Thermal resistance,microstructure and mechanical properties of type I Portland cement pastes containing low-cost nanoparticles

This study aimed to utilize laboratory-prepared nano-silica (NS) and nano-alumina (NA) as low-cost nano-oxides additions for improving the mechanical properties and thermal resistance of hardened ordinary Portland cement (OPC) pastes. NS was synthesized from rice husk ash in the absence of any surfactant, while NA was synthesized from AlCl₃ in the presence of CTAB as a surfactant. The average particle sizes of synthesized NS and NA were 30 and 40 nm, respectively. Nano-silica or nano-alumina was added to OPC as a single phase with different ratios of 0.5, 1, 2 and 3 by mass % of OPC. The physico-chemical characteristics of different OPC-NS and OPC-NA hardened pastes were studied after 1, 3, 7, 14, 28 and 90 days of hydration. The resistance of the hardened composites for firing was evaluated for specimens cured for 28 days under tap water and then fired at 300, 600 and 800 °C for 3 h. The fired specimens were cooled by two methods: gradual cooling and rapid cooling. The compressive strength test was performed for all mixes at each firing temperature. The compressive strength results revealed that the optimum addition of NS is 1, whereas the optimum addition of NA is 0.5 by mass % of OPC. XRD, TG/DTG and SEM results indicated that ill-crystalline and nearly amorphous C–S–H, C–A–S–H and C–A–H were the main hydration products.     

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.     

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.     

Calorimetry in the studies of cement hydration

Calorimetry was applied to an investigation of the early hydration of Portland cement (PC)–calcium aluminate cement (CAC) pastes. The heat evolution measurements were related to the strength tests on small cylindrical samples and standard mortar bars. Different heat-evolution profiles were observed, depending on the calcium aluminate cement/Portland cement ratio. The significant modification of Portland cement heat evolution profile within a few hours after mixing with water was observed generally in pastes containing up to 25% CAC. On the other hand the CAC hydration acceleration effect was also obtained with the 10% and 20% addition of Portland cement. As one could expect the compressive and flexural strength development was more or less changed—reduced in the presence of larger amount of the second component in the mixture, presumably because of the internal cracks generated by expansive calcium sulfoaluminate formation.     

Evaluation of Properties of Concrete Without Cement Produced Using Fly Ash-Based Geopolymer

The use of ordinary Portland cement (OPC) in the construction industry is inevitable. The huge production of OPC and its use in infrastructural development pose an environmental impact. Greenhouse gas emitted increases the global temperature and it is an alarming sign to everybody on the planet. Concrete is the most consuming material which is produced by using OPC and it is proven that OPC contributes a lot to CO₂ emission. Hence in this study attempt is made to produce concrete by using environment-friendly material like fly ash along with alkaline activators, which is termed Geo polymer concrete. The by-product fly ash is widely available worldwide. It is a by-product of thermal power plants. The use of fly ash in concrete produces less expensive and more cost-effective concrete than concrete made up using OPC. Due to its high silicate and alumina content, fly ash reacts with an alkaline solution to create an aluminosilicate gel that binds the aggregate and results in high-quality concrete. Fly ash is finer than cement, it occupies the pores of cement after hydration. This would result in denser concrete which gives higher strength. In comparison to ordinary concrete, fly ash-based geopolymer concrete offers better resistance to aggressive environments and high temperatures. In the present study, an alkaline activator of molarity 8 is used to prepare geopolymer concrete. The test specimens are cast and cured for 28 days. Test results indicate that an alkaline liquid fly-ash ratio (0.4) produces higher mechanical properties. Hence, geopolymer concrete produced in this study is found to be cost-effective and environment friendly.     

Microstructural,physical, and thermal analyses of Portland cement–fly ash–calcium hydroxide blended pastes

The effect of calcium hydroxide (CH) on the properties of Portland–fly ash cement pastes, at up to high-volume fly ash mixes has been investigated using normal consistency, setting time, compressive strength, thermal analysis and scanning electron microscope. CH as an additive material (5 and 10 wt%), lignite fly ash (FA) up to 50 wt% was used to produce Portland cement (PC)–FA–CH pastes at w/PC + FA ratio of 0.5. Water requirement for normal consistency was found to increase with increasing CH content while a decrease in initial setting time was found. Furthermore, the compressive strengths of all FA mixes with CH were found to be higher than the mixes without CH. Thermal analysis and scanning electron microscope were used to study the hydration of PC–FA–CH system. The results showed that the first phase transition detected by thermal analyses was attributed to ettringite, calcium silicate hydrate, gehlenite hydrate and was found to be higher in PC–FA–CH mixes than in pure Portland–FA cement paste resulting in an increase in compressive strength. Moreover, the hydration phases were also found to increase with increasing curing time. Overall, the results show that the additional of 5 wt% CH in Portland–FA mixes especially at high-volume FA mixes was found to accelerate FA pozzolanic reaction at early ages (7 and 28 days), resulting to an increase in compressive strength.     

Pozzolanic properties of a residual FCC catalyst during the early stages of cement hydration

The catalyst used in fluidized catalytic cracking (FCC) units of refineries after several recovery cycles in regeneration units, reduces its activity and it is partially substituted by new catalyst in the process. As it has a high silicon and aluminum oxides content, the pozzolanic properties of a Brazilian FCC spent residual catalyst, used in different substitution degrees to cement, were evaluated by three thermal analysis techniques during the early stages of hydration of a type II Portland cement. NCDTA curves show in real time that the residual catalyst, accelerates the stages of cement hydration. TG and DSC curves of respective pastes after 24 h of hydration evidence the pozzolanic activity of the waste, respectively, by the lower water mass loss during the dehydroxylation of the residual calcium hydroxide and by the lower dehydroxylation endothermal effect. Within the analyzed period, the higher is the cement substitution degree, the higher is the pozzolanic activity of the residual catalyst.     

Hybrid Cements with ZnO Additions: Hydration,Compressive Strength and Microstructure

The effect of ZnO has already been studied for Portland cement, but the study of its impact on hybrid pastes is scarce. Thus, in this investigation, the influence of ZnO addition on hydration, compressive strength, microstructure, and structure of hybrid pastes is presented. The analyses were made by setting time tests, compressive strength tests, X-ray diffraction, Fourier-transform infrared spectroscopy, thermogravimetric analysis with differential scanning calorimetry, and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. The results indicate that the setting time of the cements was delayed up to 39 min with additions of 3 wt% ZnO. Alternatively, the higher values of compressive strength were observed when 0.5 wt% ZnO was added to the cements for all curing days. In addition, no important differences in the microstructure of samples with different additions of ZnO were observed after 28 days of curing. It is expected that the use of ZnO contributes to the delay of the setting time and the increase of the compressive strength without negatively modifying the microstructure of hybrid pastes.     

Studies on the influence of different fly ashes and Portland cement on early hydration of calcium aluminate cement

The influence of three mineral additives, i.e. fly ashes from pulverized combustion and from fluidized combustion of hard coal as well as Portland cement, on early hydration (up to 28th day) of calcium aluminate cement was investigated. Cement pastes containing 0, 5 and 25 wt% of additives were studied by the use of calorimetry, thermal analysis and infrared spectroscopy methods. It was confirmed that hydration of calcium aluminate cement is closely dependent on the type of addition and its amount. The influence of additives of different properties on cement hydration was discussed basing on received results and other literature reports.     

Improve the thermal and mechanical properties of poly(L-lactide) by forming nanocomposites with pristine vermiculite

Poly(L-lactide)(PLLA)/pristine vermiculite nanocomposites were prepared by melt blending in a twin-screw extruder, and the detailed information of vermiculite dispersion state and effect of vermiculite on thermal and mechanical properties were systematically studied. The results show that the dispersion of vermiculite in the matrix is quite well when the loading content does not exceed 3 wt%. Pristine vermiculite can obviously improve the melt-crystallization temperature during the nonisothermal crystallization. Both crystallization time span and spherulitic size of PLLA decrease with the increasing amount of vermiculite under isothermal crystallization condition by enhancing the primary nucleation of PLLA. And the adding vermiculite can also improve the tensile modulus and Izod impact strength of PLLA. The intrinsic mechanism for the nucleating effect of vermiculite on PLLA is proposed to be the epitaxial crystallization and specific interaction between vermiculite and PLLA.     

Effect of polycarboxylate type of super plasticizer on the hydration properties of composite cements

The work aims to study the effect of polycarboxylate type of super plasticizer on the hydration of composite cements. In this paper we have studied the hydration of 20 wt% fly ash (FA) blended Portland cement in the presence of 0.1 wt% super plasticizer (SP). Water consistency, setting times, non-evaporable water contents, compressive strength, water percolation, and air content measurements were carried out. In addition, X-ray diffraction studies were carried out to understand the hydration process. The results indicated the increase in compressive strength of the FA blended Portland cement in the presence of SP and with the increase of the hydration time.     

Calorimetric determination of the effect of additives on cement hydration process

Possibilities of a multicell isoperibolic-semiadiabatic calorimeter application for the measurement of hydration heat and maximum temperature reached in mixtures of various compositions during their setting and early stages of hardening are presented. Measurements were aimed to determine the impact of selected components?? content on the course of ordinary Portland cement (OPC) hydration. The following components were selected for the determination of the hydration behaviour in mixtures: very finely ground granulated blast furnace slag (GBFS), silica fume (microsilica, SF), finely ground quartz sand (FGQ), and calcined bauxite (CB). A commercial polycarboxylate type superplasticizer was also added to the selected mixtures. All maximum temperatures measured for selected mineral components were lower than that reached for cement. The maximum temperature increased with the decreasing amount of components in the mixture for all components except for silica fume. For all components, except for CB, the values of total released heat were higher than those for pure Portland cement samples.     

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.     

Utilization of electric arc furnace dust as an admixture to Portland cement pastes

Electric arc furnace dust (EAFD) is termed as a hazardous waste due to its contamination with heavy metals. Inertization of such very fine dust can be occurred via stabilization and solidification process within the hydrated Portland cement matrix. In this paper, the effect of the addition of various ratios of EAFD on the properties of the hardened Portland cement paste was investigated. Compressive strength, chemically combine water and free lime contents were determined. In addition, phase composition using XRD; DTA analysis; as well as microstructure of the formed hydrates for some selected samples were investigated using SEM. The obtained results showed that the paste containing 1/mass% EAFD give the highest compressive strength values at most hydration ages, specially the later ages, compared to the neat Portland cement blank paste. Whileas, the pastes containing 3 and 5/mass% EAFD showed lower values of compressive strength compared to those of the blank paste.     

Simultaneous measurements of heat of hydration and chemical shrinkage on hardening cement pastes

Isothermal calorimetry and chemical shrinkage measurements are two independent techniques used to study the development of hydration in cementitious systems. In this study, calorimetry and chemical shrinkage measurements were combined and simultaneously performed on hydrating cement paste samples. Portland cement pastes with different water to cement ratios and a cement paste containing calcium sulfoaluminate clinker and anhydrite were studied. The combined calorimetry/chemical shrinkage test showed good reproducibility and revealed the different hydration behavior of sealed samples and open samples, i.e., samples exposed to external water during hydration. Large differences between sealed and open samples were observed in a Portland cement paste with low water to cement ratio and in the calcium sulfoaluminate paste; these effects are attributed to self-desiccation of the sealed pastes. Once the setup is fully automatized, it is expected that combined calorimetry/chemical shrinkage measurements can be routinely used for investigating cement hydration.     

Water dynamics in hardened ordinary Portland cement paste or concrete: from quasielastic neutron scattering

Portland cement reacts with water to form an amorphous paste through a chemical reaction called hydration. In concrete the formation of pastes causes the mix to harden and gain strength to form a rock-like mass. Within this process lies the key to a remarkable peculiarity of concrete: it is plastic and soft when newly mixed, strong and durable when hardened. These qualities explain why one material, concrete, can build skyscrapers, bridges, sidewalks and superhighways, houses, and dams. The character of the concrete is determined by the quality of the paste. Creep and shrinkage of concrete specimens occur during the loss and gain of water from cement paste. To better understand the role of water in mature concrete, a series of quasielastic neutron scattering (QENS) experiments were carried out on cement pastes with water/cement ratio varying between 0.32 and 0.6. The samples were cured for about 28 days in sealed containers so that the initial water content would not change. These experiments were carried out with an actual sample of Portland cement rather than with the components of cement studied by other workers. The QENS spectra differentiated between three different water interactions: water that was chemically bound into the cement paste, the physically bound or "glassy water" that interacted with the surface of the gel pores in the paste, and unbound water molecules that are confined within the larger capillary pores of cement paste. The dynamics of the "glassy" and "unboud" water in an extended time scale, from a hundred picoseconds to a few nanoseconds, could be clearly differentiated from the data. While the observed motions on the picosecond time scale are mainly stochastic reorientations of the water molecules, the dynamics observed on the nanosecond range can be attributed to long-range diffusion. Diffusive motion was characterized by diffusion constants in the range of (0.6-2) 10(-9) m(2)/s, with significant reduction compared to the rate of diffusion for bulk water. This reduction of the water diffusion is discussed in terms of the interaction of the water with the calcium silicate gel and the ions present in the pore water.     

Study of Polymer-Cement Composite Containing Portland Cement and Aqueous Poly (methyl methacrylate) Latex Polymer by Fourier-Transform Infrared (FT-IR) Spectroscopy

The polymer-cement composite is an immiscible band having modified morphology. Polymer phase improves the toughness of brittle cement and has a reinforcing effect, and interactions between cement components and polymers provide stability. In this study, polymer latex [poly(methyl methacrylate), PMMA] – cement paste was prepared with different weight proportions of polymer content. The main scientific objective of this report has been the analysis and the prediction of high strength with the aim of understanding the interactions of PMMA polymer with Portland cement after hydration reaction of cement pastes and curing the specimens for 28 days. The samples were studied by Fourier transform infrared (FT-IR) spectroscopy. The results are critically examined. It is shown that bands support the interaction of PMMA with cement in the composite.     

Study of dehydration and rehydration processes of portlandite in mature and young cement pastes

The hydration process of the cements induces the formation of different kinds of hydration products. The main products of hydration are C?CS?CH gel and portlandite [Ca(OH)₂]. The C?CS?CH gel is an amorphous compound that is discomposed progressivity with the temperature until approximately 1,000?°C, while the portlandite is discomposed between 450 and 550?°C. Also, calcium carbonate can be formed as a consequence of the portlandite carbonation. All of these processes can be analysed and quantified by simultaneous differential thermal analysis and thermogravimetric analysis. And by X-ray diffraction it is possible to identify the crystalline phases. Some authors have corroborated that the portlandite can be rehydrated, after dehydration processes due to thermal exposition of the cement paste. But all of these experiments have been made with young cement pastes or at temperatures lower than 650?°C. In this work the behaviour of young and mature cement pastes have been studied in relation with the portlandite decomposition and the possibility of the rehydration of it in water presence. We found that young pastes and old pastes, stored at laboratory conditions, and later burned, show a certain grade of rehydration, specially the pastes burned at 650?°C (with ??80% of reformation of portlandite) with respect to the pastes burned at 1,000?°C (between 20 and 40%). It is corroborate that the rehydration process is directly related to the formation of CaO during the burning. Also, a formation of unstable portlandite is detected in young pastes burned at 650?°C, which can be rehydrated easily. Although, the mature pastes that have been burned initially and stored under laboratory conditions cannot be rehydrated, due to the formation of stable products during the storage.