Strengthening Technology And Application Of Free-sintered Lightweight Aggregates

Core-shell free-sintered lightweight aggregate(LA)is a new type of low-density free-sintered LA.Due to the interface compatibility between cement-based materials and core expanded polystyrene(EPS),and the insufficient specific strength of the shell cement-based material,there are practical problems in the production of core-shell LAs with EPS as the core,such as easy exposing,low primary yield,and low overall specific strength.This paper studies from three aspects:the interface modification technology between EPS and cement-based,the shell modification technology of core-shell free-sintered LA and the exploration of functioning core-shell free-sintered LA.According to the requirements of interface strengthening between EPS and cement-based,the effects of early-strength interfacial agents,polymer interfacial agents and organic acid interfacial agents on the interface properties and the action mechanism were studied.Scanning electron microscopy(SEM)was used to determine the compactness of the interface at the microscopic level,and the effects of different interface agents on the hydration process of cement were studied by isothermal calorimetry and electrode-free resistivity experiments.According to the relevant conclusions,the LA with high specific strength was prepared,and the accuracy of the mechanism was further demonstrated.The results show that both polymer-based interface agents and organic acid-based interface agents can decrease the exposure rate of LA and increase the yield of LA.From the microscopic level,a single polymer interface agent can not make the interface between EPS and cement-based compact,while organic acid interface agent can produce uniform distribution of micropores by corroding the surface of EPS,improve the surface roughness,so as to strengthen the interface performance between EPS and cement-based.In view of the strengthening demand of core-shell LA shell,the influence of fiber and activator on the specific strength of LA is explored by adding fiber and activator into shell material,and the shell material formula is optimized.The lightweight,high strength,energy-saving and free-sintered LA is developed,and the related mechanism is studied.The results show that,by comparing and analyzing the mixing effect of pine fiber and polypropylene fiber,when the content of pine fiber is 2%,the density of light aggregate can be reduced and the cylinder compressive strength is less affected.The cylinder compressive strength of core-shell light aggregate with bulk density of 660 kg/m~3 can reach 5.3 MPa.By adding polypropylene fiber,the specific strength of light aggregate can be improved obviously,and the low-density free-sintered light aggregate can be prepared.When the dry bulk density is 450 kg/m~3,the cylinder compressive strength can reach3.5MPa.In order to expand the function and application of light aggregate,the curing-free hollow and free-sintered LA was prepared by using water absorbent resin as the core,and the phase-change energy-storage free-sintered LA was prepared by using phase change material as the core.The results show that the strength of hollow LA prepared by using water-absorbing resin as the core is close to the standard curing strength of core-shell LA with EPS as the core,which indicates that the hollow LA has good self-curing effect.The light aggregate with paraffin as the core has a higher bulk density,and the 28d compressive strength of the phase change LA with a bulk density of 776 kg/m~3 is 7.0 MPa.Using cladding and impregnation to encapsulate phase change LA can improve its strength,reduce its water absorption and heating loss rate,and the encapsulation effect is good.By adding phase change light aggregate into cementitious material,the peak value of hydration exothermic heat can be reduced and the temperature peak of hydration heat can be narrowed.