Shinzo Nishibayashi

A Study on the Properties of Fresh and Hardened Concrete Mixed Normal and Recycled Aggregate

Recycled aggregates, may give an important contribution towards decreasing the negative consequences that production and dumping of constructions and demolition waste nowadays impose on the environment.This paper describes an experimental investigation on the properties of fresh and hard of recycled concrete mixing normal aggregates with recycled ones. The results of the investigation are as follows:The recycled concrete owns almost same characteristics of consistency and entrained air as normal concrete. The mixture of recycled aggregates negatively affects the performance of fresh concrete. Meanwhile, the decrease of strength and elastic modulus in the hardened concrete is slightly small due to the increase of replacement of recycled coarse aggregates. Also in the using of large amount of recycled aggregate, it causes the deduction of durability, and the increase of drying shrinkage and carbonation.

A study on artificial lightweight aggregate concrete with superplasticizer.

It has been recognized that the use of superplasticizer is very effective to improve the workability of concrete. This study was planned to make clear the properties of fresh and hardened artificial lightweight aggregate concrete with superplasticizer, and to provide useful information for the mix proportion and the practice of such concrete.The artificial lightweight coarse and fine aggregates were used. Also, the normal crushed stone and natural sand were used as the control aggregate. The effects of the type of aggregate, the type and kind of chemical admixture, the sand/aggregate ratio and cement content on the properties of super -plasticized lightweight aggregate concrete were experimentally investigated.The slump, air content and compressive strength under various conditions were measured. The workability of superplasticized lightweight and normal aggregate concrete was evaluated by V.B. test, compacting factor test, rheological test and segregation test. It has been proved that the workability of superplasticized lightweight aggregate concrete could be improve as high as that of superplasticized normal aggregate concrete by choosing a suitable mix proportion.

Fatigue of Non-Shrinkage Mortar

Non-shrinkage mortar is being used effectively to fix shoes of bridges and base plates of machines. With the recent sharp rise in traffic volume, occasions on which non-shrinkage mortars are subjected to repeated loading are increasing more and more.In this study, fatigue tests of six kinds of non-shrinkage mortar and plain mortar in compression were performed. Since the values of fatigue life of mortar and concrete are known to scatter widely, the fatigue test results were evaluated statistically.The results suggest that the fatigue life of non-shrinkage mortar at each stress level follows a Weibull distribution or logarithmic normal distribution. No fatigue limit seems to exist for non-shrinkage mortar. However, the fatigue strengths of plain and non-shrinkage mortar, except B mortar, at 2 millions cycles can be estimated at about 60 percent of ultimate static strengths.

The Properties of Concrete with Water-Reducing Admixture, the Effects of Reduction in Cement Content

To examine the effect of reduced cement content upon the properties of concrete containing admixtures, as in the air-entraining agent, five water-reducing admixtures, four water reducing-set controlling admixtures, and five brands of normal portland cement have been selected and used with some combinations.Comparative tests have been performed of fresh concrete with respect to its water-reduction, bleeding, time of initial and final setting, and of hardened concrete with respect to its strength gain concretes with the above-mentioned admixtures with cement contents of 260, 280 and 300kg/m3, were prepared and compared with the control concrete having the cement content of 300kg/m3 and same consistency of 7.5cm without admixture.The results of the test show that the good quality of water-reducing admixtures can reduce water requirement by 10 to 15 percent, irrespective of the cement contents, and that the strength gain, the time required for setting and bleeding are affected by reduction in cement contents, and by the quality of water-reducing admixtures.