Greening effect of concrete containing granulated blast-furnace slag composite cement: Is there an environmental impact?

Abstract

The "greening effect" refers to hardened concrete containing Granulated Blast-Furnace Slag (GBFS) that displays a vivid blue-green color after removal of formwork. This temporary coloration effect, which fades within a few days to weeks, has raised concerns about its potential impact on the environment. Three types of leaching tests were conducted to assess different potential release scenarios: a sprinkling test, a static monolith tank test and a batch test on crushed samples. Slag content was linked to a higher release of sulfur anions in the leachates, in the form of sulfides, thiosulfates and sulfates. Most of these anions came from the GBFS, where sulfur is mainly in the form of sulfides with thiosulfates and sulfates as the main products of sulfide oxidation. Sulfate levels, however, were lower than threshold limit values for both inert waste and alternate materials reused in road construction. Moreover, no chromium, or other hazardous metals, were detected in the leachates.

Application of various microscopy techniques to study early‐age and longer‐term behaviour of super sulphated cement microstructure

“…The phenomenon observed on the concrete cores in Figure 7, commonly referred to as the ‘greening effect’ detected on certain spots of the concrete, is a well‐documented phenomenon in concrete containing a high level of GGBS (e.g. CEM III) as reported in existing literature 46,47 . This effect is manifested as a distinct blue‐green colour following stripping.…”

“…CEM III) as reported in existing literature. 46,47 This effect is manifested as a distinct bluegreen colour following stripping. Research indicates that this colouration only occurs in oxygen-deprived, so-called anoxic environments, as in the case prior to stripping.…”

“…Studies have identified the presence of sulphur-derived polysulphide radicals in slags, present in constant proportions whatever the origin of the slag, and these radicals are the only ones responsible for the colouration observed. 46 Consequently, the 7-month-old concrete core in Figure 7 appears more blue-green since it was stripped just before the photo was taken, indicating that it was less exposed to ambient air.…”

Temperature Effect of Hydration and Microstructure of Tricalcium Silicate–Slag Powder Hydrated Composites: An Experimental and Molecular Dynamics Investigation

“…1,2 Using slag powder to replace part of cement clinker is helpful to solve the problems of environmental pollution and resource consumption in cement production. 3 The addition of slag powder can significantly reduce the use of cement, reduce emissions of CO 2 , and protect the ecological environment, achieving sustainable development in marine and inland areas. 4,5 The partial substitution of slag powder improves the interface interaction between concrete components and enhances the fluidity and workability of composite cement materials.…”

“…Cement is a nonrenewable inorganic cementitious material, while the production and utilization of cement inevitably consume large amounts of natural resources and energy. Blast furnace slag, as a low-energy and potentially active industrial waste material, has a very promising future in the compounding of cementitious concrete. , Using slag powder to replace part of cement clinker is helpful to solve the problems of environmental pollution and resource consumption in cement production . The addition of slag powder can significantly reduce the use of cement, reduce emissions of CO 2 , and protect the ecological environment, achieving sustainable development in marine and inland areas. , The partial substitution of slag powder improves the interface interaction between concrete components and enhances the fluidity and workability of composite cement materials .…”