Strength evolution and deformation behaviour of cemented paste backfill at early ages： Effect of curing stress, filling strategy and drainage

In this study, a pressure cell apparatus is developed to investigate the early age evolution of the strength and deformation behaviour of cemented paste backfill(CPB) when subjected to various loading conditions under different curing scenarios. The different curing scenarios that are simulated include:(1)drained and undrained conditions,(2) different filling rates,(3) different filling sequences, and(4) different curing stresses. The findings show that drainage, curing stress, curing time and filling rate influence the mechanical and deformation behaviours of CPB materials. The coupled effects of consolidation, drainage and suction contribute to the strength development of drained CPB subjected to curing stress. On the other hand, particle rearrangement caused by the applied pressure and suction development due to self-desiccation plays a significant role in the strength gain of undrained CPB cured under stress.Furthermore, curing stress induces slightly faster rate of cement hydration, which can contribute to strength acquisition.

Stabilisation of estuarine sediments with an alkali-activated cement for deep soil mixing applications

In this work,an alternative alkali-activated cement(AAC)made of ladle slag precursor mixed with sodium hydroxide and sodium silicate has been developed to enhance the bearing capacity of estuarine soils in coastal conditions via deep soil mixing(DSM).The AAC was optimized to use a low reactivity precursor(ladle slag)and to deal with a contaminated high-water content natural sediment cured under water.The material performance was analysed by comparison to a mixture made with Portland cement and cured in the same conditions.Flexural and unconfined compressive strength tests as well as seismic waves measurements after 3-,7-,14-and 28-d curing were performed to obtain a relationship between elastic stiffness and strength with curing time for both mixtures.Remarkably,the AAC mix demonstrated superior strength results,exhibiting almost double flexural and compressive strengths after 28 d compared to the Portland cement mix.The AAC mix also showed a higher rate of stiffness increase than the Portland cement mix,which has a higher initial stiffness at young ages but lower stiffness evolution.Leachate analysis confirmed that the proposed AAC could effectively immobilise any contaminants from soil or precursors.The effect of curing under stress was analysed in triaxial compression tests and found to be insignificant,indicating that laboratory data obtained without stress curing can represent the material's behaviour in a DSM column,which will cure under the weight of the column.

Multiscale model of micro curing residual stress evolution in carbon fiber-reinforced thermoset polymer composites

In this study,the micro curing residual stresses of carbon fiber-reinforced thermoset polymer(CFRP)composites are evaluated using a multiscale modeling method.A thermochemical coupling model is developed at the macroscale level to obtain the distributions of temperature and degree of cure.Meanwhile,a representative volume element model of the composites is established at the microscale level.By introducing the information from the macroscale perspective,the curing residual stresses are calculated using the microscale model.The evolution of curing residual stresses reveals the interaction mechanism of fiber,matrix,and interphase period during the curing process.Results show that the curing residual stresses mostly present a tensile state in the matrix and a compressive state in the fiber.Furthermore,the curing residual stresses at different locations in the composites are calculated and discussed.Simulation results provide an important guideline for the analysis and design of CFRP composite structures.