Air-entrained concretes were subjected to extended freezing-thawing tests to determine the durability of three porous marine limestone coarse aggregates. Control concretes were made with a nonporous limestone. Prior to mixing the concrete, the coarse aggregates were soaked for 24 hr. After initial curing, the specimens were placed in a standard moist room for 13 days until freezing tests began at 14 days' age. Weight change, length change, and dynamic modulus of elasticity were monitored throughout the test. Specimens exposed to the freezing-in-air procedure were subjected to 1000 freezing-thawing cycles without showing significant deterioration. Except for the control group, all specimens subjected to the freezing-in-water procedure began to deteriorate between 250 and 350 cycles, as indicated by increasing length and decreasing modulus of elasticity. Increasing weight of the water-frozen specimens during the first 300 cycles was attributed to water absorption. Calculations suggest that the coarse aggregate in specimens frozen in water had reached 80 to 95 percent saturation when deterioration began. These results emphasize the critical role played by moisture content in determining the freezing-thawing durability of coarse aggregates and the need to develop better methods to evaluate saturation levels during testing with respect to in-place conditions.

Discusses natural and artificial carbonation of mortar and concrete. The theoretical analyses and experimental results show that in both cases the mechanism of carbonation of mortar or concrete is the same. They are comparable when CO2 diffuses in the gas phase, the carbonation coefficient equation is Q = a1(2C1 / KP)«. The experimental results also indicate that the pores with radii over 320 A have a great effect on the diffusion coefficient, and the following relation holds: ln a1 = 105.66Ec - 0.877 where Ec is the volume of these pores divided by the total volume of the system. The results point out that there are some active sites on pore walls where CaCO3 first nucleates and the Ca++ near the pore moves toward these sites as the CaCO3 crystals grow.

Freezing and thawing cycles in northern latitudes have resulted in the breakdown of some aggregates and concrete. Deicing salts have accelerated the problem. However, freezing of water cannot be the principal cause of deterioration, since in the fine-grained aggregates and cement paste the pores are too small to allow freezing. Yet it is these materials that deteriorate the most. Deicing salts likewise lower the freezing point and the number of freeze-thaw cycles, yet cause increased breakdown. The same materials susceptible to freeze-thaw breakdown also deteriorate significantly under repeated wetting-drying cycles. Laboratory experiments show these materials to expand on wetting and contract on drying. NaCl solution causes significantly greater expansion. Ice formation in the pores, therefore, is not the primary cause of breakdown. The answer may be found in the nature of the water in the small pores--water affected by the capillary and surface forces of the pore material. The pore water has lower vapor pressure, which prevents it from freezing, but which results in osmotic pressure differential, causing expansion. Deicing salt cations are preferentially adsorbed and concentrated on pore surfaces, further increasing the osmotic potential, expansion, and breakdown. Methods that determine the pore size distribution, surface sorption characteristics of the pore walls, and volume changes on wetting are suggested as more definitive measures of aggregate (and concrete) durability, compared to some of the currently accepted tests. This paper presents an overview of processes causing the aggregate breakdown, based on the theoretical and laboratory-derived evidence accumulated in the author's lab over the last 15 years.

Presents results of accelerated freezing and thawing tests on non-air-entrained concretes containing chloride when tested in water and seawater, in accordance with ASTM C 666, Procedure A. A total of 25 concrete mixes were made. The water-cement ratio of the mixes was 0.55, and the percentage of chloride content as NaCl were 0, 0.1, 0.3, 0.5, 1.0, 3.0, 5.0, and 7.0 percent of the oven-dry sand by weight. Mixing water was replaced by the seawater to add NaCl to each concrete mix. A number of test cylinders were made for testing in compression at various ages, and the test prisms were cast for determining their freezing and thawing resistance. The fundamental transverse resonant frequency, the weight, and the length change of the test prisms were measured during the freezing and thawing test. The air-void parameters of the hardened concrete were determined for using sawn sections of the test prisms. The pore-size distributions of the hardened concrete were measured by a mercury porosimeter. The test results indicated that the freezing and thawing resistance decreased with increasing chloride content in both water and seawater. The air-entrained concrete containing less than 0.3 percent NaCl showed a good freezing and thawing resistance. The air-entrained concrete containing more than 0.5 percent NaCl did not perform satisfactorily in freezing and thawing tests conducted in water and seawater.

Paper presents the results of an experimental investigation on the freeze-thaw durability of polymer modified concrete (PMC). Basically, prism specimens were subjected to a maximum of 900 cycles of freezing and thawing, using ASTM C 666 Procedure A. Five sets of specimens with various amounts of polymer content were tested. The polymer consisted of a liquid epoxy resin and a curing agent (or hardener). Weight and fundamental transverse frequency were measured at various intervals of freeze-thaw cyclic loading. The results indicate that the freeze-thaw durability of PMC is better than that of non-air-entrained plain concrete. The PMC with polymer-cement ratio of 0.4 or higher can withstand 900 cycles of freezing and thawing.