Concrete Massive Volumes, How To Handle?
Written on Saturday, November 12, 2011 by Jose Sanchez Marquez
Nowadays clients and projects demands new concrete designs, new ways of concrete distribution 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:
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When the transversal section is close or beyond 1m of high
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When the cement dosage is above of 355 kg/m3.
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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 placed. If the element have a cement dosage between 120 – 270 kg/m3, here are some tips to reduce the possibility of cracking:
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Aggregates size between 75 – 100 mm (3’’ – 6’’)
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High content of thick aggregate, at least 80% of the total content
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Hydration cement low heat
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Water to start the curing process
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Ice on concrete to reduce temperature
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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:
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Fill the entire element with concrete in a continuous and constant way until finish
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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
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The ice addition in concrete is very important to reduce temperature and it must be part in the concrete design.
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Water to start the curing process
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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 it can be see the concrete installed 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.
Oasis de Mardel, by Mardel
