Research outline

Research on Cement-mixed Soil Quality Control

Production of cement-mixed soil

Proposed quality control method

(Left) (1) Sampling of undisturbed core
(Right) (2) Measurement of soil stiffness (Repulsive force)

Research Background
A large amount of soft soil is generated at a construction field and is put to effective use all over Japan as housing site foundation and embankment by mixing it with cement to improve it. However, there is currently no established technique for accurate measurement and control of the compressive strength provided by cementation and the variation of quality thereof on construction fields.
As a result, the Construction Technology Research Team has been conducting research concerning control techniques and assessment methods in order to establish a control method to allow measurement and assessment of compressive strength on construction fields.

Proposed control method
The effective method the Team proposes is quality control of cement-mixed soil by combining (1) measurement of compressive strength by sampling of cement-mixed soil without disturbing it (undisturbed core) using a special machine and (2) use of a sensor to measure soil stiffness (repulsive force). The special machine for sampling an undisturbed core is a proprietary development of the Team.
Technique (1) provides accurate compressive strength but sampling of large amounts of data requires a lot of labor and time. Technique (2) allows sampling of large amounts of data without much labor. However, the reliability of individual data is low and conversion of stiffness data into compressive strength is required as well. We believe that combining the two techniques makes up for each technique's weaknesses, thus enabling more accurate and efficient obtaining of the compressive strength of cement-mixed soil.
At present, the Team is collecting data on construction fields and making improvements for an even better control method.

(Contact: Construction Technology Research Team)

Research on VOC Reduction in Steel Structure Paint

VOC is a cause of photochemical smog

Accelerated deterioration test (composite environment corrosion tester)

Outdoor exposure test (Okinawa exposure site: water-based paint)

Outdoor exposure test (Edogawa exposure site: solventless paint)

Steel structures such as bridges and watergates are usually coated with paint to prevent the corrosion of steel products. Paints are composed of resins (such as epoxy resin and fluororesin), pigments (such as rust-preventing pigment and color pigment), solvents, and other such materials. Hardener agents are added to these materials, stirred together, and applied on the objects to be coated (steel products). A moderate amount of thinner is added to decrease the paint viscosity and make work easier. The components gradually react to form a coating film. In this process, VOCs (volatile organic compounds) such as the thinner are released into the atmosphere. VOCs cause photochemical smog in the atmosphere together with UV rays, and emissions reduction is desired.
Techniques for reducing VOCs in paints for steel structures include use of water-based paints with solvents replaced with water and use of solventless paints. With water-based paints, however, coating films are formed by evaporation of water instead of solvents, and satisfactory coating films are not formed in low temperature environments where water does not readily evaporate or if subjected to rainfall during the coating film formation process. Solventless paints have a high viscosity, which makes painting very difficult and inefficient and poses difficulty in forming flat and smooth coating films.
At present, technological development is taking place for the application of water-based paints to land steel structures such as bridges and solventless paints to river steel structures such as watergates.
Water-based paints are inferior to solventless paints in terms of corrosion resistance, and improvement efforts are being made on this front. For solventless paints, improvements are being made to painting machines to make the compatible with viscous paints for easier painting work. Accelerated deterioration and outdoor exposure tests are being conducted to verify that coating films formed by these improved paints or painting machines have anticorrosion properties equivalent to that of solvent paints.

(Contact: Advanced Materials Research Team)