Developing a rational method to participation cementitious mortars containing Meta-Kaolin for application in additive manufacturing

There is a growing interest in adopting additive manufacturing processes using cement-based materials in the construction industry. However, the approach to developing a viable cementitious mixture for 3D printing has been empirical in nature and relies heavily on repeated trials, until suitable mixture proportions are determined for a given set of materials. Although the ultimate aim of the on-going study is to develop a rational approach for mixture proportioning cementitious mixtures for 3D printing, the focus of the present study is to examine the behavior of cementitious mixtures prepared with portland cement in combination with meta-kaolin and other admixtures such as super plasticizer (SP), viscosity modifying agent (VMA) and additives such as polypropylene (PP) fibers. In this parametric study, the influence of meta-kaolin addition at various dosage levels on the rheological and mechanical behavior of mortars was investigated Rheological properties of mortars (i.e. yield stress and plastic viscosity) were determined using ICAR PLUS rheometer to correlate the fundamental rheological properties with the performance measures such as extrudability, buildability, thixotropic open time and shape retention. Setting time of various mortar mixes were also determined using ASTM C403 method. The compressive strength and flexural strength of the material was evaluated. The bond behavior between the layers will be evaluated using pull-off testing (ASTM C 1583) in the future. The results from this investigation showed the relevance between the fundamental rheological properties and the performance measures for achieving a viable 3D printable mixture

Role of Ground Glass Fiber as a Pozzolan in Portland Cement Concrete

Millions of tons of fiberglass are produced annually for a variety of applications. Because of stringent quality requirements and operational characteristics of the manufacturing plants, a significant quantity of fiberglass that does not meet required specifications of the industry ends up as waste in landfills. This study investigated the use of ground glass fiber (GGF) that had been discarded by plants because it did not meet prescribed standards, as a supplementary cementitious material (SCM) for portland cement. Three replacement levels (10%, 20%, and 30% by mass) for portland cement in paste, mortar, and concrete mixtures were studied. Mechanical and durability properties of the mixtures were compared with two control mixtures: a mixture made up of 100% portland cement and a mixture with 25% Class F fly ash as a cement replacement material. It was observed in these studies that even though replacement of portland cement with GGF did not lead to any significant changes in the mechanical behavior of hardened concrete, there were significant improvements in durability properties at replacement levels up to as high as 20%. The use of GGF was found to improve significantly the resistance of mortar mixtures to alkali–silica reaction and sulfate attack. In addition, the use of GGF as an SCM significantly reduced the chloride ion permeability of concrete. Results of this study show that using GGF as an SCM can result in a better durability performance compared with a mixture with a similar level of Class F fly ash