Compressive Strength Performance of 7-Day Non-load Bearing Concrete Hollow Blocks with Pili Shell as Partial Replacement to Sand Using Box-Behnken Design

The Philippines is one of the leading distributors of Pili (Canarium ovatum) nut worldwide. Along with the rise of production of pili nut is the increase in the generation of residual waste specifically the pili nutshell. The present study aims to investigate the compressive strength of 7-day of non-load bearing concrete hollow block (CHB) using waste pili nutshell as partial replacement to sand in the production of non-load bearing concrete hollow block (CHB) using Box-Behnken design. The compressive strength blocks made with varying proportion of waste pili shells for fine aggregates, pili shell size, and cement-sand ratio were also evaluated for a constant curing day of seven days. The Pili shell proportions used were 3%, 6% and 9% of total sand volume. Pili shell size retained at sieve no.10, no.20 and no.30 were used. And lastly a cement-to-sand ratios of 0.5:7, 1:7, and 1.5:7 were adopted. Compressive test results showed that most of the CHB with Pili shells possessed higher compressive capacity compared to the ordinary CHB. Among the prepared 7-day composites, the highest compressive strength was 671.28 pound per square inch (psi) that was obtained by the sample with 6% pili shells that retained at sieve #10 with a mix ratio of 1.5: 7. Moreover, the present paper examines the interaction among the three parameters using Response Surface Methodology—Box Behnken Design (RSM-BBD) using three level factorial designs was used in this study. Sigma XL software suggested fifteen (15) experimental runs. Statistical testing such as Variance Inflation Factor (VIF) and ANOVA revealed the adequacy of the generated model to describe the fit of experimental data to predictor model.