Optimized mix design for 180 MPa ultra-high-strength concrete

Abstract

This study aims to optimize the proportion and constituents of the mixture used for fabricating 180 MPa ultra-high-strength concrete (UHSC) including coarse aggregate. Various parameters, such as the supplementary cementitious material (SCM) type and amount, water–binder (W/B) ratio, fine and coarse aggregate type and amount, chemical admixture, and mixing process, were considered and their effect on the compressive strength was examined. Based on several experimental tests, the optimized SCM proportions for cement, silica fume (SF), ground-granulated blast furnace slag (BFS), and gypsum are 55%, 20%, 20%, and 5%, respectively. The most appropriate W/B ratio, unit water content, and sand–total aggregate (S/a) ratio are 12.5%, 150 kg/m3, and 0.35, respectively. The use of very fine SF with a specific surface area of 13.7 m2/g and diorite, which is a type of coarse aggregate, improves the compressive strength of UHSC. The optimum amount of superplasticizer ranges between 1.3% and 1.6% and the most suitable slump flow is 750 mm. Finally, for this type of flowable UHSC, a mixing time and speed of 5 min and 40 rpm, respectively, and natural self-compacting without using a tamping bar are recommended. Based on the optimized mix design, UHSC with a compressive strength of 180 MPa can be certainly fabricated. Keywords: Ultra-high-strength concrete, Compressive strength, Supplementary cementitious materials, Self-compaction, Optimum mix design