Tuesday, December 10, 2013

Stone Mastic Asphalt Details

There are three major types of asphalt surfacing, characterized by a mixture of bitumen and stone aggregate. These are: Dense Graded asphalt (DGA); Stone Mastic Asphalt (SMA) and Open Graded Asphalt (OGA). Asphalt surfacing differs by the proportion of different size aggregate, the amount of bitumen added and the presence of other additives and material. 

Stone Mastic Asphalt
Stone mastic asphalt (SMA), also called stone-matrix asphalt, was developed in Germany in the 1960s. It provides a deformation resistant, durable surfacing material, suitable for heavily trafficked roads. SMA has found use in Europe, Australia, the United States, and Canada as a durable asphalt surfacing option for residential streets and highways. SMA has a high coarse aggregate content that interlocks to form a stone skeleton that resists permanent deformation. The stone skeleton is filled with mastic of bitumen and filler to which fibers are added to provide adequate stability of bitumen and to prevent drainage of binder during transport and placement. Typical SMA composition consists of 70−80% coarse aggregate, 8−12% filler, 6.0−7.0% binder, and 0.3 per cent fiber.

Difference Between SMA & Conventional Mixes:
Stone Mastic Asphalt Composition
Stone Mastic Asphalt Composition
SMA is successfully used by many countries in the world as highly rut resistant bituminous course, both for binder (intermediate) and wearing course. The major difference between conventional mixes and SMA is in its structural skeleton .The SMA has high percent about 70-80 percent of coarse aggregate in the mix. This increases the interlocking of the aggregates and provides better stone to stone contact, which serves as load carrying mechanism in SMA and hence provides better rut resistance and durability. On the other hand, conventional mixes contain about 40-60 percent coarse aggregate. They does have stone to stone contact, but it often means the larger grains essentially float in a matrix composed of smaller particles, filler and asphalt content .The stability of the mix is primarily controlled by the cohesion and internal friction of the matrix which supports the coarse aggregates.

The second difference lies in the binder content, which lies between 5-6 percent for conventional mixes. Below this the mix becomes highly unstable. Above this percent will lead to abrupt drop of stability because the binder fills all the available voids and the extra binder makes the aggregates to float in binder matrix. The SMA uses very high percent of binder > 6.5 percent which is attributed to filling of more amount of voids present in it, due to high coarse aggregate skeleton. The high bitumen content contributes to the longevity of the pavements.

The third difference is the use of stabilizing additives in SMA, which is attributed to the filling up of large number of voids in SMA so as to reduce the drain down due to presence of high bitumen content. On the contrary, there is no stabilizing agent in conventional mixes since the bitumen content is moderate, which only serves the purpose of filling the moderate amount of voids and binding the aggregates

Composition of SMA:

1. Asphalt (Binder)
2. Aggregate
3. Fibers
4. Mineral filler


• High stability against permanent deformation (rutting) and high wear resistance.
• Slow aging and durability to premature cracking of the asphalt
• Longer service-life
• SMA has a higher macro-texture than dense-graded pavements for better friction
• Reduced spray, reduced hydroplaning and reduced noise.
• Good low temperature performance
• Even though SMA has a higher cost than conventional dense mixes, approximately 20 to 25 percent, the advantages of longer life (decreased rutting and increased durability).


• Increased cost associated with higher binder and filler contents, and fiber Additive,
• High filler content in SMA may result in reduced productivity. This may Be overcome by suitable plant modifications,
• Possible delays in opening to traffic as SMA mix should be cooled to 40 oC to prevent flushing of the binder surface, and
• Initial skid resistance may be low until the thick binder film is worn off the top of the surface by traffic.


Friday, December 6, 2013

Engineering Milestone: World's Largest Vessel (Barge)

This is a continuation of a series of articles that tackles different engineering achievement, from world’s tallest building, longest bridge, biggest building, and the likes. Now let’s talk about the world’s largest vessel.

Before going on to the discussion bout the world’s largest vessel, let’s define first “vessel”, “barge”, and a “ship”. A vessel is a craft, especially one larger than a rowboat, designed to navigate on water. A ship is a vessel of considerable size for deep-water navigation. While barge a vessel, usually flat-bottomed and with or without its own power, used for transporting freight, especially on canals.

We defined those 3 so that we will not be confused with their meaning (if ever you’re confused). So let’s now continue.
Prelude- world's largest vessel
This one is longer than the height of Empire State Building; its storage tanks have a capacity equivalent to 175 Olympic-size swimming pools. It was designed to endure a category-five typhoon, and will be in service for around 25 years. The South Korean shipbuilder Samsung Heavy Industries floated “Prelude” the partially 1, 601-feet long and 600, 000-ton vessel off the southern shipyard in Geoje on November 30, 2013. It’s a floating liquefied natural gas (FLNG) platform, commissioned by the Dutch energy company Shell, the facility is due to be delivered by September 2016.

Prelude - World's largest barge
Prelude would operate in a remote basin around 475 kilometers (295 miles) northeast of Broome, a town in Western Australia to tap offshore gas. It is 74 meters wide and 11 meters high, and it is expected to produce 3.6 million tons a year (mtpa) of LNG, and 5.3 mtpa of liquids and other hydrocarbons. As for comparison, Shell’s US-based rival Chevron, leads the development of “Gorgon” a lan-based producing plant. Gorgon is expected to produce 15.6 mtpa when it is done in early 2015. But Gorgon is more expensive than Prelude, the former is estimated to cost around $US 52B while the latter is estimated on $US 12B.

Prelude can produce enough gas to supply a city the size of Hong Kong. It is not yet finished but Shell’s technicians are already designing a larger and tougher vessel than Prelude.


Wednesday, December 4, 2013

Engineering Milestone: World's Largest Airplane

This is a continuation of a series of articles that tackles different engineering achievement, from world’s tallest building, longest bridge, biggest building, and the likes. Now let’s talk about the world’s largest airplane.

If you wanted to lift a 200-ton cargo and transfer it to another place what you’re going to do? Well for Antonov An-255 Mriya, that’s just an easy task. Mriya is a strategic airlift cargo aircraft designed by the Soviet Union’s Antonov Design Beareau in 1984 – 1988. It’s been created to do the following missions:
  • Transportation of the wide-range of cargo (large-sized, heavy, long-size) with total weight up to 250 ton.
  • Intercontinental non-stop airlift of cargoes weighting 180−200 ton.
  • Intercontinental airlift of cargoes with weight up to 150 ton.
  • Transportation of a heavy large-size single pieces with weight up to 200 ton on the external store.
6 turbofan engines power it and it is the heaviest aircraft with a maximum takeoff weight of 640 tons and the biggest heavier-than-air aircraft in terms of length and wingspan in operational service.
Mriya An-255

Its first flight took place on December 21, 1988. It is one of the 2 An-255 aircraft that Antonov/Soviet Union planned to create. The other one have never been completed as of now. In May 2011 Antonov CEO is reported to have said that the completion of a second An-225 Mriya transport aircraft with a carrying capacity of 250 tons requires at least $300 million, but if the financing is provided, its completion could be achieved in three years. According to different sources, the second jet is 60–70% complete.
The modernization of Mriya started in 2000, the aim was to use it for commercial purposes, which transport different cargoes. The decision had been taken due to many applications sent to Antonov Airlines for transportation of cargoes heavier than the AN-124-100 Ruslan’s payload. On May 23, 2001, the Mriya passed the certification tests. Aviation Register of Interstate Aviation Committee (AR IAC) and Ukraviatrans issued type certificates to the An-225.

An-255 has a 43.32-meter length, 6.4-meter width, and 4.4-meter height of cargo compartment. That space allows the cargo to carry several cargoes inside like:
  • Sixteen standard aeronautical containers of UAC−10 type.
  • 50 cars.
  • Single piece of cargoes up to 200 t (turbines, generators, dump trucks − Belaz, Kamatsu, Euclid, etc.).
The following are the specification of An-255:

General characteristics:

  • Crew: 6
  • Length: 84 m (275 ft 7 in)
  • Wingspan: 88.4 m (290 ft 0 in)
  • Height: 18.1 m (59 ft 5 in)
  • Wing area: 905 m2 (9,740 sq ft)
  • Aspect ratio: 8.6
  • Empty weight: 285,000 kg (628,317 lb)
  • Max takeoff weight: 640,000 kg (1,410,958 lb)
  • Fuel capacity: 300000 kg
  • Cargo hold – volume 1,300m3, length 43.35m, width 6.4m, height 4.4m
  • Powerplant: 6 × ZMKB Progress D-18 turbofans, 229.5 kN (51,600 lbf) thrust each

  • Maximum speed: 850 km/h (528 mph; 459 kn)
  • Cruising speed: 800 km/h (497 mph; 432 kn)
  • Range: 15,400 km (9,569 mi; 8,315 nmi) with maximum fuel; range with maximum payload: 4,000 km (2,500 mi)
  • Service ceiling: 11,000 m (36,089 ft)
  • Wing loading: 662.9 kg/m2 (135.8 lb/sq ft)
  • Thrust/weight: 0.234

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