Search

The spreading awareness of green issues in recent years has prompted us to develop environmentally friendly concrete: ultra high strength concrete that contains high volume of by-products. Compressive strength tests were conducted using mortar and concrete specimens containing various by-products. As a result, we suggested a computation approach of the compressive strength of mortar by using a regression expression that uses the chemical composition and the mixing condition of the by-product as parameters. And CO2 emissions from the component materials of this environmentally friendly, ultra high strength concrete reduce 40% of the emissions for conventional ultra high strength concrete.

The performance of latest devices with electromagnetic induction method for the measurement of cover depth of rebar was confirmed by some experiments. The result is as follows. 1) The accuracy of latest devices was almost in the range of the standard value of JASS5T-608. 2) Mixture proportion of concrete and the age of specimen did not influence measurement values of latest devices with electromagnetic induction method.

The survey accuracy of cover depth of rebar of RC member by the devices with electromagnetic induction method was confirmed by the experiment. As a result, it was shown that measurement of actual RC members was possible. In addition, there was the case that we have to use A method or B method of JASS5 T-608.

The top-down construction method using pre-cast concrete for basement columns is more effective in improved quality of concrete, shorter construction time and economy of labor compared with traditional top-down method, requiring no column construction under the ground floor after excavation. This paper first describes the production planning and the implementation of the top-down construction method applied to an actual high-rise building using pre-cast ultra high-strength concrete with a design strength of 100 MPa for basement columns. The paper then proceeds to report on the results of the quality control tests of the high-strength concrete.

This paper discusses a measuring method of the premature stiffening zone formed at the top surface after placing of high-strength mortar with a water-binder ratio below 0.2. In this experiment, first a measuring method of the premature stiffening zone was devised by using penetration resistance measurements. The penetration resistance distribution, resistivity distribution and moisture content measurements of mortar specimens simulated high-strength concrete with a design strength of approximately 150N/mm2 were then conducted to assess the appropriateness of the measuring method of the premature stiffening zone.The results reveal that the measuring method was applicable to determining the occurrence and approximate depth of premature stiffening zone for high-strength mortar.

Test age and curing method of specimen for manufacturing control of high strength concrete were investigated and following results were obtained. 1) The strength correction value of high strength concrete is small in the order of Ordinary portland cement > Moderate heat portland cement > Low heat portland cement. Moreover, it was necessary to set test age of high strength concrete using Moderate heat portland cement and Low heat portland cement on the day after the 28th. 2) In the case to use portland cement, if strength test is set within 91 days, the strength correction value doesn't reach a big negative value. 3) In the case of binder water ratio is six to seven, even if strength test is set within 91 days, the strength correction value reaches a big negative value. 4) Also in the case with 3), reasonable manufacturing control can be done by the hot water cured specimen.