Due to its many advantages to the final product, the extrusion technology has been successfully applied in the manufacturing of short fiber reinforced cementitious composites (SFRCC). However, the rheological adjustment of fresh SFRCC, which is very important in successful extrusion, has never been tackled satisfactorily. Cost effectiveness usually becomes the main issue in searching for new formulations. In this study, a review from literatures and real experiences is first given. Then followed are systematic experimental approaches in determining the rheological properties of fresh SFRCC....[ Read more ]

Due to its many advantages to the final product, the extrusion technology has been successfully applied in the manufacturing of short fiber reinforced cementitious composites (SFRCC). However, the rheological adjustment of fresh SFRCC, which is very important in successful extrusion, has never been tackled satisfactorily. Cost effectiveness usually becomes the main issue in searching for new formulations. In this study, a review from literatures and real experiences is first given. Then followed are systematic experimental approaches in determining the rheological properties of fresh SFRCC.

First the liquid phases of four popular rheological modifiers (CMC, CMHPC, Methocel and PAM) have been studied using a Carri-Med CSL500 rheometer. The temperature and concentration influences have been investigated. Then two sets of self designed ram rheometries and the related mechanics have been utilized to find the key extrusion parameters and extrusion pressures of some typical SFRCC formulations according to Benbow and Bridgewater's Model. The factors studied include fiber type and fiber concentration, liquid phases with different types and concentrations, and binder systems either composed of pure cement or cement modified by slag, fly ash or silica fume. Finally extrusion experiments and mechanical tests of extrudates were carried out to check the influence of Methocel and PAM to the extrudate qualities in surface appearances and mechanical properties.

It has been found that PAM would be more effective than Methocel in adjusting SFRCC's rheology. Comparing to Methocel, use of PAM reduces the extrusion pressure, improves the extrudate surface quality and enhances the mechanical properties of hardened extrudate. Incorporation of slag improves the flowability of SFRCC in that extrusion pressures and parameters become smaller; while when fly ash is used, inverse effects will be observed. Empirical effects of fibers to the fresh extrudate have been thought adequate for real application. Influences of dosage and rheological behavior of liquid phases are studied in detail and the results are presented within the context.