Physico-mechanical properties of composite cement pastes containing silica fume and fly ash

AbstractThis works aims to study the effect of partial substitution of ordinary Portland cement (OPC) by silica fume (SF) and fly ash (FA) on the physico-mechanical properties of the hardened OPC–FA–SF composite cement pastes. The OPC was partially replaced by 20% and 30% fly ash along with 5% and 10% silica fume. The phase composition of the hydration products was investigated using XRD and DTA techniques. It was found that, the increase of FA content in OPC–FA–SF composite cement decreases the water consistency values and increases the setting times. On the other hand, the increase of SF content leads to increase the water of consistency and decrease the setting times. The partial substitution of OPC by FA and SF leads to higher porosity values with a consequent decrease in the compressive strength values especially during the early ages of hydration. At the later ages of hydration, however, the OPC–FA–SF cement pastes possess total porosity and compressive strength values close to those of the neat OPC paste. The lower of free lime contents were obtained for OPC–FA–SF composite cement pastes with the formation of further additional amounts of CSH as a result of the pozzolanic reaction. The results showed also that, the physico-mechanical properties of composite cement paste [OPC (65%)–FA (30%)–SF (5%)] were improved at later ages

Application of microbial biocementation to improve the physico-mechanical properties of cement mortar

AbstractCalcite is one of the most common and wide spread mineral on Earth constituting 4wt% of the Earth’s crust. It is naturally found in extensive sedimentary rock masses, as lime stone marble and calcareous sandstone in marine, fresh water and terrestrial environments. Calcium carbonate is one of the most well known mineral that bacteria deposit by the phenomenon called biocementation or microbiologically induced calcite precipitation (MICP). Such deposits have recently emerged as promising binders for protecting and consolidating various building materials. Microbially enhanced calcite precipitation on concrete or mortar has become an important area of research regarding construction materials. This study describes a method of strength and water absorption improvement of cement–sand mortar by the microbiologically induced calcium carbonate precipitation. A moderately alkalophilic aerobic Sporosarcina pasteurii was incorporated at different cell concentrations with the mixing water. The study showed that a 33% increase in 28days compressive strength of cement mortar was achieved with the addition of about one optical density (1OD) of bacterial cells with mixing water. The strength and water absorption improvement are due to the growth of calcite crystals within the pores of the cement–sand matrix as indicated from the microstructure obtained from scanning electron microscopy (SEM) examination

A novel method to produce dry geopolymer cement powder

Geopolymer cement is the result of reaction of two materials containing aluminosilicate and concentrated alkaline solution to produce an inorganic polymer binder. The alkali solutions are corrosive and often viscous solutions which are not user friendly, and would be difficult to use for bulk production. This work aims to produce one-mix geopolymer mixed water that could be an alternative to Portland cement by blending with dry activator. Sodium hydroxide (SH) was dissolved in water and added to calcium carbonate (CC) then dried at 80 °C for 8 h followed by pulverization to a fixed particle size to produce the dry activator consisting of calcium hydroxide (CH), sodium carbonate (SC) and pirssonite (P). This increases their commercial availability. The dry activator was blended with granulated blast-furnace slag (GBFS) to produce geopolymer cement powder and by addition of water; the geopolymerization process is started. The effect of W/C and SH/CC ratio on the physico-mechanical properties of slag pastes was studied. The results showed that the optimum percent of activator and CC content is 4% SH and 5% CC, by the weight of slag, which give the highest physico-mechanical properties of GBFS. The characterization of the activated slag pastes was carried out using TGA, DTG, IR spectroscopy and SEM techniques

Hydration characteristics of Portland cement – Electric arc furnace slag blends

Utilization of electric arc furnace slag (EAF slag) as blending material for Portland cement has been examined. This was done via the investigation of the hydration characteristic of EAF slag – Portland cement blended mixtures. Various ratios of EAF slag were used namely; 5, 10 and 20 wt% of solid mix. The hydration properties investigated for the various mixtures were; compressive strength, chemically combined water and free lime contents as a function of hydration times. The hydration ages were; 1, 3, 7, 28 and 90 days. In addition, phase composition of the formed hydrates was examined using XRD technique as well as differential thermal analysis (DTA) for some selected samples. The results showed that as the ratio of EAF slag increases the values of compressive strength decrease at all the hydration ages. Hydration kinetics of the investigated mixes was followed by determining the variation of free lime and chemically combined water contents with time of hydration. It was observed that hydration proceeds in four different stages. The values of chemically combined water of the cement pastes blended with EAF slag were less than those of the neat Portland cement paste at all hydration ages. The mode of variation of free lime content with time was nearly similar to that of combined water content. The results of chemically combined water, free lime, XRD analysis as well as thermal analysis were correlated well with those of compressive strength. All these results indicate that the used EAF slag has no significant pozzolanic reactivity

Catalytic

A series of dealuminated Y-zeolites impregnated by 0.5 wt% Pt catalysts promoted by different amounts of Ni, Pd or Cr (0.3 and 0.6 wt%) were prepared and characterized as hydrocracking catalysts. The physicochemical and structural characterization of the solid catalysts were investigated and reported through N2 physisorption, XRD, TGA-DSC, FT-IR and TEM techniques. Solid catalysts surface acidities were investigated through FT-IR spectroscopy aided by pyridine adsorption. The solid catalytic activities were evaluated through hydroconversion of n-hexane and n-heptane employing micro-catalytic pulse technique directly connected to a gas chromatograph analyzer. The thermal stability of the solids was also investigated up to 800 °C. Crystallinity studies using the XRD technique of all modified samples proved analogous to the parent Y-zeolite, exhibiting nearly an amorphous and microcrystalline character of the second metal oxides. Disclosure of bimetallic catalysts crystalline characterization, through XRD, was not viable. The nitrogen adsorption–desorption isotherms for all samples concluded type I adsorption isotherms, without any hysteresis loop, indicating that the entire pore system is composed of micropores. TEM micrographs of the solid catalysts demonstrate well-dispersed Pt, Ni and Cr nanoparticles having sizes of 2–4 nm and 7–8 nm, respectively. The catalytic activity results indicate that the bimetallic (0.5Pt–0.3Cr)/D18H–Y catalyst is the most active towards n-hexane and n-heptane isomerization while (0.5Pt–0.6Ni)/D18H–Y catalyst can be designed as most suitable as a cracking catalyst

Catalytic behavior of Pt nanoparticles dealuminated Y-zeolite for some n-alkane hydroisomerization

Dealuminated zeolite Y-supported platinum was prepared adopting two dealumination methods, viz. fast (1, 3 and 6 h) and slow method (18 h). The content of Pt was constant at 0.5 wt% in all investigated catalysts. The prepared samples were characterized using TGA/DSC, XRD, FTIR techniques, nitrogen adsorption at −196 °C and TEM-connected with energy dispersive spectroscopy (EDS). Surface acidity was investigated via pyridine adsorption using FT-IR spectroscopy. The parent and dealuminated Y-zeolite samples were characterized by their microporous system. By increasing the dealumination time to 6 h, the increased specific surface area and total pore volume indicated a sort of pore opening taking place with an increase in the accessibility of nitrogen molecules. DSC confirmed the thermal stability of the dealuminated zeolite samples up to 800 °C. The prepared catalysts were tested through hydroisomerization reactions of n-hexane and n-heptane using a micro-catalytic pulse technique. Different catalytic behaviors could be distinguished for the dealuminated samples based on competitive reactions; hydro-isomerization, hydrocracking and cyclization. Slow dealumination leads to the most selective catalysts for hydroisomerization. n-Heptane was converted to higher extent than n-hexane; cracking process was more evident when the former was fed to the reactor

Spectrophotometric determination of erbium using kojic acid dye in different rare earth concentrates

A sensitive and selective spectrophotometric method was studied for the determination of erbium (Er) with kojic acid dye (koj) and cetylpyridinium chloride (CPC) as a cationic surfactant from Egyptian monazite and xenotime concentrates using third derivative spectrophotometry. The calibration curve was linear from 1 to 150 µg/mL erbium. The influence of various parameters and reaction conditions for optimum complex formation were investigated. The relative standard deviation for determination of 1 µg/mL erbium was found to be 1.5 after 5 repeated determinations with percentage error for Er determination from monazite and xenotime concentrates 6.4% and 4.48% respectively. The molar absorptivity of conventional and third derivative spectrum were 0.14 × 103 M−1 cm−1 and 0.13 × 103 M−1 cm−1 respectively and the detection limit was 1 µg/mL. Keywords: Erbium, Kojic acid dye, Cetylpyridinium chloride, Egyptian monazite, Xenotim

Early hydration characteristics of oil well cement pastes admixed with newly prepared organic admixture

A number of chemical and mineral admixtures are usually used in the oil-well cement (OWC) pastes to modify and control their fluidity to resist the higher temperatures and pressures during the drilling process of the well. In this study a newly prepared aliphatic organic compound namely cyclohexanone glyoxylate condensate (CG) was synthesized. The prepared compound (CG) was characterized using Fourier Transition Infrared spectroscopy (FT-IR) and microanalysis of carbon, hydrogen, oxygen and sulfur elemental analysis techniques. The effect of additions of 0.25, 0.50, 0.75 and 1 (mass%) of this admixture on the mechanical and early hydration characteristics of OWC pastes was studied. The phase composition for some selected hardened specimens was investigated using X-ray diffraction (XRD) and thermogravemtic analysis (DTGA) techniques. The results indicated that, addition of cyclohexanone glyoxylate condensate (CG) admixture to OWC pastes causes a slight retardation for the early rate of hydration of OWC. Addition of 0.25% of CG to OWC causes a slight improvement in the compressive strength values during nearly all ages of hydrations. XRD and DTGA results for the neat and CG admixed OWC pastes, indicate that the main hydration products are nearly amorphous calcium silicate hydrates (mainly as CSH-I and CSH-II), calcium sulfoaluminate hydrates (ettringite and monosulfate hydrate) as well as portlandite (CH). Keywords: Admixtures, Oil well cement, Setting times, Compressive strengt