Multi-objective Optimization And Working State Analysis Of Cement-based Composite With PVA Fiber

Cement-based composite needs to meet various functional requirements during its service life,thus the performance targets to be investigated are of multiple categories.The mix design procedure becomes more complex with more performance targets,thereby making demands for appropriate algorithms to achieve multiobjective optimization.On the other hand,insights into essential characteristics and performance evolution of cement-based composite can be gained through correct analysis of its working state during the whole service life.Since the polyvinyl alcohol(PVA)fiber is frequently used to improve the performance of cement-based composite,the work reported herein focuses on cement-based composite with PVA fiber(PVA-CBC).Related experimental research and engineering application,as well as the existing problems are reviewed.By combining laboratory testing,statistical analysis and numerical simulation,following investigations on the engineering properties,the mix design optimization and the working state of PVA-CBC are conducted:Five typical engineering properties including flowability,compressive performance,flexural performance,chloride ion penetration resistance and frost resistance of PVA-CBC are emphasized in this investigation.Mix proportions are designed based on the Taguchi method and experimental research is conducted with reference to relevant specifications and existing literature.Flow expansion,compressive strength,flexural strength,charge passed and maximum freeze-thaw cycles are measured as the performance indices.The analysis of signal-to-noise ratio and variance are implemented to study the influence of mix proportion design factors on these engineering properties.Accordingly,the optimum mix formulation for each engineering property is estimated and the reasonable range of levels for each mix design factor is concluded.The mix design and optimization of PVA-CBC with multiple factors and performance objectives is studied.The principal component analysis(PCA)method is introduced to solve this multi-objective problem of PVA-CBC.The balance of those engineering performance indices are established to integrate them into a unique principal performance index.Therefore,the multi-objective problem is transformed into a single-objective problem from the most objective perspective.Thereafter,the influence of mix design factors on the principal performance index is analyzed using the Taguchi method.Finally,optimum mix formulations of PVA-CBC are estimated using the PCA-based Taguchi method as well as the utility concept combined with PCA method separately,and the estimated results are verified via the additional experiment.The main contents and key points of PVA-CBC's working state theory are described systematically.The working state of PVA-CBC is defined and its styles of characterization are classified into different types;The method of working state analysis is explicated,the principle of which can be described as: the objective working state mutations of specimen/component are distinguished complying with the natural course from quantitative change to qualitative change,thus these working state characteristic points are used to characterize the performance indices;The working state modes are established based on different types of numerical responses so as to reveal the reflection of global working state characteristics in local parts.This investigation also delves into the working state of PVA-CBC specimens after exposing to freeze-thaw cycles.Firstly,the dependence of response information and characteristic parameters on freeze-thaw cycles is determined according to the data collected from the rapid freezing and thawing test,which include the dynamic modulus of elasticity,flexural strength and internal strain of PVA-CBC specimens.Then,the working state characteristics of PVA-CBC over its freeze-thaw process are identified by the Mann-Kendall(M-K)criterion and verified afterwards.Accordingly,the working state of PVA-CBC is divided into three stages and features within each stage are investigated,followed by the establishment of a three-level frost resistance evaluation system.Finally,the influence of mix design factors on freeze-thaw failure indices is studied via the analysis of signal-to-noise ratio and variance.The working state of PVA-CBC link slabs subjected to monotonic cyclic loads is investigated herein.Since the strains collected from the experimental program are discontinuous,the first task is to achieve spatially continuous data using the response simulating interpolation method.Thereafter,the generalized strain energy density(GSED)is calculated to characterize the working state of PVA-CBC link slabs.The M-K criterion is introduced to detect the working state characteristics of PVA-CBC link slabs during the whole loading procedure where yielding behavior and initial failure behavior are revealed.Finally,these working state features are verified by strain/displacement-based working state modes,strain field characteristics of critical cross sections and development of internal force.