Influence of Mixing Time on Fresh and Hardened Cast-in-place Concrete

An adequate mixing time in concrete casting allows to achieve a homogeneous mass and improve compressive strength and durability. However, the lack of standards for cast-in-place concrete causes that the builders use different mixing times according to the locality usages and customs, which results in a high variability of the expected quality. In this paper, fresh and hardened cast-in-place concrete was evaluated. Seven samples were tested with different mixing time using portable rotary drum mixer. The used materials were ordinary portland cement, water and high absorption aggregates, fine and coarse, coming from a limestone crushing process. The results of the research showed that the mixing time and environmental temperature had no apparent influence on the slump of the mixtures, and trapped air and compressive strength increased slightly with increasing mixing time. Finally, it was found that the recommended mixing time, with rotation speed of 28 RPM, is 2.5 minutes, which differs from the common practice in the study area.

Specifics of Wear of Ceramic Cutting Tool Inserts Featuring Al2O3-TiC Dies when Face Milling Hardened Cast Iron

This work studies wear kinetics of index able inserts (II) made of mixed ceramics based on Russian-manufactured in case of fine milling of special hardened cast iron with globular graphite. In a wide range of cutting parameters typical for fine milling, an impact of tool insert wearing parameters on qualitative and quantitative characteristics of the cutting process have been studied. Morphological traits and nature of wear of work surfaces has been studied using optical and scanning electron microscopy. Criteria of II states, as well as specifics of contact work surface transformation, correlating with force parameters of the face milling process, have been determined.