Experimental study and computer-aided prediction of percentage of water absorption of geopolymers produced by waste fly ash and rice husk bark ash

In the present work, percentage of water absorption of geopolymers made from seeded fly ash and rice husk bark ash has been predicted by gene expression programming. Different specimens, made from a mixture of fly ash and rice husk bark ash in fine and coarse forms together with alkali activator made of water glass and NaOH solution, were subjected to permeability tests at 7 and 28 days of curing. The curing regime was different: one set of the specimens was cured at room temperature until reaching 7 and 28 days and the other sets were oven cured for 36 h at the range of 40–90 °C and then cured at room temperature until 7 and 28 days. A model based on gene expression programming for predicting the percentage of water absorption of the specimens has been presented. To build the model, training and testing using experimental results from 120 specimens were conducted. The data used as inputs in gene expression programming models are arranged in a format of six parameters that cover the percentage of fine fly ash in the ash mixture, the percentage of coarse fly ash in the ash mixture, the percentage of fine rice husk bark ash in the ash mixture, the percentage of coarse rice husk bark ash in the ash mixture, the temperature of curing and the time of water curing. According to these input parameters, in the gene expression programming models, the percentage of water absorption of each specimen was predicted. The training and testing results in gene expression programming models have shown a strong potential for predicting the percentage of water absorption of the geopolymer specimens.