Preparation and Performance Research of Cement-based Grouting Materials with High Early Strength and Expansion

Main performance of the cement grouting materials made up by Portland cement（PC） and sulphoaluminate cement（SAC） was investigated in this program, a kind of expanding agent（EA） which was mainly constituted by metakaolin and alunite was utilized for the compensation of the shrinkage, the hydration products and micro structure of the grouting materials were researched by X-ray diffraction（XRD） and scanning electron microscopy（SEM）. The results showed that a high expansion rate of the grouting materials could be reached as the expanding agent mixed in 6% of PC mass; the addition of SAC in the S2（PC：SAC：EA=34：6：2.25） brought a further improvement of the expansion rate of the grouting materials, the analysis of XRD and SEM showed that due to the reaction of expanding agent and SAC in the grouting materials, more ettringite crystal was generated, which resulted in a higher early strength, the addition of SAC played an expansion and strength reinforcement role in the grouting materials.

The Rheological Properties of Ultra-fine High Performance Grouting Cement

The material properties of surface and powder, rheological property, and mineral composition were investigated by means of SEM, XRD, Malvern laser granulometer and rotary, viscometer. The influence of a admixture on ultra-fine cement rheological properties and its mechanism, were studied in material theories. The results show that the ultra-fine fly ash has a higher zeta potential, and improves flowability of ultra-fine cement paste, decreases flowability loss as time prolonging, improves compatibility between superplasticizers and cement because of the electrostatic repulsion, ball bearing effect, filling and dispersing effect of admixtures and delay-releasing effect of superplasticizers.

Microscopic Pore and Filling Performance of Coal Gangue Cementitious Paste

To obtain the influence laws of the fine gangue rate on the properties of coal gangue cementitious paste, the slump, divergence, stratification, bleeding, setting time and mechanical strength with the change of fine gangue rate were studied on the basis of keeping the amount of cementing material and slurry concentration unchanged. The porosity and the distribution of pore diameter of the filling specimen for curing 28 d were tested by a mercury injection instrument under different fine gangue rate conditions. It was shown that the slump, divergence, setting time and compressive strength of the paste firstly increased and then decreased with increasing fine gangue rate. The stratification and bleeding rate decreased with increasing fine gangue rate. The smaller the critical pore size of the paste was, the smaller the porosity was, the smaller the average pore size was. When the fine gangue rate was 40%, the maximum critical pore diameter of the paste was 55.79 μm, and the corresponding porosity was 17.54%, and the properties of filling paste were the best. When the fine gangue rate further increased, the aggregate surface area increased, and the reaction product of cementitious materials could not effectively fill the pores. It weakened the agglomeration effect. The particles surface of coal gangue was fragmental and flake deposit with irregular shape and uneven fold morphology. It was easy to be bonded with the surface of other filling material. The hydration products of coal gangue cementitious material were a large number of C-S-H gel with fibrous shape and ettringite（AFt） with compact block structure. The theoretical reference was provided for the preparation of low cost gangue cemented filling materials in coal mines.

Effect of Natural Zeolite on Performance of Sulfoaluminate Cement-based Planting Cementitious Material

This paper aimed to improve the water-retention performance and basic physical properties of sulfoaluminate cement（SAC）-based planting cementitious material. The effect of natural zeolite on the performance of SAC-based planting material was investigated. The water-retention performance, porosity, compressive strength, and alkalinity had been tested and TG-DSC analysis had been adopted in this paper. Experimental results showed that zeolite was effective to improve the water-retention capacity and 10%, 20% and 30% natural zeolite increased the pore volume of the hardened pastes by 10.6%, 26.0%, and 38.6%, especially pore size below 0.1 μm was increased by 9.7%, 26.2% and 17.5%. And 10% zeolite was beneficial to the compressive strengths of cementitious material and 1, 3, and 28 d compressive strength reached up to 35.9, 55.0, 80.3 MPa. Furthermore zeolite decreased the alkalinity of pore fluid of hardened cementitious material, while the addition of zeolite reached up to 30%, the alkalinity of pore fluid of hardened cementitious material decreased by 8.9%. Therefore zeolite was suitable for improving the performance of SAC-based planting cementitious material.

A Novel Open C-shaped Molar Band for Orthodontic Applications： Mechanical Characterizations and Clinical Trials

To evaluate the retention properties of the novel ‘C＇-shaped molar bands at a laboratory level. Resin-modified glass ionomer cement（RMGIC） was used as a luting agent for the novel C-shaped molar band. The mechanical properties of the band were examined and the retention performance was characterized in the mesial, distal and vertical directions. A clinical trial was conducted using a spilt-mouth design on 50 patients. The novel C-shaped molar bands fit most molars without a repeated try-in process.The use of both nanoHA coating and RMGIC enhanced the tensile（8.00 ± 1.8 MPa） and shear strengths（27.17 ± 8.6 MPa） of the molar bands, leading to high retention in vertical, mesial and distal directions（ p 〈 0.001）. In clinical trials, the C-shaped molar bands had a failure rate（15%） comparable to that of traditional bands, and 93% of the failed bands demonstrated an adhesive remnant index score of 0, corroborating the observation that no luting agent residue remained on the tooth surface in most cases. The novel C-shaped molar bands appear to be a promising appliance that requires further clinical investigations, and may be used effectively in orthodontics.

Behavior of High Performance PVA Fiber Reinforced Cement Composites in Triaxial Compression

Based on an extensive experimental program,the paper studies the behavior of HPFRCC under triaxial compression. The experimental parameters are lateral confining pressure and PVA fiber content by volume. The test results indicate that ultimate strength and peak strain are significantly improved with the increases of confining pressure. The confining effect introduced by the fibers becomes minor in triaxial compression tests,where there is relatively high external confining pressure. The axial stress-strain curves with different confining pressure and different PVA fiber content by volume are obtained. Lateral confining pressure constraints the lateral expansion of HPFRCC,so there is a big plastic deformation with its ultimate strength improved. At lower confining pressure,PVA fiber content by volume has some effect on the decreased section of stress-strain curve. According to test results,the paper establishes formula of confining pressure with ultimate strength and axial peak strain respectively.