Sulphate-resisting Portland Cement Research Articles

Effect of Baltic Seawater and Binder Type on Frost Durability of Concrete

AbstractThe effects of Baltic seawater on frost durability of PC concretes using sulfate resistant portland cement and combination of rapid hardening portland cement with silica fume were studied. The freeze-thaw cycles were performed on specimens exposed to the Baltic seawater, 3% sodium chloride solution and deionized water. The freeze-thaw cycles appeared to cause the most extensive internal damage in specimens based on sulfate resistant cement (SR) and exposed to seawater. The most extensive surface scaling was observed in the case of concretes containing silica fume and exposed to deicing salts. Based on the thermo gravimetric and X-ray diffraction analyses it was concluded that extensive internal damage of concrete based on SR was caused by changes of the microstructure due to secondary formation of ettringite, carbonation, and formation of calcite. The results showed also that low C3A content of the SR did not fully mitigate formation of secondary ettringite during freeze-thaw cycles. A combination...

The aggressiveness of pig slurry to cement mortars

The aim was to measure the behaviour of various mortars employed in livestock media in central Spain and to analyse the aggressiveness of pig slurry to cement blended with fly-ash mortars. To achieve this, mortar specimens were immersed in ponds storing pig slurry. Mortar specimens, of 40 × 40 × 160 mm, were made from four types of cement commonly used and recommended for rural areas. The types were a sulphate-resistant Portland cement and three cements blended in different proportions with fly ash and limestone filler. After 3, 6, 12, 24, 36, 48 and 60 months of exposure, three or four specimens of each cement type were removed from the pond and washed with water. Their compressive strength and microstructure (X-ray diffraction, mercury intrusion pore-symmetry, thermal analysis and scanning electron microscopy) were then measured. Sulphate-resistant Portland cement (SR-PC), found to be more susceptible to degradation due to its greater proportion of macro-pores and increased total porosity, was found not to be suitable for use with livestock. After 60 months of immersion in the pig slurry medium, CEM II-A (40.3%) mortar retained the greatest compressive strength. Mortars with less than 20% replacement of cement by fly ash were found to be the most durable, with the most suitable mechanical behaviour.

Equilibrium leaching of toxic elements from cement stabilized soil

The toxicity characteristics leaching procedure (TCLP) is commonly used to assess the efficiency of solidification/stabilization (S/S) of pollutants in wastes, despite recent objections to this method. In this study, formulations of 7, 10, 15 and 20% (w/w) of calcium aluminate cement (CAC) and sulfate resistant Portland cement (SRC) were used for S/S of soil from brownfield contaminated with 43,149, 10,115, 7631, 6130, 90, 82mgkg−1 of Zn, Pb, Cu, As, Cd and Ni, respectively. CAC produced S/S soil monoliths of higher mechanical strength (up to 7.65Nmm−2). Mass-transfer analysis indicated surface wash-off as a mechanism of toxic elements release, and equilibrium leaching as a crucial parameter of S/S efficiency assessment. In the expected range of field soil pH after S/S (pH 7–9), the TCLP gave markedly different results than the multi-point pH equilibrium leaching method (using nine targeted pH values): up to 2953-, 94-, 483-, 1.3-, 27- and 1.5-times more Zn, Pb, Cu, As, Cd and Ni, respectively, was determined in the TCLP leachate. S/S with CAC reduced leachability of toxic elements more effectively than SRC. Our results indicate that, under given field conditions, the TCLP significantly underrates the efficiency of S/S of contaminated soil with cementitious binders.

Early stages hydration of high initial strength Portland cement

Thermogravimetry (TG) and derivative ther- mogravimetry (DTG) were used to analyze the early stages of hydration of a high-initial strength and sulphate resistant Portland cement (HS SR PC) within the first 24 h of set- ting. The water/cement (W/C) mass ratios used to prepare the pastes were 0.35, 0.45, and 0.55. The hydration behavior of the pastes was analyzed through TG and DTG curves obtained after different hydration times on calcined cement mass basis to have a same composition basis to compare the data. The influence of the W/C ratio on the kinetics of the hydration process was done through the quantitative analysis of the combined water of the main hydration products formed in each case. TG and DTG curves data calculated on calcined mass basis of all the results were converted to initial cement mass basis to have an easier way to analyze the influence of the W/C ratio on the free and combined water of the different main hydrated phases. The gypsum content of the pastes was totally consumed in 8 h for all cases. A significant part of the hydration process occurs within the first 14 h of setting and at 24 h the highest hydration degree, indicated by the respective content of formed calcium hydroxide, occurs in the case of the highest initial water content of the paste.

Performance of concrete incorporating GGBS in aggressive wastewater environments

Concrete is traditionally used as the main component of wastewater facilities. The sulfate and acidic environment presents significant challenges. Supplementary cementitious materials (SCM) such as GGBS are being used in increasing quantities in concrete and have been shown to provide concrete with increased durability in this particular environment. They have traditionally been used with CEM I, but in recent years a shift in concrete practice has led to the introduction of CEM II cements with reduced CO 2 footprint and obvious environmental and economic benefits. However, the change in cement chemistry associated with using CEM II and GGBS must also be accounted for in concrete specifications for aggressive environments. This has particular importance when concrete is exposed to elevated sulfate and sulfuric acid environments, such as that associated with water and wastewater treatment. The performance of CEM II/A-L cements with varying amounts of GGBS was evaluated through a series of tests conducted to determine their durability characteristics in respect of sulfate attack and sulfuric acid attack. As a benchmark, samples were also tested using CEM I cement, CEM I with GGBS, and a sulfate resistant Portland cement. Results have shown that for all cases, the addition of GGBS resulted in considerable reductions in sulfate induced expansion relative to samples using CEM I or CEM II binders alone. A slight improvement in performance relative to sulfate resisting Portland cement (SRPC) binders was also observed. However in respect of the sulfuric acid environment the regime proved too harsh and ultimately resulted in the early failure of all samples. Some difference in performance was noted, but this was not considered noteworthy. The influence of pH and acid type was studied. The conclusions were that the concretes tested cannot adequately address the durability threat to all parts of wastewater infrastructure over a significant life span due to the extraordinarily harsh nature of this form of attack.

Dielectric and Spectroscopic Studies of A Fly Ash Blended Cement Paste

The dielectric constant (?') of Sulfate Resisting Portland Cement (SRPC) blended with 30% of fly ash by addition ismeasured using microwave bench at 9.54 GHz, for initial 30 hours of hydration. The heat of hydration for the sameblend using heat of solution calorimetry is also measured. It is observed that contrary to the usual trend of retarding offly ashes, it shows an accelerating trend with increasing strength as times passes. SEM micrographs and XRD patternsare also recorded and observed that C4Al2SO16 (C4A3S¯) is found to be responsible for the accelerating trend of the mix.The hydration process in the early period is studied and it is suggested that suitable retarder should be adopted for theeffective utilization.Cement chemistry notations: C=CaO, A=Al2O3, S¯=SO3, H=H2O, F=Fe2O3, S=SiO2

Effect of Fly Ash and Water in Hydrated Srpc-A Ftir Study

The present investigation, deals with the study of both hydrated Sulfate Resisting Portland Cement (SRPC) and fly ash(fly ash 20%, 30% and 50%) composite with two different waters. Among the three percentages of fly ash addition, 30%addition is found to be optimum. The samples (SRPC and 30% fly ash) were analyzed using the Fourier TransformInfrared Spectroscopy (FTIR) spectra. The relationship between compressive strength and molecular vibration changeswere discussed using FTIR spectra. Also, the setting time is identified with the FTIR spectra and proper explanation withavailable literature for the kinetics is presented. It is inferred that increasing the fly ash concentration reduce the settingtime. This is due to the calcium sulfoaluminate (CSA) present in the fly ash. Result of this study indicates that the blendedpaste better perform than the control paste hydrated with distilled water and effluent water.

The Utilization Of Concrete Maturity To Predict Its Compressive Strength Under Variable Conditions

The aim of this research is to study the maturity of concrete for predicting in-situ compressive strength for any concrete mixture in any structural work based on the laboratory testing results of several concrete specimens, then finding a relationship between compressive strength-maturity mathematical models that can be used for predicting the compressive strength. Three type of mixes were used; first mix contains ordinary Portland cement (O.P.C), second mix contains sulphate resisting Portland cement (S.R.P.C), third mix contains ordinary Portland cement with an admixture (caco3) of (15%) replacement of cement weight. Compressive strength tests at different ages) 3,7,14,28( days and different temperatures(27±2°C) (80.6±2°F)&)34±2°C) (93.20±2°F) and curing conditions of (moist and air cured). The maturity was found for concrete samples using the Plowman technique with the datum temperature at (-11.6°C) (11°F(,the actual compressive strength values found from laboratory testing were compared with the predicted compressive strength values from Plowman equation to estimate the margin of the errors involved, the error was found to be reasonable especially for the moist cured samples.

Thaumasite Sulfate Attack, Popcorn Calcite Deposition and acid attack in concrete stored at the «Blindtarmen» test site Oslo, from 1952 to 1982

In past decades, concrete in contact with Oslo Alum Shale suffered severe deterioration, frequently involving quick and complete degradation of the cement paste matrix. The Norwegian Alum Shale Committee (1947–1972) concluded that this was due to secondary ettringite deposition and acid attack. The most resistant concrete mixes were based on Sulfate Resisting Portland Cements or those containing a pozzolanic supplementary cementitious mineral. However, the present work concludes that this “classic” sulfate attack was triggered by deleterious Thaumasite Sulfate Attack and Popcorn Calcite Deposition in close association with effects of externally derived acid attack. This paper provides an outline of the previous work and the first petrographic documentation of concrete prisms previously exposed at the “Blindtarmen” test site. Two important novel reaction mechanisms were also found: 1) the development of high crystallisation pressure associated with Thaumasite Formation, and 2) full scale Thaumasite Sulfate Attack was most efficient after partial or complete decalcification of calcium silicate hydrate: thaumasite had formed at the expense of remaining amorphous silica and associated secondary popcorn calcite. Comparison with modern sprayed concrete on Alum Shale shows that influence of Thaumasite Sulfate Attack and internal carbonation was faster under a hydraulic gradient than under static conditions.

Sodium sulphate attack on blended cements under different exposure conditions

The sulphate resistance of ordinary Portland cement, sulphate-resistant Portland cement, and blended cements with different proportions of natural pozzolan and low-lime fly ash were compared. Plain and blended cement mortar specimens were prepared and stored under three different conditions: (a) continuous curing in lime-saturated water, (b) continuous exposure to 5% Na2SO4 solution at room temperature, and (c) cyclic exposure to 5% Na2SO4 solution at room temperature in which the cycle consisted of immersion and drying exposures (each cycle was composed of immersion in 5% Na2SO4 solution for 24 h at 23 ± 2°C, oven drying at 50°C for 23 h, and cooling in air at 23 ± 2°C for 1 h). The sulphate resistance of the cements was evaluated from compressive strength and length change of mortar specimens after up to 1 year of exposure. Microstructural investigations such as X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray analysis were also used to support the explanation of deterioration. This study revealed that under continuous sodium sulphate exposure the length changes of blended cements were less than those of sulphate-resistant Portland cement with 3.6% C3A content. However, for the mortars exposed to sulphate attack and cycles of immersion and drying exposures, sulphate-resistant Portland cement was found to perform better than blended cements when compressive strengths were considered

Effects of mix composition and water–cement ratio on the sulfate resistance of blended cements

This paper presents an experimental investigation on the sulfate resistance of blended cements containing various amounts of natural pozzolan and/or Class-F fly ash. The performance of blended cements was monitored by exposing the prepared mortar specimens to a 5% Na2SO4 solution for 78 weeks. For comparison, an ordinary Portland cement (produced with the same clinker as blended cements) and a sulfate resistant Portland cement (produced from a different clinker) were also used. In addition to the cement chemistry, water–cement (w/c) ratio of mortars was another parameter selected that will presumably affect the performance of mortars. The experimental results of expansion measurements showed that the effect of w/c ratio was more pronounced for the low sulfate resistant cements with higher C3A amounts, while the blended cements were less affected by an increase in the w/c ratio.

The influence of hydration time on the Ni uptake by cement

In this study, Ni uptake by hardened cement paste has been investigated with the aim of improving our understanding of the immobilization process of Ni(II) in cement and the influence of the hydration time on the Ni speciation on the microscopic scale. Information on the Ni distribution and speciation of the Ni phases formed in the cement system has been gained by employing synchrotron-based μ-X-ray fluorescence (μ-XRF) and μ-X-ray absorption spectroscopy (μ-XAS). The Ni-doped cement samples were prepared at a water/cement ratio of 0.4 and with a metal loading of 5000 mg/kg using a sulphate-resisting Portland cement. The samples were hydrated for six hours and one year to account for the chemical environment in a fresh and aged cement paste, respectively. The μ-XAS measurements reveal that a mixture of Ni phases is formed at single regions of interests, independent of the hydration time. Data analysis further indicates that Ni(II) is predominantly immobilized in a layered double hydroxide (LDH, Ni-Al LDH) and only to a minor extent precipitates as Ni-hydroxides. A comparison of the results from this micro-spectroscopic investigation with those from an earlier macro-spectroscopic study, indicate that the same Ni phases are formed both on the macro-and micro-scale.

Microscale Investigations of Ni Uptake by Cement Using a Combination of Scanning Electron Microscopy and Synchrotron-Based Techniques

Cement is used to condition waste materials and for the construction and backfilling of repositories for low-and intermediate-level radioactive waste. In this study, Ni uptake by hardened cement paste has been investigated with the aim of improving our understanding of the immobilization process of Ni(ll) in cement on the microscale. Information on the cement microstructure, Ni distribution, Ni concentration, and speciation of the Ni phases formed in the cement system and their association with specific cement minerals has been gained by using scanning electron microscopy (SEM) and synchrotron-based micro-X-ray fluorescence (micro-XRF) and micro-X-ray absorption spectroscopy (micro-XAS). The Ni-doped samples were prepared at a water/cement ratio of 0.4 using a sulfate-resisting Portland cement and were hydrated for 30 days. The metal loadings of the system were varied from 50 up to 5000 mg/kg. SEM investigations show that for all metal loadings the Ni phases form rims around inner-calcium silicate hydrates, suggesting a direct association with this cement phase. The micro-XAS measurements further reveal that a mixture of Ni phases form at Ni-enriched regions. Data analysis indicates that Ni(ll) is predominantly immobilized in a layered double hydroxide-type phase (Ni-Al LDH) and only to a minor extent precipitates as Ni-hydroxides (alpha-Ni(OH)2 and beta-Ni(OH)2). At 50 mg/kg Ni loading, however, the p-XAS measurements suggest the presence of an additional Ni species. In the latter system Ni-Al LDH is found in Ni-rich regions, whereas at Ni-poor regions an unknown species is formed.

Sulfate resistance of plain and blended cements exposed to wetting–drying and heating–cooling environments

Exposure conditions significantly affect the resistance of cements to sulfate attack. This article investigates the sulfate resistance of ordinary portland cement (OPC), sulfate resistant portland cement (SRPC), and blended cements with different proportions of natural pozzolan and Class F fly ash when subjected to different exposure regimes. Plain and blended cement mortar specimens were stored under three different conditions: (i) continuous curing in lime-saturated water, (ii) continuous exposure to 5% Na 2SO 4 solution at room temperature, and (iii) cyclic exposure to 5% Na 2SO 4 solution at room temperature in which the cycles consisted of wetting–drying and heating–cooling. The sulfate resistance of cements was evaluated by measuring the reduction in compressive strength and length change of mortar specimens up to one year of exposure. This study revealed that the performance of blended cements under sodium sulfate solution at room temperature was better than that of SRPC with a 3.6% C 3A content when the length change was considered. However, for the structures exposed to sulfate attack and cycles of wetting–drying and heating–cooling, SRPC was found to perform better than blended cements when the compressive strength losses were considered.

Spectroscopic Investigation of Ni Speciation in Hardened Cement Paste

Cement-based materials play an important role in multi-barrier concepts developed worldwide for the safe disposal of hazardous and radioactive wastes. Cement is used to condition and stabilize the waste materials and to construct the engineered barrier systems (container, backfill, and liner materials) of repositories for radioactive waste. In this study, Ni uptake by hardened cement paste has been investigated with the aim of improving our understanding of the immobilization process of heavy metals in cement on the molecular level. X-ray absorption spectroscopy (XAS) coupled with diffuse reflectance spectroscopy (DRS) techniques were used to determine the local environment of Ni in cement systems. The Ni-doped samples were prepared at two different water/cement ratios (0.4, 1.3) and different hydration times (1 hour to 1 year) using a sulfate-resisting Portland cement. The metal loadings and the metal salts added to the system were varied (50 up to 5000 mg/kg; NO3(-), SO4(2-), Cl-). The XAS study showed that for all investigated systems Ni(ll) is predominantly immobilized in a layered double hydroxide (LDH) phase, which was corroborated by DRS measurements. Only a minor extent of Ni(ll) precipitates as Ni-hydroxides (alpha-Ni(OH)2 and beta-Ni(OH)2). This finding suggests that Ni-Al LDH, rather than Ni-hydroxides, is the solubility-limiting phase in the Ni-doped cement system.

A thermodynamic approach to the hydration of sulphate-resisting Portland cement

A thermodynamic approach is used to model changes in the hydrate assemblage and the composition of the pore solution during the hydration of calcite-free and calcite-containing sulphate-resisting Portland cement CEM I 52.5 N HTS. Modelling is based on thermodynamic data for the hydration products and calculated hydration rates for the individual clinker phases, which are used as time-dependent input parameters. Model predictions compare well with the composition of the hydrate assemblage as observed by TGA and semi-quantitative XRD and with the experimentally determined compositions of the pore solutions. The calculations show that in the presence of small amounts of calcite typically associated with Portland cement, C–S–H, portlandite, ettringite and calcium monocarbonate are the main hydration products. In the absence of calcite in the cement, however, siliceous hydrogarnet instead of calcium monocarbonate is observed to precipitate. The use of a higher water-to-cement ratio for the preparation of a calcite-containing cement paste has a minor effect on the composition of the hydrate assemblage, while it significantly changes the composition of the pore solution. In particular, lower pH value and higher Ca concentrations appear that could potentially influence the solubility and uptake of heavy metals and anions by cementitious materials.

The influence of hydration time on the Ni uptake by cement

In this study, Ni uptake by hardened cement paste has been investigated with the aim of improving our understanding of the immobilization process of Ni(II) in cement and the influence of the hydration time on the Ni speciation on the microscopic scale. Information on the Ni distribution and speciation of the Ni phases formed in the cement system has been gained by employing synchrotron-based μ-X-ray fluorescence (μ-XRF) and μ-X-ray absorption spectroscopy (μ-XAS). The Ni-doped cement samples were prepared at a water/cement ratio of 0.4 and with a metal loading of 5000 mg/kg using a sulphate-resisting Portland cement. The samples were hydrated for six hours and one year to account for the chemical environment in a fresh and aged cement paste, respectively. The μ-XAS measurements reveal that a mixture of Ni phases is formed at single regions of interests, independent of the hydration time. Data analysis further indicates that Ni(II) is predominantly immobilized in a layered double hydroxide (LDH, Ni-Al LDH) and only to a minor extent precipitates as Ni-hydroxides. A comparison of the results from this micro-spectroscopic investigation with those from an earlier macro-spectroscopic study, indicate that the same Ni phases are formed both on the macro- and micro-scale.

Thaumasite formation in concrete and mortars containing fly ash

Due to recent reports on deterioration of concrete structures, the thaumasite form of sulfate attack has become a subject of study and close investigation. This paper investigates the formation of thaumasite in concrete and mortars containing fly ash. The results show that thaumasite formation can occur within 84 days of exposure to sulfate solutions. High volumes of fly ash can limit or promote thaumasite formation depending on the type of cement used. Thaumasite and ettringite were found among the deterioration products. However, the thaumasite formation in the specimen prepared from sulfate resisting Portland cement was not accompanied by deterioration, except by 50% fly ash addition. The mixtures of Portland limestone cement with 40% fly ash exhibited a very limited thaumasite formation while the mixtures with 50% had no thaumasite at all. It is concluded that thaumasite can also be formed in mixtures incorporating fly ash.

An experimental study of combined acid and sulfate attack of concrete

Abstract There is disagreement about the role of sulfuric acid in the thaumasite form of sulfate attack (TSA) of concrete. Some researchers suggest that thaumasite is formed only at pH above 10.5, whereas others report that the primary cause of deterioration in the affected M5 bridge foundations was sulfuric acid attack followed by neutral TSA. The aim of this work is to reconcile these conflicting views by undertaking parallel studies of concrete exposed to aggressive acid and sulfate solutions and concrete/clay interface work using weathered Lower Lias clay. Concrete specimens have been exposed to BRE Digest 363 sulfate class solutions and acidic and acidic-sulfate solutions at 4.5 ± 0.5 °C. Selected samples are being characterised at intervals up to 5 years. At this stage, results are reported for 5-month samples. Various binders including Portland cement, Portland–limestone cement, blastfurnace slag cement, pulverized-fuel ash cement and sulfate-resisting Portland cement at water/binder ratios (w/b) from 0.35 to 0.5 have been studied. Initial visual observations and X-ray diffraction analyses have identified thaumasite in some of the systems after 5 months immersion in solution. An overview of the ongoing parallel concrete/clay interaction work is also presented to contextualise the concrete work.

Thaumasite and secondary calcite in some Norwegian concretes

Abstract Thaumasite formation (TF) and limited thaumasite form of sulfate attack (TSA) has recently been detected in several Norwegian sprayed concretes. TF and TSA is frequently associated with contemporaneous and late stage internal calcite formation by: (a) decalcification of calcium silicate hydrate (CSH): (b) decomposition of thaumasite associated with secondary liberation of SO 4 2− and occasional formation of subordinate gypsum; (c) supersaturation of fluids in voids. Popcorn calcite and other textural forms were characteristic for these reactions. Also co-precipitation of popcorn calcite + thaumasite, as well as later stage dissolution of both minerals occurred. The entire process was represented by a drop in pore fluid pH from about 13 towards 5–7. In this paper we study the TF–TSA–carbonation process in several environments: (1) three examples of 2–13 years old steel fibre reinforced sprayed concrete made with Sulfate Resisting Portland Cement (SRPC) and silica fume in contact with carbon-, calcite- and sulfide bearing Alum Shale: (2) two examples of ≈30 years old, and severely damaged, SRPC based sprayed concrete within the Alum Shale: (3) one 16 years old sprayed concrete made with Portland Cement (PC) and possibly fly ash in presence of sulfate bearing ground water and (4) one 10 years old steel fibre reinforced sprayed concrete in a sub-sea tunnel with inflow of somewhat modified seawater. This PC based concrete with silica fume had suffered localised crumbling and mush formation after less than 5 years. The critical factors for thaumasite formation are discussed together with consequences for further deterioration and timing of repair.