An experimental study of high-performance concrete using metakaolin additive and polymer admixture

In recent years, there has been a growing interest in the use of supplementary cementing materials and polymers to produce high-performance concrete. Utilizing a mineral substance as cement replacement in concrete has less environmental pollution and greatly increases the service life of the concrete structures due to improve the most of concrete properties in compared with conventional concrete. The aim of this project is an experimental study of high-performance concrete using metakaolin (MK) additive as partial replacement of cement and addition of the Styrene-Butadiene rubber (SBR) and Polyvinyl acetate (PVA), to conduct a novel research to investigate the effectiveness of the additives materials on the performance of concrete. It also investigates the effect of additional recycled plastic and glass fibre as reinforcements used in the modified concrete. Firstly, trial mixes of 460 cubes, 24 cylinders and 30 prisms were made to study the setting time, workability, mechanical properties and water absorption of the concrete to find the optimum metakaolin to cement ratio (MK/C), polymer to cement ratio (P/C), water to cement ratio (W/C), and the best curing method among the wet, dry and moist, respectively. The designed concrete mixes have a certain cement/sand/gravel proportion of 1:1.5:3. The trial mixtures were tested for setting time, slump of fresh concrete mix, mechanical properties, including compressive, splitting and flexural strength, and water absorption capacity at age up to 28 days. Three polymers to cement ratios, which are 2.5, 5 and 7.5%, and five metakaolin replacement ratio for the cement, which are 10, 15, 20, 30 and 40%, were studied, respectively. For these mixtures, five W/C ratios, which are 0.35, 0.38, 0.40, 0.45, and 0.50, respectively, were compared. The use of recycled plastic and glass fibre reinforcements took 5% of the total cement weight and tested for splitting and flexural strength testes. The first phase work has shown clear improvement of the performance of concrete modified by partial replacement of cement by metakaolin and adding polymers admixture together. The optimised mix was identified to be that of 5% added polymers included 80% SBR and 20% PVA, 15% metakaolin replacement for cement, 0.45 W/C ratio, and using limestone aggregate as a coarse aggregates and using moist curing method as a curing condition for the concrete. Secondly, the optimum mixture identified in the trial study was further investigated for its mechanical including compressive, flexural, and deformable proprieties at prolonged ages up to 545 days. In addition, a specific durability properties of concrete including water and gas permeability, carbonation penetration, chloride penetration, chemical attack resistance, water absorption, rate of water absorption and the corrosion rate of the steel reinforcement in the concrete. The results show that significant improvement in mechanical properties including compressive, splitting, flexural strength and deformation properties. Also, the results show improvement in durability properties including chemical resistance, water absorption, rate of water absorption, carbonation depth of penetration, chloride ion penetration, water penetration under pressure, water permeability, gas penetration and steel corrosion resistance. The optimum mix of 15% partial replacement of cement by metakaolin, 5% polymer, 0.45 W/C ratio and moist curing condition of the modified concrete produced high-performance concrete more environmental friendly due to improved overall of the mechanical and durability properties of the concrete. Finally, microscopic composition of the hydration products and the corresponding pores structure have been investigated for the optimised mixes based on the material composition analysis and microscopic images obtained using scanning electronic microscope (SEM) and the computed tomography scanner (CT) technologies. Correlation between the mechanical, durability properties and the microscopic phases has been investigated and discussed for a deep understanding of the mechanism of the optimum mixture. SEM and CT scanner technologies provide qualitative and quantitative description of the concrete properties. It’s also, proved that the concrete modified by both of metakaolin and two types of polymers have a significant change in the pores structure of concrete compared with other mixes. Scanning electron microscopy and computed tomography scanner results show that the approach can be effectively applied in high-performance concrete related studies and provide further evidence on mechanical and durability properties of concrete