Kashima
Developed “LACs Concrete(R)”, a low-cost, high-flow concrete that does not require compaction
First introduced in actual construction, reducing the number of workers by approximately 80% and the pouring time by approximately 60%.
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Kajima (President: Hiromasa Amano) has developed “LACs Concrete”*2, an inexpensive and highly fluid concrete that does not require
compaction*1, with the aim of improving productivity in the
construction of reinforced concrete structures. As a result of introducing “LACs concrete” for the first time in actual construction, we have confirmed that the number of workers can be reduced by approximately 80% and the pouring time can be reduced by approximately 60% compared to construction using ordinary concrete.
In the future, we will deploy “LACs Concrete” at each site and promote efficiency of concrete pouring work.
*1 During concrete pouring, work to expel air and excess water from the concrete and ensure that it reaches every corner of the formwork. *2 Low Action Casting / Low Actual Cost / Limited Abandoned Compaction /Lead Abbreviation Casting/Raku Concrete
[Image 1: https://prtimes.jp/i/116603/88/resize/d116603-88-76af2f016c4067374595-0.jpg&s3=116603-88-7e5d9c7c15e7f81abfce4edecf39920d-334×219.jpg] Ordinary concrete placement situation
[Image 2: https://prtimes.jp/i/116603/88/resize/d116603-88-eee7efa0c8d024246c95-1.jpg&s3=116603-88-a09387dd91a41e6ccff2b7a4d7a9cce8-333×217.jpg] LACs concrete placement status
Development background
Concrete pouring is an important process that affects the quality of a structure. Ordinary concrete is used in almost all construction work, but when pouring concrete, careful compaction work is required by many skilled workers. There is a need to improve productivity through humanization. One solution to this problem is to introduce high-flow concrete that does not require compaction, but existing high-flow concrete requires the use of special materials and the amount of powder such as cement mixed in concrete. There was a problem in that the manufacturing cost was significantly higher than that of ordinary concrete due to the increase in concrete. For this reason, high-flow concrete has only been used in limited cases under special
construction conditions, such as complex shapes or areas with high-density reinforcing bars.
Therefore, our company has been developing a high-flow concrete that is inexpensive and does not require compaction work, with a view to introducing it into reinforced concrete structures constructed under normal conditions.
Overview of “LACs Concrete”
“LACs Concrete” is made by adding our newly developed powdered dispersant*3 to the base concrete on-site to improve the fluidity of the concrete.
In addition, by increasing the amount of fine aggregate mixed into the base concrete, material separation resistance *4 can be ensured even with a unit cement amount of 300 to 350 kg/m3, which is the same as ordinary concrete. Since the fine aggregate mixed in is cheaper than cement, it is possible to suppress a significant increase in the unit price of the material.
By increasing the fluidity of concrete, we have significantly reduced casting time and the number of workers, and by increasing the amount of fine aggregate, which is cheaper than cement, we have suppressed the increase in total costs.
*3 Material that fluidizes concrete
*4 Power to prevent concrete materials from separating
[Image 3: https://prtimes.jp/i/116603/88/resize/d116603-88-9e29b3da334009611128-5.jpg&s3=116603-88-fa97121fe1664ef55ab5a940d444e1e5-1108×273.jpg] Manufacturing process of LACs concrete
[Image 4: https://prtimes.jp/i/116603/88/resize/d116603-88-8a6bd0a7fa967aa65455-3.jpg&s3=116603-88-04b9ae147c45110b7444303a99ee2012-1301×738.jpg] Comparison of mixing examples of ordinary concrete and LACs concrete ●About post-added powder dispersant
The newly developed powder dispersant is a powdered admixture whose main ingredient is a lignin derivative. Admixtures used in general high-flow concrete tend to reduce the viscosity, which contributes to concrete’s material separation resistance, so they must contain a large amount of other materials such as cement, which increases cost. That was the issue.
Therefore, in cooperation with Flowrick Co., Ltd. (President: Shoichi Yokomachi, Headquarters: Toshima-ku, Tokyo), an admixture
manufacturer, we have developed a lignin derivative that has been produced by improving its molecular structure. We have developed an admixture that provides fluidity while preventing viscosity from decreasing.
Introduction to the field and results
We have introduced “LACs concrete” for the first time in the bottom slab concrete (approximately 520 m3) in the earth and sand pit of the Yokohama Loop South Line Kouda Kasama tunnel construction commissioned by East Nippon Expressway Co., Ltd., which we are constructing in Yokohama City, Kanagawa Prefecture. As a result, we confirmed that filling was possible without material separation and that the specified quality was maintained even after curing.
If regular concrete was used at the same site, a total of 9 people would have been required: 4 people to compact the concrete, 2 people to control the hose tip, and 3 people to finish the work. On the other hand, construction using LACs concrete eliminates the need for compaction work, allowing the number of people required to be reduced to two in total. Furthermore, by eliminating the need for compaction work, we were able to shorten pouring time by approximately three and a half hours, confirming the labor-saving and labor-saving effects of introducing LACs Concrete.
[Image 5: https://prtimes.jp/i/116603/88/resize/d116603-88-55925c2733624375ce6f-4.jpg&s3=116603-88-80c99756514f616d346a588858dcc185-562×340.jpg] Comparison of number of workers
[Image 6: https://prtimes.jp/i/116603/88/resize/d116603-88-2781ae8ad77cc3a4ad80-5.jpg&s3=116603-88-520524c5638a5b2083897585b75362f2-559×348.jpg] Comparison of working time
the next deployment
In the future, Kajima will introduce “LACs concrete” to other construction projects, reducing labor hours by reducing the number of workers and shortening pouring time, and shortening the process by increasing the amount of concrete poured per day. At the same time, we aim to further improve productivity by proceeding with research and development of new construction methods that utilize LACs concrete. Construction outline
Construction name: Yokohama Loop South Line Kouda Kasama tunnel construction Construction location: Koda-cho to Iijima-cho, Sakae-ku, Yokohama City, Kanagawa Prefecture
Client: East Japan Expressway Co., Ltd.
Constructor: Kajima/Takenaka Civil Engineering/Sato Kogyo Special Construction Works Joint Venture
Construction specifications: Excavation length approximately 1.7km, lining outer diameter 15m, separation approximately 1m
Construction period: April 2016 to October 2028
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