水化硫铝酸盐水泥粉体对硫铝酸盐水泥自身水化进程的影响

制备并表征了水化硫铝酸盐水泥粉体材料(HCSAP),并结合水化热、化学收缩、XRD、TG、SEM等测试研究了HCSAP对硫铝酸盐水泥自身水化进程的影响.结果表明:在大水灰比条件下,硫铝酸盐水泥完全水化后主要生成钙矾石、水铝黄长石、单硫型水化硫铝酸钙及少量氢氧化铝.在硫铝酸盐水泥中混掺10％HCSAP,该改性浆体后期水化...     

甘蔗糖蜜对水泥缓凝和减水的性能研究

甘蔗废糖蜜对水泥同时具有缓凝和减水作用.采用酒精凝聚法分离废糖蜜得到胶体和非胶体组份:从水泥水化热、表面张力以及吸附性能阐述了其对水泥减水和缓凝的原因.结果表明,糖蜜中的胶体组份主要起分散作用,而非胶体组份主要起缓凝作用.     

Effect of temperature on porosity and on chloride diffusion in cement pastes

This paper is related to the effect of temperature upon the diffusive properties and the microstructural features of cementitious materials. Our experimental studies aim at linking the transport properties to the porosity and the cracks network of the microstructure.

The studied materials were three cement pastes having different water to cement (W/C) ratios (W/C = 0.35, 0.45 and 0.60). Rise of temperature in concrete structures was simulated by heating at different temperatures (45 °C, 80 °C and 105 °C). Evolution of microstructure was essentially characterized by mercury intrusion porosimetry (MIP). Diffusion tests in non-steady-state regime were carried out in order to characterize the diffusive properties. Apparent diffusion coefficients were determined from colorimetric method to follow the ingress of chloride and an analytical solution of Fick’s second law.

Our results showed that rise of temperature induced macroscopic cracking network and modification of pore size distribution. As a consequence, the transport properties were modified by thermal treatment. These modifications were mostly explained by the increase of capillary porosity.     

Effect of micro-silica loading on the mechanical and acoustic properties of cement pastes

This study aimed at investigating the role of ultra fine sand (UFS) in enhancing the mechanical and acoustic properties of cementitious pastes. The microstructural origin of these properties was also identified and compared to the conventional materials. The maximum particle size of the UFS used was 100 μm (100% passing) while 50% of the UFS had less than 20 μm in diameter. Ordinary Portland cement (OPC) was partially substituted by UFS at 1%, 2%, 3%, 4%, 5%, 7.5% and 10% by weight of binder. The blended compounds were prepared using the standard water of consistency. Test samples with dimension of 20 × 20 × 20 mm and 40 × 40 × 160 mm were cast for compression and bending strengths tests, respectively. Circular samples with diameters of about 100 and 29 mm and average thickness of about 30 mm were used for sound absorption tests. All samples were kept in molds for 24 h, and then de-molded and allowed to cure in water for 28 days. The specimens were dried at a temperature of 105 °C for 24 h in an oven before testing. It was found that as the loading of UFS increases both the compressive and bending strength increase up to about 5% UFS loading, then a decrease in these properties was observed. This can be attributed to the pozzolanic effect of UFS resulting in enhancing the chemical reaction between free lime in cement and silica producing more hydration products that makes the paste more homogeneous and dense. In addition, the dispersed UFS has improved the filling effect allowing denser packing of the paste. These dense microstructural features were captured by scanning electron microscope (SEM) examination of the 5% UFS modified compound. The results also showed that, the sound absorption and noise reduction coefficient (NRC) for modified cement paste decreases with the increase of UFS up to 5% and this may be due to the decrease in porosity. However, the NRC began to increase at UFS loadings of 7.5% and 10% due to the increase in the porosity of the compounds.     

Effect of nano-silica on rheology and fresh properties of cement pastes and mortars

Amorphous nano-silica (nS) particles (0–2.5 wt%) by cement were incorporated in cement pastes and mortars, and their effect on the fresh state behaviour was analysed. Rheological tests showed that after 75 min from the mixing start, the mortar having 2.5 wt% nS shows insufficient flowability to allow its continuous monitoring in a Viskomat PC viscometer. The influence of nS content was better observed on yield stress when compared with plastic viscosity values (the first increased about 66.5% while the latter just increased 3.6%). With nS addition, spread, setting time and the moment to reach the maximum temperature decreased 33%, 60% and 51.3%, respectively, when compared with samples without nS. X-ray diffraction showed presence of calcium hydroxide after 9 h in the sample with 2.5 wt% nS. The air content increased 79% and apparent density decreased 2.4% when nS was added.     

Effect of superplasticizers on workability retention and initial setting time of cement pastes

This paper presents an experimental study on the effect of a newly developed modified lignosulphonate (PLS) superplasticizer on the loss of workability and initial setting time of cement pastes in comparison to those of polycarboxylate (PCE) and polynaphthalene (PNS) superplasticizers. The workability loss was monitored by yield stress and effective viscosity of the pastes. The initial setting was monitored by heat development, change of rheological parameters with time, and penetration depth in cement pastes. The relations among these methods were discussed. Different dosages of the superplasticizers were used to obtain cement pastes with yield stress <6 Pa at 30 min at given water-to-cement ratios. The results showed that the pastes with PLS lost workability more slowly and had longer initial setting time compared with those with PCE and PNS admixtures. Although the longer workable time is beneficial for hot weather concreting, the longer initial setting time of such material has to be taken into consideration where early strength development is essential.     

粉煤灰对外掺轻烧MgO水泥浆体膨胀的影响

研究了粉煤灰对MgO膨胀剂(MEA)水泥浆体膨胀变形的影响,MEA的活性指数为50、100、190 s,MEA的掺量为6％和8％,养护温度为20、80℃.结果表明:当MEA掺量由6％增加到8％时,粉煤灰对MEA水泥浆体膨胀的抑制作用减弱.粉煤灰对掺高活性MEA水泥浆体膨胀的影响比对掺低活性MEA水泥浆体小.20℃水中养...     

水泥浆液结石体强度试验研究

为了分析不同浆液配合比对水泥浆液结石体强度的影响,采用正交试验法研究了不同的水泥、速凝早强剂、膨胀剂与水结石体无侧限抗压强度和塑性强度的关系,试验结果表明,水泥浆液最佳配比为1.5∶1,速凝早强剂用量占水泥重的1.2%,膨胀剂用量占水泥重的0.02%。     

脂肪族高效减水剂对水泥水化的微观作用机理

通过运用现代测试分析方法(RD、XRD,SEM、TG-DTA)研究了脂肪族高效减水剂对水泥水化和水泥微观结构的影响.结果分析表明,脂肪族高效减水剂能够显著有效降低水泥硬化过程中的孔隙率和孔径,改善孔的结构分布,在加入SAF减水剂1d水泥初期水化速度较慢,28d以后加入脂肪族减水剂的水泥熟料的水化程度与不加脂肪族减水剂的水泥熟料的水化程度逐渐相同.28d掺加SAF减水剂的水泥石SEM显示内部结构均匀致密、大孔减少,有大量的C-S-H凝胶生成,提高了混凝土结构的强度与耐久性.     

CFBC脱硫灰对水泥浆体水化的影响

通过对掺CFBC脱硫灰硬化水泥浆体的力学性能、结合水量、Ca(OH)2含量、水化产物以及孔隙分布的研究,分析了其对水泥浆体水化的影响。结果表明,随着CFBC脱硫灰掺量的增加,硬化水泥浆体的抗压强度降低,结合水量减少,孔隙率增加,Ca(OH)2含量减少;掺CFBC脱硫灰的水泥浆体水化产物形貌以纤维状为主,纯水泥浆体的水化产物以网络状为主。     

Mineralogy of plain Portland and blended cement pastes

The compressive strength and microstructure of blended cement was investigated in this study. The hydration products of cements were identified by means of scanning electron microscopy (SEM) and polarising microscopy (thin section). Results indicated that the blended cement required pozzolanic activity in addition to its cementing property with the addition of 30% material. Aggregations of belite grains were observed which were surrounded by alite. Blended cement exhibited high early-term strength. However, its 3d-age strength is lower than ordinary Portland cement. On the other hand, all blended cement mortars fulfil the compressive strength requirements of TS 24. Hence, it can be said that blended cement can achieve adequate early compressive strength. A reduction in the amount of CSH gel and the porosity of the matrix in mortars were found to be responsible for the poor compressive strength of the cement paste in early the age.     

Durability of gamma irradiated polymer-impregnated blended cement pastes

This study is focusing on durability of the neat blended cement paste as well as those of the polymer-impregnated paste towards seawater and various concentrations of magnesium sulfate solutions up to 6 months of curing. The neat blended cement paste was prepared by a partial substitution of ordinary Portland cement with 5% of active rice husk ash (RHA). These samples were cured under tap water for 7 days. A similar paste was impregnated with unsaturated polyester resin (UPE) followed by gamma rays ranging from 10 to 50 kGy. The obtained data indicated that the polymer-impregnated specimens higher values of compressive strength than those of the neat blended cement paste. In addition, the polymer-impregnated blended cement specimens irradiated at a dose of 30 kGy and neat blended cement specimens were immersed in seawater and different concentrations of magnesium sulfate solutions namely, 1%, 3% and 5% up to 6 months. The results showed that the polymer-impregnated blended cement (OPC–RHA–UPE) paste irradiated at a dose of 30 kGy has a good resistance towards sulfate and seawater attack as compared to the neat blended cement (OPC–RHA) paste. These results were confirmed by scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) studies.     

木灰比对水泥纤维板吸声性能与导热性能的影响

随着社会的发展,人们生活质量的不断提高,对居住声环境及保温要求也越来越高,因此改善声环境、提高居住的保温性能越来越引起大家的重视。本文研究植物纤维/水泥比(木灰比)对于水泥纤维板吸声系数和导热系数的影响。研究发现,水泥纤维板的导热系数随木灰比的增大而逐渐减小;水泥纤维板的吸声系数基本接近于1,随木灰比的变化对其影响不大,吸声性能好。     

不同水灰比水泥硬化浆体受软水溶蚀作用后的微结构变化差异

利用MIP、TGA等试验方法对不同水灰比的水泥硬化浆体在软水溶蚀作用下进行研究。结果表明:水泥硬化浆体遭受软水溶蚀后,表现出一定程度的质量损失和微观结构劣化。而低较水灰比的水泥硬化浆体抗软水溶蚀的能力明显强于高水灰比的水泥硬化浆体。高水灰比的水泥硬化浆体在软水溶蚀作用下的质量损失大、Ca(OH)2含量降低快、孔结构劣化明显。     

冷热循环负荷作用下混凝土微观形貌分析

利用扫描电镜(SEM)观察分析了冷热循环负荷作用下硅酸盐混凝土微观形貌的变化.结果表明,200℃条件下硅酸盐混凝土的水化产物和结构没有明显变化;而经过15次20℃-250℃-20℃的冷热循环后,混凝土中水化硅酸钙的形貌由絮状向点滴状转变,片层状Ca(OH)2发生一定程度的裂解,硬化浆体内部出现少量因高温-冷却过程造成的裂隙;混凝土抗压强度降低比较明显.     

The influence of SiMn slag on chemical resistance of blended cement pastes

During the last decades, industrial by-products and wastes recycling as complementary building materials is focusing a large number of researching studies, most of them dedicated to the cement and concrete production, studying technical, economical and environmental aspects.This paper presents an original contribution to this tendency, which consists on the possibility of recycling a SiMn slag from ferroalloys industry as a complementary construction material and its influence on the resistance of cement paste in different aggressive solutions. Different parameters, such as waste nature, additions, mechanical resistance, different aggressive solutions or morphological and microporosity changes were investigated. The results have showed that blended cement pastes elaborated with SiMn slag (5% and 15% additions) after 56 days of curing have a good resistance in some aggressive solutions, no losing weight and presenting an excellent resistance index compared to the reference matrix. Aggressive solutions presence do not alter elaborated pastes microporosity not minding if they are prepared with and without SiMn slag additions in the working conditions studied in this study.     

A study on the hydration rate of natural zeolite blended cement pastes

Natural zeolite is a type of mineralogical material containing large quantities of reactive SiO₂ and Al₂O_3. It is widely used in the cement industry in China as a cement blending material. Like other pozzolanic materials such as silica fume and fly ash, zeolite contributes to concrete strength mainly through the pozzolanic reaction with Ca(OH)₂, Thus, the pozzolanic reactivity of this type of material in comparison with other pozzolans is of much interest. This paper presents experimental results on the compressive strength, degree of pozzolanic reaction, and porosity of zeolite modified cement pastes. These results are compared with those obtained from similar blended cement pastes prepared with silica fume and fly ash replacements. Based on the experimental results, it can be concluded that natural zeolite is a pozzolanic material, with a reactivity between that of silica fume and fly ash. Generally, in blended cement pastes with a lower water-to-cementitious materials ratio, the natural zeolite contributes more to the strength of the pastes. But in the pastes with a higher water to cementitious ratio and a lower cement replacement level it undergoes a higher degree of reaction.     

熟料方镁石与轻烧MgO膨胀剂对水泥浆体膨胀性能的影响

研究了熟料中的方镁石(MgO)与外掺轻烧MgO膨胀剂(MEA)对水泥浆体变形性能的影响.结果表明:熟料中含4％～5％MgO的水泥浆体的膨胀速率较慢,膨胀量较小,膨胀达到稳定的时间较长;轻烧MEA中的MgO水化速度较快,90d后膨胀值基本趋于稳定,膨胀量较大;可以通过调节轻烧MgO的掺量来控制水泥浆体的膨胀量.     

水溶性聚合物对水泥浆体性能的影响

采用水溶性聚合物-聚丙烯酰胺对水泥浆体进行改性处理,对比分析了不同掺量的聚丙烯酰胺对新拌水泥浆体的凝结时间、标准稠度用水量、流动度的影响,以及对硬化水泥浆体力学性能的影响。研究结果表明:聚丙烯酰胺增加了水泥浆体标准稠度用水量,降低了水泥浆体的流动度,聚丙烯酰胺对水泥基复合材料的抗压强度无改善作用,但在其掺量为1%时,复合材料28 d的抗折强度提高了9.55%,而且随着其掺量的增加,复合材料的折压比呈增大趋势,其整体韧性得到改善。     

Nitrate removal from ground water

A new technique is described for nitrate removal from ground water. This technique is a combination of ion exchange and biological denitrification. Nitrate is removed by ion exchange. Regeneration of the resin in a closed circuit is achieved with a denitrification reactor. In contrast with traditional denitrification procedures there is no direct contact between ground water and denitrifying bacteria. Also brine production and regeneration salt requirements are minimal as compared with conventional regeneration of ion exchange resins. The basic design criteria and the first pilot plant results are presented. The pilot plant results show that the process is very attractive when compared with ion exchange and biological denitrification as separate techniques. Ground water with a relatively high sulfate concentration can be treated when a nitrate selective resin is used.