Effect of weighting materials on carbonation of oil well cement-based composites under high temperature and CO2-rich environment

As an indispensable part of cement slurry for high temperature and high pressure oil and gas wells, weighting materials have a significant impact on the carbon dioxide corrosion of oil well cement-based composites.This paper studied the carbonation process of cement with three weighting agents, and evaluated the compressive strength and carbonation depth of cement at 150 ℃. XRD, SEM and MIP were used to study the carbonation mechanism of cement. When 21 days of carbonation, the carbonation depth growth rate of hausmannite cement was 0.21 mm/d, hematite cement was 0.24 mm/d, and barite cement was 0.31 mm/d. The compressive strength of cement decreased after carbonation,and the carbonation had a minor influence on the compressive strength of hausmannite cement and the most significant impact on barite cement. The carbonation product of oil well cement was mainly calcite. Unstable vaterite mainly existed in the barite cement sample, indicating that the barite cement sample was the most serious corrosion. In the carbonation zone, the number of pores smaller than 10 nm increased the most in the hausmannite cement sample. Pores with a diameter greater than 100 nm accounted for 1.9 % in the hausmannite cement, 3.0 % in hematite cement, and 4.8 % in barite cement. The result shows that hausmannite is the most conducive to the corrosion resistance of oil well cement.     

Influences of fly ash and fluorgypsum on the hydration heat and compressive strength of cement

The hydration heat of pure cement, fly ash single-doped cement, as well as fly ash and fluorgypsum co-doped cement were investigated by means of micro-calorimetry with an eight-channel micro-calorimeter. The results showed that the hydration heat and the hydration rate could be reduced significantly by fly ash and fluorgypsum. However, the reduction was not proportional to the loading of dopant. The exothermic peak of the co-doped cement was appeared earlier than that of the single-doped cement. As the temperature decreased, the hydration heat and the hydration rate of both the doped cement were reduced, and the exothermic peak appeared later. The effect of fly ash and fluorgypsum on the compressive strength of cement was also investigated. The results revealed that the early compressive strength of concrete made up of the co-doped cement was largely higher than that of the single-doped cement. Based on the experiment results obtained in this article, we could conclude that fluorgypsum is a suitable additive for the single-doped cement.     

拱北隧道灌浆加固中注浆材料室内试验研究

为保证港珠澳大桥拱北隧道灌浆加固工程安全,进行了不同加固方法的注浆材料室内研究。研究了袖阀管单液注浆中水泥品种、水灰比、早强剂的品种、抗沉剂等对水泥浆液的物理性能和固结体抗压强度的影响,研究了袖阀管双液注浆中水泥品种、水灰比、水玻璃浆液浓度、水玻璃浆液与水泥浆的体积比等固结体抗压强度的影响,研究了高压双管旋喷注浆中水泥与土的质量比、养护条件对水泥固结体的抗压强度的影响。得到的灌浆材料优化配方可满足灌浆设计要求。     

Application of differential thermogravimetry to the hydration of expansive cement pastes

Differential thermogravimetric analysis was used to determine the hydration kinetics of expansive cement and its products at various ages of hydration. Analytical grade reagents, kaolin and Portland cement were used to prepare an expansive cement on the basis of calcium sulphoaluminate. Two mix compositions having the stoichiometric composition of trisulphate and monosulphate were synthesized from pure reagents. Three clinkers were also prepared from kaolin, gypsum and calcium carbonate with different compositions.The hydration of expansive cement prepared from the stoichiometric composition of trisulphate and Portland cement gives ettringite as the stable phase after seven days of hydration. The presence of more CaO than the stoichiometric composition of trisulphate favours the conversion of some ettringite to the monosulphate hydrate. The hydration of expansive cement prepared from the stoichiometric composition of monosulphate and Portland cement shows the presence of ettringite and the monosulphate phase. Ettringite is formed initially, and then transformed to the monosulphate form.     

A study of the properties of portland cement modified using peat-based hydrophobic admixtures

Industrial production of portland cement with the simultaneous introduction of hydrophobic components is simulated. Their effect on the properties of the modified portland cement is determined. The method developed provides insulation of the cement from drip and, partially, vaporous moisture. The interaction between the dispersed phase of the cement and molecules of the organic admixture takes place by forming hydrogen bonds between surface silanol groups of cement particles and oxygen-containing groups of the admixture. The industrial applicability of the hydrophobization method is shown.     

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.     

Hydratation mechanism of a zinc phosphate cement and development of its mechanical profile

The main objective of this study is to understand the setting mechanism of a zinc phosphate cement and the development of its mechanical hardness. This cement is widely used in dentistry and is composed of solid phase cement containing zinc oxide (ZnO) and aluminium phosphate AlPO₄ ·nH₂O, and then liquid phase cement which is composed of phosphoric acid and water. The setting of the cement is due to a mixture of both phases together. In this optic, the control of the effect of different compounds in setting mechanism and hardness is carried out by using several investigation methods such as ESM, XRD, IR, TGA, and DTA. For this study, we explain in detail each phase of the cement process, such as the preparation of raw materials, their mixing, the introduction of the solid phase of cement to the liquid phase, and then the hardening of the cement. The results obtained show the effect of powder size on the setting reaction of the cement and show that aluminium phosphate had an interesting effect on the hardening and setting time of the cement. The X-ray diffraction showed that the principal phase of the hydratation product, which is Hopeïte, is available in the mixture of initial reactants and other secondary products, which are zinc phosphate salts in primary and secondary forms.     

Environmental impact of some cement manufacturing plants in Saudi Arabia

This work is concerned with the environmental impact of the cement industry in the west of Saudi Arabia represented in two cement plants and one cement depository. The concentrations of natural and artificial radionuclides in samples of cement (raw materials and end product) and soil, collected from the cement plant and its surrounding area, were measured using γ-ray spectrometer employing a HPGe detector. In addition, the levels of 19 major and trace elements were also determined in these samples using the inductively coupled plasma atomic emission spectroscopy. The concentrations of the ²³⁸U series isotopes in soil samples show a clear radiological impact of the cement industry upon the environment. Possible contamination with Ca and some other elements in soil samples that are rich with the fine grain size was observed. Cluster analysis of soil samples using convenient attributes shows an obvious evidence of the cement industry impact upon the environment. The hidden effect of the cement industry upon the environment was observed when the convenient measured attributes were used in cluster analysis of soil samples.     

A comparative study on cement hydration and microstructure of cement paste incorporating aminosulfonate–phenol–salicylic acid–formaldehyde and aminosulfonate–phenol–formaldehyde polymer

In this article, the water-soluble aminosulfonate–phenol–salicylic acid–formaldehyde (AH) polymer and aminosulfonate–phenol–formaldehyde polymer (AS) were incorporated into cement paste, and the effect of AH polymer on cement hydration and microstructure of cement paste was compared with AS polymer by means of isothermal calorimetry, X-ray diffraction, thermal analysis, mercury intrusion porosimetry, and scanning electron microscopy. The test results showed that the incorporation of AH and AS polymers into cement paste retards the rate of hydration reaction and reduces the amount of hydration products at early stages of hydration. The use of AH and AS polymers into cement paste also improves pore structure of cement paste. The pore size distribution of cement paste shifts toward smaller pore size scope. A smaller particle size of hydration product can be found in cement paste with AH and AS polymers. The cement paste with AH and AS polymers has a higher pore volume and total porosity. The surface morphologies of cement paste with AH and AS polymers are looser and more homogeneous than blank cement paste. Moreover, at the same dosage of polymer, the effect of AH polymer on the cement hydration and microstructure of cement paste was more significant than that of AS polymer.     

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.     

磺化三聚氰胺甲醛树脂与金属钙离子的复合物对水泥的作用

研究了磺化三聚氰胺甲醛树脂（SMF）与金属钙离子的复合物SMF-Ca^2 对水泥的作用,从对水泥吸附、水化等研究结果表明,SMF和Ca^2 间存在着一定的化学作用。在水泥砂浆中加入SMF-Ca^2 复合物比加入纯的SMF树脂能使减水率、抗压强度、抗折强度获得更大的提高。     

Study on optimization of hydration process of blended cement

To optimize the hydration process of blended cement, cement clinker and supplementary cementitious materials (SCMs) were ground and classified into several fractions. Early hydration process of each cementitious materials fraction was investigated by isothermal calorimeter. The results show fine cement clinker fractions show very high hydration rate, which leads to high water requirement, while fine SCMs fractions present relatively high hydration (or pozzolanic reaction) rate. Cement clinker fractions in the range of 8–24 μm show proper hydration rate in early ages and continue to hydrate rapidly afterward. Coarse cement clinker fractions largely play “filling effect” and make little contribution to the properties of blended cement regardless of their hydration activity (or pozzolanic activity). The hydration process of blended cement can be optimized by arranging high activity SCMs, cement clinker, and low activity SCMs in fine, middle, and coarse fractions, respectively, which not only results in reduced water requirement, high packing density, and homogeneous, dense microstructure, but also in high early and late mechanical properties.     

Improved Interfacial Bonding Strength and Reliability of Functionalized Graphene Oxide for Cement Reinforcement Applications

Poor bonding strength between nanomaterials and cement composites inevitably lead to the failure of reinforcement. Herein, a novel functionalization method for the fabrication of functionalized graphene oxide (FGO), which is capable of forming highly reliable covalent bonds with cement hydration products, and therefore, suitable for use as an efficient reinforcing agent for cement composites, is discussed. The bonding strength between cement and aggregates was improved more than 21 times with the reinforcement of FGO. The fabricated FGO also demonstrated many important features, including high reliability in cement pastes, good dispersibility, and efficient structural refinement of cement hydration products. With the incorporation of FGO, cement mortar samples demonstrated up to 40 % increased early and ultimate strength. Such results make the fast demolding and manufacture of light constructions become highly possible, and show strong advantages on improving productivity, saving cost, and reducing CO₂ emissions in practical applications.     

Determination of the expected decrease in strength of high alumina cement concrete by derivatography

Methods involving the use of the derivatograph in the determination of the expected decrease in strength of high alumina cement are described. In a series of steps the strength, porosity and the cement content of the concrete are determined by physico-chemical measurements. The actual phase composition of the cement component of concrete is determined by derivatography. Methods of separating the two overlapping peaks due to the dehydration of the calcium aluminate hydrates present in the cement are described.     

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.     

Studying the physico-chemical properties of commercially available oil-well cement additives using calorimetry

Cement additives are typically used to modify the behavior of oil-well cement and to control its fluidity under well conditions. In this study, the retardation effect on cement hydration is investigated for a commercially available lignosulfonate and an NSF condensate at seven different concentrations. Additive solutions at 0.1% and 0.2% each by weight of cement (bwoc) with a ratio of (1:1) are also studied. The retardation of cement hydration process is monitored via isothermal calorimetry. Rheological studies are conducted to study the plasticizing effect induced by these additives. The mechanisms accompanying this process are better understood by studying the morphology of cement/additives systems using environmental scanning electron microscopy. The results show clearly that NSF has a retardation effect on cement hydration reflected on crystal growth. In addition, rheological measurements show that sodium lignosulfonate is more effective than NSF. The rheological effect alters with different cement/additive systems. This article provides recommendations for applying the most effective additive dosages in drilling and well-completion operations as well as enhancing the well-cementing quality.     

Differential thermal studies of polymethyl methacrylate-impregnated cement pastes

Differential thermal curves have been obtained for two polymethyl methacrylate-impregnated cement pastes prepared at a water/cement ratio of 0.37 and 0.70. Complex thermal effects, including a substantial decrease in the endothermal peak for Ca(OH)₂ decomposition, were observed in samples heated in air. These effects originate in the portland cement paste, in the polymer, and from interactions between the polymer and the hydrated cement during heating. Less complex effects resulted when DTA was carried out in N₂. There was no evidence of a reaction between the hydrated cement and PMMA during impregnation.     

Investigation of ageing of alumina cement-based mixtures using thermal analysis and calorimetry

The shelf life of cement and cement-based dry mixtures is often determined by ageing of such materials. The ageing is the result of interactions between cement and other components of cementitious mixtures with moisture as well as with CO₂ from the atmosphere. In this work, the ageing behaviour of calcium aluminate cement and its mixtures with additives of microsilica, fluidized catalytic cracking catalyst waste and ground quartz sand were investigated. The ageing was achieved by storing cement and its mixtures in a climatic chamber for 7 and 14 days at 95% relative humidity and 20 ± 1 °C temperature. Applying thermal analysis, XRD analysis as well as scanning electronic microscopy, it was established that hydration of the cement minerals takes place along with carbonation during the ageing process of cement and its mixtures. The quantities of the products formed during ageing and their crystallinity depend on the nature of additives and the duration of ageing. When applying the method of calorimetric analysis, the influence of ageing on the kinetics of hydration of cement and as well as of its mixtures with the additives used in the work has been established.     

生态水泥

介绍了生态水泥的新概念,并对城市垃圾、污泥等废弃物的处理现状、生态水泥的生产工艺和国内外生态水泥的现状进行了论述.用城市垃圾和污泥来生产生态水泥拓宽了原材料来源,减少了天然资源的消耗,降低了水泥生产的成本,是一条很有前途的、有利于水泥工业可持续发展的途径.     

Influence of fineness on the cementitious properties of steel slag

In this paper, the influence of fineness on the cementitious properties of steel slag and the properties of cement containing steel slag with different finenesses were investigated. The results show that increasing the fineness can significantly enhance the early as well as the late cementitious properties of steel slag. However, the early hydrations of cement and steel slag tend to hinder each other especially in the case of large steel slag replacement and high fineness of steel slag. Therefore, increasing fineness of steel slag cannot improve the early cementitious properties of the cement containing steel slag. At 28 days, the hydrations of steel slag and cement tend to promote each other. Increasing the fineness of steel slag enhances the late cementitious properties of the cement containing steel slag significantly.