Colored Concrete,
Concrete Testing

The question of architectural concrete’s durability has finally been answered.

A review published earlier this year by the Portland Cement Association documents the performance of 60 typical architectural finishes after 40 years of exposure in the relatively severe Chicago-area climate. Most weathered extremely well, with 93 percent of the panels receiving an “excellent” or “good” rating.

The panels were constructed in the early 1960s at the PCA Research & Development Laboratories in Skokie, Ill., and assembled into a circular outdoor display that was unofficially referred to as the “PCA Stonehenge.” The display was for a study that dealt with decorative surface treatments. It described and illustrated methods of obtaining attractive finishes on both precast and cast-in-place concrete. Many of the techniques remain viable today.

The panel project was dismantled in 2001 to allow for development of the property, but before removal, the four-decade-old panels were inspected and photographed before and after a thorough power-wash cleaning. The panels were assigned a performance rating of “excellent,” “good,” “fair” or “poor” both before and after cleaning.

All 60 panels in the study were considered durable and structurally sound. Most surfaces also were sound and their appearance relatively unchanged. A slight etching or “softening” of the sharper edges was noticeable on some surfaces, but this was not severe. Though some panels looked better after cleaning, many of them exhibited only minor staining from dirt and pollution sources, and some panels looked about the same as they did when constructed 40 years ago.

However, the integrally colored concrete panels showed significant signs of wear.

The collection of 60 panels, each measuring 5 feet by 3 feet by 4 inches, was built to demonstrate seven production procedures popular at the time.

Section 1. Horizontally Precast Exposed-Aggregate Panels: In this technique the bottom of the forms are coated with a chemical retarder to expose a colorful aggregate in the concrete cast against that surface. This is the most commonly used technique in the precast industry.

The results: Of 18 panels, 12 were rated excellent, five good, and one fair. The panel rated fair contained a pink marble that faded, was not as white as was cast 40 years ago, and had dirt streaks still evident after cleaning. In another case where a panel contained a blue pigment in the facing mixture, fading took place.