International Concrete Abstracts Portal

Use of a naphtalene-based superplasticizer at high dosages in concretes made with fly ash (100-150 kg/m3) and a moderate content of portland cement (250-300 kg/m3) results in great water reductions and high strengths (75-80 MPa after 28 days) for concretes with normal workability (slump 5-10 cm). Laboratory investigations concerning mixture proportions and pro-perties of the fresh and hardened concretes with a discussion of physical and chemical influences of the use of the superplasticizer are presented. Increasing problems with the supply of good, in-expensive, natural coarse aggregates may be solved through combined additions of superplasticizers and fly ash to the concrete. This paper further presents experimental evidence of mixture proportions and phy-sical data for socalled "sand-concrete", i.e. concrete without coarse aggregates but with "normal" contents of portland cement and water obtained by the addition of rather large amounts of fly ash and superplasticizers.

The purpose of this study was to examine the effect of adding various dosages of a melamine-based superplasticizer in the manufacture of extra-high strength block. Seven batches of block were cast as follows: a) reference mixtures in which no admixture was added; b) reference mixtures using a conventional block plasticizer; c) four mixtures using various dosages of su-perplasticizer: 1% by weight cement, 2%, 3%, and 2% with additional water. Halfway through each batch, the feed finish times were increased. The block were steam-cured at low pressure. The testing program consisted of a) impact-resistance and compressive strength at 24 hours; b) absorption and unit weight; and c) compressive strengths at 7, 14, and 28 days. All block exceeded the 5000 psi (34.5 MPa) net compressive strength requirement of extra-high strength block. The effect of the superplasticizer increased as the dosage increased. The superplasticizer also allowed for shorter feed times to achieve the same finish times. The encouraging results of this preliminary study indicate more work needs to be done to investigate the possibility of leaner cement mixes, lower temperature curing conditions, and possibly shorter feed finish times to achieve the economic advantages inherent with the use of superplasticizers.

The studies reported were concerned with the application of high-strength concrete to structural members as related to some aspects of their design, construction and behavior. With regard to construction, tests were performed on the consistencies and strengths of concretes of low water-cement ratios using superplasticizers. The superplasticizers used were the 5 brands being marketed in Japan. The influence on consistency of fineness of cement was also studied. In examinations made by design calculations, monorail piers were used as case studies. The relation between concrete strength and cross-sectional dimensions, and quality of reinforcing bars required when applying high-strength concrete to structural members were investigated. In structural tests, the stresses, bending strengths and ductilities of model piers using high-strength concrete were studied.

This paper reviews the application of a sulphonated melamine formaldehyde condensate superplasticizer (Melment L10) as a water-reducer-under laboratory conditions and in practice. Emphasis is on basic data on the compressive strength and stabi of green concrete, especially as it affects the production of concrete blocks, pipes and extruded concrete products. The results indicate that whenever high performance concrete is required, the use of the superplasticizer permits placing and proper compaction at almost any water-cement ratio, thus ensuring high quality concrete.

Strength, elasticity, shrinkage, swelling and creep of water-cured and steam-cured concretes (made with a rapid-hardening Portland cement) with and without the superplasticising admixture, Irgament ‘Mighty’ 150, have been compared over a period of one year. The mixes have the same workability but the one with the admixture clearly has a lower water-cement ratio. Compared with the admixture-free concrete, the superplasticiser concrete has a higher strength and a higher modulus of elasticity when continuously stored in water from the age of one day. However, when exposed to drying at the age of two days, the superplasticiser concrete has higher shrinkage and creep at a constant stress-strength ratio, and, at later ages, lower compressive strength and modulus of elasticity. For the tests in which the same two concretes were subjected to a six-hour cycle of steam curing and then stored in water, the compressive strength and static modulus of elasticity are initially higher but, at later ages, this is reversed for the superplasticiser concrete; in addition, the creep is higher for this concrete. When the same steam-cured concretes are exposed to drying at the age of one day, none of the properties investigated is affected by the presence of the superplasticiser.