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This study investigated the impact of different cuing history on the sulfate resistance of Portland-Limestone cement (PLC). Mortars of Portland cement (PC) and PLC with different dosages of limestone, 10%, 20%, 30% by mass, were cured in water at 20 °C and 60 °C for 28 days before immersed in Na2SO4 solution 50 g/L at 20 °C for sulfate resistance test. In addition to monitoring the length and mass changes of mortars, MIP and XRD were used to investigate microstructure and evolution of phase assemblages. Results show that PLC mortars cured at 20 °C give a poorer sulfate resistance than PC, the higher the limestone dosages in PLC, the worse sulfate resistance of the mortar. However, it is contrary for mortars cured at 60 °C. PLC shows a much better sulfate resistance than PC, and the higher the limestone dosages, the better sulfate resistance of the PLC mortars. The incorporation of limestone in PLC at dosages of 10–30% leads to the increase of carboaluminates content and the deterioration of pore structure, which is the main factor responsible for worsening the sulfate resistance of PLC mortars cured at 20 °C. When cured at 60 °C, the reduction of available aluminate caused by the dilution effect of limestone improves the sulfate resistance of PLC mortars. The formation of gypsum is not the main cause of the expansion. [ABSTRACT FROM AUTHOR]

The differences between the hydration of Portland cements with single and with mixed sulfate carriers in the presence of triethanolamine (TEA) were investigated, and possible mechanisms were proposed. Without TEA, cements with different types of sulfate carriers (gypsum, hemihydrate, anhydrite, and mixture of these) have a comparable hydration process at the same molar amount of calcium sulfate. At a TEA dosage of 0.5 wt.%, the sample with a mixture of three sulfate carriers shows substantially stronger retardation of the C3S (This publication uses the cement chemist notation: C3S = Ca3SiO5, C2S = Ca2SiO4, C3A = Ca3Al2O6, C4AF = Ca2(Al, Fe)2O5.) hydration than the cements with only one of these sulfate carriers, which is likely caused by the rapid formation of ettringite and the fast depletion of all sulfate carriers. These effects indicate that TEA influences the balance of sulfate carriers with aluminate‐containing clinker phases. On the one hand, TEA can disturb the original sulfate balance due to the accelerated dissolution of aluminate‐containing clinker phases, especially C4AF. On the other hand, these effects are closely related to the types and amounts of the sulfate carriers in the cement. A higher amount of sulfate carriers can minimize the TEA‐related retardation of the C3S hydration, and hemihydrate shows the strongest impact at the same calcium sulfate quantity. [ABSTRACT FROM AUTHOR]

Sulfate ions can induce the formation of thaumasite by sulfate attack (TSA). This attack mechanism destroys the binding capacity of the cement, resulting in surface wear and material deterioration. Research indicates that the manner of exposure to sulfates contributes to the generation of TSA, including continuous immersion and wetting/drying cycles. Although there are studies on different exposure conditions for the formation of TSA, most of them focus on the comparison with a single type of sulfate. Furthermore, the time of severe wear is quite variable. In this work, the effect of these different methods on the formation of thaumasite was studied in Portland-limestone cement (PLC) mortars exposed to Na₂SO₄ and MgSO₄ solutions at low temperatures (5 °C) for 455 days. Assessments included visual analyses, microstructure (XRD and FTIR) and monitoring changes in length and mass. The results indicated the formation of thaumasite in all mortars, intensified in the specimens under continuous immersion conditions, regardless of the type of sulfate. Delayed wear of wetting/drying cycles has been attributed to insufficient water for ion transfer and chemical reactions to initiate TSA. • Thaumasite formation was intensified in the condition of continuous immersion, regardless of the associated salt. • The high level of humidity was critical in accelerating the mortar wear process. • Continuously immersed mortars showed earlier surface wear than wet/dry cycles. • No significant surface wear occurred on samples subjected to MgSO₄ under wet/dry cycle conditions up to 455 test days. [ABSTRACT FROM AUTHOR]

• The present work investigates hydration of Portland cement at up to 7 days of reaction. • Hydration of alite is initially limited by the nucleation and growth of the hydrates, only after 4 to 10 h, the dissolution rate becomes the determining factor. • High sulfate concentrations in the solution accelerates the formation of C-S-H phase and thus hydration of alite. • Kinetics of C 3 A reaction with anhydrite is initially controlled by the precipitataion of ettringite and only later by the dissolution of calcium aluminate phase. • Hydration of silica gel from the carbonated cement paste is very rapid. In this work, the hydration kinetics and the development of concentrations in the pore solution of cement clinker, neat and composite cements pastes were investigated. Early alite hydration is mainly limited by the nucleation and growth of the hydrates (C-S-H, CH, ettringite). Only after 4 to 10 h, when the main alite reaction starts, the dissolution rate of the alite becomes the limiting factor. The kinetics of the reaction of C 3 A with anhydrite is initially limited by the slow nucleation and formation of ettringite and only later by the dissolution rate of calcium aluminate phase. The change of the mechanisms corresponds to the initiation of the portlandite precipitation. The slower reaction of clinker sample cannot be explained by the high Al concentration alone but rather by the effect of available sulfate; high sulfate concentrations accelerate the hydration. Higher alkali hydroxide concentration does not show an accelerating effect on PC hydration. [ABSTRACT FROM AUTHOR]

Supplementary cementitious materials (SCMs) can alter significantly the early hydration behavior of blended cement. While the underlying mechanisms have been intensively discussed in literature, they need to be extended regarding SCMs with complex mineralogy and surface properties, such as calcined clays. In this study, a blended Portland limestone cement was monitored during the first 48 h of hydration using in situ X-ray diffraction and isothermal calorimetry. The influence of a fine limestone and four different calcined clays, which vary in mineralogical composition and particle properties, was investigated at a replacement level of 30 wt%. The sulfate content was gradually adjusted and its influence on heat evolution and phase development was examined. It was shown, that depending on their particle properties, the investigated SCMs influence the aluminate and silicate clinker reaction by different mechanisms and to varying extents. The results underline the importance of proper sulfation of blended cements. [ABSTRACT FROM AUTHOR]