CHAPTER 6 SMALL ELEMENT PAVEMENTS - TU Delft

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RetainedOn sieveC63C45C31.5C22.4C16C8C42 mm63 µmnatural stone, blastfurnace slags,phosphorus slags,masonry granulate,mix granulate,concrete granulateMaterialshydraulic mixgranulatemix of blast furnaceslags and phosphorusslagsmin. max. min. max. min. max.-0-0-00 10 0 10 0 10------------10 40 10 40 10 40------40 70 40 70 30 7060 85 60 85 50 8094 100 ----Table 6.3 : Grading requirements (percentages by mass) for unbound and lightlyboundbase materials in The Netherlands (5).The most widely used base materials in concrete block pavements are mix granulateand hydraulic mix granulate (8).Mix granulate, a recycled material, is a mixture of crushed concrete (min. 50% andmax. 80% by mass) and crushed masonry (max. 50% by mass). The CBR-value of the‘fresh’ material (0 days), CBR 0 , should be at least 50%, while after 28 days the CBRvalue,CBR 28 , should be at least 1.25 * CBR 0 . (5).Hydraulic mix granulate is a mixture of mix granulate and hydraulic slags (between 5%and 20% by mass). The requirements for the CBR-value are on one hand CBR 0 atleast 50% and on the other hand CBR 28 at least 1.5 * CBR 0 (5).In the case of small projects (less than 3000 m 2 ) the degree of compaction should beat least 98%. For larger projects (more than 3000 m 2 ) the degree of compaction shouldbe at least 97% while the average degree of compaction should be at least 101%.The thickness of the unbound or lightly-bound base is dependent on the traffic loading,the bearing capacity of the underlying layers (including the subgrade) and theproperties of the base material itself. In practice the thickness of the base is between200 and 400 mm.In the case of an unbound or lightly-bound base the subgrade remains rather easyaccessible to install, expand or repair underground services like cables and piping.6.3.5 Sub-base:The sub-base of a pavement structure may have the following functions:- raise the road surface above the ground surface- protect the pavement structure against frost/thaw-damage- soil improvement, i.e. replacement of unsuitable subsoil- platform for construction of the overlying pavement layers195
- further spreading of the traffic loadings, in such a way that neither in the sub-basenor in the subgrade unacceptable permanent deformations occur.Because of these functions the thickness of the sub-base is dependent on the designroad surface level, the frost penetration depth, the traffic loadings, the bearing capacityof the subgrade and the properties of the sub-base material.In The Netherlands (nearly) always sand is used for the sub-base (because of itsavailability and the lack of other natural road building materials). A distinction is madebetween ‘sand for sub-base’ and ‘sand for fill’ (5).‘Sand for fill’ is used at a depth of more than 1 m below the road surface, so below thedepth of frost penetration. It must consist of material in which particles smaller than2 µm are present up to a maximum of 8% by mass. The amount of particles passingthe 63 µm sieve must be not more than 50% by mass. The degree of compactionshould be at least 93% MPD (Maximum Proctor Density) and the average degree ofcompaction should be at least 98% MPD.‘Sand for sub-base’ is applied at a depth of less than 1 m below the road surfacewhich means that it may be within the depth of frost penetration and that it clearly issubjected to traffic load stresses. Of the particles passing the 2 mm sieve, the amountof particles passing the 63 µm sieve must be not more than 15% by mass. If thisamount is between 10 and 15% by mass, then, of the particles passing the 2 mmsieve, the amount of particles passing the 20 µm sieve must be not more than 3% bymass. The degree of compaction should be at least 95% MPD and the average degreeof compaction should be at least 100% MPD.6.3.6 Edge restraints:An adequate edge restraint (figure 6.7) is very essential for every small elementpavement. The edge restraint has to lock up the small element toplayer and thebedding sand layer in the horizontal direction. The edge restraint has to be such heavythat is can resist the horizontal stresses introduced by traffic loadings in the vicinity ofthe edge restraint. The required mass of the edge restraints therefore is dependent onthe magnitude of the axle loadings on the adjacent small element pavement.The edge restraint needs to be supported at the backside by a well compacted vergeor a footway. For extremely heavily loaded concrete block pavements (such as oncontainer terminals) even a concrete backfilling of the heavy edge restraint usually isapplied.For lightly loaded small element pavements (footways, bicycle tracks, etc.) rather light‘confining edge restraints’ are adequate; however, small element pavement structuressubjected to normal road traffic require quite heavy ‘footway edge restraints’ (figure6.11).In the Dutch specifications for precast concrete edge restraints (9) the followingprofiles are distinguished (figure 6.11):footway edge restraints:130/150 * 160 mm 2 , 130/150 * 200 mm 2 , 130/150 * 250 mm 2180/200 * 160 mm 2 , 180/200 * 200 mm 2 , 180/200 * 250 mm 2confining edge restraints:50 * 150 mm 2 , 60 * 200 mm 2 , 80 * 200 mm 2 , 100 * 200 mm 2 , 120 * 250 mm 2 .Straight precast concrete edge restraints have a length of 1 m. Furthermore curvededge restraints are available.196
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CHAPTER 6 SMALL ELEMENT PAVEMENTS - TU Delft

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