Can Mixing Materials Make Them Stronger? A Materials Engineering Challenge

What You'll Learn

• Clay particles are far smaller than sand grains and bind to them when wet, hardening as they dry
• Engineers run fair tests — same water, same drying time — to compare mixture ratios
• More of a good ingredient isn't always better; there's a "sweet spot" ratio

Words to Know

Material

What something is made of

Wood, sand, and clay are all materials

Mixture

Two or more materials stirred together, without changing what they are

Stirring sand and clay together makes a mixture

Clay

A material made of super-tiny, flat flecks that stick together when wet

Squishy modeling clay you can mold with your hands

Compressive strength

How much squishing or pressing a material can take before it breaks

Testing which brick can hold the most weight on top before crumbling

Fair test

Testing only one thing at a time, so you know what really caused the result

Using the same amount of water and drying time for every brick you test

Engineer

A person who tests and designs materials and objects to solve problems

An engineer tests different brick recipes to find the strongest one

Check What You Learned

Fun Facts

• Some mud-brick (adobe) buildings have been lived in for more than 1,000 years — Taos Pueblo in New Mexico has been continuously inhabited since about 1000 CE

  Source: UNESCO World Heritage listing, Taos Pueblo

• Ancient builders in Egypt and Mesopotamia built entire cities out of mud brick more than 3,000 years ago

  Source: general archaeological/Egyptology record

• Clay particles are smaller than 0.002 millimeters while sand grains are 0.05–2 millimeters — thousands of clay flecks are smaller than a single grain of sand

  Source: USDA soil texture classification

• Dry sand alone has almost no strength — stack it and it slides and collapses, because round sand grains have nothing binding them together

  Source: basic soil mechanics / geotechnical engineering

• When wet clay dries, it hardens and binds sand grains together — this is literally how adobe and cob construction has worked for thousands of years

  Source: traditional adobe/cob construction techniques, documented in vernacular architecture studies

• Too much clay makes a brick crack as it dries and shrinks, so engineers test different sand-to-clay ratios to find the strongest mix

  Source: adobe construction guides / soil mechanics