On August 15, 2007, an earthquake, with a magnitude of 7.9 degrees on the Ricther scale, struck the Peruvian coast and affected the cities of Pisco, Ica and Cañete.
About 70 percent of the buildings, some considered as national monuments, the majority built in adobe material, collapsed. Those of cement and brick did not resist the earthquake either. The result: 16,669 homes destroyed and 80,000 damaged. Pisco, a city of 116,865 inhabitants, was the most affected. There, about 39.10 percent of its citizens lived in adobe and brick houses, while in Ica, with 290,000 inhabitants, 47 percent were built in these materials. And in Cañete, 43 percent.
In Colombia, according to official figures from the last census of 2005, carried out by the National Administrative Department of Statistics, Dane, about 16 percent of the houses have been built in adobe, mud or bahareque.
Villages located in Cundinamarca, Boyacá and Cauca, among others, are characterized by constructions made with materials on land. How to protect these houses from events like the ones that happened in Peru? Can homes with 100 or more years of history be saved from a possible earthquake? A new study, carried out by the Taller de Arquitectura en Tierra of the School of Architecture and Urbanism of the National University of Colombia, led by professor Clara Eugenia Sánchez, has analyzed this type of buildings in our country.
Investigations have found that the adobe, the tread wall and the pressed earth block serve to reinforce and build houses with an earthquake resistant property. Tradition and modernity
According to several connoisseurs of the topic of construction on land, to speak of houses made of adobe, tread wall or block of earth is to refer to the most economical and ancestral way that is known in terms of architecture. The first adobe buildings were built 7 thousand years B.C. Today adobe buildings are being built in countries such as Iran, Afghanistan and Iraq. In Latin America there are cities built with this same material, such as Antigua, in Guatemala, declared a World Heritage Site.
For Professor Sánchez, the history of these materials hides both ancient and modern techniques. "There are between 12 and 34 methods to build with earth, among which there are some systems, such as direct casting, with which some of the most famous mosques in the world were built," he said.
According to the study of the Architecture Workshop, the composition of the earth to make adobe are: sands, silts and clays. “Although ancient adobes have been studied, some types of coarse grains, close to 12 millimeters, have been found. However, the most important percentages in its components are in the following ranges: sand, 55 to 75%; silts, 10 to 28%, and clay, between 15 and 18% ”, he said. Sánchez explained that other elements used to make adobe are cattle excrement, because it contains high levels of fiber, and tamos, which are residues from the barley or oat harvest.
Because of the earthquake resistance
Knowing some of the usual materials in the manufacture of these blocks of earth, the investigation found the keys to make them earthquake resistant: “One of the basic principles is their behavior as a masonry. Adobe is a small masonry or block that is associated with others to form walls, roofs and vaults, ”said Professor Sánchez.
The study established that among the techniques used by experts, the thickness of adobe compared to brick plays an important role. “The adobe is taken, modeled and worked with the mixture and a little fine sand is added to it to give it resistance. The same goes for the earth block. The blocks do not need to be glued on the tread wall, but yarns are compacted one on top of the other ”, added Sánchez.
The teacher emphasizes that to build earthen houses, three principles must be taken into account, which influence them to be earthquake resistant and safe: the raw material, the context where it is developed (climatic conditions) and the geographical conditions. Therefore, if all these requirements are met, they will probably last up to 100 or 200 years in good condition.
With the use of X-ray diffraction equipment and tests in the laboratories of the National University in Manizales, the Taller de Arquitectura en Tierra found in the analysis of the 100 or 120-year-old adobe blocks brought from Boyacá weathered wheat, barley and cattle manure. Fibers that "persist today because time has shown that these elements remain," said Sánchez.
Another element that was identified was a type of grass called mouse tail, which is used for decks or roofs in mountain areas, which helps to reinforce the mixtures to make adobe.
The adobe was also proven to be weatherproof.
Among the tests to check how seismic resistant the adobe blocks are, Jenny Vargas, one of the members of the Workshop, explained that several samples have been analyzed, to know the composition of the material that would help make the whole seismic resistant.
"With this equipment it was proposed to advance the analysis of crystalline materials, with the use of X-ray photoelectron emission spectroscope, which allowed determining the chemical composition of the elements of the sample and the weight percentage of each one," said Vargas .
During the process, the report made by the Plasma Physics Laboratory of the La Nubia campus in Manizales indicated that the properties of the material found in an adobe, from a demolished house in Tunja, Boyacá, contained different organic and inorganic chemical components.
“Among the elements found were berlinite, halloyste, silicon dioxide and silicon sulfide. In other samples, quartz and montmorillonite were detected, which allow us to understand the resistance and durability of the materials, ”Vargas indicated.
According to Vargas, in a seismic movement, adobes adapt to the movement of the wave, while brick, due to its rigidity, does not resist the wave. “In addition, there are fibers in the adobe and it is possible to make adjustments, taking advantage of those advantages it has. But also one of the most important conclusions that must be taken into account is that a building with adobe should not be seen as a single unit, but rather the set of blocks that make it up, ”said Professor Sánchez.
Another significant point is that the thicknesses are an important factor for the adobe to have a good performance against the lesser thickness of a brick wall.
Likewise, the investigation took into account the norms established by Colombian law regarding masonry and buildings with earthquake-resistant components. It was found that houses built in adobe have an adequate response to earthquakes, due to the use of good elaboration techniques. In Colombia, the man of the coffee zone, Cundiboyacense and Cauca, after the earthquake of Popayán in 1984, used elements that allowed him to stabilize his constructions with the use of fibers and earth.
National university of Colombia