Utilization of alkali activated concrete in concrete revetment products

Abstract

Alkali activated concrete is seen as possible contender to alleviate the environmental footprint of the concrete industry. The goal of this research is to evaluate the extend to which ground granulated blast furnace slag and calcined clay-based alkali activated concrete can be utilized in concrete revetment applications with equal performance in freeze-thaw and sulfate attack resistance and lower environmental impact compared to blast-furnace slag cement concrete. This research uses a combination of ground granulated blast furnace slag and calcined clay as precursor blend which is combined with sodium silicate and sodium hydroxide activator solution. An upscaling methodology is used such that differences in material behavior between each upscaling step (paste, mortar, concrete) is explained. Mix designs are developed with the Taguchi method.The alkali activated concrete mix designs develop good compressive strength, where both mix designs reach over 12MPa after 24 hours of ambient curing and over 37MPa after 28 days of ambient curing. It fulfills the requirement for revetment products and outperforms cement concrete.The water absorption is on the high side. It does not fulfill the requirement, but the high value is attributed to non-optimal compaction as the concrete phase uses a special vibration and pressure compaction machine, which does not represent the compaction enabled in a factory process as the reference concrete also fails to meet this requirement.Freeze-thaw performance of the alkali activated mortar is sufficient as 5 of 9 mortar mix designs meet the requirement from the CDF test. Inclusion of calcined clay and the effect of the modulus clearly results in worse freeze-thaw performance due to more difficult compaction, higher absorption and more interconnected pores resulting in more scaling as the de-icing solution can penetrate further in the specimens. Freeze-thaw of the alkali activated concrete and reference concrete is insufficient with large amount of scaling at the end of the test, partially attributed to compaction. However, the retarding scaling behavior of alkali activated concrete indicates good long term performance.Sulfate attack performance is tested at mortar level where specimens are exposed to 10 % MgSO4 solution for 14 days. No degradation is visible in terms of scaling and compressive strength. Slight formation of ettringite is observed, thus it is recommended to extend the testing period.LCA is performed on product level and does not consider service life and recyclability. The alkali activated concrete mix designs show the potential to reduce the milieukostenindicator with 48 % to €5,72 and reduce the CO2 emissions with 63% towards 48kg per m3 produced concrete. These are significant reductions, but for full validation of environmental footprint performance of alkali activated concrete, service life and recyclability should also be involved in the calculations.The research proves that alkali activated concrete is a very interesting alternative for cement concrete in revetment products where the saturated Dutch GGBFS market can be alleviated partially by substitution of calcined clay. However, to apply the alkali activated concrete in revetment products, more research should be carried out with regards to durability, curing methods, recyclability and service life.