Abstract
The mix design of ultra-high performance concrete (UHPC) is complicated by the presence of many “ingredients.” The fundamental packing density allows a simpler mix design with fewer ingredients to achieve optimum packing density and dense microstructure. The optimum particle grading increases the flowability of UHPC and eliminates entrapped air. This study presents a simplified particle grading design approach that positively influences the strength, autogenous shrinkage, and microstructure characteristics of UHPC. Carbon nanofibers (CNFs) of superior mechanical properties were added to enhance the strength of UHPC and to reduce its autogenous shrinkage. In addition, ground granulated blast-furnace slag (GGBS) was used as a cement replacement material to reduce the amount of cement in UHPC mixes. Test results showed that the presence of homogeneously dispersed CNF increased the compressive strength and compensated the autogenous shrinkage of UHPC. The findings indicated that an ideal particle distribution, which is close to the modified Andreasen and Andersen grading model, contributed to achieving high compressive strength and CNFs were capable of providing nano-bridges to compensate the shrinkage caused by GGBS.
Highlights
The recent developments in concrete engineering and technology have facilitated researchers around the world to synthesize ultra-high performance concrete (UHPC) with advanced engineering properties
The use of silica fume (SF) further increases the autogenous shrinkage as a result of its high surface area; the effect is critical in low water content concrete, which thereby undergoes a significantly decreasing internal relative humidity (RH) in cement paste during hardening
Mix 1 to Mix 5 with different particle grading characteristics were prepared as the fundamental concreteand mixes to investigate the packing of each mix
Summary
The recent developments in concrete engineering and technology have facilitated researchers around the world to synthesize ultra-high performance concrete (UHPC) with advanced engineering properties. The use of SF further increases the autogenous shrinkage as a result of its high surface area; the effect is critical in low water content concrete, which thereby undergoes a significantly decreasing internal relative humidity (RH) in cement paste during hardening. Self-desiccation occurs in the absence of an external source of water [12,13] Nanomaterials such as nano-silica, nano-calcium carbonate, graphite nanoplatelets, carbon nanotubes (CNTs), and carbon nanofibers (CNFs) are used to enhance concrete properties due to their high surface area and fineness [1,15,16]. CNTs/CNFs are nano-dimensional structural ingredients that exhibit extraordinary mechanical properties in terms of Young’s modulus, tensile strength, and flexural capacity They are potential candidates as nano-reinforcement in concrete due to their nano-dimensional nature and good coverage ability in the cement matrix [16]. The microstructure of hardened UHPCs was observed by means of a SEM
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
