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white concrete

Q. Why do some new concrete driveways appear whiter than others?

A. There are a few reasons for this. The main reason is the different type of concrete mixes used. You see, concrete is a mix of cement, various aggregates, water, and admixtures such as accelerators and retarders. The cement is often replaced with a substitute known as fly ash. Cement turns white when it hardens whereas fly ash has slight brownish tint. This is the biggest difference maker in final color.

Also, admixtures will alter the final appearance. The quicker the concrete hardens the whiter it will be. Admixtures can be used to either speed up or slow down set time. Antifreeze admixtures tend to leave concrete a darker shade. I'm not sure why but it does.

There are so many other variables that contribute to the final color including water:cement ratios, air temp, wind speed, humidity, and sunlight. But in my experience, cement vs fly ash creates the major color differences.

Some contractors like to use fly ash instead of cement because it sets slower allowing more time to work with it. I like to use all cement mixes unless it's very hot and I need to slow it down some.