International Concrete Abstracts Portal

The degradation of samples of cement pastes, mortars and concretes in acidic solutions (pH 2-4) ha s b een investigated over relatively short periods, e.g. -72 hours at 25°C. The degradation rate of the cementitious material is taken as the rate of alkali leaching at constant pH; the latter is obtained directly from the amount of acid required, as function of time, to maintain the pH at a preset value. The data allow the calculation of apparent rate constants, the magnitude of which is expected to be related to the durability of the materials investigated in acidic environments. Paste degradation rates were obtained at two W/C (0.35 and 0.45); the role of several additives (silica fume, superplasticizers, air entraining agents) and the influence of solution composition (pH, ionic strength, other electrolytes) were investigated. Kinetic data were also obtained for the acid reaction rate of several mortar and concrete samples of varying mixture compositions and in the presence of S0,-2. Under the conditions of this study, the acid degradation rate appears largely controlled by H+ diffusion through the leached zone of the matrix. The diffusional rates values are moderately influenced by changes in mixture compositions, in reasonable agreement with expectations from greatly enhance the acid degradation rate, an effect zone and the related studies. Sulfate ions which can be understood from pH gradients in the leached activity coefficients of the H+ in the presence of sulfates.

In this study, the applicability of the automatic temperature control method instead of the ASTM C 672 test, for the determination of the scaling resistance on various kinds of concrete specimens was examined, because the automatic control method will be profitable from the viewpoint of the elimination of labor such as the transfer of specimen in every required cycle. The scaling damage obtained from this modified method was almost equivalent to that of the conventional ASTM test method. Using this automatic method, the characteristics of scaling were investigated using the bottom or side surface of the specimen for the test surface instead of the conventional top surface. In addition, the effects of air content, water cement ratio, de-icing salts, curing condition and use of a permeable sheet were also studied. The relation between the mass of scaled-off particles and the visual rating was also obtained. Through the examination of the characteristics of scaling, the automatic temperature control method of modifying the conventional ASTM method was judged promising for assessing the scaling resistance in the presence of de-icer salts.

The durability of cement-stabilized specimens in various aggressive media were studied by means of the Koch and Steinegger test over 56 days at 20°C. Prismatic lxlx6cm samples of normal portland cement (OPC) and normal portland cement with 80% ground granulated blast furnace slag (OPC/BFS) addition, were prepared mixing them with water containing 5,000 ppm Pb2+ (OPC samples), 15,000 ppm Pb2+ (OPC/BFS samples) or 50,000 ppm Cd 2+. Those specimens were immersed in the aggressive solutions tested: a buffered AcH/Ac- medium, a NaCl 0.45M + Na2SO4 0.03M solution (SO4= and Cl- concentrations equivalent to those of the sea water) and deionized water as reference. In addition, the concentration of toxic metals in the aggresive media. was measured I Changes into microstructure and flexural strength were evaluated by X-ray diffraction (XRD) and mercury intrusion porosimetry (MIP). The pore fluid solution extracted from specimens and the leachate solutions were analyzed for Pb2+, Cd2+, Ca2+, Na+,K+, SO4 and Cl-ions. Results show that normal portland cement and blast furnace slag blended cements are durable matrices in saline medium similar to sea water, but undergo an acid attack with formation of a porous degradation coating and dissolution of toxics metals in the acid medium of AcH/Ac- buffer solution.

This paper presents a laboratory accelerated method for measuring the effective chloride diffusion coefficient of concrete using the static diffusion cell technique. The method is based on initially saturating specimens with chlorides before testing them, in order to accelerate the time required to achieve steady state diffusion. The effective diffusion coefficient can be obtained after 7 to 10 weeks. Saturation of specimens was achieved by two procedures. The first one was simple vacuum-saturation, the second method was saturation by the applied voltage technique using 30V or 40V potential difference. The results of these experiments showed that saturating the specimens with chlorides does not affect the diffusion process, as indicated from the chloride concentration profiles across the specimens before and after testing in the diffusion cells. The steady state condition during the diffusion test is only achieved at 10 to 14 days of diffusion time. This is a relatively short time when compared to the time that it takes to obtain results using the conventional method. The total test period was reduced to 7 weeks to obtain the effective diffusion coefficient through relatively thick concrete and mortar specimens (25 mm). Data obtained for a wide range of mortars treated with surface coating compounds and for high performance concrete is compared with values of diffusion coefficients obtained from the unsteady state ponding method. A reasonable statistical conversion equation is proposed in order to compare or convert values of one test to another.

An organic shrinkage reducing agent consists mainly of lower alcohol alkylene oxide adducts. It has a great effect of reducing drying shrinkage. There are few studies on durability of concrete with the shrinkage reducing agent. This paper presents the results of a study on durability of concrete with the shrinkage reducing agent exposed to outdoor in a cold district for 10 years. Flexural strength, compressive strength and dynamic modulus of elasticity of concrete with the organic shrinkage reducing agent has not shown any problems as same as concrete without the agent even at the age of 10 years. Therefore, in a cold environment, it is thought that concrete with the shrinkage reducing agent, which contains a sufficient air content, will not be deteriorated by freezing and thawing action.