Influence of Monocylic Aromatic High Range Water reducer on Hydration and Microstructure of Cement Pastes

The influences of the monocyclic aromatic high range water reducers on cement hydration were evaluated from four factors, such as hydration heat, hydration products, pore structure, microstructures of cement pastes. With measurement of hydration heat by the TAM Ai, it was found that monocyclic aromatic high range water reducer may delay early hydration and significantly decreased early hydration heat. And the monocyclic aromatic high range water reducers tended to increase porosity and pore volume of cement pastes with MRI analysis, while pore size distribution did not change remarkably. With analysis of XRD、TG DTA and SEM, it was shown that the monocyclic aromatic high range water reducers could restrain the production of Ca(OH)2 and Hydrated Calcium Silicates in the hydration process without affecting the end products, and refine the hydration products, such as Ca(OH)2, C S H gel and ettringite crystals.     

Characteristics of Hydration Products and Pore Structure of Super Sulphated Cement

The mechanical properties, hydration products, and pore structure of SSC(super sulphated cement) were tested with universal test machine,XRD(X-ray diffraction), SEM(scanning electron microscope) and MIP(mercury intrusion porosimetry), which were compared with P·O 42.5 and slag cement. Results show that the main hydration products of SSC are ettringite, C-S-H gel and little gypsum crystals, while without calcium hydroxide; SSC hardened paste has smaller threshold pore diameter, the most probable pore diameter, middle pore diameter and average pore diameter, and has lower porosity and higher density, which can effectively promote the 90-day strength increase of SSC paste.     

Relationship between porosity and chloride diffusivity in cement-based composite materials

For investigating the effect of porosity in cement-based composite materials on diffusion coefficient of chloride ion, a series of mortar specimens with different water-cement ratios, different volume fractions and different diameters and graduation of aggregates are cast, and then chloride diffusivity of mortar specimens are measured by steady-state electric acceleration method and pore structure parameters of corresponding samples are obtained by mercury intrusion porosimetry. At the same time, the pore size distributions are visualized by X-ray micro-focus computer tomography. The results show that porous interfacial transition zones between aggregate and bulk cement paste significantly change the distribution of pore structure in hardened cement paste, and the smaller water-cement ratio is, the more significant the effect of interfacial transition zones on pore structures of hardened cement paste is. A good correlation between the total porosity, capillary porosity and the diffusion coefficient of chloride ion in cement-based composite materials has been determined and the continuous pore diameter is linearly related to the diffusion coefficient of those. Furthermore, the larger the continuous pore diameter is, the larger the value of chloride diffusivity is.     

Resistivity Method for Monitoring the Early Age Pore Structure Evolution of Cement Paste

The changes of electrical resistivity with time of cement pastes with water to cement ratio of 0.23, 0.35 and 0.53 were in situ continuously monitored by using electrodeless resistivity apparatus. Isothermal conduction calorimeter was also used to measure the hydration degree. The quantitative relationship between electrical resistivity evolution of paste and development of pore structure was proposed during hydration process. The results show that four stages (dissolution, induction, acceleration and deceleration) are identified according to the characteristics of electrical resistivity and its differential resistivity curves. In addition, a lower water to cement ratio shows a smaller capillary porosity and constriction factor as well as a higher tortuosity factor, resulting in a higher electrical resistivity of bulk paste, and the reverse phenomenon is observed with the electrical resistivity of pore solution.     

A Study on Alkali_Aggregate Reaction of Alkali_Clinker_Slag Cement Concrete

AAR expansion ratios of alkali_clinker_slag(ACS)cement mortars are studied by mortar bar test.The influences of the sort of alkalis and the content of clinker on AAR expansion ratio of ACS cement mortars are analysed.On the basis of above mentioned,the mechanism of AAR in ACS cement system is discussed.     

Micro-Mechanism of Dynamic Compaction on Collapsible Loess

Collapsible loess was collected from a suburban district of Shanxi, China. Dynamic model experiments of different hammer blows were designed to simulate the in-situ test on collapsible loess. The model experiments results showed that the density and shear strength parameters of the soil specimens increased with the increase of blows while the collapsible coefficient of the loess decreased with the increase of blows. However, after eight blows, the vertical displacement, the density, the internal friction angle and the cohesion of the loess were tend to be constant, and the collapsible coefficient was less than 0.015 that means the loess is stable. Furthermore, scanning electron microscope was used and SEM image analysis program was established to study the micro-structure of the specimens. The analysis of results showed that small pores in the soil increased with the increase of the blows; before compaction the content of pores with an equivalent pore diameter under 16 μm was 92.6%, the content of pores with an equivalent pore diameter larger than 16 μm was 7.4% and the content of pores with an equivalent pore diameter less than 4 μm was 66.9%. After ten blows, there were nearly no pores with an equivalent pore diameter larger than 16 μm, while the content of the pores with an equivalent pore diameter less than 4 μm was 81.8%. According to quantitative analysis, the relations between the blows and the plane void ratio, and the equivalent pore diameter were established. Meanwhile, the relations between the collapsible coefficient and the plane void ratio, the equivalent pore diameter were established.     

Influence of Rubber Powder Dosage on Performance of Cement Mortar

A number of rubber cement dosage specimens that rubber powder dosage different were obtained using same cement, water and fine aggregates, by adjusting the dosage of rubber powder. Then it was used to research the influence of rubber powder dosage on performance of cement mortar by measuring its liquidity, strength and toughness. The results show that: when water-cement ratio was equal and rubber powder replacing the same volume sand, the fluidity of cement mortar almost linear increased with rubber powder dosage increasing. With dosage of rubber powder increasing, compressive strength and flexural strength of 7 days and 28 days of cement mortar reduced, but toughness and wear resistant present linear growth trend when dosage of rubber powder less 30%.     

Hydration Kinetics of Cement based Materials With P2O5 Incorporated

By means of SEM, XRD and calorimeter C 80Ⅱ, the hydration characteristics and hydration kinetics of cement based materials with and without P2O5 incorporated were investigated. It is found that the amount and size of hydration products incorporated with P2O5 were decreased dramatically. When 3.5% P2O5 was added in cement, total amount of hydration heat was decreased by 32.6% and initial and final setting were delayed by 1.10 h and 12.54 h respectively. In terms of mechanism analysis, P2O5 had little impact on cement hydration mechanism, and accelerating stage was controlled by chemical reaction, decreasing stage controlled by both chemical and diffusion reaction while stabilizing stage controlled by diffusion alone. The hydration resistance in both accelerating and decreasing stage was elevated while decreased in stabilizing stage. The activation energy in both accelerating and decreasing stage were reduced and increased in stabilizing stage. P2O5 was favorable to hydration of C3A yet retarded hydration of C3S and C2S.     

Effects of Heterotrophic and Autotrophic Bacteria on the Stability of Aerobic Granular Sludge

The characteristics of granules of heterotrophic and autotrophic bacteria were studied. The autotrophic granules were characterized by smaller granule size, higher density, higher concentration of extracellular polymeric substances (EPS) and weaker strength compared with the heterotrophic ones. The diameter and density of autotrophic granules were changed in the same fashion, resulting in stable granules, and the heterotrophic granule, however, grew up with the increase of diameter and the decrease of density. According to the strength analysis, it is proposed that in the autotrophic system, the balance between EPS and porosity is the main reason for the long term stability. However, the balance could not be obtained in the heterotrophic system and that the operational conditions could not control the overgrowth of filamentous bacteria was the reason for the instability.     

Relationship Between Electrical Property and Microstructure of Mineral Admixtures-Cement Paste

The electrical properties of fly ash, slag and limestone powder-cement paste were studied by the methods of Cyclic Voltammetry and AC Impedance Spectroscopy. The results of electrical test were fitted by equivalent circuit. The correlations between electrical parameters of paste and unevaporable water content, pore structure by mercury porosimetry were compared. The results show that there is a positive relation between the unevaporable water content and the electrical resistivity of paste. If the unevaporable water content is higher, the hydration degree is higher and the electrical resistivity of paste is higher. The electrical resistivity of paste is increased with fly ash and slag, and it is unaffected with limestone powder of 5% dosage. The resistance Rs of pore solution of paste is increased with the prolongation of hydration, and the changes of resistance Rs and the electrical resistivity are unanimous. The resistance Rp and electrical capacitance C of gel are related to C-S-H content, and there is a negative relation between the resistance Rp and electrical capacitance C of gel. The complexity of pore structure of paste is increased with the prolongation of hydration. The constant phase angle exponent P by AC Impedance Spectroscopy is decreased and the value of fractal dimension by mercury porosimetry is increased.     

Mechanical and Chloride Diffusion Behavior of Kaolinite Clay Modified Cement-Based Material

The effects of kaolinite clay on the microstructure (pore structure, internal structure) and mechanical properties (workability, early-age and long-term flexural strength, chloride diffusion property) of the cementitious composites were tested. It is shown that the addition of clay improves the micro-pore structure in the cement paste and limits the introduction of chloride ions. As a result, it is suggested that the kaolinite clay would act as both filler and accelerator of cement hydration. Compared with the control specimen, the flexural strength of cement paste with 1% kaolinite clay increased by 30.41%, 39.04%, 36.27% and 38.32% at 1, 3, 7 and 90 curing ages, respectively. The 28-day flexural strength increased slightly. It is observed that the clay modified cement mortar has lower chloride diffusion coefficient values compared to the plain mortar, and the 28-day DCl of cement mortar decreased by 53.03% with 5% clay. Compared with the controlled sample, the increase in compressive strength and the reduction in chloride diffusion coefficient of the concrete with 5% clay addition is 28.4% and 18.87% respectively. The chloride diffusion coefficient of concrete decreases with the amount of clay addition exponentially. The 28-day compressive strength increases linearly with the chloride diffusion coefficient of the concrete.     

Hydration Mechanism of Cellulose Ether Modified Cement Pastes Under Rapid Water Loss

With foamed concrete as the absorbing substrate, under rapid water loss, the hydration mechanism of cellulose ether modified thin layer cement pastes was studied. The cement pastes were divided into three layers from surface to interface. Each layer cement paste of 6 h, 12 h, 1 d and 3 d ages was analyzed by using water loss speed, moisture content, XRD, FTIR and TG DSC DTG. The results show that cement pastes of different layers quickly lose water when hydration time is less than 6 hours and characteristic diffraction peaks of Ca(OH)2 are detected only in the second and third layer. The water loss speed significantly decreases when hydration time is more than 12 h and characteristic diffraction peaks of Ca(OH)2 are detected in every layer. The content of Ca(OH)2 increases continuously from the first layer cement paste to the third layer cement paste and aggregation state of ［SiO4］4- in C S H gel changes. The intensity of diffraction and vibration peaks of Ca(OH)2 within cement pastes increases as hydration time prolongs.     

The Influence on the Strength of Cement Mortars by Emulsified Epoxy

The influence on the strength of cement mortars by adding emulsified epoxy is studied, and epoxy resin polymer cement mortars with excellent performances are made up through modifying ordinary Portland cement with emulsified epoxy and micro-fine slag. The microstructure of the epoxy resin polymer cement materials are studied and their action and mechanism are discussed by means of modern detection measures such as SEM, XRD. The experimental results indicate cement mortars modifying emulsified epoxy and micro-fine slag have higher compressive strength and flexible strength. The series effects of water-reducing, density, pozzolanicity, filling and solidification cross linking through the action together of epoxy organism and micro-fine slag can endow cement-based materials with perfect mechanic performance. The main hydration products in the system are C-S-H gel and micro-crystal hydrated calcium aluminate. When epoxy resin is solidified, the organism is network. No Ca(OH) 2 has been found.     

Correlation between Particle Shape Evaluation Methods of Manufactured Sand

Particle shapes of different manufactured sand were tested by several methods such as uncompacted void content (UVC) test, flow time test and image analysis, the effect of particle size distribution and fineness modulus on test results were also studied,and then the correlation was analyzed. It is found that with the increase of particle sizes, flow time prolongs and UVC decreases. The correlation coefficient between flow time and fluidity of cement mortar is only 0.064 while that between UVC and fluidity of cement mortar is 0.719 3.     

Impact of Molecular Structure of Polycarboxylate Based Superplasticizer on Hydration Behavior of C3S

Isothermal calorimeter, thermal analysis and scanning electron microscope were employed to investigate the impact of 3 polycarboxylate based superplasticizers (PCs) on the hydration behavior of tricalcium silicate (C3S). In addition, adsorption isotherm was measured by total organic carbon. The results indicate that PCs extends the induction period of C3S. Initial hydration process of C3S is markedly retarded, whereas acceleration is observed in the period of 28 d. And it is found that PC1, with maleic anhydride for its main chain, has the strongest retardation effect. The majority of the copolymer dispersants is remained in the pore solution. Moreover, linear relationship between the content of COO- and its retardation effect is established. Accordingly it is presumed that the critical supersaturation with respect to portlandite can be expected to have a profound impact because of the addition of PCs.     

A Highly Activated Mineral Admixture Slurry Consisting of a Wet discharged Fly ash and Carbide Lime Composite

To recycle wet discharged fly ash and carbide lime effectively, a highly activated mineral admixture slurry consisting of both these components was investigated. The preparation technology of mineral admixture slurry made from a composite of wet discharged fly ash and carbide lime and the strengths, hydration products change (XRD, SEM) of cement paste made by the slurry were studied. The results indicate that the optimal proportion between wet discharged fly ash and carbide lime (solid content) is 75:25 in the process of wet milling preparation. The alkaline environment provided by carbide lime with high Ca(OH)2content and cement hydration accelerated by modified agents can promote early activation of fly ash, and accelerate its secondary hydration reaction.     

Cementation Effect with Cement during Cold In Place Recycling System of Asphalt Pavement

Different kinds of structures of RAP and different contents of cement were prepared. By means of standard compaction test, unconfined compressive strength, water stability, modulus and SEM test, the cementation effect with cement was studied. It was shown that the maximum dry density of RAP mixture rose from 1.91g/cm3 to 2.00g/cm3 with the increase of cement content when A/S was 0.4. The maximum dry density of RAP mixture would rise when adding more asphalt. The unconfined compressive strength rose from 1.48MPa to 2.63 MPa and then down to 2.28MPa when cement content was 6%. The best property could be got when A/S was 0.4 and the cement content was 6% with 9.5% water. The compressive strength of RAP mixture declined after it was cured in water for 24 h, but it had the same tendency with those of which had not been maintained in water. And it is also found that RAP does not obtain better stabilities in high temperature with modular test. From SEM test, it is shown that ettringite and C S H interlace and form the netted structure, and the aggregate would be enwrapped to increase the strength.     

Effect of Initial Curing Conditions on Thaumasite Form of Sulfate Attack of Cementitious Materials

The effects of initial high humid air curing, standard water curing and sealed curing on thaumasite form of sulfate attack (TSA) of cement based materials were studied.The Erosion products after 180 days attack in sulfate solution were analyzed by the way of X ray diffraction(XRD) and fourier transform infrared spectroscopy(FTIR).And it was found that the TSA of the cement stone was delayed in high humid air resulting from that CaCO3 generated from carbonation was filled in the pores of the specimens, forming a compacted surface and restricting SO42- intrusion.In comparison, the extent of TSA of the specimens cured in sealed condition was most severe resulting from that large amount of inter defects in specimens for the lower hydration degree, and SO42- ions could intrude into specimens more easily.     

Experimental Analysis on Mechanical Characteristic Effect of Mortar Specimen Sbujected to Hydrochloric Damage Under the Triaxial Stress

Triaxial compression tests of mortar specimens under various hydrochemical environments were carried out. The effects of the pH、concentration and composition of chemical solution on the corrosiveness and micro/meso structure of the mortar specimens were evaluated. The hydrochemical corrosion mechanisms of the mortar specimens were explored and the results revealed further influence of various hydrochemical actions on physical and mechanical parameters of the mortar specimens. A new damage parameter was proposed based on the mortar secondary porosity caused by chemical corrosion, which can quantify the evolution process of the physical & mechanical parameters of the mortar specimens during its hydrochemical damage.     

Strength and Microstructure of Sulphoaluminate Cement Containing Ultra- Fine CaCO3

The existence of ettringite in sulphoaluminate cement hardened paste is mainly in the form of pole-like crystal,which causes unfavorable effect on the cement.In this paper the strength and microstructure of the sulphoaluminate cement containing ultra-fine CaCO_3 weze discussed.Experimet results show that the strength of sulphoaluminate cement was obviously improved by adding 3% of ultra-fine CaCO_3.After curing for 28d,the compressive strength of cement paste and mortar is 100.6MPa and 94.1MPa respectively,and the bending strength of the mortar reached 12.5MPa.SEM study on hardened paste of sulphoaluminate cement containing ultra-fine CaCO_3 showed that its structure was dense and homogeneous,there was hardly any massive crystall detected.