Use of mineral admixtures to prevent thaumasite formation in limestone cement mortar

Concrete made from limestone cement may exhibit a lack of durability due to the formation of thaumasite. The addition of minerals that improve the concrete durability is expected to slow down the formation of thaumasite. In this work the effect of natural pozzolana, fly ash, ground granulated blastfurnace slag (ggbs) and metakaolin on the thaumasite formation in limestone cement mortar is examined. A limestone cement containing 15% w/w limestone was used. Mortar specimens were prepared by replacing a varying part of the limestone cement with the above minerals. Siliceous and calcareous sand was used in order to study the effect of the sand type on the thaumasite formation. The specimens were immersed in a 1.8% MgSO₄ solution and cured at 5 and 25 °C. The formation of thaumasite was checked and confirmed by visual inspection, strength tests, ultrasonic pulse velocity measurements, XRD and TGA. It is concluded that the use of specific minerals, as partial replacement of cement, inhibits the thaumasite formation in limestone cement mortar.     

Formation of thaumasite in carbonated mortars

The main objective of this study was to investigate the formation of thaumasite in carbonated Portland cement mortars. Another important purpose was to study the role that ettringite (AFt) plays in the process of formation of Th and its influence in the deterioration of the mortars.

Work was carried out with mortar prisms, elaborated using two different cements: one of them with low Al₂O₃ content (exempt of C₃A) and the other one with high Al₂O₃ content. Additions of different amounts of gypsum and/or calcium carbonate were also done. After three months of curing at 21 °C and 100% RH mortars were submitted to an accelerated carbonation process until total transformation of Ca(OH)₂ into CaCO₃.

Then mortar prisms were partially immersed in distilled water and kept at temperature ranging from 0 to 5 °C for one year. A mineralogical, micro-structural and physical characterisation was carried out on samples at different ages.

The thaumasite formation rate was much lower in those mortars elaborated with the cement exempt of C₃A than in those mortars made with the cement having high proportion of C₃A when they are conserved in water. The study of transversal sections of prisms reveals the presence of a white expansive product (thaumasite) not always homogeneously distributed.     

Parameters affecting thaumasite formation in limestone cement mortar

Concrete made from limestone cement may exhibit a lack of durability due to the formation of thaumasite. This work deals with the factors affecting thaumasite formation in cement mortars and particularly the limestone content, the curing conditions and the type of sand used. Three types of cement were examined: (i) OPC, (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% MgSO₄ solution and cured at: (i) 5 °C and (ii) 25 °C. The formation of thaumasite was checked and confirmed by XRD and TGA. In addition visual inspection, strength tests and ultrasonic pulse velocity measurements were carried out for several months. 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 at low temperature. At room temperature, no sulfate attack was observed after a year of exposure.     

Use of mineral admixtures to improve the resistance of limestone cement concrete against thaumasite form of sulfate attack

In this work the effect of mineral admixtures on the thaumasite form of sulfate attack in limestone cement concrete is studied. Additionally, the effect of the type of sand (calcareous or siliceous) and the storage temperature is investigated. Limestone cement, containing 15% limestone, was used. Concrete specimens were prepared by replacing a part of cement with the studied minerals. The specimens were immersed in a 1.8% MgSO₄ solution and stored at 5 °C and 25 °C for 3 years. A well designed concrete made with limestone cement and fly ash, blastfurnace slag or metakaolin seems to have the ability to withstand thaumasite form of sulfate attack. The addition of natural pozzolana presented only a limited improvement of concrete’s sulfate resistance. The type of the sand and its cohesion with the cement paste has a remarkable effect on the performance of concrete at low temperature. Finally, no damage was observed in the specimens exposed to sulfate solution at 25 °C.     

Influence of cement and aggregate type on thaumasite formation in concrete

In this study the influence of binder type on the formation of thaumasite in mortar prisms made with expanded clay lightweight aggregate (LWA) or quartz sand was examined. For this purpose mortar prisms were made, which after 28 days of curing in deionised water were exposed to a sulphate solution or deionised water. The length and weight change of the prisms was recorded in triplicate as a function of time of exposure to dry–wet cycles at 5 ± 1 °C.The influence of the binder type on the expansion in the sulphate solution can be ordered from strong to weak as follows: (1) CEM I + limestone filler, (2) CEM I, (3) CEM I + fly ash, and (4) CEM III/A. Because the porosity of the LWA was able to accommodate the growing sulphate crystals, the mortar prisms made with LWA were still largely intact after 3 years of exposure. The only exception being the mortar prisms containing limestone filler. The mortar prisms made with quartz sand and exposed to the sulphate solution were all bent, broken or disintegrated after 24 weeks. The prisms exposed to deionised water showed minimal expansion. Key factors controlling the formation of thaumasite are discussed.     

Investigations on the influence of cement type on thaumasite formation

A high sulfate resistance is required if cements are to be used in sulfate bearing waters and soils especially under conditions favouring thaumasite formation. A long period program of laboratory investigations was carried out on CEN cements to assess thaumasite and ettringite formation. The experimental concept involved mixing ground cement pastes with stoichiometrical components of gypsum, calcite and water. The specimens were stored at 6 °C whereby chemical worst case conditions for thaumasite formation were simulated. At time intervals XRD analysis was conducted. Apart from pure cements mixtures containing additives, pure C₃S pastes with and without Al₂O₃ addition were investigated. The results confirm that thaumasite formation can be accelerated by Al₂O₃ bearing components in cements. However, thaumasite formation is also possible without active participation of Al³⁺. The assessment of sulfate resistance of cements only from the chemical point of view apparently gives results which are contrary to the field experience.     

The effect of different mineral additions and synthetic fiber contents on properties of cement based composites

The influence of the matrix formulation and different amounts of synthetic fiber on physical and mechanical performance of asbestos free fiber cement was evaluated. Polyvinyl alcohol (PVA) fiber was tested as reinforcement in combination with mechanical and kraft cellulose pulps. Silica-fume, metakaolin and fly ash were used as pozzolanic additions in proportions up to ∼14% by mass in combination with ordinary Portland cement and carbonatic filler. Bulk densities of composites varied from 1.5 to 1.7 g/cm³. Synthetic fiber contents higher than 2% by mass (from 4% to 5% by volume of the composite) were unable to promote any further improvement in the mechanical performance of the composites at the age of 28 days. Formulations with silica fume showed better strength performance for the composites after accelerated aging test. The toughness measurements of composites after exposition to soak and dry cycles also showed that silica fume seems to prevent cellulose fiber degradation.     

Kinetics of transformation of 1,1,1-trichloroethane by Fe(II) in cement slurries

This study examines the applicability of the iron-based degradative solidification/stabilization (DS/S-Fe(II)) process to 1,1,1-trichloroethane (1,1,1-TCA), which is one of common chlorinated aliphatic hydrocarbons (CAHs) of concern at contaminated sites. DS/S-Fe(II) combines contaminant degradation by Fe(II) and immobilization by the hydration reactions of Portland cement. The transformation of 1,1,1-TCA by Fe(II) in 10% Portland cement slurries was studied using a batch slurry reactor system. The effects of Fe(II) dose, pH, and initial concentration of 1,1,1-TCA on the kinetics of 1,1,1-TCA degradation were evaluated. Degradation of 1,1,1-TCA in cement slurries including Fe(II) was very rapid and could be described by a pseudo-first-order rate law. The half-lives for 1,1,1-TCA were measured between 0.4 and 5h when Fe(II) dose ranged from 4.9 to 39.2mM. The pseudo-first-order rate constant increased with pH to a maximum near pH 12.5. A saturation rate equation was able to predict degradation kinetics over a wide range of target organic concentrations and at higher Fe(II) doses. The major transformation product of 1,1,1-TCA in mixtures of Fe(II) and cement was 1,1-dichloroethane (1,1-DCA), which indicates that degradation occurred by a hydrogenolysis pathway. A small amount of ethane was observed. The conversion of 1,1,1-TCA to ethane was better described by a parallel reaction model than by a consecutive reaction model.     

Occurrence of thaumasite in deteriorated concrete

The first case histories of thaumasite in concrete products in the United States were identified by the writer in the 1960s. There included two underground sanitary pipes, a grout in an underground lead/zinc mine, and the bottom of a concrete pavement on grade. In these cases, thaumasite was first identified by optical properties in powder mounts in a petrographic microscope, then further confirmed by X-ray diffraction and characterized in an electron microscope. Morphological similarities and positive distinction between thaumasite and ettringite are considered.     

Optimization of rheological properties of oil well cement slurries using experimental design

This paper proposes a statistical design approach based on a second order central composite response surface model to predict the rheological properties of oil well cement (OWC) slurries incorporating metakaolin (MK), silica fume (SF), rice husk ask (RHA) or fly ash (FA). The proposed models are for OWC partial replacement levels ranging from 5 to 15% by MK, SF, RHA or FA used along with a new generation polycarboxylate-based high-range water reducing admixture (PCH) at dosages ranging from 0.25 to 1.5% and at different temperatures ranging from 23 to 60°C. The significance and validity of the models were confirmed by statistical analysis and verification experiments. The regression models were used to analyze the influence of the mixture proportion as well as temperature on the rheological properties of OWC slurries. The statistical design can be applied to optimize rheological properties such as yield stress and plastic viscosity considering the addition of supplementary cementitious materials (SCMs) at different temperatures, and to gain a better understanding of trade-offs between key mixture parameters such as the superplasticizer dosage and the level of SCMs used.     

Revisiting the microstructure of hydrated tricalcium silicate––a comparison to Portland cement

The microstructures of 0.40 w/s-ratio pastes of tricalcium silicate (C₃S), alite and Portland cement have been studied at the hydration times 24 h and 1 month. A field-emission SEM (FE-SEM) was used to obtain high-resolution backscattered electron images. Comparison revealed no microstructural differences between C₃S and alite, but there were considerable differences in microstructure between C₃S and Portland cement pastes. The microstructure of the C₃S paste was simpler than that of the Portland cement, and could be described by a few characteristic features. Distribution of the reaction products differed substantially in the two systems. While hollow shells (Hadley grains) were a prominent feature of the Portland cement paste, their occurrence was more limited in the C₃S and alite pastes. Hollow shells were restricted to grains smaller than about 5 μm in the C₃S and alite pastes, and gapped hollow shells were not a common feature.     

Co-sintering of tungsten alloy slurry coated alumina composites and their properties

Tungsten layered alumina composite is being extensively used in electronic packaging. In the present work alumina substrate densification and adhesion aspects between substrates and tungsten overlays are investigated. The effects of sintering atmosphere, temperature, lubricant content, metal binders treatment and their amount on adhesion behaviour and transverse rupture strength have been reported. SEM studies have also been supplemented to correlate the structure property behaviour.     

Field experiences in concrete deterioration by thaumasite formation: possibilities and problems in thaumasite analysis

In Germany, after testing two concretes deteriorated due to the formation of thaumasite, possibilities and problems in analysing thaumasite and ettringite-containing concrete samples will be discussed. The image of polished thin sections show, that thaumasite formation leads to microstructures similar to the microstructure of ettringite. It is recognisable in the microstructure that the formation of thaumasite happens as well via deterioration of CSH-phases as via the decomposition of ettringite. The identification of thaumasite using environmental scanning electron microscopy is possible without problems. Investigations using X-ray powder diffraction did show, that quantitative analysis of thaumasite and ettringite is possible by using the Rietveld method. The samples of deteriorated concrete (excluding coarse aggregate) contain 20–75% thaumasite.     

Formation of macropores in calcium phosphate cement implants

A calcium phosphate cement (CPC) was shown to harden at ambient temperatures and form hydroxyapatite as the only end-product. Animal study results showed that CPC resorbed slowly and was replaced by new bone. For some clinical applications, it would be desirable to have macropores built into the CPC implant to obtain a more rapid resorption and concomitant osseointegration of the implant. The present study investigated the feasibility of a new method for producing macropores in CPC. Sucrose granules, NaHCO₃, and Na₂HPO₄ were sieved to obtain particle sizes in the range of 125 m to 250 m. The following mixtures of CPC powder (an equimolar mixture of tetracalcium phosphate, Ca₄(PO_{4 2}O, and dicalcium phosphate anhydrous, CaHPO₄) and one of the above additive granules were prepared: control–no additive; mixture A–0.25 mass fraction of sucrose; mixture B–0.25 mass fraction of NaHCO₃; mixture C–0.25 mass fraction of Na₂HPO₄, and mixture D–0.33 mass fraction of Na₂HPO₄. Cement samples were prepared by mixing 0.3 g of the above mixtures with 0.075 ml of the cement liquid (1 mol/l Na₂HPO₄). After hardening, the specimens were placed in water for 20 h at about 60 °C to completely dissolve the additive crystals. Well-formed macropores in the shapes of the entrapped crystals were observed by scanning electron microscope (SEM). The macroporosities (mean±standard deviation; n = 6) expressed as volume fraction in % were 0, 18.9 ± 1.7, 26.9 ± 1.6, 38.3 ± 4.4 and 50.3 ± 2.7 for the control, A, B, C and D, respectively. The diametral tensile strengths (mean±standard deviation; n = 3) expressed in MPa were 10.1 ± 0.7, 3.7 ± 0.3, 2.4 ± 0.2, 1.5 ± 0.5 and 0.4 ± 0.1, respectively, for the five groups. The results showed that macropores can readily be formed in CPC implants with the use of water-soluble crystals. The mechanical strength of CPC decreased with increasing macroporosity. © 2001 Kluwer Academic Publishers     

The formation of thaumasite in a cement:lime:sand mortar exposed to cold magnesium and potassium sulfate solutions

This paper, which is presented in two parts, describes the performance of a laboratory-prepared masonry mortar after exposure to cold magnesium and potassium sulfate solutions. The objective of the study was to investigate the conditions under which the thaumasite form of sulfate attack can affect masonry mortars. This work was funded by the UK Department of the Environment, Transport and the Regions (DETR) and information contained in the following paper was included in the recently published DETR Report on the thaumasite form of sulfate attack (Department of the Environment, Transport and the Regions. The thaumasite form of sulfate attack: risks, diagnosis, remedial works and guidance on new construction. Report of the Thaumasite Expert Group, DETR, January 1999).In Part I of the investigation, mortar tablets (10 × 28 × 34 mm³) were prepared from a 1:1:5.5 cement:lime:sand, air entrained mortar to which powdered calcite had been added during mixing. Each mortar tablet was crushed before exposure in order to facilitate reaction and stored fully immersed in 200 ml of solution for several months. Two sets of storage conditions were used – one where the experiment was exposed to the atmosphere and the other where atmospheric exposure was prevented. The test material was sampled at intervals for analysis by X-ray diffraction to determine the nature of the products and the sequence of chemical events involved. Thaumasite was readily produced in both magnesium and potassium sulfate solution, following the prior formation of ettringite. It was not formed under conditions where ettringite was unstable, suggesting some involvement of the latter in the thaumasite forming process. It was also found that a rapid type of carbonation prevailed in potassium sulfate solution exposed to the atmosphere. This process, which has been called ‘alkali carbonation’, destroyed both ettringite and thaumasite.In Part II of this investigation, the same mortar tablets were used but this time the performance of the whole tablets of uncrushed mortar was tested in the same sulfate solutions so that the physical effects of sulfate attack on hardened mortars could be assessed. The test method used was similar in principle to the BRE mortar durability test which combines the cyclic administration of sulfate solution with intermediate drying to simulate the processes occurring in practice in brickwork mortar. X-ray diffraction analysis of the tablets was carried out when first signs of sulfate attack were observed and also after severe damage had occurred. These showed that early damage appeared to be mainly due to ettringite formation but both ettringite and thaumasite were involved at the severe damage stage. Some non-calcite containing mortars were also examined during this phase of the investigation and results have found them to be slightly less durable than their added-calcite counterparts, particularly in weak magnesium sulfate solution. This was attributed to the improved impermeability of added-calcite mortars rather than any inherent chemical resistance to sulfate attack.Even though Part I concentrated purely on the ‘chemical’ interactions between mortar and solution, the reaction products and sequences were found to be very similar to those discovered in Part II, where physical barriers to sulfate ingress had to be overcome prior to chemical attack. This provides confirmation that any masonry mortar can potentially deteriorate in the presence of excess sulfates providing the temperature is low, the mortar contains an available source of calcium carbonate, the brickwork is consistently wet and the pH of the reaction zone is maintained at 10.5 or above. Having said this, the extent of sulfate attack of brickwork in the field is small and should not become a major problem in practice, provided the current recommendations [Department of the Environment, Transport and the Regions. The thaumasite form of sulfate attack: risks, diagnosis, remedial works and guidance on new construction. Report of the Thaumasite Expert Group, DETR, January 1999] (especially the avoidance of using sulfate-bearing bricks in exposed situations) are adhered to.     

Formation and Characterization of Ceramic Nanocomposite Crystalline Coatings on Aluminium by Anodization

Ceramic nanocomposite coatings have been synthesized on aluminium by using lithium sulphate electrolyte with zirconium silicate additive by anodization.The effects of current density(CD) on microhardness,structure, composition and surface topography of the oxide layer formed at various CDs(0.1-0.25 A/cm~2) have been studied.Crystalline coatings formed at 0.25 A/cm~2 have been(width 95 nm) observed with a relatively uniform distribution confirmed by scanning electron microscopy.Additionally,the average microhardness value of ceramic nanocomposite coatings fabricated from lithium sulphate—zirconium silicate bath is approximately 8.5 times higher than that of the as-received aluminium.The surface statistics of the coatings is discussed in detail to explain the roughness and related parameters for better understanding.These observations demonstrate the importance of surface statistics in controlling the morphology of the coatings and its properties.From the X-ray diffraction investigations,it can be concluded that the formed nanocomposite coatings are crystalline in nature and that the crystallinity of the coatings decreases with increasing applied current density.     

Evidence from the highways agency thaumasite investigation in Gloucestershire to support or contradict postulated mechanisms of thaumasite formation (TF) and thaumasite sulfate attack (TSA)

In March 1998 the thaumasite form of sulfate attack (TSA) was identified in the reinforced concrete foundations of Tredington Ashchurch Road Bridge on the M5 Motorway in Gloucestershire, UK and the UK Government’s Highways Agency appointed Halcrow to investigate the problem. A total of 28 structures were selected for investigation to encompass sites where bridge works were planned and structures were assessed to be at greatest risk as well as to provide a representative sample of sites and structure types.

Desk study work and peer reviews were continued throughout the project to establish protocols for the site work and facilitate the interpretation of the data. The latter included a dual approach of a systematic examination of the data collected to identify trends coupled with a review of postulated mechanisms for the formation of thaumasite from the desk study work against the data from the investigation. This paper summarises the findings of this review, which examines in detail four proposed stages in the development of TSA.     

Occurrences of thaumasite in laboratory and field concrete

The mineral thaumasite (CaSiO₃ · CaCO₃ · CaSO₄ · 15H₂O) has been observed by the authors in a number of concrete samples including (i) an 80 year-old aqueduct in Manitoba, (ii) a 33 year-old pavement in Ontario, (iii) test samples exposed to marine (tidal) conditions, and (iv) laboratory samples exposed to wet–dry cycles in sulphate solution. The source of carbonate differed for these cases being variously derived from de-dolomitization of dolostone aggregate, carbonate ions in the seawater, or atmospheric CO₂ through the process of carbonation. In some cases the thaumasite mineral was found in close association with the mineral ettringite (3CaO · Al₂O₃ · 3CaSO₄ · 31H₂O).

The paper discusses the results of detailed analyses using optical and electron microscopy. Although the mineral thaumasite can be readily identified by these techniques, it is possible that the thaumasite form of sulphate attack is frequently misdiagnosed as conventional sulphate attack due to the similarities in crystal structure and appearance of the minerals thaumasite and ettringite.     

Microscale study of poly(vinyl alcohol) as an effective additive for inhibiting recrystallization in ice slurries

Scanning tunneling microscopy (STM) was used to investigate the surface morphology of ice crystals containing adsorbed poly(vinyl alcohol) (PVOH) molecules inside a cold room at −7.0°C. PVOH was used as a substitute for antifreeze protein (AFP) type I, which is an effective additive for making ice slurries resistant to recrystallization. The STM images revealed microscale grooves on ice crystals made from PVOH solutions, indicating that PVOH molecules significantly influence the surface structure of the ice crystal. The length of each groove was similar to that of a PVOH molecule, indicating that PVOH molecules were adsorbed on the ice crystal surfaces. The interaction force between PVOH molecules and the ice surface was discussed by assuming a molecular structure of PVOH on the ice crystal surface, and the depression of the local freezing point was analyzed based on the surface curvature of ice revealed by STM.