Optimizing fiber-reinforced lightweight high strength concrete: The role of coconut shells, ground granulated blast-furnace slag, and basalt fiber in low cement content mixes / Muhammed Talha Ünal

Muhammed Talha , Ünal (2024) Optimizing fiber-reinforced lightweight high strength concrete: The role of coconut shells, ground granulated blast-furnace slag, and basalt fiber in low cement content mixes / Muhammed Talha Ünal. PhD thesis, Universiti Malaya.

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Abstract

The demand for lightweight aggregate concrete (LWAC) has been growing in the construction industry due to its potential to reduce the dead weight of structures while maintaining strength, durability, and cost-effectiveness. This study proposes a method to design LWAC by integrating coconut shell (CS) as coarse lightweight aggregate and a high volume of wet-grinded ultrafine ground granulated blast furnace slag (UGGBS). The wet grinding of GGBS has shown great potential for providing high-volume cement replacement with reduced particle size and an improved hydration property while simultaneously decreasing the density in slurry form. Also, to increase the effectiveness of the hydration reactivity of UGGBS slurry, the ratios of GGBS powder and grinding media volumes to the grinding chamber volume were examined. To optimize the mix design of LWAC, a particle packing model was employed to estimate the packing density and void ratio of the concrete mixture. The study has demonstrated that optimizing the volume content of different CS and mining sand sizes can significantly improve packing density. It is observed that higher packing densities of the aggregate phase and the entire concrete mix lead to reduced void volumes, resulting in a less porous and more compacted concrete matrix. Furthermore, the inclusion of fines and powder content has proven to be an effective method for increasing packing density, which in turn enhances the voidfilling capacity and strengthens the concrete. The optimal mix design was determined using the packing density method, and the impact of Basalt Fiber (BF) was investigated at varying levels (0%, 0.15%, and 1%). A comparative analysis was made between normal weight concrete (NWC) and the selected LWAC mixtures with different BF contents in terms of cost, CO2 emissions, saturated surface dry density, surface crack conditions, water absorption and porosity, sorptivity, compressive and flexural performances. The results revealed that the incorporation of UGGBS had a substantial positive impact on the mechanical properties of LWAC when BF was incorporated into the CS lightweight concrete mixture. Including 1% BF in the mix demonstrated superior mechanical and transport properties compared to non-fibrous LWAC, highlighting the significance of BF in enhancing the characteristics of high-strength LWAC. As a significant finding of this research, a grade 30 LWAC with a demoulded density of 1864 kg/m3 containing only 284 kg/m3 cement was produced. After considering all these approaches and implementations of green high-strength LWAC with a %40 reduction in cement, there are lower CO2 emissions and reduced manufacturing costs, making it an alternative choice for production.

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