Inadequate performance of concrete structures is often caused by deficient construction practices and lack of appropriate specifications for controlling concrete properties that are related to adequate performance during the expected service life of a structure. Work carried out for many years at the Civil Engineering Materials Unit (CEMU) of the University of Leeds has shown that the durability of concrete can be assessed effectively by measuring its permeability to gases, liquids, and ions. Paper presents the findings of a laboratory study of the properties of normal portland cement and fly ash-normal portland cement mortar and concrete mixtures that influence their oxygen and chloride-ion permeability. The study involves 28 mixtures incorporating the use of five chemically different superplasticizers and three water-cementitious materials ratios. Statistical models that relate compressive strength, porosity, pore-size distribution, and water-cementitious materials ratio to oxygen and chloride-ion permeability are presented.

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

Aim of this study is to estimate the workability of highly superplasticized concrete, which can satisfactorily fill up all the corners of the forms in reinforced concrete without using a mechanical compactor. To place concrete into reinforced concrete members, it must have segregation resistance and high fluidity. These properties are obtained by using very fine powders with an AE-type high-range water-reducing admixture. The highly superplasticized concrete was prepared by mixing blast furnace slag and limestone powder or silica fume with ordinary portland cement. The fluidity was measured by the box flow test (with and without the reinforcement) and by rheological tests of wet-screening mortar. The effects of mix proportioning and spacing of reinforcements on the fluidity of highly superplasticized concrete have been determined.

It is well known that to successfully pass ASTM C 666 (Procedure A) for rapid freeze-thaw resistance, normal strength concrete must contain an adequate amount of entrained air composed of minute air bubbles with the right spacing factor. As concrete slump is increasingly restored at the jobsite using superplasticizer instead of retempering with water, it is essential that slump increase does not alter the total air content and air-void system if the concrete is to be frost-resistant. Since mixed results have been reported when superplasticizer is added to air-entrained concrete at the jobsite, a research program was undertaken to study the compatibility between three air-entraining agents, four water reducers, and one polynaphthalene sulfonate superplasticizer currently used in Eastern Canada. Experimental results conducted on 12 different combinations of admixtures with a Type 10 (ASTM Type I) portland cement show that the addition of superplasticizer nearly always increased the air content without changing the bubble spacing. The only case in which the air bubble spacing was significantly altered was when the air content of the concrete was lower than 4.5 percent 70 min after batching. In this case, the total air content decreased after the introduction of the superplasticizer, while the spacing factor increased significantly. A second Type 10 cement was used to duplicate these results. No significant difference was found between the results of the two sets of experiments.

Flowing concrete with high flowability prepared with river gravel and crushed stone was investigated for mix proportioning, flowability, strength, shrinkage, carbonation, and freeze-thaw resistance. This concrete has proved highly feasible in terms of cost and performance. The main findings can be summarized as follows: 1) the slump of flowing concrete is capable of sufficiently filling with slight compaction ranges of 24 to 26 cm, corresponding to a flow from 50 to 60 cm, and a differential height less than 8 cm in the box test; 2) flowing concrete with a water-cement ratio from 30 to 60 percent can be made by using a new admixture and with a simple correction of the standard table of mix proportioning; 3) flowing concrete can be produced with specified concrete strengths ranging from 18 to 60 MPa; 4) strength and durability of flowing concrete showed no significant difference from that of AE concrete without any special admixtures.