Orthogonal test design for optimization of synthesis of super early strength anchoring material

Calcination of calcium sulphoaluminate cement using flue gas desulfurization gypsum as whole calcium oxide source

Carbonates and bicarbonates are two groups of accelerators which can be used in sprayed concrete. In this study, the effects of the two accelerators sodium carbonate (Na2CO3) and sodium bicarbonate (NaHCO3) (0%, 1%, 2%, 3%, and 4% by weight of ordinary Portland cement OPC) on the properties of OPC paste were compared. The results show that both of them could accelerate the initial and final setting time of OPC paste, but the effect of the two accelerators on the compressive strength were different. After 1 day, sodium bicarbonate at 3% had the highest strength while sodium carbonate at 1% had the highest strength. After 7 days, both of the two accelerators at 1% had the highest compressive strength. After 28 days, the compressive strength decreased with the increase of the two. The improved strength at 1 and 7 days was caused by the accelerated formation of ettringite and the formation of CaCO3 through the reactions between the two with portlandite. The decrease of strength was caused by the Na+ could reduce the adhesion between C-S-H gel by replacing the Ca2+. NaHCO3 was found be a better accelerator than Na2CO3.

Comparison of Effects of Sodium Bicarbonate and Sodium Carbonate on the Hydration and Properties of Portland Cement Paste.

Effects of calcium bicarbonate on the properties of ordinary Portland cement paste

Grouting materials are used frequently in grouting reinforcement projects, such as mining and coastal engineering. Double liquid grouting materials are mostly used because of the fast setting and high early strength properties when the two slurries are mixed together but high fluidity when the two slurries are separated. In our study, double liquid grouting materials were developed from CSA cement (slurry A), quicklime and fluorgypsum (slurry B). Aluminum sulfate was added in slurry B in order to counteract any adverse effects caused by the fluorgypsum, such as the decreased early compressive strength and the prolonged setting time. The effects of aluminum sulfate content and the quicklime/fluorgypsum ratio on the setting time, hydration heat, and compressive strength of the double liquid grouting materials were investigated, and the hydration products were characterized through thermogravimetry-differential thermal analysis (TG-DTA), X-ray Diffraction (XRD), and Scanning Electron Microscope (SEM) tests. The results show that the addition of aluminum sulfate can shorten the setting time and increase compressive strength at both early and later ages. Considering the setting time and compressive strength of double liquid grouting material at the same time, the optimum content of aluminum sulfate was found to be 2%, and the optimum ratio of quicklime/fluorgypsum was found to be 2:8. The values of the optimum content of aluminum sulfate and ratio of quicklime/fluorgypsum were verified from theoretical analysis.

Effects of Aluminum Sulfate and Quicklime/Fluorgypsum Ratio on the Properties of Calcium Sulfoaluminate (CSA) Cement-Based Double Liquid Grouting Materials.

Effects of lithium carbonate on performances of sulphoaluminate cement-based dual liquid high water material and its mechanisms

In order to find out the rules of the effect of temperature on performances and hydration process of sulphoaluminate cement-based dual liquid grouting material, the performances of the grouting material were studied by determining its setting time, compressive strength and setting temperature. Its hydration process, hydration products and microstructure were analyzed by using XRD, TG–DTA and SEM–DES. The results show that water temperature has a significant effect on the setting time and setting temperature. The higher the water temperature, the shorter the setting time and the higher the setting temperature. In addition, as the water temperature and curing temperature increase, the hydration rate grows faster and the early strength becomes higher. However, the later strength of samples which are with lower temperature is higher. The results of TG–DTA, XRD and SEM–DES show that ettringite (AFt) is the main hydration product. Higher water temperature and curing temperature accelerate the formation of AFt, but also restrict the later hydration rate. The type of hydration product does not change as the temperature changes, but the microstructure of hydration product does.

Effects of temperature on performances and hydration process of sulphoaluminate cement-based dual liquid grouting material and its mechanisms

Modification test of high-water packing material and application in the gob-side entry retained engineering

Shear cracking in concrete box-girder bridges, which could cause excessive deflection during the serviceability limit state, cannot be effectively avoided by code-guided design. While elastic shear deformation only accounts for a small proportion of total deformation for un-cracked reinforced concrete (RC) beams, the magnitude of after-cracking shear deformation becomes comparable to flexural deformation for RC beams. However, there is still a lack of practical models to predict the after-cracking shear deformation of RC beams. First, six thin-webbed I beams were tested to investigate the shear stiffness degradation mechanism and the decrease ratio. Then, a very simple truss strut angle formula, which is the crucial parameter for shear stiffness, was established. Furthermore, a stiffness degradation rule for partially cracked beams was proposed considering the influence of concrete tension stiffening, which is essential for predicting the development process of after-cracking shear deformation. Finally, directly measured shear strains were used to validate the proposed shear stiffness model. The results showed that the shear stiffness drops to about 30~40% of the original stiffness after the first diagonal crack, and the remaining shear stiffness is only about 10% of the original one when the stirrup yields. Increasing the stirrup ratio is a more effective method to control shear stiffness degradation for diagonally cracked RC beams. Also, the proposed shear stiffness model well captures the main features of the shear stiffness degradation, and it provides a relatively accurate prediction of the equivalent shear stiffness at the post-cracking stage.

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Yaohui Zhang

Papers

Effects of lithium carbonate on performances of sulphoaluminate cement-based dual liquid high water material and its mechanisms

Effects of temperature on performances and hydration process of sulphoaluminate cement-based dual liquid grouting material and its mechanisms

Modification test of high-water packing material and application in the gob-side entry retained engineering

Simplified Evaluation of Shear Stiffness Degradation of Diagonally Cracked Reinforced Concrete Beams