Concrete: Brittle, Bust, or Brick?

Overview

Objectives/Goals My goal was to find out if more gravel or sand makes a concrete mixture stronger. My hypothesis was that the more I increase the percentage of gravel in a mixture, the stronger it will be. Methods/Materials I made five different mixtures of concrete. My mixture materials included: Portland cement, coarse aggregate (gravel), fine aggregate (sand), water, and air. Then I poured each of the mixtures into the molds that I had prepared ahead of time using cardboard boxes and masking tape. After drying for three days, I then took the concrete bricks to the Twining Lab to test their strength. Results My hypothesis was wrong. More sand and less gravel made the strongest concrete brick. The mixture with no gravel (only sand) was the weakest, but the mixture with no sand (only gravel) was also not the strongest. Conclusions/Discussion My mixture #2 with 50% sand and 17% gravel was strongest because the sand absorbs more water than gravel and thus helps the cement #glue# the mixture together harder.

Competition history

• CSEF 2006 Structural Capability & Strength of Materials (Junior Division Only) · Entry J1815

Resources

• CSEF project summary ↗

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