chcdesign.net

substituting aggregates in concrete

By Chad Cross on October 10th, 2010

This is a study in "sustainable" materials, but more importantly "upcycled" materials – those which are put to use in a way other than that which was intended. To begin, I experimented with the process of making concrete. I chose to use the traditional method of a 1:2:3 ratio of portland:fine aggregate:coarse aggregate to use as a control. Then I substituted half of the coarse aggregate with shredded plastic grocery bags. The last test was substituting half the fine aggregate and half of the cement with fly ash. The process and results follow:

Why Plastic?

• •Durable / corrosion resistant
• •Good insulation for cold/heat/sound
• ◦saving energy and reducing noise pollution
• •Economical + long life
• •Hygienic + clean
• •Lightweight
• •Easy to process

Why Fly Ash?

• •It is a by-product of coal being burnt in a modern pulverized fuel furnace, and accounts for 90% of the total ash produced (10% furnace bottom ash)
• ◦Appearance of cement powder
• ◦Highly pozzolanic (reacts with water to produce cementitious material)
• ◦First used in 1929 – Hoover Dam
• •Spherical shape increases consistency and mobility
• ◦Less H2O needed
• ◦Smoother surface w/ sharper detail
• •Covered in kind of melted glass which reduces expansion of concrete due to sulfate attack

Control

• •1 Part Portland Cement (8 oz)
• •2 Parts Fine Aggregate (16 oz)
• •3 Parts Coarse Aggregate (24 oz)

Portland Cement -------------------- Fine Aggregate -------------------- Coarse Aggregate

Mixing Tools--------------------------Mixing Bucket

Small and Large Bricks Produced

Using Plastic as Aggregate

• •1 Part Portland Cement (8 oz)
• •1 Part Fine Aggregate (8 oz)
• •1 Part Shredded Plastic (8 oz.)
• •3 Parts Coarse Aggregate (24 oz)

Post-Consumer Plastic Shopping Bag

Method of Shredding / Acquiring Aggregate

Fine Aggregate Mixture

Small and Large Bricks Produced

Expected Results

• •20% Increase in Compressive Strength
• •Reduce Quantity of Cement by 5%
• ◦Reduce Construction Costs
• ◦Eliminate Landfilling and Incineration of Waste Plastics

Using Fly Ash as Aggregate

• •.5 Part Portland Cement (4 oz)
• •.5 Part Fine Aggregate (4 oz)
• •2 Parts Fly Ash (16 oz.)
• •3 Parts Coarse Aggregate (24 oz)

Locally Sourced Fly Ash(See Below for Source)

Small and Large Bricks Produced

Expected Results

• •Make Use of Industrial Waste
• •Less Likely to Crack (less water in mixture)
• •Stronger
• ◦Converts Calcium Hydroxide to Calcium Silicate Hydrate (CSH)
• ◦Slightly less strength initially; equal strength after 28 days; substantially greater strength within a year