Abstract
The investigation of concrete strength with nanoparticles and metakaolin in acid and sulphate solutions was the aim of this study. The nanoparticles were obtained from rice husk through sol-gel method and beneficiated metakaolin from kaolin to replace cement in concrete. The compressive strength results at 56 days were computed for various mixes. From the results, mix number 5 (1%NS 20%MK), 10(2%NS 15%MK) and 15(3%NS 10%MK) had the highest compressive strength of 39.36N/mm2, 40.20N/mm2 and 41.78N/mm2 showed the most strength development at 28days respectively. This is 10.7%, 9.8% and 14.8% strength increment over the control sample. The water absorption test of the concrete samples revealed that mix number 10 had the least water absorption at 69% less than the control sample. After 28days of 5% sulphuric acid and 5% magnesium sulphate immersion, mix number 10 also showed a compressive strength reduction by 9.7% and 7.2% more than the compressive strength before immersion. The sample with no additive was found to have 30.8% and 23.8% compressive strength reduction more than the compressive strength before immersion. The scanning electron microscopy (SEM) of the samples showed that, mix 10 had a more compact, homogenous and dense structure after 28days of immersion which explains the high strength. Energy Dispersion X-ray spectroscopy (EDS) also showed that the Ca/Si of mix 10 which was 0.83 and 0.65 after 28days of immersion in acidic and sulphate solutions respectively was within the range of optimal performance of concrete. X-ray diffraction analysis showed the development of ettringite, gypsum and silica gel as a result of the disintegration and reaction of the chemicals with hardened material.

Key words: Nanoparticles, concrete, compressive strength, Nanosilica, nanotechnology, Civil Engineering materials