International Concrete Abstracts Portal

In 1997, CANMET in association with the American Concrete Institute and several other organizations in Australia sponsored the Fourth International Conference on the subject. The conference was held in Sydney, Australia. More than 120 papers from 30 countries were received and peer reviewed in accordance with the policies of the American Concrete Institute; 81 were accepted for publication. The accepted papers deal with all aspects of durability of concrete, including chloride and sulphate attack, freezing and thawing cycling, alkali-aggregate reactions, cathodic protection, and the role of supplementary cementing materials to enhance durability of fiber-reinforced concrete and performance of repaired concrete structures. 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. SP170

Highly-flowable and self-compactable concretes (HFSCC) containing various types of powder materials were tested for their freezing and thawing resistance. The powder materials incorporated into the concrete include four kinds of cements, and two mineral admixtures that were used for replacing a part of normal portland cement. For most of concrete mixtures, water-to-powder materials ratio was fixed at 0.35 by weight, and a proper amount of viscosity-modifying admixture was added in them in addition to air-entraining and high-range water-reducing admixture. Concrete specimens were subjected to freezing and thawing test at the ages of 2 or 3 days, 14 days and 28 days. The results were analyzed utilizing a new technique proposed by one of the authors, with which the continued hydration of cementitious materials during the freezing and thawing test could be properly taken into account. It was found that the conventional procedures for determining the durability factor were not appropriate for young age concretes in which slowly hydrating cementitious materials were used. Another main conclusion was that the same precautions as those for ordinary concrete should be applied to the cold weather concreting of HFSCC, even when its water-cement ratio was as low as 0.35.

Frost damage of concrete gradually proceeds due to freezing and thawing of water in pore structure. The main cause is the expansion of frozen water, which is influenced by pore size distribution and air void spacing factor. This study focuses on the pore size distribution and the air void spacing factor. Freezing and thawing tests were conducted and the expansion was measured. Based on the test results, a strain model was proposed. Furthermore, the pore size distribution and the air void spacing factor were measured for different areas of an actual structure, and the degree of deterioration in the structures was compared with the expansion volume calculated using the model. It is found that the strain model represented the frost-resistance of concrete taking into account the difference of the pore size distribution and the air void spacing factor. That model also simulated the deterioration of an actual structure.

This report presents the results of laboratory studies conducted to determine freezing and thawing resistance of high flowing concrete. High flowing concretes were made using a combination of different cementitious materials (Fly ash, blast-furnace slag and silica fume). The water-to-cementitious materials ratio was 0.32, and the sand coarse aggregate ratio was 0.51. All mixtures used a superplasticizer and were non-air-entrained. Test cylinders were made for testing in compression at 1 , 7 and 28 days, and test prisms were cast for determining resistance to freezing and thawing cycles in accordance with ASTM C 666, Procedure A. The curing methods were water curing and steam curing. The air void parameters of the hardened concrete were determined on sawn sections. The pore size distributions of the hardened concrete was measured by mercury porosimeter. The test results have indicated that the non-air-entrained , high-flowing concrete with steam curing showed low durability factors. The high flowing concrete with the water curing performed satisfactorily when subjected to up to 900 cycles of freezing and thawing.

The relationships between the autogenous shrinkage, and the hydration reaction of cement and the structural change of hardened cement paste have been investigated by hermetically curing the cement pastes of normal portland cement, type B - blast furnace slag cement and 10% silica-fume blended cement prepared at W/C of 0.5 and 0.25 and continuously measuring the humidity changes and the shrinkage strains of hardened cement pastes to obtain the basic data for elucidating the mechanism of autogenous shrinkage. Although there was a time lag between the autogenous shrinkage and the humidity change of hardened cement paste, no autogenous shrinkage took place in the cement paste prepared at W/C of 0.5 showing no humidity reduction. The autogenous shrinkage observed in the cement paste prepared at W/C of 0.25, therefore, is considered to be caused by the self dessication at a relative humidity (RH) from 100 to 80%. The autogenous shrinkage occured mainly during a period from 8 hours to 4 days and slightly increased after that. It is considered that the autogenous shrinkage takes place because the free water contained in pores particularly in fine gel pores formed by producing a large quantity of C-S-H is consumed by the hydration reaction and the humidity in the hardened cement paste is reduced. The autogenous shrinkage of type B - blast furnace slag cement paste was approximately 1,800~ which was about 1.8 times that of normal portland cement paste. Since type B - blast furnace slag cement paste produces more C-S-H than normal portland cement paste, thereby causing remarkable autogenous shrinkage. The autogenous shrinkage of 10% silica-fume blended cement paste is about 1,000u almost same as that of normal portland cement paste, since the pozzolanic reaction is suppressed in its paste prepared at W/C of 0.25 up to 4 days.