Utilization of Basalt Saw Mud as a Spherical Porous Functional Aggregate for the Preparation of Ordinary Structure Concrete

To promote the production and application of artificial aggregates,save natural sand resources and protect the ecological environment,we evaluated the feasibility of using spherical porous functional aggregates(SPFAs) formed by basalt saw mud under autoclave curing in ordinary structural concrete.In our work,two types of prewetted functional aggregates were taken as replacements for natural aggregates with different volume substitution rates(0%,5%,10%,15%,20%,25%,and 30%) in the preparation of ordinary structural concrete with water-to-binder ratios(W/B) of 0.48 and 0.33.The effects of the functional aggregate properties and content,W/B,and curing age on the fluidity,density,mechanical properties and autogenous shrinkage of ordinary concrete were analyzed.The experimental results showed that the density of concrete declined at a rate of not more than 5%,and the 28 d compressive strength could reach 31.0-68.2 MPa.Low W/B,long curing age and high-quality functional aggregates were conducive to enhancing the mechanical properties of SPFAs concrete.Through the rolling effects,SPFAs can optimize the particle gradation of aggregate systems and improve the fluidity of concrete,and the water stored inside SPFAs provides an internal curing effect,which prolongs the cement hydration process and considerably reduces the autogenous shrinkage of concrete.SPFAs exhibits high strength and high density,as well as being more cost-effective and ecological,and is expected to be widely employed in ordinary structural concrete.

Early Debonding Detection of Rebar-Concrete Interface due to External Loading Utilizing AC Impedance Spectroscopy

A novel method for detecting early damage at the steel-concrete interface due to external loading based on AC impedance spectroscopy technology was proposed.Firstly,alkali pretreatment was introduced to ensure the accuracy and repeatability of the AC impedance test.Secondly,the AC impedance spectroscopy between the steel bar and concrete surface of different bonding positions was tested,and then the physical quantities reflecting the bonding damage condition were obtained by equivalent circuit fitting.Theoretical debonding position calculation and AC conductive structure analysis indicate that the change of interface resistance and interface capacitance can seize the development of bonding damage during the loading process.As the interface damage develops,obvious changes in interface resistance and interface capacitance are observed,and they cannot be recovered after unloading.

Thermal environment investigation of asymmetric radiation coupled with convection heating

The couple of radiation with convection heating owned advantages of less energy utilization,healthier and more comfortable indoor environment.However,local thermal discomfort was often induced by large vertical temperature difference and radiation asymmetry temperature.This work studied indoor thermal environment characteristics under different coupling ways of radiation and convection heating terminals through experiments and CFD simulation.The studied five scenarios were denoted as:(Ⅰ)lateral air supply+adjacent side wall radiation,(Ⅱ)lateral air supply+opposite side wall radiation,(Ⅲ)lateral air supply+floor radiation,(Ⅳ)lateral air supply+adjacent side wall radiation+floor radiation,and(Ⅴ)lateral air supply+opposite side wall radiation+floor radiation.The overall thermal comfort indices(including air diffusion performance index(ADPI),predicted mean vote(PMV),and predicted percent of dissatisfaction(PPD))and local thermal comfort indices under different scenarios were investigated.For Scenarios Ⅰ-Ⅲ,the local dissatisfaction rates caused by vertical air temperature difference were 0.4%,0.1%,and 0.2%,respectively,which belonged to"A”class according to the ISO-7730 Standard.While the vertical asymmetric radiation temperature of Scenario Ⅰ-Ⅱ was about 6.5℃ lower than that of Scenario Ⅲ-Ⅳ-Ⅴ.The ADPI for Scenarios Ⅲ-Ⅴ were about respectively 5.7%,16.7%,and 21.0%higher than that of Scenarios Ⅰ-Ⅱ,indicating that a large radiation area and radiation angle coefficient could reduce the discomfort caused by radiant temperature asymmetry.The coupling mode improved local discomfort by decreasing vertical temperature difference and radiation asymmetry temperature wherefore improving the PMV from-1.6 to-1.The lateral air supply coupled with asymmetric radiation heating could potentially improve the thermal comfort of occupied area,while the comprehensive effect of thermal environmental improvement,energy-saving,and cost-effectiveness needes to be further investigated.