Ellis Martin Gartner

New Control Strategies for Raw Mix Preparation

Control of raw mix composition in many cement plants is poor due to the inadequacy of conventional sampling and analysis systems. Potential sampling errors and delays in sampling and analysis prevent plant operators from taking effective and timely control actions. A new type of analysis system based on prompt gamma neutron activation analysis (PGNAA) permits elemental analysis of bulk solids in nearly real time. Raw mix control systems based on PGNAA and using feedback or predictive control algorithms were simulated by computer, and their performance was compared with simulated conventional raw mix control methods based on batch X-ray fluorescence analysis. Results show that the rapidity of analysis and small sampling error afforded by on-line PGNAA systems allow superior raw mix control.

Carbon Fiber Reinforced Cement and Mortar

Although carbon fibers have high tensile strengths and are chemically inert, their application in cementitious composites is limited due to their brittleness. An image analysis technique employed to determine the length distribution of the reinforcing fibers before and after mixing in cement paste and mortar matrices indicates that substantial fiber breakage occurs during mixing. In paste mixtures, the average fiber length after mixing remains above the critical fiber length, but in mortar mixes the average fiber length falls below the critical fiber length resulting in no significant enhancement of composite flexural properties.