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1.
2.
沈定珍 《宁波大学学报(理工版)》2006,19(3):346-349
软土地基中的支护是基础工程的关键,在节约成本的前提下,选择合理的支护结构至关重要.通过对某公司将要开发的2个基坑支护方案的项目进行的相关分析、计算和探讨,总结出了软土地基中的基坑支护方案的选择原则及其相对应的施工措施等. 相似文献
3.
The majority of previous studies of the hydration of cements using heat flow calorimetry have been carried out isothermally. However, with oilwell cements the slurry is mixed on the surface at ambient temperature and then gradually increases in temperature as it is pumped down the well. A Setaram C-80 calorimeter has been used to simulate the temperature ramp in API oilwell cement test schedules. This approach has enabled cementing reactions to be studied for the first time under conditions approaching those encountered in the field, and has shown that the results obtained from isothermal experiments may be misleading.The permission of the British Petroleum Company PLC to publish this paper is gratefully acknowledged. 相似文献
4.
Six methacrylate or acrylate derivatives of natural amino acids were synthesized and characterized. Based upon these monomers, six terpolymers [poly(acrylic) acid-co-itaconic acid-co-amino acid] were prepared and characterized. The synthesized polymers were used to formulate glass-ionomer cements (GICs) using Fuji II glass filler. The effects of the molecular weight (MW) and powder/liquid (P/L) ratio were evaluated. Scanning electron microscopy (SEM) was used to examine the fracture surfaces of the selected cement specimens. Results show that all the amino acid modified GICs exhibited higher compressive strengths (CS, 193-236 MPa) and much higher flexural strengths (FS, 55-71 MPa) as compared to commercial Fuji II GIC (191 in CS and 16 in FS). Both MW and P/L ratio affected the strength of the formed cement. It was important to find the optimal MW and P/L ratio to obtain the highest FS. In this study, optimized MW (number average) of the polyacids and P/L ratio were around 50,000 and 2.7/1, respectively. The microstructures of the fracture surfaces helped to explain the strength differences among the materials tested in the study. SEM analysis suggests that more integrated microstructures and fewer defects can lead to higher FS. 相似文献
5.
Stepkowska E.T. Perez-Rodriguez J. L. Aviles M. A. Jimenez de Haro M. C. Sayagues M. J. 《Journal of Thermal Analysis and Calorimetry》2002,70(1):181-189
Specific surface, S, of CSH-gel particles of disordered layered structure, was studied by water sorption/retention in two cement pastes differing
in strength, i.e. C-33 (weaker) and C-43 (stronger), w/c=0.4. Hydration time in liquid phase was t
h=1 and 6 months, followed by hydration in water vapour either on increasing stepwise the relative humidity, RH=0.5→0.95→1.0 (WS) or on its lowering in an inverse order (WR). Specific surface was estimated from evaporable (sorbed) water
content, EV (110°C), assuming a bi- and three-molecular sorbed water layer at RH=0.5 or 0.95, respectively (WS). On WR it was three- and three- to four-molecular (50 to 75%), respectively, causing a hysteresis
of sorption isotherm. At RH=0.5 the S increased with cement strength from 146 m2 g-1 (C-33, 1 m) to 166 m2 g-1 (C-43, 1 m) and with hydration time to 163 (C-33, 6 m) and to 204 m2 g-1 (C-43, 6 m). At RH=1.0 (and 0.95), higher S-value were measured but these differences were smaller: S amounted to 190-200 m2 g-1 in C-33 (1 and 6 m) and 198-210 m2 g-1 in C-43 (1 and 6 m). Thus no collapse occurred on air drying of paste C-43 (6 m).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
6.
The hydration of a 1:3 molar ratio of tricalcium aluminate, Ca3Al2O6, to gypsum, CaSO4·2D2O, was investigated at temperatures of 25, 50, and 80 °C using time-of-flight powder neutron diffraction combined with multiphase Rietveld structural refinement. It was shown that ettringite, Ca6[Al(OD)6]2(SO4)3·∼26D2O, was the first and only hydration product of the system, in contrast to a prior investigation which suggested the occurrence of a precursor phase prior to the formation of ettringite. Kinetics data showed that the hydration reaction is very sensitive to temperature: hydration at 25 °C was characterized by a single kinetic regime while hydration at higher temperatures consisted of two distinct kinetic regimes. The presence of two kinetic regimes was attributed to a change in either the dimensionality of the growth process or a change in the rate controlling mechanism in the hydration reaction. 相似文献
7.
Grounds T. Nowell D. V. Wilburn F. W. 《Journal of Thermal Analysis and Calorimetry》2003,72(1):181-190
One of the principal uses of supersulfated cement has been for structures exposed to sea water and sulfate bearing ground
waters. The resistance to such environments has been related to the absence of calcium hydroxide and the combination of much
of the free alumina into ettringite during hydration. This paper reports the resistance of SSC to sulfate solutions in which
ettringite has been decomposed. Prism samples were subjected to initial water storage at 25°C for both 28 days and 6 months.
Samples were also cured for 6 months at 95°C and at both 11% and 100% R.H. The control samples of 28 days were compared with
the 6 months samples of a more mature undecomposed SSC paste. After curing the prisms were measured and all the samples were
immersed in three sulfate solutions (0.7M Na2SO4 , 0.7M MgSO4 and saturated CaSO4), and water at the same time. Measurements of linear expansion over 6 months were carried out. Core and surface material
following immersion was examined by DTG and XRD. The study indicated that SSC is resistant to sodium and calcium sulfate solutions.
Strong magnesium sulfate solutions decomposed the samples under all conditions. A possible mechanism for this attack is suggested.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
Calorimetry has been used in the investigations of calcium aluminate materials produced as a binder for aluminate-corundum
composites of high refractoriness. The kinetics and of hydration process was thus characterized and the optimum compositions
of initial binders and cement-corundum refractory filler blends could be selected for further tests. The acceleration of heat
evolution - the shortening of so-called induction period and relatively high heat output in the presence of corundum was observed.
It means the acceleration of hydration process, that is early crystallisation of hydration products and subsequent further
dissolution of initial anhydrous aluminate phases. In the presence of fine grained corundum particles these phenomena should
be attributed to the nucleating effect of fine corundum particles.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
9.
The influence of spent catalyst from catalytic cracking in fluidized bed on the hydration process of cement and the properties
of cement mortars were studied. The spent catalyst was used as an additive to cement in the mortars (10 and 20% of cement).
The samples of mortars kept in water for28 days, then they were placed in sulfate and chloride media for 2 months (the control
samples were kept in water for 3 months). After this time they were subjected to bending strength and compressive strength
determinations. Thermogravimetric and infrared absorption studies were performed and capillary elevation, capability of binding
heavy metals, and changes in mass and apparent density were determined too. The studies disclosed the pozzolana nature of
spent catalyst and its influence on cement mortars being in contact with corrosive media.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
10.
The sintering and the structure of clinkers, modified by the introduction of different ionic forms of sulfur and phosphorus
into the raw mix, were examined. One reference synthetic mixture and 25 modified mixtures were prepared by mixing the reference
sample with 0.5, 1.0, 1.5, 2.0 and 2.5%w/w of chemical grade CaSO4, CaS, Ca3(PO4)2, CaHPO4 and Ca(H2PO4)2. Free lime content in all samples was measured. The sintering reactions in samples were recorded by means of differential
thermal analysis. The texture of the clinkers was examined using a scanning electron microscope and EDX. It is concluded that,
despite of their relatively low doping concentration in the raw mix, P and S affect considerably its reactivity and the texture
of the clinker. The various ionic forms of the same element (SO4
2-, S2- for S, PO4
3-, HPO4
2- and H2PO4
- for P) exhibit a different and unequivocal effect on the reactivity of the synthetic raw mix and on the texture of the corresponding
clinkers. S (in both forms) and P (added as HPO4
2-) are mainly dissolved in the melt and they have a positive effect on the burnability of the raw mix. P (added as PO4
3- or H2PO4-) is preferentially accumulated in belite. In this case further stabilization of β-C2S occurs and the binding of the free lime is hindered.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献