Close Packing Theroy Based Design Method In Developing Eco-efficient Ultra-high Performance Concrete

Ultra-high performance concrete(UHPC)is a generation of advanced cement-based material,which is characterized by ultra-high strength and excellent durability.It is a promising material in the use of super high-rise buildings,marine engineering and military facilities.However,UHPC is facing the challenge of high cost and high energy consumption,which is mainly due to the utilization of large amount of cement.An efficient way to solve this problem is the replacement of cement by wastes due to the fact 65% cement only acts as “physical filler”.The addition of waste can sharply reduce the cost and energy consumption of UHPC,thus,promoting its development and application.However,in most studies,the development of eco-efficient UHPC lacks of theoretical guidance.To solve the problem aforementioned,the modified Andreasen and Andersen(A&A)model is used to develop UHPC with dense structure and its accuracy is verified via D-optimal design.After that,close packing theory based design method is proposed to develop eco-efficient UHPC.Finally,three eco-efficient UHPCs(namely,UHPC including lead-zinc tailings,UHPC including coral filler and UHPC including construction and demolition waste)are developed.Furthermore,their properties are characterized.To be specific:(1)The applicability of the modified A&A model in developing UHPC with dense structure is verified due to the fact this model ignoring the effect of water and superplasticizer.In this study,by adopting the quadratic saturation-D optimal design method,the relationship between the raw material composition(including superplasticizer)and wet packing density is established.After that,by comparing the design results with that calculated via modified A&A model,it can be concluded that the modified A&A model is an efficient method in developing UHPC.(2)After verifing the feasibility of modified A&A model in developing UHPC,a close packing based design method is proposed in developing eco-efficient UHPC.The key is minimizing the negative effect of the addition of waste by establishing appropriate relationship between raw materials and waste since the fact dense structure is the key factor in developing UHPC with advanced properties.(3)Using the method aforemetioned,the feasibility of using lead-zinc tailings to replace cement in developing eco-efficient UHPC has been investigated.To be specific: the particle size distribution,particle shape and specific surface area of lead-zinc tailings are similar to those of cement,leading to a similar wet packing density.Replacing 30%(vol.)cement by lead-zinc tailings contributes to similar workability,ultra-high compressive strength(>150 MPa)and excellent durability compared with UHPC without lead-zinc tailings.The replacement of cement by lead-zinc tailings can not only lower the energy consumption,but also reduce the early-age autogenous shrinkage and early-age hydration heat.Besides,the leaching toxicity results indicate that UHPC can effectively consolidate the heavy metal ions in tailings.The development of UHPC including lead-zinc tailings also provides an effective way in recycling of lead-zinc tailings.(4)Based on the eco-efficient UHPC design method,a dense UHPC skeleton including coral filler(coral powder and coral sand)has been produced.Results show that the addition of coral filler can improve the workability and chloride resistance capacity of UHPC.It has been demonstrated that no obvious reduction in compressive strength can be observed when blending of 15% coral powder and 30% coral sand.The addition of coral filler is found to be effective in decreasing the autogenous shrinkage of UHPC mainly due to the internal curing effect of coral sand.Furthermore,the utilization of coral powder and coral sand simultaneously can significantly reduce the environmental impact of the UHPC.When considering the transportation cost and better control of autogenous shrinkage,the advantages of using coral filler are more obvious.(5)The construction and demolition waste(C&D waste)are utilized to replace both cement and river sand,aiming at minimizating the negative effect of the addition of C&D waste on the packing density of UHPC.Replacing 30%(vol.)cement and 9% river sand by C&D waste has no negative effect on the compressive strength development.The replacement of cement by C&D waste can also reduce the energy consumption.In summary,the applicability of the modified A&A model in developing UHPC with dense structure is verified by adopting the quadratic saturation-D optimal design method.After that,a close packing based design method has been proposed in developing eco-efficient UHPC.Based on this design method,three eco-efficient UHPCs(namely UHPC including lead-zinc tailings,UHPC including coral filler and UHPC including C&D waste)have been developed and their properties are measured.Results indicate that the close packing theroy based design method is an effective way in developing UHPC with dense structure.The addition of wastes can not only lower the energy consumption of UHPC,but also enhance the properties.In addition,the development of eco-efficient UHPC provides a new efficient way for the recycling of waste.