Written on sábado, noviembre 12, 2011 by Jose Sánchez Márquez
Nowadays clients and projects demands new concrete designs, new ways of concrete distribution technologies and a better service. Reason why, when a big concrete volume is require many things are in jeopardy, the name of the Concrete Company, the thermal Shrinkage factor, the location, the wheatear and hundreds more.
According with the ACI, American Concrete Institute:
Massive Concrete Volume is a big Concrete Volume with dimensions large enough to take necessary measures to fight overheat and volume changes to avoid cracks.
Big concrete volumes generates overheat during the curing process and hardening, due to is very difficult dissipate the heat of the element. Reason why It can reach high temperatures, higher than the environment temperature, generating Thermal Shrinkage (Gajda y Vaneem, 2002). Meanwhile the concrete temperature increase inside the element and expand, in the surface can decrease and retract, creating tension efforts that can generate surface cracks if the temperature difference between surfaces and inside is too big.
Three tips to identify it:
When the transversal section is close or beyond 1m of high
When the cement dosage is above of 355 kg/m3.
The concrete element size (volume – surface area and minimal dimension)
The pictures from the album bellow, shows Pile No.2 Viaducto de la Novena, Bucaramanga, Colombia
The cracks can appear during the (1-5 Days) after the concrete was put. If the element have a cement dosage between 120 – 270 kg/m3, here are some tips to reduce the possibility of cracking:
Aggregates size between 75 – 100 mm (3’’ – 6’’)
High content of thick aggregate, at least 80% of the total content
Hydration cement low heat
Water to start the curing process
Ice on concrete to reduce temperature
Moisten the concrete compounds(sand, aggregates) to reduce concrete temperature
But, If the element have cement dosage between 300 – 600 kg/m3, here are some tips to reduce the possibility of cracking:
Fill the entire element with concrete in a continuous and constant way until finish
Temperature control between the surface and the inside of the element, the difference should not exceed 20°C (36°F) to avoid Thermal Shrinkage and surface cracking (FitzGibbon 1977 y Dintel y Ghosh 1978).
Image taken from Diseño y Control de mezclas. Capitulo 18 Concretos Especiales. Concreto Masivo
The ice addition in concrete is very important to reduce temperature and it must be part in the concrete design.
Water to start the curing process
Moisten the concrete compounds(sand, aggregates) to reduce concrete temperature
In the picture bellow we can see part of the process of ice addition to concrete.
Building Projects examples at Bucaramanga City, Colombia
A Good example of how to handle massive concrete Volume were located in Bucaramanga, Colombia, with two projects, the bridge Viaducto Internacional de la Novena, and Oasis de Mardel, by Mardel Construction.
The bridge “Viaducto Internacional de la Novena” (Ninth International Bridge) is compound by two foundation bases, the pictures bellow shows the construction and pilling process. During the pilling process were necessary drilling of 36 piles on each foundation base, with two machines, each one working 7/24 due to the appearance of rocks in the area, at the end the process took more time than the expected.
The video bellow shows the drilling process of (1) one pile and the way how the iron nest was installed inside the excavation.
Once the 36 piles were ready, the construction of the big base started, the iron installation according to design took almost an entire month on each foundation. In the pictures bellow you are going to see the way the concrete was install inside the foundation, called foundation base #3, with two concrete boom pumps all time until the job was finish. Holcim Colombia S.A. was the concrete company in charge of the production, distribution and concrete pumps.
In the pictures bellow you are going to see the way the concrete was also install inside the foundation base # 2, approximately one month after the placement at first base # 3. It was also necessary the use of two concrete boom pumps all time until the job was finish. To control the concrete temperature the sand and aggregates were moistened. The ice addition in concrete was determinant, maintaining a average temperature of 20°C (36°F).
The video below shows how the concrete is bumps by the two Holcim’s machines at night . At the end for each foundation base was necessary to bumps 2100 m3 of concrete. On each foundation base the concrete bumps started at Saturday's night until Tuesday´s morning at 7am. Approximately the rate of concrete bumps was 48 m3/hour. Once the activity finish, the foundation was cover for 14 days, and the curing process star immediately.
Written on miércoles, agosto 10, 2011 by Jose Sánchez Márquez
Although in some cases the curing process is complicated in some projects, due the willingness is not enough or just they (engineers, workers) don't want to do it during the 7 days. Synthetic Fibers like TUF STRAND by Euclid Chemical Toxement and Forta Ferro have been shown to help reduce cracking and many more advantages, here are some:
Why use fibers?
Can be distributing randomly to the entire transversal section of the element, in two ways 2-D and 3-D. In the bi-dimensional way (2-D) is enough just to throw the fiber on the element. However If the fiber is located during the Concrete production process (Concrete Factories) the distribution it would be tri- dimensional (3-D).
Increase the relation between Reinforce area – Concrete area
Can be added in concrete on small quantities
Increase the resistance to cracks effects and decrease the crack opening if the fibers are added in a correct way (Shah, Weiss e Yang 1998).
The fiber use is ideal in sections or elements in where is very complicated install reinforced steel.
Important weight decreases compared with reinforce concrete.
SYNTHETIC FIBERS
The most used is polypropylene fiber, due to an inert material and lightweight. In the picture bellow you can see some technical information about the Synthetic Fiber TUF STRAND by Euclid Chemical Toxement.
Important General Advantages of Fiber use:
Reduce the cracking effect and plastic shrinkage
It can be added in concrete on small quantities 1.8 – 12 Kg/m3, according with the element and concrete design.
It can affect the workability in concrete
STEEL FIBERS
The use of this fiber can affect the workability in concrete. Is recommended add the steel fiber during the concrete production process in a slowly adding, because is very important guarantee a correct distribution inside the concrete to avoid lumps or balls of fibers, it would take at least 10 minutes of mixing inside the mixer vehicle. Nevertheless is very important check the concrete design, with special attention to water-reducing admixtures and plasticizers.
Steel Fibers advantages:
Increase the traction and flection resistance
In case of corrosion is only an appearance problem and not structural
Very use in airport runways, industrial floors, shotcrete elements, bridges and pavements.
Is very important testing to determine chemical additive and fiber dosage (Kg/m3), according with the element and concrete design. The curing important is very important, with or without fiber the curing process must be the same for 7 consecutive days. Follow the next link in case you want to have curing alternatives and Why cracks appears in concrete?
Building Projects examples at Bucaramanga City, Colombia
In the pictures below, synthetic fibers were used on the construction of this SkAte Park, thanks to the fibers and also to a rigorous curing process, chemical curing and covering with plastic the concrete in an early stage (fresh).
The final result was impeccable, none cracks appears in the first hours or in the next days and it was possible to give to the skate ramps the softness that the designer and professionals were expecting.
On these Industrial Floors the use of Steel fiber made not necessary the use of reinforced steel on concrete. Although this fiber can affect the workability in concrete the final result was the expected, the curing process avoid also the appearance of any cracks. Sometimes during the concrete discharge some fiber balls were visible, a normal condition. In those cases is re-mix the concrete for some minutes to guarantee a better distribution inside the mixer vehicle.
Written on jueves, marzo 31, 2011 by Jose Sánchez Márquez
Cracks appear on concrete due to the shrinkage, a volumetric change happen with the pass of time, very normal on concretes. The shrinkage is generated by changes in the humidity and Physic-chemical on concrete. The reason why it is a problem is because cracks allow the entry of harmful agents, decreasing concrete life and increasing the risk for structures.
Some factors that contribute with the shrinkage are:
There are more possibilities that cracks appear in high resistance concrete (Above 28 Mpa) than in normal concretes (21 Mpa).
High relationship between water and cement (w/c) can increase the possibilities of cracks.
Construction process of placement and compaction concrete, eliminating most of the air trapped in it.
When concrete is in fresh stage, the cracks that can appear are plastic settlement and plastic shrinkage. When it is in hardened state can appear physics, chemicals, thermals and structural cracks.
NON-STRUCTURAL CRACKS
Plastic Settlement
Occurred in the first 3 hours and it is caused mainly by the steel reinforce due to stop the free movement of concrete on the element, generating in some parts the lack of or the excess of concrete.
The best way to try to avoid it is making a good vibration meanwhile the concrete is putting. Other thing is not to add more water to concrete; the water dosage is responsibility of the manufacturer. Finally we must follow the design specifications of every country about minimum coating.
Plastic shrinkage
Mainly happen for the water lost on concrete, during the (1 – 6 hours) when concrete was put. However this kind of shrinkage doesn’t represent any structural damage on the element.
These are the principal reasons than contribute with this phenomenon:
Quick loss of moisture by high temperatures,
Big temperatures differences between day and night,
Strong winds on the zone than can dry the concrete.
Concrete Water Suction by soil or granular base on rigid pavements.
Is also very common find this cracks in:
After put concrete in fresh stage over a hardened concrete.
After put different layers of concretes (resistances, fc) top of each other.
An excess of vibrator when concretes are very fluid as consequence of the use of more water than the design dosage recommended (settlement above 7”).
When there are important concentrations of steel reinforced.
The best way to try to avoid it, is curing the concrete for 7 seven days constantly, after the concrete loses its shine. In columns and floors is recommended cover the concrete with plastic to try to keep the moisture and wind. Also is recommended the use of water irrigators to keep an average temperature. Wet all the surface in where in the concrete is going to be put, soil, steel, floor to reduce the risk of water suction and finally a good vibrating process.
Thermal shrinkage
Concretes can present volume variations due to the temperature that generates the concrete by itself when is surrounded by formwork or in contact with soil or surrounded by a previous concrete. Big volumes of concrete generates overheat during the curing process and hardening, making very difficult dissipate all the heat, reason why It can reach high temperatures higher than the environment temperature.
This is very common when there are big changes in temperature or in massive concretes that demands big volumes at the same time.The cracks can appear during the (1-5 Days) after the concrete was put.
The best way to try to avoid is using cold water or ice on the concrete dosage. A concrete average temperature of 24°C can prevent this kind of shrinkage. It is also recommended wet the aggregates and try to starts at night or day time with a standard temperature.
This is a good example of a big concrete volume, the project is located in Bucaramanga, Colombia and is one of the two piles of the bridges, called "Viaducto de la Novena". The pictures bellow shows the construction process, since the beginning until the pile was ready and waiting for concrete.
This kind of cracks are associate to deficient construction or bad structural design and is the final result when weight can't be dissipate by concrete.
These are the principal reasons than contribute with this phenomenon:
Wrong Design
Change the final use or purpose of the building or structure
Wrong location of the reinforcing steel
Heavy loads on young concretes (overloads), they don't reach final resistance age (creep)
Noticreto 97. Noviembre - Diciembre 2009. Juntas en Pavimentos de Concreto Hidraúlico. Control de la Retracción del concreto - Por: Rodrigo Salamanca Correa
Recomendaciones Cuando se presente fisuración del Concreto. Soluciones que Construyen un mejor pais. Version 2010. HOLCIM COLOMBIA S.A
Written on domingo, marzo 27, 2011 by Jose Sánchez Márquez
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.
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.
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.
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.
Noticreto 104. Enero - Febrero 2011. Edición Especial Edificaciones y Sostenibilidad Ambiental
Written on lunes, noviembre 30, 2009 by Jose Sánchez Márquez
This was my second opportunity working in the construction of highways, although I only participated in the project for four 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.
Written on jueves, junio 25, 2009 by Jose Sánchez Márquez
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 is specialized on the constructions of highways. 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. Dynapac Products
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 moduli.
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.
