International Concrete Abstracts Portal

The scaling of concrete and mortar involves sub-parallel de-laminations of material from the surface. To produce this phenomenon, differential stresses parallel to the surface and resulting in differential strain must be active. This research measured the differential strain developed along the surface of specially shaped mortar bars upon their wetting, drying, and osmosis due to application of deicer salts. Mortar bars were made at a w-c ratio of 0.4 and 0.6 with shaley sand and high quality dolomite as aggregate. The sand is known to cause surface scaling. The bars were cast in a ‘half circle’ shape. The normally cured samples were dried, and all but the outer surface of the ‘half circle’ were sealed.. This allowed the ingress of water and solutions from one direction only, such as would occur in an ‘infinite’ concrete surface. Steel pins were secured to the ends of the half circle to facilitate measurement of the strain. The strain of the specimens was measured during the following states: 1. dry samples, 2. saturating in water, 3. drying, 4. saturated, placed in saline solutions, 5. then placed in pure water. The results show that as the water entered or left the surface, stresses developed which were sufficient to deform the ends of the half circle up to 0.6% of the diameter distance. Largest deformations took place upon wetting, followed by those on drying, and the least deformation resulted from osmotic forces. When the samples had equilibrated, i.e., became either fully saturated, dried, or the pore fluid composition equaled that of the saturating medium, the strain was relaxed. Water-cement ratio influenced the time of maximum strain development and aggregate and cement type determined the magnitude of the strain.

In recent years, especially in Japan, the research on the utilization of industrial by-products and the recycled aggregates has proceeded, with emphasis of recycling and use of resources. Among the industrial by-products applicable to concrete aggregates, non-ferrous metal slags for fine aggregates such as ferronickel slag and copper slag, are examined in this study. These slags are suitable for aggregates because they are almost inert both chemically and physically in concrete. Also, concretes with these slags generally show the same strength level as normal concrete. However, the more the volume fraction of slag fine aggregates, the greater the bleeding, usually because of the heavy specific weight and glass-like surface properties with irregular grain shape. It is possible that the excessive bleeding is likely to affect the concrete quality, such as aggravating frost susceptibility. In this paper, freezing and thawing resistance of concretes, with several kinds of slag fine aggregates, are investigated. The durability factor of concrete according to ASTM C 666A, decreased with increased bleeding amount, and the severe bleeding in excess of 5 I/ m 2 aggressively impaired the frost resistance of air-entrained concrete when the water to cement ratio and the volume fraction of slag in fine aggregates exceeded 60% and 50%, respectively. The decreased freezing and thawing resistance could be attributed to the internal defects originated by the up flow of bleeding water, measurement of the air void system, etc. It is also shown that the addition of a chemical admixture compound with cellulose ether and a powder-like material, such as the lime stone powder, are highly effective to improve not only the bleeding but also the freezing and thawing resistance of concrete.

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.