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Coconut Shell Ash (CSA) is an unexplored pozzolanic material by the construction industry. CSA, when combined with nano-silica, can enhance the compressive strength of cementitious composites. A full factorial design is formulated by the design of experiments (DoE) to take account of all levels of CSA and nano-silica. The synergistic effect by the pore-filling ability of nano-silica and pozzolanic action by CSA is statistically proved by ANOVA and confirmed by Tukey test. k-Nearest Neighbour(kNN) algorithm, a lazy learning machine learning algorithmis used to predict the strength of the cementitious composites. The kNN prediction is well agreeing and confirmed for reliability by comparing it with the prediction by regression.