Alkali-activated material (AAM) is one of the most attractive alternatives to ordinary Portland cement (OPC). Recently, more and more research interests are devoted to durability performance. In cold areas, freeze-thaw resistance is a crucial durability factor for concrete. However, the understanding of the freeze-thaw resistance of AAMs is minimal. Accordingly, the subject of this thesis is drawn forth. The main aim of this study was to investigate the effects and mechanisms of using admixtures (SAP and AEA) to improve the freeze-thaw resistance of alkali-activated slag (AAS).
Regarding the general properties, such as workability and mechanical properties, it was found that the influence of adding SAP or AEA is acceptable. Then, the air-void systems created by SAP and AEA were reconstructed and characterized by the micro-CT scan. It was found that both SAP and AEA successfully entrained air voids into AASM, while the characteristics of the resultant air-void system were quite different. Further analysis on the surface condition of AASM undergoing 28-day sealed curing or preconditioning procedures in the CDF test, and the ASTM C672 test revealed that AASM shows a considerable surface microcracking potential. Samples sealed for 28 days showed a considerable extent of microcracking due to autogenous shrinkage. Samples that underwent 14-day drying after 7/14 days’ curing showed significant microcracking due to autogenous shrinkage and drying shrinkage. With the addition of SAP, the cracking caused by autogenous shrinkage was minimized, but the cracking caused by drying was only slightly reduced. With the addition of AEA, there was only a minor improvement in surface integrity.
The freeze-thaw resistance of AASM with or without the addition of SAP or AEA was investigated in the form of surface scaling damage by a modified CDF test. Plain AASM showed poor surface scaling resistance mainly attributed to the pre-existing surface microcracking. The addition of SAP and AEA successfully improved the surface scaling resistance of AASM. The improvement was more significant by adding SAP due to the effect of improving surface integrity. Based on the SAP mixtures, a good correlation was found between the SAP air-void system and the resultant surface scaling resistance. The final cumulative surface scaling generally decreased with higher entrained air content, denser air voids distribution, and smaller air voids size. A preliminary logarithm model was developed for the relationship between the reduction in surface scaling and the equivalent water/binder ratio and the air-void system. Finally, upscaling tests on the concrete scale also found that the addition of SAP improved the surface scaling resistance of AASC.
Overall, in this study, the freeze-thaw resistance of AAS was successfully improved by the SAP and AEA. The effects of adding SAP/AEA and the related factors on the selected properties of AASM were revealed. The mechanisms behind these observations were also understood and generated a series of further research possibilities. It is hoped that these findings and observations can give some guidance to the industrial applications of AAS and some inspiration to the scientific community.

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.

Alkali-activated concrete (AAC) has emerged as an environmentally friendly alternative to conventional concrete, as It is a cement-free concrete made by activating precursors (mainly low-cost, low-CO2 industrial by-products) with alkalis. AAC has demonstrated some remarkable mechanical properties and long-term performance (e.g., high strength, chemical durability, and fire resistance). However, high drying shrinkage in AAC, causing cracks degrading the long-term durability of AAC, is one of the obstacles that must be overcome before it can be widely applied in the construction field.
This study investigates the mechanisms of drying shrinkage, provides a survey and evaluation of the influencing factors, and accordingly proposes an integral solution to mitigate drying shrinkage in AAC. This was done through a qualitative approach based on literary research.
The investigation showed that the main driving forces of drying shrinkage are surface, disjoining, and capillary tension forces, and they are related to relative humidity (RH) and meniscus radius. Further, different reaction products' characteristics can be attributed to different drying shrinkage mechanisms, as they have a critical role in determining AAC properties. Furthermore, poor mechanical properties of AAC often lead to a higher drying shrinkage rate. Surveying the influencing factors of drying shrinkage of AAC, in terms of raw materials, mix designs, and curing conditions showed their significant effect on drying shrinkage magnitude and mechanical properties. These factors were accordingly evaluated and systematized. Therefore, based on the survey and evaluation, a strategy was proposed to mitigate drying shrinkage in AAC.