Showing 15 results for Cement
Salahit E., Solati Hashjin M., Nemati R., Marghusian V.,
Volume 1, Issue 2 (6-2004)
Abstract
Calcium phosphate cements (CPCs), using B-tricalcium phosphate (ß-TCP, Ca3 (P04)2), dicalcium phosphate (DCP, CaHP04), calcium carbonate (Ca CO3), and hydroxylapatite (HAp, Ca10(P04)6(OH)2) as powder cement and disodium hydrogen phosphate (Na2HP04) solution as liquid component were prepared. After mixing the powder and liquid constituents, injectable and self-setting calcium phosphate cements (CPCs) were prepared with different liquid to powder ratios (UP) that formed hydroxylapatite and ß-tricalcium phosphate as the only end products, which were characterized by FTIR, XRD and SEM techniques. The results showed that, at certain concentration of Na2HP04 (6 wt%), the initial and final setting times decreased by decreasing the UP ratio.
Nojehdehyan H., Moztar Zadeh F., Mir Zadeh Hamid, Hesaraki S., Keyanpour-Rad M.,
Volume 2, Issue 2 (6-2005)
Abstract
The effect of addition of NaHF2 on the cement setting and the set mass has been studied as an initial step to determine how fluoride influences the characteristics of a calcium phosphate cement, consisting of tetracalcium phosphate [TTCP:Ca4 (PO4)2O] and dicalcium phosphate dihydrate [DCPD:CaHPO4.2H2O].NaHF2 [0-10% wt% of powder phase] has been dissolved in double distilled water and used as the liquid phase of the apatite cement (AC). Powder X-ray diffraction analysis and FTIR measurements revealed that fluoride was necessary in promoting the formation of the apatite phase. The setting time was decreased significantly by the addition of NaHF2from 0% to 6%, but increased resulted in the AC (8-10%). The set AC (2%) has the highest compressive strength and the lowest porosity.The dissolution rate of set AC in weak acid, pH 5.5, was decreased with the amount of added NaHF2 from 0% to 6% but increased in the set AC 8-10%.The formation of fluoroapatite in AC (6%) was provided the low solubility and good acid resistance which is necessary for dental application.SEM observation showed needle-like apatite crystal growth over particulate matrix surface, however the amount of non-reactive TTCP or DCPD particles decreased by the addition of NaHF2. The Ca/P ratio, which was determined by EDAX, increased significantly with the addition of NaHF2.
E. Najafi Kani, A. Allahverdi,
Volume 8, Issue 3 (9-2011)
Abstract
Shrinkage behavior of a geopolymer cement paste prepared from pumice-type natural pozzolan was studied
by changing parameters of chemical composition including SiO2/Na2O molar ratio of activator and total molar ratios
of Na2O/Al2O3, and H2O/Al2O3. For investigating the effect of curing conditions on shrinkage, hydrothermal curing
was also applied. The obtained results clearly revealed the governing effect of chemical composition on shrinkage.
Mixes with different Na2O/Al2O3 molar ratios exhibited different shrinkage behavior due to variations made in
SiO2/Na2O molar ratio. Application of hydrothermal curing after a 7-day period of precuring in humid atmosphere
also showed strong effect on shrinkage reduction.
A. Allahverdi, E. Najafi Kani, M. Fazlinejhad,
Volume 8, Issue 4 (12-2011)
Abstract
Abstract: The linear expansion, early-age compressive strength and setting times of the binary mixtures of gypsum and Portland cement clinkers of relatively low C3A-contents were investigated. For this reason, type 1, 2, and 5 of Portland cement-clinkers were selected and a number of binary mixtures were designed. At relatively lower percentages of gypsum (about 5%), the early strength behavior is improved. Results obtained for compressive strength of mixtures with 5% gypsum confirm the possibility of achieving 28- and 90-day compressive strengths up to values higher than 100 MPa and 130 MPa, respectively. At relatively higher percentages of gypsum (more than 25%), excessive expansion caused by ettringite formation results in the formation of micro-cracks effectively weakening the strength behavior. The work suggests that type S expansive cements could be produced from Portland cement clinkers of relatively low C3Acontents.
H. R. Sobhani Kavkani, A. Mortezaei, R. Naghizadeh,
Volume 13, Issue 2 (6-2016)
Abstract
Different mineral admixtures of Indian metakaolin, Iranian silica fume and nanosilica were used to produce high performance mortars. Two different sands types with grain size of 0.015-4mm were mixed with type II Portland cement, polycarboxylate superplasticizer,mineral admixture with 650kg/m3 cement content and water/cement ratio of 0.35. Different amount of cement was replaced by metakaolin or silica fume (5-15wt%) or nanosilica (0.8-5wt%). After mixing, moulding and curing, compressive strength, electrical resistivity and abrasion resistance were studied. The maximum compressive strength of 28 days samples were 76MPa, 79MPa and 75MPa for 15wt% substitution of cement with metakaolin, silica fume and 5wt% with nanosilica. The compressive strength of these samples showed 28%, 33% and 26% increment in comparison with reference sample, respectively. X-ray patterns showed that replacing silica fume leads to reduction of Portlandite (Ca(OH)2) phase. This can be attributed to the pozzolanic reaction and formation of new hydrated calcium silicate phase (CSH) that caused improvement of strength of admixtures containing samples. The microstructure of silica fume containing sample also showed better bond between sand and matrix. The electrical resistivity of samples with 15wt% metakaolin or silica fume and 5wt% nanosilica reach to 21kΩ.cm, 15 kΩ.cm and 10kΩ.cm, respectively. These samples showed high durability and corrosion resistance relative to reference samples (3.4 kΩ.cm). The abrasion resistance of different admixtures, specially silica fume containing samples were improved.
A. Ataei, M. Jalaly, M. Tamizifar,
Volume 14, Issue 1 (3-2017)
Abstract
The boronizing of a tungsten heavy alloy containing Ni and Fe as the major alloying elements were performed in the present study to increase its surface hardening. Pack cementation method was employed as a well-known, successful solid-state process for boronizing. The coating treatment was accomplished at different temperatures of 1000, 1050 and 1100°C for 6 and 9 hours. The formation of tungsten boride phase was confirmed, although a silicide layer covered the surface of the specimen as the outer layer. The mechanism of the formation of a multilayered surface was explained. The maximum thickness of reaction zone and surface hardness achieved in the current work were 300 µm and 2470 HV, respectively.
A. Allahverdi, Z. Padar, M. Mahinroosta,
Volume 16, Issue 2 (6-2019)
Abstract
It is demonstrated that the addition of organo-modified Na-bentonite (OMB) particles to Portland cement mortar can promote its physical and mechanical properties. A series of experimental works on some important physico-mechanical properties of Portland cement mortars mixed with various dosages of hydrophobic OMB were performed. The obtained results confirm that the OMB provides a dense packing effect. An optimum replacement level of around 3.5% (by weight) at an increased water-to-cement ratio of 0.53 results in an almost 11.43% increase in 28-day compressive strength along with about 20.78 and 16.20% reductions in total volume of permeable pore space and water absorption, respectively. Also, at the optimum replacement level, an increase of about 2.72% is taken place in dry bulk specific gravity.
R. Latifi, S. Rastegari, S. H. Razavi,
Volume 16, Issue 4 (12-2019)
Abstract
In the present study, Zirconium modified aluminide coating on the nickel-base superalloy IN-738LC was first created by high activity high temperature aluminizing based on the out-of-pack cementation method. Then, Zr coatings were applied to simple aluminide coatings by sputtering and heat treatment in order to study the effect of Zr on the coating microstructure and oxide spallation. Microstructural studies were conducted by using scanning electron microscopy (SEM), Energy Dispersive X-ray Spectrometry (EDS), and x-ray diffraction (XRD) microanalysis. The results indicated that zirconium modified aluminide coating, like aluminide coating, has a two-layer structure including a uniform outer layer of NiAl and an interdiffusion layer in which zirconium is in a form of solid solution in the coating. Furthermore, the 300nm Zr-coated NiAl demonstrated an excellent scale adhesion, a slow oxidation rate and lower amounts of some other elements such as Ti and Cr in its oxide layer leading to a pure aluminide oxide layer.
M. Ghasemian Safaei, Dr. S. Rastegari, R. Latifi,
Volume 17, Issue 2 (6-2020)
Abstract
In this study, Si-modified aluminide coating on nickel-base superalloy IN-738LC was prepared using a pack cementation method with various powder compositions at 1050 °C for 6 h. The cyclic oxidation test was conducted at 1000 °C followed by cooling at room temperature for 200 h and 20 cycles. The effect of powder composition and the way of cooling on the coatings microstructure and oxidation behavior were studied. Investigations carried out using a scanning electron microscope (SEM), EDS analysis, and XRD. Microstructural observations revealed that the coating thickness of 293 and 274 µm was achieved in the case of using pure Al and Si powder and alloyed Al-20wt.%Si one in the packed mixture, respectively. It was also found that utilizing pure Al and Si powder with NH4Cl as an activator in the pack led to the formation of silicide coating, owing to the higher diffusion of Si, which showed superior cyclic oxidation performance.
Jafar Shafaghat, Ali Allahverdi,
Volume 18, Issue 1 (3-2021)
Abstract
Microscopic studies has shown that adjacent to the interface between cement paste and aggregate, there exists an area with high porosity and low binding compounds that is referred to as interfacial transition zone (ITZ). ITZ in concrete and mortar imposes a number of negative effects, including flexural and compressive strengths reduction and permeability enhancement. That’s why many research attempts have been devoted to limit ITZ and its negative effects. The present study investigates the possibility of utilizing fine Portland cement (PC) clinker as a reactive aggregate in mortar for the same purpose. For this, natural quartz sand in normal mortar (NM) was totally replaced with PC clinker of the same particle size distribution and the most important engineering properties of the new mortar referred to as Reactive Aggregate Mortar (RAM) were measured and compared with NM as control. The results of compressive strengths measurements represented 65% and 21% increases at curing ages of 7 and 90 days, respectively, for RAM compared to NM. Chloride penetration depth in RAM displayed reductions by about 33% and 26% after 14 and 28 days of exposure, respectively. The effect of PC clinker reactivity on the microstructure and size of ITZ was studied by using scanning electron microscopy.
Rabah Bobaaya, Omar Allaoui, Mokhtar Djendel, Samir Benaniba,
Volume 18, Issue 3 (9-2021)
Abstract
Coatings based on chromium borides and chromium carbides are commonly employed in applications requiring mechanical performance, such as high hardness and low friction coefficient, as well as corrosion resistance. In this work, we made layers of chromium borides and chromium carbides on the surface of low carbon steel through some specific treatments. For chromium borides, the boriding treatment in a solid medium at 900 °C for 4 hours followed by chromium electroplating on the steel surface and finally the application of annealing treatment at temperatures at 950 °C for 1 and 2 hours. For chromium carbides, the cementation in a solid medium followed by electroplating of chromium on the surface and finally the application of annealing treatment at temperatures between 500 and 1100 °C for 1 hour. The obtained results show that, in the first case, boron diffusion and chromium deposition lead to chromium borides on the treated surface. Similarly, for the second case, the cemented layer and the chromium deposited on the surface combine to form chromium carbides on the treated surface after annealing. The characteristics of the chromium borides and chromium carbides obtained are very similar to those of chromium borides and chromium carbides obtained by other processes.
Mojtaba Hosseini, Ali Allahverdi, Mohammad Jaafar Soltanian Fard,
Volume 19, Issue 1 (3-2022)
Abstract
The aim of the present research work is to evaluate the feasibility of processing and utilizing steel slag
in binary and ternary cement blends with limestone. The physical and microstructural properties of binary and
ternary composite cements produced by inter-grinding mixtures of ordinary Portland cement clinker, processed
steel slag and limestone in a laboratory ball mill with replacement levels varying from 0 wt.% to 30 wt.% were
studied. The effects of processed steel slag and limestone incorporation on density of dry cement mixes and water
consistency, setting time and volume stability of fresh and hardened cement pastes were investigated. Also,
density, water absorption, total open pore volume (%) and compressive strength of cement mortars were measured.
The mix with 15 wt.% limestone and 15 wt.% processed steel slag was selected as a typical ternary cement mix
for complementary studies including X-ray diffractometry, thermal gravimetry, Fourier-transform infrared
spectroscopy, and scanning electron microscopy analyses. The results show that removal of relatively high
metallic content of steel slag increases its grindability for mechanical activation and improves its hydraulic
properties effectively and makes it suitable for being recycled in cement industry. The results show that
mechanical activation of the cement mixes enhances the poor hydraulic activity of the processed steel slag and
compensates the strength loss to some extent. The physical and chemical properties of all studied composite
cement mixes comply with ASTM standard specifications, except the compressive strength of the cement mixes
at 28-days containing 20 wt.% or higher amounts of limestone ground to the relatively low Blaine specific surface
area of about 3000 cm2/g.
Ekaterina Dmitrieva, Ivan Korchunov, Ekaterina Potapova, Sergey Sivkov, Alexander Morozov,
Volume 19, Issue 4 (12-2022)
Abstract
The article discusses the effect of calcined clays on the properties of Portland cement. An optimal method for calcining clays is proposed, which makes it possible to reduce the proportion of Portland cement clinker in cement to 60% and increase the strength characteristics from 55 MPa to 79 MPa. The study of the composition and structure of clays made it possible to select the optimal heat treatment parameters, at which the calcination products are characterized by the highest pozzolanic activity. It is shown that the use of alkali-activated calcined clays significantly increases the strength and durability of hardened cement binders compared to the composition without additives. In addition, calcined clays increase the frost resistance of cement in a 5% NaCl solution. The obtained experimental data are confirmed by thermodynamic calculations and the results of scanning electron microscopy.
Nailia Rakhimova, Vladimir Morozov, Aleksey Eskin, Bulat Galiullin,
Volume 20, Issue 3 (9-2023)
Abstract
Sara Ahmadi, Reza Momeni,
Volume 20, Issue 4 (12-2023)
Abstract
The polymer modified cementitious tile adhesives are very significant in construction sector. In order to considerably improve the bond qualities of the tile adhesive in polymer modified mortars, the proportions of constituent ingredients should be carefully selected. Consequently, to design high performance tile adhesives, interactions between all the components, such as the adhesion mechanisms between the polymers film and the substrate and the effect of various additives should be recognized. The effect of vinyl acetate ethylene (EVA), high alumina cement (HAC), and additives such as calcium formate and polycarboxylate on the adhesion qualities of ceramic tile adhesive was explored in this study. The findings indicated that these ingredients had an impact on the mortars' adhesive properties, and it is necessary to find their optimal amounts in order to achieve the maximum adherence. The results showed that the tensile strength of mortar was increased with increasing the polymer amounts. A microstructural analysis revealed that the polymer was distributed homogenously throughout the mortar. The optimum amount of the used high alumina cement was determined 3 wt.%. Additionally, increasing the amount of accelerator and super plasticizer increased the tensile strength of ceramic tile adhesive by approximately 20-30%.
