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This paper reports on part of a substantial research programme on properties of condensed silica fume (CSF) concretes cured in temperate and climates, carried out in the Department of Civil Engineering at Loughborough. The hot The research approach was to investigate mixtures proportioned to have equal workability and 28 day strength (when water cured at 20°C). This paper examines the effect of superplastizer, curing method (water and polythene) and curing environment (temperate and hot) on the compressive strength, permeability and pore structure of 40 MPa concretes. More specifically, the paper contrasts the performance of two 15% CSF mixtures (replacement by weight of cement) where workabilities were controlled by the addition of extra water or superplasticizer. The development of the concretes’ strength and subsurface permeability index (air and water) with age (from 7 to 180 days) is described, together with the intrinsic permeability (air and water) and pore structure of their equivalent mortar fraction. The use of superplasticizer to control workability increased the compressive strength of CSF concrete mixtures by around 18% and 10% in the temperate and hot environments respectively. The super-plasticized concrete had lower air and water permeabilities which is attributed to an improved pore structure as confirmed by mercury intrusion porosimetry date. The improvements were more marked in the CSF concretes cured in a hot environment.

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

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.

High-performance concretes (HPC) typically have low w/c to achieve the desired levels of strength and durability. As a result, HPC have a tendency to be stiff and lose their workability rather quickly. Often, high-range water-reducing admixtures (HRWRA) are used to improve the workability of HPC. Care must be exercised when using any admixture, or combination of admixtures, to insure that there are no detrimental side effects that might shorten the life of the concrete. Research has shown that, although retempering concrete with an HRWRA will generally improve workability and maintain the strength of low-w/c concretes, it may also reduce freeze-thaw resistance. Therefore, an experimental study was

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.