Engineering properties and structural implications of Portland limestone cement mortar exposed to magnesium sulphate attack

Abstract

The overall aim of this paper is to establish the engineering properties and material durability of Portland limestone cements, particularly when they are exposed continually to an environment rich in magnesium sulphate ions, and conducive to thaumasite formation. In particular, non-destructive and destructive tests were used to identify and examine the interaction of the changes in mechanical properties with the onset of sulphate attack. To achieve these objectives, 40 3 40 3 160 mm mortar specimens were subjected to air curing at 58C and 208C, and also immersed in 1´8% MgSO 4 solution, again at 58C and 208C. The limestone content in the test specimens was kept at 0%, 5%, 15% and 35% replacement of cement by mass. The formation of thaumasite was checked and confirmed by x-ray diffraction supported by thermal analysis and scanning electron microscopy. The nondestructive tests used in the study included pulse velocity, dynamic modulus, shrinkage, expansion and changes in mass. In addition, flexural and compressive strengths were determined. All the tests were carried out up to one year. The results obtained from the tests have then been critically analysed. It is shown that mortar prisms containing 35% limestone and exposed to magnesium sulphate solution at 58C suffered extensive damage and deterioration within one year. In addition, prisms containing 15% limestone gave strong signs of impending damage due to sulphate attack. The results of the non-destructive and destructive tests were highly complementary, and confirmed each other. The major mechanical deterioration occurred through the loss of compressive strength of almost 75% of that of the original unaffected mortar, whilst the loss in flexural strength was relatively small. The results strongly indicate that compression members, containing 35% limestone and exposed to aggressive sulphate environment at temperatures of about 58C, can be seriously at risk in their ability to carry loads. On the other hand, it is unlikely that flexural members under these conditions would suffer the same degree of serious structural damage.

Thaumasite form of sulfate attack in limestone cement mortars: A study on long term efficiency of mineral admixtures

“…The test is, therefore, useful to detect cracking, voids, deterioration and the uniformity of the material. The presence of void or crack on the pulse path will increase the path length, as pulse goes around the void, leading to the decrease of the pulse velocity [23][24].…”

Mezcla ternaria de cemento Portland, escoria de alto horno y piedra caliza: Resistencia mecánica y durabilidad

“…Esta adición afecta el proceso de hidratación del C 3 A dando lugar a la formación de carboaluminatos y retrasando o impidiendo la transformación de etringita a monosulfoaluminatos, sin embargo acelera el proceso de hidratación del C 3 S al constituir sitios de nucleación de cristales de hidróxido de calcio, lo que se traduce en ganancia de la resistencia a edades tempranas (Bonavetti et al, 2001;Oey et al, 2013, Ramachandran & Zhang, 1986Péra et al, 1999;Vance et al, 2013). De otra parte, su uso contribuye a la mayor susceptibilidad al ataque por sulfatos de la mezcla cementicia, especialmente por la formación de taumasita, siendo este efecto dependiente del porcentaje de LS incorporado (Moir & Kelham, 1997;Hartshorn et al, 1999;Hartshorn et al, 2001;Irassar, 2009;Irassar et al, 2010).…”

Response of Fly Ash Based Quarry Dust Cement Mortar to Magnesium Sulphate Attack

“…Portland cements containing mineral additives like FA and slag are increasingly often utilized in concrete construction. There is a considerable body of scientific evidence showing judicious integration of such pozzolanic/cementitious elements in concrete can improve its qualities in the fresh and hardened phases, particularly its durability [1]. Concrete is increasingly being utilized in civil engineering structures, such as substructures, infrastructure, and industrial floors that are frequently exposed to harsh environmental conditions, because of the advantages it offers.…”