Written on Sunday, March 27, 2011 by Jose Sanchez Marquez
There are polarized opinions about what is the best material for highway construction, concrete or pavement. In Colombia, asphalt is the most common way to highway construction. However in the last years concrete highways has been taking place in urban areas.
The most important differences of these two methods are the cost, time of construction, qualified staff, durability and the Island heat effect.
Construction Cost
The first aspect about the cost, it is true that the asphalt has a lower price, due to the structure sub granular base, granular base are not so expensive and they conformed a big important percentage in the thickness structure. In concrete roads is the concrete the one that conformed the majority of the thickness structure, reason why the cost per m3 increase the value of the roadway.
Time of Construction
According with the time of construction in new roadways there are not big differences, every process can consume a similar time of delivering the roadway. However if we are talking about maintenance works with the pavement you can give way to traffic in less time, meanwhile with concrete if it is normal you need to wait at least for 28 days, waiting to reach the final resistance.
Qualified Staff
The qualified staff is very important in pavement process, due to you need to count with people that can operate for instance, a motor grader, a rolling vibratory, drum vibratory rollers a tracked paver or wheeled paver, Pneumatic rollers and trucks that carry the pavement. Also you need to count with a topography team and a specialized people that spread the asphalt and help to give the final look. Concrete process doesn’t require the same number of qualified staff and the maintenance is easier and also don't require specialized machines or people.
As a conclusion we can also said that concrete roadways consume less diesel combustible, according with the American concrete pavement Association, ACPA. An asphalt road requires 4.5 more combustible than a pavement design with concrete for the same number of traffic.
With the durability concrete doesn’t has comparison, the pavement life can be between 7 to 10 years, but with concrete the life expectance is between 20 to 25 years.
Heat Island Effect
However the most important difference is the one that few people stop to analyze, the heat island effect. Due to the cities needs roadways, parking lots and all kind of structures to may our lives easier we are changing the urban sustainability. The zones that were before moist permeable now are waterproof dry and this phenomenon is clearer in warm weather cities.
Image from http://www.acca.it/euleb/en/glossary/index.html
One benefit of use concrete is that it reflects the sunlight helping to reduce the city temperature. In the picture below we can see the differences in temperatures between concrete and asphalt. Concrete has a temperature of 38°C and the asphalt has a temperature of 55°C. Reason that explains why in warm cities is so common the use of air conditioning.
Image from http://www.celsias.com/article/cool-roof-could-offset-carbon-emissions/
We need to remember that when it leaves the asphalt plant has a temperature of (152 –154°C) during the course can it lose (2 - 4°C), when it is spread by the tracked paver, it is necessary to wait until the temperature decrease to (130 – 132°C) and then the drum vibratory rollers and Pneumatic rollers can work on the pavement. Once the process is over the asphalt con reaches easily temperatures of (48–67°C) all year long, transferring excess heat to the air above them and heating storm water as it runs off the pavement into local waterways. Further, concrete temperature when leaves plant is around (30 – 32°C) and during the course can earn (0.5 - 1°C). Once is completely finish in a very hot day can reach a temperature of (36 – 38°C).
As conclusion we can say that Concrete has a higher durability, doesn't need many qualify personnel, doesn't consume the same quantity of combustible and can mitigate in a better way the heat. Asphalt could be not so expensive, doesn’t has the same durability and it is not good in mitigate the heat.
Jose Sanchez Marquez
References.
Posted in
concrete or asphalt,
construcción de vias,
grader,
heavy machines,
highways,
island heat effect
|
Written on Monday, November 30, 2009 by Jose Sanchez Marquez
This was my second opportunity working in the construction of highways, although I only participated in the project for several months and the main idea of this project was, build a safety and well done roadway to this village, that for several years was expecting this intervention.
| PROJECT NAME: | Technical Supervision, Administrative, Financial, Social and Environmental for improvement and paving of Tona’s road, K5+00 to K18 +870, Santander – Colombia. |
| Supervisor: | JOYCO LTDA. |
| Constructor: | Consorico SE-1 |
| Contract Value: | $10.060.315.965 millions of Colombian pesos |
PROJECT DESCRIPTION:
This Project was awarded by the government of Santander to JOYCO LTDA, Joaquin Ortiz and Company. A company that specialized in the consulting and engineering design, and I worked there as a Civil Engineer.
The project was divided in two stages, STUDIES AND DESIGN and CONSTRUCTION SUPERVISION.
The first stage began in July 9 and finished in September 9, in where previous studies were reviewed and updated and in some occasions they were made it again, like the traffic study which determined that the total number of axles equivalent for the next 20 years would be 400.000 vehicles. Afterward the pavement design showed that was necessary the use of two structures in different parts of the road, asphalt and concrete pavement.
However it was also necessary to perform the CBR test (California Bearing Ratio) a penetration test for evaluation of the mechanical strength of road sub grades and base courses. Finally we made a material characterization to identify the sub base material. On the other hand, we also design culverts and concrete retaining walls with the different heights (2 – 6m).
PROJECT LOCATION
Tona village is located about 36 Km from Bucaramanga, more or less 45 minutes by car.
The video shows how the state of the roadway was before the improvement started, it only shows the first 3 kilometers from K5+000 to K8+000 of the 14 kilometers than the contract established. In the video we can also appreciated the width of the road, how small it was, and how the slopes were formed by rocks in several parts of the road.
However the road didn’t present big problems related to subsidence or landslides, thanks to this the road remained acceptable safety conditions for vehicles. On the other hand the bridges in the 14 kilometers, the majority of them with more than 20 years of existence without any kind of maintenance, reason why was necessary analyze if they were capable of resist the weight of trucks and heavy vehicles.
Also in some cases was necessary increase the width of the bridges due to only one car was able to pass over it and the main idea of the project was try to generate a comfortable and safety road.
One of the positive things that we found was the mechanical strength of the soil, after CBR tests and identified the material particles size was determined that sand was the principal material with a CBR result of 20%, and excellent soil with the possibility to withstand high loads. Reason why the pavement design didn’t have high thickness, a 15 cm of thickness for the granular sub base, 15 cm granular base and 6 cm of pavement, MDC - 2.
However the topography of the zone is abrupt, there are big and dangerous slopes along the way. Reason why more that 30.000 m3 must to be remove and transport to another place.
CONCRET WALLS CONSTRCUTION
The construction of these walls took an important role during the project, due to it were necessary before to put the pavement. But also was necessary the construction of box culvert, gutters and filters very important to drain the water of the road. The walls were design by the Eng. Rafael Zafra according to the topography of the zone.
In the picture bellow you can detail the two wall options that we had according the necessity of the road.
The first step was the wall location through coordinates and levels. Them the excavation started. In the majority of the cases the excavation was made by heavy machine to increase the work performance.
In some cases was necessary realized improvement on the soil, putting steel anchors of 5/8’’ where excavation was impossible by the rocks. In the picture bellow we can see how the steel anchors were put after put a lower concrete layer of 7 cm of thickness.
Once the improvement was done the process of install the steel anchors began. The constructor use wood frame to contain the concrete, however steel frame develop best finishes to the view. In the pictures bellow we can see how the steel was put according the wall design. Also the concrete resistance used was 21 Mpa, and CEMEX was the company who sent the concrete until there.
This was the final result of the wall. We can see also the filter that surrounds the wall. Done the wall the road finally get width of 7.0 m, necessary space for the pass of two small vehicles at the same time.
CUTS AND GRADINGS WORKS IN SLOPES
In zones where the slopes were formed essentially by rocks, the design established that the cut angle must to be almost vertical to try to ensure 6 m of width to the road and pave the mayor number of kilometers.
To do the job we count with two DOOSAN 225 crawler excavators, everyone with a loader of 1 m3 of capacity. This kind of machine made possible to achieve an impressive breakthrough in a few days.
Doosan Home Page
For every explosion was necessary made rock perforations between 0.80 and 1.0 m deep in the rock. Them the R-1 explosive was installed and was detonated by remote control.
In the next video we can see some explosions, all the personal were located to a distance of 200 m. and when the explosions finished, the expert went to the zone to supervise that everything was under control.
This was the final result of the slopes cut in one part of the road; we can see that the width allows the pass of two vehicles at the same time. Once they were made the topography team went to the field to rectify if the cut was correct or not according to the geometrical design of the road.
This video shows the variety of animals that appeared during the construction. Spiders and snakes were the most common animals to found on the mountains.
ROAD FORMATION
One of the most important Works during the construction of the pavement was the construction of the filters. They help to drain subterraneous water to the culverts of the road. Every filter had a length and width of 80x60 cm and they were located on the right side of the road, or where the mountain slope was located. In the picture we can see that the construction of one of them.
Every excavation and material placement was made with the help of the backhoe to improve the work performance.
In the next picture we can see also how difficult was the construction of the filters, rain was one the biggest problems, making the road impassible for vehicles. After the filters construction the motor grade starts the formation of the soil, leveling the soil or just cutting.
The picture bellow show a part of the road, where the filter (left) was finished and the motor grade did the soil formation. Them the vibratory roller compact the entire floor, increasing the safety of the road.
Now in the picture bellow we can see how the motor grade move the granular sub base according of design thickness, during all this time the topographer check if the machine needs to cut or move more material, until they reach an average thickness. Then the vibratory roller makes it part, compacting the entire zone.
Unfortunately I couldn’t finish the construction of the road, I wasn’t there when they started the pavement, due to I was called to work in HOLCIM COLOMBIA S.A as a WORK Inspector. However I must said that the experience was great and I learnt a lot from Eng. Jairo Gamboa and Eng. Guillermo Valencia excellent bosses and also I left excellent partners.
Work Team
Thanks for the opportunity
Posted in
construcción de vias,
grader,
heavy machines,
highways,
JOYCO LTDA.,
milling machine,
plastiment tm5,
TONA
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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 K30+570 - Length: 30m
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.
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.
This is the final appearance of the pavement after the drum vibratory roller and the pneumatic roller have compacted. In the picture we can see both machine and we can have an idea of the thickness of the pavement.
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
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