辅助胶凝材料对预应力高强混凝土管桩强度及工艺的影响

为优化混凝土管桩生产工艺,以硅灰(SF)和偏高岭土(MK)作为辅助胶凝材料,研究硅灰和偏高岭土对不同蒸养时间下混凝土抗压强度的影响,并使用X射线衍射(XRD)和扫描式电子显微镜结合能量色散谱(SEM-EDS)分析其水化产物及微观结构。通过Design-Expert8.0软件设计Box-Behnken试验,以硅灰掺量、偏高岭土掺量和蒸养时间三个因素为自变量,蒸养混凝土抗压强度为响应值,构建多因素回归方程模型。结果表明:硅灰掺量为胶凝材料质量分数8%时,对抗压强度略有提高,提高幅度为6.2%,达到83.6 MPa;5%、8%和10%(质量分数)掺量的偏高岭土均可提高蒸养混凝土的抗压强度,蒸养4 h、8 h、12 h时,10%掺量的偏高岭土对混凝土抗压强度的提升幅度依次为15.6%、13.2%和13.6%,蒸养4 h、8 h和12 h对混凝土抗压强度影响不大。XRD和SEM-EDS结果表明,硅灰和偏高岭土均消耗了Ca(OH)₂,提升了水泥早期水化程度,可以改善内部孔结构。通过响应面法建立模型可以预测,当硅灰质量分数为6.6%、偏高岭土质量分数为10%、蒸养时间为8.6 h时,混凝土抗压强度最高,达到104.8 MPa,且具有较高置信度。     

Si MAS-NMR Study of Hydrated Cement Paste and Mortar Made with and without Silica Fume

This paper presents ²⁹Si MAS-NMR measurements that trace the hydration process in both cement paste and mortar specimens made from ordinary portland cement, Type I, when the cement content is replaced by 0, 10, 15, and 20 wt% of silica fume. The specimens were moist-cured for 3, 7, 14, 28, 90, and 180 days at a laboratory temperature of 21°C (69.8°F). Compressive strength for all tested specimens was also determined. The results show that the degree of hydration (Q¹+ Q²)/(Q°+ Q¹+ Q²) increased with increasing content of silica fume, especially at the early ages of 3 to 28 days. In the same manner, compressive strength results were markedly increased up to 14 days and were lowered at later ages, compared to the control mix (0 wt% silica fume).     

Phase Composition of Hydrated DSP Cement Pastes

Cement pastes densified with small particles (DSP) containing up to 48% silica fume by weight of cement, and hydrated to up to 180 d at room temperature, have been analyzed using TMS-GPC, TGA, and ²⁹Si NMR to quantitatively estimate the amount of unreacted cement, Ca(OH)₂, and residual silica fume, respectively. Using a mass balance approach, the CaO/SiO₂ and H₂O/SiO₂ molar ratios of the C-S-H in the samples were calculated. For samples containing silica fume, the values of CaO/SiO₂ lie between 0.9 and 1.3, depending on the degree of hydration and silica fume content, whereas for samples without silica fume they were 1.6. Silicate polymerization analysis using TMS-GPC suggests that the molecular structure of the C-S-H is similar to that formed in conventional hydration. No cross-linking species were found, but the fraction of higher polymers (above octamer) increases as the CaO/SiO₂ ratio decreases.     

海水环境下矿物掺合料对硫铝酸盐水泥的水化影响

研究了海水环境下掺入硅灰、粉煤灰、矿渣对硫铝酸盐水泥抗压强度、化学收缩和水化产物的影响规律.结果表明:当硅灰的掺量为2.5%时,水泥浆体的抗压强度比空白组高.矿渣掺量为10%的水泥浆体28 d抗压强度明显超过掺入硅灰和粉煤灰时的强度,60 d强度高于空白组.掺入2.5%硅灰后,水泥浆体的化学收缩增大;在水化早期,粉煤灰和矿渣的火山灰活性很低,导致水泥浆体的化学收缩降低.掺入10%硅灰加快了硫铝酸盐水泥3 d水化反应,钙矾石生成量增多,水泥浆体早期强度比掺其它掺合料有所提高,但体积过快膨胀会破坏其内部结构,对水泥浆体的强度发展不利.     

High strength mortars containing condensed silica fume

A silica fume and a superplasticizer have been added to an ordinary easily flowing mortar composition. The optimal amounts of those constituents have been determined in order to obtain the maximum compressive strength for a constant workability. Large contents of silica fume and superplasticizer are needed (silica/cement=0.40 and superplasticizer/ce cement=2.4% in dry weights). The compressive strengths are approximately twice higher at 2,7 and 28 days as compared to the reference mortar. The drying shrinkage is slightly increased and the hydration kinetics is highly modified.     

Potential dependence of the surface plasmon dispersion relation and the role of adsorption of anions at the electrochemical interface

A new theory is elaborated for the surface plasmon frequency ω_SP (k_|) dependence on the charge of the electrode. Its essential feature is to account for adsorption of anions or oxygen (primary oxidation processes) induced by anodic polarization which modify the free electron distribution near the metal surface in contact with electrolyte. It is shown that the bending of the electromodulation plot near p.z.c. (constancy of ω_SP (k_|) in the cathodic range and an almost linear decrease with anodic polarization) is entirely determined by the charge-induced adsorption. The bending point does not depend on the “strength” of the field induced adsorption varied in the model simulation but on the critical value of the charge at which the adsorption starts. The surface plasmon electromodulation plots can, thus, be used for the evaluation of this important quantity.     

MgO活性对新型水化硅酸镁水泥性能的影响

通过对原料轻烧氧化镁粉在不同温度下进行二次恒温煅烧1.5 h制备不同活性MgO,研究了不同活性MgO与硅灰(SF)和磷酸氢二钾(K₂HPO₄)所制备的新型水化硅酸镁水泥胶凝材料(又称水化磷硅酸镁水泥,MSPHC)的凝结时间、流动度、抗压强度、反应溶液pH值。结合X射线衍射(XRD)、热重分析(TG-DTG)和扫描电子显微镜(SEM)测试手段,分析其影响机理。结果表明:随着煅烧温度的升高,MgO衍射峰强度增大,MgO活性降低;活性越高的MgO制备的MSPHC净浆凝结时间越短且流动性越差,而活性适中MgO制备的MSPHC具有较好的力学性能。MSPHC最主要的水化产物是水化硅酸镁(M-S-H)凝胶,另外还有Mg(OH)₂和MgKPO₄·6H₂O(MKP)生成,原料轻烧氧化镁粉中的MgCO₃成分不参与体系反应。活性适中的MgO制备的MSPHC在28 d龄期内的水化产物M-S-H凝胶生成量最多,因此硬化体抗压强度最高。活性越高的MgO在MSPHC反应体系中溶解的速度越快,体系水化反应进程速度也越快。     

半水磷石膏固化原状磷石膏制备胶凝材料及性能研究

以原状磷石膏（RPG）为基材,通过单因素实验研究了原状磷石膏（RPG）与β-半水磷石膏（HPG）相对掺量以及生石灰、水泥、硅灰3种掺合料对磷石膏基复合胶凝材料（PGBM）抗压强度、抗折强度及软化系数的影响规律以及作用机理。结果表明：HPG、生石灰、水泥、硅灰相对掺量的增加均能有效提高PGBM的强度及软化系数,其中硅灰的作用最为明显。但是,当生石灰和水泥的掺量（以质量分数计）分别大于4%和6%时,对PGBM耐水性能的改善不明显。当RPG与HPG相对掺量（质量分数比）为7∶3,生石灰、水泥、硅灰掺量（以质量分数计）分别为4%、12%、5%时,试件28 d抗压强度和软化系数分别可以达到26.29 MPa和0.79。微观分析表明：各掺合料主要通过水化产物填充率影响RPG颗粒之间的接触强度,进而对PGBM的强度和耐水性产生影响。     

石膏、硅灰对硅酸盐胶凝材料早期抗压强度的影响

为了研究石膏、硅灰对硅酸盐胶凝材料早期强度的影响,分别测试了石膏、硅灰不同掺量下的胶凝材料的4 h、1 d、28 d的抗压强度。利用X射线衍射仪和扫描电子显微镜分析了水化产物的微观结构特征。研究表明,在一定的试验范围内,胶凝材料的抗压强度随石膏的增加而变大,掺量为0.75%时最佳,4 h和1 d的抗压强度分别达到5.8 MPa和63.4 MPa;硅灰掺量从0%增长到15%,胶凝材料的各龄期抗压强度均随掺量的增加而呈增长趋势;硬化浆体的微观结构特征表明,一定的试验范围内,石膏使体系中的AFt数量增加,硅灰使体系中的C-S-H凝胶增多,且硅灰未水化的细小颗粒体有效填充硬化浆体的孔隙。     

海水和矿物掺合料对硫铝酸盐水泥砂浆性能的影响

本文研究了不同拌和水以及海水拌和时粉煤灰和硅灰掺量对硫铝酸盐水泥(SAC)砂浆力学性能和表观孔隙率以及净浆凝结时间、化学收缩、孔溶液pH值和氯离子结合能力等的影响,并通过XRD、SEM和EDS分析水泥水化产物和微观结构。结果表明,海水能加快SAC早期水化并提高其早期强度,但后期强度和淡水拌和时无明显差别。粉煤灰和硅灰均会延长SAC凝结时间,对早期抗压强度不利,而掺加质量分数为5.0%和7.5%的硅灰能提高SAC砂浆28 d抗压强度。硅灰掺量增加时会提高用水量和表观孔隙率,降低流动性,使水泥化学收缩增大,降低净浆pH值且减少氯离子结合量;粉煤灰能够提高砂浆流动性,减少水泥化学收缩,但掺量越大对SAC砂浆抗压强度和抗折强度越不利,掺质量分数为10%的粉煤灰可小幅提高氯离子结合量且减小表观孔隙率。     

Modelling formation and growth of H2SO4-H2O aerosols: Uncertainty analysis and experimental evaluation

An aerosol dynamics model, AERO2, is presented, which describes the formation of H₂SO₄-H₂O aerosol in a smog chamber. The model is used to analyse how the uncertainties on four input parameters are propagated through an aerosol dynamics model. The input parameters are: the rate of the reaction between SO₂ and OH (k₁), the ratio between the nucleation rate used in AERO2 and that derived from classical nucleation theory (t_n), the H₂SO₄ mass accommodation coefficient () and a measure of the turbulence intensity in the reactor (k_e). Uncertainties for these parameters are taken from the literature. One of the results of the analysis is that AERO2 and aerosol dynamics models in general can only predict upper bounds for the total number (N_tot) and total volume (V_tot) concentrations of the particles. The uncertainties on N_tot and V_tot are mainly due to the uncertainties on k₁, and t_n. An uncertainty factor of 20–100 still remains when the uncertainty on k₁, is reduced to ±5%. Aerosol measurements from three smog chamber experiments have therefore been used, in an attempt to reduce the uncertainty on k₁ and t_n. Values for k₁ are obtained in the reduced range 7.8 × 10⁻¹³ to 1.0 × 10⁻¹² cm³ s⁻¹, which is within the range found in the literature. For t_n, values in the range 10⁴–10⁷ are obtained, which is close to the upper bound of the range in literature. These values for t_n are in marked contrast with a recent set of experiments on nucleation in H₂SO₄-H₂O mixtures, which suggests a value for t_n of at most 10⁻⁵.     

碱性和无碱液体速凝剂促凝早强作用机理对比研究

碱性和无碱速凝剂掺入水泥后的水化机理不同,导致应用性能存在明显差异。本文通过测试凝结时间和砂浆抗压强度等宏观性能对比了两种速凝剂的应用性能,并通过水化放热分析、XRD定量分析、热重分析和SEM微观形貌观察等微观方法综合分析了两者的早期水化历程。结果表明:碱性速凝剂加入水泥后,[Al(OH)₄]^-加快了水泥中石膏的消耗速度,水化初期生成大量钙矾石(AFt),促进了硅酸三钙(C₃S)矿物的水化,缩短了水泥浆体的凝结时间并提高了砂浆的早期抗压强度,但石膏的加速消耗也使得单硫型水化硫铝酸钙(AFm)和水化铝酸钙(C-A-H)等水化产物提前生成,影响了水泥基材料的后期抗压强度发展;无碱速凝剂加入水泥后,[Al(OH)₄]^-和SO^2-₄在液相中生成了大量AFt,促进了铝酸三钙(C₃A)和C₃S矿物的水化,影响了氢氧化钙(CH)的结晶析出。值得注意的是,SO^2-₄不仅促进了C₃A生成AFt的过程,也延缓了水泥中石膏的消耗及AFm和C-A-H等产物的生成,因此无碱速凝剂的加入除了明显提高早期抗压强度外,后期28 d抗压强度也不受影响。     

Investigations on the compressive strength of silica fume concrete using statistical methods

The present paper deals with a mathematical model developed using statistical methods to predict the 28-day compressive strength of silica fume concrete with water-to-cementitious material (w/cm) ratios ranging from 0.3 to 0.42 and silica fume replacement percentages from 5 to 30. Strength results of 26 concrete mixes, on more than 300 test specimens, have been analyzed for statistical modeling. The ratios of compressive strengths between silica fume and control concrete have been related to silica fume replacement percentage. The expression, being derived with strength ratios and not with absolute values of strength, is independent of the specimen parameters and is applicable to all types of specimens. On examining the validity of the model with the results of previous researchers, it was observed that for results on both cubes and cylinders, predictions were obtained within 7.5% of the experimentally obtained values.     

硅灰掺量对免烧粉煤灰陶粒性能的影响

以粉煤灰为原料,辅掺硅灰制备了碱激发免烧陶粒。采用筒压强度试验、吸水率试验、含泥量试验、磨破率试验、耐腐蚀试验、X射线衍射仪和扫描电子显微镜试验,系统地研究了硅灰掺量对陶粒性能的影响。结果表明,3 d、7 d、14 d龄期时,随着硅灰掺量增加,粉煤灰陶粒的筒压强度呈逐渐增加趋势,磨破率与吸水率呈逐渐下降趋势,耐腐蚀性能也得到提高。当硅灰掺量为15%和20%(质量分数)时,龄期为14 d时,陶粒的筒压强度分别达到19.43 MPa和20.37 MPa。由微观分析知,适量的硅灰掺量可以提高粉煤灰的水化程度,增加陶粒结构密实性,但当掺量达到15%~20%时,水化程度有所减弱。     

Effects of densified silica fume on microstructure and compressive strength of blended cement pastes

Some experimental investigations on the microstructure and compressive strength development of silica fume blended cement pastes are presented in this paper. The silica fume replacement varies from 0% to 20% by weight and the water/binder ratio (w/b) is 0.4. The pore structure by mercury intrusion porosimetry (MIP), the micromorphology by scanning electron microscopy (SEM) and the compressive strength at 3, 7, 14, 28, 56 and 90 days have been studied. The test results indicate that the improvements on both microstructure and mechanical properties of hardened cement pastes by silica fume replacement are not effective due to the agglomeration of silica fume particles. The unreacted silica fume remained in cement pastes, the threshold diameter was not reduced and the increase in compressive strength was insignificant up to 28 days. It is suggested that the proper measures should be taken to disperse silica fume agglomeration to make it more effective on improving the properties of materials.     

Dissolution rate of silica fume in very high strength concrete

A very high strength concrete, having a 91 day compressive strength of 113 MPa, was developed using Type III cement, limestone aggregates, sodium naphthalene superplasticizer and silica fume, with W/C ratio of 0.24. SEM-EDXA and AEM were used to study the rate of dissolution of silica fume in this concrete, with progressive hydration. The ultrafine particle size of silica fume (< 1 μm) makes it difficult to view the state of these particles in concrete under the SEM. With AEM, however, it was possible to observe the dissolution process of silica fume particles, which begin at an early stage. Within 28 days, most of the silica fume is consumed in the pozzolanic reaction. The initial reaction product is a silica rich gel which later transforms into different morphological types of C-S-H which are compacted together. This is a major contributory factor for the very high strength of this concrete. Some partly reacted silica fume particles, however, remain in the hardened paste; lack of water most probably inhibits their complete transformation.     

29Si Magic-Angle-Spinning Nuclear Magnetic Resonance Study of Hydrated Cement Paste and Mortar

This paper presents ²⁹Si magic-angle-spinning nuclear magnetic resonance measurements that trace the cement hydration process in cement paste and mortar specimens made from ordinary portland cement, type I. These specimens were moist-cured for 3, 7, 14, and 28/31 d at temperatures ranging from 21° to 80°C. Compressive strength for all tested specimens was also determined. The results show that the degree of hydration ( Q ¹+ Q ²) and the compressive strength increase with curing times and temperatures. However, at 80°C, the compressive strength decreases while the degree of hydration increases.     

The effect of MgSO4 and HCL solutions on the strength and durability of pozzolan cement mortars

Pozzolan cements are produced by adding pozzolans such as silica fume, rice husk ash, blast furnace slag, fly ash, trass in 20% replacement for Portland cement. On the 28th day of production, the produced specimens are stored in water, in MgSO₄·7H₂O (5%) solution and in HCl (pH = 2) solution. The strengths and weights were determined after the mortars are stored in solutions for 56 days. Compressive strengths of the mortars stored in water for 28 days are silica fume, rice husk ash, and control, 43.3, 40.1, and 31.0 MPa, respectively. The highest loss of compressive strength is 20% and the highest gain of weight is 4.2%, occurring in blast furnace slag mortar in MgSO₄.     

Characterization of the granular packing and percolation threshold of reactive powder concrete

Reactive powder concrete (RPC) is a new cement-based material developed through microstructural engineering. RPC is composed of very fine powders: sand, crushed quartz and silica fume, all with particle sizes comprised between 300 and 0.02 μm, and a low water content, W/C<0.20. A very dense matrix is achieved by optimizing the granular packing of these powders. This compactness confers to RPC ultrahigh strength and durability.

The hydration kinetic of the cementitious matrix using electrical conductivity and isothermal calorimetry is presented. A linear relationship between the logarithm of conductivity ln(σ) and the degree of hydration , has been found:

ln(σ)=A_v−B_v

where A_v depends on the nature and the dosage of the different mineral and organic components, and B_v is an invariant related to the granular packing. From 19 different RPC compositions, an average value of 12.1 with a standard deviation of 1.7 were found for B_v. The capillary porosity percolation threshold was also deduced from this relationship. It has been found that when the degree of hydration is equal to 26%, the capillary pore space is discontinuous. This last result is in agreement with the prediction of the NIST microstructural model by Bentz and Garboczi [D., Bentz, E. Garboczi, Percolation of phases in a three-dimensional cement paste microstructural model, Cem Concr Res 21 (2) (1991) 325–344]. A continuous determination of the degree of hydration based on electrical conductivity is proposed.     

Hydration and strength development of cements produced from raw mixes containing MoO3, Nb2O5, WO3 and ZrO2

The purpose of this paper is to investigate the effects of MoO₃, Nb₂O₅, WO₃ and ZrO₂ on the hydration process and on the mechanical properties of cement. The above oxides were added separately to cement raw mixes and their influence on hydration of derived cements was studied by means of thermal analysis and X-Ray diffraction. Additionally, compressive strength and setting time were measured.