Portlandite Content Research Articles

Investigating the Effects of Polyaluminum Chloride on the Properties of Ordinary Portland Cement.

This study investigates the mechanical and microstructural properties of paste comprising ordinary Portland cement (OPC) added with polyaluminum chloride (PACl). The properties of the resulting mixture are analyzed using compressive strength, X-ray diffraction, scanning electron microscopy (SEM), mercury intrusion porosimetry, and thermogravimetric analysis. The results show that the addition of PACl improves the mechanical properties of OPC paste, that calcium-(aluminum)-silicate-hydrate (C-(A)-S-H) gel and Friedel’s salt are the major products forming from the reaction with the aluminum and chloride ions in PACl, and that the portlandite content decreases. Moreover, the size and number of micropores decrease, and compressive strength increases. All these phenomena are amplified by increasing PACl content. SEM images confirm these findings by revealing Friedel’s salt in the micropores. Thus, this work confirms that adding PACl to OPC results in a mixture with superior mechanical and microstructural properties.

Pozzolanic properties of ultrafine sugar cane bagasse ash produced by controlled burning

This paper evaluated the feasibility of using residual sugar cane bagasse ash with a high carbon content (as-received SCBA) as raw material to produce a pozzolan after controlled recalcination and grinding. Initially, the as-received SCBA was re-burned using rotary (continuous) and muffle (batch) kilns, both at 600 °C for 1 h. Next, the resulting ash was ground in a closed-circuit ball mill with an air classifier system to obtain a product with 50% passing particle size of approximately 10 μm (SCBA600). SCBA600 was then characterized in terms of oxide composition, loss on ignition, density, specific surface area, and pozzolanic activity. A hydration study was carried out using isothermal calorimetry, thermogravimetric analysis and mercury intrusion porosimetry. Additionally, the performance of SCBA600 in mortars was evaluated by axial compression tests. The combination of recalcination at 600 °C, low-energy ultrafine grinding of the material and classification resulted in pozzolanic SCBA. The results also showed that including SCBA600 in cement mortars reduced total accumulated heat and portlandite content in cement-based pastes, in addition to refining pore structure and significantly increasing compressive strength after 3 days of curing.

Activation of Portland cement blended with high volume of fly ash using Na2SO4

Increasing the replacement ratio of Portland cement clinker by supplementary cementing materials is one of the best strategies to reduce the impact of the cement and concrete industry on the environment. While fly ash is widely available particularly in developing countries where much of the construction activities are projected in the coming future, the replacement levels are limited to around 25–30% in practice owing to its low reactivity. This work studies the effect of sodium sulphate (Na2SO4) on the activation of Portland cement blended with 50 wt-% class F fly ash. Na2SO4 activation contributes to a significant strength increase both in the early and later ages. Flow table results indicate that mortar workability is improved. Mercury intrusion porosimetry after 28 days show considerable refinement of pore structure. An increase in the bound water content, cumulative heat release, ettringite content and reduction of portlandite and AFm content were measured.

The Influence of Fluidized Bed Combustion Fly Ash on the Phase Composition and Microstructure of Cement Paste

Fly ashes from coal combustion in circulating fluidized bed boilers in three power plants were tested as a potential additive to cement binder in concrete. The phase composition and microstructure of cement pastes containing fluidized bed fly ash was studied. The fractions of cement substitution with fluidized bed fly ash were 20% and 30% by weight. X-ray diffraction (XRD) tests and thermal analyses (derivative thermogravimetry (DTG), differential thermal analysis (DTA) and thermogravimetry (TG)) were performed on ash specimens and on hardened cement paste specimens matured in water for up to 400 days. Quantitative evaluation of the phase composition as a function of fluidized bed fly ash content revealed significant changes in portlandite content and only moderate changes in the content of ettringite.

Influence of grinding on the pozzolanic activity of granite residue

Abstract This study explores the potential of the granite residue to be applied as a supplementary cementitious material. Furthermore, the efficiency of grinding methods in the improvement of the residue reactivity was also evaluated. The granite residue was collected in a facility located in Brazil and used as a Portland cement replacement with a substitution rate of 25% in mass. The residue was submitted to wet, dry and additive dry grinding methods, with several different times. The cement-based composites were characterized by quantitative X-Ray diffraction using the Rietveld's method, thermogravimetric analysis, and compressive strength. In conclusion, there was observed a higher efficiency of the wet grinding method, followed by an increase in compressive strength results as grinding time increased. Furthermore, the portlandite content was lower in the cement-based composite with granite residue, especially in the samples ground for 60, 120, and 180 minutes; a fact that summed up with other results for the pozzolanic potential of the granite residue.

Recycling hazardous textile effluent sludge in cement-based construction materials: Physicochemical interactions between sludge and cement

The textile industry produces a large amount of textile effluent sludge (TES). Many studies have explored the potential use of TES in cement-based materials. However, the physicochemical interactions between the TES and ordinary Portland cement (OPC) have rarely been studied. In this study, the effects of increasing dosage (0–20% by OPC) of TES on the performance of OPC-TES blends were investigated in terms of hydration progress, mechanical strength, microstructure evolution and metal leachability. The results showed that TES markedly delayed the OPC hydration at the early age, and increasing dosages of TES decreased the portlandite content at 7 and 28 days’ age. Compared to the reference, the OPC-TES mortar exhibited seriously degraded mechanical strength; when using 20% TES, the decrease in compressive and flexural strength reached up to 71% and 42% respectively at the age of 28 days. Scanning electron microcopy and mercury intrusion porosimetry found the inclusion of TES introduced more weak interfaces in the cement mortar, thus increased the total porosity especially the macropores. But leachability tests revealed all the toxic metals in the TES were stabilized after the incorporation of OPC and exhibited very low metal mobility in the OPC-TES mortar, which posed no environmental risk.

Fine Grain Concrete on Mixing Water Activated in Cavitation Permanent Magnet-Type Apparatus

The authors obtained fine grain concrete based on the mortars of additives-electrolytes undergone mechanic magnetic activation and characterized by improved compression and bending strength and enhanced freeze-thaw resistance. There was investigated the impact of mechanic magnetic activation (MMA) on mixing water when adding calcium chloride and sodium thiosulphate as well as on porosity of cement stone and specific features of phase formation in cement stone. It was stated by the authors that MMA facilitates formation of nucleation centers in activated water in the presence of additives-electrolytes, optimization of porous space as well as crystallization of calcium carbonate in the form of aragonite when lowering the content of Portlandite. The mechanism of joined influence of hydrodynamic and magnetic treatment of mixing water has been determined.

High performance cement composites with colloidal nano-silica

Recent studies have demonstrated the advantages of using nano-silica in building materials such as concrete due to its nano-filler effect as well as the pozzolanic reaction. However, most of the previous findings are based on normal strength cement composites. In this study, a wide range of properties of high performance cement composites are investigated with addition of colloidal nano-silica (CNS) at dosage of 0.5%, 1.0%, 1.5% and 2.0%. Attributed to the pozzolanic reaction of CNS, the microstructures are denser and more homogenous. SEM observation, accelerated hydration rate and reduced Portlandite content verify this beneficial reaction. Hence, the CNS can help produce cement composites with higher mechanical strength and better durability regards to the impermeability to water and chloride ions. Also, it is found that the influence of CNS is more pronounced for composites with lower water-cement ratio at 0.30, in comparison with those at 0.50.

Influence of Wood-Based Biomass Ash Admixing on the Structural, Mechanical, Hygric, and Thermal Properties of Air Lime Mortars

Mechanically-activated wood-based biomass ash (WBA) was studied as a potential active admixture for design of a novel lime-pozzolan-based mortar for renovation purposes. The replacement ratio of lime hydrate in a mortar mix composition was 5%, 10%, and 15% by mass. The water/binder ratio and the sand/binder ratio were kept constant for all examined mortar mixes. Both binder constituents were characterized by their powder density, specific density, BET (Brunauer–Emmett–Teller), and Blaine specific surfaces. Their chemical composition was measured by X-ray fluorescence analysis (XRF) and mineralogical analysis was performed using X-ray diffraction (XRD). Morphology of WBA was investigated by scanning electron microscopy (SEM) and element mapping was performed using an energy dispersive spectroscopy (EDS) analyzer. The pozzolanic activity of WBA was tested by the Chapelle test and assessment of the Portlandite content used simultaneous thermal analysis (STA). For the hardened mortar samples, a complete set of structural, mechanical, hygric, and thermal parameters was experimentally determined. The mortars with WBA admixing yielded similar or better functional properties than those obtained for traditional pure lime-based plaster, pointing to their presumed application as rendering and walling renovation mortars. As the Chapelle test, STA, and mechanical test proved high pozzolanity of WBA, it was classified as an alternative eco-efficient low-cost pozzolan for use in lime blend-based building materials. The savings in CO2 emissions and energy by the use of WBA as a partial lime hydrate substitute in mortar composition were also highly appreciated with respect to the sustainability of the construction industry.

Rietveld Quantitative Phase Analysis of Oil Well Cement: In Situ Hydration Study at 150 Bars and 150 °C.

Oil and gas well cements are multimineral materials that hydrate under high pressure and temperature. Their overall reactivity at early ages is studied by a number of techniques including through the use of the consistometer. However, for a proper understanding of the performance of these cements in the field, the reactivity of every component, in real-world conditions, must be analysed. To date, in situ high energy synchrotron powder diffraction studies of hydrating oil well cement pastes have been carried out, but the quality of the data was not appropriated for Rietveld quantitative phase analyses. Therefore, the phase reactivities were followed by the inspection of the evolution of non-overlapped diffraction peaks. Very recently, we have developed a new cell specially designed to rotate under high pressure and temperature. Here, this spinning capillary cell is used for in situ studies of the hydration of a commercial oil well cement paste at 150 bars and 150 °C. The powder diffraction data were analysed by the Rietveld method to quantitatively determine the reactivities of each component phase. The reaction degree of alite was 90% after 7 h, and that of belite was 42% at 14 h. These analyses are accurate, as the in situ measured crystalline portlandite content at the end of the experiment, 12.9 wt%, compares relatively well with the value determined ex situ by thermal analysis, i.e., 14.0 wt%. The crystalline calcium silicates forming at 150 bars and 150 °C are also discussed.

Mitigating CO2 reaction with hydrated oil well cement under geologic carbon sequestration using nanoclay particles

The reaction of the cement with CO2 saturated brine leads to cement carbonation which results in numerous chemo-mechanical changes in the cement matrix. In this study, the mechanism of nanoclay (NC) to enhance the carbonation resistance of class G oil well cement (OWC) is addressed.Two cement slurries with 0% and 1% of the modified montmorillonite NC were prepared. The samples were characterized with the powder X-ray diffraction (PXRD) technique which confirmed the decrease in the portlandite (CH) content and the increase in the most thermodynamically stable calcium silicate hydrates (CSH) for the sample with 1% NC. The samples then immersed into 0.5 M NaCl solution at 95 °C and 10 MPa for 30 days and the changes in the compressive and tensile strengths, permeability, and pore structure were evaluated with the carbonation time.The results revealed that incorporating NC into OWC paste increased the concentration of the CSH, decrease the reduction in the compressive and tensile strengths to 8.56% and 9.82%, respectively, compared with the compressive and tensile strengths retrogressions of 45.67% and 27.39% for the base cement. The final permeability of the NC-based sample is 51.67% less than the base sample permeability. The decrease in the cement permeability and CH content and the increase in the CSH are the main mechanisms which enhanced the NC-based cement resistance to carbonation.

Comparison of dolostone and limestone as filler in blended cements

A dolostone from Sierras Bayas (Buenos Aires Province, Argentina) is characterized for use as supplementary cementitious material (SCM). This comparative study with usual limestone filler includes the results of grindability and the performance of blended cements with 20% filler. Carbonate stones were ground in a laboratory ball mill to attain the objective (d50 < 4 μm). For blended cements, the mini-slump, setting time and hydration heat were determined on paste with a water-to-cementitious material ratio (w/cm) of 0.40. Compressive strength was determined on mortar (w/cm = 0.50) up to 90 days, and the mineralogical composition of the hydrated pastes was determined by XRD and thermogravimetry at 28 days. Results show that the grinding time of the dolostone is shorter than that of limestone, and the volume of fine particles (< 10 μm) is increased. Dolostone filler (D-filler) cement shows behaviour analogous to limestone filler (L-filler) cement. Both fillers decrease the initial mini-slump, and the mini-slump loss rate is similar, the setting time is shorter and the heat released increases. The overall performance of blended cement appears independent of the mineralogical composition. For L-filler, the effects are more pronounced at early ages. The compressive strength of the L-filler is higher than that of the D-filler at early ages, and later the opposite is true. Preliminary analysis on hydration products and portlandite content does not justify this behaviour. The D-filler is a viable alternative as a partial replacement of portland cement, after that the chemical stability in the alkaline paste environment will be confirmed.

Influence of curing temperature on cement paste microstructure measured by 1H NMR relaxometry

1H nuclear magnetic resonance (NMR) relaxometry, supported by X-Ray diffraction and thermogravimetric analysis, has been used to characterise microstructure of white cement pastes underwater cured at temperatures in the range 10 °C to 60 °C. As the temperature increases, so the C-S-H, capillary pore water and interhydrate pore water content all increase; the ettringite and gel pore water content decrease; and the Portlandite content stays constant. A non-linear increase in the C-S-H ‘solid’ and ‘bulk’ densities, that exclude and include gel pore water respectively, has been observed with the increase of temperature. This is accompanied by a decrease in C-S-H water content but no change in the Ca/(Si + Al) ratio. The increase in the C-S-H ‘solid’ density has been attributed to a decrease in the number of locally stacked C-S-H layers. The increase in the C-S-H ‘bulk’ density is additionally attributed to the decrease in the gel porosity.

Investigation of Blended Cement Hydration in the Reactive Powder Concrete with Increasing Levels of Silica Fume Addition

Hydration is a chemical reaction in which the major compounds in cement form chemical bonds with water molecules and become hydration products. By the process of hydration Portland cement mixed with sand, gravel and water produces the synthetic rock we call concrete. The Therefore, the concrete properties always accompanies with the hydration degree of cement. This paper presents some experimental test results on how silica fume affects the cement hydration in cement pastes of the Reactive Powder Concrete as increasing levels of silica fume addition with the content from 0% to 30% of cement mass. The hydration process of cement/silica fume paste was followed from the estimation of heat of hydration, rate of heat evolution, of binder pastes obtained by isothermal calorimetry (TAM-Air). In addition, the portlandite content, the hydration degree of pure cement, reaction degree of binder paste as well as reaction degree of silica fume were investigated. The quantitative assessment on these characteristics are due to the simulation of the hydration of Portland cement pastes containing silica fume.

Performance of recycled soda–lime glass powder in mitigating alkali–silica reaction

Recycled soda–lime glass powder (SLGP) is a valuable supplementary cementitious material. However, it has a high alkali content, and its effectiveness in mitigating the alkali–silica reaction (ASR) is uncertain. In this study, the ASR performance of SLGP was evaluated using the accelerated mortar bar test (ASTM C 1567) and the concrete prism test (ASTM C 1293). It was determined that a sufficient dosage of SLGP can mitigate ASR according to ASTM C 1567, and that finer SLGP is more effective. Meanwhile, the 2-year concrete prism test showed that the same type, fineness and dosage of glass powder as tested by C 1567 does reduce ASR, but not sufficiently and below the ASTM failure threshold. Pore fluid composition monitoring revealed that SLGP, over time, serves as a net contributor to the pore solution alkalinity, but these alkalis are released slowly. Overall, SLGP can reduce ASR, albeit insufficiently and temporarily. This ASR reduction is likely through a combination of reduced pore solution pH at early ages (due to cement dilution) and reduced portlandite content and transport properties at later ages (due to pozzolanic reaction). Long-term ASR testing is necessary to determine if and at what dosage a glass pozzolan may be able to control ASR sufficiently.

Performance evaluation of steam cured HPC pipe piles produced with metakaolin based mineral additives

High performance pipe piles are widely used in precast industry. In order to improve the production efficiency and performances of the products, steam curing and mineral admixtures are usually applied. This paper evaluates the performances of HPC pipe piles produced with metakaolin-based admixtures. Quantitative phase composition analysis shows that the addition of 10 wt% metakaolin reduces the portlandite content by up to 57.1%, while increases the content of ettringite to some extent. The addition of metakaolin or metakaolin-slag/limestone blends improves the mechanical properties, especially the hybrid usage of metakaolin and limestone filler. Pore structure and microscope analyze confirm the remarkably-refined pore characteristics caused by the addition of metakaolin-based admixtures, in which case the gel pores accounts up to 85% of the total pores. Those remarkably improved properties caused by the addition of metakaolin-based admixtures indicate a promising future for their applications in producing high performance pipe piles with further modified properties.

Relationship between cement composition and the freeze–thaw resistance of concretes

Concrete exposed to cyclic freezing and thawing may deteriorate by surface scaling, internally developed cracks or both in combination. The rate of deterioration tends to be accelerated in concretes containing higher levels of supplementary cementitious materials including slag and limestone. A fundamental insight into the relationship between cement composition and freeze–thaw resistance is therefore imperative for developing durable composite cement concretes. Concrete samples prepared from CEM I, binary slag cements and ternary limestone slag cement blends at 0·5 w/b ratio without air entrainment were investigated. The freeze–thaw test was based on the CIF method according to PD CEN/TR 15177. Additionally, phase assemblages in the concretes before and after freeze–thaw damage were evaluated. Before freeze–thaw testing, compressive strengths were similar but the composite cements were slightly more susceptible to carbonation. However, the scaling and internal damage resistance decreased in the order of CEM I, binary and limestone ternary blended cements. The composition of the scaled material differed from the bulk, revealing an absence of portlandite and a marked reduction in AFm and ettringite contents. A probable explanation for the reduced freeze–thaw resistance includes the porosity differences and the lower portlandite content compared to CEM I concrete.

Hydration, shrinkage, and durability of ternary binders containing Portland cement, limestone filler and metakaolin

A partial replacement of the clinker by latent hydraulic or pozzolanic materials is encouraged due to environmental and specific technical requirements. Such substitution remains limited to a relatively low level (less than 30% by mass of cementitious materials). An experimental research work was carried out on mortars made with binary and ternary binders (Portland cement; metakaolin; limestone filler) to reach 45% total replacement. In order to investigate the activating effect of reduced water-to-cement ratio, two series of mixtures were designed with W/C0 of 0.42 and 0.5. Their heat of hydration, portlandite content, shrinkage, porosity, and carbonation were monitored. The tests were performed to understand the evolution of their relative strength (activity index) and durability parameters. The strength development of mortars with ternary binders was found to depend on metakaolin properties, including manufacturing process and particle size distribution. Reducing W/C0 ratio accelerated pozzolanic reaction and allowed improving early-age strength and durability parameters.

Potential alkali silica reaction expansion mitigation of ferronickel slag aggregate by fly ash

This study investigates the potential alkali silica reaction (ASR) of ferronickel slag (FNS) aggregate, which is a by‐product of nickel production. A class F fly ash was used as a possible ASR mitigation in accelerated mortar bar test (AMBT) specimens containing 50% FNS. There were visible surface cracks on the specimens using no fly ash or 10% fly ash. Use of 20% fly ash reduced expansion by 45% as compared to that with 10% fly ash. In accordance with the expansion limits of Australian Standard, the mixtures using 20 and 30% fly ash were categorized as slowly reactive and nonreactive, respectively. Thermogravimetric analysis (TGA) and microstructural observations confirmed the effectiveness of fly ash in reducing Portlandite content that reduced the ASR expansion. Therefore, the use of 20–30% fly ash as cement replacement is considered as an adequate ASR mitigating measure of FNS fine aggregate.

Rebound hammer test to estimate compressive strength of heat exposed concrete

The residual concrete strength is required for evaluating the safety of reinforced concrete structures after fire. Based on the surface hardness of concrete, a rebound hammer test has been used to evaluate the compressive strength at the ambient temperature and after fire. However, only few studies are available on the limitations of such indirect testing of concrete strength after fire. In this research, variations in the rebound from reinforced concrete beams before and after heating to 800 °C were investigated and compared with strength of the concrete core. The variations were plotted with average temperatures of the test specimens based on a validated finite element model. At a given temperature, the ratio of rebounds was significantly higher than the ratio of compressive strengths. The rebound did not clearly change in the temperature range up to about 420 °C. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were also carried out on the concrete samples. X-ray diffraction showed gradual reduction in portlandite content and increased calcium carbonate. SEM investigations indicated that fire exposed concrete tends to have smaller pores. This may be due to formation of calcium carbonate, which also increases surface hardness of the concrete, similar to carbonation effects. Therefore, the rebound decreased less than the compressive strength.