Blended Pastes Research Articles

Investigation of Rheological Properties of Blended Cement Pastes Using Rotational Viscometer and Dynamic Shear Rheometer

To successfully process concrete, it is necessary to predict and control its flow behavior. However, the workability of concrete is not completely measured or specified by current standard tests. Furthermore, it is only with a clear picture of cement hydration and setting that full prediction and control of concrete performance can be generalized. In order to investigate the rheological properties of blended cement pastes, a rotational viscometer (RV) was used to determine the flow characteristics of ordinary and blended pastes to provide assurance that it can be pumped and handled. Additionally, a dynamic shear rheometer (DSR) was used to characterize both the viscous and elastic components of pastes. Ordinary Portland cement paste and blended pastes (slag, fly ash, and silica fume) were investigated in this study. The stress and strain of the blended specimens were measured by the DSR, which characterizes both viscous and elastic behaviors by measuring the complex shear modulus (the ratio of total shear stress to total shear strain) and phase angle (an indicator of the relative amounts of recoverable and nonrecoverable deformation) of materials. Cement pastes generally exhibit different rheological behaviors with respect to age, mineral admixture type, and cement replacement level.

Metakaolin as an Active Pozzolan for Cement That Improves Its Properties and Reduces Its Pollution Hazard

Prepared metakaolin produced by calcination of a kaolin sample at 750&degC after soaking for 5 hrs was tested as an active pozzolan for locally produced cement. Blended pastes of partially replaced ordinary Portland cement with different metakaolin amounts 5%, 10% and 15% were prepared, then they were hydrated with water for various time intervals of 1, 3, 7, 14 and 28 days. At each time interval, the hydrated paste specimens were tested for compressive strength, hydration kinetics and followed up using differential scanning calorimetry, X-ray diffractometry analyses and scanning electron microscopy techniques. Results showed that the blended pastes OPC-MK10 recorded the highest compressive strength values at all the hydration times reaching 33.10, 86.40, 101.20, 112, and 122 MPa with increasing the age of hydration as compared with the neat samples which recorded 31.70, 65.20, 72.6, 82 and 101.30 MPa respectively. Meanwhile, the OPC-MK10 blend showed a decrease in the free CaO content reaching 4.07%, 4.27%, 4.23%, 4.19%, and 4.11% CaO with increasing age of hydration compared with the neat samples which recorded 4.27%, 5.15%, 5.42%, 5.61%, and 5.96% CaO respectively. The DSC thermograms results for the hardened neat and OPC-Mk10 pastes at the 14 and 28 hydration days showed the formation of hydrated materials mainly calcium silicate hydrates, calcium sulphoaluminate hydrates and calcium aluminates hydrates. The X-ray diffractometry analyses of both hardened neat and OPC- MK10 showed that, the intensity of calcium hydroxide peaks of OPC-MK10 was lower than in case of neat OPC, while the peak of the hydration products of calcium silicate hydrates and calcium aluminates silicate hydrates of OPC- MK10 samples were of higher intensity than in case of neat OPC. Scanning electron microscopy micrographs indicated the formation of denser micro- structure for the hardened OPC-MK10 paste as compared to neat OPC pastes after the 28 days age of hydration.

Influence of different amounts of natural pozzolan from volcanic scoria on the rheological properties of portland cement pastes

In this study, design of experiments is used to investigate the influence of ratio of Portland cement (PC) / natural pozzolan (NP) on the yield stress and plastic viscosity of blended pastes. A set of pastes specimens was made with 0%, 25%, 35% and 45% of NP. NP from a Cameroonian volcanic scoria (CVS) with four differents colors were used. The results showed that the yield stress and viscosity of pastes were generally decreased when the NP replaced part of the cement. The reduction of yield stress is around 3.72 to 29.04%, 21.12 to 44.26% and -1.99 to 58.96% for 25, 35 and 45% of replacement respectively. The reduction of plastic viscosity is around -7.60 to 26.57%, 16.67 to 34.23% and 37.5 to 56.26% for 25, 35 and 45% of replacement. However, NP exhibited a significant reduction of yield stress and plastic viscosity when amount of replacement is higher than 25%.

Effect of NaOH activation on sulphate resistance of GGBFS and binary blend pastes

This paper presents an investigation into the observed enhanced performance that alkali activated ground granulated blast furnace slag (GGBFS) and binary blends offer against sulphate attack. X-ray diffraction (XRD) was carried out to identify and quantify the crystalline phases formed in a wide range of GGBFS and GGBFS-OPC (ordinary Portland cement) blends. Furthermore, specimens were exposed to a sulphate solution to examine the evolution of compressive strength along with identification of activation and/or hydration products. XRD demonstrated that ettringite was completely decomposed into its constituents in the presence of NaOH while quantification ascertained the formation of considerable amounts of hydrotalcite in the activated GGBFS and binary blends. Alkali activated GGBFS and binary blends specimens with higher GGBFS content offered enhanced resistance against aggressive sulphate ions and no significant degradation products were observed in these specimens after 6 months of exposure to sulphate solution. The results demonstrated that hydrotalcite formation may be a major reason for the improved sulphate resistance of alkali activated GGBFS and binary blend pastes with higher GGBFS content.

Numerical simulations of permeability of plain and blended cement pastes

The durability of a concrete structure is principally dependent on its permeability, which governs the rate of transport of fluid through the concrete pore network. This paper presents a numerical model based on the lattice Boltzmann method (LBM) to calculate the saturated permeability of cement pastes, including blended cement pastes, wherein cement is replaced partially by an inert filler. The LBM uses a discretized form of the Boltzmann equation to simulate the pressure-gradient induced flow of a fluid through a porous microstructure. The accuracy of the algorithms implemented in the LBM are verified against analytical solutions of permeability of simple geometries. A microstructural model is used to generate three dimensional (3D) microstructures of cement pastes. The effects of liquid-to-solid ratio (l/s), degree of hydration of cement (DOH), filler content, and physical properties of the cement and filler (e.g., PSD: particle size distribution, affinity towards nucleation of hydrates on their surfaces) are evaluated. The simulations are verified against experimental measurements and numerically derived values of permeability published in literature. Results obtained from the simulations show that in both plain and blended pastes, the permeability increases and decreases monotonically, though in a nonlinear manner, over several orders of magnitude, in relation to the effective capillary porosity and the DOH, respectively. At equivalent DOHs, pastes consisting of finer anhydrous (i.e., cement or filler) particles have lower permeability compared to those prepared with coarser particles. This is attributed to the improved packing of finer particles at the time of mixing, which increases the likelihood of 3D percolation of solid phases and, ultimately, results in a higher connected volume of solid phases and a poorly connected capillary pore space within the microstructure. It is shown that in blended pastes, those prepared using a filler with a greater affinity towards nucleation and growth of hydrates on their surfaces have a higher volume of percolated solid phases, and, hence, lower permeability.

Effect of grinding on early age performance of high volume fly ash ternary blended pastes with CKD & OPC

This study investigated setting times and early age compressive strength of the high volume fly ash (HVFA) blended pastes prepared with ground materials. The pastes consisted of 60% Fly Ash+30% Portland cement (CEM I)+10% cement kiln dust (CKD) and tests were carried out for four different fly ashes. In phase 1, all the constituent binder materials (class F-fly ash, CEMI and CKD) were initially mixed in the relevant proportions and were ground for varying time periods (1, 2 and 4h). In phase 2, the CEM I and CKD were mixed and ground for different time periods (1 and 2h) and then added to the unground fly ash. Both wrapped and submerged curing were used for compressive strength test samples. Overall, grinding of constituents appeared to be largely ineffective at increasing 2day compressive strength although strength enhancements at 28days were generally observed. Paste samples that were made from interground constituents generally achieved higher 28day strengths than corresponding pastes where only the activators were ground, although this was not consistent throughout so further investigation is suggested in this area. Submerged curing is generally less effective in increasing compressive strength than wrapped curing as leaching of CKD is suspected to have occurred.

Blended Chitosan Paste for Infection Prevention: Preliminary and Preclinical Evaluations.

Local drug delivery devices offer a promising method for delivering vancomycin and amikacin for musculoskeletal wounds. However, current local delivery devices such as beads and sponges do not necessarily allow for full coverage of a wound surface with eluted antibiotics and do not address the need for reducing the antibiotic diffusion distance to help prevent contamination by bacteria or other microorganisms. We blended chitosan/polyethylene glycol (PEG) pastes/sponges to increase biocompatibility and improve antibiotic coverage within the wound. (1) Are blended chitosan/PEG pastes biodegradable? (2) Are the blended pastes biocompatible? (3) How much force does paste require for placement by injection? (4) Will the pastes elute active antibiotics to inhibit bacteria in vitro? (5) Can the pastes prevent infection in a preclinical model with hardware? Our blended paste/sponge formulations (0.5% acidic, 1% acidic, and acidic/neutral) along with a control neutral 1% chitosan sponge were tested in vitro for degradability, cytocompatibility, injectability tested by determining the amount of force needed to inject the pastes, elution of antibiotics, and activity tested using zone of inhibition studies. Along with these studies, in vivo models for biocompatibility and infection prevention were tested using a rodent model and an infected mouse model with hardware, respectively. By evaluating these characteristics, an improved local drug delivery device can be determined. All three of the paste formulations evaluated were almost fully degraded and with 6 days of degradation, the percent remaining being wasless than that of the control sponge (percent remaining: control 99.251% ± 1.0%; 0.5% acidic 1.6% ± 2.1%, p = 0.002; 1% acidic 1.7% ± 1.6%, p = 0.002; acidic/neutral 2.3% ± 1.7%, p = 0.010). There was good biocompatibility because cell viability in vitro was high (control 100.0 ± 14.3; 0.5% acidic formulation at 79.4 ± 12.6, p < 0.001; 1% acidic formulation at 98.6 ± 6.1, p = 0.993; acidic/neutral formulation at 106.7 ± 12.8, p = 0.543), and in vivo inflammation was moderate (control 2.1 ± 1.2; 0.5% acidic 3.3 ± 0.2, p = 0.530; 1% acidic 2.5 ± 0.9, p = 0.657; acidic/neutral 2.9 ± 1.1, p = 0.784). Force required to inject the 0.5% acidic and 1% acidic pastes was less than the acidic/neutral paste used as a control (control 167.7 ± 85.6; 0.5% acidic 41.3 ± 10.7, p = 0.070; 1% acidic 28.0 ± 7.0, p = 0.940). At 72 hours, all paste formulations exhibited in vitro activity against Staphylococcus aureus (control 2.6 ± 0.8; 0.5% acidic 98.1 ± 33.5, p = 0.002; 1% acidic 87.3 ± 17.2, p = 0.006; acidic/neutral 83.5 ± 14.3, p = 0.010) and Pseudomonas aeruginosa (control 163.0 ± 1.7; 0.5% acidic 85.7 ± 83.6, p = 0.373; 1% acidic 38.0 ± 45.1, p = 0.896; acidic/neutral 129.7 ± 78.0, p = 0.896). Also, the paste formulations were able to prevent the infection with 100% clearance on the implanted hardware and surrounding tissue with the control being a 0.5% acidic paste group without antibiotics (control 4 × 104 ± 4.8 × 104; 0.5% acidic 0.0 ± 0.0, p value: 0.050; 1% acidic 0.0 ± 0.0, p = 0.050; acidic/neutral 0.0 ± 0.0, p = 0.050). The preliminary studies demonstrated promising results for the blended chitosan/PEG pastes with antibiotics provided degradability, biocompatibility, injectability, and infection prevention for musculoskeletal-type wounds. The preliminary studies with the chitosan paste delivered antibiotics to a contaminated musculoskeletal wound with hardware and prevented infection. More studies in a complex musculoskeletal wound and dosage studies are needed for continued development.

Quality Assessment of Doughnut Prepared from Wheat Flour Enriched with Bambara Nut Flour

ABSTRACTThe proximate composition, pasting, and functional properties of flour blends from wheat and bambara nut at 10%, 20%, and 30% were carried out. The codes used were: DEL (90% wheat flour and 10% bambara nut flour), PIE (80% wheat flour and 20% bambara nut flour), ROW (70% wheat flour and 30% bambara nut flour), and ALE (100% wheat flour as control). Doughnuts were prepared using these blends and their sensory properties assessed. Results obtained revealed that the protein content of the flour increased with increase in bambara nut addition from 10.88–11.78%. Significant differences (p < 0.05) were observed in the fat, ash, and crude fiber (1.88–2.23%, 1.22–1.88%, and 3.96–4.02%) respectively. Doughnuts with 10% bambara nut flour (DEL) were most acceptable amongst the samples because there was no significant difference (p < 0.05) between this sample and the control in most parameters assessed.

Physicochemical and Rheological Properties of Optimised Cocoyam-Based Composite Flour Comprising Cassava Starch

Abstract Composite flour comprising cocoyam (Colocassia esculenta), bambara groundnut and cassava starch was produced. The proximate and minerals compositions and functional properties were optimized using optimal mixture design of response surface methodology. The antinutritional, pasting and farinograph analyses of the optimum blends were evaluated. Bambara groundnut improved protein, fibre, ash and minerals contents; cassava starch improved swelling capacity, least gelation and pasting characteristics. The optimum blends CBC1 (70% cocoyam flour, 18.33% bambara groundnut flour, 11.67% cassava starch) and CBC2 (69.17% cocoyam flour, 16.67% bambara groundnut flour, 14.17% cassava starch). were comparable to wheat–based flour samples (60% wheat, 30% cocoyam, 10% bambara groundnut flours) and (72% wheat, 19% cocoyam, 9% bambara groundnut flours) in terms of pasting and farinograph analyses.

Improving Particle Size Distribution in Cement Paste by Blending with Superfine Cement

The rheological and mechanical performance of cement paste is closely related to its packing density, which may be optimized by improving the particle size distribution in the paste mix. In this study, the authors propose modifications to the existing mathematical equations of particle size distribution. The new equation of optimal particle size distribution so formulated is verified experimentally. A series of cement paste having different water/cementitious materials (W/CM) ratios were produced by blending ordinary Portland cement (OPC) with varying contents of superfine cement (SFC). The particle size distributions of the blended paste mixes were compared with the proposed equation. The packing density of paste mixes was measured using the wet packing test method, and the flowability, rheological properties, and compressive strength of the paste mixes were tested. It is found that the particle size distribution in cement paste can be improved by blending with SFC, which can lead to enhancement in packing density, flowability, rheology and strength. The authors opine that the proposed equation of particle size distribution may be applied for mix design optimization of cementitious paste, including cementitious grout and the paste phase in mortar and concrete. DOI: http://dx.doi.org/10.5755/j01.sace.16.3.16273

Chloride binding ability and the onset corrosion threat on alkali-activated GGBFS and binary blend pastes

This paper presents an experimental study to investigate the chloride binding ability of alkali-activated ground granulated blast furnace slag (GGBFS) and binary blend pastes. Free chloride and total chloride were measured to assess the chloride binding ability. pH measurement was performed to obtain [Cl−/OH−] ratio to assess the onset corrosion threat. The results showed that bound chloride significantly increased in GGBFS pastes and it gradually increased with GGBFS content in the binary blends. GGBFS paste mixed with deionised water and binary blend pastes showed corrosion risks although their free chloride contents were significantly low. The results further demonstrated that Ordinary Portland cement may be a more appropriate option than NaOH for activating GGBFS in terms of corrosion resistance.

Quantitative 2D Restrained Shrinkage Cracking of Cement Paste with Wollastonite Microfibers

AbstractPlastic shrinkage cracking in restrained cement pastes reinforced with wollastonite particles of micro and submicron sizes was studied using a quantitative two-dimensional (2D) cracking experiment. A series of blended paste mixes with portland cement and different grades of wollastonite fibers were developed and tested under low vacuum conditions. Testing parameters included four grades of wollastonite with aspect ratio in the range of 3∶1–20∶1 and average particle size ranging from 33 to 2,000 μm at 15% cement replacement. Wollastonite beneficially altered the shrinkage cracking morphology by arresting crack growth, wherein crack lengths and widths were reduced by a factor of two, and the area by a factor of three when compared with the control specimens. However, the initial evaporation rate, early age diffusivity, and cumulative moisture loss increased. Influence of the microfibers in controlling early age drying were related to the porosity of the microstructure using mercury intrusion porosim...

Chloride binding capacity of hydrotalcite and the competition with carbonates in ground granulated blast furnace slag concrete

This paper further investigates the hypothesis and recent preliminary findings that hydrotalcite is responsible for the remarkable improvement of chloride binding in concretes containing ground granulated blast furnace slag (GGBFS). In this paper, the chloride binding capacity of hydrotalcite has been examined in a wide range of GGBFS and GGBFS-OPC (ordinary Portland cement) blends. X-ray diffraction (XRD) was conducted to identify hydrotalcite in GGBFS pastes and to distinguish it from Friedel’s salt. Using Rietica software for quantifying crystalline minerals, this paper presents quantified XRD analysis of the relative proportion of hydrotalcite formed in GGBFS and binary blend pastes. XRD revealed that hydrotalcite was formed in all pastes containing GGBFS. The results clearly demonstrated that hydrotalcite made up a significant proportion of the crystalline phase in GGBFS pastes. The results further showed that the ability of hydrotalcite to bind chlorides was not significantly impaired by the competitive adsorption of carbonates.

Comparative study of effect of raw and densified silica fume in the paste, mortar and concrete

The differences of effect of silica fume in paste, mortar and concrete were studied by determining the non-evaporable water content of pastes, measuring the compressive strengths of pastes, mortars and concretes containing 5% and 10% raw silica fume or densified silica fume with water-to-binder ratios (W/B) of 0.29 and 0.24 and investigating the properties of interfacial transition zone between hardened paste and aggregate. The results show that silica fume can significantly increase the hydration degree of paste. The addition of silica fume trends to increasing the compressive strengths of hardened pastes, mortars and concretes, and the strength activity index of densified silica fume in concrete is the highest while that in paste is the lowest. The agglomeration of silica fume has been found in blended paste which is hardly seen in concrete. The silica fume can improve the interface bond strength between hardened cement paste and aggregate. The crystalline orientation degree, the crystalline size and the content of calcium hydroxide at the interface are obviously decreased by adding silica fume. The different dispersion and the improvement of the interfacial transition zone are the main factors causing the different role of silica fume in paste, mortar and concrete.

Fabricated Carbon Nanotube Electrodes Blending with Various Metal Phthalocyanines for Detection of Five Taste Models

Electrochemical characteristic of blended multiwall carbon nanotube paste electrode (CNTPE) was investigated with five basic taste models. The multiwall carbon tube was blended with metal phthalcyanine (MPc) powders including of CoPc, FePc, MgPc, MnPc and ZnPc to produce modified working electrode. Solutions with concentration of 0.1 M of potassium chloride (KCl), magnesium chloride (MgCl2), sucrose, citric and monosodium glutamate (MSG) were used as model solutions of saltiness, bitterness, sweetness, sourness and umami, respectively. Cyclic voltammograms (CV) of the fabricated electrodes were observed in range of 0.0 to 1.0 V. Blended MPc and CNTPE showed effects on electron transfer or redox reactions in some model taste solutions. The blended fabricated electrodes indicated cross-selectivity response for these five basic model solutions. However, the CV characteristics of the all fabricated blending electrodes in KCl and MgCl2 solutions are similar due to Cl- ion in both salt solutions. The measured CV of blended electrodes in the five solution models exhibit clearly different characters by mean of its symmetry and peak feature. These characters can be used to classify the distinctive feature of five tastes for electronic tongue

Effect of silica fume and fly ash on pore structures of blended pastes at low water to binder ratios

Effect of silica fume and fly ash on pore structures of blended pastes at low water to binder ratios

Effect of silica fume and fly ash on pore structures of blended pastes at low water to binder ratios

Cementitious materials with very low water to binder (w/b) ratios such as ultra-high-performance concrete (UHPC) have been increasingly used, and their superior performance is largely dependent on the improved pore structures. The benefits of incorporating supplementary cementitious materials (SCMs) to prepare these materials have been widely recognised, whereas there is a lack of research to reveal the effect of SCMs on the pore structure. The aim of this study is to investigate the influence of silica fume and fly ash on the pore structures of blended pastes at such low w/b ratios. Two curing regimes, standard moisture curing and steam curing, were adopted and the pore structures were determined by mercury intrusion porosimetry. The results show that the addition of silica fume refined the pore structure regardless of the curing method and age. The addition of fly ash decreased the porosity after 7 d, whereas the critical pore size was almost unaffected by fly ash under standard curing. Compared to 90 d standard curing, steam curing contributed to a decreased porosity for all the pastes and a reduced critical pore size for the reference and fly ash paste. Moreover, the introduction of both SCMs resulted in a similar pore structure to that of the silica fume paste.

Impact of swelling power and granule size on pasting of blends of potato, waxy rice and maize starches

This study investigated the impact of swelling power and granule size on pasting of blends of potato starch (PS) and maize (MS) or waxy rice (WRS) starch. First, viscosity development of one starch in the blend was reduced by cross-linking it to such extent that no viscosity development was recorded with Rapid Visco Analyser at the used concentrations. This way the difference in swelling power between the starches in a blend was changed. Comparison of the pasting profiles of blends of cross-linked PS and WRS or MS with those of blends of only native starch, showed that cross-linked PS contributes to viscosity development when another starch is present by increasing the total solid content and binding some of the available water. This was also observed for blends of PS and cross-linked WRS and MS. In a second approach, the impact of granule size was investigated by size fractionation of PS into PSsmall, PSmedium and PSlarge and by blending these fractions with WRS. PSsmall had lower amylose and higher phosphorus contents, a higher swelling power and lower carbohydrate leaching than PSmedium and PSlarge. All fractions had similar pasting properties. Peak, minimum and end viscosities were higher for blends of WRS with PSsmall than for those with PSmedium or PSlarge. This is probably due to the higher swelling power and higher rigidity (due to its lower granule size) of PSsmall.

Preparation and characterization of a hybrid alkaline binder based on a fly ash with no commercial value

Alkali-activated Portland fly ash cement (FA/OPC) and alkali activated blast furnace slag-fly ash cement (FA/GBFS) were prepared using 70% of a low quality fly ash (FA). The low quality is associated with a high content of unburned material (loss of ignition of 14.6%). The hybrid cements were activated by the alkaline solution in order to obtain an overall SiO2/Al2O3 molar ratio of 5.0 and 6.0 and unique overall Na2O/SiO2 molar ratio of 0.21. The microstructural characterization of the blended pastes generated in the systems showed the coexistence of amorphous gels C-A-S-H and N-A-S-H gels in the hybrid systems. The addition of OPC or GBFS increases the compressive strength (at 28 days of curing) up to 127% compared with the geopolymer systems based only on FA used in this study. The content of silicates soluble also plays an important role in the reaction products and higher SiO2/Al2O3 lead to obtain higher mechanical performance and denser structure. The results obtained show that these hybrid cements are an effective way for valorization the waste used in this study for the production of high strength and low-carbon footprint cement-type material.

Study of the hydration of calcium zirconium aluminate (Ca7ZrAl6O18) blended with reactive alumina by calorimetry, thermogravimetry and other methods

The reactivities of hydratable alumina, calcium zirconium aluminate and their binary mixtures were investigated by calorimetric method, X-ray diffraction, Fourier transform infrared spectroscopy (FT-IR), differential thermal/thermogravimetric analysis (DTA–TG) and scanning electron microscope observations. The rate of heat evolution illustrates only one distinct exothermic peak in the mixtures containing calcium zirconium aluminate which corresponds the subsequent precipitation of hydrated material mainly in the form of amorphous CaO–Al2O3–H2O phases and crystalline C4AH19 occurs simultaneously after wetting of Ca7ZrAl6O18 grains. Nevertheless, coexistence of both unstable calcium aluminate hydrates (CAH10, C2AH8, C4AH19) and thermodynamically more stable C3AH6 detected by FT-IR and DTA–TG in the paste cured at 20 °C may have originated in the thermally induced partial conversion reaction due to the considerable amount of heat generated by the Ca7ZrAl6O18 hydration. It is also found that curing temperature affected the hydration products formed in the hydration products of both Ca7ZrAl6O18 and Ca7ZrAl6O18/Al2O3 blends. Reactive alumina influences the hydration behavior of Ca7ZrAl6O18 facilitating the nucleation and growth of hydration products, causes characteristic changes in the microstructure of hardened blended pastes and favors recrystallization of dehydrated calcium aluminates.