The evaluation of change in concrete strength due to fabric formwork

Abstract

Fabric, as a flexible formwork for concrete, gives builders, engineers, and architects the ability to form virtually any shape. This technique produces a superb concrete surface quality that requires no further touch up or finishing. Woven polyolefin fabrics are recommended for this application. The texture of this fabric allows water from concrete mix to bleed, and therefore reduces the water-cement ratio of the mix. Due to the reduction in the water-cement ratio, a higher compressive strength in fabric-formed concrete is achieved, which is also suggested by earlier studies. The current research study was conducted to investigate and document the changes in concrete strength and overall quality due to these woven polyolefin fabrics. Use of fabric formwork will result in a decrease in construction cost, construction waste, and greenhouse gas emissions. Two sets of tests were conducted in this research study: a comparison of the compressive strength of fabric-formed versus PVC-formed concrete cylinders, and a comparison of the behaviour of the fabric-formed columns versus cardboard-formed reinforced concrete columns. Variables in this research were limited to two types of fabric that included one with coarse and one with a more refined texture, and two types of concrete that included ordinary and flyash concrete. The laboratory results revealed that the effects of fabric formwork on concrete quality in a large member are limited mostly to the surface zone and the core of the concrete remains the same as a conventionally formed concrete. Even though fabric-formed cylinder tests showed an average of a 15% increase in compressive strength of the concrete samples, the compressive strength of the reinforced columns did not dramatically change when compared to the companion cardboard formed control columns. This research confirmed that fabric formwork is a structurally safe alternative for forming reinforced concrete columns.