SP173 In October 1997, the Council for the Orginazation of CANMET/ACI Conferences in association with American Concrete Institute and several cement and concrete organizations in Italy sponsored the fifth conference on the subject in Rome, Italy. This conference was aimed at transferring technology in the fastmoving field of chemical admixtures. A total of more than 60 papers from more than 20 countries were received and reviewed by the ACI review panel and 49 were accepted for publication in the proceedings of the conference. The proceedings were published as ACI special publication SP-173.

An investigation is presented to evaluate the effect an ester-amine admixture (EA) has on the durability of concrete exposed to sulfate and sulfuric acid solutions traditionally detrimental to concrete. Prisms were exposed to a MgS04 environment under cyclic wet/dry conditions for 336 days. Other prisms were exposed to a H2 S04 environment at pH=l for 100 days. During the sulfate exposures, the concrete specimens were evaluated by appearance and length change over time. During the sulfuric acid exposures, the concrete specimens were evaluated by the pH changes of the test solution. The ester-amine admixture was shown to be beneficial in reducing the initial susceptibility of concrete exposed to both environmenfs. This benefit was also observed to improve the resistance of already low permeability concrete containing pozzolans such as fly ash and silica fume. The behavior was explained by the admixture’s reaction products which line the concrete pore matrix. A mechanism that differentiates the action of the EA from other permeability reducing materials (e.g., pozzolans) is proposed.

Concrete is one of the most widely used construction materials in the world. In applications where appearance, durability, and permeability are of concern, reduction of cracking is a key need. A common cause of cracking is restrained drying shrinkage. Until very recently, drying shrinkage cracking has been controlled by reducing joint spacing, increasing reinforcement, and using expansive cements and admixtures. In this paper a new shrinkage-reducing admixture (SRA) is discussed. SRAs provide a convenient means of reducing drying shrinkage as they are added during batching and mix easily into the concrete. The SRA material discussed in this paper improved workability and finishing as an added benefit. The effects of mixture proportioning, curing conditions, and SRA content on unrestrained and restrained drying shrinkage were determined. The results show that long-term drying shrinkage reductions of 50% can be achieved, and that there is a significant improvement in restrained shrinkage performance. Even though the lowest absolute values for drying shrinkage occur with proper curing, there is still a substantial reduction in drying shrinkage for specimens cured for short times. It is shown that shrinkage reduction is directly related to the SRA addition rate as a percentage of the mixing water. Furthermore, data on large-scale field experiments show that substantial reduction in cracking is obtained for concretes treated with SRA.

Concrete tiles were produced according to a new technology based on a vacuum treatment combined with a vibro-compacting placement of superplasticized mixture. Three concrete mixtures (all vibro-compacted according to this technique) were manufactured with different water-cement ratio (0.50 or 0.32) and in the absence or in the presence of the vacuum treatment. Measurements of flexural strength, dimensional stability, SEM, image analysis and particle size distribution of anhydrous cement in concrete tiles were carried out. The vacuum treatment, which removed entrapped air voids from the fresh mixture during the vibro-compacting placement, increased flexural strength but did not change the dimensional stability. The reduction in the W/C from 0.50 to 0.32 significantly increased flexural strength. It also improved the dimensional stability in terms of a lower curling effect caused by different humidity exposures of the two opposite faces of the .concrete tile. The combination of vacuum treatment with low W/C produces a macro-defect free and low micro-porosity cement matrix which is responsible for the high strength and low curling effect of these concrete tiles.

New world record of altitude transportation of concrete (532 m) reached on the 2nd June 1994 in Riva de1 Garda Hydroelectric Power Plant. The requirement involved the construction of a new piezometric well and intake conduit and the replacing of the existing surface penstock with a new one built underground to reduce environmental impact. Two parallel tunnels were excavated: one for Ledro - Garda lakes location, the other for transporting penstock’s metal elements. The self supporting metal pipe (0 2, 30 mm, thickness 23 mm) has been blocked for all its length (790 m) by filling of the ring space between the excavation wall and the piping with 5.000 m2 of concrete. In order to reduce environmental impact it was decided to pump concrete from the l owe r end from an excavated chamber nearby the Powerhouse. The record level: 532 m (vertical) and 790 m (total length) widely exceeded the former one (432 m) obtained in 1985 in Spanish ESTANGENTO SALLENTE Power Plant.