一种高精准水泥浆体流动性测定装置

针对传统净浆流动度测试方法灵敏度不高、测试范围窄的问题,设计了一系列不同口径的玻璃管(H管)。通过对不同水灰比、不同掺量减水剂条件下水泥浆体的流变特点的对比分析,得到不同H管对应净浆流动度测试范围和减水剂最佳掺量测试方法。H管不仅灵敏度高、测试范围广,而且还可以反映浆体粘度,是一套比较全面准确的水泥浆体流动性测试方法。     

Probing development of microstructure of early cement paste using 1H low-field NMR

Development of microstructure of early cement paste (0–6 h) was investigated with ¹H low-field NMR. It was found that T ₂ (transverse relaxation time) distributions of fresh cement paste were bimodal and two peaks were ‘long component’ and ‘short component’. Separation degree of two peaks was a sign of exchange of water within flocculation and outside flocculation. Factors such as water cement ratio, specific surface area and dosage of superplasticizer had influences on the separation degree: the separation degree increased with the water cement ratio; the separation degree of cement paste prepared with cement with a high specific surface area was zero; dosage of superplasticizer will decrease separation degree. Results also suggested that T ₂ distribution gradually moved to the left and T ₂ of long component and initial fluidity were linearly correlated.     

Rheological behaviors of fresh cement pastes with polycarboxylate superplasticizer

The rheologicalbehaviors of fresh cement paste with polycarboxylate superplasticizer were systematically investigated.Influentialfactors including superplasticizer to cement ratio(Sp/C),water to cement ratio(w/c),temperature,and time were discussed.Fresh cement pastes with Sp/Cs in the range of 0 to 2.0% and varied W/Cs from 0.25 to 0.5 were prepared and tested at 0,20 and 40 °C,respectively.Flowability and rheologicaltests on cement pastes were conducted to characterize the development of the rheologicalbehavior of fresh cement pastes over time.The exprimentalresults indicate that the initialflowability and flowability retention over shelf time increase with the growth in superplasticizer dosage due to the plasticizing effect and retardation effect of superplasticizer.Higher temperature usually leads to a sharper drop in initialflowability and flowability retention.However,for the cement paste with high Sp/C or w/c,the flowability is slightly affected by temperature.Yield stress and plastic viscosity show similar variation trends to the flowability under the abovementioned influentialfactors at low Sp/C.In the case of high Sp/C,yield stress and plastic viscosity start to decline over shelf time and the decreasing rate descends at elevated temperature.Moreover,two equations to roughly predict yield stress and plastic viscosity of the fresh cement pastes incorporating Sp/C,w/c,temperature and time are developed on the basis of the existing models,in which experimentalconstants can be extracted from a database created by the rheologicaltest results.     

功能调整材料对水泥浆体流动性影响

使用自行研制的H管分别研究了不同功能调整材料对水泥浆体流动性的影响,得到不同种类矿物掺合料和增稠剂对水泥浆体流动性改性规律:粉煤灰掺量的增加引起浆体流动性先增加后减小;矿粉掺量越大,浆体流动性越大;硅灰和增稠剂掺量越大,浆体流动性越差。H管对水泥浆体流动性变化十分敏感,可以准确快速评价不同功能调整材料对水泥浆体流动性影响。     

Relaxation study of cement based grouting material using nuclear magnetic resonance

Aiming at actual condition of poor effect of hole sealing for the reason of poor cement paste fluidity in the process of coal mine gas drainage, by adding a water reducing agent, cement paste for hole sealing was produced. The changes of initial distribution, weighted average values and total relaxation signal intensity of transverse relaxation time (T₂) of water in pure cement paste and water reducing agent added cement paste were studied with low field proton nuclear magnetic resonance (NMR). The results show that there are four peaks in T₂ distribution curves of cement paste: the first peak is related to the bound water in flocculation, the second and the third peaks are related to the water in flocculation, water reducing agent makes it extending towards the long relaxation time, increasing its liquidity, and the fourth peak is related to the free water. By using weighted average values of T₂ and total relaxation signal intensity, hydration process of cement pastes could be roughly divided into four stages: the initial period, reaction period, accelerated period and steady period. By analyzing the periods, it makes sure that the grouting process should be completed in the reaction period in the site, and the drainage process should be started in the steady period. The results have great guiding significance to the hole sealing and methane drainage.     

The influence of steel slag with high Al2O3 content on the initial hydration of cement

The initial hydration of steel slag with high Al₂O₃ content and its influence on the initial hydration of cement were investigated in this study. Steel slag with high Al₂O₃ content may contain much calcium aluminate mineral but very little gypsum. The steel slag hydrates much more quickly than cement in the initial hydration period, producing many flake products which have a great influence on the fluidity, initial setting time, and adsorption level of superplasticizer of paste. Replacing part of cement by steel slag with high Al₂O₃ content can change the hydration condition of calcium aluminate mineral of the cement by decreasing the gypsum to calcium aluminate mineral ratio, resulting in accelerating the hydration rate of calcium aluminate mineral in the initial hydration period. Paste containing steel slag with high Al₂O₃ content has a shorter initial setting time, higher adsorption level of superplasticizer, and greater loss in fluidity than the pure cement paste.     

Effect of competitive adsorption between sodium tripolyphosphate and naphthalene superplasticizer on fluidity of cement paste

The adsorption amount, ζ-potential of cement particles and fluidity of cement paste were tested to research the competitive adsorption between naphthalene superplasticizer(FDN) and STPP. The experimental results showed that the presence of STPP could significantly improve the fluidity of cement paste and reduce the fluidity loss with FDN. There existed a competitive adsorption between STPP and FDN. STPP and calcium ions formed complexes; they preferentially adsorbed onto surface of cement particles and preempt adsorption points of FDN; and it reduced adsorption amount of FDN. In the absence of STPP, saturation adsorption amount of FDN was 5.93 mg/g; but when the dosage of STPP was 0.1%, it reduced to 4.3 mg/g(about 72.5%). The adsorption amount of FDN was reduced by STPP, but ζ-potential of cement particles enhanced and fluidity of cement paste increased because of strong negative charge effect of the complexes. Adsorption of the complexes would delay Ca2+ into liquid and inhibit formation of active adsorption points. Then, content of FDN in liquid increased with the addition of STPP and ζ-potential of cement particles became stable. In this way, fluidity loss of cement paste reduced.     

不同黏土对掺减水剂水泥净浆流动度影响

目的 研究4种不同黏土对掺聚羧酸减水剂及萘系减水剂水泥净浆流动度的影响规律并从黏土的吸附性能角度探究其影响机理.方法 采用水泥净浆流动度试验方法比较了4种黏土对掺聚羧酸减水剂水泥净浆流动度的影响,通过TOC总有机碳测试仪测定了4种黏土对聚羧酸减水剂的吸附量.结果 4种黏土对水泥净浆流动度的影响差异较大,其中钙基蒙脱土和钠基蒙脱土的掺量为2％时,掺聚羧酸减水剂水泥净浆已基本没有流动度,掺萘系减水剂的水泥净浆流动度也有所下降,但降幅稍小,而伊利土和高岭土对掺减水剂水泥净浆流动度无明显负面影响;钙基蒙脱土和钠基蒙脱土对聚羧酸减水剂的吸附量较大,伊利土、高岭土对聚羧酸减水剂的吸附能力和水泥相当.结论蒙脱土对掺聚羧酸减水剂水泥净浆流动度负面影响极为严重,而伊利土和高岭土对掺减水剂水泥净浆基本没有负面影响.     

Influence of elevated curing temperature on the properties of cement paste and concrete at the same hydration degree

Three different curing temperatures(20 ℃, 40 ℃, and 60 ℃) were set, so that the nonevaporable water(w_n) contents of plain cement pastes cured at these three temperatures were measured to determine the hydration degree of cement. Tests were carried out to compare the pore structure and strength of cement paste, as well as the strength and permeability of concrete under different temperature curing conditions when their cements were cured to the same hydration degree. The experimental results show that either at a relatively low hydration degree(w_n=15%) or high hydration degree(w_n=16.5%), elevated curing temperature has little influence on the hydration products of cement paste, while it has a negative influence on the pore structure and compressive strength of cement paste. However, this negative effect is weaker at high hydration degree. The large capillary pore(100 nm) volumes of cement pastes remain almost the same at high hydration degree, regardless of curing temperatures. As for the concrete, elevated curing temperature also has negative influence on its compressive strength development, at both low hydration degree and high hydration degree. And this negative effect is stronger than that on cement paste's compressive strength at the same hydration degree. On the whole, elevated curing temperature has little influence on the resistance of concrete to chloride ion penetration.     

Effect of magnesium on the C-S-H nanostructure evolution and aluminate phases transition in cement-slag blend

The microstructural study was conducted on cement and cement-slag pastes immersed in different concentrations of Mg(NO_3)_2 solutions utilizing ~(29)Si, ~(27)Al NMR spectroscopy and XRD techniques. The results show that the hydration of both the cement and cement-slag pastes is delayed when the pastes are cured in Mg(NO_3)_2 solutions as compared to the pastes cured in water. Moreover, Mg~(2+) ions also exhibit an decalcifying and dealuminizing effect on the C-A-S-H in cement and cement-slag pastes, and thereby decrease Ca/Si and Al[4]/Si ratios of the C-A-S-H. The dealuminization of C-A-S-H is mitigated for cement-slag paste as compared to pure cement paste. The depolymerized calcium and aluminum ions from C-A-S-H gel mainly enter the pore solution to maintain the pH value and form Al~[6] in TAH, respectively. On the other hand, Mg~(2+) ions exert an impact on the intra-transition between Al~[6] species, from AFm and hydrogarnet to hydrotalcite-like phase. NO_3~-ions are interstratified in the layered Mg-Al structure and formed nitrated hydrotalcite-like phase(Mg_(1-x)Al_x(OH)_2(NO_3)_x·nH_2O). Results from both ~(27)Al NMR and XRD data show that ettringite seems not to react with Mg~(2+) ions.     

氨基磺酸盐系高效减水剂的改性研究

氨基磺酸盐系减水剂具有高减水率、抑制混凝土塌落度经时损失等优点,但泌水严重,限制了其在混凝土中的应用。本文根据“分子设计”原则,通过单体A和单体U引入适当的官能团,对传统氨基磺酸盐系高效减水剂进行改性,测试了产品对水泥净浆流动度、流动度经时损失和泌水率的影响。试验表明,单体A的改性效果优于单体U,以9%的单体A改性后,减水剂的分散性和分散保持性能好,泌水率显著降低。     

Synthesis of a macromer, MPEGAA, used to prepare an AMPS-modified polyacrylic acid superplasticizer

A macromer, methoxypolyethylene glycol acrylate （MPEGAA）, was synthesized by direct esterification using methoxypolyethylene glycol （MPEG-1200） and acrylic acid （AA） as the main materials. MPEGAA was then used to prepare a polyacrylic acid superplasticizer modified with 2-acrylamido-2- methylpropane sulfonic acid （AMPS）. A single-factor test was performed to investigate the effects of the molar ratio of acid to alcohol （n（AA）/n（MPEG））, inhibitor amount, catalyst amount, temperature, and time of esterification on the synthesis of MPEGAA. The experimental results showed that the optimal esterification conditions were as follows： n（AA）/n（MPEG）, 3.5：1; amount of hydroquinone （as an inhibitor）, 1.2%; amount of para-toluenesulfonic acid （as a catalyst）, 5.5%; reaction temperature, 95 ~C; and reaction time, 6 h. The AMPS- modified polyacrylic acid superplasticizer prepared under the optimal esterification conditions enabled the achievement and maintenance of high cement dispersibility. At an admixture amount of 0.15%, the cement paste fluidity was initially as high as 300 mm, and then decreased to 315 mm after 1 h and to 290 mm after 2 h.     

聚羧酸系高效减水剂PC的合成及性能研究

以甲基丙烯酸、聚乙二醇1000、对甲苯磺酸、对苯二酚、过硫酸铵和甲基丙烯磺酸钠为原料,采用两步法合成出新型聚羧酸系高效减水剂(简称PC)。将合成的PC与目前广泛使用的萘系高效减水剂(简称FDN)相比,具有更加优异的性能,具体表现为:在掺量很少情况下,水泥净浆就具有较高的流动度;当掺量相同时,其对水泥净浆流动度远超FDN。此外,它与水泥的相容性好,具有缓凝及明显抑制水泥净浆流动度经时损失性能,对混凝土也能表现出显著的减水增强性,是一种性能优良,适合于配制高强、超高强混凝土的高效减水剂。     

Multi-scale modeling of the effective chloride ion diffusion coefficient in cement-based composite materials

N-layered spherical inclusions model was used to calculate the effective diffusion coefficient of chloride ion in cement-based materials by using multi-scale method and then to investigate the relationship between the diffusivity and the microstructure of cement-basted materials where the microstructure included the interfacial transition zone（ITZ）between the aggregates and the bulk cement pastes as well as the microstructure of the bulk cement paste itself.For the convenience of applications,the mortar and concrete were considered as a four-phase spherical model,consisting of cement continuous phase,dispersed aggregates phase,interface transition zone and their homogenized effective medium phase.A general effective medium equation was established to calculate the diffusion coefficient of the hardened cement paste by considering the microstructure.During calculation,the tortuosity（n）and constrictivity factors（D_s/D₀）of pore in the hardened pastes are n≈3.2,D_s/D₀=1.0×10^-4respectively from the test data.The calculated results using the n-layered spherical inclusions model are in good agreement with the experimental results;The effective diffusion coefficient of ITZ is 12 times that of the bulk cement for mortar and 17 times for concrete due to the difference between particle size distribution and the volume fraction of aggregates in mortar and concrete.     

Effect of superplasticizers on the early age hydration of sulfoaluminate cement

The effects of two types of superplasticizers on the properties of CSA cement pastes during early hydration were studied. The influences of two types of superplasticizers on the properties of cement pastes, including the normal consistency, setting time, fl uidity, and compressive strength, were investigated by using various methods. The hydration products of the cement pastes cured for 1 day and 3 days were studied by X-ray diffraction（XRD） and scanning electron microscopy（SEM）. The results show that the PCE type superplasticizer retards the early age hydration while the FDN type superplasticizer accelerates the early age hydration of the CSA cement. Both types of superplasticizers have no infl uence on the further hydration of CSA cement, confi rmed by the calorimeter tests as well. The ultrasonic pulse velocity measurements were used to probe the influence of two types of superplasticizers on the hydration of CSA cement pastes at a high water-cement ratio（0.45）. The results show that the PCE type superplasticizer retards the early age hydration of the CSA cement while the FDN type superplasticizer has little infl uence on the early age hydration of the CSA cement.     

Design and preparation of high elastic modulus self-compacting concrete for pre-stressed mass concrete structures

Requirements of self-compacting concrete (SCC) applied in pre-stressed mass concrete structures include high fluidity, high elastic modulus, low adiabatic temperature rise and low drying shrinkage, which cannot be satisfied by ordinary SCC. In this study, in order to solve the problem, a few principles of SCC design were proposed and the effects of binder amount, fly ash (FA) substitution, aggregate content and gradation on the workability, temperature rise, drying shrinkage and elastic modulus of SCC were investigated. The results and analysis indicate that the primary factor influencing the fluidity was paste content, and the main methods improving the elastic modulusof SCC were a lower sand ratio and an optimized coarse aggregate gradation. Lower adiabatic temperature rise and drying shrinkage were beneficial for decreasing the cement content. Further, based on the optimization of mixture, a C50 grade SCC (with binder amount of only 480 kg/ m3, fly ash substitution of 40%, sand ratio of 51% and proper coarse aggregate gradation (V _{5-10 mm}: V _{10-16 mm}: V _{16-20 mm}= 30%: 30%:40%)) with superior workability was successfully prepared. The temperature rise and drying shrinkage of the prepared SCC were significantly reduced, and the elastic modulus reached 37.6 GPa at 28 d.     

单体类型对多羧酸型高效减水剂性能的影响

用于合成多羧酸共聚物的单体结构和官能团不同，对于减水与保塑性能的影响不同；选择含不同官能团的多种单体，合成一系列多羧酸型高效减水保塑剂；通过水泥净浆试验、混凝土试验测定了减水率和保塑性能；讨论了不同单体对减水剂性能的影响，并对分子结构进行了红外光谱表征。结果表明：在分子链中引入马来酸酐对保塑性能作用明显，引入适当用量和聚合度的聚乙二醇可同时提高减水率与保塑性。     

Effect of limestone powder on microstructure of concrete

The effect of limestone powder on microstructure of concrete was studied by using mercury intrusion porosimetry (MIP), backscattering scanning electron(BSE), scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. The experimental results show that the compressive strength of concrete containing 100 kg/m³ limestone powder can meet the strength requirement. Limestone powder has not pozzolanic activity; it is still unhydrated at the age of 28 days. But its filling effect can make the paste matrix and the interfacial transition zone between matrix and aggregate denser, which will improve the performance of concrete.     

Adsorption mechanism of polycarboxylate-based superplasticizer in CFBC ash-Portland cement paste

Circulating fluidized bed combustion （CFBC） ash exhibits the desirable pozzolanic activity which makes it a potential supplementary cementitious material to replace cement for concrete production. However, the high unburnt carbon content and porous surface structure of CFBC ash may adsorb water reducer and thereby significantly reduce the efficiency of water-reducing agents. The adsorption mechanism of polycarboxylate superplasticizer in CFBC ash-Portland cement paste was investigated by ultraviolet-visible spectrophotometer, and the conception of ＂invalid adsorption site＂ of CFBC ash was presented. The results show that the adsorption behavior of polycarboxylate superplasticizer in coal ash-Portland cement paste can be described by Langmuir isothermal adsorption equation. The adsorption capacity of CFBC ash-Portland cement paste is higher than that of pulverized coal combustion （PCC） fly ash-Portland cement paste. Moreover, the adsorption amount of polycarboxylate superplasticizer increases with the ratio of ash-to-cement in the paste. At last, the fluidity of CFBC ash-Portland cement paste is lower than that of the PCC fly ash paste. This work suggests that when CFBC ash is used as concrete admixture, the poor flowability of the cementitious system due to the high adsorption of water and water-reducing agent should be taken into consideration.     

Deterioration Characteristics of Cement-Fly Ash Paste under Strong Ultraviolet Radiation and Low Temperature Conditions

The pastes containing different dosages of fly ash were taken into ultraviolet radiation and low temperature freeze condition simultaneously(URL) for 30 days and only ultraviolet radiation condition(UR) for 30 days after standard curing, so as to investigate the influences of the conditions on the deterioration characteristics of the pastes. Microscopic test methods, such as XRD, TG-DTA and SEM, were used to study the UR effect on the deterioration process of hardened paste. The results show that the deterioration tests, such as URL and UR, inhibit the common development of paste strength, especially after the standard curing age of 360 days. With the increase of fly ash dosage, from 0 to 50%, the reference value decreases, especially at early age. While at the later age, i e, 180 and 360 days, the paste strength cured for 30 days under URL and UR conditions all increase to different extent and the strength is slightly affected very low, especially for the paste containing 25% fly ash. From XRD results, URL and UR dispositions do not influence the hydration product kinds but the amount, especially Ca(OH)₂ and CaCO₃. Deterioration experiments can decrease the diffraction peak of Ca(OH)₂ sharply, and increase that of CaCO₃ rapidly, especially under only ultraviolet radiation. From TG-DTA and SEM results, with the increase of curing age, the content of Ca(OH)₂ decreases and that of CaCO₃ increases. The Ca(OH)₂ content of paste under continuous UR curing for 30 days is less than that under URL curing for 30 days, which indicates that UR has more negative effects on the pastes than URL.