Portland Limestone Cement Research Articles

A study on the parameters affecting the properties of Portland limestone cements

In this paper the parameters affecting the properties of Portland limestone cements are investigated. Portland limestone cements of different fineness and limestone content have been produced by intergrinding clinker, gypsum and limestone. Two kinds of clinker of different chemical composition, mineralogical composition and strength development and three limestones, with different contents of calcite, dolomite, quartz and clay, have been used. It is concluded that the appropriate choice of the clinker quality, limestone quality, % limestone content and cement fineness can lead to the production of a limestone cement with the desired properties. Limestone cements, having up to 10% limestone content and fineness up to a limit value, develop almost the same compressive strength, as the corresponding pure cements. The limestone cements, generally have lower paste water demand than the relative pure cements and the water demand decrease is mainly affected by the clinker type and limestone quality. In any case the properties of the limestone cements are affected by the interaction of the two components rather than their individual properties.

The effect of clinker and limestone quality on the gas permeability, water absorption and pore structure of limestone cement concrete

In this paper the effect of clinker and limestone quality on the air permeability, water absorption and pore structure of limestone cement concrete is investigated. Portland limestone cements of different fineness and limestone content have been produced by intergrinding clinker, gypsum and limestone. Two clinkers with different chemical composition, mineralogical composition and strength development as well as three limestones, differing by their calcite, dolomite, quartz and clay contents, have been used. It is shown that the clinker quality significantly affects the gas permeability and sorptivity of the limestone cement concrete. Limestone cements with high C 3A and alkalis content seem to be more appropriate for improving the permeability properties of concrete. In addition, the effect of the limestone quality on the concrete permeability is not well established. The pore size distribution and more specifically the mean pore size affects the gas permeability and the sorptivity of the concrete. Finally it is concluded that, depending on the clinker quality and the cement fineness, limestone cement concrete, with an optimum limestone content, can give lower gas permeability and water absorption rate as compared with pure cement concrete.

Thaumasite — background and nature in deterioration of cements, mortars and concretes

Thaumasite has been shown to form at low temperatures, particularly 0–5 °C, as a non-binding calcium carbonate silicate sulphate hydrate under conditions of destructive sulphate attack. Formation of thaumasite arises generally from calcium silicate hydrate CSH and Ca 2+, CO 2− 3, SO 2− 3, CO 2 and water, or from ettringite in the presence of CSH, carbonate and/or carbon dioxide and water. It basically resembles a carbonated ettringite, with which it has often been confused in the past. Conversion of the main cementitious binder CSH into the non-binder thaumasite is a destructive form of sulphate attack. Greater awareness of the potential problems that thaumasite can cause has arisen with the increased use of limestone fillers in cements, the common employment of limestone aggregates in concrete and the introduction of Portland limestone cements, together with the realisation that structural foundations of buildings are, on average, below ambient temperature and (more often than not with on- and above-ground construction) are within the optimum temperature range for thaumasite to be formed. Instances have been found in specific studies of large quantities of thaumasite being formed in foundation concretes with no evidence for any structural damage above ground level. It is important to be aware of the propensity of thaumasite to form at low temperatures for mix designs, so as not to encourage any destructive sulphate attack by thaumasite to arise. This means utilising low water cement ratios for workable mortars and concretes, so as to give reduced permeability. This will prevent, or at least suitably hinder, ingress of destructive ions and water, so that the potential for destructive sulphate attack by formation of thaumasite is not actually realised in practice.

A Study on the Hydration of Portland Limestone Cement by Means of TG

Subject of this paper is to investigate the hydration process of Portland limestone cement containing 10-35% limestone. Cements, produced by co-grinding of clinker, limestone and gypsum, were hydrated for periods 6 h to 28 d and were studied by means of TG and XRD. The Ca(OH)2 content of the cements containing limestone is higher than in pure cements, specifically for 10% limestone content and ages more than 1 day. These results are in accordance with the strength development of the studied cements. In earlier ages the Ca(OH)2 content is slightly lower in the limestone cements and independent of the limestone content. After 1 day curing, the increase of limestone addition causes a relative increase of the non evaporable water. The XRD patterns indicated the presence of carboaluminates in the hydrated limestone cements.

Strength characteristics of Portland-limestone cements

Portland-limestone cements have been investigated in which up to 25% limestone has been used to replace the Portland cement clinker. Strength development in standard tests has been compared with that in constant workability concrete at varying cement contents. The latter has been shown to be a more meaningful guide to overall performance. The addition of 5% limestone had little effect on performance although at higher addition rates the properties of the limestone were shown to be significant. The suitability of the cements for use in a range of designed strength concretes has been demonstrated.