El PLayON, MainteNance and ImProvement of the HighWay
Written on Thursday, June 25, 2009 by Jose Sanchez Marquez
I’m Jose Sanchez Marquez I graduated as a Civil Engineering on December 18th 2008 at Industrial University of Santander (UIS) in Bucaramanga, Colombia.
My first experience as engineer was with ESGAMO, Ingenieros Constructores a company who specialized on the highways constructions . The company was founded by two civil engineers, Eng. Escobar, Eng. Guillermo Garcia and the lawyer, Dr. Moreno.
| PROJECT NAME: | Improvement and maintenance of the highway Bucaramanga - San Alberto (Mejoramiento y mantenimiento de la Vía Bucaramanga - San Alberto, PR30-PR46). |
| Constructor : | ESGAMO LTDA. Ingenieros Constructores |
| Auditor : | CONSORCIO CENTRORIENTE 2008 |
| Contract value: | $4.727.520.967 millions of Colombian pesos |
PROJECT DESCRIPTION:
My participation on this contract was as Auxiliary Engineer, from March 3th until August 8th 2009. The Project Manager was Eng. Henry Castrillón, Resident Eng. Orlando Villamizar, and Environmental Eng. Fernando Rey.
The purpose of the Project was the Improvement and maintenance of the highway Bucaramanga - San Alberto, reason why we settled in Playon (Santander) town, which is located in the middle of the two points. It only takes one hour drive to get from Bucaramanga, the capital of Santander and one of the five biggest cities in Colombia.
The first activities made on the Project were the patched of the pavement in six kilometers from KM 46+000 until KM 40+000, according the design of the new pavement.
Also at the same time started the construction of the cyclopean walls, due to, many water streams in the zone, the water began to eroding the slopes of the road, putting in risk the life of drivers, with the constructions of this wall the main idea was try to earn more space, and recover the land lost. However cyclopean walls must have a firm land unsettled (rocks), because this type of wall aren’t flexible, they are very rigid and heavy and very likely to present fissures if the land is not very resistant.
These walls were located on the kilometers, K30+570, K32+750, K33+380, and my job was to control the preparation of concrete of 14 Mpa.CONCRETE ELEMENTS
All the walls, roadside ditches and drainage works were built with concrete of 14 Mpa, in Colombia we called Class G concrete. However in places where the traffic was very heavy and the majority of the vehicles had the tendency to stop, on these places the concrete resistance was increased to 21Mpa.
Cyclopean Wall, located K32+750 - Length: 70m
This was the first wall in where I was in charged. It has more than 170 m3 of concrete and an average height of 3.0 m.
As we can see in the picture bellow, this was the kind of metal formwork used to put the concrete inside for the walls construction. This metal formwork let concrete had a better lock.
At the beginning the concrete preparation we had to make it at place, because on that time we didn’t count with a concrete plant, not even mixers cars. It was a difficult and amazing task because never in my life I had been made concrete or been in charge of a group of hard workers.
It was necessary take control on concrete dosages, but especially in the relation between cement and water, also volumes and other technical conditions. On the other hand for being a cyclopean wall was necessary paid special attention on rocks quantities due to a cyclopean wall is conform by a relation of 60/40, 60% concrete and 40% of rocks.
The construction process demand always put first concrete, like 15 - 20 cm of thickness and then a rock layer, however rocks must have irregular forms to guarantee concrete adherence, the rocks must be putted by hand around the concrete layer.
Finally, cyclopean walls are very rigid elements for that reason curing is so important and is necessary to do it for seven days row, to prevent plastic shrinkage cracking or other kind of cracking.
On the other hand for the roadside ditches construction we counted with a concrete plant and two mixers. However due to the hot weather in the zone was necessary to use Plastiment a product by Sika, a water Reducing and retarding Admixture. With this product concrete workability is enhanced and a superior surface finish is obtained.
Other advantages are showed from Sika website below:
In mass concrete pours Plastiment controls temperature rise and reduces the risk of thermal cracking.
Initial set times are delayed, allowing time for proper placement and finishing without cold joints in hot weather conditions.
Plastiment increases concrete density and delivers increased early and ultimate, compressive and flexural strengths.
For flatwork applications Plastiment acts as a finishing aid, workability is improved, bleeding is controlled and a superior surface finish is obtained.
Lower water cement ratios provide decreased permeability and increased durability”.
Nevertheless we use other kind of product to prevent cracking in roadside ditches once the concrete had reached its curing, because the ditches are exposed to sun all day. The product used was also from Sika and is called antisol rojo, special for hot weather and in places where water is not easy to find.
The main function is creating a vapor barrier preventing in that way the premature loss of moisture to ensure a complete curing of the material.
PAVEMENT PATCHING, CONSTRUCTION PROCESS
This process was the first step according to the object of the contract “Improvement and maintenance of the highway Bucaramanga - San Alberto”. We made this work in six kilometers, from kilometer 40 to 46, in both lanes of road; having done this the second step was re-paved these same kilometers.
Due to the many years of the pavement and due to the increase on heavy traffic was necessary milling some part of pavement specially in places where fatigue cracking's appears, deformations or just in places where pavement was not enough to drive safely.
The places damaged were located and marked; always trying to mark them in squares or with no more than six corners.
Next the milling machine is carried to mill the old pavement, process that lasted no more than 5 minutes in areas of 2m2 and with thickness of 7 cm. after this milling; box is cleared with brooms or air compressors eliminating all dust and pavement particles.
Below appears an example machine, Image taken from: WAPA Asphalt Pavement Guide
When the area is completely clean, over the surface is spread emulsion, thin bituminous liquid asphalt, called Tack Coats, its principal job is promote bonding between construction pavement and the existing road surface. The bonding is very important because the adjacent layers must behave as only one for accommodate the anticipated traffic-imposed.
If they behave as independent layers with the pass of the year will appear longitudinal wheel path cracking, fatigue cracking, potholes, reducing pavement life.
After the emulsion is spread takes like 30 minutes in change it color to brown, like chocolate. Indicating that the bonding is ready, so the paver machine is carried to the place and then the asphalt is put there.
We used an asphalt called MDC – 2 (dense hot mix-2) very used in our country. The asphalt with a temperature of 152°c is leveling by the paver machine and by workers. Then we must wait until the asphalt temperature get down, like - 20°c so that the drum roller and pneumatic roller can pass until the box is well compacted, leaving the road without any pothole, cracks or any imperfection.
PAVEMENT RECYCLING, CONSTRUCTION PROCESS
In this part of the Project the designer determined that from the kilometer 36+500 to kilometer 40+250 was necessary the pavement recycling due to the many cracking and road holes. For that reason this degraded pavement was necessary modifying it and transforming it into a homogeneous structure that can help to support the traffic requirements.
To achieve this was necessary reusing the materials from the existing pavement for the construction of a new layer with the Recycling machine Wirtgen 2000 who is in charge of the pulverization of the existing pavement up to a certain depth; these operations were performed in-situ.
The video below shows the recycling machine Wirtgen 2000 spraying the degraded pavement to an average depth of 19 cm (8’’).
The machine counts with a 2.0 meters rotor of a 1.50 m diameter conformed by 168 bases in where are connected the same quantities of teeth’s or tips. In the recycling process the machine consumed 1778 tips and 150 gallons of motor oil each day, recycling at the end 3750 meters and 7.60 m of track gauge.
In the picture bellow appears the operator and his assistant changing all the rotor tips. For this kind of machines is very important had a good operator due to this person must feel when is necessary stop and change or replace the tips for new ones, because there is not a electronic signal that shows you that tips are deteriorated.
When the recycling is finished is necessary leveling the pavement with a motor grader, and the machine must to follow the indications made it by the topographer with the design of the new layer. Afterward a water tank car spread water above the conformed area to help in the process of compaction.
A sealing coat is then applied on the recycled layer to protect it against traffic during the works, with one or two layers of asphalt concrete later applied to ensure the functionality and bearing capacity of the pavement. However in this project according to the designer it was not necessary the addition of a binder like cement or hydraulic road binder, sometimes combined with bituminous emulsion.
Advantages:
1. Re-use of old, polluted or inadequate materials in the existing pavement
2. Uniformity of the pavement, both in strength and in geometry
3. Reduction in waste and extraction of aggregates from quarries or pits, with the associated environmental advantages
4. Lower costs of renewal of worn pavements,
5. Maintenance of the surface to a level which will not need hard shoulders and curbs to be raised, and will not reduce the clearance under bridges.
I had the opportunity of driving this machine, and the feeling is amazing. Despite the vehicle can’t reach a high speed you can feel the power and how complicated is for drive.
This is the final result when the pavement recycling was made, then the topography comission starts leveling the playing field, putting marks to indicate to the moto grader how many inches must raise or lower.
Done this the water tanker spread water over the surface, then the vibrating roller starts compacting the new area. Final result.
PAVEMENT, CONSTRUCTION PROCESS
For this contract were designed two pavements for different parts of the road, the first one was since Km 46+00 to Km 41+250, in where was put a 7 cm layer of pavement after the pavement patching.
According to the second design was necessary put 11.5 cm layer of pavement over recycling pavement. Due to the thickness of the pavement was split it in two layers, the first one with 6 cm and 5.5 cm the second.
The beginning was 11th of May of 2009, with an average advance of 400 ml per day and a thickness of 7cm.
The picture shows how the truck approaches to the finisher machine or tracked paver. However before was spread asphalt emulsion that is the mix between asphalt, water with petroleum solvents and has for purpose to join the old pavement with new one.
The type of pavement used was MDC-2, which gave to the surface a rough finish ideal for national roadways with high number of vehicles.
In the picture below appears the finisher machine with the workers, which finally gave the finisher to the asphalt with rakes. They are known as “patiasados”, due to they are exposed to high temperatures all day. The activity that they develop improves a lot the final appearance of the pavement.
The temperature in which the pavement is spread is 150°C, after done this the compacting process stars when the temperature of the pavement got down until 130°C, the compacting is made with a single drum vibratory roller or with a double drum vibratory roller.
In the picture bellow we can see the tracked paver and behind a single drum vibratory roller compacting the pavement and also all the team of workers re-leveling the surface. Finally we can see how the asphalt emulsion has changed of color, from black to chocolate what means that is ready to help to join the underground layer with the one who is up.
In this picture we can see working the pneumatic roller sealing the pavement to finally give free way to the vehicles.
When the pavement finally reaches the curing stage, after 25 days, we proceed to use the falling weight deflectometer (FWD). With this testing device we can obtain deflections and stiffness of the pavement and finally know the elastic modulus.
The test is simple; the FWD is located in the middle of the wheels of the axle of the truck, which must weight 8.2 Ton. The clocks are put in zero, done this the driver receive a signal and the truck is moved backward and the clocks shows the deflections, due to the force that the truck produces in the pavement.
FiNAL RESULTS
These images are from some parts of the road that were pave with MDC-2, from K36+500 to K46+000.
However from the K36+500 to K40+000 the old pavement was recycling and then was put a pavement layer of 11.5 cm, more or less 281.750 m3 of pavement.
From K40+00 to K46+00 pavement patching was carried out and then was put a pavement layer of 7.5 cm, for a big amount of 596.750 m3 of pavement.
Thank so much to ESGAMO for the opportunity to work and learn, but specially to Eng. Villamizar for sharing all his knowledge and experiences with me.
Posted in
cyclopean walls,
emulsion,
falling weight deflectometer,
grader,
heavy machines,
highways,
milling machine,
milling pavement,
pavement recycling system,
plastiment tm5,
sika,
tack coats,
wirtgen
