It’s nearly the one-year anniversary of the huge earthquake that crumbled Port-au-Prince and other parts of Haiti, and, unfortunately, reconstruction has taken place only on a very small scale. The reasons for the slow pace are complicated: political uncertainties, uncoordinated plans and financing and, fundamentally, the underlying poverty of the nation and its accompanying lack of infrastructure, construction equipment, etc.
One bright note is that a group of civil engineering and concrete researchers at Georgia Tech have been able to demonstrate an important new angle on Haiti’s reconstruction, one that can speed up the building process, preserve natural resources, protect the environment and citizens’ health and make houses and other structures much stronger than before: concrete recycling.
In a paper published today in ACerS’s Bulletin magazine, researchers Reginald DesRoches, Kimberly E. Kurtis and Joshua J. Gresham report that they succeeded in making new concrete – which meets or exceeds the minimum strength standards used in the United States – from recycled concrete fragments and other raw materials from Haiti using simple techniques. They say the test they made on their recycled aggregate concrete points to a successful and sustainable strategy for managing an unprecedented amount of waste, estimated to be 20 million cubic yards.
DesRoches, a professor and Associated Chair of Civil and Environmental Engineering at Georgia Tech, was born in Haiti and in the past year has made many trips there as part of various groups documenting the structural damage and making recommendations on reconstruction. He also realized that “the commodious piles of concrete rubble and construction debris form huge impediments to reconstruction and are often contaminated.”
DesRoches (who I first wrote about several weeks ago) had a hunch that Haitians could get multiple benefits by trying to recycle the concrete instead of dumping it. On one trip to Port-au-Prince, DesRoches and grad student Gresham took samples of concrete mix from several reconstruction sites and cast their own concrete blocks. The two also studied local concrete preparation techniques – prepared manually in virtually all cases – particularly noting that large variations in composition occurred in part because laborers were guessing at volumes of ingredients or making measurements “by eye.”
They brought these blocks back to Georgia Tech where they joined up with Kurtis, another professor at the university and chair of the American Concrete Institute‘s Materials Science of Concrete Committee, to test their strength. To their alarm, they found the blocks’ average compressive strength was less than half of the minimum compressive strength required in the United States (3000 pounds per square inch), suggesting that a new round of poor construction susceptible to earthquake damage had already started.
The group then crushed these samples to use as coarse aggregate for a new “recycled” concrete mix. This time, however, they also employed samples of readily available sands that DesRoches and Gresham had taken from Haiti to use as fine aggregate. Finally, they carefully measured of all of the materials 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 provided good news: The compressive strength of both of the types of new test blocks, still composed of Haitian materials, dramatically increased, showing an average over 3,000 pounds per square inch.
“Based upon these results, we now believe that Haitian concrete debris, even of inferior quality, can be effectively used as recycled coarse aggregate in new construction,” says Kurtis, who is also a member of ACerS Cements Division. “It can work effectively, even if mixed by hand. The key is having a consistent mix of materials that can be easily measured and, when using recycled concrete, crushing the material to an appropriate size. We are confident these results can be achieved in large-scale reconstruction by proportioning the mix procedure and measuring quantities using common, inexpensive construction equipment.”
DesRoches is pleased because recycling eliminates two hurdles to reconstruction. “First, removing the remaining debris is nearly impossible because there are few, if any, safe landfill sites near Port-au-Prince, and the nation lacks the trucks and infrastructure to haul it away. It is better to use it than to move it.”
“Second,” DesRoches says, “Finding fresh aggregate is more difficult than getting rid of the debris. It is costly to find, mine and truck in.”
The trio notes recycled concrete aggregate has been used worldwide for roadbeds, drainage, etc., and that many European Union countries commonly use 20 percent recycled aggregates in structural concrete. Published research by others has also demonstrated that the use of local-sourced recycled aggregate concrete production can be more sustainable.
Because of the urgency of quick and safe reconstruction, the researchers urge that recycling the debris quickly move from proof-of-concept to large scale testing. “More work must be done to characterize the recycled materials, test additional performance parameters and gauge the safest ways to crush the rubble.
Seismic behavior and building codes must be studied. But, these tests can and should be done dynamically, during reconstruction, because the benefits can be so immediate and significant,” says DesRoches.
DesRoches, Kurtis and Gresham say they plan on sharing their research with Haitian government officials and nongovernmental organizations working on reconstruction projects. DesRoches is hopeful that a debris strategy and infrastructure will eventually emerge from the government once the disputed presidential elections in Haiti are resolved. “Some think that many rebuilding projects have been put on hold for the past few months because of distraction from the elections. The next round of elections is this month, so it soon may be possible to accelerate reconstruction,” he says.