Aggregate is the component of a composite material that resists compressive stress and provides bulk to the composite material. For efficient filling, aggregate should be much smaller than the finished item, but have a wide variety of sizes. Aggregates are generally added to increase the strength of composite materials. For example, the particles of stone used to make concrete typically include both sand and gravel . Many construction cement add in aggregates to increase its mechanical strength. Aggregates make up 60-80% of the volume of concrete and 70-85% of the mass of concrete. [1]
28-620: The Portugués Dam (Spanish: Represa Portugués ) is a roller-compacted concrete thick arch dam on the Portugués River , three miles (5 km) northwest of the city Ponce , in Barrio Tibes , Ponce, Puerto Rico . Construction on the dam began in April 2008, soon after the U.S. Army Corps of Engineers , Jacksonville District awarded the Spanish firm Dragados USA , a division of Grupo ACS , with
56-572: A $ 180 million contract in March 2008 to build the dam. The primary purpose of the dam is flood control ; it provides flood protection for 40,000 people and over 13,000 residential structures. The dam is the final component of the Portugués and Bucana Flood Protection Project and the first dam of its type constructed by the U.S. Army Corps of Engineers in the United States or Caribbean . The final cost of
84-481: A 130 ft × 160 ft (40 m × 49 m) Pre-Columbian era ceremonial plaza (" batey " or ball court) used by the ancient Tainos was discovered at a construction site used for disposing of the Portugués Dam's construction rubbish. A 60 ft (18 m) long row of intricately carved stones bearing petroglyphs that appeared to date to the 11th or 12th century was also discovered. Additionally,
112-488: A burial ground containing 40 well-preserved sets of human remains was discovered. Fifteen percent of the site was believed to have been uncovered up to that point and it was reported that as many as 400 bodies may be buried there. The site had been initially marked during a cultural resource survey in 1979 but excavation work in 2007 prompted the major discovery. The Army Corps of Engineers found an alternate rubbish disposal site and performed mitigation work in order to preserve
140-535: A small scale, and form attachments between particles. The matrix is specifically chosen to serve this role, but its abilities should not be abused. Experiments and mathematical models show that more of a given volume can be filled with hard spheres if it is first filled with large spheres, then the spaces between ( interstices ) are filled with smaller spheres, and the new interstices filled with still smaller spheres as many times as possible. For this reason, control of particle size distribution can be quite important in
168-427: A weak matrix will be weak in tension , whereas fibers can be less sensitive to matrix properties, especially if they are properly oriented and run the entire length of the part (i.e., a continuous filament ). Most composites are filled with particles whose aspect ratio lies somewhere between oriented filaments and spherical aggregates. A good compromise is chopped fiber , where the performance of filament or cloth
196-417: Is glass microspheres . Often called microballoons , they consist of a hollow shell several tens of nanometers thick and approximately one micrometer in diameter. Casting them in a polymer matrix yields syntactic foam , with extremely high compressive strength for its low density. Many traditional nanocomposites escape the problem of aggregate synthesis in one of two ways: Natural aggregates : By far
224-422: Is 110 feet (34 m) thick at its base and 35 feet (11 m) thick at its crest. The dam has an uncontrolled spillway center-left side, over the river bed; 21 ft (6.4 m) below the dams crest of 534.6 ft (162.9 m) above sea level. The center of the dam straddles an intake and outlet structure which will draw water from behind the dam and discharge it into the river valley. During excavation,
252-554: Is implemented to orient the particles in micro- or nano-composites, their small size and (usually) high strength relative to the particle-matrix bond allows any macroscopic object made from them to be treated as an aggregate composite in many respects. While bulk synthesis of such nanoparticles as carbon nanotubes is currently too expensive for widespread use, some less extreme nanostructured materials can be synthesized by traditional methods, including electrospinning and spray pyrolysis . One important aggregate made by spray pyrolysis
280-399: Is not included in concrete because it would "absorb" the matrix, preventing a strong bond to other aggregate particles). Particle size distribution is also the subject of much study in the fields of ceramics and powder metallurgy . Some exceptions to this rule include: Toughness is a compromise between the (often contradictory) requirements of strength and plasticity . In many cases,
308-410: Is traded off in favor of more aggregate-like processing techniques. Ellipsoid and plate-shaped aggregates are also used. In most cases, the ideal finished piece would be 100% aggregate. A given application's most desirable quality (be it high strength, low cost, high dielectric constant, or low density) is usually most prominent in the aggregate itself; all the aggregate lacks is the ability to flow on
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#1732869706780336-444: The interface between them, in the manner of a detergent . Since the number of this type of molecule determines the interfacial area, and since spheres naturally form to minimize surface tension , synthetic chemists can control the size of polybutadiene droplets in the molten mix, which harden to form rubbery aggregates in a hard matrix. Dispersion strengthening is a similar example from the field of metallurgy . In glass-ceramics ,
364-478: The 1970s, the U.S. Army Corps of Engineers had been investigating a site to build the Portugués Dam. Despite the many different geographic challenges, the Army Corps was able to choose a suitable dam location and double-curvature thin arch dam design in the 1980s. In the 1990s, foundation test grouting and foundation curtain grouting along with the excavation of 350,000 cubic yards (270,000 m) of material for
392-550: The Financial Means to Satisfy Them). It was a report to the Mayor of Ponce, Luis Porrata-Doria . Up to that point, the recommended solution to control the river had generally been to change its course, but Gandia Cordoba opposed it recommending instead that a dam be created. While other measures were undergone, such as widening the path of the river within the city of Ponce, no dam-building would take place for over seven decades. Since
420-681: The Wikimedia System Administrators, please include the details below. Request from 172.68.168.226 via cp1108 cp1108, Varnish XID 826362724 Upstream caches: cp1108 int Error: 429, Too Many Requests at Fri, 29 Nov 2024 08:41:46 GMT Aggregate (composite) Aggregate composites tend to be much easier to fabricate, and much more predictable in their finished properties, than fiber composites . Fiber orientation and continuity can have an overwhelming effect, but can be difficult to control and assess. Fabrication aside, aggregate materials themselves also tend to be less expensive;
448-594: The aggregate production, and ½ dam RCC placement tasks; Phase 4, at $ 41.1 million, involved the final dam RCC placement, the spillway, and the intake structure jobs; and Phase 5, at a cost of $ 29.7 million included the remaining items, such as the valve house, the access road, and mechanical and electrical structures. As of March 2011, Phase 3 work was underway and the project was 48% complete. The rolled-compacted concrete production facilities had been completed, 700,500 tons of aggregate (for use in concrete) had been produced while foundation preparation continued. RCC placement
476-401: The aggregate will have one of these properties, and will benefit if the matrix can add what it lacks. Perhaps the most accessible examples of this are composites with an organic matrix and ceramic aggregate, such as asphalt concrete ("tarmac") and filled plastic (i.e., Nylon mixed with powdered glass ), although most metal matrix composites also benefit from this effect. In this case,
504-450: The choice of aggregate; appropriate simulations or experiments are necessary to determine the optimal proportions of different-sized particles. The upper limit to particle size depends on the amount of flow required before the composite sets (the gravel in paving concrete can be fairly coarse, but fine sand must be used for tile mortar ), whereas the lower limit is due to the thickness of matrix material at which its properties change (clay
532-435: The correct balance of hard and soft components is necessary or the material will become either too weak or too brittle. Many materials properties change radically at small length scales (see nanotechnology ). In the case where this change is desirable, a certain range of aggregate size is necessary to ensure good performance. This naturally sets a lower limit to the amount of matrix material used. Unless some practical method
560-529: The dam was estimated at $ 375 million; 75% is funded by the U.S. Government and 25% by the Government of Puerto Rico . It is the first dam ever built in the United States that uses the single-centered roller-compacted concrete thick arch technique. An estimated inauguration date of October 2013 was announced in 2011 but was not met. Subsequently, an inauguration date of 28 January 2014 was also announced. The dam
588-501: The dam were requested in 2007 and Dragados USA was awarded an $ 180 million contract in March 2008 to finish the dam project. Construction on the dam began in April 2008 and consisted of five phases. Phase 1, at a cost of $ 24.5 million, included the mobilization, clearing, quarry overburden excavation, power-line relocation activities; Phase 2, costing $ 47.6 million involved the foundation excavation, aggregate production, dental concrete chores; Phase 3, budgeted at $ 37.3 million, comprised
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#1732869706780616-462: The left and right abutments took place. When the dam was advertised for construction in 2000, only one proposal was received, and its cost was over the government's budget. To reduce costs, a five-year technical review program was started to research new, lower-cost designs for the dam. The investigation resulted in a lower cost design, switching from the double-curvature thin arch to a single-centered roller-compacted concrete thick arch. Proposals for
644-493: The mid-20th century), often with matrix materials such as linoleum and Portland cement . In-situ aggregate formation : Many micro-composites form their aggregate particles by a process of self-assembly. For example, in high impact polystyrene , two immiscible phases of polymer (including brittle polystyrene and rubbery polybutadiene ) are mixed together. Special molecules ( graft copolymers ) include separate portions which are soluble in each phase, and so are only stable at
672-419: The most common aggregates mentioned above are found in nature and can often be used with only minimal processing. Not all composite materials include aggregate. Aggregate particles tend to have about the same dimensions in every direction (that is, an aspect ratio of about one), so that aggregate composites do not display the level of synergy that fiber composites often do. A strong aggregate held together by
700-563: The most widely used aggregates for nano-composites are naturally occurring. Usually these are ceramic materials whose crystalline structure is extremely directional, allowing it to be easily separated into flakes or fibers. The nanotechnology touted by General Motors for automotive use is in the former category: a fine-grained clay with a laminar structure suspended in a thermoplastic olefin (a class which includes many common plastics like polyethylene and polypropylene ). The latter category includes fibrous asbestos composites (popular in
728-524: The site, adding $ 3 million in additional project costs. Despite objections of locals, the Army Corps was bound by federal law and had to transport artifacts and human remains to a federally-approved laboratory in Georgia . The artifacts and human remains would, reportedly, be returned to Puerto Rico when the investigation is complete. The site was covered, awaiting future excavation. Roller-compacted concrete Too Many Requests If you report this error to
756-540: Was placed in 47 ft (14 m) of dam. Construction was initially expected to be completed by 2012, but was later postponed. In December 2013 the dam was completed and its inauguration occurred on 5 February 2014. Pending reservoir-filling and testing of the dam, making it operational was announced for early 2015. The Portugués Dam is a 220 feet (67 m) high and 1,230 feet (370 m) long single-centered roller-compacted concrete thick arch. Containing 367,000 cubic yards (281,000 m) of roller-compacted concrete, it
784-749: Was structurally completed in December 2013 and inaugurated on 5 February 2014. The dam is operated by the Puerto Rico Department of Natural and Environmental Resources . The first government official known to have proposed building a dam to tame Rio Portugues from its devastating effects on the lives and properties of Ponceños was Ponce's 1899 Municipal Engineer-Architect Ramon Gandia Cordoba in his 16 March 1899 report titled Estado Actual de Ponce: Sus Necesidades y Medios Economicos para Satisfacerlas (Current State of [the Municipality of] Ponce, its Needs, and
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