Research on Low CO2 Cement (ECM Cement) and the Optimum Structure

Pursuit of Environmentally-Friendly Technology by Blending Cement and Structural Technologies

November 5, 2010Takenaka CorporationNational University Corporation, Tokyo Institute of Technology

Takenaka Corporation (President: Toichi Takenaka) and the Tokyo Institute of Technology (President: Kenichi Iga) have, jointly with D.C. Co., Ltd., Takemoto Oil & Fat Co., Ltd., and Kurimoto Ltd., developed cement which does not require calcination and consists mainly of blast furnace slag, a by-product of steelmaking [ECM (Energy CO2, Minimum) cement], and a structure which is best-suited for this cement, and are carrying out research to establish these as commercial technologies.
Conventional cement is produced by calcinating limestone or similar raw material at high temperature resulting, in the case of ordinary Portland Cement for example, the generation of approximately 750 kilogram of CO2 per ton of cement. The total emissions of CO2 by cement makers equals 4% of that emitted from all sources in Japan. ECM cement can reduce emissions of CO2 to between 20% and 40% of that produced by conventional ordinary Portland cement.
This research has been conducted under contract from the New Energy and Industrial Technology Development Organization (NEDO) since 2008.

【Problems when making cement with blast furnace slag as its principal raw material and development to overcome these problems】 (Problems)

It has been known for a long time that cement with blast furnace slag, which is a by-product of steelmaking, as its major raw material would not require calcination and that it could sharply cut emissions of CO2, but using such cement has faced the following problems.

1. It would take a long time to manifest its strength.
2. It would crack easily when it shrinks.
3. Methane fermentation system
This system divides the raw garbage, kitchenNeutralization of the concrete caused by carbon-dioxide gas in the atmosphere (the phenomenon, a loss of alkalinity which prevents iron from rusting), would encourage the rapid corrosion of the internal steel reinforcing bars.

(Development to resolve the above problems)

The goal was to overcome these problems through the development mentioned below in order to apply cement with blast furnace slag as its major raw material to the construction of structural bodies.

  • To resolve problems 1 and 2 development of ECM cement which rapidly manifests its strength and resists cracking caused by shrinkage by conducting research on the constituents which are added to blast furnace slag.
  • To resolve problem 3, developing reinforced concrete structure in which atmospheric carbon dioxide gas will not penetrate the concrete, by using structural members consisting of reinforced concrete with their surfaces covered with steel plate; and as the foundation supporting this structural body, developing improved soil piles which provide high strength and ductility, and which are made by mixing ground with ECM cement but without using steel reinforcing bars executed in-situ, thereby solving the problems caused by neutralization.

Takenaka Corporation and the Tokyo Institute of Technology have positioned the ECM cement and the structural body to be made of ECM, which were the goals of the development, as environmentally friendly technologies, and are continuing research and development in order to prove their durability and structural performance and to complete them as commercial technologies.

Takenaka Corporation and Tokyo Institute of Technology Group have applied for patents on ECM cement and on the structural body.

【Outline of ECM Cement】

ECM cement is made with blast furnace slag, which is a by-product of steelmaking, as its major raw material, and also using recycled powder produced by recycling demolished concrete and special constituent as the reaction stimulation agents necessary to harden the blast furnace slag. The special constituents harden the cement quickly, reducing shrinkage. Concrete recycling was formerly limited to recycling aggregate, but the ability to reuse recycled powder has opened the way to the achievement of complete recycling of concrete.

【Outline of research on a structure suitable for ECM cement】

Frame structure (aboveground structure)

In a conventional reinforced concrete member, the steel reinforcing bars in the concrete are protected (corrosion is prevented) by the alkalinity of the concrete, maintaining the durability of the structural body. Research on a variety of structures has been undertaken to ensure that neutralization is not a problem in structural bodies made using ECM cement. In a reinforced concrete-filled steel pipe, steel plating is installed on the surface of the structural body, so atmospheric carbon dioxide gas, which accelerates neutralization, does not penetrate the structural body. Even in a conventional reinforced concrete member, using high-strength and refined concrete can prevent the penetration of carbon dioxide gas.

Research on the structural performance of frame structures made of ECM cement has confirmed that their performance is equal to that of members made of conventional cement, so research intended to bring it to the practical stages continues.

Foundation structure

The weight of a building is supported by a foundation structure (piles) made of reinforced concrete protected basically by the alkalinity of the concrete. In contrast, a foundation structure made using ECM cement supports a building using improved soil piles without steel reinforcing bars. A high strength and high ductility improved soil with strength five times or more and toughness (deformation performance) three times or more than the strength and toughness respectively of a conventional improved soil is formed and used as the foundation structure.

The feasibility of a foundation structure of this kind has been confirmed by testing, so research on an execution method necessary to apply it to actual construction work is underway.