A cement of high fineness (Microfine@ Cement) was specified for grouting the dry joints in the Huites Dam by Lombardi Consultants, Zurich, Switzerland. The first half of the paper contains specifications on the Microfine Cements by Onoda Cement in Japan and test data on the Microfine Cements developed at Northwestern University under the direction of Professor Raymond Krizek. The second half includes specification and application of 120 metric tonnes of Microfine Cement into the dry joints of the Huites Dam. The Huite Dam is located over the Fuerte River in the north part of Sinoloa State, Mexico. The dam will regulate the flow of the river, provide 440 megawatts of electricity and irrigation waters for 70000 hectacres. Total reservoir capacity is 4568 million cubic metres. In March of 1995, the dam construction was completed and the reservoir was filled. For structural reasons, it was necessary joints before the concrete reaghed 24 &o inject some opened slightly on reaching 24 C. C, the joints Therefore, it was necessary to reinject Microfine Cement, the product that had been approved for use at this building site.

The objectives of the studies presented in this paper were to investigate the effects caused by steel reinforcing bars on determining the depth of cracks which appear on the surface of a concrete structure. Numerical studies were performed to investigate the interaction of stress waves with reinforcing bars. A full scale reinforced concrete beam was constructed as an experimental specimen. The specimen was loaded until cracks occurred. To measure the depth of a crack penetrating into the specimens, two receivers were used and located on the opposite sides of the crack. The first receiver on the impact side is used to obtain the time of impact initiation. The second receiver located on the other side of the crack is used to trace the arrival of the P-wave diffracted from the bottom edge of the crack. Subsequently, the depth of the crack can be determined. Experimental results show that if tests are performed on the regions without reinforcing bars, the crack depth can be obtained easily because the second receiver initially responds to the arrival of the diffracted P-wave. In the presence of reinforcing bars, the initial disturbance at the second receiver is caused by the arrival of P-wave propagating through reinforcing bars but its amplitude is much smaller than that associated with the following arrival of the P-wave diffracted from the bottom edge of the crack. It is concluded that the presence of reinforcing bars does not make it difficult to measure the crack depth.

The self-compacting concrete, which was developed in 1988 in Japan, can be filled in a formwork without using any vibrators. It is an effective means of ensuring consistent quality in concrete structures, as the human factor in consolidation can be eliminated. This type of concrete has markedly increased deformability without segregation; high deformability is achieved mainly through the use of superplasticizers, while segregation resistance is achieved mainly through viscosity of the mortar or paste components of the concrete. The focus of this study is on experimental assessment of the effects of each component of concrete mixture in self-compacting concrete on the fresh state. The main findings are as follows: (1) There are certain combinations of slump flow and funnel speed that gave optimum self-compactability, with self-compactability falling off as one moves away from these combinations. This agrees with the results of the previous studies. (2) Increasin g the coarse aggregate content above the range G/Glim = 0.50 results in loss of compaction. The decrease in compaction is in a non-linear relationship with the increase in coarse aggregate, showing a rapid falling-off in self-compactability over G/Glim = 0.50. (3) If the quantity of coarse aggregate is varied while the quantity of fine aggregate remains fixed, no clear change can be seen in the water-powder volume ratio required to achieve self-compacting concrete, but the quantity of super-plasticizer required increases.

This paper deals with the mixture proportions of high perform-ance concrete (HPC), and its mechanical properties, durability and applica-tion in projects. Compared with normal Portland cement concrete (NPC) with the same cement content, HPC has following advantages: its compressive strength at 28-day is increased by 52~ 56%, tensile strength at 28-day by 34%, resistance to freezing-thawing by 10 times, impermeability by 6~ 15 times, resistance to carbonation increased by over 5 times, resistance to chloride-ion by over 10 times, protection of rebar from corrosion of chloride by 50 times, resistance to abrasion erosion by 0.5~ 2.5 times and resistance to cavitation by 3- 6 times. By using suitable expanding admixture to compen-sate for early shrinkage, shrinkage of HPC is less than that of NPC, thus its dimentional stability is superior. Based upon results from 6 projects, it can be stated that HPC has good workability, and very little bleeding, and construc-tion quality could be easily controlled. Satisfactory results have been achieved after its 2~ 9 years of service.

A research program was carried out to evaluate the chloride-ion penetration of both air and non-air entrained concretes made with mineral admixtures as partial replacements of cement. Two series of investigations (Series 1 and Series 2) were carried out. The mixtures were proportioned to have 28-day strengths of 35 MPa for Series 1 and 69 MPa for Series 2. Chloride-ion penetration was determined in accordance with ASTM C 1202. Series 1 mixtures contained a Class C fly ash whereas Series 2 mixtures contained the fly ash and silica fume. In general, all the concrete mixtures, with or without mineral admixtures, exhibited low values of chloride-ion penetration. In this work, a concrete containing 37% Class C fly ash showed results comparable to a concrete containing 11% Class C fly ash plus 8 % silica fume with respect to chloride-ion penetration. The chloride-ion penetration of high-quality concrete system was found to be unaffected when silica fume concentration was increased from 8 % to 11% .