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This project originated because of premature deterioration of concrete pavements in Wisconsin. The deterioration took the form of a “V” at ,the joints of the pavements. A number of hypotheses had been put forward by various investigators of the damaged concrete. These included filling of the air voids by ettringite, which was thought to reduce the ability of the air void system to protect the concrete against frost damage. The purpose of the work reported here was to recreate the damage mechanism in the laboratory and investigate the sequence of events leading to the deterioration of the concrete. Three cements produced from the same raw materials were used in the project. Two were commercial Type I and Type II cements; the third was made by intergrinding the Type I cement with additional gypsum to increase the amount of available sulfate in the concrete. Concrete prisms 3 x 3 x ll-l/ 4 inches (75 x 75 x 285 mm) were subjected to the conditions specified by ASTM C 666 Procedure A, except that 3% NaCl solutions either with or without added gypsum (to simulate road salt) were used instead of water. The freeze/thaw cycles were interrupted over the weekends, when the specimens were allowed to dry out in laboratory air. The specimens were tested to destruction in most cases. Companion specimens were examined petrographically during the course of the test period in order to establish a sequence of ettringite deposition and damage. Damage was measured by mass loss, length change, and relative dynamic modulus. The findings show that the ettringite deposited in the air voids did not cause cracking, nor did it contribute to the propagation of existing cracks. Rather, it appears to have been opportunistic: cracks due to frost damage created space for ettringite crystals to grow.

The effect of infilling of air voids by ettringite on resistance of concretes to freezing and thawing was studied. Nine concrete mixtures, made with five cements with or without Class C fly ash, were exposed to freezing-thawing cycles following 110 to 222 days of moist curing. Prior to freezing-thawing, the specimens were examined by a low-vacuum scanning electron microscope (SEM) for the degree of infilling. It was found that the extent of the infilling depends on the length of moist curing as well as the wet/dry treatment. The infilling implies that these air voids are water-accessible. The function of the air-void system to protect concrete from freezing and thawing has been compromised due to the presence of water in some air voids. The infilling seems also to increase effective spacing factor. These might cause concrete to be more vulnerable to freezing-thawing damage.

Since the past 25 to 30 years, preferably heat treated precast concrete members (> 70 “C) manufactured with high early strength Portland Cements with higher sulphate contents, under adverse exposure conditions have some-times exhibited structural damage in the form of map cracking and loss of strength. These damages are characterized as Damaging Late Ettringite Formation (DLEF) (1). The cause for the increased occurrence of DLEF starting about 1970 is to our opinion the world wide increase of the permissible sulphate contents of the Portland-Cements (2-5). It is important that 1 wt.-% SO3 can form 5 wt.-% of ettringite or 7.7 wt.-% thaumasite. In “German directions“ a maximum heat treatment (HT) temperature of 80°C is specified for concrete exposed to dry environmental conditions. For concrete‘ exposed to intermediate or permanent wet conditions, a maximum HT temperature of 60°C is specified. Though the standard does not provide clear directions, if is believed that cements containing pozzolanic admixtures can be subjected to more intensive HT (6). DLEF is caused by a formation, destruction and a later renewed forma-tion of ettringite occuring preferably after HT at > 70°C of pastes, mortars and concretes made with high strength Portland cements. - Very early start of HT showed no significant influence on DLEF. Late or repeated HT resulted in more severe or repeated damaging. - Humidities < 95 % at 20°C resulted up to 780 d of starage in no DLEF. - After treatment with interim some FTC and/or cured at low temperatures provoked more early and severe destruction.

Changes in the cement manufacturing process such as the use of higher sulfur fuels have tended to raise clinker sulfate levels and SO3/alkali ratios. As a consequence, interground gypsum additions to cement have dropped because more sulfate is available from the clinker. Also, these clinker sulfates tend to be available as double sulfate salts; calcium langbeinite instead of potassium sulfate. What is the impact of clinkers with high SO, level on concrete performance; mainly on its workability and durability ? The aim of this study is to provide some answers to this question. Cements made from either high SO, clinker or low SO, clinker and gypsum or hemihydrate, but with a given chemical composition, have been simulated by pure phase materials and hydrated up to one hour. Calcium langbeinite is rapidly dissolved. Because of its dissolution rate and ability to form “blocking ettringite”, high calcium langbeinite clinkers should provide improved rheological properties. Moreover, cements made with clinkers containing significant quantities of calcium langbeinite should have a similar workability and durability to a cement made with a low sulfate clinker to which larger quantities of gypsum have been added. The dissolution rate of anhydrite potentially existing in very high SO3/alkali clinker has also been simulated. Experiments indicate that it dissolves and reacts quite quickly so that it should not provide any durability problem if present in cement and concrete.

The volume stabilities of mortars have been monitored for periods up to 5 years. In addition to controls maintained at 20°C, prisms were subjected to high temperature curing regimes, typically 12 hours at 70, 80 or 9OO C. Curing temperature was found to be the dominant factor in determining whether significant (>O. 1%) expansion took place during subsequent water storage at 20°C. Most of the mortars expanded after curing at 90°C but very few at 80°C and none at 70°C. Analysis of the results for mortars cured at 90°C indicated that expansion increased with cement fineness and levels of alkali, C3 A, C3 S and MgO and showed a maximum at a cement SO3 content of -4%. The pessimum SO3 content increased with cement alkali content. The incorporation of ground limestone accelerated expansion but did not affect the ultimate value. Cement replacement levels of 30% or 40% with siliceous fly ash and 30% or 50% with ground granulated blastfurnace slag appeared to prevent expansion. A sample of Type IS cement gave only moderate expansion. The mortars that expanded after curing at 80°C had high alkali levels, through the incorporation of KOH or K2 SO4 in the mixing water. At 20°C no long-term expansions were observed, despite the inclusion of cements with total SO3 levels up to 5.6% and clinker SO3 levels up to 2.6%. The Type K cement expanded by -0.05% within the first 7 days and was then stable. Cements based on a high C3 A clinker gave early expansions (-56 days) which increased as the cement SO3 content increased and as the specific surface area decreased, although all expansions were <0. 1%.