Defect mode and crystal-electric-field effects on the thermal expansion and heat capacity of RB<Subscript>50</Subscript> boride

This study aimed to evaluate the suitability of using unfired and fired pumice as cement replacement materials as well as their effect on the thermal resistance of hardened ordinary Portland cement (OPC) pastes. Different OPC–pumice (unfired and fired) blends were prepared by partial replacement of OPC by 0, 10 and 20 of pumice (mass%). The effect of the addition of 1 and 5 % of active alumina on the mechanical properties and thermal resistance of different OPC–pumice (unfired) blends was investigated. The fire resistance test was done by exposing the hardened blended cement cubes to elevated temperatures of 200, 400, 600 and 800 °C for 3 h and allowed them to cool down to room temperature before testing for their mechanical properties. The phase composition and thermal analysis of some selected specimens were investigated by XRD, DSC and DTA/TG techniques. The obtained results indicated that replacing OPC by 10 and 20 % by pumice (unfired and fired) improved its thermal stability at different firing temperatures. The cement blend prepared by replacement of OPC with 10 % pumice showed the highest fire resistance. The addition of 1 and 5 % of alumina (A) to OPC–pumice blends causes a notable improve in their mechanical properties and thermal resistance.     

Improvement of acid resistance of Portland cement pastes using rice husk ash and cement kiln dust as additives

This paper represents a laboratory study on the acid resistance of hardened ordinary Portland cement (OPC) and blended OPC pastes at two different curing temperatures. The blended materials used are rice husk ash (RHA) and cement kiln dust (CKD). The blended cement pastes were prepared using a water/solid (W/S) ratio of 0.3. The effects of immersion in deionized water (pH 7) and sulfuric acid solutions (pH 1, 2 and 3) at two temperatures (20 and 50 °C) on the compressive strength and phase composition of the various hardened blended cement pastes were studied. The results of compressive strength revealed that the increase of curing temperature from 20 to 50 °C resulted in increase the reduction of compressive strength due to acid attack up 2 months, but the resistance to sulfuric acid attack increases after that time due to the formation of crystalline calcium silicate hydrates (CSH) which have higher resistance to acid attack than the amorphous CSH formed at the early ages of hydration. The presence of RHA and CKD improves the resistance to sulfuric acid attack at both curing conditions. From the results of X-ray diffraction analysis and differential scanning calorimetric technique curves, the main hydration products identified are CSH, portlandite, and calcium sulfoaluminate hydrates.     

Effect of addition of nano-magnetite on the hydration characteristics of hardened Portland cement and high slag cement pastes

In this investigation the effect of addition of magnetite nanoparticles on the hydration characteristics of both ordinary Portland cement (OPC) and high slag cement (HSC) pastes was studied. The cement pastes were prepared using a water/solid (W/S) mass ratio of 0.3 with addition of 0.05, 0.1, and 0.3 % of magnetic fluid Fe₃O₄ nanoparticles by mass of cement. An aqueous stable magnetic fluid containing Fe₃O₄ nanoparticles, with a mean diameter in the range of super-paramagnetism, was prepared via co-precipitation method from ferrous and ferric solutions. The admixed magnetite-cement pastes were examined for compressive strength, chemically combined water content, X-ray diffraction analysis, and differential scanning calorimetry. The results of compressive strength revealed that the hardened pastes made from OPC and HSC admixed with different amounts of magnetic fluid have higher compressive strength values than those of the neat cement OPC and HSC cement pastes at almost all ages of hydration. The results of chemically combined water content for the admixed cement pastes showed almost the same general trend and nearly comparable values as those of the neat cement pastes. From the XRD diffractograms obtained for the neat OPC and HSC cement pastes, the main hydration products identified are calcium silicate hydrates, portlandite, and calcium sulfoaluminate hydrates. Addition of magnetic fluid nanoparticles to both of OPC and HSC did not affect the main hydration products of the neat OPC or HSC cement in addition to one main basic difference, namely, the formation of calcium iron hydroxide silicate as a new hydration product with a reasonable hydraulic character.     

Artificial pozzolanic cement pastes containing burnt clay with and without silica fume

Pozzolanic cement blends were prepared by the partial substitution of ordinary Portland cement (OPC) with different percentages of burnt clay (BC), Libyan clay fired at 700 °C, of 10, 20, and 30%. The pastes were made using an initial water/solid ratio of 0.30 by mass of each cement blend and hydrated for 1, 3, 7, 28, and 90 days. The pozzolanic OPC–BC blend containing 30% BC was also admixed with 2.5 and 5% silica fume (SF) to improve the physicomechanical characteristics. The hardened pozzolanic cement pastes were subjected to compressive strength and hydration kinetics tests. The results of compressive strength indicated slightly higher values for the paste made of OPC–BC blend containing 10% BC The results of DSC and XRD studies indicated the formation and later the stabilization of calcium silicates hydrates (CSH) and calcium aluminosilicate hydrates (C₃ASH₄ and C₂ASH₈) as the main hydration products in addition to free calcium hydroxide (CH). Scanning electron microscopic (SEM) examination revealed that the pozzolanic cement pastes made of OPC–BC mixes possesses a denser structure than that of the neat OPC paste. Furthermore, the addition of SF resulted in a further densification of the microstructure of the hardened OPC–BC–SF pastes; this was reflected on the observed improvement in the compressive strength values at all ages of hydration.     

Thermal resistance of hardened cement pastes containing vermiculite and expanded vermiculite

The durability and thermal stability of hardened Portland cement pastes containing vermiculite (V) and expanded vermiculite (EV) exposed to high temperatures were studied. Different mixtures were prepared using 2.5, 5, and 10 wt% of both types of V. Each mixture, after 28?days of hydration, was heated at 300, 600, and 800?°C for 3?h. Two modes of cooling were used; gradual cooling in air and rapid cooling in cold water. The percentage of residual strength, chemically combined water content, change in phase composition, and the thermal stability of the heated specimens were studied. The specimens cooled in water showed greater loss in strength than the air-cooled specimens. The presence of V improved the heat resistance of ordinary type I Portland cement (OPC) pastes. 5 wt% replacement revealed the best performance at all heating temperatures. The EV showed better thermal resistance than the nonexpanded one. Addition of silica fume (SF) with V in OPC pastes lead to superior performance. This can be explained as result of the combined effects of insulation properties of V and pozzolanic reactivity of SF which accounts for the notable increase in the residual strength for these mixes.     

Consumption of calcium hydroxide and formation of C–S–H in cement pastes

The pozzolanic properties of the equilibrium catalyst (Ecat), an abundant waste from fluid catalytic cracking units of oil refineries, have been studied in cementitious matrices. The consumption of calcium hydroxide is usually taken as a means to assess the pozzolanicity of a material, ignoring the formation of C–S–H and other hydrates, the main product of the pozzolanic reaction. The use of thermal analysis methods allows the identification and quantification of the products of the hydration reaction, based on the loss of chemically combined water of phases present in a cementitious matrix. In the present study, TG/DTG techniques were used to quantify the amount of C–S–H + ettringite, C–A–S–H + C–A–H, and calcium hydroxide in cement–Ecat pastes, containing 0–40 % Ecat, aged for 1–28 days. The influence of the content of these phases on the mechanical properties of the resulting samples was also investigated by axial compression. The results further confirmed the pozzolanic activity of Ecat, so that the production of C–S–H and C–A–S–H increased with the aging time, but in a smaller amount than in the reference paste. The compressive strength test showed that the pastes containing 10 % Ecat, aged for 14 and 28 days, presented improved properties as compared to the corresponding references.     

Comparing study on hydration properties of various cementitious systems

The hydration properties of slag sulfate cement (SSC), slag Portland cement (PSC), and ordinary Portland cement (POC) were compared in this study by determining the compressive strength of pastes, the hydration heat of binders within 72 h, the pore structure, the hydration products, and the hydration degree. The results indicated that main hydration products of PSC paste and POC paste are calcium hydroxide and C–S–H gel, while those of SSC paste are ettringite and C–S–H gel from the analyses of XRD, TG–DTA, and SEM. At the early curing age, the compressive strength depends on the clinker content in the cementitious system, while at the late curing age, which is related to the potential reactivity of slag. From hydration heat analysis, the cumulative hydration heat of PSC is lower than that of POC, but higher than that of SSC. Slag can limit chemical reaction and the delayed coagulation of gypsum, which also plays a role in the early hydration. So SSC shows the lowest heat release and slag can’t be simulated without a suitable alkaline solution. Based on MIP analysis, the porosity of POC paste is the smallest while the average pore size is the biggest. At the age of 90 days, the compressive strength of SSC can get higher development because of its relative smaller pore size than that of PSC and POC paste.     

Effects of nano-limestone on hydration properties of tricalcium silicate

In this research, the influences of nano-limestone (NC) on tricalcium silicate (C₃S) hydration, including early hydration rate, setting time, Ca(OH)₂ content, quantification of C–S–H, micrographs of hydration products and compressive strength, were investigated by different methods. Calorimetry results show that the first and second exothermic peak of C₃S with 1 mass% NC is ~29 and ~5% higher than that of control sample and the second peak appears 32 min in advance. Besides, the total hydration heat of C₃S with 1 mass% NC increases by 10.08% compared to control sample at 72 h. The initial and final setting time of C₃S with 1 mass% NC shortens by 23 and 17 min, respectively. In addition, thermal analysis results show that adding NC leads to higher Ca(OH)₂ and C–S–H content at all ages (1, 3 and 28 days). All of the above results imply that the hydration progress of C₃S is accelerated by NC. Correspondingly, the compressive strength of C₃S with 1 mass% NC increases by 9.88% at 28 days. Besides, EDS results reveal that the Ca/Si ratio of C–S–H gel decreases after NC modification. However, excessive content NC (4 mass%) reduces the acceleration effect of NC on C₃S hydration and finally leads to relative low content of Ca(OH)₂ and C–S–H compared with C₃S sample containing 1 mass% NC.     

The role of MgO in the thermal behavior of MgO–silica fume pastes

The compounds of MgO–silica fume (SF) pastes constitute magnesium silicate hydrate (M–S–H) in a new generation of basic castables. However, Mg(OH)₂ is a common reaction product with the formation of M–S–H. This study aims to reduce the formation of Mg(OH)₂ in MgO–SF pastes. In this study, MgO powders were prepared by calcining magnesite at different temperatures and then mixed with SF and water to prepare MgO–SF pastes. The properties of MgO powders were characterized, and the pH values in the pore solutions of MgO–SF pastes were measured. The MgO–SF pastes cured for 90 days were calcined at 500, 700, 900 and 1200 °C, and the microstructure was characterized afterward. The results showed that both the reactivity of MgO powders and the pH value of the pore solution of MgO–SF pastes were diverse, which essentially depended on the grain sizes and the crystalline degree of MgO. Increasing the calcination temperature of MgO was beneficial to reduce the formation of Mg(OH)₂ or even stop it when using MgO calcined at 1450 °C. Enstatite and forsterite formed for all MgO–SF pastes after calcination. However, the microstructure of MgO–SF paste with MgO calcined at 1450 °C was denser than others. MgO–SF pastes were suitable for the new-generation refractory castables. Notably, using MgO calcined at 1450 °C is more appropriate.     

Mineralogical evolution of cement pastes at early ages based on thermogravimetric analysis (TG)

Ordinary thermogravimetric analysis (TG) and high-resolution TG tests were carried out on three different Portland cement pastes to study the phases present during the first day of hydration. Tests were run at 1, 6, 12 and 24 h of hydration, in order to determine the phases at these ages. High-resolution TG tests were used to separate decompositions presented in the 100–200 °C interval. The non-evaporable water determined by TG was used to determine hydration degree for the different ages. The effect of particle size distribution (PSD) on mineralogical evolution was established, as well as the addition of calcite as mineralogical filler. Finer PSD and calcite addition accelerate the hydration process, increasing the hydration degree on the first day of reaction between water and cement. According to high-resolution TG results, it was demonstrated that ettringite was the only decomposed phase in the 100–200 °C interval during the first 6 h of hydration for all studied cements. C-S-H phase starts to appear in all cements after 12 h of hydration.     

Thermal transformations of floor tile pastes containing petroleum waste

This study focuses on the thermal and mineralogical transformations of floor tile pastes containing petroleum waste. The tile pastes prepared by the dry process contain up to 10 wt% of petroleum waste in replacement of kaolin. Thermal and mineralogical changes occurring during firing were characterized by differential thermal analysis, thermogravimetry analysis, derivative thermogravimetry, dilatometric analysis, open photoacoustic cell technique, X-ray diffraction, and scanning electron microscopy. During heating an endothermic transformation within the 511.4–577.5 °C range and an exothermic transformation within the 997.8–1001.6 °C range were identified. The endothermic transformation can be mainly attributed to the dehydroxylation of kaolinite. The exothermic transformation is mainly associated with the crystallization of primary mullite. TG measurements indicate that the total mass loss of the floor tile pastes is dependent on the amount of petroleum waste addition. It was found that the replacement of kaolin with petroleum waste, in the range up to 10 wt%, influenced the thermal expansion–shrinkage curve. In addition, the floor tile pastes containing petroleum waste have low values of thermal diffusivity.     

Thermal study of clay ceramic pastes containing sugarcane bagasse ash waste

This study focuses on the thermal and mineralogical transformations of clay ceramic pastes. The pastes contain different amounts of sugarcane bagasse ash waste. Thermal and mineralogical changes occurring during firing were characterized by differential thermal analysis, thermogravimetry analysis (TG), X-ray diffraction (XRD), and scanning electron microscopy. On heating three endothermic events within the 73.5–75.7, 276.9–283.5, and 567.1–573.5 °C temperature ranges were identified. The endothermic valleys could be mainly interpreted as the release of physically adsorbed water, dehydration of hydroxides, and dehydroxylation of kaolinite, respectively. Two exothermic events within the 618.9–690.1 and 948 °C temperature ranges were identified. The exothermic peaks are associated with the decomposition of organic compounds and crystallization of mullite from metakaolinite, respectively. TG results indicate that the clay ceramic pastes had a total mass loss in the 13.1–13.6 % range, and are dependent on the sugarcane bagasse ash waste amount added. It was found that the replacement of natural clay with sugarcane bagasse ash waste, in the range up to 20 wt%, influenced the thermal behavior and technological properties of the clay ceramic pastes. In addition, the thermal analysis results agree well with the XRD.     

Performance of G-Oil Well cement exposed to elevated hydrothermal curing conditions

G-Oil Well cement was modified by blending it with blast furnace slag and silica fume at various ratios. The hydration was carried out under the hydrothermal conditions (200 °C and 1.2 MPa) up to 7 days. TG and DTG were performed on cured pastes to identify the hydrated products, their quantity and their stability under given hydrothermal curing conditions. The microstructure of samples was observed by a scanning electron microscope. The mechanical compressive strength was determined and the pore structure was analyzed using mercury intrusion porosimeter. It was found out that the compressive strength values of blend G-Oil Well cements markedly increased with increasing blast furnace/silica ratio. The pore structure was consolidated, as demonstrated by the displacement of pore size distribution to the region of micro and nano pores.     

A comparison of early hydration properties of cement–steel slag binder and cement–limestone powder binder

The early hydration properties of cement–steel slag composite binder and cement–limestone powder composite binder were compared in this study by determining the hydration heat of binder within 3 days, the pore structure of paste and the compressive strength of mortar at the age of 3 days. Results show that at the curing temperature of 25 °C, the early hydration heat of the binder containing steel slag is smaller, and the early pore structure of the paste containing steel slag is coarser, but the early compressive strength of the mortar containing steel slag is higher compared with the mix containing limestone powder. Though the early reaction degree of steel slag is low, its chemical contribution to the strength of mortar cannot be neglected. At the curing temperature of 50 °C, the early hydration heat of the binder containing steel slag is larger, and the early pore structure of the paste containing steel slag is finer, and the early compressive strength of the mortar containing steel slag is even higher compared with the mix containing limestone powder. Raising curing temperature can enhance the role played by steel slag more significantly than that played by limestone powder in the hydration and hardening of the composite binder.     

Synthesis and Properties of a New Piperazine-Based Bicaudate Gemini Surfactant

A novel bicaudate gemini surfactant was synthesized with anhydrous piperazine, chloride- bian, and 1-bromo dodecane as raw materials. Its structure was verified by infrared and ¹H NMR. The surface active properties of the bicaudate gemini surfactant in water were measured at 55°C. Its critical micelle concentration (cmc) and γ cmc was 0.50 mmol · L^?1 and 28.95 mN · m^?1, respectively. Results indicate that there was not a remarkable difference in γ_cmc values between the synthesized bicaudate surfactant and conventional gemini surfactant N,N′–bis (dodecyl dimethyl ammonium bromide)-3-oxa-1,5-pentadiammonium. The sterilizing antimicrobial performance of the bicaudate gemini surfactant was examined. The bicaudate gemini surfactant show excellent inhibition against 18 types of bacteria compared with conventional monomeric surfactant and gemini surfactant at concentrations of 50 mg/L.     

Release characteristics of semi-volatile heavy metals during co-combustion of sewage sludge and coal under the O<Subscript>2</Subscript>/CO<Subscript>2</Subscript> atmosphere

Oil well cementing is a vital operation to assure casing stability and zonal isolation for oil and gas exploration. However, some scenarios demand the cemented region to withstand high thermal gradients and imposed deformations, as occurs in the case of oil wells subjected to cyclic steam injection at temperatures up to 250 °C, to reduce oil viscosity and to increase well pressure to facilitate heavy oil recovery. In this paper, the hydration of ductile special cement systems using styrene-butadiene latex (SBR) and carboxylated styrene-butadiene latex (XSBR) addition was studied by conduction calorimetry. The resulting heat flow curves, presented in log–log plots, were used to analyze the influence of those copolymers on the hydration stages of three families of cement pastes of different complexity. The simpler cement systems (SCCS) contained water, oil well Portland cement class G and SBR or XSBR in its composition. In medium complexity systems silica fume was added and in the higher complexity ones (HCCS), superplasticizer as well. The primary objective of adding those copolymers into the Portland cement paste is to obtain higher ductility properties after setting, silica fume to have good thermal stability up to 300 °C, while superplasticizer was added to guarantee good workability. Rheological tests were carried out to evaluate the effect of the copolymers on the composite viscosity. Thermogravimetric analysis of selected SCCS and HCCS samples was performed to quantify the main formed phases up to 24 h of cement hydration. From the obtained results, it was noticed that SBR and XSBR addition substantially affects hydration kinetics at all early age stages. Starting from pre-induction and induction periods, the main observed effect during these stages, was related to the increased viscosity of the pastes, which was higher in XSBR containing pastes, retarding the hydration reactions of respective following stages, when compared to pastes with the same cementitious matrix without copolymer addition.     

Effect of hydrothermal curing on early hydration of G-Oil well cement

G-Oil well cement has been cured under standard and hydrothermal conditions with different steam pressures and temperatures. Compressive strength, pore structure parameters, microstructure, and hydrated products were evaluated after 7 days curing by using SEM, MIP, and simultaneous TGA/DSC. Obtained results showed that 7 days aged sample cured under standard conditions has the highest compressive strength with compact pore structure and hydrated products similar to those found after hydration of Ordinary Portland cement. With increasing temperature and pressure from standard conditions (25 °C, 10125 Pa) to hydrothermal ones (150 °C and 0.3 MPa, 200 °C and 1.2 MPa), compressive strength has drastically decreased from 77.5 ± 2.0 to 20.5 ± 1.0 MPa due to the transformation of original hydrated products (C–S–H) to crystallized α-C₂SH and C₆S₂H₃. The crystallization has led, under hydrothermal curing, to the increase of permeability and pore structure depletion. The final compressive strength after curing for 7 days at 150 °C (51.8 ± 2.0 MPa) and 200 °C (20.5 ± 1.0 MPa), which significantly exceeds the recommended values of 3.45 MPa according to API to hold many casings of oil wells is questionable for application in geothermal ones.     

A comparison of hydration properties of cement–low quality fly ash binder and cement–limestone powder binder

The hydration properties of the binder containing low quality fly ash or limestone powder were compared in this study. Isothermal calorimetry was performed to measure the hydration heat of the binders during the first 3 days. Mercury intrusion porosimetry, scanning electron microscope, and thermogravimetry–differential thermal analysis were all used to determine the pore structure and hydration products of paste. The compressive strength of the pastes of age 3, 7, 28, and 90 days was also tested. The results indicate that the ground low quality fly ash can improve the mechanical properties of composite cementitious material and ameliorate the hydration properties and microstructure compared with the inert admixture limestone powder. The chemical activity of low quality fly ash presents gradually and appears high pozzolanic effect at later period, and it can accelerate the generation of hydration products containing more chemically bonded water. This leads to the higher rate of strength growth and cement hydration degree, the more compact microstructure and reasonable pore size distribution. Additionally, low quality fly ash delays the induction period, but shortens the acceleration period, therefore there is no significant influence on the second exothermic peak occurrence time.     

Physical and chemical studies on cement containing sugarcane molasses

Molasses is generally used as a grinding aid in cement and as a water reducer and retarder in concrete. In China, the output primarily consists of sugarcane molasses. In this paper, the effects of sugarcane molasses on the physical performance and hydration chemistry of conventional Portland cement were investigated. The setting times, the normal consistency of cement pastes, the compressive strengths and fluidities of the mortars were respectively determined according to Chinese Standard GB/T 1346, GB/T17671 and GB/T 2419. The effect of molasses on the hydration kinetics of cement was investigated using a calorimeter. The hydration products and pore size distribution of the cement pastes were analysed by X-ray powder diffraction, differential scanning calorimetry and a mercury injection apparatus. The results show that a small amount of sugarcane molasses retards the setting and hardening of cement paste and increases the fluidity of cement mortar, while excess molasses accelerates the setting and hardening. Molasses improves significantly the compressive strength at 3d due to the decrease of porosity. The addition of 1.0 % molasses accelerates the formation of ettringite, prevents the second hydration of aluminate phase and delays the hydration of C₃S.     

Study on the Inhibition of Mild Steel Corrosion by Cationic Gemini Surfactant in 1 M HCl

The cationic gemini surfactant 1,2-bis(N-tetradecyl-N,N-dimethylammonium)ethane dibromide (14-2-14) was synthesized using a previously described method. The surfactant was characterized using ¹H NMR. The corrosion inhibition effect of 14-2-14 on mild steel in 1 M HCl at temperatures 30–60°C was studied using weight loss measurements, potentiodynamic polarization measurements and electrochemical impedance spectroscopy. Morphology of the corroded mild steel specimens was examined using scanning electron microscopy (SEM). The results of the studies show that gemini surfactant is an efficient inhibitor for mild steel corrosion in 1 M HCl; the maximum inhibition efficiency (IE) of 98.06% is observed at surfactant concentration of 100 ppm at 60°C. The %IE increases with the increasing inhibitor concentration and temperature. The adsorption of inhibitor on the mild steel surface obeys Langmuir adsorption isotherm. SEM studies confirmed smoother surface for inhibited mild steel specimen.