Sectiunea transversala a Structurii unui Drum

Sectiunea transversala a Structurii unui Drum este compusa din urmatoarele componente:\n

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1. Sub Baza
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2. Stratul de Baza
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3. Sub Grade
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4. Suprafata/Stratul de uzura
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1. Sub Baza:

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• Este stratul de material granular aflat deasupra unui subgrade generally natural gravel. De obicei, nu este provided on subgrade de buna calitate.
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a. Functia de Sub baza in Sectiunea transversala a Drumului

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• Permite ca tensiunile din trafic sa fie reduse la nivele acceptabile in subgrade.
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• Functioneaza ca o platforma de lucru pentru constructia straturilor superioare de pavaj.
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• Functioneaza ca un strat de drenare, protejand the subgrade de udare.
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• Intercepteaza miscarea in sus a apei prin actiune capilara.
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• Functioneaza ca un strat separat intre subgrade si baza drumului. Prin aceasta se previne ca cele doua straturi sa se amestece.
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b. Caracteristicile materialelor folosite in Sub Baze:

\nMaterialul de subgrade va fi curat si fara materiale organice si vor putea sa fie compactate cu un roller, pentru a forma o sub-base stabila. Materialul va avea urmatoarele caracteristici.\n

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• Well graded uniformity coefficient (D60/D10) should not be less than 3.
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• Fraction passing sieve #200 shall not be greater than 2/3rd of the fraction passing sieve #40.
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• Va avea un L.L nu mai mare de 25%.
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• P.I nu mai mare de 6
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• CBR nu va fi mai mic de 25.
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• In coarse grain, aggregate retained by #10 sieve, %age of wear shall not be greater than 5%.
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• Diametrul maxim al oricarei particule nu va fi mai mare de 2/3 din grosimea stratului sub-basei.
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• Typical particle size distribution for the sub-base (granular) when will meet strength requirement are
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B.S Sieve Size	% By mass of total Aggr passing test sieve
50	100
37.5	80-100
20	60-100
5	30-100
1.15	170-75
0.3	9-50
0075	5-25

\n* To avoid intrusion of silt and clay material in sub-base from subgrade

D15 (sub base) < 5

D15 (sub grade)\n

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• Recommended plasticity characteristic for granular Sub Base (Road Note 31) are;
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\n Climate \n	\n Liquid Limit (L.L) \n	\n Plasticity Index (P.I) \n
\n Moist or wet tropical \n	< 35	< 6
\n Seasonal wet tropical \n	< 45	< 12
\n Arid & Semi Arid \n	< 55	< 20

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2. Straturi de Baza

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• Este stratul imediat de sub suprafata de uzura (Se aplica daca suprafata de uzura este bituminoasa sau din beton de ciment).
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• Deoarece stratul de baza se intinde imediat sub suprafata pavajului, este supusa la incarcari severe. Materialul dintr-un strat de baza trebuie sa fie de o calitate extrem de inalta calitate si constructia sa trebuie sa fie facuta cu multa atentie.
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a. Tipuri de Straturi de Baza

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1. Strat de baza granular:

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Un amestec de particule de sol pornind de la brute pana la fine. Processing involve crushing oversized particles and screening where it is necessary to secure the desired grading. The requirements of a satisfactory soil aggregate surface are;\n

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• Stability
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• Resistance to abrasion
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• Resistance to penetration of water
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• Capillary properties to replace moisture lost by surface evaporation upon the addition of wearing course requirement change.
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2. Baza din Macadam:

\nStraturi succesive de piatra zdrobita mecanic locked by rolling and bonded by stone screening (rock duct, stone chips etc).

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3. In-water bound Macadam:

\nThe crushed stones are laid, shaped and compacted and then finer materials are added and washed into surface to provide a dense material.\n

4. Baze tratate:

\nCompose of mineral aggregate and additive to make them strong or more resistant to moisture. Among the treating agents is bitumen.

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4. Stratul de Suprafata/Uzura:

\nSunt straturile superioare de pavaj care sunt in contact direct cu rotile vehiculului. De obicei sunt construite din materiale in care bitumul este folosit ca liant.\n

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a. Pavaj bituminos:

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\nConsta din combinatii de agregate minerale cu un liant bituminos incepand de la un tratament ieftin de suprafata de ¼ in sau mai subtire pana la beton asfaltic.

Pentru o buna functionare pe toata durata sa de viata, pavajul bituminos trebuie sa aiba urmatoarele calitati:\n

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• Freedom from cracking or raveling.
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• Resistance to weather including the effect of surface water heat and cold.
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• Rezistenta la umezeala interna, mai ales la vaporii de apa.
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• Suprafata puternic impermeabila sau poroasa (în cazul în care este necesara stabilitatea de izolare fata de suport sau subgrade).
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• Smooth riding and non skidding surface.
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\nDesignul va fi facut astfel incat sa indeplineasca cerintele de mai sus pentru un numar considerabil de ani (necesita proiectare corecta si supervizare a constructiei).

Pavement meeting all the requirements above have been product if six distinctly different construction processes as follows.\n

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• Heat a viscous bituminous binder to make it fluid, then in a plant mix it with heated aggregate place and compact the mixture while it is hot.
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• Use fluid bituminous binder, mix it with aggregate at normal temperature. Mixing may be done at a plant (plant mix) or on the prepared roadway base (road mix). Spread and compact the mixture at normal temperature.
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• Add solvent such as naphtha or kerosene to a viscose bituminous binder to make it fluid with aggregate at normal temperature by either plant or road mix methods. Spread and compact at normal temperature before solvent evaporates.
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• Use fluid emulsion of viscose bituminous binder in water, mix it with aggregate at normal temperature by either plant or road mix method. Spread and compact at normal temperature before the emulsion breaks down with its components.
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• Spread and compact clean crushed aggregate as for water bound macadam. Over it spray heated dissolved or emulsified bituminous binder which penetrates open areas of the rock and binds the aggregate together. Thus is commonly called “Penetration Method”.
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• Spread bituminous binder over the roadway surface then cover it with properly selected aggregate. This is commonly called the “Inverted Penetration Method”.
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\nSelections based on the requirements and economy, large volume of heavy vehicles, low traffic volume etc.