CO2 Concrete and Its Practical Value

Abstract

Carbon-conditioning is the process by which carbon dioxide (CO2) is injected into recycled aggregate within a pressurised chamber to improve upon overall properties. The accelerated dosage of CO2 is able to deliver a chemical reaction in which calcium hydroxide is converted into calcium carbonate. Calcium carbonate crystals are smaller than that of calcium hydroxide and consequently, recycled aggregate is made denser. The enhancement of the recycled aggregate manifests within the final concrete product, a high performance recycled concrete know as CO2 concrete. However, whilst there is an understanding of carbon-conditioning and the mechanism of generating CO2 concrete, there are many that have not yet been investigated. This paper examines a number of characteristics that require examination to identify whether CO2 concrete is promising or lacks in certain key areas that apply to structural grade concrete.

The properties of CO2 aggregate and concrete are greatly affected by both the pressure and duration of time that recycled aggregate is placed within in its sealed chamber. Upon the optimal selection of these variables recycled aggregate experiences an improvement in density and porosity while water absorption is reduced. The resulting CO2 aggregate enables for greater workability due to the reduced water absorption and greater mechanical property by way of greater density. The compressive strength, tensile strength, flexural strength and modulus of elasticity all become greater. These mechanical properties can provide a matching strength when compared to virgin aggregate of the same mix design.

The durability of CO2 concrete can also compete with virgin aggregate concrete. The shrinkage of CO2 concrete can surpass that of virgin concrete in performance. Furthermore, CO2 concrete provides parody results in terms of water permeability. Whilst under the influence of accelerated curing conditions, carbon-conditioned concrete exhibits compressive strength results which rival that of virgin concrete.

The enhancement of the concrete can also be observed via microstructure analysis. A greater amount of calcium carbonate and improved structure can be observed when placed under macroscopic scrutiny.

The overall performance of CO2 concrete is improved in all characteristics. These trends are predictable and consistent. The enhancement of CO2 concrete alongside the consistency that the material can display provides a great deal of future value.

Keywords: Recycled Aggregate Concrete, Carbon-Dioxide, CO2 Concrete, Carbon-Conditioning