Bituminous Surface Dressing 715q2r

Bituminous Surface Dressing (BSD) • Thin film of bituminous binder is sprayed on the road surface covered by a coat of mineral aggregate sand rolled • Functions – Thin wearing course of pavement and protect base course – Water proof the pavement surface and prevent surface water infiltration – Provide dust free surface in dry weather and mud free surface in wet weather

Seal Coat • Top coat over pervious bituminous pavements such as premixed carpet and grouted macadam • Thin surface treatment or single coat dressing applied over an existing black top surface • Functions – Seal surfacing against water ingress – Develop skid resistant texture

Built–up Spray Grout (BUSG) • Two layer composition of compacted crushed aggregate sand application of binder after each layer for bonding and finished it aggregate sat the top • Total Thickness–75mm • Suitable for strengthening of existing bituminous pavements • Wearing course is provided over this layer

Penetration Macadam • Used as binder or base course • Coarse aggregates are spread and compacted and then hot bituminous binder of high viscosity is spread at the top • Bitumen penetrates the void sand binds the aggregates together

Premix methods • Aggregate sand binder are mixed before spreading and compacting • Classified based on gradation of aggregates chosen as – Open Graded – Semi dense and dense mixes Common types are Bituminous Macadam Bituminous Carpet

Bituminous Concrete

Bituminous Macadam • Consist of one or more courses of compacted aggregates premixed with binder, laid immediately after mixing • Laid in compacted thicknesses of 75mm or 50mm • Essentially a base course or binder course and should have surfacing • Superior to other base course materials w.r.t load dispersion and durability

Bituminous Premixed Carpet • Coarse aggregates of 12.5 mm and 10mm size premixed with binder and compacted to thickness of 20 mm to serve as a base course • Should be covered by a sealcoat • Semi‐dense carpet‐Well graded aggregate is used for construction of bituminous carpet of thickness 20 or25mm

Bituminous Concrete or Asphaltic Concrete • Densegradedpremixedbituminousmixthatiswellc ompactedtoformapavementsurfacecourse • Mixture of coarse aggregates, filler and fine aggregates • Thickness–40‐75mm • IRC specification–40mm thick course for highway pavements

AC surface

Sheet Asphalt • Dense sand– bitumen pre‐ mix used as wearing course–compacted thickness of 25mm • Well graded coarse to fine sand without coarse aggregate sand bitumen • Laid over cement concrete pavement • Protects ts and helps in reduction in warping stresses

Mastic Asphalt • Mixture of bitumen, fine aggregate sand filler • Whencooledresultsinahard,stableanddurabl elayerthatwithstandsheavytraffic • Absorbs vibrations • Suitable surfacing material for bridge deck slabs

Bituminous Construction Procedures • Surface Dressing • Grouted or Penetration Macadam • Built‐up Spray Grout • Bitumen bound Macadam • Bituminous Carpet • Bituminous Concrete

Surface Dressing (BSD) • Done in either single coat or in two coats over an existing pavement for renewal or as a wearing course over a WBM road • Bitumengrades–80/100

• Construction Steps – Surface Preparation – Application of binder – Application of stone chippings – Rolling of first or final coat – Application of binder and stone chippings for second coat – Rolling of second coat – Finishing and opening to traffic‐ after 24 hours

Bituminous Concrete Construction • Proper design of mixes–essential • Dense grading of coarse aggregates, fine aggregate sand mineral fillet coated with bitumen binder • Prepared in a hot‐mix plant • Thickness depends on traffic and quality of base course

• Construction Steps – Preparation of existing base course layer – Application of tack coat– 6 ‐ 7.5kg of bitumen per10 m2area – Preparation and placing of premix • Bitumen heated to1500C–1770C & aggregate temperature should not difer by over 140C from binder temperature • Spreadatatemperatureof1210C‐1630C

– Rolling – Initial – 8‐ 12 trolled & intermediate– 15‐30t ; final– 8‐ 12t roller – Quality Control– Bitumen grade, temperature of aggregate, temperature during mixing and compaction Marshall Tests conducted 1 sampleoutofevery100tofmixdischarged is tested Forevery100 m2of compacted surface, one field density test is done Variation in thickness–6mm per 4.5mofconstruction – Finished surface‐checked for longitudinal undulations – not greater

than 8mm.

Cement Concrete Pavements • Excellent riding surface & pleasing appearance • Longer life • Design on rational basis • Cost saving and excellent performance • High initial investment • ts–planes of weakness • Curing period‐necessary

Construction of Cement Concrete Pavement Slab • Cement grouted layer course

Suitable for base

• Rolled concrete layer • Cement Concrete slab – Cement grouted layer • Opengradedaggregatemixwithaggregat eshavingmaximumsize–18‐25mm‐ dryrolled • Cement grout is applied on the surface ‐

Rolled Concrete layer

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Lean mix concrete issued

Methods of Construction • Alternate Bay Method–constructing a bay or one slab in alternate succession leaving the next to immediate bay to follow up after a gap of a week • Advantages •

Working convenience for slab laying

• t construction easier Disadvantages Large no of transverse ts to be provided •

Complete diversion of traffic necessary

Continuous Bay Method ‐ preferred 34

Material Specifications • Cement– OPC or Rapid Hardening Cement • Aggregates – Max size not greater than one fourth slab thickness – Gradationofcoarseaggregate–50 to4.75 mm or 40 to 4.75 mm in two size ranges, one below and the other above 20mm – Crushing value ‐30%max – Impact value–30%max – Los Angeles Abrasion value–35% max as per IRC Fine aggregate– natural sand or

crushed stone Concrete–Min Modulus of Rupture of 40kg/cm2 after 28 days of curing or compressive strength of280 kg/cm2

Plants & Equipments required • Concrete Mixer & Batching Device • Vibrating Screed

Plants & Equipments required • Internal Vibrators • Straight Edge • Belt • Fibre Brush • Edging Tool

Construction Steps • Preparation of Sub grade and Sub‐base – Uniformly compacted sub grade –extending 30cmoneithersideofwidthtobeconcreted – Properly drained – Min ‘k’ value of 5.54 kg/cm2 – To be kept in moist condition – Water proof paper to be placed in case concrete is placed directly over sub grade

• Placing of Forms – Steel or wooden forms • Batching of material and Mixing • Transporting and Placing of concrete • Compaction and Finishing • Floating and Straight Edging • Belting, Brooming and Edging • Curing

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