International Concrete Abstracts Portal

Editors: Mohamed T. Bassuoni, R. Doug Hooton, and Thanos Drimalas

The papers presented in this volume were included in a three-part session sponsored by ACI Committee 201, Durability of Concrete, about sulfate attack on concrete at the ACI Convention in Philadelphia, PA, on October 23-24, 2016. In line with the practice and requirements of the American Concrete Institute, peer review, followed by appropriate response and revision by authors, has been used.

Deterioration of concrete due to sulfate attack is a complex process characterized by multiple damage manifestations including volumetric expansion, cracking, spalling, softening, and in some cases mushiness. Sulfate attack can generally be classified as internal or external to the cementitious matrix, and the underlying damage modes can be chemical or physical. The scope of papers involves a multitude of theoretical and experimental aspects of different forms of sulfate attack. Readers are urged to critically evaluate the work presented herein, in the light of the large body of knowledge and scientific literature on this durability topic.

Note: The individual papers are also available. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP-317

External sulfate attack is often described by a diffusion-reaction mechanism which leads to the decomposition of hardened cement paste and cracking of concrete. In most studies, the linear expansion of mortar/concrete prisms is measured according to ASTM C1012. Even though this test can be used to determine the suitability of a mixture for specific sulfate exposure conditions, it does not provide insights on the actual degradation process. This paper presents a series of experiments performed to quantify the damage evolution on cement-based mortars with and without fly ash. Conventional expansion tests were conducted, followed by measuring the chemical and mechanical changes on the cross section of the specimens using EDS and microhardness techniques. The overall damage was further evaluated using a novel flexural fracture test on the specimens. It was observed that partial replacement of cement with class F fly ash reduced the level of mechanical damage in exposure to sulfate attack.

This paper presents research on the sulfate resistance of concrete mixtures as it relates to ACI 318 Code requirements for sulfate resistance. The study evaluates the provisions of ACI 318 for various concrete mixtures containing sulfate resisting portland cements and supplementary cementitious materials with w/cm varying between 0.40 and 0.60. The sulfate resistance of concrete mixtures was evaluated using prolonged exposure in a concentrated sulfate solution in accordance with USBR Test 4908. The results on the concrete evaluation reveal that the ACI requirements are considerably conservative for most concrete mixtures that contain a sulfate resisting cementitious system with supplementary cementitious materials. Sulfate resisting portland cements did not perform as well in the associated exposure class defined in ACI 318. While a performance-based alternative to the requirement for a maximum w/cm was attempted, no clear criteria could be achieved. The paper proposes alternative criteria to those in ACI 318 for sulfate resistance based on the performance of concrete mixtures evaluated in this study.

The phenomena involving hydrated cement paste and a source of sulfate anion have been extensively studied over the last four decades. The present publication provides an overview of past external sulfate attack studies along with current views on the accuracy of standard methods to evaluate the performance of a concrete mixture in service; illustrating the need to find other means of laboratory testing based on “real” exposure conditions representative of sulfate reaction kinetics encountered in field structures. This study evaluates the efficacy of stresswave propagation testing to detect concrete microstructural disparities related to sulfate-induced damage. While respecting traditional means of inducing an external sulfate attack in the laboratory (complete immersion in a 5% sodium sulfate solution), the experimental study proposed a different methodology for evaluating the extent of sulfate degraded concrete in the laboratory. Over a 2-year exposure term, the extent of degradation of various specimen types, replicating transport mechanisms reminiscent of those seen in the field, were evaluated using ultrasonic pulse velocity. Through statistical analysis, the results discussed demonstrated that the test procedures conducted were reliable for assessing the changes in behaviour observed.

Synopsis: Mortar bars (CSA A3004-C8) were cast with portland and portland limestone cements in combination with various supplementary cementitious materials. The mortar bars were exposed to sodium sulfate solution at 1°C, 5°C, 10°C, and 23°C (34°F, 41°F, 50°F, 73°F); the length change due to external sulfate attack was monitored over time. Mortar cubes were also cast and stored in limewater at 5°C, 23°C, and 38°C (41°F, 73°F, 100°F). The compressive strengths of the mortar cubes were tested at regular intervals to determine the rates of compressive strength gain of the various mortars as a function of curing temperature. The results generally reveal that external sulfate attack is accelerated in cold temperature sulfate exposure, particularly among the mortars with higher supplementary cementitious material replacement levels. The results reveal that the hydration of supplementary cementitious materials is severely diminished upon early-age exposure to cold temperatures, leading to a more permeable pore structure and diminished resistance to sulfate attack. The compressive strength gain of the mortar cubes containing supplementary cementitious materials was retarded at cold temperatures; the impact was much less severe with control mortars. At temperatures ≥10°C (50°F) supplementary cementitious materials greatly enhance resistance to external sulfate attack relative to the control mortars.