Portland Limestone Cement Research Articles

Effects of w/c ratio on Portland limestone cement concrete

Hitherto, limestone has been recognised as a suitable substitute for cement replacement. The present study was an experimental investigation of the properties of Portland limestone cement and the effects of water-to-cement (w/c) ratio on performance of concretes containing it. The Portland limestone cement concrete specimens (containing 14% limestone) with w/c ratio of 0·35, 0·45 and 0·55 were experimentally compared to ordinary Portland cement concrete specimens. The results demonstrated that w/c ratio has a prominent effect on the performance of Portland limestone cement concretes, with higher w/c resulting in weaker performance. Therefore Portland limestone cement containing 14% limestone can be considered as a low-cost, effective and available supplementary cementing material.

A Study on the Chloride Diffusion into Portland Limestone Cement Concrete

In this paper the diffusion of chloride ions through limestone cement concrete is studied. The Portland limestone cements have many benefits and the new European Standard EN 197-1 identifies 4 types of Portland limestone cement containing 6-20% limestone (types II/A-L and II/A-LL) and 21-35% limestone (types II/B-L and II/B-LL), respectively. Portland limestone cements of different fineness and limestone content (0-35% w/w) have been produced by inter-grinding clinker, gypsum and limestone. Six concrete mixtures were prepared and the Nordtest Method (accelerated chloride penetration) was applied for the determination of penetration parameters for estimating the resistance against chloride penetration into hardened concrete. The diffusion equation of Fick’s second law was used for the determination of the effective chloride transport coefficient. It is concluded that Portland limestone cement concrete indicates competitive behavior with the Portland cement concrete. Limestone content up to 15% has a positive effect on the concrete resistance against chloride penetration.

The Effect of Chlorides on the Thaumasite Form of Sulfate Attack in Limestone Cement Concrete

In this paper the effect of chlorides on the thaumasite form of sulfate attack in limestone cement concrete is studied. Concrete specimens made from ordinary Portland cement and two Portland limestone cements (limestone content 15% and 35% respectively) were prepared. After 28 days of curing the specimens were immersed in six solutions of various sulfate and chloride content and stored at 5oC. Visual assessment of the specimens, mass measurements and compressive strength tests took place for a period of 24 months. XRD method was used to identify thaumasite in the deteriorated parts of the specimens. All measurements showed that Portland cement concrete exhibits a lower degree of deterioration than Portland limestone cement concrete. Specimen disintegration was more severe, the higher the limestone contents of the cements and the higher the sulfate content of the corrosive storage solutions. Chlorides play an inhibitory role, delaying the deterioration of the concrete specimens. XRD analysis showed the presence of thaumasite at the deteriorated parts of the specimens after nine months of curing.

Influence of cement type on ITZ porosity and chloride resistance of self-compacting concrete

With the increasing use of self-compacting concrete (SCC) its durability has come into focus. Concerning the microstructure of concrete, the porosity in the interfacial transition zone (ITZ) is regarded as a key feature for permeability and durability. Generally, a combination of cement and mineral admixtures is used for the production of SCC. In the present study, ITZ porosity of four SCC mixtures produced with ordinary Portland cement, Portland limestone cement, slag cement and ordinary Portland cement combined with fly ash is analyzed. Additionally, the chloride migration coefficient is determined. ITZ porosity and width of the SCC mixtures are similar. The substantial differences in the chloride migration coefficients show that the binder type has a stronger influence on permeability than the pore volume in the ITZ.

High porosity (> 90%) cementitious foams

High porosity foams based on Portland limestone cement or gypsum plaster were prepared by a simple method of stirring and drying using low levels of the food additives: methyl cellulose and iota carageenan gum. Thermal conductivity of 0.11 W m − 1 K − 1 at 92% porosity was achieved but compressive strength was also very low. Foams were almost closed cell. Attempts to improve strength by incorporation of short staple glass fibre were only partially successful because of a change in the failure mode from progressive collapse to uniform fibre-cement debonding facilitated by the ability of the fibre network to transmit stress throughout the assembly. This approach to fire resistant insulation materials does not yet match the high strength/conductivity ratios of calcium silicate products but deserves exploring because of the simplicity of preparation and the compositional freedom for using mixtures of hydraulic cement and other powders.

Calorimetric study of ternary binder of calcium aluminate cement, Portland-limestone cement and FGD gypsum

To use flue gas desulfurization (FGD) gypsum and limestone as supplement of cement, conduction calorimetry was applied to investigate the early hydration of ternary binder of calcium aluminate cement (CAC), Portland-limestone cement (PLC), and FGD gypsum, supplemented with the determination of setting times and X-ray diffraction (XRD) analysis. Different exothermal profiles were presented in two groups of pastes, in which one group (group A) sets the mass ratio of FGD gypsum/CAC at 0.25 and the other group (group B) sets the mass ratio of PLC/CAC at 0.25. Besides the two common exothermal peaks in cement hydration, a third exothermal peak appears in the pastes with 5–15% FGD gypsum after gypsum is depleted. It is found that not PLC but FGD gypsum plays the key role in such ternary binder where the reaction of ettringite formation dominates the hydration process. PLC accelerates the hydration of ternary binder, which mainly attributes to the nucleating effect of fine limestone particles and PC clinker. The modified hydration process and mechanism in this case is well visualized by the means of calorimetry and it helps us to optimize such design of ternary cementitious material.

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 .

Influence of various amounts of limestone powder on performance of Portland limestone cement concretes

Abstract The benefits of limestone as a partial replacement for Portland Cement (PC) are well established. Economic and environmental advantages by reducing CO2 emissions are well known. The paper describes the effect of various amounts of limestone on compressive strength, water penetration, sorptivity, electrical resistivity and rapid chloride permeability on concretes produced by using a combination of PC and limestone at 28, 90 and 180 days. The percentages of limestone that replace PC in this research are 0%, 5%, 10%, 15% and 20% by mass. The water/(clinker + limestone) or (w/b) ratios are 0.37, 0.45 and 0.55 having a constant total binder content of 350 kg/m3. Generally, results show that the Portland limestone cement (PLC) concretes having up to 10% limestone provide competitive properties with PC concretes.

Portland Limestone Cement Part I - Preparation of Cements

This paper is the first part of a research project which was supported by TUBITAK titled “Determination of Optimum Limestone Content in Portland Limestone Cement Production from the View Point of Mechanical Performance and Sulfate Originated Durability Problems”. In this stage, blended cements incorporating different amounts of limestone powders from 5 to 40% were prepared. The problems observed in the preparation stage of limestone blended cements and the effects of limestone replacement on the physical and mechanical properties were investigated. Increasing of limestone replacement ratios resulted in a wider particle size distribution. In contrast with the increases in Blaine values, fineness (residue at 32 µm) values of cements have also increased. Mortars had a sticky and cohesive consistency. Also, increasing the limestone incorporation caused decreases in unit weights and compressive strength values of mortars with a parallel increase in water absorption values at all ages.

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.

Calcite Morphology and Aggregation in the Presence of Comb-like Polymers Adsorbed on Cement Particles

Comb-like polymers have an important application in cement industries, where they are referred to as polymeric admixtures/superplasticizers. They are used to increase the workability of fresh cementitious mixtures as well as to improve the strength and durability of the hardened state. So far, the interaction of polymer/Portland-limestone cement particles has been poorly investigated. This paper describes the overgrowth of calcite on Portland-limestone cement particles, a mixture of ground clinker and calcite, in the presence of comb-like polymers. The morphological and aggregational variation of overgrown calcite crystals is used as a model to evaluate the interaction occurring between cement particles and polymeric admixtures. Rhombohedral, spherulitic, microtrumpet, or fibrous calcite crystals were observed as a function of the kind of cement particles and comb-like polymers used. These results suggest that comb-like polymers may assume diverse conformations when associated with the different particles that constitute Portland-limestone cement.

Early hydration and setting of Portland cement monitored by IR, SEM and Vicat techniques

Diffuse Reflectance Infrared DR-FTIR spectroscopy is employed to monitor chemical transformations in pastes of Portland limestone cement. To obtain a sufficient time resolution a freeze-dry procedure is used to instantaneously ceasing the hydration process. Rapid re-crystallization of sulphates is observed during the first 15 s, and appears to be complete after ~ 30 min. After ~ 60 min, spectroscopic signatures of polymerizing silica start to emerge. A hump at 970–1100 cm − 1 in conjunction with increasing intensity in the water bending mode region at 1500–1700 cm − 1 is indicative of the formation of Calcium Silicate Hydrate, C-S-H. Simultaneously with the development of the C-S-H signatures, a dip feature develops at 800–970 cm − 1 , reflecting the dissolution of Alite, C 3S. Setting times, 180 (initial) and 240 (final) minutes, are determined by the Vicat technique. Combining DR-FTIR, SEM and Vicat measurements it is concluded that the setting is caused by inter-particle coalescence of C-S-H.

Microstructure changes in mortars attacked by sulphates at 5 °C

In this study mortars have been produced using ordinary Portland cement (CEM I – 32.5) and limestone cement with 15% limestone addition (CEM II/A-LL – 32.5). The mortars were immersed in a solution of 5% Na 2SO 4 at 5 °C for 6 months and the caused deterioration was observed visually at a regular basis. The deterioration product of the surface of both mortars has been identified as thaumasite by the means of XRD, FT-IR, DTA and SEM/EDAX analysis. The damage caused due to formation of thaumasite in both mortars was approximately the same and not influenced by the addition of limestone. Furthermore, expansion and compressive strength of the mortars were studied as a function of time and it was proved they were not influenced by thaumasite formation at the age of 6 months.

Experimental Analysis of Concrete Strength at High Temperatures and after Cooling

In recent years, the cement industry has been criticized for emitting large amounts of carbon dioxide; hence it is developing environment-friendly cement, e.g., blended, supersulfated slag cement (SSC). This paper presents an experimental analysis of the compressive strength development of concrete made from blended cement in comparison to ordinary cement at high temperature. Three different types of cement were used during these tests, an ordinary portland cement (CEM I), a portland limestone cement (CEM II-A-LL) and a new, supersulfated slag cement (SSC). The compressive strength development for a full thermal cycle, including cooling down phase, was investigated on concrete cylinders. It is shown that the SSC concrete specimens perform similar to ordinary cement specimens.

The assessment of porosity and pore size distribution of limestone Portland cement pastes

The cement production industry is one of the most energy and raw materials consuming one. Over the last years a great effort is performed in order to substitute clinker for less energy demanding materials. Nevertheless, construction industry needs durable materials with improved properties. Limestone is being used in blended cements widely. The most important parameter that affects all the properties of cement paste is its pore structure. In this study, four different limestone cements were produced and their pore structure was determined by means of mercury intrusion porosimetry (MIP) and nuclear magnetic resonance (NMR) cryoporometry. The conclusion of the study was that limestone addition affects the pore structure of the cement paste by increasing linearly the size of capillary pores from 20 nm to 40 nm when the maximum amount (35%) of limestone that is allowed by EN 197-1 is used. On the other hand the threshold diameter decreases exponentially and it is evident that limestone hardened cement pastes have many pores of the same size due to the filling effect that minerals additives have. Furthermore, limestone decreases the size of gel pores which is related to higher hydration rates. Hence, the use of limestone in cement produces a material that is structurally adequate to be used in construction.

The effect of temperature on thaumasite formation

Abstract In this study mortars have been produced using ordinary Portland cement (CEM I – 32.5) and limestone cement with 15% limestone addition (CEM II/A-LL – 32.5). The mortars were immersed in a solution of 5% Na 2 SO 4 at 5 °C, 10 °C and 20 °C for 1 year and the caused deterioration was visually observed on a regular basis. The deterioration product on the surface of the mortars has been identified as thaumasite by means of XRD, FT-IR, DTG and SEM/EDAX analyses. Mortars immersed in a solution of 5% Na 2 SO 4 at 10 °C for a year suffered limited surface damage, which was identified as thaumasite formation and carbonation. Similar damage appeared for mortars immersed in a solution of 5% Na 2 SO 4 at 5 °C for 6 months and that led to the conclusion that thaumasite formation is related inversely to the conservation temperature of the mortars. Finally, mortars immersed in a solution of 5% Na 2 SO 4 at 20 °C for a year were intact and thaumasite could not be identified.

Performance of limestone cement mortars in a high sulfates environment

With the aim of studying the influence of cement composition on resistance in high sulfates environment, standard mortars have been produced using ordinary Portland cement (CEM I – 32.5) and limestone cement with 35% limestone (CEM II/B-LL – 32.5). The pore size distribution of the cement pastes was measured. The mortars were immersed in a 5% Na 2SO 4 solution at 20 °C for 1.5 years and the caused deterioration was been visually observed at a regular basis. Furthermore, the mortars expansion was being estimated by measuring the change of length. At the end of the experiment the compressive strength of the mortars was measured. The deterioration products of the mortars have been identified by means of X-ray diffraction, optical microscopy and environmental scanning electron microscopy. The limestone cement based mortar presented cracking that started at the age of 6 months and continued throughout the experiment. It also displayed high expansion after 250 days of immersion in a 5% Na 2SO 4 caused, as proved using the analytical techniques, by the formation of gypsum and ettringite. Concluding, the cement with 35% limestone did not perform as well as ordinary Portland cement under the most aggressive laboratory conditions. Hence, it is obvious that the addition of limestone in the cement leads to a totally different behaviour than Portland cement with respect to the resistance in high sulfates environment.

Evaluation of Portland limestone cements for use in concrete construction

The paper describes a study carried out to examine the performance of concrete produced using combinations of Portland cement (PC) and limestone (LS), covering compositions for Portland limestone cement (PLC) conforming to BS EN 197-1: 2000, and up to 45% LS. In particular, key engineering (mechanical) and durability properties of concrete were studied. The results indicate only minor differences in performance between PC and 15% PLC concretes of the same cement content and water/cement (w/c) ratio (cement = Portland cement + addition). However, there was an adverse effect with increasing LS content beyond 15% of the cement content for many properties. It is shown that for 35 N/mm2 cube strength concrete the adjustment to w/c ratio to match the compressive strength of PC concrete was in the region of 0.08 for each 10% LS added (water curing at 20°C) above this level. Studies of permeation and concrete durability performance, including, initial surface absorption, carbonation resistance, chloride diffusion, freeze/thaw scaling and abrasion resistance, indicate that in general the test concretes followed single relationships with strength for most properties. Consideration is given to the practical implications of the main outcomes of the study.

Thaumasite form of sulfate attack (TSA) in limestone cement pastes

The thaumasite form of sulphate attack (TSA) concerns cements and concretes containing limestone and is attributed to the formation of thaumasite (CaSiO 3·CaCO 3·CaSO 4·15H 2O). During the last 10 years, the TSA has been found in field structures and buildings in many countries worldwide. In the present work the behavior of Portland limestone cements was studied in the presence of sulfate ions at low temperatures. Cement paste specimens were constructed using Portland cement, Portland cement with 15% (w/w) limestone content and Portland cement with 30% (w/w) limestone content. Twenty-eight days paste specimens were cured in 1.8% (w/w) magnesium sulfate solution of temperature 5 °C. Visual inspection, mass measurements and ultrasonic pulse velocity measurements were carried out for 1 year. Pastes containing limestone are susceptible to the thaumasite formation of sulfate attack and the deterioration is severer, the higher the limestone content.

A study on thaumasite form of sulfate attack (TSA) using XRD, TG and SEM

The thaumasite form of sulphate attack (TSA) concerns cements and concretes containing limestone and is attributed to the formation of thaumasite. This work deals with the confirmation of thaumasite formation in cement mortars. Three types of cement were examined: Portland cement and Portland limestone cement containing 15 and 30% mass/mass limestone. The specimens were cured at 5°C, for 12 months, in a 1.8% MgSO4 solution. The formation of thaumasite was checked and confirmed by XRD, TG and SEM. It was concluded that mortars containing limestone suffer from TSA at low temperature. The combination of XRD, TG and SEM leads to the positive identification of thaumasite and resolves the well known problem of thaumasite and ettringite confusion.