Recycled Haitian Concrete Found Safe, Strong

(U.S. Agency for International Development)

Nearly one year after a 7.0-magnitude earthquake rocked Haiti, engineering and concrete experts at Georgia Institute of Technology in Atlanta report that concrete and other debris in Port-au-Prince can be safely recycled into strong new construction material. Their findings appear in the Bulletin of the American Ceramic Society, published today (4 January 2011).

Georgia Tech researchers Reginald DesRoches, Kimberly Kurtis and Joshua Gresham say they made new concrete from recycled rubble and other indigenous raw materials using simple techniques. And their recycled product meets or exceeds the minimum strength standards used in the United States.

DesRoches, a professor engineering who was born in Haiti, gathered samples of typical concrete rubble in Port-au-Prince. He also collected samples of two readily available sand types used as fine aggregates in some concrete preparation.

He and civil engineering student Gresham also studied the methods, tools, and raw materials used by local laborers to make concrete mixes. DesRoches says, “All of the construction crews were manually batching smaller amounts of concrete” without mixing trucks. He noted that they also mixed concrete “by eye” as well as by hand, which leads to an inconsistent and poor quality product.

Before leaving, DesRoches and Gresham manually cast an initial set of standard 3-inch by 6-inch concrete test blocks using mixes from several different construction sites. Back in Atlanta they were joined by engineering faculty colleague Kurtis, who is also an expert on the materials science of concrete.

They discovered that the concrete test samples cast in Haiti were of poor quality, with average compressive strength of 1,300 pounds per square inch. Concrete produced in the U.S., by comparison, is  expected to have a minimum strength of 3,000 pounds per square inch.

The team manually crushed the Haitian samples to make a course aggregate, which they combined with the sand from Haiti brought back by DesRoches. Instead of guessing at the amounts of materials, as DesRoches witnessed in Haiti, they carefully measured volumes using methods prescribed by the American Concrete Institute. The materials were still mixed by hand to replicate the conditions in Haiti.

Subsequent tests of samples made from each type of sand showed the compressive strength of both types of new test blocks — still composed of Haitian materials — much higher, to an average of over 3,000 pounds per square inch: the minimum standard expected for U.S. produced concrete.

Kurtis notes, “We now believe that Haitian concrete debris, even of inferior quality, can be effectively used as recycled course aggregate in new construction.” The team believes its results can be scaled up to where quantities can be measured using common, inexpensive construction equipment.

Because of the urgency of quick and safe reconstruction, the researchers recommend that recycling the debris quickly move from proof-of-concept to large scale testing. Most of the damaged areas of Haiti are still in ruins. The trio says their work points to a successful and sustainable strategy for managing an unprecedented amount of waste, estimated to be 20 million cubic yards.

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