Portland Limestone Cement Mortars Research Articles

Thaumasite formation in Portland-limestone cement mortars: Effect of wetting/drying cycles and continuous immersion in different sulfate sources

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.

Assessment of Durability Indicators for Service Life Prediction of Portland Limestone Cementitious Systems Produced with Permeability-Reducing Admixtures

Supplementary cementing materials (SCMs) and the challenges associated with admixture compatibility and durability performance are continuous challenges for the construction industry. Utilizing SCMs has apparent benefits in reducing the carbon footprint and improving the durability performance of concrete structures. This work investigates the performance of mortars composed of Portland limestone cement, calcium carbonate, butyl stearate, and oleic acid. The effort focuses on transport properties using electrical resistivity, chloride migration, porosity, and water permeability measurements. Then, various methods based on the last parameters are compared to assess the changes in the effective chloride diffusion coefficient and the intrinsic liquid water permeability. Measurements for drying shrinkage, thermal expansion, and compressive strength are conducted to verify durability and mechanical performance. The effect of the admixture addition on the service life of a structure fully submerged in marine exposure conditions is then evaluated using Fick’s second law of diffusion and the approach described by FIB model code 34. The results indicate that incorporating calcium carbonate, butyl stearate, and oleic acid in mortar mixtures provides enhanced durability compared to plain Portland limestone cement mortars.

Sulfate resistance of Portland-Limestone cement mortars cured at 20 °C and 60 °C

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.

Durability performance of Portland limestone cement mortar containing butyl and zinc stearate admixtures

The benefits of partial replacement of Portland cement by limestone are well established. This study investigates the impact of zinc and butyl stearates, as water-repellent additives, on the compressive strength, flexural strength, water penetration, absorption, chloride migration, density, drying shrinkage, and thermal expansion of Portland Limestone Cement mortars. The contents of stearates in this work are 1%, 2%, 3%, 4%, 5% by mass of binder content. Spectroscopic analyses using scanning electron microscopy and X-ray diffraction revealed discrete changes in the derived cement composite microstructure. The results of hardened mortar evaluation showed a negligible effect of zinc stearate on durability performance. In contrast to that, incorporation of butyl stearate in the mixtures enhanced resistivity to water permeability and chloride migration.

Fresh and hardened properties of self consolidating Portland limestone cement mortars: Effect of high volume limestone powder replaced by cement

The main purpose of this experimental study is to elucidate the performance of self-compacting mortars (SCMs) composed of high volume limestone powder (LSP). In accordance with this purpose, four different SCMs at which limestone content varied as 0%, 15%, 25% and 35% were designed and later on fresh, hardened and durability properties of the mixtures were investigated for different curing ages depending on the testing method. Compressive strength, splitting tensile strength, rheological properties, mini-slump cone, carbonation, UPV and capillary water absorption were investigated in terms of fresh and hardened performance properties. In term of fresh properties, test results showed that there was a clear increase in the yield stress up to LSP content of 15% and beyond this level there was a tendency of reduction of the yield stress with the increase of limestone addition and also slumps values increased and pointed out a satisfactory fresh property in accordance with the increase in the replacement level of LSP. For mechanical properties, there was a steady decrease in the compressive strength values with the increase in LSP content while the addition of LSP in SCMs more than 15% did not improve splitting tensile strength of the mixtures for all curing ages. As a durability property, carbonation resistance of SCMs samples decreased with the increase in LSP replacement level for all of the mixtures and also UPV values were in an acceptable range of good (for 15%) and doubtful (for 35%) category intervals. Furthermore, the control mixture with the only PC had the lowest sorptivity coefficient as 2.73 cm/s1/2 followed by SCMs with 15%, 25% and 35% LSP as 5.11, 6.13 and 6.14 cm/s1/2, respectively.

The Behavior of Portland Limestone-Calcined Clays Cement at 5°C

The effect of calcined clays of the swelling type, on the strength and expansion behavior of Portland limestone cement is studied at 5°C. Local clays were thermally activated by burning one hour at 900 °C and were ground to a Blaine of 2842 (cm2/g). The pozzolanic reactivity of the activated clays was defined chemically and according to ASTM C311/C311M-13. Portland limestone cement was prepared by replacing 30% CEM I 42.5 N by limestone powder. Pozzolanic cements were prepared by replacing 10 and 20% of the limestone powder by calcined clays, the mixes were used to replace 30% of CEM I. Mortars specimens pre-cured for 28-day long as well as for a short period of one day, were immersed in sulfate solutions at 5°C for time up to 90 days. The compressive strength and length change were measured for the samples.The results show that replacement of limestone with calcined clays improves the compressive strength and the expansion of Portland limestone cement mortars in water and sulfate solutions. Ettringite was detected in the expanded mortars and no thaumasite formed. The results are interpreted in terms of the mechanism of thaumasite formation.

The influence of water-repellent admixtures on the behaviour and the effectiveness of Portland limestone cement mortars

Water-repellent mortars were prepared using different hydrophobic compounds as admixtures. Calcium and zinc stearates, silane/siloxane products (as liquid solution and powder) were mixed into limestone cement mortars for obtaining in-bulk water-repellent mortars suitable for building protection and resistant to the degrading action of water. The influences of the admixtures on the hydration and structure of the designed mortars were investigated by SEM, TG–DSC, FT-IR, XRD, and isothermal calorimetry. The effectiveness of these agents against water action was evaluated by using techniques and methods such as mercury intrusion porosimetry, water absorption tests and contact angle measurements. Siloxane products conveyed good water-repellent effectiveness, without strongly influencing the setting and hydration of the binder, while the zinc stearates slowed down the hydration reactions.

Varying fly ash and slag contents in Portland limestone cement mortars exposed to external sulfates

The partial replacement of Portland cement with supplementary cementing materials (SCMs) is known to improve concrete’s resistance to external sulfate attack. However, an increase in thaumasite formation has been observed in Portland cements with interground limestone. The effects of varying SCM and limestone replacement levels on the severity of external sulfate attack in moderate-C3A and high-C3A Portland cements in 5°C and 23°C Na2SO4 solution are studied. The partial replacement of Portland cement with SCMs greatly enhances the resistance to external sulfate attack, including thaumasite sulfate attack. The rate of deterioration is strongly correlated to SCM content, C3A content, and temperature.

Evaluation of the effect of tricalcium aluminate content on the severity of sulfate attack in Portland cement and Portland limestone cement mortars

It is widely understood that the tricalcium aluminate content of Portland cement is inversely related to the concrete’s ability to resist external sulfate attack. Furthermore, recent research has demonstrated a link between elevated levels of interground limestone and accelerated sulfate attack, particularly thaumasite sulfate attack at low-temperatures (below 10°C). In this paper the relationships between Portland cement C3A-content, interground limestone content and supplementary cementitious materials (Type F fly ash and silica fume) are explored. The mortar bars cast with high-C3A cement failed much earlier than the same bars cast with moderate-C3A cement. External sulfate attack occurred more rapidly at 5°C than at 23°C. Limestone content did not affect the rate of external sulfate attack.

Thaumasite sulfate attack in Portland and Portland-limestone cement mortars exposed to sulfate solution

The resistance of a plain Portland cement and a Portland-limestone cement to sulfate attack at 5°C was evaluated. The expansion of mortar bars exposed to a sodium sulfate solution was measured over time and different phases formed at various stages of the sulfate attack were identified using XRD. Results show that the mortar bars initially formed ettringite and gypsum causing some expansion, but expanded much more and ultimately disintegrated due to thaumasite formation. The opening up of the microstructure, caused by extensive cracking of the samples at the early stages was a prerequisite for the formation of thaumasite.

The effect of C3A content on sulfate durability of Portland limestone cement mortars

The effect of C3A content on sulfate resistance of limestone incorporated cements has been investigated within the scope of this study. Cements with two different C3A contents (4.6%, 11.2%) have been used. Blended cements have been prepared by separate grinding and mixing method. Limestone incorporation ratios were 5%, 10%, 20% and 40%, respectively. Standard mortar samples of 50×50×50mm cubes and 25×25×285mm prisms have been prepared. After 1months of water curing, samples have been exposed to different sulfate solutions (Na2SO4 and MgSO4) and temperatures (5 and 20°C) for a period of 6months. During this period length changes were monitored and compressive strength values have been determined at 3 and 6months intervals of sulfate exposure. Furthermore microstructure investigations have been conducted on selected samples.Test results showed that increasing C3A content propagate the deterioration rate of limestone blended cement mortars exposed to both Na2SO4 and MgSO4 solutions. This situation is more significant at higher limestone replacement ratios and low temperatures. Microstructural investigations revealed that deterioration mechanism of limestone blended samples due to sulfate attack depend on the C3A content and cation type of sulfate solutions. As a general consideration, limestone replacement ratios at and above 20% will be a serious problem for mortars incorporating high C3A content from the view point of sulfate durability.

Long term behavior of Portland limestone cement mortars exposed to magnesium sulfate attack

Concrete and mortar made from limestone cement may exhibit a lack of durability due to the formation of thaumasite. This work deals with the long term behavior of limestone cement mortars in relation to the limestone content, the curing conditions and the type of the sand. Three types of cement were examined: (i) Portland cement (PC), (ii) Portland limestone cement containing 15% w/w limestone and (iii) Portland limestone cement containing 30% w/w limestone. Mortar specimens were prepared using calcareous and siliceous sand. The specimens were immersed in a 1.8% MgSO 4 solution and cured at: (i) 5 °C and (ii) 25 °C. The status of the samples for a storage period of 5 years are reported, based on visual inspection, compressive strength , mass measurements, ultrasonic pulse velocity measurements and analytical techniques, including X-ray diffraction, thermal analysis and scanning electron microscopy. It is concluded that mortars containing limestone, either as sand or as a main constituent of the cement, suffer from the thaumasite form of sulfate attack (TSA) at low temperature. In some cases, the TSA leads to almost complete damage of the specimens after only 60 months of exposure. At 25 °C the specimens do not show any signs of conventional sulfate attack, even after 60 months of exposure to sulfate solution .

Effects of limestone replacement ratio on the sulfate resistance of Portland limestone cement mortars exposed to extraordinary high sulfate concentrations

A comparative study has been performed on the sulfate resistance of Portland limestone cement (PLC) mortars exposed to extraordinary high sulfate concentrations (200 g/l). PLCs have been prepared by using two types of clinkers having different C 3S/C 2S ratios and interstitial phase morphologies. Blended cements have been prepared by replacing 5%, 10%, 20% and 40% of clinker with limestone. Cubic (50 × 50 × 50 mm) and prismatic (25 × 25 × 285 mm) cement mortars were prepared. After two months initial water curing, these samples were exposed to three different sulfate solutions (Na 2SO 4 at 20 °C and 5 °C, MgSO 4 at 5 °C). Solutions were not refreshed and pH values of solutions were monitored during the testing stage. The compressive strength and length changes of samples have been monitored for a period of 1 year. Additional microstructural analyses have been conducted by XRD and SEM/EDS studies. Results indicated that in general, limestone replacement ratio and low temperature negatively affect the sulfate resistance of cement mortars. Additionally, clinkers of high C 3S/C 2S ratios with dendritic interstitial phase structure were found to be more prone to sulfate attack in the presence of high amounts of limestone. From the results, it is postulated that in the absence of solution change, extraordinary high sulfate content modified the mechanism of sulfate reactions and formation of related products. At high limestone replacement ratios, XRD and SEM/EDS studies revealed that while ettringite is the main deterioration product for the samples exposed to Na 2SO 4, gypsum and thaumasite formation were dominant products of deterioration in the case of MgSO 4 attack. It can be concluded that, the difference between reaction mechanisms of Na 2SO 4 and MgSO 4 attack to limestone cement mortars strongly depends on the pH change of sulfate solutions.

Long term durability of Portland-limestone cement mortars exposed to magnesium sulfate attack

Mortar prisms made with Portland-limestone cement have been stored in air and in 1.8% magnesium sulfate solution at 5 °C and have been examined over a period of 5 years. This paper is primarily concerned with the results obtained at the end of this period. The limestone content in the samples varied from 0% to 35%, but the water to cement plus limestone powder ratio was kept constant. The status of the samples after storage for 5 years is reported based on visual examination and a thorough characterisation using X-ray diffraction, infra-red spectroscopy and scanning electron microscopy. The prisms stored in magnesium sulfate solution were all showing clear signs of deterioration, increasing in intensity with limestone content. The mortar prism with 5% limestone replacement was, however, seriously degraded in comparison with the ordinary Portland cement control prism, and it is shown that this was due to the thaumasite form of sulfate attack .

The thaumasite form of sulfate attack in Portland-limestone cement mortars stored in magnesium sulfate solution

Mortar prisms (40×40×160 mm 3) made at a water:solids ratio of 0.5 and a cement:aggregate ratio of 1:2.5 from Portland cement with 0%, 5%, 15% and 35% limestone additions were cured in water at 20 °C for 28 days. They were subsequently stored in air and submerged in 1.8% magnesium sulfate solution at 5 and 20 °C for a year. The prisms were inspected visually every 28 days, the solution was changed every 84 days, and selected samples were examined by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) after specified intervals. The thaumasite form of sulfate attack was readily identified in the ordinary Portland cement (OPC) – 35% limestone mortar after 126 days storage in magnesium sulfate solution. The surface layer of the prism had spalled and was mushy, while the core was still solid and sound. Gypsum, thaumasite and brucite were identified in the surface layer. Secondary electron images of polished sections of deteriorated Portland-limestone cement mortars revealed the microstructure of the cement to be suffering from the thaumasite form of sulfate attack. The extent of this attack was greater at 5 °C than at 20 °C, although some thaumasite was formed even at the higher temperature.

Performance of Portland limestone cements in mortar prisms immersed in sulfate solutions at 5 °C

The results of a test programme to investigate the sulfate resistance of mortars, immersed up to 12 months at 5 °C in magnesium sulfate and sodium sulfate solutions, is described. The mortars were prepared from four cements; a Portland cement, a sulfate-resisting Portland cement and two Portland limestone cements containing 15% by mass of an oolitic limestone and a carboniferous limestone. The mortar specimens were subject to BS 5328 Class 4A and 4B sulfate exposure conditions. These are the highest classes for concretes prepared using sulfate-resisting Portland cement (SRPC) before surface protection is required and are two and three classes higher than those recommended for concretes prepared using Portland cement (PC) and Portland limestone cement (PLC), respectively. Two free water-cement ratios were used, 0.5 and 0.75. Performance was monitored by visual assessment, expansion and changes in flexural and compressive strengths. At a free water-cement ratio of 0.75, the PC mortars and PLC mortars exhibited visually very severe attack with the former showing expansion and reductions in strength, and the latter mainly reductions in strength. At a free water-cement ratio of 0.50 both the PC mortars and PLC mortars showed slight/moderate to severe visual attack, the degree of deterioration appearing slightly greater in the PLC mortars, more especially those made with oolitic limestone. The PLC mortars also exhibited reductions in compressive failure load. The SRPC mortars exhibited little visual deterioration, no expansion, a small increase in flexural strength and no significant reductions in compressive strength. At a free water-cement ratio of 0.75 substantial amounts of thaumasite, together with ettringite was present in the surface layers of the deteriorated PLC mortars whilst ettringite was present in the surface layers of the deteriorated PC mortars. It is concluded that mortars made with a PC with a C 3A content of about 10% by mass were broadly similar in their vulnerability to sulfate attack at 5 °C as PLC mortars containing 15% limestone by mass, although the mode of attack was different.