aluminate–based CTA base during construction period and operation period.The variation law of bottom tensile stress of CTA base layer with the number of pavement layers and the modulus of CTA was analyzed.The strength standard of sulfur aluminate–based CTA during construction and operation period is calculated.The unconfined compressive strength of sulfur aluminate–based CTA at 1d could meet the strength standards of construction period and operation period.