Problemática psicoafectiva derivada de las prolongadas hospitalizaciones

Resurfacing is the placement of fresh material on an existing surfacing to enhance its structur-al strength. Asphstructur-alt resufacing is the most pop-ular method of pavement rehabilitation in Malaysia. When done properly, this method is appropriate since the addition of new layers strengthens the road pavement making it capa

Figure 5.6. Methods Of Reducing Reflection Cracks Using Interlayers

raelled, and those that are bleeding. Proper evaluation of the existing pavement condition is neccessary to determine the extent of pre-treatment required. The following paragraphs describe some of the aspects that should be considered prior to resurfacing.

Resurfacing on Cracked Surfaces Cracks occur frequently on roads in Malaysia.

These cracks should be treated early to stop ingress of water into the road base layer there-by weakening it. The common practice of over-laying the cracked pavements without prior treatment to the cracked surface. causes the cracks to reflect through the new layer as early as within 3 months depending on the deflection of the road section and the traffic level. It is therefore very important that cracked surfaces must be treated before overlay. Alternatively, more expensive techniques such as using inter-layers to absorb the stresses and strains of the crack tips can be used.

One common pre-treatment method is to 'cut and patch' before overlay. This results not only in delaying reflective cracking but it also gives a slight increase in the strengnh of the pave-ment.

The rate of progression of the cracks reflecting through the new asphaltic layer depends on the structural strength of the pavements. Pavements with higher deflection. causing higher crack movements, tend to be the first to crack.

Another method of reducing reflection cracks is by introducing a separating layer (Figure 5.6) to absorb the stresses from the crack move-ments. An example of this stress-absorbing layer is the geosynthetic material. There are many types of geosynthetic materials available, and most of them claimed to be effective in mitigating reflection cracks. However, the con-struction procedures have to be properly looked into to ensure that the geosynthetic materials are laid in accordance to the manufacturer's specifications.

There are basically two types of geosynthetic

materials available in the market, the grid and the non-woven geotextiles. When using the grid, care should be taken to reduce the

possibility of the picking up or stretching the grid by lorry tyres. When this happens, the grids will warp and the resultant displacement of the grids will lead to poor compaction of the asphalt layer. This leads to cracking. On the other hand, if the non-woven materials are used, care should be taken on the amount and type of tack coat used. If used in excess, the nonwoven material will become saturated and will lead to bleeding. If the bitumen tack coat is too soft the material can slide at the exsiting road/material interface.

Other types of Stress Absorbing Membrane Interlayers (SAMI) are also available. These can be in the forms of aggregate interlayers (e.g. surface dressings) or modified bitumen with or without chippings. At 1KRAM studies are being carried out on the use of some of these interlayers. Laboratory experiments are also being carried out on the manufacture of SAMIs using natural rubber blended into bitu-men.

Crushed aggregates have also been used as an interlayer. This method has perform positively even with crack movements of l.5mm. In one of the trials constricted by IKRAM, the crushed aggregates were laid on top of segmented con-crete pavement where the movements at the joints were substantial. Previously, asphalt overlays without prior treatment Nvould only last about 2 months. But with this method, the cracks from the concrete.joints have vet to come through after a couple of years.

Resurfacing on Rutted Surfaces Resurfacing ou existing pavements with sur-face nits require special considerations. Dense bituminous surfacings nit when it loses its sta-bility properties. These usually occur in areas where there are prolonged loading periods of slow moving or stopped heavy vehicles, namely at climbing lanes and at intersections.

The high stresses imposed on the asphalt layer causes it to densify and with the reduction in

voids in the mix, the mix becomes unstable.

This layer must be removed by milling prior to overlaying it with a fresh asphalt layer.

Bituminous mixes designed by the Marshall method have been shown to perform poorly in high stress areas. To counter this, polymer modified bitumen can be used in asphaltic con-crete on climbing lanes and junctions. The rate of rutting of these mixes are slower than the normal asphaltic nixes. However, the use of the polymer modified bitumen can increase the cost of the asphalt to double its normal cost.

In an effort to find a cheaper solution to the above problem, IKRAM has introduced a new mix for the surfacing, called the HCM

Bituminous Surfacing. The mix was tried in a trial at the Bukit Tinggi climbing lanes along the Kuala Lumpur - Karak Highway. In the same trial, other mixes using polymers and additives were also tried. After nearly 3 years in service, the HCM Bituminous Surfacing has performed on par to the more expensive poly-mer modified wearing courses.

Resurfacing on Bleeding Surface

If the existing pavement surface which needs strengthening is suffering from bleeding, it is advisable to consider the possibility of the excess bitumen migrating into the new layer.

The application of hot sand should be consid-ered.

Resurfacing on Corrugated Surface If corrugations are the result of unstable surfac-ing materials, it should be replace before resur-facing. If it is due to unstable granular pave-ment layers then partial reconstruction will be a better solution.

Resurfacing on Ravelling or Weathered Surfaces

If the existing surface is experiencing ravelling and loss of aggregates, no pre-treatment is nec-essary.

Cost :

A major portion of the cost in carrying out a structural resurfacing job goes to the pretreat-ment works. The cost of the asphaltic concrete itself is around RM 10.00 per square metre, whilst the costs of pre-treatment such as the use of grid geosynthetic materials may push the cost up by between RM 8.00 to RM 20.00 per square metre. The use of fabric geosynthetic materials would reduce the total construction cost as the fabrics may add about 30-40% more to the cost.

Reliabilitv :

Structural resurfacing can last the design life if proper pre-treament work is carried out. Most of the resurfacing works which show early signs of distress are due to improper pre-treat-ment works.

5.5 RECONSTRUCTION

Description: Reconstruction is the removal and rebuilding of all (including subgrade) or part of the road pavement using fresh material and new construction specifications. Pavements that have failed Beverly are usually those where deterioration has been allowed to occur without maintenance. The condition of thee

lower granular layers of the pavement is best determined by destructive testing.

There are two types of reconstruction, namely, full reconstruction and partial reconstruction.

Full reconstruction is needed when the sub-grade layer as well as the pavement layers has deteriorated beyond repair. In full reconstruc-tion, the rebuilding includes the subgrade.

Partial reconstruction is needed when the road base has been contaminated and it has lost its inherent stability. In this case the rebuilding does not include the subgrade.

In the case where the failure of the road base is extensive and conventional partial reconstruc

tion method is uneconomical, it is advisable to carry out recycling. Recycling of the road base is a partial reconstruction alternative where the existing surfacing and/or part of the road base is pulverised, and replaced as a new road base layer. The process breaks up the existing asphalt layer into small pieces thereby remov-ing existremov-ing cracks and at the same time allow-ing addition of road base thickness. It therefore can be used to eliminate reflective cracking problems and correct thickness deficiencies.

Base recycling is suitable where the deteriora-tion of the surfacing has become so extensive that partial reconstruction option will not be economical. The deterioration can be due to a Plate 5.8. Reconstruction Works

Plate 5.9. Recycling For Base

poor road base layer or insufficient base thick-ness. Additional aggregates and stabilisers can be included in the mix to improve its perform-ance.

Among the common stabilisers suitable for base recyling are :

i) cut-back bitumen ii) cement

iii) bitumen emulsion

The correct choice of stabilisers will depend on the existing pavement material type, its condi-tion and composicondi-tions.

Condition or Use :

Identifying areas needing reconstruction requires evaluation of the pavement conditions.

However, experience has shown that the fol-lowing rule-of-thumb to be reasonably accept-able in identifying localised reconstruction

areas:

Identifying full reconstruction

Full reconstruction may be needed for the fol-lowing combination of failures.

i) Pavement surface which suffer from crocodile cracks with rut depths of more than 25 mm, without shoving.

ii) Pavement surface which suffers crack ing with rut depth of more than 15 mm and deep shoving.

Identifying partial and base reconstruction Partial reconstruction may be needed for the following failures or combination of failures.

i) Spalling and crocodile cracking with rut depth of less than 15 mm.

ii) Shoving with rut depth less than 15 mm.

Figure 5.7. Full Reconstruction

iii) Crocodile cracking with block size less than 100 mm with shoving.

Confirmatory test using the Dynamic Cone Penetrometer (DCP)

If the site engineer is not certain of the extent of reconstruction required, the DCP can be used to estimate the pavement layer strength and thus identify which materials needs to be removed. Partial reconstruction can be carried out if it is not necessary to replace the subgrade or the sub-base.

Construction :

Reconstruction requires more lane closure time than resurfacing, since the work includes breaking up the pavement, removal and

rebuilding of existing layers. The time taken for a partial reconstruction is less than that for the full reconstruction.

Allowances should be made for the possibility of secondary compaction of the reconstructed areas by opening them to traffic for a period of time before applying the final overlay.

Particular attention should be given to the pro-vision of adequate drainage when reconstruct-ing roads with high water table.

Marking the areas to be reconstructed Marking of the areas to be reconstructed is best done a few days before construction.

Temporary marking can be used if contruction is to follow immediately otherwise permanent marking can be carried out. It is advisable to extend the area needing reconstruction beyond the area over which it occurs. Marking is best carried out by experienced personnel in identi-fying serious pavement defects. This task is critical in optimising the probability of success of the rehabilitation job.

Construction of Base Recycling

The construction ol` recycled stabilised base normally requires specialised machinery.

Standard construction method may not be

suit-able and can be expensive. The works involved in base recycling are:

Pulverisation or ripping

Mechanical pulverisors can break up any of the the pavement layer and reduce it to uniform sizes. The pulverised materials should be inspected where all large pavement chunks and organic substances should be removed.

Addition of stabilisers may_ be introduced at this stage.

Stabiliser distribution

Cement stabilisers can be spread by a bulk spreader or manually depending on the job size. The spread rate, water content and mixing process is critical for efficient stabilisation.

Bituminous stabilisers are mechanically spread and are seldom used for base recycling.

Compaction

Compaction can be carried out using normal vibratory rollers. The number of roller passes is critical, as over-compacting cement stabilised base may overstress the surface. Bitumen sta-bilised road base do not have this problem.

Cost :

Reconstruction is an expensive option and should be considered only if the pavement has suffered beyond economic repair. Partial recon-struction can cost between RM 35.00 to RM 45.00. Full reconstruction is more costly. It can range between RM 40.00 to RM 50.00.

Reliability :

Reconstruction work done to a high construc-tion standard will have a life surpassing all other rehabilitation options. In fact, it can be designed to any desired performance period.

However, it is expensive and should only be carried out where necessary.