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Ultra-high performance concrete (UHPC) mixtures are typically proportioned using high binder content and low water-to-binder ratio (w/b). Yet, in most cases, such recipes denote the presence of unhydrated cement and other pozzolanic materials, thus playing the role of costly fillers in the matrix. Two UHPC categories proportioned with two cement types and various binder contents ranging from 505 to 1050 kg/m3 are investigated in this study. Test results showed that the compressive and flexural strengths followed an increasing trend with binder additions, but then tended to stabilize or decrease at higher binder concentration. The highest strengths were achieved at binder contents hovering about 575 or 690 kg/m3 for 0.26 w/b mixtures prepared with river or quartz sands, respectively. The thermogravimetric analysis showed that UHPC made with higher binder contents exhibited increased mass loss at 500 °C, which corroborates the presence of increased amounts of unreacted cement compounds (i.e., CH) in matrices containing high binder content. The effect of reducing w/b and/or incorporating silica fume or metakaolin helped improving the strength of UHPC prepared with given binder content. The use of CEM I (52.5 MPa strength cement class) yielded consistently superior mechanical properties than equivalent mixtures containing CEM II (42.5 MPa strength class). The resistance against water permeability improved for UHPC containing higher binder content, suggesting that the increased cementitious phase plays a beneficial role to block the capillary pores and refine the matrix porosity. [ABSTRACT FROM AUTHOR]

Self-compacting concrete has gained a wide range of applications as a result of its unique properties, which can offer high strength and durable type of concrete with the proper selection of the raw materials. The purpose of this study was to show the effect of the use of high dosage of air entraining admixture on the properties of self-compacting concrete. An experimental investigation on the frost-salt scaling resistance of conventional and air entraining self-compacting concrete incorporating slag-blended cement and supplementary cementitious materials was carried out. Further fresh and hardened properties tests including slump flow, V-funnel, compressive strength, splitting tensile strength, air void characteristics and water absorption tests were performed to obtain an objective evaluation between air and non-air entrained self-compacting concrete mixtures. Air void characteristics were evaluated through the automated image analysis procedure to enrich this investigation. Results indicate the following: the air entraining admixture highly decreased the compressive strength up to 52% and the metakaolin was the governing supplementary cementitious material concerning the scaling resistance and water absorption in comparison with the silica fume. [ABSTRACT FROM AUTHOR]

Diagnostic of concrete structure properties is essential towards assessing the properties of the evaluated element. Since the Schmidt hammer is categorized as an economic and effective non-destructive testing tool, an extensive investigation is applied on several hundred of concrete specimens produced from several types, in order to assess the compressive strength and understand the limitations and boundaries of rebound hardness. From normally vibrated concrete to ultra-high strength concrete, water-binder ratio, water-powder ratio, supplementary cementitious materials and admixtures are relatively affecting the response of rebound index of the Schmidt hammer in terms of repeatability for compressive strength prediction. Additional porosity measurements were performed to enhance this statement. [ABSTRACT FROM AUTHOR]

High strength concrete (HSC ) and ultra-high strength concrete (UHSC ) have become today highly required due to their enhanced properties in terms of strength and durability. An experimental program was executed at BME , Department of Construction Materials and Technologies in order to evaluate the mechanical properties of HSC and UHSC mixtures including supplementary cementitious materials (SCM ) such as silica fume and metakaolin, to achieve the optimal mixture for site applications. Compressive strength was evaluated at different ages. Variable parameters were the amount of water, cement and SCM . Several alterations were performed to reach the required strength by the designers. Based on the laboratory experiment results, the most effective replacement amount of cement is 8% for SF and 17% for MK . [ABSTRACT FROM AUTHOR]

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