Strength Of Alkali-activated Concrete Research Articles

Long-term durability properties of geopolymer concrete: An in-depth review

Geopolymer concretes (geocretes) are considered as eco-friendly materials for various building applications. Geocrete has high early strength, less consumption of natural resources, cost-effectiveness, capacity to form different structural configurations and to remain intact for extended periods without repair works. Meanwhile, geocretes have still exhibited an unstable behavior over time compared to traditional cementitious composites. To overcome this disadvantage, hundreds of studies have focused on the improvement of the microstructure of geocretes with a wide range of improved durability characteristics. Therefore, the review paper has an objective to make available an inclusive review on the production of supplemental-cementing-materials (SCMs), their economic returns, environmental and durability impacts, the conceptual model for geopolymerization, durability affecting factors, and function and long-term durability properties of geocrete. It is concluded that geocrete demonstrated a better resistance against aggressive environment compared to normal concrete, due to its less porous structures. Moreover, it is found that the strength of alkali-activated concrete was found to improve in chloride environment, unlike OPC based concrete. It is also concluded that, the presence of GGBS and MK in alkali-activated materials reduces its alkali-silica reactivity while it is recommended to use high calcium FA in geocrete production for durable concrete and geopolymerization. The higher the molarity of NaOH solution for a given quantity of Na2SiO3 the faster the geopolymerization process and the higher the compressive strength of concrete corrosion current than the OPC concrete. Further long-term durability studies are required to provide test methods and validation techniques since most studies focus on the 28-day curing regime.

Effect of Specimen Size and Curing Condition on the Compressive Strength of Alkali-Activated Concrete

Alkali-activated concrete is a rapidly emerging sustainable alternative to portland cement concrete. The compressive strength behavior of alkali-activated concrete has been reported by various studies to a limited extent, but these discussions have been based on minimal evidence. Furthermore, although it is known that specimen size has a distinct effect on the apparent compressive strength of concrete, this effect has yet to be modeled for alkali-activated concrete. This paper presents the results of a comprehensive study of the effects of curing condition (i.e., moist-cured at ambient temperature for 28 days or heat-cured at 50çC for 48 h) and specimen size on the compressive strength of sodium silicate–activated fly ash and slag cement concrete. The heat-cured strength of alkali-activated slag cement concrete was linearly related to the moist-cured strength; the former was about 5% greater than the latter. Heat curing also improved the strength of alkali-activated fly ash concrete, although the effect was greatly magnified for lower-strength mixtures and was much less significant at higher strengths. Existing size effect laws employed for portland cement concrete proved reasonably accurate in describing the effect of specimen size on the apparent strength of alkali-activated slag cement concrete. However, these existing models greatly underestimated the size effect in alkali-activated fly ash concrete; the authors suggest that this finding was the result of significant microcracking in the alkali-activated fly ash concrete.

Rheological Characteristics of Alkali Activated Fly-Ash Concrete Mixtures

This paper describes rheological characteristics of concrete mixtures based on alkali-activated fly ash. There are shown relationships between workability of fly-ash fresh concrete mixtures and water–fly-ash ratio in fresh alkali-activated concrete. In addition, there is described relationship between workability in fresh mixture on compressive strength of alkali-activated concrete.

Freeze-Thaw Resistance with Sodium Chloride Solution of Fly-Ash Concrete Mixtures

This paper describes freeze-thaw resistance with sodium chloride solution of concrete mixtures based on alkali-activated fly ash. There are shown relationships between freeze-thaw resistance with sodium chloride solution and air content in fresh alkali-activated concrete and relationship between freeze-thaw resistance with sodium chloride solution and spacing factor of alkali-activated concrete. Also there is described relationship between air content in fresh mixture and compressive strength of alkali-activated concrete.