Foamed concrete has proven to be an effective alternative to granular fills and is now widely used internationally. With increasing demand for lightweight materials for buildings in order to improve sustainability, foamed concrete has also developed as an ideal material for this purpose, and many countries utilise construction with precast foamed concrete blocks. However, at densities lower than current technology allows, typically <500 kg/m 3 , foamed Magazine of Concrete Research Volume 68 Issue 11 Jones, Ozlutas and Zheng Stability and instability of foamed concrete
Accurate prediction of the carbonation rate of a particular concrete is important for the correct assessment of both durability and environmental impact of reinforced concrete (RC) structures. Applied loading and caused by it concrete cracking are major factors affecting the carbonation, which so far have received little attention of researchers, especially this concerns 'green' concretes, i.e. concretes in which Portland cement (PC) is partially replaced by supplementary cementitious materials such as fly ash (FA) and ground granulated blast-furnace slag (GGBS). The aim of this paper is to present laboratory data arising from experiments to study the influence of static loading and associated concrete cracking on the carbonation resistance of RC elements made of PC concretes and 'green' concretes containing significant amounts FA and GGBS. For this purpose, six different concrete mixes with two different water/binder (w/b) ratios (0.40 and 0.55) and different proportions of PC, FA and GGBS were prepared. Twelve RC beams (100×120×900mm) and a number of 100-mm concrete cubes were cast, 28-day cured and then kept for three months under temperature and relative humidity to reach equilibrium with those of an carbonation-accelerated chamber used in the tests. The RC beam specimens were loaded in four-point bending to produce tensile cracks of different widths and then placed into the carbonation chamber along with unloaded cube specimens to be subjected to accelerated carbonation for 120 days. Results of the experiments show a significant effect of loading (both tensile and compressive stresses) on the carbonation resistance of the concretes, especially of 'green' concretes.
The potential of TiO2-based photocatalysts in mitigating the effects of environmental pollutants is evident in the scientific literature but the large-scale implementation of photocatalytic concretes still appears limited, despite the current global concerns over urban NOx pollution. Improvements in cost-effectiveness are required to enhance the case for a photocatalyst-modified infrastructure and this must address catalyst efficiency, catalyst loading and performance durability. This paper compares photocatalytic efficiencies of TiO2 supported on mortar surfaces with the more conventional TiO2 dispersed in mortar. The influences of environmental conditions, such as NO concentration and flow rate, UVA light intensity and relative humidity, on photocatalytic performance are also investigated using photonic efficiency as an indicator. The supported TiO2 shows greater degradation of NOx (De-NOx), at about 9 times higher than TiO2 powder dispersed in the mortar, ca. 150 times higher utilization efficiency, than that of TiO2 in traditional photocatalytic mortar (with 5% loading).
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