Reported herein are the results of laboratory studies on the concretes and intrusion mortars to be employed for the maritime construction works at Onahama and Nakanosaku Harbors of Fukushima Prefecture in northern part of Japan. These studies were carried out under the contract between the Department of Public Works, Fukushima Prefecture, and the Port and Harbor Technical Research Institute, Ministry of Transportation, during the period March 1963 to June 1963.
　One of the main purposes of these studies is to evaluate the Samekawa Gravel as a coarse aggregate and to find proper mix proportioning of concretes with the gravel which will fulfill the minimum requirements for the construction works. The others are to investigate the applicability of two types of sand, namely, Natsuigawa and Hamamachi Sands, as fine aggregates for intrusion mortar and also to find appropriate mix proportionings of the mortar with the sands. Also reported herein are the results of studies on the effects of temperature rise, aeration of cement, and type or brand of cement upon the fresh and hardened properties of intrusi on mortar.
　The river system of Samekawa is considered practically the sole resource of natural gravel in the vicinity of Onahama and the neighbouring ports. The results of petrographical and physical investigations on Samekawa Gravel and other tests on concretes with it clearly demonstrate that the gravel has a potential to yield concretes of required properties for the construction works in spite of its extremely flat shape of particles, provided reasonable mix proportionings would be employed. Based on the test results, a graphical method of mix design is given for the particular gravel, a certain brand of cement, and Natsuigawa Sand. This method is to give the concrete of nominal cement factor of 200 to 350kg/m3, the compressive strength at 28 days of which will range from 80 to 250 kg/cm2.
　Both Nastuigawa and Hamamachi Sands are considered a little coarser than those generally used for intrusion mortar, the fineness moduli of which are 2.46 amd 2.70, respectively. The petrographical and physical investigations and tests on the intrusion mortar using the sands show that these sands may be used as fine aggre
gates for intrusion mortar if the mix proportioning is designed to give the mix of high water retentivity and of little bleeding. Suggested mix proportionings are shown in this report. In connection with this subject, a general method of mix design of intrusion mortar is presented. This method suggests that the factors such as pozzolan-cement ratio (P/C+P), sand-cement ratio (S/C+P), water-cement ratio (W/C+P), and dosages of cement dispersing agent and powdered aluminum should be selected considering properties of the mortar, i. e., flowability, water retentivity, bleeding, expansibility, and strength. The general tendency of effects of these factors mentioned above upon the properties of intrusion mortar are also descrived.
　Temperature rise of intrusion mortar brings out the loss of its flowability, This effect becomes considerably prominent when the original mix is so called stiff
-mix and is accelerated with the degree of temperature rise. One of the most effective remedy for this adverse effect is to decrease sand-cement ratio maintaining the other factors constant. To increase water-cement ratio should be avoided, since it will decrease water retentivity of the mortar, consequently resulting in an accelerated segregation of materials and low strength after hardened.
　Aeration of cement presents serious problems, that is, considerable loss of flowability of the motar and its strength. One of the test results shows that the mortar with aerated cement for 24 hours at 80 percent relative humidity and 20°C lost 30 percent in flowability and 20 percent in compressive strength at 28 days. Since the effects of the aeration of cement is quite unstable, there is no effective remedy for it. As commonly warned, therefore, no cement may be employed when it is aerated or in doubt of aeration until tests on the cement show that it can be used.
　Type or brand of cement also has considerable effects on the properties of intrusion mortar. Test results are given to show that a certain brand of portland flyash cement of B Type is more preferable to an ordinary portland cement, a part of which is replaced by fly ash to the equivalent amount as in the fly ash cement, since the former yields much less bleeding, higher water retentivity and higher compressive strength than the latter. The intrusion mortar made of a high early strength portland cement seems to give a more cohesive and less flowable mix than an ordinary portland cement if the identical water-cement ratio is employed.