Influence of Alternation of Sulfate Attack and Freeze-Thaw on Microstructure of Concrete

The effects of sulfate attack and freeze-thaw alternation on the concrete microstructure were systemically investigated by advanced test methods such as water absorption method, air void analysis, XRD, and SEM. The experimental results indicated that freeze-thaw damage is the major effective factor in the sulfate attack and freeze-thaw alternation test. In the alternation test, average aperture of capillary pores of specimens was smaller, pores uniformity was better, and water absorption rate was lower than those specimens used in the single freeze-thaw damage test. The average aperture and uniformity of pores could be improved by adding fly ash and slag. Damage was accumulated in many cycles of freeze-thaw and microcracks increased during the test. At the same time, the hydration products of the concrete developed into expansive gypsum, AFt, and TSA without any strength during sulfate attack. The results of the microstructure analysis form XRD and SEM are in accordance with that of AFt, about 3 μm length, around which other hydration products decomposed by C-S-H after sulfate attack resulted in loss of concrete strength

Analysis of the characteristics and development trends of the “7•5” catastrophic debris flow in Xiangjiao gully, Muli County, Sichuan

On July 5, 2021, a catastrophic debris flow disaster occured in Xiangjiao gully, Muli County, Sichuan Province. This study analyzed the formation conditions, eruption process and eruption characteristics of the debris flow through field investigation and characteristic parameter calculation. Based on the results of on-site inspection, this debris flow was mainly caused by the combined effects of forest fires, short-term heavy rainfall, and channel topography. It was a post-fire debris flow caused by rainfall runoff erosion. The heavy rain caused powerful flood erosion on the slope surface, eroded the channel, led to collapse and landslides on both sides of the channel, and resulted in significant damming effects, which enlarged the scale of the debris flow. The forest fire area in Xiangjiao gully reached 74.61%, and the high-intensity burned area was 57.98%. The critical rainfall intensity for this debris flow was 77.84 mm/h, and the cumulative rainfall was 141.60 mm. According to the calculation results of characteristic parameters, the density of this debris flow was in the range of 1.83 ～1.93 g/cm3, indicating it was a viscous debris flow. The flow velocity at the downstream outlet of the main channel was 7.22 m/s, and the peak flow rate was 759.08 m3/s. Combined with the results of the rainfall-runoff method and the morphology investigation method, the recurrence interval of this debris flow was estimated to be once in a hundred years. Considering the development trend of debris flow, it is believed that there is still a possibility of large-scale debris flow in the basin. Therefore, prevention and control suggestions including slope reinforcement in the upstream, regulation in the middle reach, and drainage in the downstream are proposed

Numerical Simulation Research on Energy Dissipation Characteristics of Fish Scale Weir

In order to make the design of hydro buildings no longer limited to traditional models, Zhejiang Province has built various forms of novel art dams. Based on the numerical simulation method, the numerical simulation distribution of pressure and the influencing factors of the energy dissipation rate of the fish scale weir are studied. The results show that with the increase of the head h on the weir, the negative pressure area on the fish scale weir increases, but the negative pressure value remains unchanged or decreases; the h value (0.120m≤h≤0.140m) is inversely proportional to the energy dissipation rate of the fish scale weir, and the θ value (135°≤θ≤180°) is proportional to the energy dissipation rate of the fish scale weir

EFFECTS OF MINERAL ADMIXTURE ON THE CARBONIC ACID LEACHING RESISTANCE OF CEMENT-BASED MATERIALS

In order to reveal the degradation process and deterioration mechanism of cement-based materials, this paper analyzes the effects of carbonic acid leaching on the mechanical strength of mortars, as well as relative mass loss, microstructure, and composition of various cement pastes. The results indicate that cement pastes containing less than 20 % fly ash have higher carbonic acid leaching resistance than cement pastes without fly ash. However, after carbonic acid leaching, the compressive strength of the samples with fly ash is lower than that of the cement pastes without fly ash. The leaching resistance is good for samples cured at an early age before leaching. Carbonic acid leaching proceeds from the paste surface to the interior. The incorporation of an appropriate amount of slag powder helps to increase the density of the paste. Due to the pozzolanic activity of fly ash at late-stage leaching, a mixture of fly ash (≤ 20 %) and slag powder (≤ 20 %) effectively improves carbonic acid leaching resistance. The products of early-stage leaching were mainly CaCO₃ and small amounts of SiO₂ and Fe₂O₃. The C-S-H phase at the paste surface suffered serious damage after long periods of leaching, and the main products of leaching were SiO₂ and Fe₂O₃

Effect of Atmospheric Pressure on Performance of AEA and Air Entraining Concrete

The effect of atmospheric pressure on performance of air entraining agent (AEA) and air entraining concrete was studied in Tibet and Hubei, China. The result shows that the reduced atmospheric pressure increased surface tension and lowered foaming property of solution. The AEA with excellent foaming ability and stability is preferred in low atmospheric pressure. The freeze-thaw deterioration process of hardened pastes is relatively faster under low atmospheric pressure. The effect of air pressure on concrete frost resistance performance is more sensitive than the mechanical property. The bigger pores and poor uniformity of internal pore size distribution led to the deterioration of concrete macroscopic properties. Therefore, the AEA varieties should be preferred, the dosage of AEA should be increased, and pore structure of pastes should be optimized to ensure the durability of concrete frost resistance for construction in low-pressure areas

Finite Groups with Some -Supplemented Subgroups

Let be a subgroup of a finite group , a prime dividing the order of , and a Sylow -subgroup of for prime We say that is -supplemented in if there is a subgroup of such that and where denotes the subgroup of generated by all those subgroups of which are -quasinormally embedded in In this paper, we characterize -nilpotency and supersolvability of under the assumption that all maximal subgroups of are -supplemented in

Endoscopic Treatment of Symptomatic Foot and Ankle Bone Cyst with 3D Printing Application

Objective. To study the efficacy of arthroscopy for treating symptomatic bone cysts of the foot and ankle through the follow-up of patients and to further explore the application value of 3D printing technology in this treatment. Methods. Twenty-one patients with symptomatic bone cysts in the foot and ankle who underwent arthroscopic surgery in our Center from March 2010 to December 2018 were enrolled, including 11 in the experimental group and 10 in the control group. For the control group, C-arm fluoroscopy was used intraoperatively to confirm the positioning of the cysts; for the experimental group, a 3D model of the lesion tissue and the 3D-printed individualized guides were prepared to assist the positioning of the cysts. Debridement of the lesion tissues was conducted under an arthroscope. Regular follow-ups were conducted. The time of establishing arthroscopic approaches and the times of intraoperative fluoroscopy between the two groups were compared. Significance was determined as P<0.05. Results. The postoperative pathology of the patients confirmed the diagnosis. No significant perioperative complications were observed in either group, and no recurrence of bone cysts was seen at the last follow-up. The VAS scores and AOFAS scores of the two groups at the last follow-up were significantly improved compared with the preoperative data, but there was no statistical difference between the two groups. All surgeries were performed by the same senior surgeon. The time taken to establish the arthroscopic approaches between the two groups was statistically significant (P<0.001), and the times of intraoperative fluoroscopy required to establish the approach were also statistically significant (P<0.001). The intraoperative bleeding between the two groups was statistically significant (P<0.01). There was 1 case in each group whose postoperative CT showed insufficient bone grafting, but no increase in cavity volume was observed during the follow-up. Conclusion. With the assistance of the 3D printing technology for treating symptomatic bone cysts of the ankle and foot, the surgeon can design the operation preoperatively and perform the rehearsal, which would make it easier to establish the arthroscopic approach, better understand the anatomy, and make the operation smoother. This trial is registered with http://www.clinicaltrials.govNCT03152916