Fuzzy logic model for the prediction of cement compressive strength

A fuzzy logic prediction model for the 28-day compressive strength of cement mortar under standard curing conditions was created. Data collected from a cement plant were used in the model construction and testing. The input variables of alkali, Blaine, SO₃, and C₃S and the output variable of 28-day cement strength were fuzzified by the use of artificial neural networks (ANNs), and triangular membership functions were employed for the fuzzy subsets. The Mamdani fuzzy rules relating the input variables to the output variable were created by the ANN model and were laid out in the If-Then format. Product (prod) inference operator and the centre of gravity (COG; centroid) defuzzification methods were employed. The prediction of 50 sets of the 28-day cement strength data by the developed fuzzy model was quite satisfactory. The average percentage error levels in the fuzzy model were successfully low (2.69%). The model was compared with the ANN model for its error levels and ease of application. The results indicated that through the application of fuzzy logic algorithm, a more user friendly and more explicit model than the ANNs could be produced within successfully low error margins.     

Physicochemical and biological properties of composite bone cement based on octacalcium phosphate and tricalcium silicate

Biocompatible tricalcium silicate (C₃S) bone cement is widely used as dental and bone repair material; however, its long setting time, poor injectability and low initial mechanical properties limit clinical applications. In order to improve C₃S silicate bone cement and its derivatives to play a more important role in tooth restoration, bone defect repair, implant coating and tissue engineering scaffolds, a novel C₃S and octacalcium phosphate (OCP) composite bone cement (OCP/C₃S) was prepared and evaluated for setting time, injectability, anti-flocculation, pH, microstructure, bioactivity and cytotoxicity. The setting time of the OCP/C₃S composite bone cement was controlled within the clinically operable time range (8.3–13.7 min); the cement exhibited good compressive strength, injectability (93.54%), and anti-collapse performance. The 20% OCP/C₃S composite bone cement had a compressive strength of 28.94 MPa, 93% stronger than pure C₃S (14.98 MPa). An in vitro immersion test showed that the composite bone cement had excellent hydroxyapatite forming ability, proper degradation rate, and a low pH value. Cellular experiments confirmed the low cytotoxicity of the composite bone cement and its great capacity for cell proliferation. These results indicate that 20% OCP/C₃S composite bone cement is a promising biomaterial.     

Long-term effects of cement SO3 content on the properties of normal and high-strength concrete. Part I. The effect on strength

Six brands of cement were each manufactured at four SO₃ contents, in full scale plants. Strengths were determined, at up to one year, in concretes of high and low water/cement ratio. Strength was usually independent of, or linearly related to, the SO₃ content of cement. Only rarely was a well defined optimum SO₃ content observed. With each cement, the strength-SO₃ relationship at 28 days was usually similar to that at one year. At 28 days the association between strength and the C₃A content of cement varied considerably with SO₃ content, whereas the corresponding association for C₃S did not. With one-year concrete strength, the dominant factor of cement composition was C₃A. At this age the correlation coefficient of strength with C₃A varied with SO₃. Undersulphated cements displayed a strongly negative association between strength and C₃A content, which could account for up to 10 MPa difference in strength at either 0.45 or 0.75 water/cement ratio.     

城市污水厂剩余活性污泥生产生态水泥

引言 随着我国对城市生活污水处理能力以及污水处理率的不断提高,污水处理厂的污泥产量也不断增长.由于其产量较大,含水率高,同时含有大量有机质、病菌、寄生虫和重金属等[1-2],如果处理处置不当,会给环境带来严重的二次污染.     

Hydroxyapatite/tricalcium silicate composites cement derived from novel two-step sol-gel process with good biocompatibility and applications as bone cement and potential coating materials

Tricalcium silicate (C₃S) and hydroxyapatite (HAp) composites were fabricated through the sol-gel process. The aim of this research is to improve the biocompatibility of C₃S through HAp addition and study the potential of using this as coating materials. The composites (HAp/C₃S) were characterised by Fourier transform infrared spectrometry, thermal gravity-differential thermal analysis and X-ray diffraction. The working and setting times of cement pastes were tested using Gillmore needle. Mechanical properties were examined by nanoindentation and material testing system. In vitro biocompatibility of the materials were studied by cell attachment and viability of L929 and MG-63 cells. HAp/C₃S as a coating material on gelatin film were measured with the surface roughness and imaged by scanning electron microscope. With the addition of HAp, no undesirable free CaO was detected with the synthesis by the sol-gel preparation. The pH values of HAp added groups were between 7.54 and 8.76, which were much lower than pure C₃S group (pH?=?11.75). For in vitro studies, the presence of HAp could effectively enhance the cell attachment and viability of both L929 and MG-63 cells grown in the extract or directly on the composites. However, the mechanical properties of the composites were impaired as compared to pure C₃S. Lastly, HAp/C₃S cement could be evenly coated on gelatin film. HAp is successfully demonstrated to improve C₃S biocompatibility with this new composites HAp/C₃S. C-75 (75% C₃S and 25% HAp), in particular, has good biocompatibility, relatively high compressive strength and can be uniformly coated onto gelatin film. Thus, C-75 is a promising material for further investigation as a coating on other biopolymers.     

The influence of SO3 content of portland cement on the creep and other physical properties of concrete

It is shown that the creep of concrete is very sensitive to the SO₃ content of cement. Examples are given in which creep doubles when SO₃ is reduced from 3.7 to 1.6%. The SO₃ requirement for minimum creep is high, and can exceed 4.0% even when the C₃A¹ and alkali contents of the cement are low to medium and fineness is moderate. It is also demonstrated that the dependence of creep on the SO₃ contents of the cement does not vary with the duration of the creep test. Compressive strength to 1 year, modulus of elasticity, drying shrinkage and 3-year expansion in water were measured and the relationships between these properties of concrete and the SO₃ content of cement were determined.     

影响水泥抗压强度的成型条件研究

水泥抗压强度的测定过程有成型、养护、破型三个主要环节。各环节的试验条件不同,将直接影响抗压强度的测定结果。研究了水泥试件成型过程中流动度、试件尺寸、表面状态等试验条件对试件抗压强度测定结果的影响。结果表明：在一定范围内水灰比与抗压强度呈正相关关系,即水灰比越大,其流动度越好,抗压强度越高,当超过这个范围后,随着水灰比的增大,抗压强度逐渐减小;随着试件尺寸逐渐变大,抗压强度依次降低;试模涂油量多少不同,导致试件表面状态存在差异,涂油量过多或过少都会使抗压强度的测定结果偏低。     

Effect of prolonged heating at elevated temperatures on the phase composition and textures of portland cement clinker

Two kinds of portland cement clinker with widely different MgO and SO₃ content were reheated for a long time at elevated temperature. With the clinker rich in MgO and SO₃, alite increased while belite decreased in quantity after reheating. The alite crystals, overgrown with new precipitates, gave zonal structures. Thin platy hexagonal crystals were occasionally nucleated and grown separately in the bulk liquid. High degree of supercooling produced dismembered dendritic crystals of belite. The C/S ratio of the interstitial phase decreased with reheating. The above changes occur in association with the process in which the interstitial liquid, initially variable in basicity, is transformed to the uniform and most acidic one. This process is controlled by the counterdiffusion of CaO and SiO₂, the rate of which is such that, in normal clinker processing, the clinkering reaction terminates before reaching this stage. Rise in firing temperature increases the concentration of SiO₂ in the interstitial liquid and leads to higher solid C₃S/C₂S ratio in clinker. The presence of MgO and SO₃ in abundance lowers the viscosity of the liquid and hence accelerates the changes. No appreciable change could be recognized for the clinker low in MgO and SO₃ content.     

Influence of the clinker SO3 on the cement characteristics

This paper aims to clarify the influence of the clinker SO₃ on the cement characteristics. The impact on the strength development rate and the level of sulfate resistance were studied .The results show that increasing the amount of clinker SO₃ at low alkali level reduces the percentages of the tricalcium aluminate (C₃A) and alite as well as the alite/belite ratio, leading to a modification in the cement quality.For these reasons cements produced from a clinker containing high sulfate and low alkali, have slower strength development and higher sulfate resisting level than that produced with low sulfate clinker.     

Fast-setting and high fracture toughness Ce-TZP/tricalcium silicate composite dental cement

For dental materials, a certain defect tolerance would be beneficial. Some Ceria-stabilized zirconia (Ce-TZP) composites are promising dental repair materials, as they have been shown to exhibit an obvious amount of transformation-induced plasticity with almost no dispersion in strength data. The purpose of this study was to design a novel tricalcium silicate (C₃S)-based dental repair material by adding 10 mol.% Ce-TZP to improve fracture toughness and dipotassium hydrogen phosphate (K₂HPO₄) as the setting accelerator. The study evaluated the physicochemical properties, in vitro cell activity, and antibacterial activity of Ce-TZP/C₃S composite cement, and the results revealed that Ce-TZP/C₃S cement showed a fast-setting ability and good washout resistance when the setting time was controlled within 26–43 min. With increasing Ce-TZP content, the mechanical properties, especially the flexural strength and fracture toughness, were gradually enhanced. Additionally, the 30% Ce-TZP/C₃S composite showed good antibacterial activity and in vitro cytocompatibility. The study concluded that 30% Ce-TZP/C₃S composites could be regarded as ideal candidates in the field of dental materials due to their excellent physical and chemical properties, antimicrobial activity, in vitro cytocompatibility, outstanding fracture toughness and fast-setting ability.     

Strengthening effect and mechanism of titanium extraction slag on the mechanical property of calcium aluminate cement

In heavy oil recovery, calcium aluminate cement (CAC) is in the working environment of “low-temperature hardening and ultrahigh temperature service.” However, the formation of C₃AH₆ under low temperatures results in a decrease in strength and reduce the cementing quality. In this study, titanium extraction slag (TES) was used to inhibit CAC strength deterioration. TES, characterized by a high Ti content, presents challenges in terms of utilization and poses significant ecological risks owing to its large accumulation. Cementite hydration with 0%, 20%, 30%, and 40% TES relative to CAC was examined at 30 °C for 28 d. The high C₃AH₆ content of the pure CAC increased the strength deterioration, pore size, and cementite carbonation. With 20% TES, a dilution effect was observed without strength improvement. Furthermore, 30% TES generated layered double hydroxides and converted C–S–H into C–A–S–H, thereby increasing compressive strength. By-products were generated with 40% TES, which inhibited the strength development while generating C–A–S–H to maintain the compressive strength. Therefore, TES can inhibit the strength decline of CAC, and the byproducts of the LDH structure can improve corrosion resistance.     

Effect of size fraction and glass structure of siliceous fly ashes on fly ash cement hydration

Paper presents effect of size fraction and glass structure of fly ashes on cement hydration. Fly ashes below 16 μm and 16–32 μm, both from the 1st and 3rd section of electro-filter, were applied. Hydration heat, content of Ca(OH)₂ and unreacted C₃S were studied and compressive strength and microstructure were analysed. Results show that finer ashes have higher depolymerization degree of SiO₄ units in glass what increases pozzolanic reactivity. Incorporation of fly ashes below 16 μm from the 3rd section gives cement class 52.5 N. At 180 day, Ca(OH)₂ content decreases by 67% and C₃S hydration degree increases by 50% relative to control sample.     

Model for the quantitative description of the kinetics of hardening of portland cements

A new mathematical form of a cement model is introduced for the prediction of concrete strengths obtained at various curing temperatures from the properties of the cement used. This model considers the hydrations of C₃S and C₂S as first order reactions in which the C₃A acts as catalyst. Not only does this model reproduce the strengths of various portland cements, but also it provides quantitative information about several important characteristics of the kinetics of hydration as a function of curing temperature. These characteristics are: the time of beginning of the hardening; rates of hardening; the time when the diffusion control of hydration starts; how much this strength is; and, the final strength potential of various portland cements.It is shown that the new model is well supported by experimentally obtained strength results.     

Incorporation of trace elements in Portland cement clinker: Thresholds limits for Cu, Ni, Sn or Zn

This paper aims at defining precisely, the threshold limits for several trace elements (Cu, Ni, Sn or Zn) which correspond to the maximum amount that could be incorporated into a standard clinker whilst reaching the limit of solid solution of its four major phases (C₃S, C₂S, C₃A and C₄AF). These threshold limits were investigated through laboratory synthesised clinkers that were mainly studied by X-ray Diffraction and Scanning Electron Microscopy. The reference clinker was close to a typical Portland clinker (65% C₃S, 18% C₂S, 8% C₃A and 8% C₄AF). The threshold limits for Cu, Ni, Zn and Sn are quite high with respect to the current contents in clinker and were respectively equal to 0.35, 0.5, 0.7 and 1 wt.%. It appeared that beyond the defined threshold limits, trace elements had different behaviours. Ni was associated with Mg as a magnesium nickel oxide (MgNiO₂) and Sn reacted with lime to form a calcium stannate (Ca₂SnO₄). Cu changed the crystallisation process and affected therefore the formation of C₃S. Indeed a high content of Cu in clinker led to the decomposition of C₃S into C₂S and of free lime. Zn, in turn, affected the formation of C₃A. Ca₆Zn₃Al₄O₁₅ was formed whilst a tremendous reduction of C₃A content was identified. The reactivity of cements made with the clinkers at the threshold limits was followed by calorimetry and compressive strength measurements on cement paste. The results revealed that the doped cements were at least as reactive as the reference cement.     

Hydration characteristics of waste sludge ash utilized as raw cement material

In this study, the hydration characteristics and the engineering properties of three types of eco-cement pastes, including their compressive strength, speciation, degree of hydration, and microstructure, were studied and compared with those of ASTM type I ordinary Portland cement. The results indicate that it is feasible to use sludge ash and steel-making waste to replace up to 20% of the mineral components of the raw material of cement. Furthermore, all the tested clinkers met the toxicity characteristic leaching procedure requirements. The major components of Portland cement, C₃S (i.e., 3CaO·SiO₂), C₂S (i.e., 2CaO·SiO₂), C₃A (i.e., 3CaOAl₂O₃) and C₄AF (i.e., 4CaO·Al₂O₃·Fe₂O₃), were all found in the waste-derived clinkers. All three types of eco-cements were confirmed to produce calcium hydroxide (Ca(OH)₂) and calcium silicate hydrates (CSH) during the hydration process, increasing densification with the curing age. The thermal analysis results indicate that the hydration proceeded up to 90 days, with the amount of Ca(OH)₂ and CSH increasing. The chemical shift of the silicates, and the resultant degree of hydration, and the increase in the length of the CSH gels with the curing age, were confirmed by ²⁹Si NMR techniques. Compressive strength and microstructural evaluations confirm the usefulness of eco-cement.     

Structure and mechanical properties of aluminosilicate geopolymer composites with Portland cement and its constituent minerals

The compressive strengths and structures of composites of aluminosilicate geopolymer with the synthetic cement minerals C₃S, β-C₂S, C₃A and commercial OPC were investigated. All the composites showed lower strengths than the geopolymer and OPC paste alone. X-ray diffraction, ²⁹Si and ²⁷Al MAS NMR and SEM/EDS observations indicate that hydration of the cement minerals and OPC is hindered in the presence of geopolymer, even though sufficient water was present in the mix for hydration to occur. In the absence of SEM evidence for the formation of an impervious layer around the cement mineral grains, the poor strength development is suggested to be due to the retarded development of C-S-H because of the preferential removal from the system of available Si because geopolymer formation is more rapid than the hydration of the cement minerals. This possibility is supported by experiments in which the rate of geopolymer formation is retarded by the substitution of potassium for sodium, by the reduction of the alkali content of the geopolymer paste or by the addition of borate. In all these cases the strength of the OPC-geopolymer composite was increased, particularly by the combination of the borate additive with the potassium geopolymer, producing an OPC-geopolymer composite stronger than hydrated OPC paste alone.     

不同C_3S含量阿利特-硫铝酸盐水泥熟料与粉煤灰混合材的适应性研究

研究了不同C3S含量的阿利特-硫铝酸盐水泥熟料与粉煤灰混合材的适应性。结果表明：C3S含量一定时,随粉煤灰掺量增加,水泥的凝结时间延长,抗压强度降低;粉煤灰掺量一定时,随C3S含量的增加,水泥的凝结时间延长,抗压强度增大;C3S含量增大时,随着粉煤灰掺量增多,水泥各龄期抗压强度降幅减小;掺加粉煤灰后水泥的早期抗压强度降低幅度较大,后期抗压强度降幅较小。熟料中C3S含量低时,对高粉煤灰掺量的适应性差;C3S含量高时,其适应性好。     

The effectuation of seawater on the microstructural features and the compressive strength of fly ash blended cement at early and later ages

The current work scrutinizes the effectuation of seawater on morphological properties, pore structure, and compressive strength during the hydration process of fly ash blended cement at 3, 7, 28, 56, and 90 days to better understand the influence of salinity conditions of seawater on the microstructural modification and strength development of the hydration products as well as the total porosity. The chemical reaction's mechanism of mightily soluble salts, for example, Mg₂SO₄ and NaCl, with hydrated fly ash and blended cement (calcium-bearing phases) was also confirmed. Fourier-transform infrared spectroscopy has been appointed to observe and characterize the energetics of variation in the formulation of portlandite (CH), calcium silicate hydrate, gypsum (Gy), ettringite (AFt), and calcium chloroaluminate (Friedel's salt [FS]) throughout the hydration process of fly ash blended cement with seawater in comparison with deionized water. X-ray diffraction analysis exposed that the peak intensities of FS, portlandite, and some particular phases of the hydrated fly ash blended cement in seawater are higher and sharper than the comparable peaks in deionized water. Mercury intrusion porosimetry-measurements have been appointed that the total porosity of artificial seawater (ASW) was decreased from 28.9% at 3 days to 19.4% at 56 days. In addition, the average, median, and critical pore diameter were decreased in ASW while compared to deionized water (DIW). The reaction products of this work were also characterized using scanning electron microscopy, EDS, compressive strength, and isothermal calorimeter.     

CaCO3 addition effect on the hydration and mechanical strength evolution of calcium aluminate cement for endodontic applications

Calcium aluminate cement (CAC) hydrates conversion can be inhibited by adding CaCO₃, leading to C₃A·CaCO₃·11H (3CaO·Al₂O₃·CaCO₃·11H₂O) formation. However, despite its benefits, the stability of this monocarbonate hydrate is not fully understood, especially when the samples are kept in contact with liquid during the curing step. Thus, taking into account the increasing interest in the CAC application as a biomaterial in the endodontic area, this work addresses the evaluation of the mechanical strength and phase transformations of a commercial cement (Secar 71) containing 15 or 20 wt% of CaCO₃. Compressive strength, apparent porosity, dimensional linear changes, X ray diffraction and thermogravimetric tests were carried out to evaluate samples immersed in water and kept at 37 °C between 1 and 30 days of curing. According to the collected results, CAH₁₀ and C₂AH₈ formation were inhibited in CaCO₃ containing compositions and the presence of the C₃A.CaCO₃.11H phase led to a significant cement mechanical strength increase. Nevertheless, the partial decomposition of this monocarbonate hydrate was detected at 37 °C in the range of 1-7 days and the continuous hydration of CA and CA₂ also affected the compressive strength behavior of the evaluated samples.