醇胺类助磨剂对硅酸盐水泥水化及胶砂强度影响的研究

研究了C和D两种醇胺类助磨剂对硅酸盐水泥水化过程及胶砂强度的影响。化学结合水、水化热分析、综合热分析及XRD结果表明,C加快了水泥3d水化放热和28d水化速度及水化放热,促进了铁铝酸盐矿物的水化;D加快了水泥3d水化速度和水化放热：C、D复合加快了水泥3d和28d的水化,且复合作用优于两者的叠加效应。胶砂强度结果表明,C对水泥28d胶砂抗压强度提高幅度显著;D的加入有利于提高水泥3d胶砂抗压强度;C和D复合对28d抗压强度的增幅远高于两者的叠加效应。     

复合外加剂对水泥净浆水化热及砂浆强度的影响

系统地考察了矿物—化学复合外加剂对水泥净浆的水化热影响，外加剂对水泥砂浆各龄期强度发展的影响。分析了不同外加剂之间的交互作用及制约规律。     

蒸发温度和冷凝温度变化对制冷机性能的影响

分析了蒸发温度和冷凝温度的相互关系及其对制冷机性能的影响     

稻草纤维对硫铝酸盐水泥水化特性的影响

通过对凝结时间、电阻率和强度的测定,研究了稻草纤维对硫铝酸盐水泥水化特性和力学性能的影响。结果表明,(1)稻草纤维浸提液延长了硫铝酸盐水泥的凝结时间,但会降低硫铝酸盐水泥的强度,且随着浸提液浓度的增加,强度越低;对硫铝酸盐水泥水化产物的种类无影响。(2)用冷水、热水和氢氧化钠预处理稻草纤维,可降低稻草纤维对硫铝酸盐水泥水化的延缓作用和强度的不利影响。     

尿素水溶液液滴的蒸发特性

在石英管式炉上通过挂滴法来观察单个尿素水溶液（urea-aqueous-solution,UAS）液滴的具体蒸发过程,比较了不同环境温度以及不同初始直径大小下液滴的蒸发特性。结果表明,尿素溶液液滴在100～1300 ℃的温度范围内呈现出了不同的蒸发行为。在较高的温度下,液滴的蒸发行为较为复杂,如气泡的产生、液滴的变形以及发生微爆的现象;但是,随着环境温度的降低,这些现象就变得非常微弱甚至消失。同时,还定量分析了稳态蒸发常数与温度、液滴初始直径之间的变化关系,发现在初始直径为2.5 mm、温度在100～600 ℃之间变化的情况下,稳态蒸发常数从0.02075 mm2/s增加到了0.23953 mm2/s,增大了10倍左右。此外,还对气流流速为0.25～1.25 m/s范围内的液滴蒸发特性作了实验研究。当液滴周围有强迫气流存在时,液滴与气体间的换热方式由导热转变为对流换热,从而增强了液滴表面的传热传质能力,促进了液滴的蒸发。     

Polymer characteristics and fracture morphology of radiation-polymerized styrene-impregnated mortar

Mechanical and durability properties and the fracture morphology of polystyrene-impregnated mortar composites prepared by impregnation of styrene and its in situ polymerization by gamma radiation have been studied. Variation of flexural strength of the composites, percent extractable polystyrene, and its molecular weight suggest crosslinking of the impregnated polymer under the influence of prolonged gamma irradiation. Moreover, crosslinking appears to contribute toward the improvement in flexural strength but has little effect on durability properties. SEM micrographs of the composites reveal a very weak cement–polymer interfacial bonding which is believed to be responsible for poor durability properties of the composites.     

ISO标准砂对砂浆流动度的影响

砂浆流动度试验是用来测定水泥标准砂砂浆的流动性及减水剂的减水率，以其作为混凝土中掺加减水剂的参考依据，适用于工业、民用建筑及构筑物混凝土用减水剂质量的鉴定。GB8076-1997(混凝土外加剂)和JGJ56-1984(混凝土减水剂质量标准和试验方法)中规定了砂浆流动度测定方法。虽然     

Effect of treatment temperature on the early hydration characteristics of superplasticized silica fume blended cement pastes

In this investigation, two mixes were used: ordinary Portland cement (OPC) and a blended cement prepared with the partial substitution of OPC by 10 mass% silica fume (SF). The setting and hardening characteristics were monitored by the aid of electrical conductivity as a function of curing time. The shear stress and electrical conductivity were studied at different temperatures, namely, 20, 35, 45 and 55 °C. As the temperature increases, the shear stresses decrease with the increase of shear rate. The height of electrical conductivity peaks of superplasticized cement pastes increases due to the increase of the paste fluidity. In the presence of 1.0% polycarboxylate (PC), the electrical conductivity of cement pastes decreases from 1 to 28 days. PC retards the hydration of cement pastes. The presence of PC extended the setting times of cement pastes at 35 °C than at 20 °C due to the increase in the adsorption capacity at this temperature. PC extends the dormant stage of the hydration process and delays the onset of the accelerating stage, without affecting its rate.     

Walnut structure and its influence on the hydration and drying characteristics

Abstract

Fresh harvested walnuts are dehulled, washed, and then dried by hot air (HA) as a continuous process in the industry. The objective of the current work was to study the walnut structure and investigate its effect on the moisture transfer characteristics during the walnut soaking and drying processes. Moisture transport pathways into the walnuts were determined using fluorescence tracer approach, and the hydration kinetics of walnuts under different soaking temperatures (15, 25, and 35?°C) was studied using Peleg model. HA drying experiments in single layer in a self-designed automatic HA dryer at 43?°C and air velocity of 1.41?m/s. The influence of the stem pore (sealed and non-sealed) and the soaking process (0, 2- and 5-min soaking time) on the walnut drying characteristics were investigated systematically. The results indicated that both the presence of the stem pore and the soaking time had significant influence (p < 0.05) on the hydration and drying characteristics of walnuts. Moisture absorptions through the stem pore and the shell were equally important during the soaking process. Two to five minutes soaking process led to 2–4?h additional drying time. This study contributed valuable knowledge for the simulation and prediction of moisture transfer characteristics during the walnut soaking and drying processes. The findings from this study could potentially be applied to the walnut drying industry for more efficient processing     

Effects of temperature on the hydration characteristics of free lime

The rate of heat evolution of hydrating CaO has been determined quantitatively by means of a conductive microcalorimetry, and the hydration kinetics of CaO has been studied. Some regularity of the influence of temperature on the hydration characteristics of free lime (f-CaO) has been discussed as well. Based on the present research, the mechanism of effects of temperature in the calcining process and the hydration process on the hydration of CaO has been illustrated.     

Effects of maximum void size and aggregate characteristics on the strength of mortar

The effects of the maximum void size and aggregate shape and roughness on the flexural strength of high strength mortar were investigated. Substantial reductions in the maximum void size and air content of quartz aggregate mortars resulted in flexural strength increases. These increases in flexural strength were somewhat lower than predicted by Griffith's theory, thus suggesting that the maximum void size did not act as the critical flaw controlling the flexural strength. Factors relating to the cement-aggregate bond, including aggregate shape and roughness, appeared to affect the flexural strength more than the maximum void size.     

Influence of triethanolamine on the hydration characteristics of tricalcium silicate

The hydration characteristics of 3CaO.SiO₂ or β2CaO.SiO₂ are studied by an addition of 0.0, 0.1, 0.5 or 1.0% triethanolamine. The amount of Ca(OH)₂ found at 1, 3, 7 or 28 days was in the order C₃S + 0% TEA > C₃S +0.1% TEA > C₃S + 0.5% TEA > C₃S+1.0% TEA, irrespective of whether lime was estimated by X-ray, DTA, TGA or chemical analysis. The rate of hydration, in terms of the disappearance of 3CaO.SiO₂, showed that hydration proceeded faster in the presence of TEA after 1 day. Additions of TEA increase the induction period, promote the formation of a C-S-H with higher CaO/SiO₂ ratio, increase the formation of non-crystalline Ca(OH)₂ and enhance the surface area of the hydrated silicate product.     

Polymer characteristics and fracture morphology of radiation-polymerized methyl methacrylate-impregnated mortar

Normal portland cement mortar–PMMA composites have been prepared under different doses of Co-60 gamma irradiation. The polymerization characteristics of MMA inside mortar and in bulk, mechanical and durability properties, and fracture morphology of the composites have been studied. The rate of in situ polymerization has been found to be faster than that in bulk. The molecular weights of the in situ and bulk PMMA were greatly reduced when a relatively higher dose of radiation was employed for the polymerization. However, the molecular weight of the PMMA-bulk was found to be higher than that of PMMA-in situ. The flexural/compressive strength and chemical durability in dil·H₂SO₄ medium of mortar–PMMA composites were, in general, superior to those of mortar–PS, though they declined under prolonged exposure to gamma irradiation. SEM micrographs of the fractured surface of the composites suggest a strong mortar–PMMA interfacial bonding and varied texture of the imbibed polymer in the matrix.     

盐离子对蒙脱石水化膨胀特性的影响

采用热失重法与经离心法、直接烘干法、冷冻干燥法结合对蒙脱石样品水含量进行测量,分析了NaCl浓度对蒙脱石中结合水与自由水含量的影响,探讨了蒙脱石中总含水量及结合水含量随NaCl溶液浓度变化的规律,研究了NaCl溶液中蒙脱石的水化膨胀特性及盐离子的抑制作用。结果表明,蒙脱石的水化膨胀受盐离子的抑制,盐离子的存在减小了渗透水化力,影响了水分子间的范德华力及水分子和蒙脱石表面间的氢键力和静电引力,总含水量随盐离子浓度增加而降低,盐离子浓度为0.2 mol/L时趋近最低值,样品膨胀程度由6.6缩小至1.6,盐离子对蒙脱石水化膨胀的抑制作用达峰值。盐离子浓度大于0.2 mol/L时,随盐离子浓度增加,自由水与结合水含量变化不明显。     

Effect of gluconates on the hydration of cement

The effect of various gluconates on the hydration of portland cement has been studied employing isothermal microcalorimetry, x-ray diffraction and differential thermal analyses. The results indicate that gluconates act as retarders as follows: Sodium gluconate > Potassium gluconate > Magnesium gluconate > Calcium gluconate     

Structural characteristics and hydration kinetics of modified steel slag

This study investigates the structural characteristics and hydration kinetics of modified basic oxygen furnace steel slag. The basic oxygen furnace steel slag (BOFS) was mixed with electric arc furnace steel slag (EAFS) in appropriate ratios and heated again at high temperature in the laboratory. The mineralogical and structural characteristics of both BOFS and modified steel slag (MSS) were characterized by X-ray diffraction, optical microscopy, scanning electron microscopy, Raman and Fourier transform infrared spectroscopies. The results show that modification increases alite content in MSS and decreases alite crystal size with the formation of C₆AF₂. One more obvious heat evolution peak appears in MSS's heat-flow rate curves in comparison to BOFS, becoming similar to that of typical Portland cement paste. As a result, its cementitious activity is much improved.     

The roles of hydration and evaporation during the drying of a cement paste by localized NMR

The moisture distribution during the setting of a thin mortar layer can be particularly complex to manage under dry (20% RH) and hot weather (above 25 °C) conditions. To better understand the fundamental phenomena at stake, we used static gradient relaxation NMR tools such as Profile MOUSE and STRAFI. This allowed disentangling the mutual effect of evaporation and self-desiccation by hydration. The interest of combining the two techniques is that the capillary water is observed with the MOUSE while STRAFI reveals quantitatively the build-up of the hydrate gel nanostructure. Spatially resolved and 2D relaxation exchange experiments on a model white cement paste revealed that although evaporation induced a capillary water gradient, the kinetics of the building of the pore structure and its homogeneity remained unaffected.     

Effect of blended inorganic salts containing negative hydration ions on hydration and properties of alkali-activated slag cement

Water glass (WG) is generally considered to be the most effective activator to prepare alkali-activated slag (AAS) cement in terms of strength and durability. However, the rapid setting and hardening of WG activated slag results in rapid loss of fluidity of AAS concrete mixture, which limits its engineering application. In the paper, the effect of blended inorganic salts containing negative hydration ions on the fluidity, setting time and mechanical strength of AAS cement was studied. The hydration process and hydration products were used to explore the action mechanism. Ba(NO₃)₂ greatly delayed the hydration of AAS cement. The four inorganic salts (KCl, KNO₃, KBr and NaCl) blended with a small amount of Ba(NO₃)₂ can improve both the initial fluidity and fluidity retention, and a wide setting time range can be obtained to meet engineering requirements. The compressive strength decreased with the increase of inorganic salts. The incorporation of inorganic salt did not change the composition of the main hydration products. Considering the fluidity required by construction, mechanical properties and the durability of structure, it is recommended to add 4%–5% KBr or KNO₃ blended with no more than 0.2% Ba(NO₃)₂ into AAS cement.     

Mechanical,hydration, and durability modifications provided to mortar made with crushed sand and blended cements

This work aims to evaluate the characteristics of crushed sand (CS), resulting from limestone quarries, when it replaces natural sand (NS) in mortar, and to identify its performances with three types of cement and three W/C ratio. It is concluded that CS has a great effect on mortar properties; it accelerates the hydration of cement grains leading to a shorter setting time, increases the flexural and compressive strengths, generates more hydration heat, and improves the mortar durability. The properties of CS mortar can be predicted as simple relationships of those of NS with an acceptable correlation coefficient.