Study On The Volume Stability Of Limestone Powder-Fly Ash-Slag Recycled Concrete

Traditional concrete belongs to high energy consumption and high pollution industries from its raw material acquisition and use.The mineral admixture(consisting of limestone powder,fly ash and slag)and recycled aggregate are mixed into concrete.On the one hand,the amount of cement can be reduced and the energy consumption and cost of raw materials can be reduced,at the same time,the problem of increasing shortage of fly ash and slag can be solved by using limestone powder to a certain extent.On the other hand,the use of recycled aggregate can fundamentally solve the way out of waste concrete,save energy and benefit waste,and promote sustainable development.Through physical experiment and theoretical analysis on wet expansion,autogenous shrinkage,drying shrinkage and creep of limestone powder-fly ash-slag recycled concrete mixed with mineral admixtures and recycled aggregate,the effects of water-binder ratio,mineral admixtures and recycled aggregate on volume stability of limestone powder-fly ash-slag recycled concrete are studied,which provides theoretical support for the application of mineral admixtures and recycled aggregates.The main conclusions and innovative achievements are as follows.1.Mineral admixtures and recycled aggregates affected the strength development of limestone powder-fly ash-slag recycled concrete.Mineral admixtures can inhibit the early strength growth,and promote the later strength growth.The influence of recycled aggregate on the strength of concrete has two sides: higher or lower replacement rate of recycled aggregate will reduce the strength,and there is an optimal replacement rate,when the replacement rate of recycled aggregate is the optimal replacement rate or close to the optimal replacement rate,the strength of limestone powder-fly ash-slag recycled concrete is higher.The effect of water-binder ratio on the strength is the largest,followed by recycled aggregate and mineral admixture.2.The water-binder ratio changed the wet expansion,autogenous shrinkage,drying shrinkage and creep properties of limestone powder-fly ash-slag recycled concrete.The smaller the water-binder ratio is,the larger the wet expansion and autogenous shrinkage are,while the smaller the dry shrinkage and creep are.3.Mineral admixtures affected the wet expansion,autogenous shrinkage,drying shrinkage and creep properties of limestone powder-fly ash-slag recycled concrete.Mineral admixtures can inhibit the wet expansion in the early stage and promote it in the later stage,and from the final effect,mineral admixtures increase the wet expansion deformation of concrete.Mineral admixtures can inhibit the autogenous shrinkage,drying shrinkage and creep deformation.4.Recycled aggregate deteriorated the wet expansion,autogenous shrinkage,drying shrinkage and creep properties of limestone powder-fly ash-slag recycled concrete.Recycled aggregate can inhibit the early wet expansion,and promote the later wet expansion,and ultimately increase the wet expansion deformation.Recycled aggregate can increase the autogenous shrinkage,drying shrinkage and creep,and the higher the replacement rate of recycled aggregate,the more obvious the increase effect.5.The main factors affecting wet expansion,autogenous shrinkage,drying shrinkage and creep of limestone powder-fly ash-slag recycled concrete were studied.The wet expansion,autogenous shrinkage and dry shrinkage are most affected by recycled aggregate,followed by water-binder ratio and mineral admixture.The creep is most affected by water-binder ratio,followed by recycled aggregate and mineral admixture.6.Expansion pressure theory and surface tension theory are used to explain the wet expansion mechanism of limestone powder-fly ash-slag recycled concrete,and capillary tension theory is used to explain the autogenous shrinkage mechanism.The wet expansion rate and autogenous shrinkage rate of limestone powder-fly ash-slag recycled concrete are approximately linear with the replacement rate of recycled aggregate,based on it,the corresponding models were established to describe the variation law of wet expansion and autogenous shrinkage respectively.The model has a high degree of correlation and can be used to predict the wet expansion and autogenous shrinkage of limestone powder-fly ash-slag recycled concrete with different replacement rate of recycled aggregate.7.The drying shrinkage mechanism of limestone powder-fly ash-slag recycled concrete was explained by capillary tension theory and "V"-shaped contact point theory.The drying shrinkage rate of limestone powder-fly ash-slag recycled concrete is approximately linear with the replacement rate of recycled aggregate,based on this,the hyperbolic model of drying shrinkage is modified,and the drying shrinkage model of limestone powder-fly ash-slag recycled concrete is obtained.8.The creep mechanism of limestone powder-fly ash-slag recycled concrete was explained by viscoelastic theory,viscous flow theory and seepage theory.Based on Kelvin rheological model,the creep model,which is established by parallel connection of Hooker solid and Newton liquid,can better predict the creep performance of limestone powder-fly ash-slag recycled concrete.9.Feasibility analysis of volume stability of limestone powder-fly ash-slag recycled concrete was made.Based on the analysis of raw material acquisition,mix design and optimization,mechanical properties and working performance,it is feasible to study the volume stability of limestone powder-fly ash-slag recycled concrete.