Alkali–silica reaction

Have you ever seen a big building or a bridge? They are made of concrete, which is super strong! But sometimes, concrete can get a little sick.

It's like when you eat something that doesn't agree with your tummy. This sickness is called the alkali-silica reaction. It happens inside the concrete, like a secret problem nobody can see at first.

It's a chemical reaction, which means tiny parts of the concrete are changing and making a mess.

This reaction happens when two things inside the concrete, called cement paste and aggregates (which are like tiny rocks mixed in), start to talk to each other in a bad way. They need water to start this chat. When they chat, they make a sticky, gooey stuff, like a super-thick jelly.

This jelly loves to soak up water, and when it does, it gets bigger and bigger, pushing the concrete apart from the inside. It’s like a balloon inflating inside a box!

When that jelly-like stuff swells up, it pushes and pushes on the concrete. This can make tiny cracks appear, and then bigger cracks. Sometimes, pieces of the concrete can even break off, like chipping a cookie.

This is called spalling. If this happens a lot, the whole concrete structure can become weak and might even need to be taken down. It’s like a building getting a bad case of the sniffles that turns into a big problem.

Scientists are like detectives for problems like this. A long time ago, in a place called California, a scientist named Thomas E. Stanton was studying why some concrete was cracking.

He discovered this sneaky reaction in the 1930s. He figured out that certain types of rocks mixed into the concrete were reacting with the cement when there was enough water. His discovery helped people understand how to build stronger concrete that lasts longer.