Utilization of Dredged River Sediment in Preparing Autoclaved Aerated Concrete Blocks

In this study,the dredged river sediment,soft texture and fine particles,is mixed with other materials and transformed into eco-friendly autoclaved aerated concrete(hereinafter referred to as AAC)blocks.The results indicated the bricks produced under the conditions of 30%–34%dredged river sediment,24%cement,10%quick lime,30%fly ash,2%gypsum and 0.09%aluminum powder with 0.5 water to material ratio,2.2 MPa autoclave pressure and 6 h autoclave time,the average compressive strength of 4.5 MPa and average dry density of 716.56 kg/m³were obtained,the two parameters(strength&density)both met the requirement of national industry standard.At the same time,the contents of dredged river sediment,cement,lime,fly ash,gypsum and aluminum powder were 15%,48%,20%,15%,2%and 0.09%,respectively,and the non-AAC block made of 0.5 water to material ratio,the average compressive strength of 3.1 MPa and average dry density of 924.19 kg/m³were obtained,the two parameters(strength&density)also met the requirement of national industry standard.In addition,the AAC block’s phase composition and morphology were micro-analyzed by SEM and XRD,the main substances in AAC block were found to be tobermorite and CSH,Among them,the chemical bond between Si-O-Si and Al-O-Al is broken,Al-O-Si is regenerated,Al substituted tobermorite with better strength is formed,and the compressive strength of AAC is further improved.

The relationship between diameter and depth of potholes eroded by running water

Geometrical analyses of 3930 potholes （3565 fluvial potholes, 237 marine potholes and 128 hillside potholes） from 33 localities in the world reveal a consistent, linear relationship： D Nh ＋ M, where h and D are, respectively, the depth and mean diameter of pothole, M is a critical size of the initial concavities （seminal potholes） that subsequently underwent growth, and N is the ratio of diameter expanding （wall erosion） speed to deepening （floor abrasion） speed. For the stream potholes, N is generally less than 1 with an average value of 0.67, M varies from 5.3 cm to 40.5 cm with an average of 20 cm, and N decreases gently with increasing M. However, the marine and hillside potholes are generally characterized by N 〉 1 and M 〈 10-14 cm, and a power-law relationship N 4.24M o.78 （coefficient of determination R2 0.75, M is in cm） exists. The results indicate that depth increases faster than diameter for stream potholes due to the larger size of grinding stones （〉5-10 cm）, while depth increases slower than diameter for marine potholes and hillside potholes due to the smaller size of grinding stones （〈5-10 cm）. The pothole h-D relationship is nearly independent of rock type. Knowledge of the pothole depth-diameter relationship is useful in a number of contexts, including simulation of hydraulic dynamics, theoretical considerations of erosion, comprehension of channel incision and development of canyons and gorges, and accurate estimation of excavation volume and mechanical strength ofpotholed bedrock in the design and stability analysis of hydraulic and environmental engineering projects （e.g. dam construction and river dredging）.

Controlled sintering for cadmium stabilization by beneficially using the dredged river sediment

Cd-bearing solid wastes are considered to be a serious threat to the environment,and effective strategies for their treatment are urgently needed.Ceramic sintering has been considered as a promising method for efficiently incorporating heavy metal-containing solid wastes into various ceramic products.Mineral-rich dredged river sediment,especially Al and Si-containing oxides,can be treated as alternative ceramic precursors rather than being disposed of as solid wastes.To examine the feasibility of using waste sediment for Cd stabilization and the phase transition mechanisms,this study conducted a sintering scheme for the mixtures of CdO and dredged river sediment with different(Al+Si):Cd mole ratios.Detailed investigations have been performed on phases transformation,Cd incorporation mechanisms,elemental distribution,and leaching behaviors of the sintered products.Results showed that Cd incorporation and transformation in the sintered products were influenced by the mole ratio of(Al+Si):Cd.Among the high-Cd series((Al+Si):Cd=6:1),CdSiO_(3),Cd_(2)SiO_(4),CdAl_(2)(SiO_(4))_(2) and Cd_(2)Al_(2)Si_(2)O_(9) were predominant Cd-containing product phases,while Cd2Al2Si2O9 was replaced by CdAl_(4)O_(7) when the mole ratio of(Al+Si):Cd was 12:1(low-Cd series).Cd was efficiently stabilized in both reaction series after being sintered at≥900℃,with<5%leached ratio even after a prolonged leaching time,indicating excellent long-term Cd stabilization.This study demonstrated that both Cd-containing phases and the amorphous Al-/Si-containing matrices all played critical roles in Cd stabilization.A promising strategy can be proposed to simultaneously reuse the solid waste as ceramic precursors and stabilize heavy metals in the ceramic products.