No abstract

This paper presents research on transport properties and alkali-silica reaction (ASR) susceptibility of mortars containing a pozzolanic waste generated in the fluid catalytic cracking (wFCC) unit by the Portuguese oil-refinery. For this purpose, two series of mortars were prepared by partially replacing cement with 5%, 10% and 15% of wFCC catalyst. The main difference between the two series of mortars is the sand reactivity used in their composition. The results revealed that wFCC catalyst blended cement mortars exhibit an increased resistance against capillary water absorption and chloride migration, as well as a considerable inhibition effect on deleterious ASR expansion. However, under the adopted experimental conditions the incorporation of wFCC catalyst in mortars decreases their carbonation resistance.

Due to the improvement of several properties, such as lower water absorption and increasing resistance to microcracking, polymer modification of mortar and concrete potentially leads to an inhibiting effect on alkalisilica reaction (ASR). In this study, polymer-cement mortars (PCMs) were subjected to accelerated alkali reactivity tests and their performance compared to that of an unmodified cement mortar (CM). Expansion of PCMs was overall higher, but SEM observations revealed apparent lower microcracking intensity of the cement paste, compared to the unmodified CM. Subsequent stiffness damage tests (SDTs) quantified the existing damage after alkali reactivity tests and confirmed the lower microcracking intensity in PCMs.

This paper compares the factors known to influence the deleterious alkali-silica reaction in concrete with the properties that polymers tend to modify in cementitious materials. A discussion on the potential ASR-influencing mechanisms of polymer additions is provided, along with a critical review of the existing literature on the subject. The influence of the potentially significant differences in mechanical properties and sorptivity between polymer-modified and unmodified cementitious materials on the expansion results of alkali reactivity tests is also discussed. According to the available results, the influence of polymers on ASR-related expansion seems to depend on both polymer type and dosage, suggesting the existence of concurrent, not yet well understood mechanisms by which polymers may influence ASRrelated expansion. As polymer modification of cementitious materials can lead to significantly lower modulus of elasticity, higher tensile strength and resistance to microcracking, it is suggested that further research on the subject includes not only expansion tests but also an assessment of the resistance of polymer-modified cementitious materials to ASRrelated damage, the main concern due to this deleterious phenomena.

To reduce the size and amount of shrinkage cracks that frequently occur in Portland cement concrete, expansive cements have been developed, namely sulfoaluminate-type cements. These cements are increasingly used for the repair of concrete structures.This paper reports an approach to general concepts associated with sultbaluminate-type cements. The procedure for mix proportioning of the calcium sulfoaluminate cement blend using kaolin as a source of aluminates is described and the results of an experimental investigation of the behaviour of expansive cement mortars with respect to expansion and strength characteristics are presented. The hydrated crystalline products are also identified. RI~SUMI ~Afin de r~duire les dimensions et le hombre des fissures de retrait qui se produisent souvent clans le b(ton • base de ciment Portland, des ciments expansifs ont (t( d&elopp&. Ce sont des ciments de type sul~baluminate, de plus en plus souvent utilis& pour la r(paration des ouvrages en b&on. Cet article pr&ente une approche aux concepts g&~raux associ& aux ciments de type sulfoaluminate. On d&rit le procM( de dosage d'un ciment compos( h base de sulfoaluminate de calcium, ainsi que les r&ultats d'une 8tude exp&imentale du comportement des mortiers de ciment expansif, en ce qui concerne leur expansion et leur r&istance. Les produits cristallins hydrat& out (galement ~tk ident~'&.