Concrete solution to Haiti rubble

A year after a 7.0 magnitude earthquake rocked the Republic of Haiti, engineering experts at Georgia Tech in the United States are confident that concrete and other debris in Port-au-Prince can be safely recycled into strong new construction material.

In a paper in The Bulletin of the American Ceramic Society, researchers Reginald DesRoches, Kimberly Kurtis and Joshua Gresham wrote that they had produced new concrete from recycled rubble and other indigenous raw materials using techniques which either met or exceeded the minimum strength standards used in the US.

Most of Port-au-Prince is still in ruins. As of July 2010, 98 per cent of the rubble was uncleared. Around 1.6 million people have been living in relief camps since the quake and almost no transitional housing 12 months on has been built.

The three researchers say that their work points to a successful, sustainable strategy for managing 18 million cubic metres of rubble.

?The piles of rubble cause impediments to reconstruction and are often contaminated,? explains Reginald DesRoches, professor and Associated Chair of Civil and Environmental Engineering at Georgia Tech. ?There are political and economic dilemmas as well, but we believe we can turn one of the dilemmas ? the rubble – into a solution via fairly simple methods of recycling the rubble and debris into new concrete.?

Professor DesRoches travelled several times to Port-au-Prince to gather samples of typical concrete rubble and two sand types used as fine aggregates in some concrete preparation. He and Joshua Gresham also studied the methods, tools and raw materials used by local labourers to make concrete mixes.

Reginald DesRoches recalls that there were no mixing trucks. ?The construction crews were manually batching small amounts of concrete and mixing volumes of materials ?by eye,? an unreliable practice that probably caused much of the poor construction and building failure during the earthquake.?

Before leaving Haiti, the pair manually cast a set of standard 76mm by 152mm concrete test blocks, using mixes from different construction sites. They returned to Georgia Tech with their cast blocks, sand samples and notes, where they were joined by Kimberly Kurtis, also a professor and chairman of the American Concrete Institute?s Materials Science of Concrete Committee.

They concluded that the concrete test samples cast in Haiti were of poor quality. ?The Haitian-made concrete had an average compressive strength of 0.5 tonnes per square millimetre,? Kimberly Kurtis explains. ?Concrete in the US requires a minimum strength of 1.3 tonnes per square millimetre.? The trio then manually crushed the samples with a hammer to provide coarse aggregate for a second round of tests. They made concrete samples from mixes that combined the coarse aggregate with one of the two types of sands they had collected. However, instead of ?eye-balling? the amounts of materials, they carefully measured volumes using methods prescribed by the American Concrete Institute. The materials were still mixed by hand to replicate Haiti conditions.

Subsequent tests of samples made from each type of sand revealed that the compressive strength of both of the types of new test blocks, still composed of Haitian materials, dramatically increased to an average over 1.3 tonnes per square millimetre.

?Based upon these results, we believe that Haitian concrete debris can be used as recycled coarse aggregate in new construction,? says Kimberly Kurtis. ?It can work effectively, even if mixed by hand. The key is having a consistent mix of materials that can be measured. We are confident the results can be scaled up in a mix procedure where quantities can be measured using common, inexpensive construction equipment.?

Reginald DesRoches says recycling will solve two hurdles to reconstruction. ?First, the debris is impossible to move because there are few safe landfill sites near Port-au-Prince, and Haiti lacks the trucks and infrastructure to haul it away,? he says. ?It?s better to use it than move it. Second, finding fresh aggregate is more difficult than getting rid of the debris. It is costly to find, mine and truck in.?

Sources: Aggregate Research,

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