Two different types of latex modifier were used to determine how curing conditions and latex-modifier content influenced compressive strength and durability. Freeze-thaw resistance in the presence of a 2.5 percent NaCl solution was evaluated by measuring both relative dynamic modulus and mass of scaled material. While all specimens were 14 days old at the start of testing, compressive strength increased as the period of initial wet-curing increased, durability factor values (ASTM C 666) were insensitive to the period of initial wet-curing, and scaling resistance was improved by increasing the wet-curing time. The air-void system, described by the spacing factor, was found to have a greater influence on durability and scaling than either latex-modifier content or duration of wet cure. A control mix made using a high-range water-reducing admixture (HRWRA) was used as a basis of comparison.

In October, 1994, CANMET in association with the American Concrete Institute sponsored a fourth conference on the superplasticizers and chemical admixtures in Montreal. The objective of this conference was to bring to the attention of the concrete community the new developments in chemical admixtures since the last conference in 1989. A total of 25 papers were accepted for publication in this special proceedings from the conference. If you are involved with superplasticizers and chemical admixtures, this special publication is a must. Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP148

Various types of superplasticizer that maintain concrete slump for longer periods have been extensively investigated. A new type of superplasticizer with high-range water-reducing slump-maintaining capacities, composed of sulfonic acid polymer with methacrylic acid derivatives, has recently been developed. In this study, influence of cement type, concrete temperature, and pozzolans on properties of fresh and hardened concrete with this type of superplasticizer was investigated. Two reference superplasticizers were widely used naphthalene-based and amino sulfonic acid-based. A significant increase in water-reducing capacity to obtain the same consistency was observed at a much lower dosage. Absolute value of zeta potential of cement particles with the superplasticizer increased with elapsed time until 90 min after mixing, which explains the high-slump-retention capacity of the concrete. Plasticizing effects of superplasticizers were more pronounced for concretes with fly ash or blast furnace slag as blending agents. Concrete bleeding decreased slightly. Properties of hardened concrete, such as compressive strength and drying shrinkage, were at nearly the same level as those of concrete with naphthalene-based superplasticizer.

The key to casting high-strength concrete with compressive strength of more than 100 MPa into complicated reinforced structures is to give the concrete high fluidity as well as to improve strength. The authors developed an acrylic copolymer-based new superplasticizer that can improve fluidity of concrete with water-binder ratio of around 0.20. Paper presents results of a series of studies conducted to determine the properties of fresh and hardened high-strength concrete using the newly developed superplasticizer. The effect of the new superplasticizer was examined with varying water-binder ratio, type of cement, and temperature compared with conventional superplasticizers. The new superplasticizer needed a much lower dosage than conventional superplasticizers to attain a certain slump (250 mm) for a water-binder ratio of around 0.20, and it significantly reduced concrete viscosity. Sufficient workability was kept for 2 hr without much delay in setting time, while conventional superplasticizers showed large slump loss and excessive delay in setting time. Results of strength development, drying shrinkage, and freeze-thaw resistance did not show any harmful effect. Field studies were conducted on application of the high-strength concrete to a prestressed concrete bridge with design strength of 100 MPa using the new superplasticizer. Workability and strength development of concrete were tested and resulted in sufficient quality.

Two well-understood and defined reactions in concrete are known as alkali-silica reaction (ASR) and alkali-carbonate reaction (ACR). These two reactions are extremely detrimental to the integrity of concrete structures. It is known that lithium-based chemical compounds can control and/or eliminate the expansion caused by ASR. Based on this technology, a commercial chemical admixture has been developed. The admixture is a ready-to-use liquid product formulated to meet ASTM C 494 requirements as a Type A water-reducing admixture. This product is not intended to control ACR-induced expansion. Therefore, identification of the types of alkali-aggregate reactions is necessary to effectively control concrete expansion.