Sulphate-resisting Portland Cement Research Articles

Study some mechanical properties of self-compacting concrete with nano silica under severe saline environment conditions

The main aim of this research is to evaluate the performance of Nano silica self-compacting concrete which is subjected to severe saline conditions that contain sulfates and chlorides at concentrations similar to those existing in the soils and ground water of the middle and southern parts of Iraq. For this purpose, ordinary and sulfate resistant Portland cement without and with 3% Nano silica addition by weight of cementitious materials were used. Splitting tensile strength, flexural strength, static modulus of elasticity and ultrasonic pulse velocity were investigated for all exposure conditions and all types of mixes of self-compacting concrete at ages of 28, 60, 90, 120 and 180 days. Test results revealed that the inclusion of Nano Silica in concrete mixes improved clearly the mechanical properties of self-compacting concrete compared with reference concrete.

Modeling of proportions and prediction of properties of macadam and sand mixes stabilized with mineral binders with the ant additive

Optimization of the proportion and the properties of stabilized macadam and sand mixes (MSM) with introduction of the ANT additive was carried out by means of the mathematical designing of the experiment. This method allows a rather full and comprehensive assessment of the effect of the components on the properties of stabilized macadam and sand mixes (MSM), obtaining of the mathematical model of the process in graphic form, and obtaining of the theoretical model of assessment and prediction of the physical-mechanical and performance properties of the materials under study.At the first stage of the research percentages of a mineral binder, water and an additive were selected and the effect of the variability factor of these components on the mix’s physical-mechanical properties was studied. The following factors were selected as variates: X1 standing for quantity of water, %; X2 standing for the content of sulfate-resistant portland cement grade 500, %; X3 standing for the content of the ANT ionic stabilizer being essentially a water-soluble active organo-mineral additive containing amphoteric surfactants and microelements, %. The experimental design and the levels of the factors’ variability were specified on the basis of the test results.The principal factor exerting influence on the strength property of stabilized macadam and sand mixes is application of the ANT X3 ionic stabilizer.

Influence of Silica Fume Addition in the Long-Term Performance of Sustainable Cement Grouts for Micropiles Exposed to a Sulphate Aggressive Medium.

At present, sustainability is of major importance in the cement industry, and the use of additions such as silica fume as clinker replacement contributes towards that goal. Special foundations, and particularly micropiles, are one of the most suitable areas for the use of sustainable cements. The aim of this research is to analyse the effects in the very long-term (for 600 days) produced by sulphate attack in the microstructure of grouts for micropiles in which OPC (ordinary Portland cement) has been replaced by 5% and 10% silica fume. This line of study is building on a previous work, where these effects were studied in slag and fly ash grouts. Grouts made using a commercial sulphate-resisting Portland cement were also studied. The non-destructive impedance spectroscopy technique, mercury intrusion porosimetry, and Wenner resistivity testing were used. Mass variation and the compressive strength have also been analysed. Apparently, impedance spectroscopy is the most suitable technique for studying sulphate attack development. According to the results obtained, grouts for micropiles with a content of silica fume up to 10% and exposed to an aggressive sulphate medium, have a similar or even better behaviour in the very long-term, compared to grouts prepared using sulphate-resisting Portland cement.

Effect of temperature and type of sand on the magnesium sulphate attack in sulphate resisting Portland cement mortars

External Sulphate Attack on sulphate-resisting Portland cement concretes is a well-researched field. However, the effect of temperature on the performance of sulphate attack requires further attention. For this purpose, cubic mortars were made with sulphate resisting Portland cement (low C3A) and two types of sand, silica and limestone, which were then immersed in a 5% MgSO4 solution at different temperatures: 5, 20 and 50 °C, for 24 months. The deterioration of mortars due to magnesium sulphate attack was evaluated by measuring changes in mass, compressive strength, porosity and sorptivity. The X-ray diffraction was also used to determine the different mineral phases, and the pH of the conservation solutions was monitored. No damage was observed on the samples exposed at 50 °C. However, serious damage was noted on mortars made with silica sand exposed at 5 °C. Results show that high temperature improved some physical and mechanical properties and do not necessarily accelerate the degradation due to magnesium sulphate attack. Sulphate-resisting Portland cements with limited C3A content was found to be susceptible to Thaumasite Sulphate Attack. The type of sand has a remarkable effect on the performance of mortars at low temperature compared to high temperature. The samples with limestone sand showed better resistance against magnesium sulphate attacks.

A study of CO2 capture by high initial strength Portland cement pastes at early curing stages by new non-conventional thermogravimetry and non-conventional differential thermal analysis

Although the literature presents intensive studies based on monitoring cement hydration in adiabatic and semi-adiabatic environments, such as non-conventional differential thermal analysis (NCDTA) systems, studies of cement hydration in controlled climatic chambers are very rare. Using three W/C ratios (0.5, 0.6 and 0.7) and three relative humidity conditions (60, 80 and 100%) at 25 °C, the authors analyzed in real time the evolution of cement hydration reaction during the first 24 h in an environmental-controlled chamber. The main objective of this paper is to present two new developed systems of NCDTA (NNCDTA) and non-conventional TG and to show, using high-strength sulfate-resistant Portland cement pastes in a controlled chamber as application examples, how the developed systems measure on real time the thermal effects and the mass changes that occur during hydration and carbonation reactions. The captured CO2 mass can be quantified as it occurs by carbonation curves. The results are in agreement with the mechanical and structural properties of the used pastes and with their TG/DTG data, after being processed by different operational conditions. Carbonation for 24 h alters significantly the cement hydrated paste composition, resulting in final poor mechanical resistance properties. However, carbonation for 1 h, in specific conditions, enhances them when compared to a non-carbonated reference paste, due to a final higher content of silica and alumina hydrated phases and to a lower mass ratio between that of their combined water and their total mass as well.

Influence of Cement Type and Water-to-Cement Ratio on the Formation of Thaumasite

Cement mortar prisms were prepared with three different cement types and different water-to-cement ratios plus 30% mass of limestone filler. After 28 days of curing in water at room temperature, these samples were submerged in 2% magnesium sulfate solution at 5°C and the visual appearance and strength development for every mortar were measured at intervals up to 1 year. Samples selected from the surface of prisms after 1-year immersion were examined by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The results show that mortars with sulfate resisting Portland cement (SRC) or sulphoaluminate cement (SAC) underwent weaker degradation due to the thaumasite form of sulfate attack than mortars with ordinary Portland cement (OPC). A lower water-to-cement ratio leads to better resistance to the thaumasite form of sulfate attack of the cement mortar. A great deal of thaumasite or thaumasite-containing materials formed in the OPC mortar, and a trace of thaumasite can also be detected in SRC and SAC mortars. Therefore, the thaumasite form of sulfate attack can be alleviated but cannot be avoided by the use of SAC or SRC.

Corrosion resistance of sulfated cements in carbonate and in carbonate-sulfate mediums

Corrosion resistance of sulfated cements in carbonate and in carbonate-sulfate mediums has been studied. The samples have been placed in carbonate and carbonate-sulfate mediums for investigation stability of sulfated cements. The same researches were done with sulfate resistant portland cement to compare stability of samples. High corrosive resistant of sulfated cements is conditioned by forming dense and strong cement stone. The obtaining of corrosion resistant cements is possible with usage of the ordinary portland cement clinker with inclusion to them sulfoferrite and sulfoalumoferrite clinkers. Sulfated cements have the higher corrosion stability in contrast to ordinary sulfate resistant cement.

Sulfate Resistance in OPC and SRPC Containing Calcined Paper Sludge Waste: Ettringite or Thaumasite Formation

AbstractThe Le Chatelier–Anstett test was used to study the sulfate resistance of cement pastes containing calcined paper sludge waste (MC). MC was blended with two types of portland cement (PC): P1 with and P2 without C3A (ordinary portland cement, OPC, and sulfate-resistant portland cement, SRPC, respectively). The study of thaumasite formation required the utilization of a third PC, P3. The results showed that sulfate resistance always decreased at higher ratios of PC replacement by MC. This behavior was attributable to the expansive synergic effect (ESE), originated by the coprecipitation of ettringite from two resources in a gypsum and water medium. Part of the ettringite formed rapidly from the Al2O3r− in MC, and rapidly or slowly from the C3A in P1, depending on whether its early pozzolanic activity was sufficient or not. Rapid-forming ettringite of both origins was induced by the sufficient specific, fast, and early pozzolanic activity resulting in the indirect stimulation of sulfate-mediated P1 h...

A Comparative Study Between the Early Stages Hydration of a High Strength and Sulphate Resistant Portland Cement and the Type II F Portland Cement Through Non Conventional Differential Thermal Analysis and Thermogravimetry

This work presents a study, which compares the early stages of hydration of a High Initial Strength and Sulphate Resistant Portland Cement (HIS SR PC) with those of Type II F Portland Cement (PC II), by Non-Conventional Differential Thermal Analysis (NCDTA) within the first 24 hours of hydration. Water/cement (w/c) ratios equal to 0.5, 0.6 and 0.66 were used to prepare the pastes. The hydration of these two types of cement was monitored on real time by NCDTA curves, through the thermal effects of the hydration reactions, from which cumulative evolved energy curves were obtained. These techniques allow one to analyse the influence of each type of cement on the main stages that occur during the hydration process. Thermogravimetric analysis were also performed at 4 and 24h of hydration for both cements, to analyse the influence of each kind of cement on the amount of the main formed hydrated products. The results showed that with 4h of hydration, the total combined water amount released from the hydrated products was higher for the PC II pastes than for the HIS SR PC pastes. Otherwise, with 24h of hydration, the amount of the total combined water released from the hydrated products was higher for the HIS SR PC pastes than for the PC II pastes.

The effects of the early carbonation curing on the mechanical and porosity properties of high initial strength Portland cement pastes

Mechanical and porosity related properties of high initial strength sulfate resistant Portland cement (HS SR PC) pastes subjected to early age carbonation curing were investigated. This work presents the characterization through mechanical properties, of carbonated HS SR PC pastes and of non-carbonated references. They were treated at two different times of carbonation (1h and 24h), at the best conditions of capturing, previously determined by the authors. The mechanical properties were characterized by compressive strength, tensile strength by diametrical compression, elastic modulus and Poisson’s coefficient. It was found that 1h of carbonation improved the mechanical properties, while the increase of carbonation time to 24h, decreased significantly the same properties in relation to the reference specimens. The porosity related properties were characterized by total absorption, absorption by capillarity, gas permeability, and mercury intrusion porosity. It was noticed that the increase of the carbonation time from 1h to 24h, increased substantially the absorption properties. Despite the mechanical properties of the 1h carbonated paste were better than those of the reference, the absorbed water content of the carbonated specimen was slightly higher than that of the reference.

Effect of Using Well Water as Mixing Waterin Concrete

Water quality has been a matter of concern in civil engineering projects.Most specifications require the use of potable water because its chemical composition is known and well regulated. In some situations where potable water is not ready available, many water types which are unacceptable for drinking may be satisfactorily used in concrete, such as the well water. In this study, Well water is being investigated the feasibility of using well water as a mixing water in concrete. Water samples were obtained from three different wells. The chemical properties of these samples were investigated in the laboratory. Eight mixes were prepared from two types of cement (ordinary and sulfate resisting Portland cements) and these samples of well water as well as distilled water in order to make a comparative study. The concrete specimens were cured and tested for compressive,splitting tensile and flexural strengths at(3, 7, 28) days. The results, when compared with the results of control mixes (made with distilled water), showed that same effect of well water on the concrete strengths approximately. Therefore, the well water with acceptable limits in its chemical analysiswas suitable for use in production of concrete with acceptable strength.

Mechanical and Physical Properties of Early Carbonated High Initial Strength Portland Cement Pastes

After submitted to early age carbonation curing, mechanical and physical properties of high initial strength sulfate resistant Portland cement (HS SR PC) pastes were investigated, which were compared to those of non-carbonated reference pastes. Carbonation was performed for 1 and 24 hours, at the best conditions of CO2capturing, previously determined by the authors. Despite the compressive strength and elastic modulus of the 1h carbonated pastes were slightly higher than those of the reference pastes, their absorbed water content and porosity was slightly higher than that of the reference. In the case of 24h carbonation, its compressive strength decreases significantly because of its much higher porosity, although the new solid carbonated calcium silicate phase presents a much higher specific mass than those of the solid phases of the 1 hour and non-carbonated pastes.

Influence of the sulphate content of recycled aggregates on the properties of cement-treated granular materials using Sulphate-Resistant Portland Cement

The present work discusses the results of an experimental study investigating the performance of cement-treated granular materials, which were prepared from natural aggregates, recycled concrete aggregates, crushed clay bricks and gypsum. Recycled aggregates can potentially contain large amounts of acid-soluble sulphates. High sulphate contents can lead to the formation of ettringite, which causes dimensional instability in cement-treated materials. The tested samples were manufactured with different types of cement (CEM II and Sulphate-Resistant Portland Cement) and different compositions of the recycled materials to observe the effects of the sulphate content on the mechanical behaviour and the dimensional stability. As a result, the influence of the amount of sulphates on the deformation was determined, which is an aspect that must be considered in applications of this recycled product in road layers.

Reactive transport modelling of long-term carbonation

Concrete specimens of sulphate resistant Portland cement (SRPC) exposed to natural carbonation in a controlled environment for 13years revealed that the carbonation was significantly underestimated by accelerated tests and extrapolation by a linear diffusion equation. The results confirmed that carbonation as a phenomenon is too complex to be predicted by a conventional diffusion equation for periods considerably exceeding the experimentally covered period. A comprehensive approach consisting of a thermodynamic model and a statistical methodology to simulate long-term carbonation verified by versatile experimental data was presented. As an application of the method, long-term carbonation was simulated for the SRPC concretes.

Laboratory study of the long-term durability of buried concrete exposed to Lower Lias Clay

This paper describes a long-term investigation into chemical degradation vulnerability of four different types of concrete that were exposed to pyrite rich clay. In this, four 100mm square by 1.2m long concrete columns made from Portland cement (PC), Portland limestone cement (PLC), sulfate resisting Portland cement (SRPC) and Portland cement blended with 25% pulverised fuel ash (PC–PFA) were buried for 9years in slightly weathered Lower Lias Clay of water soluble sulfate class DS-2. One face of each concrete column was coated with bitumen to test the performance of this method of protection. The temperature was controlled at 4.5±0.5°C using a cold water circulation system. The performance of the different concretes was assessed by means of visual observation supported by X-ray diffraction (XRD), Infra-red Scanning (IR) and Scanning Electron Microscopy with Energy Dispersive X-ray analysis (SEM-EDX) to identify the deterioration products.It was found that deterioration due to the thaumasite form of sulfate attack occurred in all four concretes with PLC concrete being the worst affected. The thickness of thaumasite deterioration into the concretes over the 9-year exposure was as follows: PLC=47; PC=33; SRPC=22 and PC–PFA=10mm. The study affirmed the susceptibility to Thaumasite Sulfate Attack (TSA) of both PC–25% PFA replacement and SRPC concretes. It was also found that, the amount of concrete deterioration decreased with increasing burial depth, which was probably due to reduced access to air. The bitumen coating, even if damaged, was an effective barrier at preventing deterioration in all concretes.

Some durability aspects of hybrid alkaline cements

Blended cements that contain a high content of fly ash and a low content of Portland cement typically suffer from low early strength development and long setting times. Recently, one method of overcoming these problems has been to use an alkali activator to enhance the reactivity of fly ash particles at early ages. Such cements can be grouped under the generic term “hybrid alkaline cements”, where both cement clinker and fly ash, encouraged by the presence of alkalis, are expected to contribute to cementitious gel formation. The work presented here examines some of the durability aspects of high fly ash content hybrid alkaline cement. Specifically, the aspects investigated were: exposure at high temperatures (up to 1000°C), resistance to immersion in aggressive solutions and susceptibility to the alkali aggregate reaction. All tests were repeated with a commercially available sulfate resistant Portland cement for comparison. When exposed to high temperatures, the hybrid alkaline cement showed strikingly different behaviour compared to the control Portland cement, showing fewer micro-cracks and maintaining residual compressive strengths at least equal to original strengths. Beyond 700°C, the hybrid alkaline cement began to sinter, which resulted in shrinkage of around 5% and a 100% increase in residual compressive strengths. No such sintering event was noted in the control Portland cement, which showed a drastic loss in residual compressive strengths upon heating. In immersion tests, the hybrid alkaline cement possessed excellent resistance to sulfate and seawater attack, similar to the control sulfate resistant cement. Both cements were however severely degraded by immersion in 0.1M HCl for 90 days. Both binders complied with the accelerated alkali-aggregate test but when this test was extended, the hybrid alkaline binder showed much greater dimensional stability. Possible reasons for the differences in durability behaviour in both cements are discussed, based on experimental evidence provided.

Compressive Strength in Sulphate Resisting Portland Cement (SRPC)

The compressive strength of cement is regarded as a principal indicator to determine the quality of cement. Therefore, efforts were focused to combine the factors which affect compressive strength together in such a form to develop suitable statistical models for predicting strength of cement at various ages (3 and 7 days). Using SPSS16 software, a statistical analysis is performed for (574) observations taken from archive of quality control at Kerbala Cement Plant, which produces low alkalis sulphate resisting Portland cement. These data sets include compressive strength at 3 and 7 days with various independent variables. Stepwise regression results in multiple linear models that explain (99.7 %) and (99.9 %) of variations in 3-days and 7-days compressive strength respectively in function of; C3S, C2S, C3A, SO3 contents, and Insoluble residue (IR). The developed models show that these contents positive effect on strength, but (I.R) content has a negative one. Such models could be used in quality control of SRPC factories to enable the manufacturer to make corrections in process within production stage. The sufficient data used in the analysis assures confidence of the developed statistical model.

A study of the carbonation profile of cement pastes by thermogravimetry and its effect on the compressive strength

In a previous work, the authors have carbonated totally high initial strength and sulfate-resistant Portland cement pastes. In order to solve the mechanical problems caused by the intense carbonation that occurred during those experiments, new carbonation conditions were applied in this study. The obtained products were analyzed with respect to the carbonation reactions by thermogravimetry and compressive mechanical strength. Comparative analysis with reference pastes obtained without carbonation at the same age shows that CO2 capture increases with carbonation time. However, there is an optimum time, up to which the carbonation treatment does not affect the mechanical properties of the paste. Below this time, the lower is the carbonation time the higher is the increase of compressive strength, when compared to that of the reference pastes processed at same operating conditions without carbonation.

CO2 sequestration by high initial strength Portland cement pastes

During the formation of pastes, mortar and concretes have been used to capture CO2. This work presents a methodology to estimate the carbon dioxide (CO2) sequestered by high strength and sulfate-resistant Portland cement pastes during their early stages of hydration, by Thermogravimetry and Derivative Thermogravimetry. Water to cement ratio equal to 0.50 and 0.70 were evaluated and the captured CO2 amount was determined through TG/DTG curve data on initial cement mass basis, obtained during accelerated carbonation from the fluid state and accelerated carbonation after a first hydration process. The experiments were performed in a controlled chamber, maintaining the CO2 content at 20 vol % and the temperature at 25 °C, at different relative humidity (RH) (60 and 80 %) ambient. The procedure allows one to estimate the amount of CO2 sequestered by the initial cement mass of a given volume of paste, as well as to evaluate the RH and W/C ratio influence on the amount of hydrated formed products, mainly on the Ca(OH)2, important for CO2 fixation.

A model for a long-term diffusion of multispecies in concrete based on ion–cement-hydrate interaction

A model for simulating a long-term diffusion in concrete under submerged conditions has been developed. The model focuses on the interaction between cement hydrates and electrolyte solution adopting the physical properties of concrete as alternative parameters for estimating long-term diffusion. The model was verified by the large variety of long-term experimental data involving verification of cement hydrates, porosity properties, pH value, element distribution, and chloride penetration for sulphate-resistant Portland cement (SRPC) concretes. Evaluating impacts of hundreds of years’ exposure on concrete durability, a simulation was also performed for an exposure time of 500 years. The results confirmed the importance of ion–cement-hydrate interaction in the evaluation of a long-term diffusion of harmful substances such as chlorides into concrete. The simulation results show also that the solid phases of the SRPC concrete mix that was used are stable in the long-term. The threshold concentration of chlorides which may initiate reinforcement corrosion defined as Cl−/OH− ratio could be exceeded in concrete after moderate exposure period under the conditions investigated with typical protective concrete layers. Using of case-specific values for a threshold chloride content and evaluating the method used for estimating the initiation time of reinforcement corrosion are recommended in the structures with a long-design service life.